Meat Science 101 (2015) 42–47
Contents lists available at ScienceDirect
Meat Science journal homepage: www.elsevier.com/locate/meatsci
Effects of vacuum packaging conditions on the quality, biochemical changes and the durability of ostrich meat Martina Brenesselová ⁎, Beáta Koréneková, Ján Mačanga, Slavomír Marcinčák, Pavlína Jevinová, Monika Pipová, Peter Turek Department of Food Hygiene and Technology, University of Veterinary Medicine and Pharmacy, 041 81 Košice, Slovak Republic
a r t i c l e
i n f o
Article history: Received 26 February 2014 Received in revised form 10 September 2014 Accepted 6 November 2014 Available online 13 November 2014 Keywords: Ostrich meat Lactic acid pH Malondialdehyde Microbial analysis Sensory analysis
a b s t r a c t In this study, the effects of vacuum packaging conditions on the concentrations of lactic acid, malondialdehyde, pH, microbial and sensory analysis were determined during chilled storage of ostrich meat. Meat was packed as follows: vacuum packed from 1st day (VP-1), vacuum packed from 3rd day (VP-3) and non-vacuum packed (NVP). Analysis were performed at 1st, 7th, 14th, 21st day after slaughter. Meat consisted of 74.69% water, 2.29% fats, 20.95% proteins. Package conditions had significant effect on the pH (NVP: 6.54 on the 14th day, VP-1: 6.05 and VP-3: 6.07 on the 21th day p b 0.001), amount of malondialdehyde (NVP: 8.62 mg/kg on the 14th day; VP-1: 1.95 and VP-3: 2.55 on the 21th day; p b 0.001) and total microbial count (NVP: 7.4 log CFU/g on the 14th day; VP-1: 6.7 and VP-3: 6.8 on the 21th day p b 0.01). Based on these results we can assess that vacuum packed from 1st day is necessary for the 21 days storage of ostrich meat. © 2014 Published by Elsevier Ltd.
1. Introduction The African ostrich (Struthio camelus) is the largest of all birds. Until the middle 1900s, ostriches lived in South western Asia, Africa, and the Arabian Peninsula. Currently, the wild ostriches are only found in desert regions in Africa. Through the commercial ostrich industry, farm-raised ostriches are now found in the countries all over the world. In the past, ostrich farms had been mainly focused for production the feathers (Alonso-Calleja, Martinez-Fernández, Capita, & Prieto, 2002). In present, the consumption of ostrich meat and its popularity in European countries is increasing, due to its suitable properties, such as low fat and fragility. In recent years the ostrich farms are developed also in Slovakia. In the meat industry, ostrich meat gain attention as a new alternative red meat due to a favourable fatty acid profile. Intramuscular fat consists of high content of polyunsaturated fatty acids and low intramuscular fat content (Sales, 1998). The structure and taste is similar to beef meat, however it contains about 40 percent less fat. The typical colour of ostrich meat is red. The meat which we mark as a red meat has less level of fat and cholesterol as turkey meat and chicken meat and is rich in iron and protein (Polawska et al., 2011). One of the most critical factors affecting the quality of the meat after slaughter is the process of its maturation (Atanassova, Apelt, Reich, & Klein, 2008). The muscles fibres are subjected to biochemical changes in the meat. The conversion of the muscle to a meat during the ripening ⁎ Corresponding author. E-mail address: [email protected] (M. Brenesselová).
http://dx.doi.org/10.1016/j.meatsci.2014.11.003 0309-1740/© 2014 Published by Elsevier Ltd.
process is an energy-demanding process. The energy is provided by degradation of glycogen in the muscle. Energy-rich phosphates are participating on the enzymatic degradation of glycogen to the lactic acid following decrease of pH. At a low pH many of microorganisms cannot survive, or their division is slowing down. Because of this, the decrease of pH provides some protection from bacterial spoilage. Almost all major components of the muscle are subject to a biochemical changes and emerging metabolic products contribute to the typical sensory properties. Very suitable example is the lactic acid and phosphates, which contribute to the typical flavor of the meat and are also related with improving of organoleptic and technological properties of meat (Dalle Zotte, 2002; Čuboň et al., 2004; Winkelmayer et al., 2005). The meat maturation is followed by a second phase, where proteins are degraded, with the accumulation of lowmolecular nitrogenous compounds and a slight rise in pH. It is not easy to clearly separate advanced aging from the onset on spoilage, but typically, in later contaminant bacteria are involved (Koréneková et al., 2014). In addition to the growth of microorganisms lipid oxidation is an important factor regarding shelf life and consumer acceptance of fresh meat (Jacobsen & Bertelsen, 2000). The oxidative deterioration of the polyunsaturated lipids of foods leads through formation of hydroperoxides to short-chain aldehydes, ketones and other oxygenated compounds, which are considered to be responsible for the development of rancidity in stored foods. The most widely used assay to quantify lipid oxidation products in meat is the thiobarbituric acid (TBA) test because of its simplicity and fastness. TBA test determines the amount of malondialdehyde (MDA), a major secondary by-product of lipid oxidation in a sample (Marcinčák et al., 2003).
M. Brenesselová et al. / Meat Science 101 (2015) 42–47
To the author's knowledge, little information is available on the microbiological aspects and keeping quality of this foodstuff, especially of the refrigerated and vacuum-packed meat, which is frequently purchased in developed countries. Factors, such as pH, that has been considered as a main parameter in the microbiological quality of the meat, the initial bacterial contamination, temperature of the meat during the storage, packing in modified atmosphere, plays a major role in the final quality of meat (Capita, Diaz-rodriguez, Prieto, & Alonso-Calleja, 2006; Blixt & Borch, 2002). As the other types of meat of slaughtered animals, the ostrich meat couldn´t be completely sterile after the cutting carcasses. After skinning, the ostrich meat is exposed to microbial contaminations which may come from a variety of external sources including the hands of workers (Karama, 2001; Hoffman, 2005, 2008). Using the appropriate method of packaging and storage conditions, we can greatly affect the microbial quality of post-mortem and also the durability of ostrich meat. Ostrich body is usually refrigerated 24–48 hours post-mortem, cut and immediately vacuum-packed or frozen. The consumers receives either fresh or frozen meat. The consumption of ostrich meat in the world is increasing and therefore improving the hygiene and extent shelf-life of meat are crucial for potential consumers. Using the modern techniques of packaging we can maintain the microbial and also the sensory quality of the products during the storage (Seydim, Acton, Hall, & Dawson, 2006). The aim of this study was to evaluate the effects of vacuum packaging on the quality, biochemical changes and shelf-life with a focus on the concentrations of lactic acid, pH value, amount of malondialdehyde, microbial and sensory analysis. 2. Materials and methods 2.1. Samples Thigh muscles of eight 16-month-old ostriches (Struthio camelus) were used for the experiment. The ostriches were obtained from the same farm in Slovakia. Animals were stunned and slaughtered under the provisions of EU Council Directive 1099/2009/EC, 1099/2009/EC (2009). Thigh muscles, immediately after slaughter of animals, were delivered in a cooler (+ 4 °C) to the Department of Food Hygiene and Technology in the University of Veterinary Medicine and Pharmacy in Košice (Slovakia). 2.2. Experimental design The meat samples of ostriches consisted of thigh muscles (M. iliotrochantericus cranialis, M. iliofemoralis, M. iliotrochantericus caudalis, M. pubo-ischio-femoralis) were sampled from right and left leg. The samples were firstly examined as starting material (chemical composition, sensory analysis, pH value, determination of lactic acid, malondialdehyde, microbial analysis). The other thigh muscles were carved to 60 pieces, which were divided into three groups. Each group (20 packs) was stored in different package conditions. Every package contains approximately 1000 g of meat. The thigh muscles of the first group (20 packs) were vacuum-packed within 24 hours after slaughter and stored in a refrigerator at 2 °C for 21 days. The second group of the muscles (20 packs) was firstly stored in the normal atmosphere longer than 48 hours in the plastic bags at 2 °C (because the speed of post-mortal processes probably depended on the occurrence of oxygen). Then the samples were vacuum-packed from 3rd day after arrival and stored at the same temperature to 21st day. The thigh muscles of the third group (20 packs) were stored in the plastic bags (normal atmosphere) at 2 °C for all the time of the experiment. Samples of the thigh muscles of the first two groups were analyzed on days 7, 14 and 21 of storage. Muscles of third group were examined only on days 7 and 14, because after 21 days of storage the significant
43
signs of decay appeared. 5 packages of samples were analyzed on each measurement day. 2.3. Chemical composition of meat Dry matter was determined by oven-drying at 105 °C (AOAC, 1997). Kjeltec Auto, type 1030 (Tecator Co., Hoganas, Sweden) analyser was used to determine the crude protein content. Lipids were isolated in ground samples with petroleum ether with Soxhlet apparatus (LTHS 500, Brnenská Druteva v.d., Czech Republic) and were determined gravimetrically (Floch, Lees, & Sloane Stanley, 1957). 11 g of ostrich meat were used for chemical composition analysis. 2.4. pH values Samples (50 g) from each group of meat were homogenized for 10 min. After that 10 g was used for extraction by distilled water (100 ml) and filtrated. The water extract of the muscle was used for analysis of pH values by a digital pH meter (inoLab pH720, WTW, Weilheim, Germany) with glass electrode. 2.5. Determination of lactic acid The measurement of lactic acid was performed from the water extract that was used for the pH measurements. One milliliter of water extracts of meat samples was put into 10 ml flasks and filled with distilled water and immediately analyzed by use of an electrophoretic analyser (Type EA102) with a conductive detector (Villa Labeco, Slovak Republic) according to Mačanga et al. (2011). The electrophoretic separation system used consisted of a leading electrolyte-10 mM HCl, β-alanine and 0.1% methyhydroxyethylcellulose, pH 3.2 and terminating electrolyte-5 mM caproic acid and 5 mM hydroxymethy-aminomethane. The direct currents used in pre-separation and analytical columns were 250 μA and 50 μA. The results of analysis were evaluated by the computer programme ITPP pro 32 and expressed in g/100 g of meat. 2.6. Determination of thiobarbituric acid assay To determine the lipid oxidation changes of thigh muscles, the method of thiobarbituric value (TBA) determination, expressing the degree of secondary damage of lipids, contingent upon the oxidation of unsaturated fatty acids, was used. The extent of lipid oxidation was evaluated as thiobarbituric acid reactive substances (TBARS) by method of Marcinčák et al. (2004). Sample (20 g of meat) was mixed with 50 ml distilled water and homogenized one minute. After that 50 ml 10% trichloracetic acid was added and kept in the lab temperature for 10 min. Then the sample was filtered. Four milliliter of filtrate and 1 ml thiobarbituric acid was inserted into stopper fitted flasks and then incubated in hot water (80 °C) for 90 min. After cooling, the samples were analyzed. TBARS values were measured spectrophotometrically at 532 nm (Helios γ, v. 4. 6. Thermo spectronic, Cambridge, UK). Results were quantified as malondialdehyde (MDA) equivalents (mg/MDA/kg muscle). 2.7. Microbial analysis Samples (10 g) for microbiological analysis were taken aseptically from the ostrich muscles. The initial dilution, as well as further subsequent decimal dilutions were prepared in accordance with the requirements of valid food standards (STN EN ISO 6887–1). 2.7.1. Enumeration procedures Violet Red Bile Glucose Agar (VRBG) was used to enumerate Enterobacteriaceae (STN ISO, 21528–2). One milliliter of the first two decimal dilutions was placed into sterile Petri dishes and suffused with VRBG (Hi-Media, India). The plates were incubated at 37 °C for 48 h.
