Low-Dose Irradiation Can be Used as a Phytosanitary Treatment for Fresh Table Grapes Gina C. Kim, Cyril Rakovski, Fred Caporaso, and Anuradha Prakash
Abstract: Grapes (Vitis vinifera var. Sugraone and Vitis labrusca var. Crimson Seedless) were treated with 400, 600, and 800 Gy and the effects on physicochemical factors were measured alongside sensory testing during 3 wk of storage. Significant changes in texture and color with irradiation and age were measured but little visual difference was seen between control and irradiated grapes. However, age had a greater effect on firmness than irradiation for Sugraone grapes. Irradiation did not significantly (P ≤ 0.05) affect the SSC/TA ratio, which increased during storage. The trained panel detected significant changes in the berry texture and rachis color but rated sweetness and flavor significantly higher (P ≤ 0.05) for irradiated Sugraone as compared to the control. Consumers liked both the untreated and 800 Gy treated Sugraone grapes, but liked the untreated grapes more for texture (P ≤ 0.05). However, there was no difference in liking between irradiated (600 Gy or 800 Gy) and control samples of Crimson Seedless for any attribute. The results show that there are varietal differences in response to irradiation but the overall maintenance in quality of irradiated grapes during 3 wk of storage indicates that irradiation can serve as a viable phytosanitary treatment. Keywords: gamma irradiation, phytosanitary, table grapes, quality, sensory
This study shows that Sugraone and Crimson Seedless table grapes have very good tolerance to irradiation at dose levels needed for insect disinfestation and should be considered for use as a phytosanitary treatment in the export of these varieties. There were some differences in the responses of the 2 varieties to treatment indicating the need to evaluate each variety. Further research should be performed with commercial conditions of gamma irradiation treatment and distribution. A comparison study with other phytosanitary treatments on the quality of these table grapes would also be valuable.
Introduction According to the USDA Natl. Agriculture Statistics Service (USDA NASS), 7.4 million tons of grapes were produced in the United States in 2010 with a value of 3.6 billion dollars (NASS 2011). Approximately 90% of grapes in the United States are grown in California, which contributes to the world grape market by exporting more than 328000 tons to over 60 different countries. Phytosanitary treatments are used to prevent the introduction or spread of quarantine pests. There are several methods that can be used to treat grapes for phytosanitary purposes (APHIS 2012). Currently, the most widely used treatment for grapes is methyl bromide fumigation. However, methyl bromide is in the process of being phased out as mandated by the Montreal Protocol because it is an environmental pollutant that is depleting the ozone layer (US EPA 2012). In June 2012, Australia amended their import conditions of table grapes from California to no longer accept methyl bromide fumigation for imported fresh table grapes (AQIS 2012). Australia instead requires imported grapes to be treated with a mixture of SO2 and CO2 , followed by cold treatment. Carbon dioxide in conjunction with cold storage is effective against common table grape insect pests such as Omnivorous Leaf Roller (Platynota stultana), Western Flower Thrips (Frankliniella occidentalis), Spider
MS 20130241 Submitted 2/20/2013, Accepted 9/21/2013. Authors are with Chapman Univ., 1 Univ. Drive, Orange, CA 92866, U.S.A. Direct inquiries to author Prakash (E-mail: [email protected]).
R C 2013 Institute of Food Technologists
doi: 10.1111/1750-3841.12307 Further reproduction without permission is prohibited
Mites, Grape Mealy Bug (Pseudococcus maritimus) (Mitcham and others 1997) as well as black widow spiders (Chervin and others 2012). Irradiation can be an alternative to methyl bromide, carbon dioxide, and cold treatments and is gaining use all over the world as a phytosanitary treatment for various fruit due to its efficacy on insects and maintenance of fruit quality (Hallman 2012). The objective of irradiation is not necessarily mortality, but rather the prevention of immature pests developing into maturity and sterility of adults that may be present in the fruit. Low levels of irradiation can break the bonds in the genetic material of the pests to kill or sterilize while leaving no residue on the food. At the present time, it is one of the best substitutes for fumigants in the disinfestation of produce since low doses can control quarantine pests and adverse changes in produce may be insignificant at those levels. The USDA has approved irradiation at a generic dose of 150 Gy for fruit flies of the Tephritidae family and 400 Gy for all insects except pupae and adult of Lepidoptera (APHIS 2012). The upper limit for treatment of fresh produce in the United States is 1000 Gy (21 CFR 179.26). Several factors such as fruit maturity, the specific cultivar/varieties, and other inherent physical or chemical properties can affect how fruit quality responds to irradiation (McDonald and others 2012) but there is limited information available on the effect of irradiation of grapes. Kock and Holz (1991) evaluated the use of gamma irradiation up to 3.0 kGy to control postharvest Botrytis cinerea rot in several varieties of cold-stored SO2 treated table grapes. Treating the table
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Practical Application:
Effects of irradiation on table grapes . . . Table 1–Anchors on 15-point unstructured scales for Sugraone grape attributes. Attribute
0
Skin color Skin blemishes Skin bruising Skin bloom Rachis browning Stem quality Detachment force Finger firmness
Bright green None None Dull Green Brittle None None
Skin texture
None
Flesh firmness
None
Teeth firmness
None
Juiciness
None (Carrot)
Sweetness
None
Sour
None
Flavor
None
Off-flavor Astringency
None None
1
Kraft Philadelphia Cream Cheese Kraft Philadelphia Cream Cheese Kraft Philadelphia Cream Cheese Kraft Philadelphia Cream Cheese
2.5
Boiled egg white Boiled egg white Boiled egg white Boiled egg white
S: Sensory & Food Quality
grapes with irradiation closer to the packing day was found to be more effective and resulted in less decay than treatments applied after storing the fruit for 9 d. In general, a decrease in Botrytis cinerea occurrence was observed in irradiated grapes. Combining irradiation with SO2 treatment was found to be efficacious but color changes occurred in Bien Donn´e and Waltham Cross berries at 2 to 3 kGy. No other adverse effects on quality were observed due to irradiation. Irradiation improved the shelf life of 2 cultivars of Syrian grapes, Helwani and Baladi (Al-Bachir 1999). A measurement of weight loss and assessment of fungal growth was used to determine total loss. Each variety responded differently to treatment levels and the authors suggested that optimum irradiation dose for reducing fungal decay and extending shelf life in cold storage is related to the thickness of skin, firmness, and hardness of the flesh of the grape berries. These studies indicate that different cultivars of grapes have differing radiotolerance to irradiation. However, none of these studies evaluated changes in sensory qualities of the grapes; their focus was on using irradiation to limit fungal decay. The objective of this study was to determine the effects of phytosanitary irradiation treatment on the physicochemical properties and sensory quality of 2 table grape varieties, Vitis vinifera var. Sugraone and Vitis labrusca var. Crimson Seedless, which are grown in California and have a high export value (CTGC 2012). While 400 Gy is the target phytosanitary dose, commercial irradiation treatment delivers a range of dose levels. In some package configurations, doubling of the target dose may occur depending on uniformity of treatment. Thus in this study, we evaluated the radiotolerance of Sugraone and Crimson Seedless grapes treated up to 800 Gy. The physicochemical parameters of quality such as color, soluble solid content, titratable acidity, texture, and shelf life were measured using analytical instrumentation. A trained sensory panel evaluated attributes that may have changed due to irradiation and storage. Consumer panels were used to determine overall liking of the irradiated grapes compared to control. S82 Journal of Food Science r Vol. 79, Nr. 1, 2014
6
Goya Olive Goya Olive Goya Olive Goya Olive
9.5
Nabisco Planter Peanut Nabisco Planter Peanut Nabisco Planter Peanut Nabisco Planter Peanut
14.5
Nabisco LifeSaver hard candy Nabisco LifeSaver hard candy Nabisco LifeSaver hard candy Nabisco LifeSaver hard candy
15 Brown Intense Intense Shiny Brown Strong Intense Intense Intense Intense Intense Intense (Watermelon) Intense (Pure sugar) Intense (Lemon wedge) Intense (Grape juice) Intense Intense (Dry red wine)
Table 2–Values of F-statistic and the respective levels of significance for the Sugraone sensory attributes evaluated by judges. Sensory descriptor Color Blemish Bruising Bloom Finger firmness Teeth firmness Juiciness Sweet Sour Overall flavor Off-flavor
Fsample × judge
P-value
0.49 0.47 0.57 0.36 0.72 0.63 0.85 0.54 0.65 0.72 1.15
0.99 0.99 0.99 0.99 0.98 0.98 0.95 0.99 0.98 0.98 0.87
Fsample × judge : F-statistic (ANOVA) for sample and judge interaction. P-value: significance level at 5% probability.
Materials and Methods Sample procurement Fresh green grapes (Vitis vinifera) var. Sugraone, and fresh red grapes (Vitis labrusca) var. Crimson Seedless were obtained from a farm in the San Joaquin Valley region of California in July and October 2011, respectively. Immediately following harvest, the grapes were treated with SO2 in cold storage for approximately 8 h and precooled using forced-air to 1 to 2 ◦ C. They were bulk packed in 9 kg Styrofoam boxes that contained 8 perforated bags, each bag weighing approximately 1100 g. The grapes were stored at 0 to 1 ◦ C in a warehouse for 1 wk. Forty cases of grapes were then transported by refrigerated truck (1 to 3 ◦ C) to Sterigenics Intl., Inc. (Sterigenics) in Tustin, California for gamma irradiation treatment. Irradiation treatment The target irradiation dose levels were 400, 600, and 800 Gy. The cases of grapes were placed at a precise distance from a Co 60 source (approximately 1 million curies) to receive treatment
4.48 4.88 4.44 4.75 Day 1 ± 0.18 ay ± 0.20 by ± 0.20 ay ± 0.20 aby 4.93 5.33 4.89 5.20 Day 22 14.12 ± 0.25 ay 13.69 ± 0.24 aby 13.45 ± 0.24 by 14.13 ± 0.24 ay
Sample preparation Sugraone grapes were evaluated 7 and 21 d after irradiation treatment and the Crimson Seedless grapes were evaluated 1, 8, and 22 d after treatment. Evaluation of Sugraone grapes on day 1 could not be performed due to a scheduling conflict. One day before each evaluation, clusters from 3 cases of grapes of each dose level were prepared for analysis. The top 1 or 2 secondary rachis and the bottom 3 to 4 inches of the grape clusters were removed. For analytical testing, unwashed grapes were set aside and kept in cold storage. The grapes for sensory evaluation were washed, patted dry with paper towels, placed in a container, covered with plastic wrap, and kept in refrigeration until the following day. The grapes were pulled out from cold storage 2 h prior to analytical and sensory testing to bring them to room temperature. For each of the analytical tests, grape berries were selected at random and removed from the rachis right before testing. For the sensory evaluation, the grapes were kept on the rachis and cut into smaller clusters to serve to trained panelists and consumers on paper boats. Analytical testing Color. The color of 50 grape berries treated at each dose level was measured using a Konica Minolta Spectrophotometer CM2500d (Konica Minolta Sensing Americas, Inc., Ramsey, N.J., USA). Opposite sides of each grape berry were measured for a total of 100 measurements for each dose level. There were 5 color components that were measured: L∗ (lightness 100 = white,
Day 1 38.77 ± 0.30 ax 39.57 ± 0.34 bx 39.01 ± 0.34 ax 38.89 ± 0.34 ax Dose (Gy) 0 400 600 800
L
Day 8 38.15 ± 0.30 ay 38.95 ± 0.30 by 38.39 ± 0.30 ay 38.27 ± 0.30 ay
Day 22 40.78 ± 0.30 az 41.58 ± 0.30 bz 41.02 ± 0.30 az 40.90 ± 0.30 az
Day 1 14.58 ± 0.22 ax 14.41 ± 0.26 ax 13.98 ± 0.26 bx 14.67 ± 0.26 ax
Day 8 14.18 ± 0.22 ax 14.02 ± 0.22 ax 13.59 ± 0.22 bx 14.28 ± 0.22 ax
Day 22 15.65 ± 0.22 ay 15.49 ± 0.22 ay 15.06 ± 0.22 by 15.75 ± 0.22 ay
Day 1 20.34 ± 1.13 ax 23.86 ± 1.31 bx 21.37 ± 1.31 ax 21.32 ± 1.31 ax
Day 8 18.48 ± 1.13 ax 22.00 ± 1.12 bx 19.51 ± 1.12 ax 19.46 ± 1.12 ax
Day 22 23.38 ± 1.12 ay 26.90 ± 1.12 by 24.41 ± 1.12 ay 24.36 ± 1.12 ay
13.37 12.95 12.71 13.39
Day 1 ± 0.25 ax ± 0.29 abx ± 0.29 bx ± 0.29 ax
13.28 12.86 12.62 13.30
Day 8 ± 0.25 ax ± 0.24 abx ± 0.24 bx ± 0.24 ax
C Crimson Seedless grapes b a
Day 7 − 4.61 ± 0.06 ax − 4.37 ± 0.07 bx − 3.95 ± 0.07 cx − 3.59 ± 0.07 dx Day 21 49.52 ± 0.28 dy 46.80 ± 0.31 by 46.90 ± 0.31 cy 44.08 ± 0.31 ay Day 7 52.45 ± 0.31 dx 49.73 ± 0.40 bx 49.84 ± 0.40 cx 47.01 ± 0.40 ax Dose (Gy) 0 400 600 800
at a dose rate of 1000 Gy/h. The cases were arranged in two rows of 5 cases stacked one on top of the other. Midway through the treatment, the boxes were rotated 180◦ for uniformity of the treatment. Dose mapping was also conducted to ensure uniformity of dose, with dummy cases in the same exact configuration using alanine pellet dosimeters (Far West Technology, Inc., Goleta, Calif., U.S.A.). The cases treated with 400 Gy received a maximum dose of 500 Gy and minimum dose of 300 Gy for a Dmax/Dmin of 1.67. The target dose of 600 Gy resulted in a range of 500 to 700 Gy for a Dmax/Dmin of 1.4 and the 800 Gy target achieved an absorbed dose range of 700 to 900 Gy, respectively, for a Dmax/Dmin of 1.3. Following the treatment, the grapes were transported to Chapman Univ. where they were stored at 3 to 5 ◦ C until testing.
