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Effect of modified atmosphere packaging on structural and physical changes in buffalo meat
MEAT SCIENCE Meat Science 72 (2006) 211–215 www.elsevier.com/locate/meatsci
Effect of modified atmosphere packaging on structural and physical changes in buffalo meat q A. Sekar, K. Dushyanthan *, K.T. Radhakrishnan, R. Narendra Babu Department of Meat Science and Technology, Madras Veterinary College, Chennai 600 007, India Received 2 August 2004; received in revised form 11 May 2005; accepted 1 July 2005
Abstract The effect of modified atmosphere packaging of buffalo meat on the structural parameters viz., fibre diameter, sarcomere length and myofibrillar fragmentation index and physical parameters viz., pH, drip loss and colour scores were studied. The buffalo meat was packed under aerobic, vacuum and modified atmosphere (80% oxygen + 20% carbon dioxide) and stored at 4 ± 1 C upto 21 days. The results obtained revealed that vacuum-packed buffalo meat had the lowest fibre diameter and myofibrillar fragmentation index and the highest sarcomere length, vacuum thus appears to enhance ageing. Buffalo meat packed in modified atmosphere had a low drip loss and a desirable colour. The modified atmosphere packed and vacuum-packed buffalo meat was acceptable for upto 14 days at 4 ± 1 C. 2005 Elsevier Ltd. All rights reserved. Keywords: Modified atmosphere packaging; Vacuum packaging; Fibre diameter; Sarcomere length; Myofibrillar fragmentation index; Vacuum packaging; Drip loss
1. Introduction The increase in income and standard of living of the present day consumers of India has created a change in their culture and habit of consuming food. Buffalo meat is gaining popularity and does not possess any taboo against its consumption; hence there are opportunities for the development of the buffalo meat industry to cater for the needs of the domestic market in the near future. Buffaloes contribute about 35.7% of total meat production in India (Murthy & Devadason, 2003). The implementation of the new world trade agreements and change in the eating habits of the consumers has created more demand for preservative free, fresh and safe meat and meat products. So to protect the products in the q Part of the thesis submitted to the Tamil Nadu Veterinary and Animal Sciences University, Chennai, India for the M.V.Sc. degree. * Corresponding author. Tel.: +91 44 25381506; fax: +91 44 25362787. E-mail address: [email protected] (K. Dushyanthan).
0309-1740/$ - see front matter 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.meatsci.2005.07.003
domestic market and to compete globally, it is important to practice newer packaging and preservation techniques. Modified atmosphere packaging (MAP) is one such preservative and packaging technique that will satisfy the present day consumersÕ demand. It is well known as a method for extending the shelf-life of a variety of foods, including fresh meat. Ahvenainen (1989) recommended that the most suitable gas mixture for retailing fresh red meats was 20% CO2 + 80% O2. Little work has been done on the structure of packed meat. The structural changes due to MAP are assessed by measuring the fibre diameter since the average fibre size was correlated (P < 0.01) to sensory panel tenderness and shear force measurements (Seideman, Koohmaraie, & Crouse, 1988); sarcomere length is related to the ageing response in that, muscles with shorter sarcomere lengths had a greater ageing response (Koohmaraie, Babiker, Merkel, & Dutson, 1988) and myofibrillar fragmentation index (MFI) is important because, it is a measure of structural change in native
212
A. Sekar et al. / Meat Science 72 (2006) 211–215
myofibrils (Moller, Vestergard, & Pederson, 1973; Olson, Parrish, & Stromer, 1976). The important physical changes to be assessed are pH and drip loss, since they affect the shelf-life of the product and appearance of the pack. In view of the contribution of buffalo meat to the Indian economy and the necessity for proper packaging of meat, it was decided to study the effect of MAP on the physico-chemical and structural changes of buffalo meat.
2. Materials and methods 2.1. Preparation of meat samples Fresh quadriceps muscles were obtained from 12 female buffaloes (Babulus bubalis) slaughtered under the Halal method in Chennai Corporation Slaughterhouse, Perambur, Chennai. The samples were wrapped in clean sterile polyethylene bags and transported in a clean cool box containing ice cubes to the laboratory of the Department of Meat Science and Technology. The samples was received within 45 min of slaughter and subjected to the different packaging treatments, viz., aerobic, vacuum and modified atmosphere (80% oxygen and 20% carbon dioxide) using sterile polyester polyethylene (PET/Poly) pouches (thickness – 62 lm, oxygen transmission rate – 140–150 cc/sq.m/24 h/atm at 37 C). After removing the visible fat and tendons, each sample was cut into 13 pieces, each weighing 100 g and about 2.5 cm thick. Of the 13 pieces four were placed in the pouches and sealed (aerobic method); four were vacuum packed and another four were packed under modified atmosphere. The remaining one piece was used for fresh sample analysis carried out on the day of packaging and were used as initial values for all three treatments. The packed samples were assessed for fibre diameter, sarcomere length, myofibrillar fragmentation index (MFI), pH, drip loss and color score on the third, seventh, 14th, and 21st day of storage at 4 ± 1 C. In MAP the meat to gas volume ratio was 1:1. 2.2. Structural parameters 2.2.1. Fibre diameter Fibre diameter of fresh, packed and stored buffalo meat samples were assessed according to the method outline by Jeremiah and Martin (1982). Five grams of the sample were cut into small pieces and homogenised in a blender at low speed for two 15 s periods interspaced with a 5 s resting interval in a 30 ml solution containing 0.25 M sucrose and 1 mM EDTA (ethylene diaminetetraacetic acid) to produce a slurry. One or two drops of the slurry was then transferred on to a microscope slide and covered with a cover slip. The suspension was examined directly under a light microscope with 10· objective and 8· eyepiece equipped
