Department of Food Science and Technology, Faculty of Agriculture, Cairo University, Giza, and Department of Food Science and Technology, Assuit University, ARE
Control of Postharvest Decay in Fruits and Vegetables by Irradiation F. A. ISMAIL and S. A.
-4FlFI
This paper deals with theeffed of postharvest gamma-irradiation of strawberries and carrots on their organoleptic quality, storage capacity and chemical composition. Radiation doses of 2j kracl for strawbemies and 75 krad for carrots were chosen as optimum doses not causing significant changes in the organoleptic quality. We found that strawberries and carrots irradiated a t a dose of zj und 75 h a d respectively, retained its microbiological stability even during storage at 1 2 'C(strawberries) andat 2 5 - 3 0 O C (carrots), respectively. It was also found that changes in chemical composition depend on storage temperature and time and are not affected substantially by irradiation.
The postharvest decay is a serious problem when plant commodities are stored under high ambient temperature (25-35 "C) prevailing during most part of the year in subtropical regions like Egypt. Irradiation has proved to be a useful method for the extension of the shelf life of certain fruits and vegetables [g]. The postharvest fungal decay in tropical fruits like figs, grapes and bananas was controlled by use of low-dose irradiation [16]. However, the optimum radiation level should be used to fulfil the preservation requirements without causing serious chemical alteration of the food, which would affect its organoleptic acceptability and wholesomeness. Gamma-irradiation has been utilized to maintain a better storage capacity of Egyptian potatoes and onions [12]. Irradiation was also found to improve the keeping quality of some tropical and subtropical fruits during storage [8]. This paper deals with the quality aspects of strawberries and carrots which have been irradiated to improve stability during storage. The starting-point in the choice of irradiation-doses was to determine their effect on the organoleptic quality of the samples. The samples have been irradiated ranging from 10 to roo krad to inhibit mould formation. To make changes in the physico-chemical properties more distinctly, doses above zoo krad were also used, The after-effect of irradiation on microbiological and chemical aspects of the irradiated samples compared with the unirradiated one was investigated. Materials and Methods
Materials Strambevvies. Baladi variety of strawberries was harvested in the morning, moved within 3 11to the laboratory and irradiated immediately. Storage followed in a cold-storage room a t 2 'C (95 bis iooyo R.H.) and a t sub-room temperature of f 1 2 OC & 2 O C (80---60O,!,R.H.). Samples to be analyzed for replication were taken a t suitable time intervals.
586
ISM AIL/A FIFI
+
Carrots. Chantenay variety of carrots was harvested, stored immediately at 2 OC in non-circulating air at 95- 100%R.H. for 12h, irradiated and stored again. Storage took place in a coldstorage room at + 2 O C (g5-100% R.H.) and a t room temperature (25-30 “C and 50-60% R.H.). Representative samples for analysis were taken at suitable time intervals.
Irradiation treatment The samples were irradiated in a Noratom-Norcontrol A.S. gamma 3500 unit in MERRC (Middle Eastern Regional Radioisotope Centre, Dokki, Cairo) equipped with a source of gamma B°Co a t a dose rate of 105 r/s. The doses applied were 10,15,25,50,75,100, zoo and 300 krad. The unirradiated samples served as a control.
Methods for sensory evalzcation Hedonic scale scoring. The irradiated and control samples served in randomized order for rating on a 9-point hedonic scale, where g represented “like extremely” [2]. The test was judged by a panel of 5 trained persons t o select the suitable irradiation-doses. Preference f e d . An untrained consumer-type panel of 24 persons selected a t random was used to determine the relative preference among samples irradiated a t relatively low doses (10, I 5. 25, 50 and 75 krad) and control in a paired comparison preference test [6].Four replications were pTepared and served a t one sitting. Thus, each panelist judged 4 pairs in which the order of samples was alternated betwcen pairs.
M icvobiological test Stored strawberries and carrots were periodically investigated for deformation and signs of bacterial or fungal infection. The total count of microorganisms in the samples was determined by using total plate count agar media [7]. This media contained 5.0 g trypton, 2.5 g yeast extract, I .o g glucose and 15 g agar per I litre of distilled water. The plates were incubated a t 32 O C for z days.
Chemical analysis Dry weight. Dry weight was determined by drying the homogenized samples a t 105 OC for 12 h. Ascorbic acid. Ascorbic acid was determined by the 2.4-dinitrophenyl hydrazine method [3]. Total acids. Tdtal acids were determined by the method of the Association of Official Agricultural Chemists [ I I]. Sugars. The homogenized samples were extracted with 80% ethanol, total and reducing sugars copper sulphate-arsenomolybdate procedure [5]. were determined by the NELSON-SOMOGYI Carotenoids. a- and 8-carotene were determined by the method also described by the Association of Vitamin Chemists [3]. \
Statistical analysis The regression coefficient (b)was calculated t o cvaluate the increase or decrease of the chemical components of the irradiated and control samples as a function of storage. Storage experiments were also analyzed for the statistical significances of the correlation coefficients ( Y ) [15].