44
M. Brenesselová et al. / Meat Science 101 (2015) 42–47
Plate Count Agar (PCA) was used to enumerate the total count of microorganisms (STN EN ISO 4833). One milliliter of the initial dilution as well as two subsequent decimal dilutions was placed into sterile Petri dishes and suffused with PCA (Hi-Media, India). The plates were incubated at 30 °C for 72 h. Baird Parker agar medium was used to enumerate coagulasepositive staphylococci. As described by the standard procedure (STN EN ISO 6888–1), the decimal dilutions were spread on the surface of Baird Parker agar medium (Hi-Media, India) in an amount of 0.1 milliliter and incubated for 48 h at 37 °C. Suspect colonies were further evaluated for their coagulase activity. One milliliter of the reconstituted commercial freeze-dried rabbit plasma (Staphylo PK, Imuna Pharm, Slovakia) was placed into a small test tube. Then 0.1 milliliter of the over-night staphylococcal culture in brain heart infusion broth was added and the tube content was mixed. Test tubes were incubated at 37 °C for 1, 2, 4, 6 and 24 h. Within this period, fibrinogen was converted to fibrin by the staphylococcal coagulase enzymes. A positive result was manifested by clotting of the plasma in the test tube. After incubation of inoculated Petri dishes at appropriate temperatures the counts of characteristic colonies were enumerated, calculated and displayed in CFU/g. 2.8. Sensory analysis Sensory examination of quality of ostrich meat (aroma, flavor, juiciness, tenderness) was realized by the methods for sensory evaluation of meat (Príbela, 2001). Sensory analysis was performed by six experienced evaluators using five-point rating scale (from one to five points) on days 1, 7, 14 and 21 of storage. The samples of ostrich meat were boiled (70 °C). Every panelist removed the meat samples from the package by opening it with knife and examined three samples (VP, VP-3 and NVP) which were placed on the white glass plate. The each sample was coded with a random letter. The number five indicated the highest quality of evaluated parameter and the number one indicated the lowest quality. The points were summarized with maximum count 20. 2.9. Statistical evaluation All the data were analyzed statistically using GraphPad Prism Software, Version 4.00 (Graphpad Prism, 2003). One-way analysis of variance (ANOVA) with the post hoc Tukey's multiple comparison test was used to evaluate statistical significance of differences between three groups of meat with different package conditions (statistical significant differences are illustrated in the tables by numbers) and between days of the experiment (statistical significant differences are illustrated in the tables by letters).
20.60–21.70%. Interesting is also the proportion of fatty acids in the fat of the meat. The fat in the muscle of ostrich contains up 27–33% polyunsaturated fatty acids Girolami, Marsico, D´Andrea, Braghieri, and Napolitano (2003). It may also be a cause of the lower oxidative stability of meat during the storage and the needful heightened protection against the oxidation of fats (vacuum-packaging). 3.2. pH value and lactic acid Production of lactic acid, pH changes and progress of the ripening process are shown in Tables 2 and 3. The initial pH (Table 2) was 6.18 ± 0.01 and the most significant increased (6.54 ± 0.07; p b 0.001) was recorded in the muscle stored in non-vacuum conditions on the day 14. In the samples which were vacuum-packed from the day 1 was the most significant decrease recorded (6.05 ± 0.06; p b 0.001) on the day 21. Significant increase (6.07 ± 0.02; p b 0.001) was observed in the vacuum-packed samples from day 3 day 21. The increase of pH value was observed only in the muscle, which was stored in a vacuum. Fernández-López et al. (2008) showed only a gradual lowering of the pH from the value of 6.04 to below 5.60 during a vacuum storage conditions and to above 5.66 during air storage condition on 18th day. But Botha, Hoffman, and Britz (2006) found, that the pH value of the muscle tissue of ostriches till day 14 increased from the original value 5.8 to a value of under 6.0. Statistically significant differences in pH values were found on the day 14 of storage in the samples which were vacuum-packed from the day 1 of storage (6.22 ± 0.07; p b 0.001) and vacuum-packed from the day 3 (6.20 ± 0.01; p b 0.001) compared to non-vacuum-packed samples. The results shows (Table 3) that in the samples stored in vacuum from day 1 the dynamics of changes in concentration of lactic acid till the day 7 increased and at the day 14 decreased. The most significant (1.18 ± 0.08; p b 0.01) decrease was recorded on day 21. In the samples stored in vacuum from day 3 the level of lactic acid decreased no significantly till day 14 and on day 21 increased. The most significant increase (1.64 ± 0.36; p b 0.05) of lactic acid was observed on the day 21. In the samples stored in normal atmosphere (without vacuum) the level of lactic acid did not increased significantly till day 7and on day 14 decreased. The concentration of lactic acid in the samples depends on the forms of storage. The most significant differences (p b 0.05) were recorded only between the samples which were vacuum packed from the day 1 (1.18 ± 0.08) and the vacuum packed from the day 3 (1.64 ± 0.36) on the day 21 of storage.
3. Results and discussion 3.3. Degradation of lipids in muscles 3.1. Chemical composition The chemical composition of ostrich meat is shown in the Table 1. In our experiment were found that ostrich thigh muscle contains an average of 20.95% protein, 2.29% fat and 74.69% water. Therefore, from a health perspective is highly prized food. Similar results of fat and nitrogenous proteins were previously reported by Majewska et al. (2009). The contents of fats and proteins reported in their study were as follows: the fat 0.90–1.34% and protein
Table 1 Chemical composition of ostrich thigh muscle (%) (mean ± SD). Samples
Dry matter
Water
Fat
Proteins
Thigh muscle
25.31 ± 0.72
74.69 ± 0.72
2.29 ± 0.19
20.95 ± 0.26
The rate of secondary damage of fat in the muscles of ostriches expressed as the amount of malondialdehyde is shown in Table 4. The
Table 2 The changes of pH values in the ostrich meat during various form of storage (mean ± SD). Package conditions
Day1
Day 7
Day 14
Day 21
VP – 1 VP – 3 NVP
6.18 ± 0.01a 6.20 ± 0.09a;1 6.22 ± 0.07a;2 6.05 ± 0.06b;1 6.18 ± 0.01a 6.19 ± 0.01a;1 6.20 ± 0.01a;2 6.07 ± 0.02b;1 6.18 ± 0.01b 6.16 ± 0.04b;1 6.54 ± 0.07a;1 –
Means in the lines with the same superscript (a. b) and means in the columns with the same superscript (1. 2) do not differ significantly. VP – 1 vacuum-packed from day 3, VP – 3 vacuum-packed from day 3, NVP – non-vacuum packed.
M. Brenesselová et al. / Meat Science 101 (2015) 42–47 Table 3 The changes of lactic acid concentration in the ostrich meat during various form of storage (g/100 g) (mean ± SD). Package conditions
Day 1
Day 7
Day 14
Day 21
VP – 1 VP – 3 NVP
1.43 ± 0.11a.b;1 1.18 ± 0.08b;2 1.47 ± 0.13a.b 1.75 ± 0.45a;1 1.47 ± 0.13a.b 1.36 ± 0.06a.b;1 1.22 ± 0.13b;1 1.64 ± 0.36a;1 1.47 ± 0.13a 1.51 ± 0.10a;1 1.13 ± 0.03a;1 –
Means in the lines with the same superscript (a. b) and means in the columns with the same superscript (1. 2) do not differ significantly. VP – 1 vacuum-packed from day 1, VP – 3 vacuum packed-from day 3, NVP – non-vacuum packed.
initial amount of malondialdehyde measured within 24 hours after kill was 0.67 ± 0.04. Leygonie, Britz, and Hoffman (2012) recorded higher amount of malondialdehyde in fresh ostrich meat: 1.76 ± 0.03 mg/kg. On the day 7 of storage, the malondialdehyde measured in the thigh muscle which was vacuum-packed from day 3 increased significantly (p b 0.001) to the value 3.16 ± 0.24. During the following days of storage, the quantity of malondialdehyde did not change significantly. The quantity of malondialdehyde in the meat samples vacuumpacked from day 1 significantly increased until on the day 14 (1.80 ± 0.27; p b 0.001). On the day 21 of storage no significant increase of the malondialdehyde was recorded. The amount of malondialdehyde measured in the samples of meat which were stored in the plastic bags (normal atmosphere) was increasing throughout the experiment. The most significant increase was recorded on the day 7 (7.67 ± 0.61; p b 0.001). As show in Table 4, amounts of malondialdehyde measured in the samples of ostrich meat were significantly differed depending on the method of packing. The statistically highest amount of malondialdehyde was measured in the samples of meat which were stored in the plastic bags in the normal atmosphere (p b 0.001). On the other hand, degradation changes of fats were the least intensive in the vacuum-packed samples. The effects of storage time and package method as the significant factors for amount of malondialdehyde are also confirmed by other authors. Fernández-López et al. (2008) stored ostrich steaks in different package conditions for 18 days at 2 °C. Measured malondialdehyde in the samples exposed to air (above 1.2 mg/kg on the day 18) were significantly higher compared with vacuum-packed (approximately 0.5 mg/kg on the day 18). In the meat samples stored in modified atmosphere even lower amounts of malondialdehyde were recorded (under 0.4 mg/kg on the day 18). Similar results are recorded in the work of Seydim et al. (2006), who stored ostrich meat for 9 days at 4 °C. Differences in malondialdehyde between samples exposed to air and vacuum-packed listed in the studies of both authors are similar to ours results, however values of malondialdehyde are lower than ours. On the other hand, level of malondialdehyde reported in this study are similar to results of Filgueras et al. (2010), who compared lipid stability of Rhea Americana meat during air (stored 5 days) and vacuumpacked storage (stored 28 days) at 4 °C.