with calibrated micrometer. Muscle fibre diameter was measured as the mean cross-sectional distance in micrometers between the exterior surfaces of the sarcolemmas of 25 randomly selected fibres. 2.2.2. Sarcomere length Sarcomere length of the fresh, packed and stored buffalo meat samples was determined as described by Cross, West, and Dutson (1981). Five grams of meat sample were blended with 35 ml of 0.25 M sucrose solution for one minute in a blender at low speed. Immediately after blending, a drop of the slurry containing the fibre fragments was transferred on to a microscope slide and covered with a cover slip. The suspension was examined under a microscope using an 8· eyepiece with a calibrated micrometer under oil immersion objective. Sarcomere length was measured as the mean length of 10 sarcomeres on 25 randomly selected myofibrils. 2.2.3. Myofibrillar fragmentation index The myofibrillar fragmentation index was determined in fresh, packed and stored samples as described by Davis, Dutson, Smith, and Carpenter (1980) with slight modifications. After removal of epimysial tissue and fat 7 mm cubes were prepared from the meat samples. Ten grams of such cubes were transferred to a 250 ml Virtis flouted glass homogenization cup containing 50 ml of cold 0.25 M sucrose and 0.02 M potassium chloride solutions. The muscle cubes were allowed to equilibrate for 5 min. With two Virtis macro-stainless steel blades aligned and positioned 1 mm below the surface of the solution and set in a reverse position, the sample was homogenized for 40 s at full speed. The homogenate was filtered through a pre-weighed 250 lm pore stainless steel wire cloth screen in a filtration unit. The homogenate was stirred with a glass rod to hasten filtration. The resulting fraction of muscle fragments, greater than 250 lm in size collected on the screen was blotted with Whatman No. 3 filter paper. The weight of the sample with the screen was taken after 40 min of drying at 25 C. The fragmentation index was obtained by multiplying the weight of the fraction remaining on the screen (in grams) by 100. 2.3. Physical parameters 2.3.1. pH The pH of the fresh and stored buffalo meat was measured using a digital pH meter. About 5 g of sample were cut into small pieces to which 45 ml of distilled water was added and a slurry was made using a blender and the pH was recorded. 2.3.2. Drip loss The amount of drip in each pack was estimated by weighing the pack of meat before opening, and subtract-
Overall means bearing different superscripts between rows (A, B) and between columns (w–z) differ significantly (P < 0.05 or P < 0.01). Interaction means bearing different superscripts (a–g) differ significantly (P < 0.01).
733.20AB ± 15.31 717.07A ± 12.13 737.43B ± 9.90 – 692.79 ± 11.82 673.04 ± 8.64 694.42 ± 9.53 687.75x ± 10.00 699.84 ± 24.59 681.49 ± 17.11 712.53 ± 14.56 697.96xy ± 18.75 728.92 ± 9.85 713.58 ± 17.97 731.77 ± 8.41 724.75y ± 12.08 780.65 ± 10.70 780.65 ± 10.70 780.65 ± 10.70 780.65z ± 10.70 Myofibrillar fragmentation index Aerobic Vacuum Modified atmosphere Overall mean (pooled over methods)
763.78 ± 19.58 736.57 ± 6.24 767.78 ± 6.27 756.04z ± 10.70
–
1.57A ± 0.03 1.62B ± 0.03 1.56A ± 0.03 1.84 ± 0.04 1.93 ± 0.03 1.84 ± 0.02 1.87z ± 0.03 1.78 ± 0.03 1.80 ± 0.03 1.73 ± 0.03 1.77y ± 0.03 1.54 ± 0.03 1.60 ± 0.02 1.59 ± 0.04 1.58x ± 0.03 1.21 ± 0.03 1.21 ± 0.03 1.21 ± 0.03 1.21w ± 0.03 Sarcomere length (l) Aerobic Vacuum Modified atmosphere Overall mean (pooled over methods)
1.51 ± 0.04 1.56 ± 0.01 1.46 ± 0.04 1.51x ± 0.03
56.47ab ± 0.69 53.68a ± 1.32 61.02bc ± 1.71 57.06w ± 1.24
21
–
66.67B ± 1.27 60.82A ± 1.37 67.30B ± 1.42
Overall mean (pooled over days) 14
60.75bc ± 1.89 53.46a ± 1.39 64.29cde ± 1.17 59.50w ± 1.49 67.84ef ± 1.39 57.39ab ± 1.19 66.10de ± 1.60 63.78x ± 1.39 71.49f ± 1.00 62.80cd ± 1.61 68.31ef ± 1.27 67.53y ± 1.30
The analysis of variance revealed a highly significant (P < 0.01) difference in fibre diameter of the packaged buffalo meat samples between the packaging methods, between storage periods and the interaction between packaging methods and storage periods. A significant (P < 0.05) difference in sarcomere length of the packaged buffalo meat samples between the packaging methods and highly significant (P < 0.01) difference between storage periods was noticed. There was a significant (P < 0.05) difference in myofibrillar fragmentation index of the packaged buffalo meat samples between the packaging methods and highly significant (P < 0.01) difference between storage periods. Buffalo meat samples packed under vacuum had significantly (P < 0.01) smaller fibre diameter, longer sarcomere length and smaller MFI than those packed under modified atmosphere and aerobically. The decrease in fibre diameter and the MFI (Silva, Patarata, & Martin, 1999); and the increase in sarcomere length are associated with ageing of meat. The lack of oxygen could have resulted in lower fibre diameters in vacuum-packed samples. The increasing sarcomere length is due to degradation of the structure of the sarcomere and the calpains
76.79g ± 1.36 76.79g ± 1.36 76.79g ± 1.36 76.79z ± 1.36
3.1. Fibre diameter (l), sarcomere length (l) and myofibrillar fragmentation index (MFI)
7
The mean and ANOVA values of fibre diameter, sarcomere length, myofibrillar fragmentation index, pH, drip loss and colour score of fresh and packed buffalo meat samples under aerobic, vacuum and modified atmosphere in PET/Poly pouches and stored for up to 21 days at 4 ± 1 C are presented in Tables Tables 1–3.