Figure 1–Appearance of Sugraone grapes treated with irradiation at 0, 400, 600, and 800 Gy and stored for 7 and 21 d.
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Day 22 ± 0.18 az ± 0.18 bz ± 0.18 az ± 0.18 abz h
Day 8 ± 0.18 ax ± 0.18 bx ± 0.18 ax ± 0.18 abx
5.88 6.28 5.84 6.15
Day 21 108.53 ± 0.22 ay 107.12 ± 0.24 by 106.13 ± 0.24 cy 107.20 ± 0.24 by h Day 7 107.40 ± 0.24 ax 105.99 ± 0.30 bx 105.00 ± 0.30 cx 106.07 ± 0.30 bx Day 21 14.38 ± 0.26 ay 14.56 ± 0.29 ay 13.99 ± 0.29 ay 11.77 ± 0.29 by C Day 7 15.94 ± 0.29 ax 16.12 ± 0.36 ax 15.55 ± 0.36 ax 13.34 ± 0.36 bx Day 21 13.68 ± 0.26 ay 13.94 ± 0.28 ay 13.47 ± 0.28 ay 13.51 ± 0.28 by Day 7 15.24 ± 0.29 ax 15.50 ± 0.36 ax 15.03 ± 0.36 ax 12.84 ± 0.36 bx Day 21 − 4.38 ± 0.05 ay − 4.14 ± 0.06 by − 3.72 ± 0.06 cy − 3.36 ± 0.06 dy
Sugraone grapes b a L
Table 3–Estimated means for L, a, b, C, h color parameters for Sugraone and Crimson Seedless grapes. Values in the same row/column that are followed by the same letter are not significantly different (a-c for row or dose, x-y for column or age).
Effects of irradiation on table grapes . . .
Effects of irradiation on table grapes . . . 0 = black), C∗ (0 = no saturation, 100 = complete saturation), h∗ (0◦ = red, 90◦ = yellow, 180◦ = green, 270◦ = blue), a∗ (negative values = green, positive values = red), and b∗ (negative values = blue, positive values = yellow). Texture. The texture was measured in 2 ways: Compression firmness. A BioWorks Firmtech II Texture Analyzer (BioWorks, Inc., Wamego, Kans., U.S.A.) was used to measure the compression firmness, the amount of force required to compress each grape berry by one mm at a load cell speed of 15 mm/s and table speed at 0.98 mm/s. The compression firmness of 200 berries was measured for each dose level. Kramer shear. The texture of grapes was also measured using a Kramer shear press with 5 blades (TA-91) attached to a Stable Micro System Texture Analyzer (Model TA-XT2, Texture Technology Corp., Scarsdale, NY/Stable Microsystems, Godalming, UK). One hundred fifty grams of grapes were placed in the metal container of the Kramer shear cell. The 5-blade probe was set at
60 mm from the bottom of the 5-blade plunger. The test speed of the probe was set at 4.0 mm/s and the post-test speed was set at 10.0 mm/s. The shear force (kg) required to cut through the berries was recorded was measured as the peak force. The highest force occurred at maximum deformation. The measurements were replicated 6 times for each dose level. Soluble solids content (SSC). The grape berries used for texture measurement were collected and immediately juiced (Elite Gourmet Maxi-matic Juice Extractor TS-738; City of Industry, Calif., U.S.A.) then filtered through 12 layers of cheesecloth to remove pulp. A drop of the grape juice was placed on the prism of a handheld digital refractometer (LR45227 Milton Roy Co., Ivyland, Pa., U.S.A.) to determine SSC. This measurement was done in triplicate for each dose. Titratable acidity (TA). Five mL of the grape juice was combined with 50 mL of CO2 -free deionized water. Initial pH of the grape juice solution was measured (pH200 Hannah
Figure 2–Appearance of Crimson Seedless grapes treated with irradiation at 0, 400, 600, and 800 Gy and stored for 1, 8, and 22 d.
S: Sensory & Food Quality Figure 3–Effect of irradiation and storage on estimated means for compression firmness (the amount of force required to compress 1 mm) of Sugraone and Crimson Seedless grapes. Bars with the same letter for each variety are not significantly P ≤ 0.05 different (a-c for dose and x-y for age).
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Effects of irradiation on table grapes . . . Instruments, Woonsocket, R.I., U.S.A.) and titrated to pH 8.2 with 0.1 N NaOH. This was done in triplicate for each dose. Titratable acidity was calculated as % tartaric acid using the following equation: % Acid : (mL Base x N of base x 75.03) / (sample vol. x 1 0)
S: Sensory & Food Quality
Weight loss. One case of grapes from each dose level was set aside to determine overall weight loss during storage. The boxes of grapes were stored at 3 ◦ C. Weight measurements were taken throughout shelf life. Berry shatter. Ten bags of grapes were selected from the 3 cases of grapes of each dose level on each evaluation day. Each bag was weighed then the grape clusters were removed from the bag and gently shaken for 15 s. The grape berries that became detached were weighed and expressed as a percentage of the total weight of the bag (Lydakis and Aked 2003). Sensory evaluation. All sensory testing was conducted using ASTM Committee E-18 guidelines (Chambers and Wolf 1996; Stone and Sidel 2004; Lawless and Heymann 2010). Descriptive testing. Trained panelists were chosen based on interest and performance on preliminary screening tests. Ten panelists were selected to evaluate both Sugraone and Crimson Seedless grapes; however, one panelist withdrew from the Crimson Seedless evaluation for personal reasons. Five 60-min training sessions allowed the establishment of the vocabulary and scales to describe key attributes of grapes: color, blemishes, bruising, rachis (or stem) browning, finger firmness (firmness by pressing each grape berry between the forefinger and thumb), skin firmness (firmness of biting only grape skin in mouth), flesh firmness (firmness of biting only flesh in mouth), teeth firmness (firmness of biting whole grape berry in mouth), detachment force (pulling off grape berries from the rachis), juiciness, sweetness, sourness, flavor, off flavor,
and astringency. These characteristics were rated on a 15-point unstructured, anchored scale. All panelists agreed on the anchors on the scale for each attribute (Table 1). For attributes related to texture, products (shown in Table 1) associated with the standard hardness scale provided in an ASTM manual (MNL 13) were used (Hootman 1992). For attributes related to appearance, fresh grapes with no visible flaws purchased at a grocery store were used as the control. Damaged fruit or fruit at the end of shelf life were used as references for the right hand anchor of the appearancerelated attribute scales. The panelists evaluated the control and all dose levels of irradiated grapes (0, 400, 600, 800 Gy) throughout the investigation. Each panelist visually inspected a whole grape cluster for color, blemishes, bruising, and rachis browning. For the touch and taste evaluation, 10 to 12 grape berries that were attached to the rachis were served to each panelist. The panelists evaluated finger firmness, skin firmness, flesh firmness, teeth firmness, detachment force, juiciness, sweetness, sourness, flavor, off flavor, and astringency. Grape samples were presented in paper boats marked with 3-digit random number codes. To prevent any position bias, samples were served in a random balanced order so that each sample would be served 1st, 2nd, 3rd, or last randomly. Panelists were provided with unsalted soda crackers and filtered water for palate cleansing between taste attributes and samples (Chambers and Wolf 1996). An analysis of variance (Table 2) verified the judges were trained sufficiently. A low P-value for the F-statistic indicates inconsistency in judges’ scores in respect to each attribute. A P-value > 0.05 indicates the judges’ assessments are not significant from each other. It was concluded the panelists were sufficiently trained and their assessments are consistent and reliable. Consumer testing. For Sugraone grapes, consumers evaluated only the control and 800 Gy treated samples. For Crimson Seedless grapes, consumers were served control and 800 Gy treated
Figure 4–Effect of irradiation and storage on estimated means of the Kramer shear force (the amount of force need to cut through 150 g of grape berries) for Sugraone and Crimson Seedless grapes. Bars with the same letter for each variety are not significantly P ≤ 0.05 different (a-c for dose and x-y for age).
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Effects of irradiation on table grapes . . . Table 4–Effect of irradiation and storage on estimated means of SSC and TA. SSC and TA were used to calculate the SSC/TA ratio. Values in the same row/column that are followed by the same letter are not significantly different (a-c for row and dose, x-y for column and age). Sugraone grapes Day 7
Dose Gy 0 400 600 800
% SSC 14.70 14.92 14.77 14.30
± ± ± ±
Day 21
% TA
0.18 abx 0.23 bx 0.23 bx 0.23 ax
0.45 0.49 0.46 0.45
± ± ± ±
SSC/TA ratio
0.01 ax 0.02 bx 0.02 ax 0.02 ax
% SSC
32.67 30.45 32.11 31.04
14.50 14.72 14.57 14.10
± ± ± ±
% TA
0.16 abx 0.18 bx 0.18 bx 0.18 ax
± ± ± ±
0.20 0.24 0.21 0.20
SSC/TA ratio
0.01 ay 0.01 by 0.01 ay 0.01 ay
72.50 61.33 69.38 70.40
Crimson Seedless grapes Day 1 Dose Gy 0 400 600 800
% SSC 20.20 20.21 20.43 20.04
± ± ± ±
0.09 abx 0.11 abx 0.11 bx 0.11 ax
Day 8
% TA 0.37 0.42 0.36 0.38
± ± ± ±
0.09 ax 0.11 ax 0.11 ax 0.11 ax
SSC/TA ratio 54.59 48.12 56.75 52.74
% SSC 20.82 20.83 21.05 20.66
± ± ± ±
% TA
0.09 az 0.09 az 0.09 bz 0.09 az
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grapes on day 1 but on day 8 and 22, they were served control and 600 Gy treated grapes. Panel sizes ranged from 75 to 96 consumers on the various evaluation days. Some consumers were present for multiple evaluation days. Consumers rated the degree of liking for the appearance, flavor, texture, juiciness, and overall liking of the grapes on a 9-point hedonic scale (Peryam and Pilgrim 1957). Small clusters with 3 or 4 grape berries attached to the rachis were served on white paper boats labeled with 3-digit number codes. To prevent any position bias, samples were served to consumers randomly in a balanced order. Therefore, consumers received a control or irradiated sample first an equal number of times. Consumers were asked to cleanse their palate with an unsalted soda cracker and filtered water between samples.
