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Lactic acid bacteria play an important role in milk coagulation and cheese ripening. To select strains showing interesting industrial features, two indigenous lactobacilli (Lactobacillus brevis and Lactobacillus plantarum) were studied for aminopeptidase activity. Cell and cells free extract were tested for leucyl aminopeptidase activity on the chromogenic leucyl-p-nitroanilide substrate. Intracellular and membrane enzymes were solubilized with glycine /lyzozyme treatment then purified by ammonium sulphate precipitation followed by Sephadex G100 and diethylaminoethyl (DEAE) ions exchange chromatography's separation. The molecular weight of denatured proteins was estimated on sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS PAGE). Effects of several parameters, pH, temperature, some ions and inhibitors on purified enzyme activity were studied. Cellular aminopeptidase activity was higher for CHTD 27 strain than BH14 strain. No aminopeptidase activity was noted in the cell free extract. The results of chromatography sephadex G100 combined to those of electrophoresis allowed suggesting a dimer structure for the native enzyme. The Lb CHTD27 purified enzyme showed maximal activity at pH 6.6 and at 40°C. This enzyme was partially inhibited by ethylenediamine acetic acid (EDTA) and Cu 2+ ions but increased by Na 2+ and Co 2+ ions. The aminopeptidase extracted from Lb BH14 was inhibited by EDTA and phenylmethanesulfonylfluoride or phenylmethylsulfonyl fluoride (PMSF), its maximal activity was observed at pH 7.5 and 40°C. In addition to other characteristics as proteolysis and autolysis, in this paper we showed that both studied strains were also able to degrade peptide with specific peptidases which are important characters in cheese manufacturing.

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The lipolytic and esterase activities of fifteen strains of lactic acid bacteria isolated from different biotopes of Algeria and Mauritania were tested on MRS medium supplemented with lipidic substrates. Five of them showed maximum activity in the presence of tributyrin; the activity is therefore a tributyrin esterase. These strains were identified by MALDI-TOF in Enterococcus faecium and Enterococcus durans. The study of growth kinetics as a function of time shows a start of fatty acid production during the exponential phase to reach its maximum in the stationary phase. A better esterase activity is observed at between pH 6 and 9 and at an optimal temperature of 30 to 40°C for the five strains. The influence of metal and additive ions on the esterase activity varies between bacteria but generally, total inhibition was observed in all strains tested in the presence of SDS, NaN 3 , CuCl 2 , EDTA, AgNO 3 and HgCl 2 .

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