Results and Discussion Selection of irradiation dose Sensory evaluations of the irradiated and control samples were undertaken immediately after irradiation and before storage. The aim of this investigation was t o find out whether any undesirable organoleptic factors were formed as a result of irradiation treatment and t o select the suitable dose of irradiation. The taste ratings by a panel based on a g-point hedonic scale were 7.2, 7.7, 7 . 5 6 . 3 , 6.2, 5.0, 5.0, 4.6 and 4.7 for strawberries irradiated a t 0, 10,15, 2 5 , 50, 75, 100,200
587
Postharvest decay in fruits
and 300 krad, respectively, and 8.3, 8.3, 8.6, 8.8, 7.5, 8.5,8.2, 75. and 5.5 for carrots irradiated at a dose of O , I O , 15, 25,50,75, 100,zoo and 300 krad, respectively. From the above results is evident that the quality of strawberries irradiated at a dose of 10,15 and 25 krad was fairly good. The samples irradiated at doses ranging from 50 to IOO krad appeared softer and were slightly darker than the control. Strawberries irradiated a t doses of 200 and 300 krad were significantly inferior in taste appeal. Repeated organoleptic tests on freshly irradiated carrots showed that there was an increase in orange colour at a dose of 50 krad. Thus, irradiation could bring about an improvement in the external appearance of carrots. Similar radiation-induced formation of anthocyanin pigments was observed in peaches [I]. There was also a softness in the texture of carrots at a dose over 10krad. Textural changes occurringnin carrots as the effect of irradiation have been mentioned [17]. The results of preference test among samples of strawberries irradiated at 0, 10, 15 and 25 krad and carrots irradiated at 0,10,15,25, 50,75 and IOO krad are shown in Table I. For strawberries the tests showed no significant preference of the control Table i Sensory preference test Comparison pairs
Preference Sample
No. tasters
No. choices
Significance
none none none none
20
12
20
10
18
13
NS NS NS
IS
I0
NS
I0
24 24
18 13
NS
20 20 20
I0
NS
'3 17
NS
78 13
13
NS
10
NS
I8
15
**
none
15
I 0
NS
25
'7
none 50 75
'5
16 8
NS
19
16
19
17
Strawberries 0 0
1% ' I 0 1's. L5
o VS.
25 15 IV VS. 25 1j VS. 25 Carrots 1 0 VS.
0
vs. vs.
I0
15 o VS. 25 v VS. 50 0 vs. 75
0
0
25
VS.
100
1's. 75
25 VS. loo 50 vs. 75 jo
vs. I 0 0
75 13.
100
none none none 25 none none 0
15, 25, 50, 75 and IOO = irradiation levels [krad]. ZiS = not significant, = 5% level of significance, * * =
0, 10,
*** = o.x%level
*
*
.*
*** **
*** 1%
level.
over the irradiated sample. Some panelists commented that the irradiated strawberries were more flavorous. 37% of the panelists detected a stronger flavor and sweetness in the irradiated samples. Thus, this test showed equal acceptability between the control and the samples irradiated at a dose of 25 h a d , and this dose was chosen as optimum radiation dose. Among control and irradiated carrots (above IOO krad), no preference was detected. A t IOO krad 59% of panel members judged
588
ISMAIL/AFIFI
the irradiated sample to be more tender than the control, furthermore there was slight darkening or fading of tint. Therefore, 75 krad level was chosen as the optimum dose of irradiation.
