Isolation and characterization of nonstarter Lactobacillus spp. in Swiss cheese and assessment of their role on Swiss cheese quality
Nonstarter Lactobacillus strains affect the quality of many cheese varieties. Though the use of Lactobacillus casei as an adjunct culture is common for Swiss-type cheese manufactured in Switzerland, few published reports exist on adjunct use and none exist for adjunct use in U.S.-manufactured Swiss cheese. The objectives of this study were to isolate and identify nonstarter Lactobacillus strains in high quality commercial Swiss cheeses and 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 domestic and European Swiss cheeses and the strains were genetically typed and speciated. Qualitative and quantitative citrate utilization assays were performed on each strain. The total lactobacilli counts ranged from 4.7 to 7.9 log 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 including different strains of L. casei , L. rhamnosus , L. gasseri , L. delbrüeckii , and L. fermentum . Among the strains tested, L. casei strains were strong citrate utilizers followed by L. rhamnosus , L. fermentum , and L. gasseri strains. A putative citP gene fragment from one citrate-utilizing L. casei strain was amplified, cloned, and sequenced. Distribution of the putative citP gene in Swiss cheese nonstarter lactobacilli was determined. Selected nonstarter Lactobacillus strains isolated from commercial cheeses were utilized as adjunct cultures for cheese manufacture. Lactobacillus casei strains utilized 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. However, sensory properties were affected. Fifteen commercial cheeses were analyzed for microbiological, physical, and compositional characteristics. These results will complement descriptive sensory and consumer preference studies. Understanding the occurrence, types, and metabolic capabilities of nonstarter Lactobacillus spp. in Swiss cheese will allow further studies of their role in cheese ripening and their effect on Propionibacterium fermentation.
School:The Ohio State University
School Location:USA - Ohio
Source Type:Master's Thesis
Keywords:nonstarter lactobacilli swiss cheese citrate permease
Date of Publication:01/01/2005