Shelf life of boiled restructured buffalo meat rolls in refrigerated storage under vacuum packaging condition

Abstract

Cooked restructured buffalo meat rolls prepared from restructuring process were stored at 4 ± 1°C in polyethylene terephthalate laminated with polythene pouches under vacuum packaging condition. The samples were evaluated for physicochemical parameters, microbial quality and sensory attributes at regular intervals of 0, 5, 10, 15, 25 and 30 days of storage. A significant decrease in pH, extract release volume values, was observed with increasing storage period. Overall days mean for moisture decreased with increasing storage period, however, no significant difference in overall days mean for moisture content was observed on from day 0 to day 30 of storage. A significant (P < 0.01) increase in thiobarbituric acid value and tyrosine value was observed with increase in storage period. Microbiological counts increased with the advancement of storage period. However, throughout the storage period, all microbial counts were within the acceptable limits of cooked meat products. Boiled restructured buffalo meat rolls did not show any symptoms of spoilage such as off odour and surface slime on day 30 of storage and were acceptable for sensory quality up to 30 days of refrigerated storage (4 ± 1°C) under vacuum packaging. Thus, the present study indicates that vacuum packaging could be used as a way to improve the shelf life of boiled restructured buffalo meat rolls without affecting the physicochemical, microbiological and sensory qualities of the products.

Keywords:

• boiled buffalo meat
• restructuring
• rolls
• vacuum packaging
• quality
• storage stability

Introduction

India is endowed with the largest buffalo population in the world. About 10.66 million buffaloes are slaughtered annually producing 1.47 million tons of buffalo meat. Buffalo meat processing is important to provide a wide variety of meat products for the consumers and for increasing the marketability. At present, processing of buffalo meat is very less in India, but rapid urbanization and changing lifestyle demand ready-to-eat and convenient processed buffalo meat products. Restructured meat using flaking and forming or chunking and forming to produce low cost steaks has provided new steak products to consuming public (Mandigo 1986). Products that undergone desinewing and particle size reduction such as sectioning, chunking, slicing, blade tenderization, flaking, chopping followed by forming into steaks, roasts or patties are called restructured meats (Hedrick et al. 1994). Various types of food packaging in combination with different storage techniques can be used in order to extend the shelf life of meat. The causes of product deterioration are microbial spoilage, moisture loss, colour change and oxidative rancidity (Sinhamahapatra et al. 2013). Vacuum packaging, a form of modified atmosphere packaging, is often used to extend the shelf life of meat and meat products (Silliker & Wolf 1980) and is being increasingly applied for product distribution and retail sale (Stiles 1990). During refrigeration, the vacuum allows the shelf life of the meat to be extended by reducing oxidation and the growth of aerobic micro-organisms. Vacuum packaging has proven to be efficient in extending shelf life, preserving the sensory characteristics inherent to the product for a period sufficiently long for its turnover (Maria et al. 2011). The shelf life of meat products can be considerably extended by vacuum packaging in a film of low gas permeability (Pavankumar et al. 2003). Due to paucity of information on effect of vacuum packaging on quality attributes and shelf life of boiled buffalo meat rolls stored under refrigeration, the present study was undertaken. Hence, the objective of the present study was to prepare and evaluate the quality and acceptability of boiled restructured buffalo meat rolls in refrigerated storage (4 ± 1°C) under vacuum packaging condition.

Materials and methods

Buffalo meat

Round portion of buffalo's skeletal meat was purchased from the local buffalo meat stall, and it was cut into small chunks and frozen for 1–2 h to ensure easy mincing. The buffalo meat chunks were minced twice through the meat mincer (Model WD 114, Seydelmann, Germany) using 5 mm plate. The minced buffalo meat was used in the preparation of boiled buffalo restructured meat roll.

Weasands

Pre-processed ready-to-use weasands (casings prepared from buffalo oesophagus) of average diameter of 10–12 cm were purchased from the local buffalo casings processor. Just before stuffing, the weasands were thoroughly cleaned and flushed with water and then soaked in 10% salt solution for 1 min and again washed with water.

