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Li, Su

Nutritional and Food Sciences

2006

MS

To investigate the interactions between Lactobacillus acidophilus and starter cultures during fermentation of goat's milk, three strains of L. acidophilus: ATCC-11975, LA-5 and NCFM, and starter cultures (Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus) isolated from the commercial yogurt starter culture YC350 (Chr. Hansen Inc.) were used in this study. Selective enumeration methods for each species were validated. MRS (deMann Rogosa and Sharpe) agar with 0.2% bile, and anaerobic incubation at 37°C for 72 h was suitable for L. acidophilus strains. MRS agar with pH adjusted to 5.2, and anaerobic incubation at 37°C for 24 h was suitable for L. delbrueckii subsp. bulgaricus strain LB350. And MI7 agar with 0.5% lactose, and aerobic incubation at 37°C for 24 h was suitable for S. thermophilus strain ST350. Addition of LB350, or ST350, or both, into the goat's milk inoculated with L. acidophilus strains accelerated the pH decrease, and the pH of goat's milk inoculated with L. acidophilus strains alone was significantly higher during 24 h fermentation. Antagonism between different L. acidophilus strains and LB350 was observed, and L. acidophilus strains built a stronger symbiotic relationship with ST350 than that between LB350 and ST350, indicating the promise of using starter culture absent of L. delbrueckii subsp. bulgaricus. However, these observations might be strain specific, and the survivability of these L. acidophilus strains and the quality characteristics of these fermented goat's milks need to be further investigated.