Table 4 The amount of malondialdehyde (mg/kg) in muscle samples of ostriches during storage in different package conditions (mean ± SD). Package conditions
Day 1
Day 7
Day 14
Day 21
VP – 1 VP – 3 NVP
0.67 ± 0.04b 0.40 ± 0.12b;2 1.80 ± 0.27a;2 1.95 ± 0.20a;1 0.67 ± 0.04b 3.16 ± 0.24a;3 2.70 ± 0.19a;3 2.55 ± 0.26a;1 0.67 ± 0.04c 7.67 ± 0.61b;1 8.62 ± 0.29a;1 –
Statistic: means in the lines with the same superscript (a, b, c) and means in the columns with the same superscript (1, 2, 3) do not differ significantly. VP – 1 vacuum-packed from day 1, VP – 3 vacuum-packed from day 3, NVP – non-vacuum packed.
45
3.4. Microbial analysis Changes in microbial populations are shown in the Table 5. Initial microbial counts for total viable counts (TVC) on day 1 of storage were 3.8 ± 0.3 log CFU/g. On day 7 of storage significant increase (p b 0.01) of TVC was recorded only in group of meat stored in the plastic bags with normal atmosphere. These results are consistent with those of other studies that found 3.92 log CFU/g; Seydim et al. (2006) and 4.5 log CFU/g Bingol and Ergun (2012). During following days of storage TVC were significantly increasing (p b 0.001) in all experimental groups. The obtained results suggest that meat samples stored in the plastic bags, with normal atmosphere, contained during storage more counts for TVC with comparison to the other two experimental meat groups, which were vacuum-packed (p b 0.001). Counts for TVC in this group increased on day 14 to 7.4 ± 0.2 log CFU/g and this value is higher than those recorded on day 21 in the meats samples stored in vacuum (p b 0.001). No significant differences were observed between meat samples stored in vacuum from day 1 and samples stored in vacuum from day 3 of experiment. Similar differences in TVC between air and vacuum packed ostrich meat were listed in the work of FernándezLópez et al. (2008). They also found out that the counts of aerobic bacteria in ostrich meat during 18 days of storage in vacuum were similar to meat samples stored in the modified atmospheres. Total aerobic counts in vacuum-packed ostrich meat during 21 days of storage recorded by Otremba, Dikeman, and Boyle (1999) were similar to our results. On the other hand Alonso-Calleja, MartinezFernández, Prieto, and Capita (2004) found that between 3 – 7 days after packaging total aerobic counts were higher compared with our results. We found out that on day 7 of vacuum-packed storage, TVC in the ostrich meat (pH of meat was 6.20 ± 0.09) was 3.8 ± 0.3 log CFU/ g. The results of mentioned authors are as follows: 6.52 ± 0.24 log CFU/g/pH ≤ 5.8; 7.44 ± 0.51 log CFU/g/pH 5.8 – 6.2; 7.75 ± 0.34 log CFU/g/pH N 6.2 (total aerobic counts/pH of meat). Initial count for Enterobacteriaceae (Table 5) was b 1 log CFU/g. This value is lower in comparison with the other works. Bingol and Ergun (2012) reported initial count for this family 3.5 log CFU/g, Seydim et al. (2006) 2.3 log CFU/g and Fernández-López et al. (2008) 2.0 log CFU/g. During storage, Enterobacteriaceae counts were significantly increasing (p b 0.001) in all three groups of package meat samples. During the first seven days of storage package conditions had not significant effect on the Enterobacteriaceae counts. Significant differences were observed on day 14. Meat samples stored in the plastic bags (normal atmosphere) contained more Enterobacteriaceae counts (p b 0.001) than all vacuum-packed samples. No significant differences
Table 5 Microbial populations for ostrich meat (log CFU/g) during storage in different package conditions (mean ± SD). Package conditions
Day 7
Day 14
Day 21
Total viable count of microorganisms VP – 1 3.8 ± 0.3c VP – 3 3.8 ± 0.3 c NVP 3.8 ± 0.3 c
Day 1
3.8 ± 0.3c;2 3.4 ± 0.3c;2 4.4 ± 0.2b;1
5.3 ± 0.2b;2 5.0 ± 0.3b;2 7.4 ± 0.2a;1
6.7 ± 0.3a;1 6.8 ± 0.2a;1 –
Enterobacteriaceae VP – 1 VP – 3 NVP
b 1d b1d b1c
1.8 ± 0.4c;1 1.6 ± 0.2c;1 2.2 ± 0.2b;1
3.1 ± 0.2b;2 2.5 ± 0.4b;2 4.7 ± 0.1a;1
3.8 ± 0.2a;1 4.1 ± 0.4a;1 –
Staphylococcus VP – 1 VP – 3 NVP
b 2c b2c b2b
b 2c;1 b2c;1 b2b;1
3.0 ± 0.3b;2 2.3 ± 0.2b;3 5.2 ± 0.2a;1
6.0 ± 0.2a;1 6.2 ± 0.2a;1 –
Means in the lines with the same superscript (a, b, c) and means in the columns with the same superscript (1, 2, 3) do not differ significantly. VP – 1 vacuum-packed from day 1, VP – 3 vacuum-packed from day 3, NVP – non-vacuum packed.
46
M. Brenesselová et al. / Meat Science 101 (2015) 42–47
Table 6 Results of sensory analysis of ostrich meat during various form of storage (mean ± SD). Package conditions F
A
J
T
Sensory Sum score
VP – 1 VP – 3 NVP VP – 1 VP – 3 NVP VP – 1 VP – 3 NVP VP – 1 VP – 3 NVP VP – 1 VP – 3 NVP
Day 1 4.17 ± 0.75a,b
4.83 ± 0.41a
3.17 ± 0.75
3.17 ± 0.41
15.33 ± 2.32
Day 7 4.33 4.17 3.67 4.33 4.33 4.00 3.50 3.00 3.33 3.50 3.00 3.00 15.67 15.50 14.00
Day 14 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
0.82a 0.75 0.52 0.52 0.52 0.63a,b 0.84 1.10 1.03 0.55 0.89 0.89 2.72 3.26 3.08
5.00 4.00 3.00 4.50 3.83 3.33 3.50 4.17 2.83 3.67 4.17 2.83 16.67 16.17 12.00
± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
Day 21 0.00a; 1 0.891,2 1.102 0.55 0.75 0.82b 0.55 0.75 0.75 0.52 0.75 0.98 1.61 3.15 3.65
2.80 ± 0.45 b;2 4.40 ± 0.55 1 – 3.60 ± 0.55 4.20 ± 0.84 – 3.40 ± 0.89 3.80 ± 0.84 – 3.60 ± 1.14 4.20 ± 0.84 – 13.40 ± 3.03 16.60 ± 3.06 –
Means in the lines with the same superscript (a. b) and means in the columns with the same superscript (1. 2) do not differ significantly. F - flavour, A - aroma, J - juiciness, T- tenderness, VP – 1 vacuum-packed from day 1s, VP – 3 vacuum-packed from day 3, NVP – non-vacuum packed.
were observed between meat samples stored in vacuum from day 1 and samples stored in vacuum from the day 3 of experiment. The counts of Staphylococcus spp. (Table 5) were during first 7 days of storage b2 log CFU/g. This result agrees with Alonso-Calleja et al. (2004). Increasing in this count was observed on day 14 and subsequently on day 21 of storage (p b 0.001) in all monitored groups. Similarly as in the other monitored microbial counts, Staphylococcus spp. counts were higher (p b 0.001) in the meat samples stored in the plastic bags with normal atmosphere. The shelf-life of meat is mainly influenced by the number of present microorganisms, which is closely related to the pH value of the meat. The most significant differences in these parameters were observed on day 14 of storage (Tables 2 and 5). On day 14 of storage the highest pH value was measured in the meat of group NVP (6.54), this resulted in higher numbers of microorganisms in the meat of this group (TVC, Enterobacteriaceae, Staphylococcus) compared to group VP1 and VP2.
