CONICET | Buscador de Institutos y Recursos Humanos

Fat hydrolysis, proteolysis and lactose degradation, constitute the main biochemical changes during cheese ripening. Lactic acid bacteria represent the predominant flora of ewes milk cheeses. These microorganisms play an important role in the proteolysis and lipolysis that result in the development of flavour, taste ant texture. In this communication we report the intracellular esterolytic activities of some predominant flora strains of dairy products from ewes milk, in order to reach a better understanding on the esterolytic systems of these microorganisms. The esterolytic activities of cell-free extracts were determined by: 1- Post-electrophoretic detection using a-napthyl derivatives of fatty acids as substrates; 2- Spectrophotometric method using p-nitrophenyl derivatives of fatty acids Using a-napthyl derivatives of fatty acids as substrates, different profiles were obtained in all the bacteria studied. Strains O-177, O-257, O-236 and O-233 presented two or three bands with acetate and butyrate substrates at different intensity. O-174 and O-190 shown the same band for acetate esterase activity. O-257 and O-236 presented caprylate esterase activities. When a-napthyl laurate was used as substrate, no strains gave reaction on the gel. The acetate esterase specific activity of 0-236 was 27.39 ± 1.5 U/ mg prot, determined spectrophotometry. The butyrate esterase was 46.47 ± 3.80 U/ mg prot. The other strains studied presented acetate esterase activities similar at O-236. Butyrate esterase activities were two at four times lower that O-236. In conclusion, these lactic acid bacteria possess a complex esterolytic system. It is specific towards short chain fatty acids. O-236 presents a high butyrate esterase activity. This esterase system could be efficiently incorporated directly into milk to produce enzyme-modified cheese (EMC) as well as in accelerated-ripened cheese (ARC).

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