Product formulation and product preparation

The formula for boiled restructured buffalo meat roll was developed after conducting a series of preliminary trails. The product formulation consisted of 100% minced buffalo meat, 2.5% salt, 2.5% cane sugar, 0.5% sodium tripolyphosphate, 0.015% sodium nitrite, 0.15% sodium ascorbate, 2.0% spice mix, 6.0% condiments mix (onion, garlic and ginger, 2:1:1) and 10% ice flakes. Weighed quantity of minced buffalo meat samples was mixed in a meat mixer (N50 5-quart mixer, Hobart, Germany) at a speed of 200 rpm for 2 min with salt (2.7%), sodium tripolyphosphate (0.5%) and minced buffalo meat (25%). Thereafter, sodium nitrite (0.015%), sodium ascorbate (0.15%), spice mix (2.0%) condiments mix (6.0%) and ice flakes (10%) were added to mixer, and mixing was further continued for 3 min so as to obtain the homogenous mixture. Then about 500 g of meat mix was stuffed manually into a weasand. The raw rolls were cooked in preheated water up to an internal temperature of 82 ± 1°C and maintained at this temperature for about 10 min. After cooking, the cooked rolls were allowed to cool down, packaged in low-density polyethylene pouches and chilled in refrigerator. After 12 h of chilling, the boiled rolls were sliced using meat slicer and packaged under vacuum in polyethylene terephthalate laminated with polythene (PET/PE) pouches using a Roschermatic packaging machine (Model VM19S, Osnabrück, Germany). The samples were kept at 4 ± 1°C and examined at intervals of 5 days up to 30 days.

Analytical procedures

Physicochemical analysis

pH was determined using a digital pH metre. Moisture content of the product was determined as per the procedure of AOAC (1995). For determination of extract release volume (ERV), 15 g of minced stored sample was blended with 60 ml of distilled water in a homogenizer, and homogenate was transferred as quickly as possible into a funnel, equipped with a Whatman filter paper no. 1. The volume of filtrate collected in first 15 min was recorded as ERV of the respective sample. The procedure of Witte et al. (1970) was followed to estimate thiobarbituric acid value (TBA). Trichloroacetic acid extract of each sample was used for measuring the absorbance at 532 nm. TBA value was calculated as mg malonaldehyde per kg meat sample by referring to a standard graph prepared using known concentration of malonaldehyde. Tyrosine value of stored samples was determined based on the procedure of Strange et al. (1977).

Microbiological analysis

Total plate, psychrotrophic, coliform, yeast and mould and staphylococcal counts of stored samples were determined by the methods described by APHA (1984). Ready-made media was (Hi-media Laboratory Pvt. Ltd., Mumbai, India) used for enumeration of microbes. Preparation of samples and serial dilutions were done near the flame in a horizontal laminar flow apparatus which was pre-sterilized by ultraviolet irradiation (Yarco Sales Pvt. Ltd., New Delhi, India) by observing all possible aseptic precautions. Tenfold dilutions of each sample were prepared aseptically by blending 10 g of sample with 10 ml of 0.1% sterile peptone water in a pre-sterilized blender. Plating medium was prepared by dissolving 23.5 g of plate count agar in 1 litre of distilled water and pH was adjusted to 7.0 ± 0.2. Media was autoclaved at 15 1b pressure for 15 min before plating. The plates were incubated at 30 ± 1°C for 48 h for total plate count (TPC) and at 4 ± 1°C for 14 days for psychrotrophic counts. Coliform count was detected by using Violet Red Bile Agar, and plates were incubated at 37 ± 1°C for 48 h. Potato Dextrose Agar was used for enumeration of yeast and mould count, and the plates were incubated at 25 ± 1°C for 5 days. Baird Parker Agar was used for enumeration of staphylococcal count. Before plating, the medium was tempered to 50°C and egg yolk tellurite emulsion was added to the medium. The plates were incubated at 37 ± 1°C for 48 h. Following incubation, plates showing 30–300 colonies were counted. The average number of colonies for each species was expressed as log₁₀ cfu/g sample.

Sensory evaluation

Slices of boiled restructured buffalo meat rolls were served to an experienced panel of scientists and students to determine their sensory characteristics. The panellists were trained and well acquainted with different sensory attributes during their postgraduate/doctoral programme. They were briefly explained about the nature of the experiment without disclosing the identity of samples. The stored samples were warmed (40–45°C) using microwave oven for 1 min and served to the panellists. The sensory attributes like appearance and colour, flavour, juiciness, tenderness, binding and overall acceptability were evaluated on an 8-point descriptive scale as suggested by Keeton (1983). The sensory score of 8 was extremely desirable, whereas a score of 1 was extremely undesirable.

Statistical analysis

The data generated from four trials for each experiment were analysed by following two-way analysis of variance as described by Snedecor and Cochran (1989) by using a Statistical Package for Social Sciences (SPSS version 11.0) for comparing the means and to determine the effect of treatments and storage.