Day 22
0.31 0.36 0.30 0.32
± ± ± ±
0.03 ax 0.03 ax 0.03 ax 0.03 ax
SSC/TA ratio 67.16 57.86 70.17 64.56
% SSC 20.41 20.42 20.64 20.25
± ± ± ±
0.09 ay 0.09 ay 0.09 by 0.09 ay
% TA
SSC/TA ratio
– – – –
– – – –
and trained sensory panel data analyses, linear mixed models were implemented with random effects for judges to assess the effects of age and irradiation dose on all evaluated attributes while accounting for the correlations among the repeated measurements per judge. All statistical analyses steps were carried out using the R statistical software package (www.r-project.org).
Results and Discussion
Effect of irradiation on quality factors Color. For Sugraone grapes, L∗ , a∗ , and h∗ were affected by all dose levels (P ≤ 0.05) with increasing doses resulting in darker and less green grapes (Table 3). However, the differences are not Statistical analysis. Linear fixed effect models were imple- visually obvious (Figure 1) and the trained panel did not detect mented to assess the effects of age and irradiation dose on each of any dose-dependent differences. The b∗ and C∗ values were only the dependent variables in the analytical study. In the consumer affected by 800 Gy. There was no significant change (P ≤ 0.05)
Figure 5–Effect of irradiation and storage on the overall weight loss of one box of Sugraone grapes (above) and one box of Crimson Seedless grapes (below).
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Effects of irradiation on table grapes . . . Table 5–Effect of irradiation and storage on estimated means of % berry shatter (% of grape berries that fell off the rachis with shaking) for Sugraone and Crimson Seedless grapes. Values in the same column that are followed by the same letter are not significantly different. There was no significant difference due to storage. Sugraone grapes Dose (Gy)
Day 7
0 400 600 800
18.0 19.7 12.4 21.9
± ± ± ±
Crimson Seedless grapes Day 21
2.1 a 2.6 a 2.6 b 2.6 a
18.0 19.7 12.4 21.9
± ± ± ±
Day 1
1.9 a 2.1 a 2.1 b 2.1 a
9.3 7.1 12.3 6.5
± ± ± ±
Day 8
2.5 a 2.9 a 2.9 a 2.9 a
8.7 6.5 11.7 5.9
± ± ± ±
Day 22
2.5 a 2.5 a 2.5 b 2.5 a
13.7 11.5 16.7 10.9
± ± ± ±
2.5 a 2.5 a 2.5 b 2.5 a
Table 6–Estimated means measured by a trained sensory panel for Sugraone grape attributes that were significantly (P ≤ 0.05) different from control using unstructured, anchored 15 cm scalesa,b .
0 400 600 800
Day 7 9.26 7.58 6.60 5.35
± ± ± ±
Skin Firmness
Day 21
0.71 ax 0.58 bx 0.58 bcx 0.58 cx
8.91 7.22 6.25 5.00
± ± ± ±
0.42 ax 0.70 bx 0.70 bcx 0.70 cx
Day 7 7.17 6.45 6.25 5.82
± ± ± ±
2.70 4.72 2.93 2.73
Day 7 ± 0.74 ax ± 0.77 bx ± 0.77 ax ± 0.77 ax
7.39 9.06 9.02 8.94
Day 7 ± 1.05 ax ± 0.48 bx ± 0.48 bx ± 0.48 bx
6.88 6.16 5.96 5.52
± ± ± ±
0.31 ax 0.40 abx 0.40 bx 0.40 bx
Day 7 5.26 4.85 4.33 3.34
± ± ± ±
Day 21
0.50 ax 0.46 abx 0.46 bx 0.46 cx
Bruising 4.59 6.61 4.82 4.62
Day 21 ± 0.55 ay ± 0.72 by ± 0.72 ay ± 0.72 ay
0.13 2.32 1.20 1.10
Day 7 ± 0.59 ax ± 0.41 cx ± 0.41 bx ± 0.41 bx
Sweetness Dose (Gy) 0 400 600 800
Day 21
0.41 ax 0.43 abx 0.43 bx 0.43 bx
Color Dose (Gy) 0 400 600 800
Flesh Firmness
8.20 9.87 9.83 9.75
7.91 9.44 9.34 9.36
Day 7 ± 0.84 ax ± 0.55 bx ± 0.55 bx ± 0.55 bx
± ± ± ±
0.33 ax 0.49 abx 0.49 bx 0.49 cx
Bloom
Day 21 1.71 ± 0.30 ay 3.90 ± 0.58 cy 2.78 ± 0.58 by 2.67 ± 0.58 by
1.86 1.86 3.19 3.76
Flavor Day 21 ± 0.35 ay ± 1.04 by ± 1.04 by ± 1.04 by
5.01 4.60 4.09 3.09
Day 7 ± 0.59 ax ± 0.58 ax ± 0.58 bx ± 0.58 bx
Day 21 3.38 ± 0.42 ay 3.38 ± 0.58 ay 4.70 ± 0.58 by 3.76 ± 0.58 by
Juiciness
Day 21 8.58 ± 0.40 ax 10.78 ± 0.83 bx 10.01 ± 0.83 bx 10.03 ± 0.83 bx
8.83 9.94 10.40 10.28
Day 7 ± 0.57 ax ± 0.55 bx ± 0.55 bx ± 0.55 bx
Day 21 9.63 ± 0.39 ay 10.75 ± 0.56 by 11.21 ± 0.56 by 11.09 ± 0.56 by
a Teeth Firmness, Skin Firmness, Flesh Firmness, Bruising, Sweetness, Flavor 0 = none 15 = very intense; Bloom 0 = very intense 15 = none; Color 0 = very green 15 = very brown; Juiciness 0 = none 15 = intense juiciness. b Values in the same column/row that are followed by the same letter are not significantly P ≤ 0.05 different (a-c for row or dose and x-y for column or age).
in color due to age. With Crimson Seedless, no consistent effect of irradiation dose on color was discerned (Table 3) and no visual difference between control and irradiated grapes were observed (Figure 2). Kock and Holz (1991) observed that treatment at 2.0 and 3.0 kGy caused the yellow-green grapes of the Bien Donn´e variety to turn brown with dark longitudinal stripes and some Waltham Cross grape berries turned caramel brown; however, the color changes were attributed to the gibberellic acid that was applied during growth. Texture. For Sugraone grapes on day 7, the compression firmness of the grapes treated with 600 and 800 Gy was significantly (P ≤ 0.05) lower than the control (Figure 3). On day 21, all dose levels of Sugraone grapes were significantly softer than the grapes on day 7, revealing an interaction effect of irradiation and age. The Kramer shear force for the Sugraone grapes decreased significantly (P ≤ 0.05) with increasing irradiation dose levels, displaying a dose dependency (Figure 4). However, the loss in firmness due to age (14.5% to 17.1%) was greater than the decrease due to irradiation (3.4% to 15.5%). The compression firmness and Kramer shear force of Crimson Seedless grapes was significantly (P ≤ 0.05) lower with all dose levels of irradiation (6.5% to 10.3%) (Figure 3 and 4). Age also affected compression firmness (0.8% to 3.2%), but irradiation had a significantly (P ≤ 0.05) greater effect than age. The differences between dose levels were not significant and the dose dependency observed in Sugraone grapes was not evident in Crimson Seed-
less grapes. The Kramer shear force for Crimson Seedless grapes was not significantly affected by age. Thus, there appears to be differences in varietal response. The Sugraone grapes were more affected by age as compared to the Crimson Seedless. Berry softening postharvest is mainly due to water loss but a decrease in pectin content also occurs during postharvest storage (Chervin and others 2012). The decrease in softness with irradiation may be due to an accelerated decrease in pectin and breakdown of other structural polysaccharides. Kock and Holz (1991) observed softening in the Waltham Cross variety of grapes at 3.0 kGy. More recently, McDonald and others (2012) observed irradiation induced loss of firmness in peaches. In a study by Prakash and others (2002), tissue softening was observed in irradiated tomatoes and it was attributed to changes in the cell wall components, particularly the water-soluble pectin, although breakdown of other structural components such as cellulose and hemicellulose may have also contributed to the loss in firmness. SSC and TA. Sugraone grapes had an SSC below 16.5 but the Crimson Seedless had an SSC closer to 20 (Table 4). In both grape varieties, there were neither dose- nor age-dependent changes in SSC. In a study by Moreno and others (2007), irradiation levels below 1.1 kGy did not affect SSC in blueberries. McDonald and others (2012) reported that peaches treated at 0.49 kGy had significantly (P ≤ 0.05) lower Brix values compared to control but the difference was small, at most 0.68%. Vol. 79, Nr. 1, 2014 r Journal of Food Science S87
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Teeth Firmness Dose (Gy)
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Day 1 10.98 ± 0.76 ax 11.12 ± 0.46 ax 11.49 ± 0.46 ax 11.54 ± 0.46 ax
Dose (Gy) 0 400 600 800 Day 8 10.15 ± 0.40 ay 10.29 ± 0.76 ay 10.66 ± 0.76 ay 10.71 ± 0.76 ay
Sweetness
Day 8 7.18 ± 0.32 ay 6.96 ± 0.53 ay 6.58 ± 0.53 ay 6.67 ± 0.53 ay
Finger firmness
± ± ± ± 0.49 ay 0.49 ay 0.49 ay 0.49 ay
Day 22 10.84 ± 0.40 ax 10.98 ± 0.76 ax 11.35 ± 0.76 ax 11.40 ± 0.76 ax
Day 22 6.51 ± 0.32 ay 6.29 ± 0.53 ay 5.91 ± 0.53 ay 6.00 ± 0.53 ay
9.77 9.38 8.76 9.06
Day 22
10.89 10.83 10.80 11.06
4.85 4.65 6.20 5.01
7.56 6.36 6.30 7.04
0.68 ax 0.57 bx 0.57 bx 0.57 ax
Day 1 ± 0.69 ax ± 0.52 ax ± 0.52 ax ± 0.52 ax
Day 1 ± 0.44 ax ± 0.51 abx ± 0.51 bx ± 0.51 abx
± ± ± ±
Day 1
9.56 9.50 9.47 9.73
5.20 5.00 6.55 5.36
7.79 6.59 6.53 7.27
0.49 ax 0.68 bx 0.68 bx 0.68 ax
Day 8 ± 0.45 ay ± 0.69 ay ± 0.69 ay ± 0.69 ay
Flavor
Day 8 ± 0.44 ax ± 0.44 abx ± 0.44 bx ± 0.44 abx
Color
± ± ± ±
Day 8
Skin firmness
± ± ± ± 0.49 ay 0.68 by 0.68 by 0.68 ay
Day 22 10.39 ± 0.45 ax 10.33 ± 0.69 ax 10.30 ± 0.69 ax 10.56 ± 0.69 ax
Day 22 5.49 ± 0.44 ax 5.29 ± 0.44 abx 6.84 ± 0.44 bx 5.65 ± 0.44 abx
6.31 5.11 5.05 5.79
Day 22 ± ± ± ±
0.46 ax 0.41 ax 0.41 bx 0.41 ax
Day 1 11.30 ± 0.36 ax 11.92 ± 0.33 ax 11.78 ± 0.33 ax 11.73 ± 0.33 ax
Day 1 2.42 ± 0.59 ax 4.30 ± 0.62 bx 6.16 ± 0.62 bx 5.72 ± 0.62 bx
5.79 5.42 4.77 5.09
Day 1
± ± ± ±
0.35 ax 0.47 ax 0.47 bx 0.47 ax
Day 8 10.35 ± 0.29 ay 10.97 ± 0.36 ay 10.83 ± 0.36 ay 10.78 ± 0.36 ay
Juiciness
Day 8 4.91 ± 0.53 ay 6.79 ± 0.59 by 8.65 ± 0.59 by 8.21 ± 0.59 by
Rachis
5.56 5.19 4.54 4.86
Day 8
Flesh firmness
0.35 ax 0.47 ax 0.47 bx 0.47 ax
Day 22 10.37 ± 0.29 ay 10.99 ± 0.36 ay 10.85 ± 0.36 ay 10.80 ± 0.36 ay
Day 22 6.52 ± 0.53 ay 8.40 ± 0.59 by 10.26 ± 0.59 by 9.82 ± 0.59 by
± ± ± ±
Day 22 5.36 4.99 4.34 4.66
Teeth Firmness, Skin Firmness, Flesh Firmness, Bruise, Sweetness, Flavor 0 = none 15 = very intense; Bloom 0 = very intense 15 = none; Color 0 = green/cream 15 = purple/black; Juiciness 0 = none 15 = intense juiciness. Values in the same column/row that are followed by the same letter are not significantly P ≤ 0.05 different (a-c for row or dose and x-z for column or age).