3
3. Results and discussion
0
The data obtained in this study were analysed by randomized block design treating the three packaging methods as blocks and the four periods of storage as the main effects. Using two-way analysis of variance and two-way interactions main effects were analyzed for significance as outlined by Snedecor and Cochran (1994).
213
Fibre diameter (l) Aerobic Vacuum Modified atmosphere Overall mean (pooled over methods)
2.4. Statistical analysis
Storage period (days)
2.3.3. Colour score assessment Fresh, packed and stored samples were subjectively evaluated by a trained five member panel for muscle colour using a nine-point hedonic scale (9 = bright red; 1 = greenish grey).
Packaging methods
ing the weight of meat plus packing after blotting dry. Drip loss was expressed as a percentage of the initial weight of meat (Taylor, Down, & Shaw, 1990).
Table 1 Mean (±SE) fibre diameter (l), sarcomere length (l) and myofibrillar fragmentation index of buffalo meat packed under different atmospheres and stored at 4 ± 1 C for upto 21 days
A. Sekar et al. / Meat Science 72 (2006) 211–215
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A. Sekar et al. / Meat Science 72 (2006) 211–215
Table 2 Mean (±SE) of pH, drip loss (per cent) and colour scores of buffalo meat packed under different atmospheres and stored at 4 ± 1 C for up to 21 days Packaging methods
Storage periods (days)
Overall mean (pooled over days)
0
3
7
14
pH Aerobic Vacuum Modified atmosphere Overall mean (pooled over methods)
21
6.62 ± 0.04 6.62 ± 0.04 6.62 ± 0.04 6.62z ± 0.04
5.72 ± 0.02 5.73 ± 0.03 5.75 ± 0.01 5.73w ± 0.02
5.84 ± 0.04 5.77 ± 0.02 5.73 ± 0.03 5.78w ± 0.03
5.86 ± 0.07 5.84 ± 0.06 5.76 ± 0.04 5.82x ± 0.05
6.03 ± 0.04 5.89 ± 0.03 5.95 ± 0.06 596y ± 0.04
6.01 ± 0.05 5.97 ± 0.04 5.96 ± 0.04
Drip loss (per cent) Aerobic Vacuum Modified atmosphere Overall mean (pooled over methods)
0.00 0.00 0.00 0.00v
1.14 ± 0.18 1.43 ± 0.23 1.27 ± 0.18 1.28w ± 0.20
1.79 ± 0.19 2.15 ± 0.21 1.44 ± 0.18 1.79x ± 0.19
2.80 ± 0.33 2.99 ± 0.17 2.44 ± 0.23 2.75y ± 0.24
3.74 ± 0.20 3.89 ± 0.22 3.70 ± 0.14 3.78z ± 0.19
1.90A ± 0.18 2.09B ± 0.17 1.77A ± 0.14
Colour scores Aerobic Vacuum Modified atmosphere Overall mean (pooled over methods)
7.99j ± 0.05 7.99j ± 0.05 7.99j ± 0.05 7.99z ± 0.05
6.62g ± 0.07 5.47de ± 0.13 8.38k ± 0.05 6.82y ± 0.08
6.15f ± 0.10 5.14cd ± 0.05 7.47i ± 0.08 6.25x ± 0.09
5.63e ± 0.14 4.93c ± 0.11 7.08h ± 0.06 5.88w ± 0.10
3.07a ± 0.20 4.13b ± 0.05 6.10f ± 0.06 4.43v ± 0.10
5.89B ± 0.11 5.53A ± 0.08 7.40C ± 0.06 –
Overall means bearing different superscripts between rows (A, B) and between columns (v–z) differ significantly (P < 0.05 or P < 0.01). Interaction means bearing different superscripts (a–j) differ significantly (P < 0.01). P-analysis was carried out after conversion of percent values into arc sine values and after analysis of the mean ± SE values were converted into percent and presented.