3.5. Sensory analysis The results of the sensory evaluation are expressed in the Table 6. The best sensory properties were achieved in the meat vacuumpacked from the first day on the storage day 14. The meat which was vacuum-packed from the third day of storage reached the highest sensory quality on 21 day. Only minimal differences had been recorded between the vacuumpacked meat from day 1 and the vacuum-packed from day 3 of storage. In the non-vacuum-packed meat the best sensory quality was found on day 1 of storage and the following days of storage the sensory quality gradually declined. This change is also significantly related to higher fat decomposition during the storage Bingol and Ergun (2012). On the other side, both groups of vacuum-packed samples improved the sensory quality. The taste evaluation showed statistically significant decreases in the samples which were vacuum-packed from day 1 on the 21st day of storage (2.80 ± 0.45) compared with the day 7 (p b 0.05) and compared with the day 14 (p b 0.001) in the same packed conditions. The statistically significant decrease (p b 0.001) of flavor we recorded on day 14 of storage between the samples non-vacuum packed (3.00 ± 1.10) and the vacuum-packed from the day 1 (5.00 ± 0.00). On day 21 of storage we recorded statistically significant increase (p b 0.05) of flavour between the samples vacuum-packed from the day 1 (2.80 ± 0.45) and the samples which were vacuum-packed from the day 3 (4.40 ± 0.55). We recorded better results in sensory properties of ostrich meat in VP3 samples on day 21 than in the VP1 samples because the longer aerobic atmosphere affected the ripening process of ostrich meat which caused better sensory properties.
The results of sensory analysis were influenced mainly by pH, TBA values and microbial spoilage, however these parameters were higher in group NVP in comparison with both vacuum-packed meat groups. 4. Conclusion The results of this study showed that the shelf-life of ostrich meat stored at 2 °C were affected by using different packaging conditions (vacuum from day 1, vacuum from day 3 and in the normal atmosphere). The storage of ostrich´s meat in both vacuum-packed groups had a positive effect on the biochemical, microbiological and sensory parameters compare to non-vacuum packed meat. In both vacuumpacked samples was recorded reduction of not only the oxidation process but also the microbial spoilage. The level of lactic acid and pH value in ripening process of ostrich meat were influenced by different storage conditions and affected the final quality of the meat. The better sensory analysis was recorded on day 14 of storage in the VP1 compared with VP3. We recorded the highest scores of the sensory evaluation in the non-vacuum packed meat on day 1 and subsequently during the shelf-life the sensory scores decreased. The vacuum packed storage applied in this study is useful in practical application in the meat industry for improving durability of ostrich meat. Acknowledgement The present work was supported by VEGA scientific grant 1/0457/14 from the Ministry of Education of the Slovak Republic. References Alonso-Calleja, C., Martinez-Fernández, B., Capita, R., & Prieto, M. (2002). La carne de avestruz: valor nutritivo y calidad higiénica. Alimentación, Equipos y Tecnologia, 57–62 (Octubre). Alonso-Calleja, C., Martinez-Fernández, B., Prieto, M., & Capita, R. (2004). Microbiological quality of vacuum-packed retail ostrich meat in Spain. Food Microbiology, 21, 241–246. Atanassova, V., Apelt, J., Reich, F., & Klein, G. (2008). Microbiological quality of freshly shot game in Germany. Meat Science, 78, 414–419. AOAC (1997). Official methods of analysis of the Association of Analytical Chemists. Washington D.C. Bingol, E. B., & Ergun, O. (2012). Effects of modified atmosphere packaging (MAP) on the microbiological quality and shelf life of ostrich meat. Meat Science, 90(1), 276–277. Blixt, Y., & Borch, E. (2002). Comparison of shelf life of vacuum-packed pork and beef. Meat Science, 60, 371–378. Botha, S. St. C., Hoffman, L. C., & Britz, T. J. (2006). Effect of hot-deboning on the physical quality characteristics of ostrich meat. South African Journal of Animal Science, 36, 197–208. Capita, R., Diaz-rodriguez, N., Prieto, M., & Alonso-Calleja, C. (2006). Effects of temperature, oxygen exclusion, and storage on the microbial loads and pH of packed ostrich steaks. Meat Science, 73, 498–502.
M. Brenesselová et al. / Meat Science 101 (2015) 42–47 Čuboň, J., Haščík, P., Mojto, J., Kačániová, M., Vagač, V., Košťalová, D., & Pavličová, S. (2004). Effect of sodium lactate on microbiological, physical and sensory characteristics of beef. Acta fytotechnica et zootechnica, 3, 62–66 (In Slovak). Dalle Zotte, A. (2002). Perception of rabbit meat quality and major factors influencing the rabbit carcass and meat quality. Livestock Production Science, 75, 11–32. EU Council Directive 1099/2009/EC (2009). On the protection of animals at the time of slaughter or killing. Official Journal of European Community, 303, 1–30. Fernández-López, J., Sayas-Barberá, E., Munoz, T., Sendra, E., Navarro, C., & Pérez-Alvarez, J. A. (2008). Effect of packaging conditions on shelf-life of ostrich steaks. Meat Science, 70, 143–152. Filgueras, R. S., Gatellier, P., Aubry, L., Thomas, A., Bauchart, D., Durand, D., Zambiazi, R. C., & Santé-Lhoutellier, V. (2010). Colour, lipid and protein stability of Rhea americana meat during air- and vacuum-packaged storage: influence of muscle on oxidative processes. Meat Science, 86, 665–673. Floch, J., Lees, M., & Sloane Stanley, G. H. (1957). A simple method for the isolation and purification of total lipids from animal tissues. The Journal of Biological Chemistry, 226, 497–509. Girolami, A., Marsico, I., D´Andrea, G., Braghieri, A., & Napolitano, F. (2003). Fatty acid profile, cholesterol content and tenderness of ostrich meat as influenced by age at slaughter and muscle type. Meat Science, 64(3), 309–315. GraphPad Prism (2003). Version 4.00 for Windows. GraphPad Software San Diego (California). Hoffman, L. C. (2005). A review of the research conducted on ostrich meat. Proceedings of the 3rd International Ratite Science Symposium of the WPSA (pp. 107–119) (October 2005. Madrid, Spain). Hoffman, L. C. (2008). Value adding and processing of Ratite meat: a review. Australian Journal of Experimantal Agriculture, 48, 1–6. Jacobsen, M., & Bertelsen, G. (2000). Colours stability and lipid oxidation of fresh beef. Development of a response surface model for predicting the effects of temperature, storage time and modified atmosphere and composition. Meat Science, 54, 49–57. Karama, M. (2001). The microbiological quality of ostrich carcasses producted at an exportapproved South African abatoir. South Africe: MMved (Hyg) study at University of Pretoria, 97. Koréneková, B., Nagy, J., Smulders, F. J. M., Paulsen, P., Mačanga, J., Popelka, P., Marcinčák, S., & Korének, M. (2014). Lactic acid concentration and pH values in muscles of European brown hare. In P. Paulsen, A. Bauer, & F. J. M. Smulders (Eds.), Trends in game meat hygiene, from forest to fork (pp. 400). The Netherlands: Wageningen Academic Publishers978-90-8686-238-2. Leygonie, C., Britz, T. J., & Hoffman, L. C. (2012). Meat quality comparison between fresh and frozen/thawed ostrich M. iliofibularis. Meat Science, 91, 364–368.
47
Mačanga, J., Koréneková, B., Nagy, J., Marcinčák, S., Popelka, P., Kožárová, I., & Korének, M. (2011). Post-mortem changes in the concentration of lactic acid, phosphates and pH in the muscles of wild rabbits (Oryctolagus cuniculus) according to the perimortal situation. Meat Science, 88, 701–704. Majewska, D., Jakubowska, M., Ligocki, M., Tarasewicz, Z., Szczerbińska, D., Karamucki, T., & Sales, J. (2009). Physicochemical characteristics, proximate analysis and mineral composition of ostrich meat as influenced by muscle. Food Chemistry, 117, 207–211. Marcinčák, S., Sokol, J., Bystrický, P., Popelka, P., Turek, P., Bhide, M., & Máté, D. (2004). Determination of lipid oxidation level in broiler meat by liquid chromatography. Journal of AOAC International, 87(5), 1148–1152. Marcinčák, S., Sokol, J., Turek, P., Różaňska, H., Dičáková, Z., Máté, D., Popelka, P., & Korim, P. (2003). Comparative evaluation of analytical techniques to quantify malondialdehyde in broiler meat. Bulletin of the Veterinary Institute in Pulawy, 47, 491–496. Otremba, M. M., Dikeman, M. E., & Boyle, E. A. E. (1999). Refrigerated shelf life of vacuumpacked, previously frozen ostrich meat. Meat Science, 52, 279–283. Polawska, E., Marchewska, J., Cooper, R. G., Sartowska, K., Pomianowski, J., Jóźwik, A., Strza kowska, N., & Horbańczuk, J. O. (2011). The ostrich meat-an updated review, II. Nutritive value. Animal Science Papers and Report, 29(2), 89–97. Príbela, A. (2001). Sensory evaluation of food materials, additives and products. Košice: Institute of veterinarians education, 87–94 (In Slovak). Sales, J. (1998). Fatty acid composition and cholesterol content of different ostrich muscles. Meat Science, 49, 489–495. Seydim, A. C., Acton, J. C., Hall, M. A., & Dawson, P. L. (2006). Effects of packaging atmospheres on shelf-life quality of ground ostrich meat. Meat Science, 73, 503–510. STN EN ISO 4833 (2003). Microbiology of food and animal feeding stuffs. Horizontal method for the enumeration of microorganisms. Colony-count technique at 30 °C. SÚTN Bratislava. STN EN ISO 6887–1 (2001). Microbiology of food and animal feeding stuffs. Preparation of test samples, initial suspension and decimal dilutions for microbilogical examination. Part 1: General rules for the preparation of the initial suspension and decimal dilutions. SÚTN Bratislava. STN EN ISO 6888–1 (2001). Microbiology of food and animal feeding stuffs. Horizontal method for the enumeration of coagulase-positive staphylococci (Staphylococcus aureus and other species). Part 1: Technique using Baird-Parker agar medium. SÚTN Bratislava. STN ISO 21528–2 (2004). Microbiology of food and animal feeding stuffs. Horizontal method for the detection and enumeration of Enterobacteriaceae. Part 2: Colony-count method. SÚTN Bratislava. Winkelmayer, R., Lebersorger, P., Zedka, H. F., Forejtek, P., Vodňanský, M., & Večerek, V. (2005). Game hygiene Central European Institute of Wildlife Ecology. Wien-Brno-Nitra (In Czech).
