Isolation, characterization, and influence of native, nonstarter lactic acid bacteria on Cheddar cheese quality.

To determine whether adventitious nonstarter lactic acid bacteria (NSLAB) might affect cheese flavor and quality, we studied a population of NSLAB present in 30 premium quality Cheddar cheeses (3-mo ripened) produced at a commercial facility in the United States. DNA fingerprinting analysis with a sensitive strategy for arbitrary priming polymerase chain reaction showed that 75 isolates corresponded to at least 18 distinct nonstarter organisms. According to ribotype database comparisons of representatives from the 18 groups, 9 matched Lactobacillus (closest to paracasei species), 8 matched Streptococcus thermophilus, and 1 matched to a Lactococcus species. This finding indicated that among the 75 NSLAB isolates, Lactobacillus made up 64%, S. thermophilus 32%, and Lactococcus 4%. Isolates representing 11 NSLAB groups were characterized for protease, peptidase, and diacetyl production. Based on this phenotypic analysis, two Lactobacillus isolates were evaluated as adjuncts in Cheddar cheese. All of the NSLAB identified from the adjunct cheese at 3 mo by DNA fingerprinting consisted of the adjunct lactobacilli, showing that the adjunct strains predominated throughout the early stages of ripening. The impact of adjunct lactobacilli was evident after 6 mo when free amino acids significantly increased and sensory scores improved in adjunct cheese as compared with a control cheese. The largest impact was found in adjunct cheese containing a blend of both lactobacilli strains. These results show that certain adventitious NSLAB positively contribute to flavor development.