Role of adventitious microflora in proteolysis and lipolysis of Serra cheese: Preliminary screening

Six different types of bacteria (five strains of lactic acid bacterium and one strain of coliform) isolated from 35-day-old Serra cheese were assayed for proteolytic and lipolytic activities on milk agar and tributyrin agar, respectively. Peptidase and lipase activities were further studied via analytical assaying of free amino acids by spectrophotometry and of free fatty acids by HPLC in in vitro curdled milk (previously prepared from heat-sterilized ovine milk coagulated with thistle flower) subject to ripening for 21 days at 5°C and 95% relative humidity. Leuconostoc mesenteroides ssp. mesenteroides/dextranicum and Lactococcus lactis ssp. lactis displayed significant proteinase and peptidase activities, where Leuconostoc lactis and Enterococcus faecium only exhibited peptidase activity. Leuc. mesenteroides ssp. mesenteroides/dextranicum, Ent. faecium, and L. lactis ssp. lactis only showed lipase activity on milk fat after a long incubation period. Short- and medium-chain fatty acid residues were released preferentially by microbial lipases, although long-chain fatty acids were also significantly released by lipases from Leuc. mesenteroides ssp. mesenteroides/ dextranicum. Lactobacillus paracasei ssp. paracasei and Hafnia alvei did not display measurable protease, peptidase, or lipase activities. In view of their hydrolase activities, it is suggested that L. lactis ssp. lactis and Leuconostoc spp. (with possible incorporation of Ent. faecium) are a potential mixed-strain starter for Serra cheesemaking.