Contents lists available at ScienceDirect
Meat Science journal homepage: www.elsevier.com/locate/meatsci
Effects of vacuum packaging conditions on the quality, biochemical changes and the durability of ostrich meat Martina Brenesselová ⁎, Beáta Koréneková, Ján Mačanga, Slavomír Marcinčák, Pavlína Jevinová, Monika Pipová, Peter Turek Department of Food Hygiene and Technology, University of Veterinary Medicine and Pharmacy, 041 81 Košice, Slovak Republic
a r t i c l e
i n f o
Article history: Received 26 February 2014 Received in revised form 10 September 2014 Accepted 6 November 2014 Available online 13 November 2014 Keywords: Ostrich meat Lactic acid pH Malondialdehyde Microbial analysis Sensory analysis
a b s t r a c t In this study, the effects of vacuum packaging conditions on the concentrations of lactic acid, malondialdehyde, pH, microbial and sensory analysis were determined during chilled storage of ostrich meat. Meat was packed as follows: vacuum packed from 1st day (VP-1), vacuum packed from 3rd day (VP-3) and non-vacuum packed (NVP). Analysis were performed at 1st, 7th, 14th, 21st day after slaughter. Meat consisted of 74.69% water, 2.29% fats, 20.95% proteins. Package conditions had significant effect on the pH (NVP: 6.54 on the 14th day, VP-1: 6.05 and VP-3: 6.07 on the 21th day p b 0.001), amount of malondialdehyde (NVP: 8.62 mg/kg on the 14th day; VP-1: 1.95 and VP-3: 2.55 on the 21th day; p b 0.001) and total microbial count (NVP: 7.4 log CFU/g on the 14th day; VP-1: 6.7 and VP-3: 6.8 on the 21th day p b 0.01). Based on these results we can assess that vacuum packed from 1st day is necessary for the 21 days storage of ostrich meat. © 2014 Published by Elsevier Ltd.
1. Introduction The African ostrich (Struthio camelus) is the largest of all birds. Until the middle 1900s, ostriches lived in South western Asia, Africa, and the Arabian Peninsula. Currently, the wild ostriches are only found in desert regions in Africa. Through the commercial ostrich industry, farm-raised ostriches are now found in the countries all over the world. In the past, ostrich farms had been mainly focused for production the feathers (Alonso-Calleja, Martinez-Fernández, Capita, & Prieto, 2002). In present, the consumption of ostrich meat and its popularity in European countries is increasing, due to its suitable properties, such as low fat and fragility. In recent years the ostrich farms are developed also in Slovakia. In the meat industry, ostrich meat gain attention as a new alternative red meat due to a favourable fatty acid profile. Intramuscular fat consists of high content of polyunsaturated fatty acids and low intramuscular fat content (Sales, 1998). The structure and taste is similar to beef meat, however it contains about 40 percent less fat. The typical colour of ostrich meat is red. The meat which we mark as a red meat has less level of fat and cholesterol as turkey meat and chicken meat and is rich in iron and protein (Polawska et al., 2011). One of the most critical factors affecting the quality of the meat after slaughter is the process of its maturation (Atanassova, Apelt, Reich, & Klein, 2008). The muscles fibres are subjected to biochemical changes in the meat. The conversion of the muscle to a meat during the ripening ⁎ Corresponding author. E-mail address: [email protected] (M. Brenesselová).
http://dx.doi.org/10.1016/j.meatsci.2014.11.003 0309-1740/© 2014 Published by Elsevier Ltd.
process is an energy-demanding process. The energy is provided by degradation of glycogen in the muscle. Energy-rich phosphates are participating on the enzymatic degradation of glycogen to the lactic acid following decrease of pH. At a low pH many of microorganisms cannot survive, or their division is slowing down. Because of this, the decrease of pH provides some protection from bacterial spoilage. Almost all major components of the muscle are subject to a biochemical changes and emerging metabolic products contribute to the typical sensory properties. Very suitable example is the lactic acid and phosphates, which contribute to the typical flavor of the meat and are also related with improving of organoleptic and technological properties of meat (Dalle Zotte, 2002; Čuboň et al., 2004; Winkelmayer et al., 2005). The meat maturation is followed by a second phase, where proteins are degraded, with the accumulation of lowmolecular nitrogenous compounds and a slight rise in pH. It is not easy to clearly separate advanced aging from the onset on spoilage, but typically, in later contaminant bacteria are involved (Koréneková et al., 2014). In addition to the growth of microorganisms lipid oxidation is an important factor regarding shelf life and consumer acceptance of fresh meat (Jacobsen & Bertelsen, 2000). The oxidative deterioration of the polyunsaturated lipids of foods leads through formation of hydroperoxides to short-chain aldehydes, ketones and other oxygenated compounds, which are considered to be responsible for the development of rancidity in stored foods. The most widely used assay to quantify lipid oxidation products in meat is the thiobarbituric acid (TBA) test because of its simplicity and fastness. TBA test determines the amount of malondialdehyde (MDA), a major secondary by-product of lipid oxidation in a sample (Marcinčák et al., 2003).
M. Brenesselová et al. / Meat Science 101 (2015) 42–47
To the author's knowledge, little information is available on the microbiological aspects and keeping quality of this foodstuff, especially of the refrigerated and vacuum-packed meat, which is frequently purchased in developed countries. Factors, such as pH, that has been considered as a main parameter in the microbiological quality of the meat, the initial bacterial contamination, temperature of the meat during the storage, packing in modified atmosphere, plays a major role in the final quality of meat (Capita, Diaz-rodriguez, Prieto, & Alonso-Calleja, 2006; Blixt & Borch, 2002). As the other types of meat of slaughtered animals, the ostrich meat couldn´t be completely sterile after the cutting carcasses. After skinning, the ostrich meat is exposed to microbial contaminations which may come from a variety of external sources including the hands of workers (Karama, 2001; Hoffman, 2005, 2008). Using the appropriate method of packaging and storage conditions, we can greatly affect the microbial quality of post-mortem and also the durability of ostrich meat. Ostrich body is usually refrigerated 24–48 hours post-mortem, cut and immediately vacuum-packed or frozen. The consumers receives either fresh or frozen meat. The consumption of ostrich meat in the world is increasing and therefore improving the hygiene and extent shelf-life of meat are crucial for potential consumers. Using the modern techniques of packaging we can maintain the microbial and also the sensory quality of the products during the storage (Seydim, Acton, Hall, & Dawson, 2006). The aim of this study was to evaluate the effects of vacuum packaging on the quality, biochemical changes and shelf-life with a focus on the concentrations of lactic acid, pH value, amount of malondialdehyde, microbial and sensory analysis. 2. Materials and methods 2.1. Samples Thigh muscles of eight 16-month-old ostriches (Struthio camelus) were used for the experiment. The ostriches were obtained from the same farm in Slovakia. Animals were stunned and slaughtered under the provisions of EU Council Directive 1099/2009/EC, 1099/2009/EC (2009). Thigh muscles, immediately after slaughter of animals, were delivered in a cooler (+ 4 °C) to the Department of Food Hygiene and Technology in the University of Veterinary Medicine and Pharmacy in Košice (Slovakia). 2.2. Experimental design The meat samples of ostriches consisted of thigh muscles (M. iliotrochantericus cranialis, M. iliofemoralis, M. iliotrochantericus caudalis, M. pubo-ischio-femoralis) were sampled from right and left leg. The samples were firstly examined as starting material (chemical composition, sensory analysis, pH value, determination of lactic acid, malondialdehyde, microbial analysis). The other thigh muscles were carved to 60 pieces, which were divided into three groups. Each group (20 packs) was stored in different package conditions. Every package contains approximately 1000 g of meat. The thigh muscles of the first group (20 packs) were vacuum-packed within 24 hours after slaughter and stored in a refrigerator at 2 °C for 21 days. The second group of the muscles (20 packs) was firstly stored in the normal atmosphere longer than 48 hours in the plastic bags at 2 °C (because the speed of post-mortal processes probably depended on the occurrence of oxygen). Then the samples were vacuum-packed from 3rd day after arrival and stored at the same temperature to 21st day. The thigh muscles of the third group (20 packs) were stored in the plastic bags (normal atmosphere) at 2 °C for all the time of the experiment. Samples of the thigh muscles of the first two groups were analyzed on days 7, 14 and 21 of storage. Muscles of third group were examined only on days 7 and 14, because after 21 days of storage the significant
43
signs of decay appeared. 5 packages of samples were analyzed on each measurement day. 2.3. Chemical composition of meat Dry matter was determined by oven-drying at 105 °C (AOAC, 1997). Kjeltec Auto, type 1030 (Tecator Co., Hoganas, Sweden) analyser was used to determine the crude protein content. Lipids were isolated in ground samples with petroleum ether with Soxhlet apparatus (LTHS 500, Brnenská Druteva v.d., Czech Republic) and were determined gravimetrically (Floch, Lees, & Sloane Stanley, 1957). 11 g of ostrich meat were used for chemical composition analysis. 2.4. pH values Samples (50 g) from each group of meat were homogenized for 10 min. After that 10 g was used for extraction by distilled water (100 ml) and filtrated. The water extract of the muscle was used for analysis of pH values by a digital pH meter (inoLab pH720, WTW, Weilheim, Germany) with glass electrode. 2.5. Determination of lactic acid The measurement of lactic acid was performed from the water extract that was used for the pH measurements. One milliliter of water extracts of meat samples was put into 10 ml flasks and filled with distilled water and immediately analyzed by use of an electrophoretic analyser (Type EA102) with a conductive detector (Villa Labeco, Slovak Republic) according to Mačanga et al. (2011). The electrophoretic separation system used consisted of a leading electrolyte-10 mM HCl, β-alanine and 0.1% methyhydroxyethylcellulose, pH 3.2 and terminating electrolyte-5 mM caproic acid and 5 mM hydroxymethy-aminomethane. The direct currents used in pre-separation and analytical columns were 250 μA and 50 μA. The results of analysis were evaluated by the computer programme ITPP pro 32 and expressed in g/100 g of meat. 2.6. Determination of thiobarbituric acid assay To determine the lipid oxidation changes of thigh muscles, the method of thiobarbituric value (TBA) determination, expressing the degree of secondary damage of lipids, contingent upon the oxidation of unsaturated fatty acids, was used. The extent of lipid oxidation was evaluated as thiobarbituric acid reactive substances (TBARS) by method of Marcinčák et al. (2004). Sample (20 g of meat) was mixed with 50 ml distilled water and homogenized one minute. After that 50 ml 10% trichloracetic acid was added and kept in the lab temperature for 10 min. Then the sample was filtered. Four milliliter of filtrate and 1 ml thiobarbituric acid was inserted into stopper fitted flasks and then incubated in hot water (80 °C) for 90 min. After cooling, the samples were analyzed. TBARS values were measured spectrophotometrically at 532 nm (Helios γ, v. 4. 6. Thermo spectronic, Cambridge, UK). Results were quantified as malondialdehyde (MDA) equivalents (mg/MDA/kg muscle). 2.7. Microbial analysis Samples (10 g) for microbiological analysis were taken aseptically from the ostrich muscles. The initial dilution, as well as further subsequent decimal dilutions were prepared in accordance with the requirements of valid food standards (STN EN ISO 6887–1). 2.7.1. Enumeration procedures Violet Red Bile Glucose Agar (VRBG) was used to enumerate Enterobacteriaceae (STN ISO, 21528–2). One milliliter of the first two decimal dilutions was placed into sterile Petri dishes and suffused with VRBG (Hi-Media, India). The plates were incubated at 37 °C for 48 h.
