Proteolysis and lipolysis in an aseptic meat model system for dry sausages

Department of Animal Production, Faculty of Agricultural and Applied Biological Sciences, Ghent University, Proefhoevestraat 10, 9090 Melle, Belgium “Present adress: Department of Marine fisheries, Ministry of Agriculture, Ankerstraat 1, 8400 Oostende,^ Belgium. b; ar Background Fermented meat products are produced through a complex series of microbial, physical (drying, gel formation,...) and (bio) ¡̂ chemical changes (proteolysis, lipolysis, colour formation,...) and their interactions. The overall quality of a fermented sausage ¡-' determined by the balance of these changes depending on processing conditions, starters and raw material properties (Demeyer et a l ^ 1 1986; Molly et al., 1997; Montel et al., 1998). A detailed knowledge of such changes would allow a better standardisation an ^ ( optimisation of the quality and safety of the fermented meat product. Recent data suggest that in the first stages of the fermentation' process endogenous proteolysis and lipolysis by animal tissue enzymes are more important than bacterial metabolism (Verplaetse et al 1989; Molly et al., 1997). As muscle enzyme activity may vary with carcass and raw meat characteristics (Uyterhaegen et al., 1991^' Toldrá et al., 1996), the latter may be important for development of sausage quality. ^ M Objectives M 1. Development of an aseptic meat model system (AMMS) to simulate the initial stage of the fermentation process ^ 2. Evaluating the effect of different pork carcass meat percentages on initial proteolytic and lipolytic activity in an AMMS 0< Tc Methods Pj Development o f an AMMS Sc Twenty Belgian Landrace Negative x Piétrain crossbred pigs with an average live weight of 101 kg (SD 3) were slaughtered^ 2 Carcass meat percentages varied from 50 % to 68 %. The group consisted of 10 barrows and 10 gilts. The exterior of the m. tricep•' e brachii of the right carcass half was burned off with a portable blowtorch (Laser camping, oxyturbo, Italy). Then, surfaces were remove^"0 using sterile knives and the remaining meat was divided into thick slices and vacuum-packed stored at -18°C. All the meat was s to red frozen for exactly 4 months. Before utilisation, each frozen muscle was cut into cubic blocs of 3 to 5 cm and randomised. ̂ representative meat sample with 1 % of glucono-delta-lactone (GDL), 3 % of colouring salt (NaCl containing 0.6 % NaN02) and mixture of antibiotics was minced for 1 min in a sterilised, mincer (maxi 300 chopper, SEB, Dijon, France) (soaked for 24 hours in *1*1 mixture of ethanol and acetic acid (3/1 v/v)). GDL was added as a chemical acidulent to compensate for absent microbial acid production and corresponding pH drop. The addition of 1000 U penicillin G (continental Pharma), 200 pg amphotericin B (Bristol-Myers SquibblTal and 1 mg streptomycin sulfate (Sigma) per g mixture was necessary to inhibit microbial growth, mainly yeasts. Meat mixtures of 50 !D ; were vacuum packed into polyethylene bags and incubated in duplicate for 3 days at 25°C. Under these circumstances, an average pH O’anc 4.8 was achieved comparable with the final pH after a Northern fermentation process (Molly et al., 1997). N, Methods o f analysis fra( Total cathepsin D activity, important in proteolysis during dry sausage fermentation ( Verplaetse et al., 1989), and acid lipas* activity were determined on the m. triceps brachii by a modification of the procedures described by respectively Barret and Kirsch^ (1981) and Motilva and Toldrá (1993). Before and after incubation, the following analyses were performed on the meat mixtures: viable aerobic and micro-aerophilic counts were measured on Plate Count Agar. Proteins were separated using SDS-PAGE as describe1̂ by Greaser et al. (1983). Free non-protein a-NH2-nitrogen was extracted with 0.6 M H C IO 4 and determined by a method of Odd! (1974). Total proteolytic activity was evaluated by analysing the total tryptophan content in the non-protein nitrogen fraction accordingtf Messineo and Musarra (1972). Ammonia contents were determined using a 692 pH/ionmeter equipped with an ammonia selective gi electrode (Metrohm, Herisau, Switzerland). Free fatty acids (FFA) were extracted with a chloroform/methanol (2/1) mixture (Folch et d 1957) and determined according to Koops and Klomp (1977).