Microbiological studies The results obtained are given in Table 2. After treatment of strawberries and carrots with 25 krad and 75 krad respectively, the total cell count was lower than in the control samples. A posteffect of irradiation was also observed during storage. Determinations made after different time intervals revealed the number of marked microorganisms in irradiated samples to be smaller than in the control. Table 2 Total cell count of microorganisms in strawberries and carrots after varying periods of cold and ordinary storage Total cell countlg
__
Storage conditions
Control Strawberries (25 krad) at $2 O C o days
2.8 x lol
0.3
x
101
1.2
x
I01
8 days days
x I02 7.7 x 1o=* 1.8 x xoS*
5.7 x 1.9 x
I01 TO2
days 4 days 6 days
7.5 x I01 9.8 x I O ~ * 4.4 x 106*
0.8 x I O ~ 1.3 x 101 3.8 x lo8*
4 days
1.0
12
Sub-room temperature
Irradiated
2
Carrots (75 krad) at + 2 'C o days 16days 32 days 45 days Room 2 days temperature 4. days . 8days
* = visible signs of
1.0
x
I01
101
x
TO1
1.2
2.3 x 1o1 3.9 x lo=*
2.1
4.5 x
I01
1.7 X 10'
j
0.3 x
1.9 x 101
2.3 x
103*
1.7 x x 1.5
x
5.9 x 7.9 x
101
to** 101 101 102
bacterial or fungal infection
Effect of irradiation on chemical composition The analytical results are calculated on the fresh weight basis. S t r a w b e r r i e s : The results are shown in Table 3 . Dry weight. During storage, dry weight increased in control as well as in irradiated samples. Correlation between storage time and the increase in dry weight was more linear a t +IZ "C storage-temperature then at +z "C. Increase of dry weight could be due t o loss of moisture during storage. Ascorbic acid. Ascorbic acid was generally decreased in control and irradiated samples during storage. Irradiation treatment had no systematic effect on this decrease. The linearity of correlation was highly significant a t +12 "C. It has been reported that irradiation of strawberries causes a modest decrease in ascorbic acid [LO].
1
8.9
o.89**
0.06
12.6
I,
I
1
!
o.91** I
13.7 0.06
11.5
10.4
11.1
10.0
0.61*
0.03
10.0
0.05 0.78*
10.0
1.6
I
11.3
10.1
10.1
Trr.
Dry weight
Control
____
19
38
62
64
69
82 72 74 64
16
51 29
89 85 68
In.
Control
_. .
Ascorbic acid [rnglroa g]
( b ) = regression coefficient; (I) = correlation coefficient; NS = not significant. * = 5% level of significance * * = I yo level * * * = 0.I yo level
Storage time [days]
I
1
44I
7'0 650 5'0 308
Control
.-I
442
510
7 ' 5 608
490 300
720 680
IIT.
Total acids [ m g l ~ o g] o
- __
Table 3
7.9 7.8
8.0 8.2
7.3 7.2
8.0 8.x
-0.57NS
7.6 -0.03
8.2 8.2 7.9
-0.33 N!
-0.07
10.6
11.5
8.9 10.4
IIT.
Total sugars [%I Control
4.5 4.4 0.04 0.98***
4.1
3.7
o.gg***
3.7 4.2 4.8 5.5 0.05
0.72*
0.0I
4.5
0.83'
3.7 4.5 4.1 4.3 0.03
Reducing sugars [%I - -_____ Control Irr.
R
'd
w
c
2
rt.
3P
B
1
!
10.1
10.5 I 1.7
10.2
11.5 12.6 0.06 o.8g***
**
(Y)
i
I
1
!
1
I
I
o.roNS
0.00
'3.7 I 6.0 15.5 I 6.9 '5.7
'4.5 16.4 14.9 I 5.5 14.2 -.o.oz -0.22 N S
13.7 15.1
1%
+2
OC
Control
Storage at
In. 0.5 "C
Irr.
Total acids [mg/roo g]
level;
*** = 0.1% level.
I
o.oiNS
0.33 XS
197 266 243 262 17.2 183 250 15.8 16.5 175 24 7 14.2 17.9 2 75 321 -0.02 0.01 9.90 0.10 0.36 NS 0.48 NS -0.22 N S 0.64** 1 Storage a t room temperature (+25 OC 5 5 "C) 14.5 16.4 14.9
Control
Ascorbic acid [mg/ioo g]
= correlation coefficient;
13.1 0.06 o.gr***
11.8
10.0
10.0
10.4
11 I
0.03 0.61 *
10.2
0.05 0.78 *
11.5
10.1
1.4
8.9
9.2
8.8 8.9
I
IIT.
Control
Dry weight
(b) = regression coefficient; NS = not significant; * = 5yb level of significance
Storage time [days]
-____
0.84** *
0.I 7
o.g1***
0.12
21.2
20. I
16.4 17.1 I 7.0
0.03 o , i g NS
66.4 135.8 98.0 102.4 104.8
o.iSN5
o.81*** 1
'5.7 16.6 17.7 18.7 23. I
0.01
0.02
42.0 49-8 47.0 54.2 44.8
Control
o.g1***
'9.3 17.5 18.7 19.8 25.4
Irr.
59.7 114.3 99.8 99.8 92.8 0.04 0.31 N S
0.50 SS
0.02
42.5 47.0 48.8 44.6
30.2
Irr.