44
M. Brenesselová et al. / Meat Science 101 (2015) 42–47
Plate Count Agar (PCA) was used to enumerate the total count of microorganisms (STN EN ISO 4833). One milliliter of the initial dilution as well as two subsequent decimal dilutions was placed into sterile Petri dishes and suffused with PCA (Hi-Media, India). The plates were incubated at 30 °C for 72 h. Baird Parker agar medium was used to enumerate coagulasepositive staphylococci. As described by the standard procedure (STN EN ISO 6888–1), the decimal dilutions were spread on the surface of Baird Parker agar medium (Hi-Media, India) in an amount of 0.1 milliliter and incubated for 48 h at 37 °C. Suspect colonies were further evaluated for their coagulase activity. One milliliter of the reconstituted commercial freeze-dried rabbit plasma (Staphylo PK, Imuna Pharm, Slovakia) was placed into a small test tube. Then 0.1 milliliter of the over-night staphylococcal culture in brain heart infusion broth was added and the tube content was mixed. Test tubes were incubated at 37 °C for 1, 2, 4, 6 and 24 h. Within this period, fibrinogen was converted to fibrin by the staphylococcal coagulase enzymes. A positive result was manifested by clotting of the plasma in the test tube. After incubation of inoculated Petri dishes at appropriate temperatures the counts of characteristic colonies were enumerated, calculated and displayed in CFU/g. 2.8. Sensory analysis Sensory examination of quality of ostrich meat (aroma, flavor, juiciness, tenderness) was realized by the methods for sensory evaluation of meat (Príbela, 2001). Sensory analysis was performed by six experienced evaluators using five-point rating scale (from one to five points) on days 1, 7, 14 and 21 of storage. The samples of ostrich meat were boiled (70 °C). Every panelist removed the meat samples from the package by opening it with knife and examined three samples (VP, VP-3 and NVP) which were placed on the white glass plate. The each sample was coded with a random letter. The number five indicated the highest quality of evaluated parameter and the number one indicated the lowest quality. The points were summarized with maximum count 20. 2.9. Statistical evaluation All the data were analyzed statistically using GraphPad Prism Software, Version 4.00 (Graphpad Prism, 2003). One-way analysis of variance (ANOVA) with the post hoc Tukey's multiple comparison test was used to evaluate statistical significance of differences between three groups of meat with different package conditions (statistical significant differences are illustrated in the tables by numbers) and between days of the experiment (statistical significant differences are illustrated in the tables by letters).
20.60–21.70%. Interesting is also the proportion of fatty acids in the fat of the meat. The fat in the muscle of ostrich contains up 27–33% polyunsaturated fatty acids Girolami, Marsico, D´Andrea, Braghieri, and Napolitano (2003). It may also be a cause of the lower oxidative stability of meat during the storage and the needful heightened protection against the oxidation of fats (vacuum-packaging). 3.2. pH value and lactic acid Production of lactic acid, pH changes and progress of the ripening process are shown in Tables 2 and 3. The initial pH (Table 2) was 6.18 ± 0.01 and the most significant increased (6.54 ± 0.07; p b 0.001) was recorded in the muscle stored in non-vacuum conditions on the day 14. In the samples which were vacuum-packed from the day 1 was the most significant decrease recorded (6.05 ± 0.06; p b 0.001) on the day 21. Significant increase (6.07 ± 0.02; p b 0.001) was observed in the vacuum-packed samples from day 3 day 21. The increase of pH value was observed only in the muscle, which was stored in a vacuum. Fernández-López et al. (2008) showed only a gradual lowering of the pH from the value of 6.04 to below 5.60 during a vacuum storage conditions and to above 5.66 during air storage condition on 18th day. But Botha, Hoffman, and Britz (2006) found, that the pH value of the muscle tissue of ostriches till day 14 increased from the original value 5.8 to a value of under 6.0. Statistically significant differences in pH values were found on the day 14 of storage in the samples which were vacuum-packed from the day 1 of storage (6.22 ± 0.07; p b 0.001) and vacuum-packed from the day 3 (6.20 ± 0.01; p b 0.001) compared to non-vacuum-packed samples. The results shows (Table 3) that in the samples stored in vacuum from day 1 the dynamics of changes in concentration of lactic acid till the day 7 increased and at the day 14 decreased. The most significant (1.18 ± 0.08; p b 0.01) decrease was recorded on day 21. In the samples stored in vacuum from day 3 the level of lactic acid decreased no significantly till day 14 and on day 21 increased. The most significant increase (1.64 ± 0.36; p b 0.05) of lactic acid was observed on the day 21. In the samples stored in normal atmosphere (without vacuum) the level of lactic acid did not increased significantly till day 7and on day 14 decreased. The concentration of lactic acid in the samples depends on the forms of storage. The most significant differences (p b 0.05) were recorded only between the samples which were vacuum packed from the day 1 (1.18 ± 0.08) and the vacuum packed from the day 3 (1.64 ± 0.36) on the day 21 of storage.
3. Results and discussion 3.3. Degradation of lipids in muscles 3.1. Chemical composition The chemical composition of ostrich meat is shown in the Table 1. In our experiment were found that ostrich thigh muscle contains an average of 20.95% protein, 2.29% fat and 74.69% water. Therefore, from a health perspective is highly prized food. Similar results of fat and nitrogenous proteins were previously reported by Majewska et al. (2009). The contents of fats and proteins reported in their study were as follows: the fat 0.90–1.34% and protein
Table 1 Chemical composition of ostrich thigh muscle (%) (mean ± SD). Samples
Dry matter
Water
Fat
Proteins
Thigh muscle
25.31 ± 0.72
74.69 ± 0.72
2.29 ± 0.19
20.95 ± 0.26
The rate of secondary damage of fat in the muscles of ostriches expressed as the amount of malondialdehyde is shown in Table 4. The
Table 2 The changes of pH values in the ostrich meat during various form of storage (mean ± SD). Package conditions
Day1
Day 7
Day 14
Day 21
VP – 1 VP – 3 NVP
6.18 ± 0.01a 6.20 ± 0.09a;1 6.22 ± 0.07a;2 6.05 ± 0.06b;1 6.18 ± 0.01a 6.19 ± 0.01a;1 6.20 ± 0.01a;2 6.07 ± 0.02b;1 6.18 ± 0.01b 6.16 ± 0.04b;1 6.54 ± 0.07a;1 –
Means in the lines with the same superscript (a. b) and means in the columns with the same superscript (1. 2) do not differ significantly. VP – 1 vacuum-packed from day 3, VP – 3 vacuum-packed from day 3, NVP – non-vacuum packed.
M. Brenesselová et al. / Meat Science 101 (2015) 42–47 Table 3 The changes of lactic acid concentration in the ostrich meat during various form of storage (g/100 g) (mean ± SD). Package conditions
Day 1
Day 7
Day 14
Day 21
VP – 1 VP – 3 NVP
1.43 ± 0.11a.b;1 1.18 ± 0.08b;2 1.47 ± 0.13a.b 1.75 ± 0.45a;1 1.47 ± 0.13a.b 1.36 ± 0.06a.b;1 1.22 ± 0.13b;1 1.64 ± 0.36a;1 1.47 ± 0.13a 1.51 ± 0.10a;1 1.13 ± 0.03a;1 –
Means in the lines with the same superscript (a. b) and means in the columns with the same superscript (1. 2) do not differ significantly. VP – 1 vacuum-packed from day 1, VP – 3 vacuum packed-from day 3, NVP – non-vacuum packed.
initial amount of malondialdehyde measured within 24 hours after kill was 0.67 ± 0.04. Leygonie, Britz, and Hoffman (2012) recorded higher amount of malondialdehyde in fresh ostrich meat: 1.76 ± 0.03 mg/kg. On the day 7 of storage, the malondialdehyde measured in the thigh muscle which was vacuum-packed from day 3 increased significantly (p b 0.001) to the value 3.16 ± 0.24. During the following days of storage, the quantity of malondialdehyde did not change significantly. The quantity of malondialdehyde in the meat samples vacuumpacked from day 1 significantly increased until on the day 14 (1.80 ± 0.27; p b 0.001). On the day 21 of storage no significant increase of the malondialdehyde was recorded. The amount of malondialdehyde measured in the samples of meat which were stored in the plastic bags (normal atmosphere) was increasing throughout the experiment. The most significant increase was recorded on the day 7 (7.67 ± 0.61; p b 0.001). As show in Table 4, amounts of malondialdehyde measured in the samples of ostrich meat were significantly differed depending on the method of packing. The statistically highest amount of malondialdehyde was measured in the samples of meat which were stored in the plastic bags in the normal atmosphere (p b 0.001). On the other hand, degradation changes of fats were the least intensive in the vacuum-packed samples. The effects of storage time and package method as the significant factors for amount of malondialdehyde are also confirmed by other authors. Fernández-López et al. (2008) stored ostrich steaks in different package conditions for 18 days at 2 °C. Measured malondialdehyde in the samples exposed to air (above 1.2 mg/kg on the day 18) were significantly higher compared with vacuum-packed (approximately 0.5 mg/kg on the day 18). In the meat samples stored in modified atmosphere even lower amounts of malondialdehyde were recorded (under 0.4 mg/kg on the day 18). Similar results are recorded in the work of Seydim et al. (2006), who stored ostrich meat for 9 days at 4 °C. Differences in malondialdehyde between samples exposed to air and vacuum-packed listed in the studies of both authors are similar to ours results, however values of malondialdehyde are lower than ours. On the other hand, level of malondialdehyde reported in this study are similar to results of Filgueras et al. (2010), who compared lipid stability of Rhea Americana meat during air (stored 5 days) and vacuumpacked storage (stored 28 days) at 4 °C.