b
a
Day 1 8.17 ± 0.53 ax 7.95 ± 0.37 ax 7.57 ± 0.37 ax 7.66 ± 0.37 ax
Dose (Gy) 0 400 600 800
0.49 ax 0.49 ax 0.49 ax 0.49 ax
± ± ± ±
10.28 9.89 9.27 9.57
± ± ± ±
11.08 10.69 10.07 10.37
0 400 600 800
0.49 ax 0.57 ax 0.57 ax 0.57 ax
Day 8
Day 1
Dose (Gy)
Teeth firmness
Table 7–Estimated means measured by a trained sensory panel for Crimson Seedless grape attributes that were significantly (P ≤ 0.05) different from control using unstructured, anchored 15 cm scalesa,b .
Effects of irradiation on table grapes . . .
Effects of irradiation on table grapes . . . Similarly, irradiation did not significantly (P ≤ 0.05) affect TA (Table 4), except 400 Gy for Sugraone grapes but TA decreased with age. Moreno and others (2007) found similar results where treatment up to 3.2 kGy did not significantly (P < 0.05) affect the pH or acidity in blueberries. McDonald and others (2012) only observed a statistically significant (P ≤ 0.05) decrease in TA with peaches treated at 0.9 kGy but considered the difference negligible. The TA for Crimson Seedless grapes on day 22 was unable to be measured so the decrease in pH could not be observed. In the United States, when the SSC is less than 16.5, the SSC/TA ratio needs to be greater than 20 (Chervin and others 2012), which was observed for both varieties of grapes (Table 4). In this study, the SSC/TA ratio increased during storage but was unaffected by irradiation. Weight loss. Grapes lost up to 11% to 12% of their weight during the 3 wk of storage likely due to dehydration and the rate of weight loss was similar for all dose levels (Figure 5). Al-Bachir (1999) found that the Helwani variety of grape irradiated at 500 Gy and stored for up to 12 wk showed no difference in weight loss as compared to the control but the Baladi variety of grapes treated at 500 Gy had an increased weight loss.
Effect of irradiation on sensory properties Descriptive testing. Firmness, bruising, bloom, rachis, color, juiciness, sweetness, and flavor were significantly (P ≤ 0.05) affected by irradiation in Sugraone grapes (Table 6). On day 7, the Sugraone grapes showed a dose dependency in texture, increasing in softness with increasing dose. These results correspond with the analytical measurements made with the Kramer shear. Firmness was not significantly affected by age (P > 0.05). The juiciness of the Sugraone grapes increased significantly (P ≤ 0.05) with irradiation and age and may be correlated to the increased softness in texture. Bruising in Sugraone grapes was significantly (P ≤ 0.05) greater in irradiated samples but it was not dose dependent. The 400 Gy treated grapes was reported to have a significantly greater amount of bruising than 600 Gy and 800 Gy. The color of 400 Gy treated grapes was also reported as significantly darker than the control, which may correlate to the bruising. There was also significantly (P ≤ 0.05) less bloom on the 600 Gy and 800 Gy treated grapes that continued to decrease with age that suggests irradiation at the higher doses may accelerate the breakdown of the waxy protective coating. All dose levels of irradiation increased the sweetness and flavor in the Sugraone grapes significantly (P < 0.05) but there were no differences between irradiation dose levels. Sweetness also significantly (P ≤ 0.05) increased with age for all dose levels including control. Finger firmness and juiciness of Crimson Seedless grapes were not significantly (P < 0.05) affected by irradiation but were significantly affected by age (Table 7). The sweetness and flavor for Crimson Seedless grapes were significantly (P ≤ 0.05) lower on day 8 but increased on day 22 for all dose levels including control.
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Berry shatter. Irradiation dose did not influence berry shatter (Table 5) except for an anomaly at 600 Gy where the 600 Gy treated Sugraone grapes had a significantly lower level and the 600 Gy treated Crimson Seedless had a significantly higher level (P < 0.05) of berry shatter as compared to the other dose levels. Storage had no effect on berry shatter for Sugraone grapes. For the Crimson Seedless grapes, berry shatter increased during storage but remained lower overall than the Sugraone grapes. Berry shatter can occur due to water loss, and physiological, pathological, and mechanical causes (Chervin and others 2012);
however, it does not appear that irradiation caused additional stress to impact berry shatter.
Figure 6–Estimated hedonic scores, or the degree of liking, of Sugraone grapes for overall liking, texture, appearance, flavor, and juiciness for control and 800 Gy treated grapes. Bars with the same letter for each variety are not significantly P ≤ 0.05 different (a-c for dose and x-y for age).
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Effects of irradiation on table grapes . . .
Figure 7–Estimated hedonic scores, or the degree of liking, of Crimson Seedless grapes for overall liking, texture, appearance, flavor, and juiciness for control and treated samples. Bars with the same letter for each variety are not significantly P ≤ 0.05 different (a-c for dose and x-y for age).
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The rachis of Crimson Seedless grapes was significantly (P ≤ 0.05) browner with irradiation. The respiration rate of the rachis may be up to 15 times that of the berries and can contribute to its browning (Chervin and others 2012). There is also a strong correlation between water loss in the cluster and stem browning; a water loss of 2% or more will result in browning after 7 d of cold storage. It is possible that irradiation accelerated the respiration rate, which may have enhanced the browning of the rachis, especially the 800 Gy treated samples.
Conclusions Irradiation affected each variety of grapes differently. The primary effect of irradiation on the quality of Sugraone and Crimson Seedless table grape varieties was softening in texture; however, Sugraone grapes were more sensitive to changes in texture than the Crimson Seedless. Sensory attributes that were affected for both varieties were berry softening and rachis browning. The negative effects observed in Sugraone grapes were an increase in bruising and decrease in bloom, and the positive effects were an increase in sweetness, flavor, and juiciness with irradiation. Consumer acceptance was statistically significantly lower only in the texture of Sugraone treated grapes with a difference of 0.59 from control on a 9-point scale. Consumers could not tell irradiated Crimson Seedless grapes from control and scored them both above “Like Very Much” on the 9-point scale for all attributes. The consumers tasted 800 Gy treated samples for Sugraone grapes, which is the highest likely dose level under commercial conditions in grapes treated at a target dose of 400 Gy. Thus, irradiation levels required for phytosanitary purposes appear to maintain grape quality during 3 wk of storage. Further research should be performed to measure the quality of Sugraone and Crimson Seedless grapes treated under commercial conditions. A comparison of quality with other phytosanitary treatments would also be valuable.
Consumer acceptability of irradiated grapes. On day 7, consumers liked the control samples of Sugraone grapes significantly (P ≤ 0.05) more than the 800 Gy treated samples only in texture but the degree of liking for both samples were close in value on the 9-point hedonic scale (Figure 6). The biggest difference in rating was for the “appearance” which was rated 0.5 lower on the 9-point scale but it was not significant. The degree of liking for both control and treated samples decreased with age. On day 21, consumers liked control more than treated samples and the difference in rating was 0.59 on the 9-point scale but it was not significant. For Crimson Seedless grapes, the 800 Gy samples were tested on day 1 and 600 Gy treated grapes were tested on day 8 and day 22. There were no significant (P ≤ 0.05) differences between control and 800 Gy or 600 Gy irradiated Crimson Seedless grapes for any of the attributes (Figure 7). Consumers scored the flavor, juiciness, and overall liking of control and 800 Gy or control and 600 Gy similarly. Consumers liked the texture of Crimson Acknowledgments Seedless grapes more with age, where the texture of the grapes The project was funded by a TASC grant from USDA-FAS. was softer, although the difference was not significant (P ≤ 0.05). Based on the results of the trained panel, it is highly unlikely References that consumers would score 600 Gy and 800 Gy treated grapes Al-Bachir M. 1999. Effect of gamma irradiation on storability of two cultivars of Syrian grapes differently. (Vitis vinifera). Radiat Phys Chem 55(1):81–5. S90 Journal of Food Science r Vol. 79, Nr. 1, 2014
Effects of irradiation on table grapes . . . McDonald H, McCulloch M, Caporaso F, Winborne I, Oubichon M, Rakovski C, Prakash A. 2012. Commercial scale irradiation for insect disinfestation preserves peach quality. Radiat Phys Chem 81(6):697–704. Mitcham EJ, Ahumada M, Shorey H. Controlled atmospheres as a potential quarantine treatment for table grapes [Internet]. Perishables Handling Newsletter Issue Nr. 9. Dept. of Pomology, UC Davis; May 1997. Available from: http://ucce.ucdavis.edu/files/datastore/234--161.pdf. Accessed Dec 11, 2012. Moreno MA, Castell-Perez ME, Gomes C, Da Silva PF, Moreira RG. 2007. Quality of electron beam irradiation of blueberries (Vaccinium corymbosum L.) at medium dose levels (1.0–3.2 kGy). LWT-Food Sci Technol 40(7):1123–32. National Agricultural Statistics Service (NASS): 2011 Agricultural statistics annual [Internet]. Washington, D.C.: USDA NASS; c1957–2012. Available from: http://www.nass.usda. gov/Publications/Ag_Statistics/2011/index.asp. Accessed Dec 1, 2012. Peryam DR, Pilgrim FJ. 1957. Hedonic scale method of measuring food preferences. Food Technol 11:9–14. Prakash A, Manley J, DeCosta S, Caporaso F, Foley D. 2002. The effects of gamma irradiation on microbiological, physical, and sensory qualities of diced tomatoes. Radiat Phys Chem 63(3–6):387–90. Stone H, Sidel JL. 2004. Sensory evaluation practices. 3rd ed. San Diego, Calif.: Elsevier Academic. p 408. US EPA (United States Environmental Protection Agency): The phaseout of methyl bromide [Internet]. Washington, D.C.: USEPA: c1970–2012. Available from: http://www. epa.gov/ozone/mbr/. Accessed December 1, 2012.