Table 3 Analysis of variance of fibre diameter (l), sarcomere length (l) and myofibrillar fragmentation index, pH, drip loss and colour scores of buffalo meat packed under different atmospheres and stored at 4 ± 1 C up to 21 days Source of variation
dt
Mean square Fibre diameter
Between packaging methods Between storage periods Between packaging methods · Storage periods Error NS * **
2 4 8 165
**
765.73 2161.71** 93.38** 22.94
Sarcomere length *
0.09 2.44** 0.03NS 0.02
Myofibrillar fragmentation index *
6928.03 55490.89** 576.02NS 2168.64
pH
Drip loss NS
0.04 4.8** 0.02NS 0.02
*
Colour scores
1.59 74.26** 0.31NS
59.14** 61.23** 6.44**
0.43
0.11
Not significant. Significant (P < 0.05). Highly significant (P < 0.01).
are primarily responsible for postmortem proteolysis. In addition to a calcium requirement, calpains also require a reducing environment for their activity (Guttmann, Elce, Bell, Isbell, & Johnson, 1997). Vacuum packaging provides the reducing environment required for enhanced ageing, thus the sarcomere length is higher in vacuum-packed samples. Koohmaraie et al. (1988) observed that myofibril fragmentation changes were calpain mediated. Since calpains require a reducing environment for their activity (Guttmann et al., 1997) myofibrillar fragmentation was the highest in the vacuum-packed samples and lowest in the MAP samples.
for up to 3 days in the case of the vacuum and aerobically packed samples and up to seven days in case of the MAP samples. The pH increased gradually thereafter up to 21 days of storage in all the treatments. The initial fall in pH is a normal postmortem consequence, owing to the postmortem-glycolysis and subsequent lactic acid accumulation. The overall pH decrease during the first three days of storage and progressive increase thereafter agrees with the findings of Narendra Babu, Venkataramanujam, and Shanmugam (2002).
3.2. pH
The analysis of variance between the drip loss of buffalo meat packed under aerobic, vacuum and modified atmosphere methods of packaging revealed a significant (P < 0.05) difference. A highly significant (P < 0.01) difference was noticed between the drip loss of buffalo
The analysis of variance between the pH of buffalo meat stored for different periods showed highly significant (P < 0.01) differences. A fall in pH was seen initially
3.3. Drip loss (per cent)
A. Sekar et al. / Meat Science 72 (2006) 211–215
meat stored for the different periods. Drip loss significantly (P < 0.01) increased with storage, in all treatments. Similar findings were reported by Payne, Durhan, Scott, and Devine (1998). Drip losses in vacuum-packed sample were the highest (P < 0.05) in comparison to the aerobically and MAP samples. The findings are in agreement with Rousset and Renerre (1991). The increased drip loss in vacuum may be due to the squeezing of meat associated with vacuum packaging (Payne et al., 1998). The drip loss was lower in MAP than aerobically packed samples, which might be attributed to the head space gas pressure maintained in the package (Daniels, Krishnamurthi, & Rizvi, 1985). 3.4. Colour score The analysis of variance revealed a highly significant (P < 0.01) difference between the packaging methods, storage periods and interactions between packaging methods and storage periods. The mean colour score of the buffalo meat packed aerobically and in vacuum decreased from the day of packaging to the 21st day of storage. The mean colour score of the samples packed in modified atmosphere increased from the day of packaging to the third day and decreased gradually up to the 21st day of storage. The mean colour score in the samples packed in modified atmosphere were the highest. This finding is in agreement with Jones (1989). The mean colour score in the samples packed in modified atmosphere showed that they were bright red upto the third day and red upto to the 14th day and light red upto the 21st day. This finding is in agreement with Narendra Babu et al. (2002). Based on the findings, vacuum-packed buffalo meat had the lowest fibre diameter and myofibrillar fragmentation index and the highest sarcomere length, since vacuum enhanced ageing. The modified atmosphere packed buffalo meat structure underwent the normal postmortem changes showing no adverse effect. Buffalo meat packed in modified atmosphere had a desirable colour and a low drip loss. Buffalo meat packed under modified atmosphere and vacuum kept safely up to 14 days of storage at 4 ± 1 C.
Acknowledgements The authors extend their sincere gratitude to the Tamil Nadu Veterinary and Animal Sciences University, Chennai, India for having provided all facilities to conduct the above research work.
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References Ahvenainen, R. (1989). Gas packaging of chilled meat products and ready to eat foods. Technical Research Centre for Finland, Publications 58, pp. 3–68. Cross, H. R., West, R. L., & Dutson, T. R. (1981). Comparison of methods for measuring sarcomere length in beef semitendinosus muscle. Meat Science, 5, 261–266. Daniels, J. A., Krishnamurthi, R., & Rizvi, S. S. H. (1985). A review of effects of carbon dioxide on microbial growth and food quality. Journal of Food Protection, 48, 532–537. Davis, G. W., Dutson, T. R., Smith, G. C., & Carpenter, Z. L. (1980). Fragmentation procedure for bovine longissimus muscle as an index of cooked steak tenderness. Journal of Food Science, 45, 880–885. Guttmann, R. P., Elce, J. S., Bell, P. D., Isbell, J. C., & Johnson, G. V. W. (1997). Oxidation inhibits substrate proteolysis by calpain I but not autolysis. Journal of Biological Chemistry, 272, 2005– 2012. Jeremiah, L. E., & Martin, A. H. (1982). Effects of prerigor chilling and freezing and subcutaneous fat cover upon the histological and shear properties of bovine longissimus dorsi muscle. Journal of Animal Science, 62, 353–361. Jones, M. V. (1989). Modified Atmospheres. In Mechanisms of action of food preservation procedures (pp. 247–284). London: Elsevier Applied Science, Quoted