@-Carotene[mg/kgj
0.02
25.5
21.1
I 8.3
18.2
18.8
Control
a-Carotene [mg/kg]
Postharvest decay in fruits
591
Total acids. A marked increase of total acids occurred during storage of control and irradiated samples. The linear correlations were highly significant. Sugars. During storage decreased the total sugars in the samples, and reducing sugars increased. In control samples reducing sugars increased linearly (r = 0.98 a t +IZ "C and Y = 0.99 at $2 "C)and faster than in the irradiated strawberries (Y = 0.72 a t +12 "C and 0.83 at +z "C): Ca r r ot s: The results are shown in Table 4. Dry weight. Dry weight increased in control and irradiated samples during storage. Accordingly, the correlation between the storage time and the increase in dry weight was more linear a t +IZ "C than at $2 "C. Ascorbic acid. There was a slight decrease in ascorbic acid during storage. Irradiated carrots stored a t +z "Cshowed a slight increase of ascorbic acid during storage with linear correlation with storage time (Y = 0.64). Total acids. The amounts of total acids generally increased during storage. The linearity of the correlations was not significant in any case. The increase observed in total acids is in accord with values reported by others [13]. Carotenoides. u- and 6-carotene showed slight increase during storage of carrots. The trend of increase was the same in both control and irradiated samples. The linear correlation between concentration of a-carotene and storage time was highly significant, on the other hand, the correlation of the !-carotene was not significant. Conclusions On the basis of investigations on irradiation of strawberries and carrots to delay postharvest decay, it can be stated that the overall extent of irradiation effect a t low doses is relatively small and it is possible to radurize fruits and vegetables with quite low doses of gamma-irradiation. Organoleptic changes in strawberries at doses up to 50 krad are not detectable; 25 krad was the optimum dose of irradiation. The chemical compositions of irradiated strawberries does not undergo any changes in comparison with unirradiated control samples. It has been reported that low-dose y-irradiation of fresh whole strawberries produced no changes in chemical or cytotoxic properties [4.14:. 75 h a d were found to be the optimum dose for irradiation of carrots. I t has also been observed that irradiated carrots, stored at room temperature or conventional cold-storage, revealed the same chemical changes as unirradiated samples. Zusammenfassung F. A. ISMAILund S. A. AFIFI:Einschrankung des Verderbs von Obst und Gemtise nach der Ernte durch Bestrahlung Die Arbeit beschwgt sich mit dem EinfluB der Gamma-Bestrahlung von Erdbeeren und Mohren nach der Ernte auf die sensorische Qualit&, auf die Lagerstabilitat und auf die chemische Zusammensetzung. Bestrahlungsdosen von 25 krad far Erdbeeren und 75 krad far Mohren wurden als optimale Dosis gewihlt; diese Dosen ftihrten zu keiner Veranderung der sensorischen Qualitlt. Die bestrahlten Erdbeeren und Mohren behielten ihre mikrobiologische Stabilitst sogar bei Lagertemperaturen von 12 "C (Erdbeeren) bzw. 25-30 OC (Mohren) bei. Veranderungen der chemischen Zusammensetzung sind abhangig von Lagertemperatur und -dauer; durch die Bestrahlung werden sie nicht wesentlich beeinfluot.
592
ISM AIL/AFIFI
Peam~e
a.A. klcnrannb M C. A. A @ U ~ MCakimeatle : nop~ki~ P Y K T O BB oBolrIeii nocae y60pu11 YpOmaH
MeTOaOM 0 6 a y s e a s ~
H 3 y Y e H O BnURHkie o 6 n y n e ~ a3eMJlflHEII\’kl ~ kl MOPIEOBB nocne Y6OPKH ypoxarr yt l 3 n y s e ~ n eH~a opraaonenTnsecme CBottcTBa, c n o c o 6 ~ o c ~Kb xpaHenmo M XRMMYeCKUfi COCTPB. B KaYeCTBe OIITaMaJIbHO# AO3Ld 06nyseHHR Bb16panBCb 25 HpaA (&nR BeMJlflHBUM) B 75 KpaH (nJIR MOPKOBM); npy TaKklX A03aX H e H ~ ~ J I H ~ ~ ~RJ3M I eO HeCHE ~ lfi opraHonenmqeCtwx C B O ~ ~ C T B IIocne . 06nyseanrr ~ ~ M J I F I H U BK ~Moprcosb coxpaarrnil ~ ~ ~ p o 6 a o n o r e ~ e cycTofisuBocTb ~y10 name n p ~TeMnepaTypax xpaszeaun B 12 “C (3eMJIRHUKa) II 20-30OC(MOPK0Bb). klaMeHeHBJ3 XBMH9eCKOrO COCTaBa 3aBHCRT OT TeMIIeae~ paTypbl ST npononwwrenbaocm xpaHeam ; 06nyseaue H e o ~ a 3 b 1 ~ 3~1ami~enb~01-0 BJIUflHEIfI.