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APHIS PPQ (Animal and Plant Health Inspection Service Plant Protection and Quarantine): Treatment manual – chemical treatments – fumigants [Internet]. Riverdale, Md.: USDA APHIS PPQ; c1972–2012. Available from: http://www.aphis.usda.gov/ import_export/plants/manuals/ports/downloads/treatment.pdf. Accessed Dec 1, 2012. AQIS (Australian Quarantine Inspection Service Dept. of Agriculture, Fisheries, and Forestry). 2012. Quarantine alert. Available from: http://www.aqis.gov.au/icon32/asp/ex_ topiccontent.asp?TopicType = Quarantine+Alert&TopicID=24745. Accessed Dec 11, 2012. California Table Grape Commission (CTGC): California varieties [Internet]. Fresno, Calif.: CTGC; c2000–2012. Available from: http://www.freshcaliforniagrapes.com/docs/ VarietyChart2011.pdf. Accessed Dec 1, 2012. Chambers E, Wolf MB. 1996. Sensory testing methods. 2nd ed. MNL-26. West Conshohocken: American Society for Testing and Materials Intl. p 115. Chervin C, Aked J, Crisosto CH. 2012. Grapes. In: Rees D, Farrell G, Orchard J, editors. Crop post-harvest: science and technology. 1st ed. Oxford: Blackwell Publishing Ltd. p. 187–210. Code of Federal Regulations. 2012. Ionizing radiation for the treatment of food. 21 C.F.R. § 179.26. Washington, D.C.: U.S. Government Printing Office. Hallman GJ. 2012. Generic phytosanitary irradiation treatments. Rad Phys Chem 81:861–6. Hootman RC. 1992. Descriptive analysis testing for sensory evaluation. MNL 13. West Conshohocken: American Society for Testing and Materials International. p 40. Kock PJ de, Holz G. 1991. Use of gamma irradiation for control of postharvest Botrytis cinerea bunch rot of table grapes in cold storage. S Afr J Enol Vitic 12(2):82–6. Lawless HT, Heymann H. 2010. Sensory evaluation of food: principles and practices. 2nd ed. New York: Springer. p 596. Lydakis D, Aked J. 2003. Vapour heat treatment of Sultanina table grapes. II: Effects on postharvest quality. Postharv Biol Tec 27(2):117–26.
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Abstract: Grapes (Vitis vinifera var. Sugraone and Vitis labrusca var. Crimson Seedless) were treated with 400, 600, and 800 Gy and the effects on physicochemical factors were measured alongside sensory testing during 3 wk of storage. Significant changes in texture and color with irradiation and age were measured but little visual difference was seen between control and irradiated grapes. However, age had a greater effect on firmness than irradiation for Sugraone grapes. Irradiation did not significantly (P ≤ 0.05) affect the SSC/TA ratio, which increased during storage. The trained panel detected significant changes in the berry texture and rachis color but rated sweetness and flavor significantly higher (P ≤ 0.05) for irradiated Sugraone as compared to the control. Consumers liked both the untreated and 800 Gy treated Sugraone grapes, but liked the untreated grapes more for texture (P ≤ 0.05). However, there was no difference in liking between irradiated (600 Gy or 800 Gy) and control samples of Crimson Seedless for any attribute. The results show that there are varietal differences in response to irradiation but the overall maintenance in quality of irradiated grapes during 3 wk of storage indicates that irradiation can serve as a viable phytosanitary treatment. Keywords: gamma irradiation, phytosanitary, table grapes, quality, sensory
This study shows that Sugraone and Crimson Seedless table grapes have very good tolerance to irradiation at dose levels needed for insect disinfestation and should be considered for use as a phytosanitary treatment in the export of these varieties. There were some differences in the responses of the 2 varieties to treatment indicating the need to evaluate each variety. Further research should be performed with commercial conditions of gamma irradiation treatment and distribution. A comparison study with other phytosanitary treatments on the quality of these table grapes would also be valuable.
Introduction According to the USDA Natl. Agriculture Statistics Service (USDA NASS), 7.4 million tons of grapes were produced in the United States in 2010 with a value of 3.6 billion dollars (NASS 2011). Approximately 90% of grapes in the United States are grown in California, which contributes to the world grape market by exporting more than 328000 tons to over 60 different countries. Phytosanitary treatments are used to prevent the introduction or spread of quarantine pests. There are several methods that can be used to treat grapes for phytosanitary purposes (APHIS 2012). Currently, the most widely used treatment for grapes is methyl bromide fumigation. However, methyl bromide is in the process of being phased out as mandated by the Montreal Protocol because it is an environmental pollutant that is depleting the ozone layer (US EPA 2012). In June 2012, Australia amended their import conditions of table grapes from California to no longer accept methyl bromide fumigation for imported fresh table grapes (AQIS 2012). Australia instead requires imported grapes to be treated with a mixture of SO2 and CO2 , followed by cold treatment. Carbon dioxide in conjunction with cold storage is effective against common table grape insect pests such as Omnivorous Leaf Roller (Platynota stultana), Western Flower Thrips (Frankliniella occidentalis), Spider
MS 20130241 Submitted 2/20/2013, Accepted 9/21/2013. Authors are with Chapman Univ., 1 Univ. Drive, Orange, CA 92866, U.S.A. Direct inquiries to author Prakash (E-mail: [email protected]).
R C 2013 Institute of Food Technologists
doi: 10.1111/1750-3841.12307 Further reproduction without permission is prohibited
Mites, Grape Mealy Bug (Pseudococcus maritimus) (Mitcham and others 1997) as well as black widow spiders (Chervin and others 2012). Irradiation can be an alternative to methyl bromide, carbon dioxide, and cold treatments and is gaining use all over the world as a phytosanitary treatment for various fruit due to its efficacy on insects and maintenance of fruit quality (Hallman 2012). The objective of irradiation is not necessarily mortality, but rather the prevention of immature pests developing into maturity and sterility of adults that may be present in the fruit. Low levels of irradiation can break the bonds in the genetic material of the pests to kill or sterilize while leaving no residue on the food. At the present time, it is one of the best substitutes for fumigants in the disinfestation of produce since low doses can control quarantine pests and adverse changes in produce may be insignificant at those levels. The USDA has approved irradiation at a generic dose of 150 Gy for fruit flies of the Tephritidae family and 400 Gy for all insects except pupae and adult of Lepidoptera (APHIS 2012). The upper limit for treatment of fresh produce in the United States is 1000 Gy (21 CFR 179.26). Several factors such as fruit maturity, the specific cultivar/varieties, and other inherent physical or chemical properties can affect how fruit quality responds to irradiation (McDonald and others 2012) but there is limited information available on the effect of irradiation of grapes. Kock and Holz (1991) evaluated the use of gamma irradiation up to 3.0 kGy to control postharvest Botrytis cinerea rot in several varieties of cold-stored SO2 treated table grapes. Treating the table
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Practical Application:
Effects of irradiation on table grapes . . . Table 1–Anchors on 15-point unstructured scales for Sugraone grape attributes. Attribute
0
Skin color Skin blemishes Skin bruising Skin bloom Rachis browning Stem quality Detachment force Finger firmness
Bright green None None Dull Green Brittle None None
Skin texture
None
Flesh firmness
None
Teeth firmness
None
Juiciness
None (Carrot)
Sweetness
None
Sour
None
Flavor
None
Off-flavor Astringency
None None
1
Kraft Philadelphia Cream Cheese Kraft Philadelphia Cream Cheese Kraft Philadelphia Cream Cheese Kraft Philadelphia Cream Cheese
2.5
Boiled egg white Boiled egg white Boiled egg white Boiled egg white
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grapes with irradiation closer to the packing day was found to be more effective and resulted in less decay than treatments applied after storing the fruit for 9 d. In general, a decrease in Botrytis cinerea occurrence was observed in irradiated grapes. Combining irradiation with SO2 treatment was found to be efficacious but color changes occurred in Bien Donn´e and Waltham Cross berries at 2 to 3 kGy. No other adverse effects on quality were observed due to irradiation. Irradiation improved the shelf life of 2 cultivars of Syrian grapes, Helwani and Baladi (Al-Bachir 1999). A measurement of weight loss and assessment of fungal growth was used to determine total loss. Each variety responded differently to treatment levels and the authors suggested that optimum irradiation dose for reducing fungal decay and extending shelf life in cold storage is related to the thickness of skin, firmness, and hardness of the flesh of the grape berries. These studies indicate that different cultivars of grapes have differing radiotolerance to irradiation. However, none of these studies evaluated changes in sensory qualities of the grapes; their focus was on using irradiation to limit fungal decay. The objective of this study was to determine the effects of phytosanitary irradiation treatment on the physicochemical properties and sensory quality of 2 table grape varieties, Vitis vinifera var. Sugraone and Vitis labrusca var. Crimson Seedless, which are grown in California and have a high export value (CTGC 2012). While 400 Gy is the target phytosanitary dose, commercial irradiation treatment delivers a range of dose levels. In some package configurations, doubling of the target dose may occur depending on uniformity of treatment. Thus in this study, we evaluated the radiotolerance of Sugraone and Crimson Seedless grapes treated up to 800 Gy. The physicochemical parameters of quality such as color, soluble solid content, titratable acidity, texture, and shelf life were measured using analytical instrumentation. A trained sensory panel evaluated attributes that may have changed due to irradiation and storage. Consumer panels were used to determine overall liking of the irradiated grapes compared to control. S82 Journal of Food Science r Vol. 79, Nr. 1, 2014
6
Goya Olive Goya Olive Goya Olive Goya Olive
9.5
Nabisco Planter Peanut Nabisco Planter Peanut Nabisco Planter Peanut Nabisco Planter Peanut
14.5
Nabisco LifeSaver hard candy Nabisco LifeSaver hard candy Nabisco LifeSaver hard candy Nabisco LifeSaver hard candy
15 Brown Intense Intense Shiny Brown Strong Intense Intense Intense Intense Intense Intense (Watermelon) Intense (Pure sugar) Intense (Lemon wedge) Intense (Grape juice) Intense Intense (Dry red wine)
Table 2–Values of F-statistic and the respective levels of significance for the Sugraone sensory attributes evaluated by judges. Sensory descriptor Color Blemish Bruising Bloom Finger firmness Teeth firmness Juiciness Sweet Sour Overall flavor Off-flavor
Fsample × judge
P-value
0.49 0.47 0.57 0.36 0.72 0.63 0.85 0.54 0.65 0.72 1.15
0.99 0.99 0.99 0.99 0.98 0.98 0.95 0.99 0.98 0.98 0.87
Fsample × judge : F-statistic (ANOVA) for sample and judge interaction. P-value: significance level at 5% probability.