by Sahoo, J. & Anjaneyulu, A.S.R. 1995. Modified atmosphere packaging of muscle foods. Technology, Shelf life and safety aspects. Indian Food Industry 14, 28–36. Koohmaraie, M., Babiker, A. S., Merkel, R. A., & Dutson, T. R. (1988). Role of Ca++ dependent protease and lysosomal enzymes in post-mortem changes in bovine skeletal muscle. Journal of Food Science, 53, 1253–1257. Moller, A. J., Vestergard, T., & Pederson, J. W. (1973). Myofibril fragmentation in bovine longissimus dorsi as an index of tenderness. Journal of Food Science, 38, 824–825. Murthy, T. R. K. & Devadason, I. P. (2003). Buffalo meat and meat products – An overview. In Proceedings of the fourth Asian buffalo congress on buffalo for food security and rural employment, New Delhi, pp. 193–199. Narendra Babu, R., Venkataramanujam, V., & Shanmugam (2002). Effect of modified atmosphere packaging on fresh buffalo meat quality. Buffalo Journal, 18, 171–182. Olson, D. E., Parrish, F. C., & Stromer, M. H. (1976). Myofibril fragmentation and shear resistance of three bovine muscles during postmortem storage. Journal of Food Science, 41, 1036. Payne, S. R., Durhan, C. J., Scott, S. M., & Devine, C. E. (1998). The effects of non-vacuum packaging systems on drip loss from chilled beef. Meat Science, 49, 277–287. Rousset, S., & Renerre, M. (1991). Effect of CO2 or vacuum packaging on normal and high pH meat shelf-life. International Journal of Food Science and Technology, 26, 641–652. Seideman, S. C., Koohmaraie, M., & Crouse, J. D. (1988). The influence of muscle fibre size on tenderness in A maturity heifers. Journal of Food Quality, 11, 27–34. Silva, J. A., Patarata, L. A., & Martin, C. (1999). Influence of ultimate pH on bovine meat tenderness during ageing. Meat Science, 52, 453–459. Snedecor, G. W., & Cochran, W. G. (1994). Statistical methods. Calcutta: Oxford and IBH Publishing Co.. Taylor, A. A., Down, N. F., & Shaw, B. G. (1990). A comparison of modified atmosphere and vacuum skin packing for the storage of red meats. International Journal of Food Science and Technology, 25, 98–109.
Effect of modified atmosphere packaging on structural and physical changes in buffalo meat q A. Sekar, K. Dushyanthan *, K.T. Radhakrishnan, R. Narendra Babu Department of Meat Science and Technology, Madras Veterinary College, Chennai 600 007, India Received 2 August 2004; received in revised form 11 May 2005; accepted 1 July 2005
Abstract The effect of modified atmosphere packaging of buffalo meat on the structural parameters viz., fibre diameter, sarcomere length and myofibrillar fragmentation index and physical parameters viz., pH, drip loss and colour scores were studied. The buffalo meat was packed under aerobic, vacuum and modified atmosphere (80% oxygen + 20% carbon dioxide) and stored at 4 ± 1 C upto 21 days. The results obtained revealed that vacuum-packed buffalo meat had the lowest fibre diameter and myofibrillar fragmentation index and the highest sarcomere length, vacuum thus appears to enhance ageing. Buffalo meat packed in modified atmosphere had a low drip loss and a desirable colour. The modified atmosphere packed and vacuum-packed buffalo meat was acceptable for upto 14 days at 4 ± 1 C. 2005 Elsevier Ltd. All rights reserved. Keywords: Modified atmosphere packaging; Vacuum packaging; Fibre diameter; Sarcomere length; Myofibrillar fragmentation index; Vacuum packaging; Drip loss
1. Introduction The increase in income and standard of living of the present day consumers of India has created a change in their culture and habit of consuming food. Buffalo meat is gaining popularity and does not possess any taboo against its consumption; hence there are opportunities for the development of the buffalo meat industry to cater for the needs of the domestic market in the near future. Buffaloes contribute about 35.7% of total meat production in India (Murthy & Devadason, 2003). The implementation of the new world trade agreements and change in the eating habits of the consumers has created more demand for preservative free, fresh and safe meat and meat products. So to protect the products in the q Part of the thesis submitted to the Tamil Nadu Veterinary and Animal Sciences University, Chennai, India for the M.V.Sc. degree. * Corresponding author. Tel.: +91 44 25381506; fax: +91 44 25362787. E-mail address: [email protected] (K. Dushyanthan).
0309-1740/$ - see front matter 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.meatsci.2005.07.003
domestic market and to compete globally, it is important to practice newer packaging and preservation techniques. Modified atmosphere packaging (MAP) is one such preservative and packaging technique that will satisfy the present day consumersÕ demand. It is well known as a method for extending the shelf-life of a variety of foods, including fresh meat. Ahvenainen (1989) recommended that the most suitable gas mixture for retailing fresh red meats was 20% CO2 + 80% O2. Little work has been done on the structure of packed meat. The structural changes due to MAP are assessed by measuring the fibre diameter since the average fibre size was correlated (P < 0.01) to sensory panel tenderness and shear force measurements (Seideman, Koohmaraie, & Crouse, 1988); sarcomere length is related to the ageing response in that, muscles with shorter sarcomere lengths had a greater ageing response (Koohmaraie, Babiker, Merkel, & Dutson, 1988) and myofibrillar fragmentation index (MFI) is important because, it is a measure of structural change in native
212
A. Sekar et al. / Meat Science 72 (2006) 211–215
myofibrils (Moller, Vestergard, & Pederson, 1973; Olson, Parrish, & Stromer, 1976). The important physical changes to be assessed are pH and drip loss, since they affect the shelf-life of the product and appearance of the pack. In view of the contribution of buffalo meat to the Indian economy and the necessity for proper packaging of meat, it was decided to study the effect of MAP on the physico-chemical and structural changes of buffalo meat.
