Factors affecting the activity of enzymes involved in peptide and amino acid catabolism in non-starter lactic acid bacteria isolated from Cheddar cheese

Peptidolytic and aminotransferase enzymes involved in amino acid release and catabolism were formed constitutively by cheese lactobacilli. Activities in controlled batch and continuous cultures of Lactobacillus rhamnosus F3 were affected by the rate and stage of growth and declined, under aerobic and anaerobic conditions, in the stationary growth phase. Enzyme formation was repressed by glucose and activity in cell lysates was affected by the nitrogen source. Activity was retained when cell integrity was maintained at pH 5.0–6.5 and at salinities of 5 g 100 mL−1. Aminotransferase activity in lysates of two Lb. paracasei strains was maximal at, or close to, pH 6.0 and 30°C but was detectable under simulated cheese conditions. The activity response to increasing salinity differed with leucine and phenylalanine as substrates. Aromatic, branched-chain and sulphur-containing amino acids were the most effective substrates for glutamate formation with α-ketoglutarate as acceptor, and although other keto acids functioned as acceptors for leucine and phenylalanine transamination activities were highest with α-ketoglutarate.