Materials and Methods Sample procurement Fresh green grapes (Vitis vinifera) var. Sugraone, and fresh red grapes (Vitis labrusca) var. Crimson Seedless were obtained from a farm in the San Joaquin Valley region of California in July and October 2011, respectively. Immediately following harvest, the grapes were treated with SO2 in cold storage for approximately 8 h and precooled using forced-air to 1 to 2 ◦ C. They were bulk packed in 9 kg Styrofoam boxes that contained 8 perforated bags, each bag weighing approximately 1100 g. The grapes were stored at 0 to 1 ◦ C in a warehouse for 1 wk. Forty cases of grapes were then transported by refrigerated truck (1 to 3 ◦ C) to Sterigenics Intl., Inc. (Sterigenics) in Tustin, California for gamma irradiation treatment. Irradiation treatment The target irradiation dose levels were 400, 600, and 800 Gy. The cases of grapes were placed at a precise distance from a Co 60 source (approximately 1 million curies) to receive treatment
4.48 4.88 4.44 4.75 Day 1 ± 0.18 ay ± 0.20 by ± 0.20 ay ± 0.20 aby 4.93 5.33 4.89 5.20 Day 22 14.12 ± 0.25 ay 13.69 ± 0.24 aby 13.45 ± 0.24 by 14.13 ± 0.24 ay
Sample preparation Sugraone grapes were evaluated 7 and 21 d after irradiation treatment and the Crimson Seedless grapes were evaluated 1, 8, and 22 d after treatment. Evaluation of Sugraone grapes on day 1 could not be performed due to a scheduling conflict. One day before each evaluation, clusters from 3 cases of grapes of each dose level were prepared for analysis. The top 1 or 2 secondary rachis and the bottom 3 to 4 inches of the grape clusters were removed. For analytical testing, unwashed grapes were set aside and kept in cold storage. The grapes for sensory evaluation were washed, patted dry with paper towels, placed in a container, covered with plastic wrap, and kept in refrigeration until the following day. The grapes were pulled out from cold storage 2 h prior to analytical and sensory testing to bring them to room temperature. For each of the analytical tests, grape berries were selected at random and removed from the rachis right before testing. For the sensory evaluation, the grapes were kept on the rachis and cut into smaller clusters to serve to trained panelists and consumers on paper boats. Analytical testing Color. The color of 50 grape berries treated at each dose level was measured using a Konica Minolta Spectrophotometer CM2500d (Konica Minolta Sensing Americas, Inc., Ramsey, N.J., USA). Opposite sides of each grape berry were measured for a total of 100 measurements for each dose level. There were 5 color components that were measured: L∗ (lightness 100 = white,
Day 1 38.77 ± 0.30 ax 39.57 ± 0.34 bx 39.01 ± 0.34 ax 38.89 ± 0.34 ax Dose (Gy) 0 400 600 800
L
Day 8 38.15 ± 0.30 ay 38.95 ± 0.30 by 38.39 ± 0.30 ay 38.27 ± 0.30 ay
Day 22 40.78 ± 0.30 az 41.58 ± 0.30 bz 41.02 ± 0.30 az 40.90 ± 0.30 az
Day 1 14.58 ± 0.22 ax 14.41 ± 0.26 ax 13.98 ± 0.26 bx 14.67 ± 0.26 ax
Day 8 14.18 ± 0.22 ax 14.02 ± 0.22 ax 13.59 ± 0.22 bx 14.28 ± 0.22 ax
Day 22 15.65 ± 0.22 ay 15.49 ± 0.22 ay 15.06 ± 0.22 by 15.75 ± 0.22 ay
Day 1 20.34 ± 1.13 ax 23.86 ± 1.31 bx 21.37 ± 1.31 ax 21.32 ± 1.31 ax
Day 8 18.48 ± 1.13 ax 22.00 ± 1.12 bx 19.51 ± 1.12 ax 19.46 ± 1.12 ax
Day 22 23.38 ± 1.12 ay 26.90 ± 1.12 by 24.41 ± 1.12 ay 24.36 ± 1.12 ay
13.37 12.95 12.71 13.39
Day 1 ± 0.25 ax ± 0.29 abx ± 0.29 bx ± 0.29 ax
13.28 12.86 12.62 13.30
Day 8 ± 0.25 ax ± 0.24 abx ± 0.24 bx ± 0.24 ax
C Crimson Seedless grapes b a
Day 7 − 4.61 ± 0.06 ax − 4.37 ± 0.07 bx − 3.95 ± 0.07 cx − 3.59 ± 0.07 dx Day 21 49.52 ± 0.28 dy 46.80 ± 0.31 by 46.90 ± 0.31 cy 44.08 ± 0.31 ay Day 7 52.45 ± 0.31 dx 49.73 ± 0.40 bx 49.84 ± 0.40 cx 47.01 ± 0.40 ax Dose (Gy) 0 400 600 800
at a dose rate of 1000 Gy/h. The cases were arranged in two rows of 5 cases stacked one on top of the other. Midway through the treatment, the boxes were rotated 180◦ for uniformity of the treatment. Dose mapping was also conducted to ensure uniformity of dose, with dummy cases in the same exact configuration using alanine pellet dosimeters (Far West Technology, Inc., Goleta, Calif., U.S.A.). The cases treated with 400 Gy received a maximum dose of 500 Gy and minimum dose of 300 Gy for a Dmax/Dmin of 1.67. The target dose of 600 Gy resulted in a range of 500 to 700 Gy for a Dmax/Dmin of 1.4 and the 800 Gy target achieved an absorbed dose range of 700 to 900 Gy, respectively, for a Dmax/Dmin of 1.3. Following the treatment, the grapes were transported to Chapman Univ. where they were stored at 3 to 5 ◦ C until testing.
Figure 1–Appearance of Sugraone grapes treated with irradiation at 0, 400, 600, and 800 Gy and stored for 7 and 21 d.
Vol. 79, Nr. 1, 2014 r Journal of Food Science S83
S: Sensory & Food Quality
Day 22 ± 0.18 az ± 0.18 bz ± 0.18 az ± 0.18 abz h
Day 8 ± 0.18 ax ± 0.18 bx ± 0.18 ax ± 0.18 abx
5.88 6.28 5.84 6.15
Day 21 108.53 ± 0.22 ay 107.12 ± 0.24 by 106.13 ± 0.24 cy 107.20 ± 0.24 by h Day 7 107.40 ± 0.24 ax 105.99 ± 0.30 bx 105.00 ± 0.30 cx 106.07 ± 0.30 bx Day 21 14.38 ± 0.26 ay 14.56 ± 0.29 ay 13.99 ± 0.29 ay 11.77 ± 0.29 by C Day 7 15.94 ± 0.29 ax 16.12 ± 0.36 ax 15.55 ± 0.36 ax 13.34 ± 0.36 bx Day 21 13.68 ± 0.26 ay 13.94 ± 0.28 ay 13.47 ± 0.28 ay 13.51 ± 0.28 by Day 7 15.24 ± 0.29 ax 15.50 ± 0.36 ax 15.03 ± 0.36 ax 12.84 ± 0.36 bx Day 21 − 4.38 ± 0.05 ay − 4.14 ± 0.06 by − 3.72 ± 0.06 cy − 3.36 ± 0.06 dy
Sugraone grapes b a L
Table 3–Estimated means for L, a, b, C, h color parameters for Sugraone and Crimson Seedless grapes. Values in the same row/column that are followed by the same letter are not significantly different (a-c for row or dose, x-y for column or age).
Effects of irradiation on table grapes . . .
Effects of irradiation on table grapes . . . 0 = black), C∗ (0 = no saturation, 100 = complete saturation), h∗ (0◦ = red, 90◦ = yellow, 180◦ = green, 270◦ = blue), a∗ (negative values = green, positive values = red), and b∗ (negative values = blue, positive values = yellow). Texture. The texture was measured in 2 ways: Compression firmness. A BioWorks Firmtech II Texture Analyzer (BioWorks, Inc., Wamego, Kans., U.S.A.) was used to measure the compression firmness, the amount of force required to compress each grape berry by one mm at a load cell speed of 15 mm/s and table speed at 0.98 mm/s. The compression firmness of 200 berries was measured for each dose level. Kramer shear. The texture of grapes was also measured using a Kramer shear press with 5 blades (TA-91) attached to a Stable Micro System Texture Analyzer (Model TA-XT2, Texture Technology Corp., Scarsdale, NY/Stable Microsystems, Godalming, UK). One hundred fifty grams of grapes were placed in the metal container of the Kramer shear cell. The 5-blade probe was set at
60 mm from the bottom of the 5-blade plunger. The test speed of the probe was set at 4.0 mm/s and the post-test speed was set at 10.0 mm/s. The shear force (kg) required to cut through the berries was recorded was measured as the peak force. The highest force occurred at maximum deformation. The measurements were replicated 6 times for each dose level. Soluble solids content (SSC). The grape berries used for texture measurement were collected and immediately juiced (Elite Gourmet Maxi-matic Juice Extractor TS-738; City of Industry, Calif., U.S.A.) then filtered through 12 layers of cheesecloth to remove pulp. A drop of the grape juice was placed on the prism of a handheld digital refractometer (LR45227 Milton Roy Co., Ivyland, Pa., U.S.A.) to determine SSC. This measurement was done in triplicate for each dose. Titratable acidity (TA). Five mL of the grape juice was combined with 50 mL of CO2 -free deionized water. Initial pH of the grape juice solution was measured (pH200 Hannah
Figure 2–Appearance of Crimson Seedless grapes treated with irradiation at 0, 400, 600, and 800 Gy and stored for 1, 8, and 22 d.
S: Sensory & Food Quality Figure 3–Effect of irradiation and storage on estimated means for compression firmness (the amount of force required to compress 1 mm) of Sugraone and Crimson Seedless grapes. Bars with the same letter for each variety are not significantly P ≤ 0.05 different (a-c for dose and x-y for age).
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Effects of irradiation on table grapes . . . Instruments, Woonsocket, R.I., U.S.A.) and titrated to pH 8.2 with 0.1 N NaOH. This was done in triplicate for each dose. Titratable acidity was calculated as % tartaric acid using the following equation: % Acid : (mL Base x N of base x 75.03) / (sample vol. x 1 0)
S: Sensory & Food Quality
Weight loss. One case of grapes from each dose level was set aside to determine overall weight loss during storage. The boxes of grapes were stored at 3 ◦ C. Weight measurements were taken throughout shelf life. Berry shatter. Ten bags of grapes were selected from the 3 cases of grapes of each dose level on each evaluation day. Each bag was weighed then the grape clusters were removed from the bag and gently shaken for 15 s. The grape berries that became detached were weighed and expressed as a percentage of the total weight of the bag (Lydakis and Aked 2003). Sensory evaluation. All sensory testing was conducted using ASTM Committee E-18 guidelines (Chambers and Wolf 1996; Stone and Sidel 2004; Lawless and Heymann 2010). Descriptive testing. Trained panelists were chosen based on interest and performance on preliminary screening tests. Ten panelists were selected to evaluate both Sugraone and Crimson Seedless grapes; however, one panelist withdrew from the Crimson Seedless evaluation for personal reasons. Five 60-min training sessions allowed the establishment of the vocabulary and scales to describe key attributes of grapes: color, blemishes, bruising, rachis (or stem) browning, finger firmness (firmness by pressing each grape berry between the forefinger and thumb), skin firmness (firmness of biting only grape skin in mouth), flesh firmness (firmness of biting only flesh in mouth), teeth firmness (firmness of biting whole grape berry in mouth), detachment force (pulling off grape berries from the rachis), juiciness, sweetness, sourness, flavor, off flavor,
and astringency. These characteristics were rated on a 15-point unstructured, anchored scale. All panelists agreed on the anchors on the scale for each attribute (Table 1). For attributes related to texture, products (shown in Table 1) associated with the standard hardness scale provided in an ASTM manual (MNL 13) were used (Hootman 1992). For attributes related to appearance, fresh grapes with no visible flaws purchased at a grocery store were used as the control. Damaged fruit or fruit at the end of shelf life were used as references for the right hand anchor of the appearancerelated attribute scales. The panelists evaluated the control and all dose levels of irradiated grapes (0, 400, 600, 800 Gy) throughout the investigation. Each panelist visually inspected a whole grape cluster for color, blemishes, bruising, and rachis browning. For the touch and taste evaluation, 10 to 12 grape berries that were attached to the rachis were served to each panelist. The panelists evaluated finger firmness, skin firmness, flesh firmness, teeth firmness, detachment force, juiciness, sweetness, sourness, flavor, off flavor, and astringency. Grape samples were presented in paper boats marked with 3-digit random number codes. To prevent any position bias, samples were served in a random balanced order so that each sample would be served 1st, 2nd, 3rd, or last randomly. Panelists were provided with unsalted soda crackers and filtered water for palate cleansing between taste attributes and samples (Chambers and Wolf 1996). An analysis of variance (Table 2) verified the judges were trained sufficiently. A low P-value for the F-statistic indicates inconsistency in judges’ scores in respect to each attribute. A P-value > 0.05 indicates the judges’ assessments are not significant from each other. It was concluded the panelists were sufficiently trained and their assessments are consistent and reliable. Consumer testing. For Sugraone grapes, consumers evaluated only the control and 800 Gy treated samples. For Crimson Seedless grapes, consumers were served control and 800 Gy treated
Figure 4–Effect of irradiation and storage on estimated means of the Kramer shear force (the amount of force need to cut through 150 g of grape berries) for Sugraone and Crimson Seedless grapes. Bars with the same letter for each variety are not significantly P ≤ 0.05 different (a-c for dose and x-y for age).
