Isolation and characterization of nonstarter Lactobacillus spp. in Swiss cheese and assessment of their role on Swiss cheese quality.

摘要

The objectives of this study were to isolate and identify nonstarter Lactobacillus strains in high quality commercial Swiss cheeses, to investigate citrate metabolism among nonstarter lactobacilli, to study the effect of nonstarter Lactobacillus strains as adjunct cultures on Swiss cheese characteristics, and to determine chemical, microbiological, and physical characteristics of commercial Swiss-type cheeses.; Lactobacilli were selected from six domestic and two European Swiss cheeses with selective medium and the strains from each cheese were genetically typed and speciated. Qualitative and quantitative citrate utilization assays were performed on each strain. The total number of Lactobacillus cells ranged from 4.8 x 104 to 7.1 x 10 7 CFU/g cheese. Strains belonging to L. casei, L. rhamnosus , and L. fermentum species were most frequently encountered. Lactobacillus casei strains predominated in the cheeses originating in Switzerland; whereas, the domestic cheeses contained a wider variety of Lactobacillus species, including different strains of L. casei, L. rhamnosus, L. gasseri, L. delbrueckii , and L. fermentum. Citrate differential medium was valuable in rapid assessment of citrate utilization of lactobacilli. On this medium, L. helveticus, L. gasseri, and L. delbrueckii strains did not metabolize citrate, while, L. casei, L. fermentum, and L. rhamnosus strains utilized citrate.; Twelve cheeses were manufactured using a commercial starter combination and three previously isolated nonstarter Lactobacillus strains, L. casei A26, L. casei B21, and L. rhamnosus H2. Cheeses were analyzed during ripening for microbial and chemical composition. The use of adjunct cultures diminished high variability in total Lactobacillus counts in cheeses manufactured without adjunct addition. Lactobacillus casei strains were able to utilize all citrate present in cheese before the end of the warm room ripening phase. There were no significant differences among cheeses in regards to protein, fat, moisture, and salt contents.; Understanding the occurrence, types, and metabolic capabilities of nonstarter Lactobacillus in Swiss cheese will allow further studies of their role in cheese ripening and their effect on Propionibacterium fermentation. Characterization of nonstarter strains from high quality cheeses may lead to new adjunct cultures specific for Swiss cheese. Chemical, microbiological, and physical characterization of Swiss cheeses, combined with sensory evaluation results may allow manufacturers to predict the acceptability of their cheese. (Abstract shortened by UMI.)