References AHMED,E. M.. R. A. DENNISON andM. S. MERKLEY,Annual report. Dept. of Food Sci., Florida Univ. Gainesrill, Florida, USA 1969. [z] AMERINE, M., R. M. PANGBORN and E. B. ROESSLER, Principles of Sensory Evaluation of Food. p. 277-278. Academic Press Inc., New York 1965. [3] Association of Vitamin Chemists. Methods of vitamin assays. 2nd ed. Interscience Pub]., N e w York 1966. [41 COOPER, G . M.,and D. W. SALUNKHE, Food Technol. 17, 123-129 (1963). [5] JACOBS,If. B., The chemical analysis of Foods and Food Products, 3rd Ed. Princeton, N.J., D. van Nostrand Co., Inc., 1958. [6] LARMOND, E., Methods for sensory evaluation of food, Canada department of agriculture Publ. 1234. 37. 39. 1970. [7] LODDER, J., and N. J. W. l
Control of Postharvest Decay in Fruits and Vegetables by Irradiation F. A. ISMAIL and S. A.
-4FlFI
This paper deals with theeffed of postharvest gamma-irradiation of strawberries and carrots on their organoleptic quality, storage capacity and chemical composition. Radiation doses of 2j kracl for strawbemies and 75 krad for carrots were chosen as optimum doses not causing significant changes in the organoleptic quality. We found that strawberries and carrots irradiated a t a dose of zj und 75 h a d respectively, retained its microbiological stability even during storage at 1 2 'C(strawberries) andat 2 5 - 3 0 O C (carrots), respectively. It was also found that changes in chemical composition depend on storage temperature and time and are not affected substantially by irradiation.
The postharvest decay is a serious problem when plant commodities are stored under high ambient temperature (25-35 "C) prevailing during most part of the year in subtropical regions like Egypt. Irradiation has proved to be a useful method for the extension of the shelf life of certain fruits and vegetables [g]. The postharvest fungal decay in tropical fruits like figs, grapes and bananas was controlled by use of low-dose irradiation [16]. However, the optimum radiation level should be used to fulfil the preservation requirements without causing serious chemical alteration of the food, which would affect its organoleptic acceptability and wholesomeness. Gamma-irradiation has been utilized to maintain a better storage capacity of Egyptian potatoes and onions [12]. Irradiation was also found to improve the keeping quality of some tropical and subtropical fruits during storage [8]. This paper deals with the quality aspects of strawberries and carrots which have been irradiated to improve stability during storage. The starting-point in the choice of irradiation-doses was to determine their effect on the organoleptic quality of the samples. The samples have been irradiated ranging from 10 to roo krad to inhibit mould formation. To make changes in the physico-chemical properties more distinctly, doses above zoo krad were also used, The after-effect of irradiation on microbiological and chemical aspects of the irradiated samples compared with the unirradiated one was investigated. Materials and Methods
Materials Strambevvies. Baladi variety of strawberries was harvested in the morning, moved within 3 11to the laboratory and irradiated immediately. Storage followed in a cold-storage room a t 2 'C (95 bis iooyo R.H.) and a t sub-room temperature of f 1 2 OC & 2 O C (80---60O,!,R.H.). Samples to be analyzed for replication were taken a t suitable time intervals.
586
ISM AIL/A FIFI
+
Carrots. Chantenay variety of carrots was harvested, stored immediately at 2 OC in non-circulating air at 95- 100%R.H. for 12h, irradiated and stored again. Storage took place in a coldstorage room at + 2 O C (g5-100% R.H.) and a t room temperature (25-30 “C and 50-60% R.H.). Representative samples for analysis were taken at suitable time intervals.
Irradiation treatment The samples were irradiated in a Noratom-Norcontrol A.S. gamma 3500 unit in MERRC (Middle Eastern Regional Radioisotope Centre, Dokki, Cairo) equipped with a source of gamma B°Co a t a dose rate of 105 r/s. The doses applied were 10,15,25,50,75,100, zoo and 300 krad. The unirradiated samples served as a control.
Methods for sensory evalzcation Hedonic scale scoring. The irradiated and control samples served in randomized order for rating on a 9-point hedonic scale, where g represented “like extremely” [2]. The test was judged by a panel of 5 trained persons t o select the suitable irradiation-doses. Preference f e d . An untrained consumer-type panel of 24 persons selected a t random was used to determine the relative preference among samples irradiated a t relatively low doses (10, I 5. 25, 50 and 75 krad) and control in a paired comparison preference test [6].Four replications were pTepared and served a t one sitting. Thus, each panelist judged 4 pairs in which the order of samples was alternated betwcen pairs.