Table 4 The amount of malondialdehyde (mg/kg) in muscle samples of ostriches during storage in different package conditions (mean ± SD). Package conditions
Day 1
Day 7
Day 14
Day 21
VP – 1 VP – 3 NVP
0.67 ± 0.04b 0.40 ± 0.12b;2 1.80 ± 0.27a;2 1.95 ± 0.20a;1 0.67 ± 0.04b 3.16 ± 0.24a;3 2.70 ± 0.19a;3 2.55 ± 0.26a;1 0.67 ± 0.04c 7.67 ± 0.61b;1 8.62 ± 0.29a;1 –
Statistic: means in the lines with the same superscript (a, b, c) and means in the columns with the same superscript (1, 2, 3) do not differ significantly. VP – 1 vacuum-packed from day 1, VP – 3 vacuum-packed from day 3, NVP – non-vacuum packed.
45
3.4. Microbial analysis Changes in microbial populations are shown in the Table 5. Initial microbial counts for total viable counts (TVC) on day 1 of storage were 3.8 ± 0.3 log CFU/g. On day 7 of storage significant increase (p b 0.01) of TVC was recorded only in group of meat stored in the plastic bags with normal atmosphere. These results are consistent with those of other studies that found 3.92 log CFU/g; Seydim et al. (2006) and 4.5 log CFU/g Bingol and Ergun (2012). During following days of storage TVC were significantly increasing (p b 0.001) in all experimental groups. The obtained results suggest that meat samples stored in the plastic bags, with normal atmosphere, contained during storage more counts for TVC with comparison to the other two experimental meat groups, which were vacuum-packed (p b 0.001). Counts for TVC in this group increased on day 14 to 7.4 ± 0.2 log CFU/g and this value is higher than those recorded on day 21 in the meats samples stored in vacuum (p b 0.001). No significant differences were observed between meat samples stored in vacuum from day 1 and samples stored in vacuum from day 3 of experiment. Similar differences in TVC between air and vacuum packed ostrich meat were listed in the work of FernándezLópez et al. (2008). They also found out that the counts of aerobic bacteria in ostrich meat during 18 days of storage in vacuum were similar to meat samples stored in the modified atmospheres. Total aerobic counts in vacuum-packed ostrich meat during 21 days of storage recorded by Otremba, Dikeman, and Boyle (1999) were similar to our results. On the other hand Alonso-Calleja, MartinezFernández, Prieto, and Capita (2004) found that between 3 – 7 days after packaging total aerobic counts were higher compared with our results. We found out that on day 7 of vacuum-packed storage, TVC in the ostrich meat (pH of meat was 6.20 ± 0.09) was 3.8 ± 0.3 log CFU/ g. The results of mentioned authors are as follows: 6.52 ± 0.24 log CFU/g/pH ≤ 5.8; 7.44 ± 0.51 log CFU/g/pH 5.8 – 6.2; 7.75 ± 0.34 log CFU/g/pH N 6.2 (total aerobic counts/pH of meat). Initial count for Enterobacteriaceae (Table 5) was b 1 log CFU/g. This value is lower in comparison with the other works. Bingol and Ergun (2012) reported initial count for this family 3.5 log CFU/g, Seydim et al. (2006) 2.3 log CFU/g and Fernández-López et al. (2008) 2.0 log CFU/g. During storage, Enterobacteriaceae counts were significantly increasing (p b 0.001) in all three groups of package meat samples. During the first seven days of storage package conditions had not significant effect on the Enterobacteriaceae counts. Significant differences were observed on day 14. Meat samples stored in the plastic bags (normal atmosphere) contained more Enterobacteriaceae counts (p b 0.001) than all vacuum-packed samples. No significant differences
Table 5 Microbial populations for ostrich meat (log CFU/g) during storage in different package conditions (mean ± SD). Package conditions
Day 7
Day 14
Day 21
Total viable count of microorganisms VP – 1 3.8 ± 0.3c VP – 3 3.8 ± 0.3 c NVP 3.8 ± 0.3 c
Day 1
3.8 ± 0.3c;2 3.4 ± 0.3c;2 4.4 ± 0.2b;1
5.3 ± 0.2b;2 5.0 ± 0.3b;2 7.4 ± 0.2a;1
6.7 ± 0.3a;1 6.8 ± 0.2a;1 –
Enterobacteriaceae VP – 1 VP – 3 NVP
b 1d b1d b1c
1.8 ± 0.4c;1 1.6 ± 0.2c;1 2.2 ± 0.2b;1
3.1 ± 0.2b;2 2.5 ± 0.4b;2 4.7 ± 0.1a;1
3.8 ± 0.2a;1 4.1 ± 0.4a;1 –
Staphylococcus VP – 1 VP – 3 NVP
b 2c b2c b2b
b 2c;1 b2c;1 b2b;1
3.0 ± 0.3b;2 2.3 ± 0.2b;3 5.2 ± 0.2a;1
6.0 ± 0.2a;1 6.2 ± 0.2a;1 –
Means in the lines with the same superscript (a, b, c) and means in the columns with the same superscript (1, 2, 3) do not differ significantly. VP – 1 vacuum-packed from day 1, VP – 3 vacuum-packed from day 3, NVP – non-vacuum packed.
46
M. Brenesselová et al. / Meat Science 101 (2015) 42–47
Table 6 Results of sensory analysis of ostrich meat during various form of storage (mean ± SD). Package conditions F
A
J
T
Sensory Sum score
VP – 1 VP – 3 NVP VP – 1 VP – 3 NVP VP – 1 VP – 3 NVP VP – 1 VP – 3 NVP VP – 1 VP – 3 NVP
Day 1 4.17 ± 0.75a,b
4.83 ± 0.41a
3.17 ± 0.75
3.17 ± 0.41
15.33 ± 2.32
Day 7 4.33 4.17 3.67 4.33 4.33 4.00 3.50 3.00 3.33 3.50 3.00 3.00 15.67 15.50 14.00
Day 14 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
0.82a 0.75 0.52 0.52 0.52 0.63a,b 0.84 1.10 1.03 0.55 0.89 0.89 2.72 3.26 3.08
5.00 4.00 3.00 4.50 3.83 3.33 3.50 4.17 2.83 3.67 4.17 2.83 16.67 16.17 12.00
± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
Day 21 0.00a; 1 0.891,2 1.102 0.55 0.75 0.82b 0.55 0.75 0.75 0.52 0.75 0.98 1.61 3.15 3.65
2.80 ± 0.45 b;2 4.40 ± 0.55 1 – 3.60 ± 0.55 4.20 ± 0.84 – 3.40 ± 0.89 3.80 ± 0.84 – 3.60 ± 1.14 4.20 ± 0.84 – 13.40 ± 3.03 16.60 ± 3.06 –
Means in the lines with the same superscript (a. b) and means in the columns with the same superscript (1. 2) do not differ significantly. F - flavour, A - aroma, J - juiciness, T- tenderness, VP – 1 vacuum-packed from day 1s, VP – 3 vacuum-packed from day 3, NVP – non-vacuum packed.
were observed between meat samples stored in vacuum from day 1 and samples stored in vacuum from the day 3 of experiment. The counts of Staphylococcus spp. (Table 5) were during first 7 days of storage b2 log CFU/g. This result agrees with Alonso-Calleja et al. (2004). Increasing in this count was observed on day 14 and subsequently on day 21 of storage (p b 0.001) in all monitored groups. Similarly as in the other monitored microbial counts, Staphylococcus spp. counts were higher (p b 0.001) in the meat samples stored in the plastic bags with normal atmosphere. The shelf-life of meat is mainly influenced by the number of present microorganisms, which is closely related to the pH value of the meat. The most significant differences in these parameters were observed on day 14 of storage (Tables 2 and 5). On day 14 of storage the highest pH value was measured in the meat of group NVP (6.54), this resulted in higher numbers of microorganisms in the meat of this group (TVC, Enterobacteriaceae, Staphylococcus) compared to group VP1 and VP2.
