Viability of yoghurt and probiotic bacteria in yoghurts made from commercial starter cultures

Viability of yoghurt and probiotic bacteria was assessed during manufacture and 35 d storage in yoghurt made from four commercial starter cultures. The titratable acidity, pH and dissolved oxygen content showed similar patterns of increase or decrease during manufacture and storage of yoghurt, whereas concentration of hydrogen peroxide increased in the product prepared with cultures that contained L. delbrueckii ssp. bulgaricus. The increase in numbers of probiotic organisms during manufacture and the viability of these organisms during storage were dependent on the species and strain of associative yoghurt organisms. The viability of L. acidophilus was affected by the presence of L. delbrueckii ssp. bulgaricus, whereas bifidobacteria exhibited better stability in the yoghurt prepared from cultures that contained L. delbrueckii ssp. bulgaricus. The viability of both probiotic organisms was improved when the dissolved oxygen concentration was low in the product. The storage temperature of yoghurt affected the viability of bifidobacteria, but not L. acidophilus. The variations in titratable acidity, pH, dissolved oxygen and hydrogen peroxide were almost identical at storage temperatures of 4 and 10 degrees C. In one of the commercial cultures, 3 log cycles inhibition of bifidobacteria was observed from initial counts of > 10(6) mL(-1). (C) 1997 Elsevier Science Limited.