2. Materials and methods 2.1. Preparation of meat samples Fresh quadriceps muscles were obtained from 12 female buffaloes (Babulus bubalis) slaughtered under the Halal method in Chennai Corporation Slaughterhouse, Perambur, Chennai. The samples were wrapped in clean sterile polyethylene bags and transported in a clean cool box containing ice cubes to the laboratory of the Department of Meat Science and Technology. The samples was received within 45 min of slaughter and subjected to the different packaging treatments, viz., aerobic, vacuum and modified atmosphere (80% oxygen and 20% carbon dioxide) using sterile polyester polyethylene (PET/Poly) pouches (thickness – 62 lm, oxygen transmission rate – 140–150 cc/sq.m/24 h/atm at 37 C). After removing the visible fat and tendons, each sample was cut into 13 pieces, each weighing 100 g and about 2.5 cm thick. Of the 13 pieces four were placed in the pouches and sealed (aerobic method); four were vacuum packed and another four were packed under modified atmosphere. The remaining one piece was used for fresh sample analysis carried out on the day of packaging and were used as initial values for all three treatments. The packed samples were assessed for fibre diameter, sarcomere length, myofibrillar fragmentation index (MFI), pH, drip loss and color score on the third, seventh, 14th, and 21st day of storage at 4 ± 1 C. In MAP the meat to gas volume ratio was 1:1. 2.2. Structural parameters 2.2.1. Fibre diameter Fibre diameter of fresh, packed and stored buffalo meat samples were assessed according to the method outline by Jeremiah and Martin (1982). Five grams of the sample were cut into small pieces and homogenised in a blender at low speed for two 15 s periods interspaced with a 5 s resting interval in a 30 ml solution containing 0.25 M sucrose and 1 mM EDTA (ethylene diaminetetraacetic acid) to produce a slurry. One or two drops of the slurry was then transferred on to a microscope slide and covered with a cover slip. The suspension was examined directly under a light microscope with 10· objective and 8· eyepiece equipped
with calibrated micrometer. Muscle fibre diameter was measured as the mean cross-sectional distance in micrometers between the exterior surfaces of the sarcolemmas of 25 randomly selected fibres. 2.2.2. Sarcomere length Sarcomere length of the fresh, packed and stored buffalo meat samples was determined as described by Cross, West, and Dutson (1981). Five grams of meat sample were blended with 35 ml of 0.25 M sucrose solution for one minute in a blender at low speed. Immediately after blending, a drop of the slurry containing the fibre fragments was transferred on to a microscope slide and covered with a cover slip. The suspension was examined under a microscope using an 8· eyepiece with a calibrated micrometer under oil immersion objective. Sarcomere length was measured as the mean length of 10 sarcomeres on 25 randomly selected myofibrils. 2.2.3. Myofibrillar fragmentation index The myofibrillar fragmentation index was determined in fresh, packed and stored samples as described by Davis, Dutson, Smith, and Carpenter (1980) with slight modifications. After removal of epimysial tissue and fat 7 mm cubes were prepared from the meat samples. Ten grams of such cubes were transferred to a 250 ml Virtis flouted glass homogenization cup containing 50 ml of cold 0.25 M sucrose and 0.02 M potassium chloride solutions. The muscle cubes were allowed to equilibrate for 5 min. With two Virtis macro-stainless steel blades aligned and positioned 1 mm below the surface of the solution and set in a reverse position, the sample was homogenized for 40 s at full speed. The homogenate was filtered through a pre-weighed 250 lm pore stainless steel wire cloth screen in a filtration unit. The homogenate was stirred with a glass rod to hasten filtration. The resulting fraction of muscle fragments, greater than 250 lm in size collected on the screen was blotted with Whatman No. 3 filter paper. The weight of the sample with the screen was taken after 40 min of drying at 25 C. The fragmentation index was obtained by multiplying the weight of the fraction remaining on the screen (in grams) by 100. 2.3. Physical parameters 2.3.1. pH The pH of the fresh and stored buffalo meat was measured using a digital pH meter. About 5 g of sample were cut into small pieces to which 45 ml of distilled water was added and a slurry was made using a blender and the pH was recorded. 2.3.2. Drip loss The amount of drip in each pack was estimated by weighing the pack of meat before opening, and subtract-
Overall means bearing different superscripts between rows (A, B) and between columns (w–z) differ significantly (P < 0.05 or P < 0.01). Interaction means bearing different superscripts (a–g) differ significantly (P < 0.01).