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Effects of irradiation on table grapes . . . Table 4–Effect of irradiation and storage on estimated means of SSC and TA. SSC and TA were used to calculate the SSC/TA ratio. Values in the same row/column that are followed by the same letter are not significantly different (a-c for row and dose, x-y for column and age). Sugraone grapes Day 7
Dose Gy 0 400 600 800
% SSC 14.70 14.92 14.77 14.30
± ± ± ±
Day 21
% TA
0.18 abx 0.23 bx 0.23 bx 0.23 ax
0.45 0.49 0.46 0.45
± ± ± ±
SSC/TA ratio
0.01 ax 0.02 bx 0.02 ax 0.02 ax
% SSC
32.67 30.45 32.11 31.04
14.50 14.72 14.57 14.10
± ± ± ±
% TA
0.16 abx 0.18 bx 0.18 bx 0.18 ax
± ± ± ±
0.20 0.24 0.21 0.20
SSC/TA ratio
0.01 ay 0.01 by 0.01 ay 0.01 ay
72.50 61.33 69.38 70.40
Crimson Seedless grapes Day 1 Dose Gy 0 400 600 800
% SSC 20.20 20.21 20.43 20.04
± ± ± ±
0.09 abx 0.11 abx 0.11 bx 0.11 ax
Day 8
% TA 0.37 0.42 0.36 0.38
± ± ± ±
0.09 ax 0.11 ax 0.11 ax 0.11 ax
SSC/TA ratio 54.59 48.12 56.75 52.74
% SSC 20.82 20.83 21.05 20.66
± ± ± ±
% TA
0.09 az 0.09 az 0.09 bz 0.09 az
S: Sensory & Food Quality
grapes on day 1 but on day 8 and 22, they were served control and 600 Gy treated grapes. Panel sizes ranged from 75 to 96 consumers on the various evaluation days. Some consumers were present for multiple evaluation days. Consumers rated the degree of liking for the appearance, flavor, texture, juiciness, and overall liking of the grapes on a 9-point hedonic scale (Peryam and Pilgrim 1957). Small clusters with 3 or 4 grape berries attached to the rachis were served on white paper boats labeled with 3-digit number codes. To prevent any position bias, samples were served to consumers randomly in a balanced order. Therefore, consumers received a control or irradiated sample first an equal number of times. Consumers were asked to cleanse their palate with an unsalted soda cracker and filtered water between samples.
Day 22
0.31 0.36 0.30 0.32
± ± ± ±
0.03 ax 0.03 ax 0.03 ax 0.03 ax
SSC/TA ratio 67.16 57.86 70.17 64.56
% SSC 20.41 20.42 20.64 20.25
± ± ± ±
0.09 ay 0.09 ay 0.09 by 0.09 ay
% TA
SSC/TA ratio
– – – –
– – – –
and trained sensory panel data analyses, linear mixed models were implemented with random effects for judges to assess the effects of age and irradiation dose on all evaluated attributes while accounting for the correlations among the repeated measurements per judge. All statistical analyses steps were carried out using the R statistical software package (www.r-project.org).
Results and Discussion
Effect of irradiation on quality factors Color. For Sugraone grapes, L∗ , a∗ , and h∗ were affected by all dose levels (P ≤ 0.05) with increasing doses resulting in darker and less green grapes (Table 3). However, the differences are not Statistical analysis. Linear fixed effect models were imple- visually obvious (Figure 1) and the trained panel did not detect mented to assess the effects of age and irradiation dose on each of any dose-dependent differences. The b∗ and C∗ values were only the dependent variables in the analytical study. In the consumer affected by 800 Gy. There was no significant change (P ≤ 0.05)
Figure 5–Effect of irradiation and storage on the overall weight loss of one box of Sugraone grapes (above) and one box of Crimson Seedless grapes (below).
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Effects of irradiation on table grapes . . . Table 5–Effect of irradiation and storage on estimated means of % berry shatter (% of grape berries that fell off the rachis with shaking) for Sugraone and Crimson Seedless grapes. Values in the same column that are followed by the same letter are not significantly different. There was no significant difference due to storage. Sugraone grapes Dose (Gy)
Day 7
0 400 600 800
18.0 19.7 12.4 21.9
± ± ± ±
Crimson Seedless grapes Day 21
2.1 a 2.6 a 2.6 b 2.6 a
18.0 19.7 12.4 21.9
± ± ± ±
Day 1
1.9 a 2.1 a 2.1 b 2.1 a
9.3 7.1 12.3 6.5
± ± ± ±
Day 8
2.5 a 2.9 a 2.9 a 2.9 a
8.7 6.5 11.7 5.9
± ± ± ±
Day 22
2.5 a 2.5 a 2.5 b 2.5 a
13.7 11.5 16.7 10.9
± ± ± ±
2.5 a 2.5 a 2.5 b 2.5 a
Table 6–Estimated means measured by a trained sensory panel for Sugraone grape attributes that were significantly (P ≤ 0.05) different from control using unstructured, anchored 15 cm scalesa,b .
0 400 600 800
Day 7 9.26 7.58 6.60 5.35
± ± ± ±
Skin Firmness
Day 21
0.71 ax 0.58 bx 0.58 bcx 0.58 cx
8.91 7.22 6.25 5.00
± ± ± ±
0.42 ax 0.70 bx 0.70 bcx 0.70 cx
Day 7 7.17 6.45 6.25 5.82
± ± ± ±
2.70 4.72 2.93 2.73
Day 7 ± 0.74 ax ± 0.77 bx ± 0.77 ax ± 0.77 ax
7.39 9.06 9.02 8.94
Day 7 ± 1.05 ax ± 0.48 bx ± 0.48 bx ± 0.48 bx
6.88 6.16 5.96 5.52
± ± ± ±
0.31 ax 0.40 abx 0.40 bx 0.40 bx
Day 7 5.26 4.85 4.33 3.34
± ± ± ±
Day 21
0.50 ax 0.46 abx 0.46 bx 0.46 cx
Bruising 4.59 6.61 4.82 4.62
Day 21 ± 0.55 ay ± 0.72 by ± 0.72 ay ± 0.72 ay
0.13 2.32 1.20 1.10
Day 7 ± 0.59 ax ± 0.41 cx ± 0.41 bx ± 0.41 bx
Sweetness Dose (Gy) 0 400 600 800
Day 21
0.41 ax 0.43 abx 0.43 bx 0.43 bx
Color Dose (Gy) 0 400 600 800
Flesh Firmness
8.20 9.87 9.83 9.75
7.91 9.44 9.34 9.36
Day 7 ± 0.84 ax ± 0.55 bx ± 0.55 bx ± 0.55 bx
± ± ± ±
0.33 ax 0.49 abx 0.49 bx 0.49 cx
Bloom
Day 21 1.71 ± 0.30 ay 3.90 ± 0.58 cy 2.78 ± 0.58 by 2.67 ± 0.58 by
1.86 1.86 3.19 3.76
Flavor Day 21 ± 0.35 ay ± 1.04 by ± 1.04 by ± 1.04 by
5.01 4.60 4.09 3.09
Day 7 ± 0.59 ax ± 0.58 ax ± 0.58 bx ± 0.58 bx
Day 21 3.38 ± 0.42 ay 3.38 ± 0.58 ay 4.70 ± 0.58 by 3.76 ± 0.58 by
Juiciness
Day 21 8.58 ± 0.40 ax 10.78 ± 0.83 bx 10.01 ± 0.83 bx 10.03 ± 0.83 bx
8.83 9.94 10.40 10.28
Day 7 ± 0.57 ax ± 0.55 bx ± 0.55 bx ± 0.55 bx
Day 21 9.63 ± 0.39 ay 10.75 ± 0.56 by 11.21 ± 0.56 by 11.09 ± 0.56 by
a Teeth Firmness, Skin Firmness, Flesh Firmness, Bruising, Sweetness, Flavor 0 = none 15 = very intense; Bloom 0 = very intense 15 = none; Color 0 = very green 15 = very brown; Juiciness 0 = none 15 = intense juiciness. b Values in the same column/row that are followed by the same letter are not significantly P ≤ 0.05 different (a-c for row or dose and x-y for column or age).