M icvobiological test Stored strawberries and carrots were periodically investigated for deformation and signs of bacterial or fungal infection. The total count of microorganisms in the samples was determined by using total plate count agar media [7]. This media contained 5.0 g trypton, 2.5 g yeast extract, I .o g glucose and 15 g agar per I litre of distilled water. The plates were incubated a t 32 O C for z days.
Chemical analysis Dry weight. Dry weight was determined by drying the homogenized samples a t 105 OC for 12 h. Ascorbic acid. Ascorbic acid was determined by the 2.4-dinitrophenyl hydrazine method [3]. Total acids. Tdtal acids were determined by the method of the Association of Official Agricultural Chemists [ I I]. Sugars. The homogenized samples were extracted with 80% ethanol, total and reducing sugars copper sulphate-arsenomolybdate procedure [5]. were determined by the NELSON-SOMOGYI Carotenoids. a- and 8-carotene were determined by the method also described by the Association of Vitamin Chemists [3]. \
Statistical analysis The regression coefficient (b)was calculated t o cvaluate the increase or decrease of the chemical components of the irradiated and control samples as a function of storage. Storage experiments were also analyzed for the statistical significances of the correlation coefficients ( Y ) [15].
Results and Discussion Selection of irradiation dose Sensory evaluations of the irradiated and control samples were undertaken immediately after irradiation and before storage. The aim of this investigation was t o find out whether any undesirable organoleptic factors were formed as a result of irradiation treatment and t o select the suitable dose of irradiation. The taste ratings by a panel based on a g-point hedonic scale were 7.2, 7.7, 7 . 5 6 . 3 , 6.2, 5.0, 5.0, 4.6 and 4.7 for strawberries irradiated a t 0, 10,15, 2 5 , 50, 75, 100,200
587
Postharvest decay in fruits
and 300 krad, respectively, and 8.3, 8.3, 8.6, 8.8, 7.5, 8.5,8.2, 75. and 5.5 for carrots irradiated at a dose of O , I O , 15, 25,50,75, 100,zoo and 300 krad, respectively. From the above results is evident that the quality of strawberries irradiated at a dose of 10,15 and 25 krad was fairly good. The samples irradiated at doses ranging from 50 to IOO krad appeared softer and were slightly darker than the control. Strawberries irradiated a t doses of 200 and 300 krad were significantly inferior in taste appeal. Repeated organoleptic tests on freshly irradiated carrots showed that there was an increase in orange colour at a dose of 50 krad. Thus, irradiation could bring about an improvement in the external appearance of carrots. Similar radiation-induced formation of anthocyanin pigments was observed in peaches [I]. There was also a softness in the texture of carrots at a dose over 10krad. Textural changes occurringnin carrots as the effect of irradiation have been mentioned [17]. The results of preference test among samples of strawberries irradiated at 0, 10, 15 and 25 krad and carrots irradiated at 0,10,15,25, 50,75 and IOO krad are shown in Table I. For strawberries the tests showed no significant preference of the control Table i Sensory preference test Comparison pairs
Preference Sample
No. tasters
No. choices
Significance
none none none none
20
12
20
10
18
13
NS NS NS
IS
I0
NS
I0
24 24
18 13
NS
20 20 20
I0
NS
'3 17
NS
78 13
13
NS
10
NS
I8
15
**
none
15
I 0
NS
25
'7
none 50 75
'5
16 8
NS
19
16
19
17
Strawberries 0 0
1% ' I 0 1's. L5
o VS.
25 15 IV VS. 25 1j VS. 25 Carrots 1 0 VS.
0
vs. vs.
I0
15 o VS. 25 v VS. 50 0 vs. 75
0
0
25
VS.
100
1's. 75
25 VS. loo 50 vs. 75 jo
vs. I 0 0
75 13.
100
none none none 25 none none 0
15, 25, 50, 75 and IOO = irradiation levels [krad]. ZiS = not significant, = 5% level of significance, * * =
0, 10,
*** = o.x%level
*
*
.*
*** **
*** 1%
level.
over the irradiated sample. Some panelists commented that the irradiated strawberries were more flavorous. 37% of the panelists detected a stronger flavor and sweetness in the irradiated samples. Thus, this test showed equal acceptability between the control and the samples irradiated at a dose of 25 h a d , and this dose was chosen as optimum radiation dose. Among control and irradiated carrots (above IOO krad), no preference was detected. A t IOO krad 59% of panel members judged
588
ISMAIL/AFIFI
the irradiated sample to be more tender than the control, furthermore there was slight darkening or fading of tint. Therefore, 75 krad level was chosen as the optimum dose of irradiation.
