2011, Vol. 6 No. 2, Article 98
Effect of Hurdles on the Quality of Low Fat
Pork Sausages in Storage
E. Naga Mallika* and K. Prabhakar
NTR College of Veterinary Science
Gannavaram, A. P. 521 175
e-mail address: email@example.com
Preservation studies were under taken by employing different hurdles like vacuum packaging and heat treatment. The vacuum packaged samples recorded significantly (p<0.05) better sensory scores and lower microbial counts along with low fat oxidation and protein denaturation. Heat treatment was effective in partially reducing the microbial counts but decreased the sensory quality and enhanced fat oxidation and protein denaturation.The formulation with a combination of hurdles recorded significantly lower thio barbituric acid reactive substance values, tyrosine values, free amino acid values, free fatty acid values and plate counts towards the end of storage period.
Pork, sausage, hurdles.
Low fat products that meet the nutritional criteria, taste expectations and convenience are at demand due to the changing lifestyle of the people now a day. Pork can be a part of healthy diet. Processed meats are convenient but considered to be high fat foods. There fore currently the focus has been given to employ various approaches for the reduction of fat in the formulation of meat products with acceptable flavor and texture. The microbial stability and safety of most traditional and novel foods is based on a combination of several factors. The hurdle effect is of fundamental importance for preservation of foods since the hurdles inherent in a product control microbial spoilage and food poisoning (Listener and Gorris 1995).
Several hurdles are used minimally in optimum combinations which contribute to improvement in sensory qualities, microbial stability, energy saving and pose either no or minimal legal problems due to lower levels of addition in the products (Listener 1994). Interaction of various hurdles such as water activity and storage temperatures (Harner and angnostopoulor 1993, Listener 1978) indicate that there is a great potential for combining more than two hurdles in preserving meat products. Therefore an attempt was made to study the effect of combination of hurdles like cooking, vacuum packaging and storage temperature on the quality and stability of low fat pork sausages.
MATERIALS AND METHODS
The selected formulation of low fat pork sausages along with control was prepared and half of the batch was given heat treatment by cooking in a pressure cooker at 15 lb/sq. inch of pressure for 7 minutes, while other half was kept as raw. Half of the batch of each raw and heat treated products of control as well as the selected formulations were vacuum packaged in multilayer (polyester/ polyethylene) pouches of size 6”
X 9” and the other half sealed aerobically and subjected to freezing (-18±2ºC) temperature. The product was evaluated at 15 days intervals till 75 days of storage. The free fatty acid content was measured according to the method of Pearson et al (1973). Thiobarbituric acid reactive substance values of the sausages were determined by following the method of Tarladis et al (1960). Tyrosine value was determined by the modified method of Strange et al (1977). Total viable count, psychrophil count, yeast and mould counts, coliform, staphylococcal and salmonella counts of fresh and stored meat samples were determined by the method of APHA (1992). Organoleptic characteristics like color, flavor, juiciness, tenderness and overall acceptability of the product were evaluated by employing a semi-trained taste panel using 9 point hedonic scale.
Table 1 shows that the 2-Thiobarbituric acid Reactive substance (TBARS) values of vacuum packaged samples were lower than their aerobic packaged counter parts in both unheated and heated sausages. TBARS values were significantly (P<0.05) higher in heat treated sausages in aerobic and vacuum packages. During frozen storage, heat treated sausages recorded higher TBARS values irrespective of type of packaging and MCP incorporation. The lower TBARS values in vacuum packaged sausages might be due to lower oxygen permeability of packaging material. The heat treatment breaks chemical bonds in triacylglycerides and produce carbonyl compounds such as Cn-1 and Cn-2:1 hydrocarbons which leads to increased oxidation. The findings of present study were in conformity with those of Ho et al. (1995), Jo et al. (1999). The TBARS values) increased during storage irrespective of type of packaging and initial heat treatment. The values increased at steadily. Hurdle treatment significantly reduced the fat oxidation as indicated by a slow increase in the TBARS values of MCP incorporated and packaged under vacuum.
Tyrosine values indicative of proteolysis brought about by microbial growth or chemical reaction were lower in all treated samples when compared with control. The vacuum packaged samples recorded lower values than that of aerobic packaged samples. MCP incorporated vacuum packaged heat processed sausages recorded lowest tyrosine value . This might be due to the optimum combination of hurdles. The values increased with increase in storage periods. These results were in accordance with Morrissey et al (1980) and Agnihotri (1988).