3.5. Sensory analysis The results of the sensory evaluation are expressed in the Table 6. The best sensory properties were achieved in the meat vacuumpacked from the first day on the storage day 14. The meat which was vacuum-packed from the third day of storage reached the highest sensory quality on 21 day. Only minimal differences had been recorded between the vacuumpacked meat from day 1 and the vacuum-packed from day 3 of storage. In the non-vacuum-packed meat the best sensory quality was found on day 1 of storage and the following days of storage the sensory quality gradually declined. This change is also significantly related to higher fat decomposition during the storage Bingol and Ergun (2012). On the other side, both groups of vacuum-packed samples improved the sensory quality. The taste evaluation showed statistically significant decreases in the samples which were vacuum-packed from day 1 on the 21st day of storage (2.80 ± 0.45) compared with the day 7 (p b 0.05) and compared with the day 14 (p b 0.001) in the same packed conditions. The statistically significant decrease (p b 0.001) of flavor we recorded on day 14 of storage between the samples non-vacuum packed (3.00 ± 1.10) and the vacuum-packed from the day 1 (5.00 ± 0.00). On day 21 of storage we recorded statistically significant increase (p b 0.05) of flavour between the samples vacuum-packed from the day 1 (2.80 ± 0.45) and the samples which were vacuum-packed from the day 3 (4.40 ± 0.55). We recorded better results in sensory properties of ostrich meat in VP3 samples on day 21 than in the VP1 samples because the longer aerobic atmosphere affected the ripening process of ostrich meat which caused better sensory properties.
The results of sensory analysis were influenced mainly by pH, TBA values and microbial spoilage, however these parameters were higher in group NVP in comparison with both vacuum-packed meat groups. 4. Conclusion The results of this study showed that the shelf-life of ostrich meat stored at 2 °C were affected by using different packaging conditions (vacuum from day 1, vacuum from day 3 and in the normal atmosphere). The storage of ostrich´s meat in both vacuum-packed groups had a positive effect on the biochemical, microbiological and sensory parameters compare to non-vacuum packed meat. In both vacuumpacked samples was recorded reduction of not only the oxidation process but also the microbial spoilage. The level of lactic acid and pH value in ripening process of ostrich meat were influenced by different storage conditions and affected the final quality of the meat. The better sensory analysis was recorded on day 14 of storage in the VP1 compared with VP3. We recorded the highest scores of the sensory evaluation in the non-vacuum packed meat on day 1 and subsequently during the shelf-life the sensory scores decreased. The vacuum packed storage applied in this study is useful in practical application in the meat industry for improving durability of ostrich meat. Acknowledgement The present work was supported by VEGA scientific grant 1/0457/14 from the Ministry of Education of the Slovak Republic. References Alonso-Calleja, C., Martinez-Fernández, B., Capita, R., & Prieto, M. (2002). La carne de avestruz: valor nutritivo y calidad higiénica. Alimentación, Equipos y Tecnologia, 57–62 (Octubre). Alonso-Calleja, C., Martinez-Fernández, B., Prieto, M., & Capita, R. (2004). Microbiological quality of vacuum-packed retail ostrich meat in Spain. Food Microbiology, 21, 241–246. Atanassova, V., Apelt, J., Reich, F., & Klein, G. (2008). Microbiological quality of freshly shot game in Germany. Meat Science, 78, 414–419. AOAC (1997). Official methods of analysis of the Association of Analytical Chemists. Washington D.C. Bingol, E. B., & Ergun, O. (2012). Effects of modified atmosphere packaging (MAP) on the microbiological quality and shelf life of ostrich meat. Meat Science, 90(1), 276–277. Blixt, Y., & Borch, E. (2002). Comparison of shelf life of vacuum-packed pork and beef. Meat Science, 60, 371–378. Botha, S. St. C., Hoffman, L. C., & Britz, T. J. (2006). Effect of hot-deboning on the physical quality characteristics of ostrich meat. South African Journal of Animal Science, 36, 197–208. Capita, R., Diaz-rodriguez, N., Prieto, M., & Alonso-Calleja, C. (2006). Effects of temperature, oxygen exclusion, and storage on the microbial loads and pH of packed ostrich steaks. Meat Science, 73, 498–502.
M. Brenesselová et al. / Meat Science 101 (2015) 42–47 Čuboň, J., Haščík, P., Mojto, J., Kačániová, M., Vagač, V., Košťalová, D., & Pavličová, S. (2004). Effect of sodium lactate on microbiological, physical and sensory characteristics of beef. Acta fytotechnica et zootechnica, 3, 62–66 (In Slovak). Dalle Zotte, A. (2002). Perception of rabbit meat quality and major factors influencing the rabbit carcass and meat quality. Livestock Production Science, 75, 11–32. EU Council Directive 1099/2009/EC (2009). On the protection of animals at the time of slaughter or killing. Official Journal of European Community, 303, 1–30. Fernández-López, J., Sayas-Barberá, E., Munoz, T., Sendra, E., Navarro, C., & Pérez-Alvarez, J. A. (2008). Effect of packaging conditions on shelf-life of ostrich steaks. Meat Science, 70, 143–152. Filgueras, R. S., Gatellier, P., Aubry, L., Thomas, A., Bauchart, D., Durand, D., Zambiazi, R. C., & Santé-Lhoutellier, V. (2010). Colour, lipid and protein stability of Rhea americana meat during air- and vacuum-packaged storage: influence of muscle on oxidative processes. Meat Science, 86, 665–673. Floch, J., Lees, M., & Sloane Stanley, G. H. (1957). A simple method for the isolation and purification of total lipids from animal tissues. The Journal of Biological Chemistry, 226, 497–509. Girolami, A., Marsico, I., D´Andrea, G., Braghieri, A., & Napolitano, F. (2003). Fatty acid profile, cholesterol content and tenderness of ostrich meat as influenced by age at slaughter and muscle type. Meat Science, 64(3), 309–315. GraphPad Prism (2003). Version 4.00 for Windows. GraphPad Software San Diego (California). Hoffman, L. C. (2005). A review of the research conducted on ostrich meat. Proceedings of the 3rd International Ratite Science Symposium of the WPSA (pp. 107–119) (October 2005. Madrid, Spain). Hoffman, L. C. (2008). Value adding and processing of Ratite meat: a review. Australian Journal of Experimantal Agriculture, 48, 1–6. Jacobsen, M., & Bertelsen, G. (2000). Colours stability and lipid oxidation of fresh beef. Development of a response surface model for predicting the effects of temperature, storage time and modified atmosphere and composition. Meat Science, 54, 49–57. Karama, M. (2001). The microbiological quality of ostrich carcasses producted at an exportapproved South African abatoir. South Africe: MMved (Hyg) study at University of Pretoria, 97. Koréneková, B., Nagy, J., Smulders, F. J. M., Paulsen, P., Mačanga, J., Popelka, P., Marcinčák, S., & Korének, M. (2014). Lactic acid concentration and pH values in muscles of European brown hare. In P. Paulsen, A. Bauer, & F. J. M. Smulders (Eds.), Trends in game meat hygiene, from forest to fork (pp. 400). The Netherlands: Wageningen Academic Publishers978-90-8686-238-2. Leygonie, C., Britz, T. J., & Hoffman, L. C. (2012). Meat quality comparison between fresh and frozen/thawed ostrich M. iliofibularis. Meat Science, 91, 364–368.
47
Mačanga, J., Koréneková, B., Nagy, J., Marcinčák, S., Popelka, P., Kožárová, I., & Korének, M. (2011). Post-mortem changes in the concentration of lactic acid, phosphates and pH in the muscles of wild rabbits (Oryctolagus cuniculus) according to the perimortal situation. Meat Science, 88, 701–704. Majewska, D., Jakubowska, M., Ligocki, M., Tarasewicz, Z., Szczerbińska, D., Karamucki, T., & Sales, J. (2009). Physicochemical characteristics, proximate analysis and mineral composition of ostrich meat as influenced by muscle. Food Chemistry, 117, 207–211. Marcinčák, S., Sokol, J., Bystrický, P., Popelka, P., Turek, P., Bhide, M., & Máté, D. (2004). Determination of lipid oxidation level in broiler meat by liquid chromatography. Journal of AOAC International, 87(5), 1148–1152. Marcinčák, S., Sokol, J., Turek, P., Różaňska, H., Dičáková, Z., Máté, D., Popelka, P., & Korim, P. (2003). Comparative evaluation of analytical techniques to quantify malondialdehyde in broiler meat. Bulletin of the Veterinary Institute in Pulawy, 47, 491–496. Otremba, M. M., Dikeman, M. E., & Boyle, E. A. E. (1999). Refrigerated shelf life of vacuumpacked, previously frozen ostrich meat. Meat Science, 52, 279–283. Polawska, E., Marchewska, J., Cooper, R. G., Sartowska, K., Pomianowski, J., Jóźwik, A., Strza kowska, N., & Horbańczuk, J. O. (2011). The ostrich meat-an updated review, II. Nutritive value. Animal Science Papers and Report, 29(2), 89–97. Príbela, A. (2001). Sensory evaluation of food materials, additives and products. Košice: Institute of veterinarians education, 87–94 (In Slovak). Sales, J. (1998). Fatty acid composition and cholesterol content of different ostrich muscles. Meat Science, 49, 489–495. Seydim, A. C., Acton, J. C., Hall, M. A., & Dawson, P. L. (2006). Effects of packaging atmospheres on shelf-life quality of ground ostrich meat. Meat Science, 73, 503–510. STN EN ISO 4833 (2003). Microbiology of food and animal feeding stuffs. Horizontal method for the enumeration of microorganisms. Colony-count technique at 30 °C. SÚTN Bratislava. STN EN ISO 6887–1 (2001). Microbiology of food and animal feeding stuffs. Preparation of test samples, initial suspension and decimal dilutions for microbilogical examination. Part 1: General rules for the preparation of the initial suspension and decimal dilutions. SÚTN Bratislava. STN EN ISO 6888–1 (2001). Microbiology of food and animal feeding stuffs. Horizontal method for the enumeration of coagulase-positive staphylococci (Staphylococcus aureus and other species). Part 1: Technique using Baird-Parker agar medium. SÚTN Bratislava. STN ISO 21528–2 (2004). Microbiology of food and animal feeding stuffs. Horizontal method for the detection and enumeration of Enterobacteriaceae. Part 2: Colony-count method. SÚTN Bratislava. Winkelmayer, R., Lebersorger, P., Zedka, H. F., Forejtek, P., Vodňanský, M., & Večerek, V. (2005). Game hygiene Central European Institute of Wildlife Ecology. Wien-Brno-Nitra (In Czech).