Microbiological studies The results obtained are given in Table 2. After treatment of strawberries and carrots with 25 krad and 75 krad respectively, the total cell count was lower than in the control samples. A posteffect of irradiation was also observed during storage. Determinations made after different time intervals revealed the number of marked microorganisms in irradiated samples to be smaller than in the control. Table 2 Total cell count of microorganisms in strawberries and carrots after varying periods of cold and ordinary storage Total cell countlg
__
Storage conditions
Control Strawberries (25 krad) at $2 O C o days
2.8 x lol
0.3
x
101
1.2
x
I01
8 days days
x I02 7.7 x 1o=* 1.8 x xoS*
5.7 x 1.9 x
I01 TO2
days 4 days 6 days
7.5 x I01 9.8 x I O ~ * 4.4 x 106*
0.8 x I O ~ 1.3 x 101 3.8 x lo8*
4 days
1.0
12
Sub-room temperature
Irradiated
2
Carrots (75 krad) at + 2 'C o days 16days 32 days 45 days Room 2 days temperature 4. days . 8days
* = visible signs of
1.0
x
I01
101
x
TO1
1.2
2.3 x 1o1 3.9 x lo=*
2.1
4.5 x
I01
1.7 X 10'
j
0.3 x
1.9 x 101
2.3 x
103*
1.7 x x 1.5
x
5.9 x 7.9 x
101
to** 101 101 102
bacterial or fungal infection
Effect of irradiation on chemical composition The analytical results are calculated on the fresh weight basis. S t r a w b e r r i e s : The results are shown in Table 3 . Dry weight. During storage, dry weight increased in control as well as in irradiated samples. Correlation between storage time and the increase in dry weight was more linear a t +IZ "C storage-temperature then at +z "C. Increase of dry weight could be due t o loss of moisture during storage. Ascorbic acid. Ascorbic acid was generally decreased in control and irradiated samples during storage. Irradiation treatment had no systematic effect on this decrease. The linearity of correlation was highly significant a t +12 "C. It has been reported that irradiation of strawberries causes a modest decrease in ascorbic acid [LO].
1
8.9
o.89**
0.06
12.6
I,
I
1
!
o.91** I
13.7 0.06
11.5
10.4
11.1
10.0
0.61*
0.03
10.0
0.05 0.78*
10.0
1.6
I
11.3
10.1
10.1
Trr.
Dry weight
Control
____
19
38
62
64
69
82 72 74 64
16
51 29
89 85 68
In.
Control
_. .
Ascorbic acid [rnglroa g]
( b ) = regression coefficient; (I) = correlation coefficient; NS = not significant. * = 5% level of significance * * = I yo level * * * = 0.I yo level
Storage time [days]
I
1
44I
7'0 650 5'0 308
Control
.-I
442
510
7 ' 5 608
490 300
720 680
IIT.
Total acids [ m g l ~ o g] o
- __
Table 3
7.9 7.8
8.0 8.2
7.3 7.2
8.0 8.x
-0.57NS
7.6 -0.03
8.2 8.2 7.9
-0.33 N!
-0.07
10.6
11.5
8.9 10.4
IIT.
Total sugars [%I Control
4.5 4.4 0.04 0.98***
4.1
3.7
o.gg***
3.7 4.2 4.8 5.5 0.05
0.72*
0.0I
4.5
0.83'
3.7 4.5 4.1 4.3 0.03
Reducing sugars [%I - -_____ Control Irr.
R
'd
w
c
2
rt.
3P
B
1
!
10.1
10.5 I 1.7
10.2
11.5 12.6 0.06 o.8g***
**
(Y)
i
I
1
!
1
I
I
o.roNS
0.00
'3.7 I 6.0 15.5 I 6.9 '5.7
'4.5 16.4 14.9 I 5.5 14.2 -.o.oz -0.22 N S
13.7 15.1
1%
+2
OC
Control
Storage at
In. 0.5 "C
Irr.
Total acids [mg/roo g]
level;
*** = 0.1% level.
I
o.oiNS
0.33 XS
197 266 243 262 17.2 183 250 15.8 16.5 175 24 7 14.2 17.9 2 75 321 -0.02 0.01 9.90 0.10 0.36 NS 0.48 NS -0.22 N S 0.64** 1 Storage a t room temperature (+25 OC 5 5 "C) 14.5 16.4 14.9
Control
Ascorbic acid [mg/ioo g]
= correlation coefficient;
13.1 0.06 o.gr***
11.8
10.0
10.0
10.4
11 I
0.03 0.61 *
10.2
0.05 0.78 *
11.5
10.1
1.4
8.9
9.2
8.8 8.9
I
IIT.