Free Amino acid values were significantly lower in all treated samples in comparison to control. Vacuum packaged samples recorded lower values when compared to aerobic packaged ones. MCP incorporated, vacuum packaged heat processed pork sausages recorded the lowest free amino acid values. This might be due to the lower protein hydrolysis consequent to lower enzymatic activity with decreasing storage temperatures. The higher values of free amino acids in heat treated product might be due to the presence of soluble peptides in the filtrates of the heated samples. The low free amino acid content of vacuum packaged product might be due to the lowered exopeptidase activity. The free amino acid values of low fat pork sausages were increased with increasing storage periods at ambient, refrigerated and frozen storage temperatures. The increase in the free amino acid content might be due to increased proteolysis. The low free amino acid content of the hurdle treated product might be due to the low exopeptidase activity under these hurdles. Vacuum packaging and temperature were effective in lowering the free amino acid content of the pork sausages.
Free fatty acid content can be considered as an indicator for the lipid oxidation and flavor of the product. The free fatty acid values (FFA) of the vacuum packaged samples were significantly (P<0.05) lower than their aerobic packaged counterparts. MCP incorporated sausages under vacuum packaging in both heat processed and without heat processing revealed lower free fatty acid values. Free fatty acid values gradually increased along with increasing storage periods. The present findings were in agreement with those of Gopal Reddy et al (1978). The lowered FFA values in vacuum packaged sausages might be due to the relative oxygen impermeability of the packaging material. This trend in heat treated products might be due to the enhanced break down of chemical bonds in triglycerides liberating free carbonyl compounds which leads to increased oxidation. Sahu and Anjaneyulu (1997) and Diana Ansorena and Iciar Astiansarar (2004) also noticed lower FFA values under vacuum packaging.
Microbial counts were lower in heat treated sausages when compared to their unheated counter parts. Vacuum packaging significantly reduced the microbial proliferation. This might be due to cessation of growth of bacteria as oxygen is removed and packaged in oxygen barrier films. Hurdle concept involved with heat processing, vacuum packaging and MCP incorporation had evidently resulted in lower plate counts, coliform, salmonella and staphylococcal counts. At initial levels counts were lower due to shock developed and after adaptation process microbes started growing which was evidenced by a slow increase in the counts afterwards. Coliform counts, Salmonella counts and staphylococcal counts were significantly lower in all the vacuum packaged samples than their aerobic packaged ones.
On sensory evaluation all hurdles were found to contribute to lighter color in pork sausages. This might be due to synergistic effect of MCP incorporation and lower levels of oxymyoglobin prevailing due to vacuum packaging and heat processing causing mild protein denaturation on the surface of the sausages. Flavor scores indicated higher values for all the vacuum packaged samples than their aerobically packaged counterparts in all samples. This might be due to lower fat oxidation in vacuum packaged products. Heat processing alone might have contributed towards lower flavor scores in all the samples. This might be ascribed to higher fat oxidation and protein denaturation tendency of the heat treated product. MCP incorporated sausages recorded higher flavor scores. This might be due to the desired flavour contributed by the milk co-precipitates.
Juiciness, tenderness and overall acceptability scores also revealed similar pattern in almost all the samples. MCP incorporated, heat processed, vacuum packaged samples recorded highest juiciness, tenderness and overall acceptability scores.
Vacuum packaging of the samples lead to better preservation of the sensory quality of the samples besides effectively lowering the microbiological counts besides lowering fat oxidation and protein denaturation when compared to the aerobic packaged counterparts. Heat treatment although effective in partial reduction of the microbial counts but reduced the sensory quality and enhanced the fat oxidation and protein denaturation. A combination of all the hurdles was certainly desirable as indicated by the higher sensory, microbiological and biochemical quality of the F8 formulation, incorporated with MCP and heat processed and packaged under vacuum. Against this background, higher cooking yield and higher emulsion stability achieved due to MCP incorporation can contribute towards significant economic gains with enhanced shelf life and better sensory attributes in combination with heat processing and vacuum packaging.
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Table-1: Mean ± SE of physico-chemical characteristics of low fat pork sausages as influenced
by packaging and initial heat treatment at frozen temperature
(click to enlarge)
Table-2: Mean ± SE of Overall acceptability scores of low fat pork sausages as influenced
by packaging and initial heat treatment at frozen temperature
(click to enlarge)
Fig. 1: Total plate counts at freezing temperature
Fig. 2: Flavour scores at freezing temperature