Multiple microbial cell-free extracts improve the microbiological, biochemical and sensory features of ewes' milk cheese.

This study used cell-free enzyme (CFE) extracts from Lactobacillus casei, Hafnia alvei, Debaryomyces hansenii and Saccharomyces cerevisiae to condition or accelerate Pecorino-type cheese ripening. Compositional, microbiological, and biochemical analyses were performed, and volatile and sensory profiles were obtained. Lactobacilli and cocci increased during ripening, especially in cheeses containing CFE from L. casei, H. alvei and D. hansenii (LHD-C) and L. casei, H. alvei and S. cerevisiae (LHS-C). Compared to control cheese (CC), several enzymatic activities were higher (P < 0.05) in CFE-supplemented cheeses. Compared to the CC (1907 mg kg-1 of cheese), the free amino acid level increased (P < 0.05) in CFE-supplemented cheeses, ranging from approximately 2575 (LHS-C) to 5720 (LHD-C) mg kg-1 of cheese after 60 days of CFE-supplemented ripening. As shown by GC/MS analysis, the levels of several volatile organic compounds were significantly (P < 0.05) lower in CC than in CFE-supplemented cheeses. All cheeses manufactured by adding multiple CFEs exhibited higher scores (P < 0.05) for internal structure, acid taste and juiciness than CC samples. This study shows the possibility of producing ewes' milk cheese with standardized characteristics and improved flavor intensity in a relatively short time.

Microbial cell-free extracts as sources of enzyme activities to be used for enhancement flavor development of ewe milk cheese.

Freeze-dried cell-free extracts (CFE) from Lactobacillus casei LC01, Weissella cibaria 1XF5, Hafnia alvei Moller ATCC 51815, and Debaryomyces hansenii LCF-558 were used as sources of enzyme activities for conditioning the ripening of ewe milk cheese. Compared with control cheese (CC), CFE did not affect the gross composition and the growth of the main microbial groups of the cheeses. As shown through urea-PAGE electrophoresis of the pH 4.6-soluble nitrogen fraction and the analysis of free AA, the secondary proteolysis of the cheeses with CFE added was markedly differed from that of the CC. Compared with CC, several enzyme activities were higher in the water-soluble extracts from cheeses made with CFE. In agreement, the levels of 49 volatile compounds significantly differentiated CC from the cheeses made with CFE. The level of some alcohols, ketones, sulfur compounds, and furans were the lowest in the CC, whereas most aldehydes were the highest. Each CFE seemed to affect a specific class of chemical compounds (e.g., the CFE from H. alvei ATCC 51815 mainly influenced the synthesis of sulfur compounds). Apart from the microbial source used, the cheeses with the addition of CFE showed higher score for acceptability than the control cheese. Cheese ripening was accelerated or conditioned using CFE as sources of tailored enzyme activities.