Results and discussion

Changes in physicochemical characteristics

The mean values for physicochemical characteristics of boiled restructured buffalo meat roll during refrigerated storage are presented in Table 1. The overall days means showed a significant (P < 0.01) decline in pH with increasing storage period up to 15 days. Thereafter, a significant increase in the pH was recorded. It is believed that cross-linking reactions, by removing amino groups from the meat, cause a decrease in pH (Ockonkwo et al. 1992), but proteolysis may have produced nitrogenous compounds which may have caused increase in the pH values (Aksu & Kaya 2005). Incze (1992) reported that decrease in the pH values might be due to significant (P < 0.05) increase in microbial count during storage period producing lactic acid by breakdown of carbohydrates. The resultant pH changes of the present study were also seemed to be governed by the relative rates of above reactions. Moisture content values decreased gradually during the entire period of storage. However, no significant difference in overall days mean for moisture content was observed between day 0 and day 30 of storage. A significant decrease in ERV values was observed with increasing storage period. However, decrease in ERV values between day 5 and day 15 and between day 20 and day 25 of storage did not turn out to be statistically significant. Although, ERV values decreased gradually during the entire period of storage, these values were well within the acceptable limit of 17 ml (Pearson 1967). The decrease in ERV value might be attributed to the increase in microbial population (Kumar et al. 2007). A significant (P < 0.01) and progressive increase in TBA value was observed with increase in storage period. But the values remained well within the threshold limit of 1–2 mg malonaldehyde/kg of meat product during the entire storage period under vacuum packaging. A positive correlation between microbial load and TBA value was reported by many workers (Sudheer et al. 2011). Increase of microbial load in meat samples could have caused increased oxidative changes. These oxidative changes might be attributed to increase in TBA value (Jay 1996). Tyrosine value increased significantly (P < 0.01) with increasing storage period. The increase in tyrosine value during storage might be due to denaturation and subsequent proteolysis (Daly et al. 1976). Pearson (1967) had attributed the increased tyrosine value in beef during storage due to the formation of free amino acids from denaturation process.

Table 1. Changes in physicochemical characteristics of vacuum-packaged, boiled restructured buffalo meat rolls during refrigerator storage (4 ± 1°C).

	Storage period in days
Parameters	0	5	10	15	20	25	30	Overall mean	Total SEM (±)
Physicochemical characteristics (n = 4)
pH	6.36 ± 0.01^a	6.27 ± 0.01^a	6.15 ± 0.02^b	6.04 ± 0.02^c	6.08 ± 0.01^c	6.15 ± 0.02^b	6.18 ± 0.02^b	6.17	0.11
Moisture	72.12 ± 0.82	72.12 ± 0.26	71.54 ± 0.22	71.27 ± 0.28	70.46 ± 0.18	70.06 ± 0.12	69.74 ± 0.24	71.04	2.12
ERV	21.06 ± 0.58^a	20.62 ± 0.42^b	20.06 ± 0.38^b	20.67 ± 0.26^b	19.29 ± 0.20^c	19.73 ± 0.18^c	17.49 ± 0.24^d	19.84	2.26
TBA value	0.51 ± 0.04^a	0.59 ± 0.02^a	0.66 ± 0.01^b	0.69 ± 0.02^b	0.75 ± 0.02^c	0.78 ± 0.01^c	0.80 ± 0.02^c	0.68	0.14
Tyrosine value	0.46 ± 0.02^a	0.49 ± 0.01^a	0.57 ± 0.02^b	0.64 ± 0.02^b	0.67 ± 0.02^b	0.69 ± 0.01^b	0.74 ± 0.10^bc	0.61	0.20

SEM, standard error mean

Note: Means bearing same superscripts row wise do not differ significantly (P < 0.01).

n, number of observations.

Changes in microbial quality

The mean values for microbial profile of boiled restructured buffalo meat roll during refrigerated storage are presented in Table 2. TPCs, psychrotrophic count, coliform count, yeast and mould count, staphylococcal count and lactobacillus count were increased significantly (P < 0.01) with increasing storage period. However, the products did not show any symptoms of spoilage such as off odour and surface slime on day 30 of storage. During the storage period, microbiological counts were well below the standards for cooked products (Jay 1996) that could cause microbiological spoilage of the product (Thomas et al. 2006). Increases of microbial counts were also observed in meat products as the refrigerated storage advanced (Thomas et al. 2006). The low microbial counts of present study were in accordance with Sinhamahapatra et al. (2013) on vacuum-packed chicken meat balls.

Table 2. Changes in microbial profile of vacuum-packaged, boiled restructured buffalo meat rolls during refrigerator storage (4 ± 1°C).

