Survival of Lactobacillus bulgaricus and Bifidobacterium animalis in yoghurts made from commercial starter cultures during refrigerated storage

All over the world, fermented dairy products have been consumed for nutrition and maintenance of good health for a very long time. This study evaluated the survival of Lactobacillus delbrueckii ssp. bulgaricus and Bifidobacterium animalis ssp. lactis BB-12 in yoghurts after the manufacturing during the shelf-life up to 21 days at 4 °C, which is mostly accepted by the consumers. The titratable acidity and pH showed the same patterns of increase or decline after manufacturing and storage of yoghurts. There was a significant difference (p <0.05) in acidity between yoghurts in glass bottle and plastic cup. The increase in numbers of lactobacilli and bifidobacteria and their survival during storage time were dependent on the species and strain of associative yoghurt bacteria (control-only yoghurt lactic acid bacteria and experimental containing except yoghurt culture also Bifidobacterium animalis ssp. lactis BB-12) and on the packaging material (glass bottle versus plastic cup). It was observed, that counts of bifidobacteria were lower than counts of Lactobacillus delbrueckii ssp. bulgaricus (190 to 434 x 107 at 1d) and slowly increased (p <0.001) at maximum level on day 7 (294.3 - 754 x 107) and then slowly declined to 6.33 x 107 in glass bottle and 2.33 x 107 in plastic cups, respectively. Lactobacillus delbrueckii ssp. bulgaricus multiplied better in glass bottles than in plastic cups, as observed during experimental period in-group with Bifidobacterium animalis ssp. lactis BB-12. At the end of the storage period at 4 ºC, viable counts of lactobacilli were higher (p <0.001) in glass bottles. Al the yoghurts, contained the recommended levels of lactobacilli and bifidobacteria (107 cfu.g-1) at the end of storage period (21 d)