733.20AB ± 15.31 717.07A ± 12.13 737.43B ± 9.90 – 692.79 ± 11.82 673.04 ± 8.64 694.42 ± 9.53 687.75x ± 10.00 699.84 ± 24.59 681.49 ± 17.11 712.53 ± 14.56 697.96xy ± 18.75 728.92 ± 9.85 713.58 ± 17.97 731.77 ± 8.41 724.75y ± 12.08 780.65 ± 10.70 780.65 ± 10.70 780.65 ± 10.70 780.65z ± 10.70 Myofibrillar fragmentation index Aerobic Vacuum Modified atmosphere Overall mean (pooled over methods)
763.78 ± 19.58 736.57 ± 6.24 767.78 ± 6.27 756.04z ± 10.70
–
1.57A ± 0.03 1.62B ± 0.03 1.56A ± 0.03 1.84 ± 0.04 1.93 ± 0.03 1.84 ± 0.02 1.87z ± 0.03 1.78 ± 0.03 1.80 ± 0.03 1.73 ± 0.03 1.77y ± 0.03 1.54 ± 0.03 1.60 ± 0.02 1.59 ± 0.04 1.58x ± 0.03 1.21 ± 0.03 1.21 ± 0.03 1.21 ± 0.03 1.21w ± 0.03 Sarcomere length (l) Aerobic Vacuum Modified atmosphere Overall mean (pooled over methods)
1.51 ± 0.04 1.56 ± 0.01 1.46 ± 0.04 1.51x ± 0.03
56.47ab ± 0.69 53.68a ± 1.32 61.02bc ± 1.71 57.06w ± 1.24
21
–
66.67B ± 1.27 60.82A ± 1.37 67.30B ± 1.42
Overall mean (pooled over days) 14
60.75bc ± 1.89 53.46a ± 1.39 64.29cde ± 1.17 59.50w ± 1.49 67.84ef ± 1.39 57.39ab ± 1.19 66.10de ± 1.60 63.78x ± 1.39 71.49f ± 1.00 62.80cd ± 1.61 68.31ef ± 1.27 67.53y ± 1.30
The analysis of variance revealed a highly significant (P < 0.01) difference in fibre diameter of the packaged buffalo meat samples between the packaging methods, between storage periods and the interaction between packaging methods and storage periods. A significant (P < 0.05) difference in sarcomere length of the packaged buffalo meat samples between the packaging methods and highly significant (P < 0.01) difference between storage periods was noticed. There was a significant (P < 0.05) difference in myofibrillar fragmentation index of the packaged buffalo meat samples between the packaging methods and highly significant (P < 0.01) difference between storage periods. Buffalo meat samples packed under vacuum had significantly (P < 0.01) smaller fibre diameter, longer sarcomere length and smaller MFI than those packed under modified atmosphere and aerobically. The decrease in fibre diameter and the MFI (Silva, Patarata, & Martin, 1999); and the increase in sarcomere length are associated with ageing of meat. The lack of oxygen could have resulted in lower fibre diameters in vacuum-packed samples. The increasing sarcomere length is due to degradation of the structure of the sarcomere and the calpains
76.79g ± 1.36 76.79g ± 1.36 76.79g ± 1.36 76.79z ± 1.36
3.1. Fibre diameter (l), sarcomere length (l) and myofibrillar fragmentation index (MFI)
7
The mean and ANOVA values of fibre diameter, sarcomere length, myofibrillar fragmentation index, pH, drip loss and colour score of fresh and packed buffalo meat samples under aerobic, vacuum and modified atmosphere in PET/Poly pouches and stored for up to 21 days at 4 ± 1 C are presented in Tables Tables 1–3.
3
3. Results and discussion
0
The data obtained in this study were analysed by randomized block design treating the three packaging methods as blocks and the four periods of storage as the main effects. Using two-way analysis of variance and two-way interactions main effects were analyzed for significance as outlined by Snedecor and Cochran (1994).
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Fibre diameter (l) Aerobic Vacuum Modified atmosphere Overall mean (pooled over methods)
2.4. Statistical analysis
Storage period (days)
2.3.3. Colour score assessment Fresh, packed and stored samples were subjectively evaluated by a trained five member panel for muscle colour using a nine-point hedonic scale (9 = bright red; 1 = greenish grey).
Packaging methods
ing the weight of meat plus packing after blotting dry. Drip loss was expressed as a percentage of the initial weight of meat (Taylor, Down, & Shaw, 1990).
Table 1 Mean (±SE) fibre diameter (l), sarcomere length (l) and myofibrillar fragmentation index of buffalo meat packed under different atmospheres and stored at 4 ± 1 C for upto 21 days
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A. Sekar et al. / Meat Science 72 (2006) 211–215
Table 2 Mean (±SE) of pH, drip loss (per cent) and colour scores of buffalo meat packed under different atmospheres and stored at 4 ± 1 C for up to 21 days Packaging methods
Storage periods (days)
Overall mean (pooled over days)
0
3
7
14
pH Aerobic Vacuum Modified atmosphere Overall mean (pooled over methods)
21
6.62 ± 0.04 6.62 ± 0.04 6.62 ± 0.04 6.62z ± 0.04
5.72 ± 0.02 5.73 ± 0.03 5.75 ± 0.01 5.73w ± 0.02
5.84 ± 0.04 5.77 ± 0.02 5.73 ± 0.03 5.78w ± 0.03
5.86 ± 0.07 5.84 ± 0.06 5.76 ± 0.04 5.82x ± 0.05
6.03 ± 0.04 5.89 ± 0.03 5.95 ± 0.06 596y ± 0.04
6.01 ± 0.05 5.97 ± 0.04 5.96 ± 0.04
Drip loss (per cent) Aerobic Vacuum Modified atmosphere Overall mean (pooled over methods)
0.00 0.00 0.00 0.00v
1.14 ± 0.18 1.43 ± 0.23 1.27 ± 0.18 1.28w ± 0.20
1.79 ± 0.19 2.15 ± 0.21 1.44 ± 0.18 1.79x ± 0.19
2.80 ± 0.33 2.99 ± 0.17 2.44 ± 0.23 2.75y ± 0.24
3.74 ± 0.20 3.89 ± 0.22 3.70 ± 0.14 3.78z ± 0.19
1.90A ± 0.18 2.09B ± 0.17 1.77A ± 0.14
Colour scores Aerobic Vacuum Modified atmosphere Overall mean (pooled over methods)
7.99j ± 0.05 7.99j ± 0.05 7.99j ± 0.05 7.99z ± 0.05
6.62g ± 0.07 5.47de ± 0.13 8.38k ± 0.05 6.82y ± 0.08
6.15f ± 0.10 5.14cd ± 0.05 7.47i ± 0.08 6.25x ± 0.09
5.63e ± 0.14 4.93c ± 0.11 7.08h ± 0.06 5.88w ± 0.10
3.07a ± 0.20 4.13b ± 0.05 6.10f ± 0.06 4.43v ± 0.10
5.89B ± 0.11 5.53A ± 0.08 7.40C ± 0.06 –
Overall means bearing different superscripts between rows (A, B) and between columns (v–z) differ significantly (P < 0.05 or P < 0.01). Interaction means bearing different superscripts (a–j) differ significantly (P < 0.01). P-analysis was carried out after conversion of percent values into arc sine values and after analysis of the mean ± SE values were converted into percent and presented.