	Storage period in days
Parameters	0	5	10	15	20	25	30	Overall mean	Total SEM (±)
Physicochemical characteristics (n = 4)
TPC	2.30 ± 0.08^a	2.34 ± 0.04^a	3.51 ± 0.06^b	4.37 ± 0.11^c	4.39 ± 0.18^c	4.85 ± 0.12^d	5.56 ± 0.22^e	3.90	0.81
Psychrotrophic count	ND	2.15 ± 0.16^a	2.39 ± 0.21^a	2.92 ± 0.28^a	3.36 ± 0.23^b	4.17 ± 0.21^c	4.46 ± 0.23^d	3.24	1.32
Coliform count	ND	1.34 ± 0.14^a	1.38 ± 0.08^a	1.53 ± 0.16^b	1.57 ± 0.10^b	1.74 ± 0.12^c	1.79 ± 0.11^c	1.56	0.71
Yeast and mould count	2.26 ± 0.08^a	2.49 ± 0.11^a	3.24 ± 0.08^b	3.36 ± 0.12^b	3.63 ± 0.14^b	3.76 ± 0.18^b	4.12 ± 0.10^c	3.26	0.81
Staphylococcal count	1.26 ± 0.14^a	1.29 ± 0.08^a	1.37 ± 0.04^a	1.38 ± 0.08^a	1.41 ± 0.10^a	1.70 ± 0.02^b	2.11 ± 0.04^c	1.50	0.50
Lactobacillus count	1.29 ± 0.08^a	1.37 ± 0.09^a	1.41 ± 0.09^a	1.83 ± 0.09^b	1.86 ± 0.09^b	2.56 ± 0.10^c	2.61 ± 0.15^c	1.85	0.69

ND, not detected; SEM, standard error mean

Note: Means bearing same superscripts row wise do not differ significantly (P < 0.01).

n, number of observations.

Changes in sensory attributes

The mean values for sensory attributes of boiled restructured buffalo meat roll during refrigerated storage are presented in Table 3. The sensory attributes like appearance and colour, flavour, juiciness, texture and overall acceptability scores were decreased with increasing storage period. Decrease in overall acceptability scores with increasing storage period might be due to decrease in appearance and colour, flavour, juiciness and texture scores. The possible reason for decrease in appearance and colour scores during refrigerated storage might be due to surface drying or lipid oxidation causing non-enzymatic browning (Chenman et al. 1995). Flavour reduction during storage might be due to microbial growth and lipid oxidation (Devatkal & Mendiratta 2001). Dehydration and moisture reduction of the product with advancement of refrigerated storage could be the reason for lower juiciness scores. Similar observation of decrease in overall acceptability with increasing storage period was also reported by Devatkal and Mendiratta (2001) in pork rolls.

Table 3. Changes in sensory characteristics of vacuum-packaged, boiled restructured buffalo meat rolls during refrigerator storage (4 ± 1°C).

	Storage period in days
Parameters	0	5	10	15	20	25	30	Overall mean	Total SEM (±)
Sensory attributes^a (n = 20)
Appearance and colour	7.1 ± 0.09^a	7.1 ± 0.04^a	7.0 ± 0.04^a	7.0 ± 0.04^a	6.8 ± 0.08^b	6.6 ± 0.04^b	6.5 ± 0.04^b	6.87	0.37
Flavour	7.0 ± 0.08^a	6.9 ± 0.08^a	6.8 ± 0.10^a	6.7 ± 0.08^b	6.6 ± 0.29^b	6.5 ± 0.04^b	6.0 ± 0.04^c	6.64	0.71
Juiciness	6.8 ± 0.06^a	6.7 ± 0.04^a	6.7 ± 0.06^a	6.6 ± 0.08^a	6.0 ± 0.10^b	5.8 ± 0.08^b	5.6 ± 0.04^b	6.31	0.46
Texture	6.9 ± 0.10^a	6.9 ± 0.12^a	6.4 ± 0.04^b	6.3 ± 0.10^b	6.2 ± 0.08^b	6.1 ± 0.04^b	5.8 ± 0.08^c	6.37	0.56
Over all acceptability	7.0 ± 0.06^a	6.9 ± 0.04^a	6.8 ± 0.11^a	6.2 ± 0.08^b	6.1 ± 0.10^b	6.2 ± 0.04^c	6.1 ± 0.08^c	6.47	0.51

SEM, standard error mean.

Note: Means bearing same superscripts row wise do not differ significantly (P < 0.01).

n, number of observations.

^a Sensory attributes were evaluated on an 8-point descriptive scale (wherein 1 = extremely undesirable and 8 = extremely desirable).

Conclusions

Based on the above results, it can be concluded that vacuum packaging had definite advantage in preserving the sensory and microbial quality of boiled restructured buffalo meat rolls. The boiled restructured buffalo meat rolls had better acceptability up to 30 days of storage at 4 ± 1°C in PET/PE pouches under vacuum packaging condition.