Yoghurt fermented by Lactobacillus delbrueckii subsp. bulgaricus H+-ATPase-defective mutants exhibits enhanced viability of Bifidobacterium breve during storage

Persistent acid production by Lactobacillus delbrueckii subsp. bulgaricus during refrigerated storage is a major cause of reduced viability of probiotic strains such as Bifidobacterium breve in yoghurt. It was established that H+-ATPase-defective mutants of lactic acid bacteria have reduced growth and metabolism in low pH environments. Therefore, the aim of this study was to evaluate inhibition of post-acidification and maintenance of B. breve viability in yoghurt fermented by L. delbrueckii subsp. bulgaricus mutants with reduced membrane-bound H+-ATPase activity during refrigerated storage. Spontaneous neomycin mutants of L. delbrueckii subsp. bulgaricus that had a significantly (P ≤ 0.05) reduced H+-ATPase activity were successfully isolated. Yoghurt fermented using L. delbrueckii subsp. bulgaricus SBT0164 No. 55-1 (mutant) starter culture had markedly reduced post-acidification and maintained viability (≥ 108 CFU/ml) of both Bifidobacteruim breve JCM 1192T and Bifidobacteruim breve JCM 7017 during storage at 10 °C for 21 days. These results clearly showed that yoghurt fermented by mutants of L. delbrueckii subsp. bulgaricus with reduced membrane-bound H+-ATPase activity has reduced post-acidification that prolongs viability of B. breve in yoghurt during refrigerated storage.