Table 3 Analysis of variance of fibre diameter (l), sarcomere length (l) and myofibrillar fragmentation index, pH, drip loss and colour scores of buffalo meat packed under different atmospheres and stored at 4 ± 1 C up to 21 days Source of variation
dt
Mean square Fibre diameter
Between packaging methods Between storage periods Between packaging methods · Storage periods Error NS * **
2 4 8 165
**
765.73 2161.71** 93.38** 22.94
Sarcomere length *
0.09 2.44** 0.03NS 0.02
Myofibrillar fragmentation index *
6928.03 55490.89** 576.02NS 2168.64
pH
Drip loss NS
0.04 4.8** 0.02NS 0.02
*
Colour scores
1.59 74.26** 0.31NS
59.14** 61.23** 6.44**
0.43
0.11
Not significant. Significant (P < 0.05). Highly significant (P < 0.01).
are primarily responsible for postmortem proteolysis. In addition to a calcium requirement, calpains also require a reducing environment for their activity (Guttmann, Elce, Bell, Isbell, & Johnson, 1997). Vacuum packaging provides the reducing environment required for enhanced ageing, thus the sarcomere length is higher in vacuum-packed samples. Koohmaraie et al. (1988) observed that myofibril fragmentation changes were calpain mediated. Since calpains require a reducing environment for their activity (Guttmann et al., 1997) myofibrillar fragmentation was the highest in the vacuum-packed samples and lowest in the MAP samples.
for up to 3 days in the case of the vacuum and aerobically packed samples and up to seven days in case of the MAP samples. The pH increased gradually thereafter up to 21 days of storage in all the treatments. The initial fall in pH is a normal postmortem consequence, owing to the postmortem-glycolysis and subsequent lactic acid accumulation. The overall pH decrease during the first three days of storage and progressive increase thereafter agrees with the findings of Narendra Babu, Venkataramanujam, and Shanmugam (2002).
3.2. pH
The analysis of variance between the drip loss of buffalo meat packed under aerobic, vacuum and modified atmosphere methods of packaging revealed a significant (P < 0.05) difference. A highly significant (P < 0.01) difference was noticed between the drip loss of buffalo
The analysis of variance between the pH of buffalo meat stored for different periods showed highly significant (P < 0.01) differences. A fall in pH was seen initially
3.3. Drip loss (per cent)
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meat stored for the different periods. Drip loss significantly (P < 0.01) increased with storage, in all treatments. Similar findings were reported by Payne, Durhan, Scott, and Devine (1998). Drip losses in vacuum-packed sample were the highest (P < 0.05) in comparison to the aerobically and MAP samples. The findings are in agreement with Rousset and Renerre (1991). The increased drip loss in vacuum may be due to the squeezing of meat associated with vacuum packaging (Payne et al., 1998). The drip loss was lower in MAP than aerobically packed samples, which might be attributed to the head space gas pressure maintained in the package (Daniels, Krishnamurthi, & Rizvi, 1985). 3.4. Colour score The analysis of variance revealed a highly significant (P < 0.01) difference between the packaging methods, storage periods and interactions between packaging methods and storage periods. The mean colour score of the buffalo meat packed aerobically and in vacuum decreased from the day of packaging to the 21st day of storage. The mean colour score of the samples packed in modified atmosphere increased from the day of packaging to the third day and decreased gradually up to the 21st day of storage. The mean colour score in the samples packed in modified atmosphere were the highest. This finding is in agreement with Jones (1989). The mean colour score in the samples packed in modified atmosphere showed that they were bright red upto the third day and red upto to the 14th day and light red upto the 21st day. This finding is in agreement with Narendra Babu et al. (2002). Based on the findings, vacuum-packed buffalo meat had the lowest fibre diameter and myofibrillar fragmentation index and the highest sarcomere length, since vacuum enhanced ageing. The modified atmosphere packed buffalo meat structure underwent the normal postmortem changes showing no adverse effect. Buffalo meat packed in modified atmosphere had a desirable colour and a low drip loss. Buffalo meat packed under modified atmosphere and vacuum kept safely up to 14 days of storage at 4 ± 1 C.
Acknowledgements The authors extend their sincere gratitude to the Tamil Nadu Veterinary and Animal Sciences University, Chennai, India for having provided all facilities to conduct the above research work.
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