Identification of bacterial strains in viili by molecular taxonomy and their synergistic effects on milk curd and exopolysaccharides production
Viili, also known as viilia, is a traditional fermented dairy product, which is popular in Finland. However, little research has been conducted on organisms’ isolation and their interaction during milk fermentation. In this study, culture-dependent and independent methods had been used to identify isolates. Also, their synergistic effects on milk curd and exopolysaccharides (EPSs) yield was evaluated. When Lactobacillus plantarum, Streptococcus thermophilus, Lactobacillus paracasei, Bacillus cereus and Lactobacillus delbrueckii were successfully separated and screened from viili by using the combination of conventional microbiological cultivation with polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE), they were individually inoculated into sterilized skimmed milk or combined as co-cultures to determine the curd time and the yield of EPSs. Results show that L. delbrueckii presented the strongest curding capability at 5 h and combination of L. paracasei, B. cereus and L. plantarum brought the highest yields of EPSs (186.71 mg/L). Moreover, it suggested that the synergistic effects among the isolates had shortened the curding time and increased the production of EPSs.
Key words: Viili, PCR-DGGE, exopolysaccharides, lactic acid bacteria.