Characterization and extracellular activity of psychrotrophic bacteria isolated from Villalَn cheese (fresh variety of Spanish sheepʹs milk cheese)

The incidence of psychrotrophic bacteria was investigated in a Spanish fresh ewesʹ cheese (Villalَn). Counts of mesophiles and psychrotrophs were (log cfug) 5.72 ± 1.10 and 3.90 ± 1.01, respectively, for factory cheeses made from pasteurized-milk. Figures for hand-made cheeses made from raw-milk were 7.35 ± 0.48 and 6.94 ± 0.65, respectively. A total of 59 representative psychrotrophic isolates were characterized and tested for protease and lipase production at 7 and 30 °C. The strains were assigned to Enterobacteriaceae (predominant in raw-milk cheese), heterofermentative lactic acid bacteria (dominant in pasteurized-milk cheese and absent in raw-milk cheese) and Pseudomonas. More than 73% of the Enterobacteriaceae produced both proteolytic and lipolytic enzymes at either 30 or 7 °C. This percentage is considerably higher than those previously reported. The seven isolates of pseudomonads investigated produced proteases at 7 °C and six were positive at 30 dgC; lipolytic activity was shown by five of the isolates at both temperatures. Among the heterofermentative lactic acid bacteria seven of the ten isolates were proteolytic at 30 °C.