in color due to age. With Crimson Seedless, no consistent effect of irradiation dose on color was discerned (Table 3) and no visual difference between control and irradiated grapes were observed (Figure 2). Kock and Holz (1991) observed that treatment at 2.0 and 3.0 kGy caused the yellow-green grapes of the Bien Donn´e variety to turn brown with dark longitudinal stripes and some Waltham Cross grape berries turned caramel brown; however, the color changes were attributed to the gibberellic acid that was applied during growth. Texture. For Sugraone grapes on day 7, the compression firmness of the grapes treated with 600 and 800 Gy was significantly (P ≤ 0.05) lower than the control (Figure 3). On day 21, all dose levels of Sugraone grapes were significantly softer than the grapes on day 7, revealing an interaction effect of irradiation and age. The Kramer shear force for the Sugraone grapes decreased significantly (P ≤ 0.05) with increasing irradiation dose levels, displaying a dose dependency (Figure 4). However, the loss in firmness due to age (14.5% to 17.1%) was greater than the decrease due to irradiation (3.4% to 15.5%). The compression firmness and Kramer shear force of Crimson Seedless grapes was significantly (P ≤ 0.05) lower with all dose levels of irradiation (6.5% to 10.3%) (Figure 3 and 4). Age also affected compression firmness (0.8% to 3.2%), but irradiation had a significantly (P ≤ 0.05) greater effect than age. The differences between dose levels were not significant and the dose dependency observed in Sugraone grapes was not evident in Crimson Seed-
less grapes. The Kramer shear force for Crimson Seedless grapes was not significantly affected by age. Thus, there appears to be differences in varietal response. The Sugraone grapes were more affected by age as compared to the Crimson Seedless. Berry softening postharvest is mainly due to water loss but a decrease in pectin content also occurs during postharvest storage (Chervin and others 2012). The decrease in softness with irradiation may be due to an accelerated decrease in pectin and breakdown of other structural polysaccharides. Kock and Holz (1991) observed softening in the Waltham Cross variety of grapes at 3.0 kGy. More recently, McDonald and others (2012) observed irradiation induced loss of firmness in peaches. In a study by Prakash and others (2002), tissue softening was observed in irradiated tomatoes and it was attributed to changes in the cell wall components, particularly the water-soluble pectin, although breakdown of other structural components such as cellulose and hemicellulose may have also contributed to the loss in firmness. SSC and TA. Sugraone grapes had an SSC below 16.5 but the Crimson Seedless had an SSC closer to 20 (Table 4). In both grape varieties, there were neither dose- nor age-dependent changes in SSC. In a study by Moreno and others (2007), irradiation levels below 1.1 kGy did not affect SSC in blueberries. McDonald and others (2012) reported that peaches treated at 0.49 kGy had significantly (P ≤ 0.05) lower Brix values compared to control but the difference was small, at most 0.68%. Vol. 79, Nr. 1, 2014 r Journal of Food Science S87
S: Sensory & Food Quality
Teeth Firmness Dose (Gy)
S: Sensory & Food Quality
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Day 1 10.98 ± 0.76 ax 11.12 ± 0.46 ax 11.49 ± 0.46 ax 11.54 ± 0.46 ax
Dose (Gy) 0 400 600 800 Day 8 10.15 ± 0.40 ay 10.29 ± 0.76 ay 10.66 ± 0.76 ay 10.71 ± 0.76 ay
Sweetness
Day 8 7.18 ± 0.32 ay 6.96 ± 0.53 ay 6.58 ± 0.53 ay 6.67 ± 0.53 ay
Finger firmness
± ± ± ± 0.49 ay 0.49 ay 0.49 ay 0.49 ay
Day 22 10.84 ± 0.40 ax 10.98 ± 0.76 ax 11.35 ± 0.76 ax 11.40 ± 0.76 ax
Day 22 6.51 ± 0.32 ay 6.29 ± 0.53 ay 5.91 ± 0.53 ay 6.00 ± 0.53 ay
9.77 9.38 8.76 9.06
Day 22
10.89 10.83 10.80 11.06
4.85 4.65 6.20 5.01
7.56 6.36 6.30 7.04
0.68 ax 0.57 bx 0.57 bx 0.57 ax
Day 1 ± 0.69 ax ± 0.52 ax ± 0.52 ax ± 0.52 ax
Day 1 ± 0.44 ax ± 0.51 abx ± 0.51 bx ± 0.51 abx
± ± ± ±
Day 1
9.56 9.50 9.47 9.73
5.20 5.00 6.55 5.36
7.79 6.59 6.53 7.27
0.49 ax 0.68 bx 0.68 bx 0.68 ax
Day 8 ± 0.45 ay ± 0.69 ay ± 0.69 ay ± 0.69 ay
Flavor
Day 8 ± 0.44 ax ± 0.44 abx ± 0.44 bx ± 0.44 abx
Color
± ± ± ±
Day 8
Skin firmness
± ± ± ± 0.49 ay 0.68 by 0.68 by 0.68 ay
Day 22 10.39 ± 0.45 ax 10.33 ± 0.69 ax 10.30 ± 0.69 ax 10.56 ± 0.69 ax
Day 22 5.49 ± 0.44 ax 5.29 ± 0.44 abx 6.84 ± 0.44 bx 5.65 ± 0.44 abx
6.31 5.11 5.05 5.79
Day 22 ± ± ± ±
0.46 ax 0.41 ax 0.41 bx 0.41 ax
Day 1 11.30 ± 0.36 ax 11.92 ± 0.33 ax 11.78 ± 0.33 ax 11.73 ± 0.33 ax
Day 1 2.42 ± 0.59 ax 4.30 ± 0.62 bx 6.16 ± 0.62 bx 5.72 ± 0.62 bx
5.79 5.42 4.77 5.09
Day 1
± ± ± ±
0.35 ax 0.47 ax 0.47 bx 0.47 ax
Day 8 10.35 ± 0.29 ay 10.97 ± 0.36 ay 10.83 ± 0.36 ay 10.78 ± 0.36 ay
Juiciness
Day 8 4.91 ± 0.53 ay 6.79 ± 0.59 by 8.65 ± 0.59 by 8.21 ± 0.59 by
Rachis
5.56 5.19 4.54 4.86
Day 8
Flesh firmness
0.35 ax 0.47 ax 0.47 bx 0.47 ax
Day 22 10.37 ± 0.29 ay 10.99 ± 0.36 ay 10.85 ± 0.36 ay 10.80 ± 0.36 ay
Day 22 6.52 ± 0.53 ay 8.40 ± 0.59 by 10.26 ± 0.59 by 9.82 ± 0.59 by
± ± ± ±
Day 22 5.36 4.99 4.34 4.66
Teeth Firmness, Skin Firmness, Flesh Firmness, Bruise, Sweetness, Flavor 0 = none 15 = very intense; Bloom 0 = very intense 15 = none; Color 0 = green/cream 15 = purple/black; Juiciness 0 = none 15 = intense juiciness. Values in the same column/row that are followed by the same letter are not significantly P ≤ 0.05 different (a-c for row or dose and x-z for column or age).
b
a
Day 1 8.17 ± 0.53 ax 7.95 ± 0.37 ax 7.57 ± 0.37 ax 7.66 ± 0.37 ax
Dose (Gy) 0 400 600 800
0.49 ax 0.49 ax 0.49 ax 0.49 ax
± ± ± ±
10.28 9.89 9.27 9.57
± ± ± ±
11.08 10.69 10.07 10.37
0 400 600 800
0.49 ax 0.57 ax 0.57 ax 0.57 ax
Day 8
Day 1
Dose (Gy)
Teeth firmness
Table 7–Estimated means measured by a trained sensory panel for Crimson Seedless grape attributes that were significantly (P ≤ 0.05) different from control using unstructured, anchored 15 cm scalesa,b .
Effects of irradiation on table grapes . . .
Effects of irradiation on table grapes . . . Similarly, irradiation did not significantly (P ≤ 0.05) affect TA (Table 4), except 400 Gy for Sugraone grapes but TA decreased with age. Moreno and others (2007) found similar results where treatment up to 3.2 kGy did not significantly (P < 0.05) affect the pH or acidity in blueberries. McDonald and others (2012) only observed a statistically significant (P ≤ 0.05) decrease in TA with peaches treated at 0.9 kGy but considered the difference negligible. The TA for Crimson Seedless grapes on day 22 was unable to be measured so the decrease in pH could not be observed. In the United States, when the SSC is less than 16.5, the SSC/TA ratio needs to be greater than 20 (Chervin and others 2012), which was observed for both varieties of grapes (Table 4). In this study, the SSC/TA ratio increased during storage but was unaffected by irradiation. Weight loss. Grapes lost up to 11% to 12% of their weight during the 3 wk of storage likely due to dehydration and the rate of weight loss was similar for all dose levels (Figure 5). Al-Bachir (1999) found that the Helwani variety of grape irradiated at 500 Gy and stored for up to 12 wk showed no difference in weight loss as compared to the control but the Baladi variety of grapes treated at 500 Gy had an increased weight loss.
Effect of irradiation on sensory properties Descriptive testing. Firmness, bruising, bloom, rachis, color, juiciness, sweetness, and flavor were significantly (P ≤ 0.05) affected by irradiation in Sugraone grapes (Table 6). On day 7, the Sugraone grapes showed a dose dependency in texture, increasing in softness with increasing dose. These results correspond with the analytical measurements made with the Kramer shear. Firmness was not significantly affected by age (P > 0.05). The juiciness of the Sugraone grapes increased significantly (P ≤ 0.05) with irradiation and age and may be correlated to the increased softness in texture. Bruising in Sugraone grapes was significantly (P ≤ 0.05) greater in irradiated samples but it was not dose dependent. The 400 Gy treated grapes was reported to have a significantly greater amount of bruising than 600 Gy and 800 Gy. The color of 400 Gy treated grapes was also reported as significantly darker than the control, which may correlate to the bruising. There was also significantly (P ≤ 0.05) less bloom on the 600 Gy and 800 Gy treated grapes that continued to decrease with age that suggests irradiation at the higher doses may accelerate the breakdown of the waxy protective coating. All dose levels of irradiation increased the sweetness and flavor in the Sugraone grapes significantly (P < 0.05) but there were no differences between irradiation dose levels. Sweetness also significantly (P ≤ 0.05) increased with age for all dose levels including control. Finger firmness and juiciness of Crimson Seedless grapes were not significantly (P < 0.05) affected by irradiation but were significantly affected by age (Table 7). The sweetness and flavor for Crimson Seedless grapes were significantly (P ≤ 0.05) lower on day 8 but increased on day 22 for all dose levels including control.
S: Sensory & Food Quality
Berry shatter. Irradiation dose did not influence berry shatter (Table 5) except for an anomaly at 600 Gy where the 600 Gy treated Sugraone grapes had a significantly lower level and the 600 Gy treated Crimson Seedless had a significantly higher level (P < 0.05) of berry shatter as compared to the other dose levels. Storage had no effect on berry shatter for Sugraone grapes. For the Crimson Seedless grapes, berry shatter increased during storage but remained lower overall than the Sugraone grapes. Berry shatter can occur due to water loss, and physiological, pathological, and mechanical causes (Chervin and others 2012);
however, it does not appear that irradiation caused additional stress to impact berry shatter.
Figure 6–Estimated hedonic scores, or the degree of liking, of Sugraone grapes for overall liking, texture, appearance, flavor, and juiciness for control and 800 Gy treated grapes. Bars with the same letter for each variety are not significantly P ≤ 0.05 different (a-c for dose and x-y for age).
Vol. 79, Nr. 1, 2014 r Journal of Food Science S89
Effects of irradiation on table grapes . . .
Figure 7–Estimated hedonic scores, or the degree of liking, of Crimson Seedless grapes for overall liking, texture, appearance, flavor, and juiciness for control and treated samples. Bars with the same letter for each variety are not significantly P ≤ 0.05 different (a-c for dose and x-y for age).
S: Sensory & Food Quality
The rachis of Crimson Seedless grapes was significantly (P ≤ 0.05) browner with irradiation. The respiration rate of the rachis may be up to 15 times that of the berries and can contribute to its browning (Chervin and others 2012). There is also a strong correlation between water loss in the cluster and stem browning; a water loss of 2% or more will result in browning after 7 d of cold storage. It is possible that irradiation accelerated the respiration rate, which may have enhanced the browning of the rachis, especially the 800 Gy treated samples.
Conclusions Irradiation affected each variety of grapes differently. The primary effect of irradiation on the quality of Sugraone and Crimson Seedless table grape varieties was softening in texture; however, Sugraone grapes were more sensitive to changes in texture than the Crimson Seedless. Sensory attributes that were affected for both varieties were berry softening and rachis browning. The negative effects observed in Sugraone grapes were an increase in bruising and decrease in bloom, and the positive effects were an increase in sweetness, flavor, and juiciness with irradiation. Consumer acceptance was statistically significantly lower only in the texture of Sugraone treated grapes with a difference of 0.59 from control on a 9-point scale. Consumers could not tell irradiated Crimson Seedless grapes from control and scored them both above “Like Very Much” on the 9-point scale for all attributes. The consumers tasted 800 Gy treated samples for Sugraone grapes, which is the highest likely dose level under commercial conditions in grapes treated at a target dose of 400 Gy. Thus, irradiation levels required for phytosanitary purposes appear to maintain grape quality during 3 wk of storage. Further research should be performed to measure the quality of Sugraone and Crimson Seedless grapes treated under commercial conditions. A comparison of quality with other phytosanitary treatments would also be valuable.
Consumer acceptability of irradiated grapes. On day 7, consumers liked the control samples of Sugraone grapes significantly (P ≤ 0.05) more than the 800 Gy treated samples only in texture but the degree of liking for both samples were close in value on the 9-point hedonic scale (Figure 6). The biggest difference in rating was for the “appearance” which was rated 0.5 lower on the 9-point scale but it was not significant. The degree of liking for both control and treated samples decreased with age. On day 21, consumers liked control more than treated samples and the difference in rating was 0.59 on the 9-point scale but it was not significant. For Crimson Seedless grapes, the 800 Gy samples were tested on day 1 and 600 Gy treated grapes were tested on day 8 and day 22. There were no significant (P ≤ 0.05) differences between control and 800 Gy or 600 Gy irradiated Crimson Seedless grapes for any of the attributes (Figure 7). Consumers scored the flavor, juiciness, and overall liking of control and 800 Gy or control and 600 Gy similarly. Consumers liked the texture of Crimson Acknowledgments Seedless grapes more with age, where the texture of the grapes The project was funded by a TASC grant from USDA-FAS. was softer, although the difference was not significant (P ≤ 0.05). Based on the results of the trained panel, it is highly unlikely References that consumers would score 600 Gy and 800 Gy treated grapes Al-Bachir M. 1999. Effect of gamma irradiation on storability of two cultivars of Syrian grapes differently. (Vitis vinifera). Radiat Phys Chem 55(1):81–5. S90 Journal of Food Science r Vol. 79, Nr. 1, 2014
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