Proteolytic, lipolytic and autolytic activities of enterococci strains isolated from Egyptian dairy products

Enterococci were isolated from Egyptian Domiatti and Mish cheeses made from raw milk. The proteolytic, lipolytic and autolytic activities of the isolated strains were studied to select the most appropriate cultures to be used for the enhancement of the organoleptic properties of cheese. The intracellular peptide hydrolase activities of enterococci strains were determined using various synthetic aminopeptidase and dipeptidyl-aminopeptidase substrates. 4-nitrophenyl and 2-nitrophenyl derivatives of fatty acids were used to measure the esterolytic activity of the different strains while emulsions of various triglycerides and butter fat were used to evaluate their lipolytic activities.The autolytic properties of the cultures were also considered. Three strains of Enterococcus faecium were freeze-shocked and evaluated as adjunct cultures in a cheese slurry system. All the strains exhibited an aminopeptidase activity hydrolysing leucyl 4-nitroanilide faster than the arginyl, alanyl, prolyl or glycyl derivatives. An active dipeptidyl-aminopeptidase activity was also detected. The Enterococcus faecium strains showed an active esterase system. The 4-nitrophenyl derivatives of the fatty acids were hydrolysed faster than the 2-nitrophenyl. The lipase substrates were hydrolysed according to the following order: tributyrin > tricaproin > tricaprylin > butterfat. The autolytic properties varied according to the strains tested. Cheese slurries ripened with adjunct Enterococcus faecium exhibited considerably higher levels of water-soluble nitrogen (WSN) and total free amino acids (FAA) when compared to the control after incubation for 5 d at 32 o C. With this finding, a high variability of some technologically relevant properties was found and could be the basis for the selection of specific cultures to be used as adjunct cultures in the production of traditional cheeses.