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Sausage is a homogenous mixture which comprises of minced lean meat, fat and mixed with additives which include salt, spices and seasoning (Girard, Denoyer, & Maillard, 1988). Also the physical aspects of processing like mincing and massaging can also lead to changes to the structure of the meat (Astruc et al., 2006; Labas, Astruc, Taylor, Martin, & Vendeuvre, 2006; Theno, Siegel, & Schmidt, 1978; Tyszkiewicz & Jakubiec-Puka, 1995).
In certain formulations different salts have been incorporated especially sodium chloride as they improve the overall functionality of the product. The effects which are observed are better gelation, higher water-holding capacity and retention of fat, lower cooking losses and reducing microbial growth during storage (Desmond, 2006). Also Hamm (1972) and Offer and Knight (1988) have shown the relationship of salt with meat thereby helping in water binding and reducing cooking loss. Studies have shown that sodium chloride has added values such as flavour enhancer which improves the flavour characteristic of the meat products (Gillette, 1985; Matulis, McKeith, & Brewer, 1994; Ruusunen, Simolin, & Puolanne, 2001; Ruusunen et al., 1999).
High pressure processing (HPP) is another interesting technique by which the functional properties of the muscle proteins can be improved. Studies using this technique have shown to increase the solubility of certain myofibrillar proteins (Macfarlane, 1974; Macfarlane and McKenzie, 1976) and also the binding between the meat particles of the sample have been increased after subsequent heat denaturation (Macfarlane, McKenzie, Turner and Jones, 1984).
In a particular study of HHP with various salts and concentration on pork sausages, it was observed that with low-salt levels of 1.5% and pressures of 100 to 200MPa resulted in reduced cooking losses and enhanced texture, while the effects were the highest in low-fat, i.e., 7% formulations (Mandava, Fernández, and Juillerat, 1994). The other uses of HHP treatment are that it can be used as an alternative to heat treatment for preservation (Gould, 1995) and also for its potential to inactivate micro-organisms and shelf-life extension (Ledward, 1998). In commercial processed (cooked or cured) meat products, HHP treatment is currently being implemented in order to improve the shelf-life, eradicate pathogenic micro-organisms, obtain greater sensory properties and improved safety (PFV, 2009).
The present study is to investigate the possibility of applying various levels of high pressure to sausages with low salt concentration in order to achieve similar or better attributes as when compared to a normal sausage having normal salt concentration. Since salt has several added values apart from imparting flavour characteristic, the aim of this study is to determine if HHP treatment is sufficient enough to satisfy the reduction of salt levels without reducing any functional properties of the sausage. Also sensory analysis of the product is carried out to ensure if the product can be accepted for commercial approval. According to Tuomilehto et al. (2001) high sodium intake can result in increased chances of stroke and premature death from cardiovascular diseases. Hence it is quite beneficial to develop a novel-food product which is healthy and has improved characteristics.
Materials and Methods:
Meat Samples and Formulations
The meat samples used for this project were purchased from a local meat supplier (Jennings of Caversham, Reading) on two separate occasions. The lean meat was obtained from the raw meat sample (Pork leg - deboned and rolled: low fat and high grade quality) after all the subcutaneous, intramuscular fat and the visible connective tissues were removed. And the fat used was from pork back-fat. The seasoning used was from Kerry Foods and the composition of it is given as follows:
Rusk (Prepared from Wheat Flour),
Raising Agent E503(ii),
Stabiliser [E451(i)], where stabiliser E451 - Sodium tripolyphosphate,
Preservative (E223), and,
The lean meat and the back fat were separately minced and ground through a 9-mm plate using the Kenwood mixer (Major titanium model). The minced samples were then placed individually in polyethylene bags, labelled, vacuum sealed using a vacuum packaging system and stored at 4°C until required. The meat batter formulations used throughout was chosen so that the differences between treatments, i.e., pressure, would be the most evident. This was achieved by formulating two types of batter mixtures, one containing the normal salt concentration (control) and the other (test) having a reduced salt concentration and the composition of both are shown in Table 1. The control batter was prepared using 2.2% sodium chloride (2.2g NaCl/100g product) and the test batter samples were made using 1.5% sodium chloride (1.5g NaCl/100g product). The raw meat batters were prepared by mixing the lean meat (50%), back fat (30%) along with the specific NaCl concentration depending upon the mixture using the Kenwood mixer (Major titanium model). After the mixture has been blended in so that the protein extraction is completed (3-5 minutes), ice/water (20%) is added along with the seasoning to obtain a proper mixture. During the mixing process, the batter was maintained at a temperature of less than 12°C. The batters were then filled into sausage casings and linked every 90 mm. The entire processing was carried out in a pilot plant in an aseptic environment and the equipment used were sterilised in order to maintain hygienic condition.
Soon after the preparation of the sausage formulations, the sausages were individually labelled, packed, and sealed in polyethylene bags and kept in 4°C prior to the HHP treatments. The HHP treatments were carried out after 24hrs of their making.
Cooking of batters and HPP treatments
The control samples (no pressure treatment) were placed in two separate trays with tissues (so as to absorb the fat loss) so that replicates could be obtained. And they are cooked directly in a fan-assisted oven in 190°C/374°F for a period of 30-35 minutes till an internal temperature (of the sausage) of 72°C is achieved. The pressure treatments were carried out using Mini FoodLab high pressure vessel and the compression fluid which was used in the sample chamber was made up of 30% 1, 2-propanediol in water (v/v). The test formulation sausages were subjected to various pressures ranging from 100MPa to 300MPa for a specific time period ranging from 10min to 30 min. In total there were 9 different types of pressure treatments as given in the Table 2. After the test samples were given pressure treatments, they were cooked using the same temperature settings as the control samples. The samples were cooled and packed in labelled polyethylene bags and were placed in the 4°C fridge until required for further analysis.
After cooking and cooling the sausages, they were then analysed for the cooking loss. The initial weight of the raw sausage was calculated after the batters were stuffed into the casings. After cooking at 190°C for 30-35 minutes, the cooked samples were cooled and then kept at 4°C overnight and then their weight was observed and the cooking loss was calculated (Lee et al., 2008). The formula used for calculating is
Weight of raw sausage (g) Weight of cooked sausage (g) Cooking Loss (g/100g) 100
Weight of raw sausage (g)
The colour of each sausage was determined using a colorimeter (calibrated with a white plate, L* = 94.25, a* = -0.83, b* = 0.79). Six measurements for each ten samples were taken. Lightness (CIE L* -value), redness (CIE a* - value), and yellowness (CIE b*-value) values were recorded.
Texture profile analysis
At room temperature the sausages were analysed with a texture analyser (TA-XT2i, Stable Micro Systems Ltd., Surrey, England) for the Texture Profile Analysis (TPA). The meat batters were prepared and then stuffed into the casings followed by cooking for the control sample and for the test samples; they were first subjected to pressure treatment and then cooked. The cooked samples were then cooled to the room temperature and then kept at 4°C overnight. Prior to the analysis, the samples were allowed to remain outside so that its temperature is almost equal to that of the room temperature. The samples were cut (20mm) from the sausages and the values for hardness, springiness, cohesiveness, gumminess, and chewiness were determined as described by Bourne (1978).
All the tests conducted were recorded and the values were reported. An analysis of variance was performed on all the variables using Minitab software (version 16).
Results and Discussion:
Tables and figures:
Table 1. Meat batter formulations (units: g/100gram)
Pork meat (lean meat)
Table 2. Pressure Treatments