Control
Dry weight
(b) = regression coefficient; NS = not significant; * = 5yb level of significance
Storage time [days]
-____
0.84** *
0.I 7
o.g1***
0.12
21.2
20. I
16.4 17.1 I 7.0
0.03 o , i g NS
66.4 135.8 98.0 102.4 104.8
o.iSN5
o.81*** 1
'5.7 16.6 17.7 18.7 23. I
0.01
0.02
42.0 49-8 47.0 54.2 44.8
Control
o.g1***
'9.3 17.5 18.7 19.8 25.4
Irr.
59.7 114.3 99.8 99.8 92.8 0.04 0.31 N S
0.50 SS
0.02
42.5 47.0 48.8 44.6
30.2
Irr.
@-Carotene[mg/kgj
0.02
25.5
21.1
I 8.3
18.2
18.8
Control
a-Carotene [mg/kg]
Postharvest decay in fruits
591
Total acids. A marked increase of total acids occurred during storage of control and irradiated samples. The linear correlations were highly significant. Sugars. During storage decreased the total sugars in the samples, and reducing sugars increased. In control samples reducing sugars increased linearly (r = 0.98 a t +IZ "C and Y = 0.99 at $2 "C)and faster than in the irradiated strawberries (Y = 0.72 a t +12 "C and 0.83 at +z "C): Ca r r ot s: The results are shown in Table 4. Dry weight. Dry weight increased in control and irradiated samples during storage. Accordingly, the correlation between the storage time and the increase in dry weight was more linear a t +IZ "C than at $2 "C. Ascorbic acid. There was a slight decrease in ascorbic acid during storage. Irradiated carrots stored a t +z "Cshowed a slight increase of ascorbic acid during storage with linear correlation with storage time (Y = 0.64). Total acids. The amounts of total acids generally increased during storage. The linearity of the correlations was not significant in any case. The increase observed in total acids is in accord with values reported by others [13]. Carotenoides. u- and 6-carotene showed slight increase during storage of carrots. The trend of increase was the same in both control and irradiated samples. The linear correlation between concentration of a-carotene and storage time was highly significant, on the other hand, the correlation of the !-carotene was not significant. Conclusions On the basis of investigations on irradiation of strawberries and carrots to delay postharvest decay, it can be stated that the overall extent of irradiation effect a t low doses is relatively small and it is possible to radurize fruits and vegetables with quite low doses of gamma-irradiation. Organoleptic changes in strawberries at doses up to 50 krad are not detectable; 25 krad was the optimum dose of irradiation. The chemical compositions of irradiated strawberries does not undergo any changes in comparison with unirradiated control samples. It has been reported that low-dose y-irradiation of fresh whole strawberries produced no changes in chemical or cytotoxic properties [4.14:. 75 h a d were found to be the optimum dose for irradiation of carrots. I t has also been observed that irradiated carrots, stored at room temperature or conventional cold-storage, revealed the same chemical changes as unirradiated samples. Zusammenfassung F. A. ISMAILund S. A. AFIFI:Einschrankung des Verderbs von Obst und Gemtise nach der Ernte durch Bestrahlung Die Arbeit beschwgt sich mit dem EinfluB der Gamma-Bestrahlung von Erdbeeren und Mohren nach der Ernte auf die sensorische Qualit&, auf die Lagerstabilitat und auf die chemische Zusammensetzung. Bestrahlungsdosen von 25 krad far Erdbeeren und 75 krad far Mohren wurden als optimale Dosis gewihlt; diese Dosen ftihrten zu keiner Veranderung der sensorischen Qualitlt. Die bestrahlten Erdbeeren und Mohren behielten ihre mikrobiologische Stabilitst sogar bei Lagertemperaturen von 12 "C (Erdbeeren) bzw. 25-30 OC (Mohren) bei. Veranderungen der chemischen Zusammensetzung sind abhangig von Lagertemperatur und -dauer; durch die Bestrahlung werden sie nicht wesentlich beeinfluot.
592
ISM AIL/AFIFI
Peam~e
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References AHMED,E. M.. R. A. DENNISON andM. S. MERKLEY,Annual report. Dept. of Food Sci., Florida Univ. Gainesrill, Florida, USA 1969. [z] AMERINE, M., R. M. PANGBORN and E. B. ROESSLER, Principles of Sensory Evaluation of Food. p. 277-278. Academic Press Inc., New York 1965. [3] Association of Vitamin Chemists. Methods of vitamin assays. 2nd ed. Interscience Pub]., N e w York 1966. [41 COOPER, G . M.,and D. W. SALUNKHE, Food Technol. 17, 123-129 (1963). [5] JACOBS,If. B., The chemical analysis of Foods and Food Products, 3rd Ed. Princeton, N.J., D. van Nostrand Co., Inc., 1958. [6] LARMOND, E., Methods for sensory evaluation of food, Canada department of agriculture Publ. 1234. 37. 39. 1970. [7] LODDER, J., and N. J. W. l
