ACTIVITIES OF PORK MUSCLE PROTEASES IN MODEL CURED MEAT SYSTEMS

The effect of curing agents (salt, nitrate, ascorbic acid and glucose) and processing parameters (pH, water activity and drying and cooking temperatures) on pork muscle cathepsins B, D, H and L as well as leucyl, arginyl and tyrosyl hydrolysing activities is reported. Salt (60 g/l) showed a powerful inhibitory effect, especially on cathepsin D and aminopeptidase activities where less than 13% of the original activity was recovered. Cathepsin H was also affected (38% of the original activity) while cathepsins B and B + L recovered 72.5 and 63.0%, respectively. Nitrate (0.2-0.25 g/l ) and ascorbic acid (0.2-0.4 g/l) did not significantly affect the enzyme activities. On the other hand, 0.5-2 g/l of glucose activated both cathepsins B and D with an increase of 39.5 and 28.5% and also leucyl and arginyl hydrolysing activities which were 75.0 and 24.0%, respectively. No aminopeptidase activity was detected when assayed in 100 mM sodium citrate buffer, pH 5.1. Cathepsin H was also very affected at that pH and only 12.0% of activity was recovered. A decrease in water activity, especially below 0.84, also affected the enzyme activities which were found below 50%. Temperatures in the usual range of the drying process (22 and 30-degrees-C) gave substantial enzyme activities (around 40-50 and 80%, respectively). In vitro simulations of different stages in the processing of dry-cured hams and sausages revealed that cathepsins B, B + L, H and leucyl hydrolysing activity were very active (38-82%) in the conditions of ham processing and less favoured (< 36%) in the conditions of fermented sausages processing, especially aminopeptidases and cathepsin H activities which were very low (< 10%) due to the acid pH values. Cooking treatment (65 and 69-degrees-C for 15 min) inactivated both cathepsin B and arginyl hydrolysing activities while the remaining activity of the cathepsin H and leucyl and tyrosyl hydrolysing activities were very low(< 4%). The activity of cathepsin B + L was less affected by cooking (61.0 and 25.7%, respectively) as well as cathepsin D (30.0 and 14.0%, respectively) so that both cathepsins D and L might play an important role in cooked cured meat products.