EFFECT OF LEVEL OF STARTER CULTURE ON VIABILITY OF YOGURT AND PROBIOTIC BACTERIA IN YOGURTS

The effect of level of inoculum on viability of yoghurt bacteria (Stre ptococcus thermophilus and Lactobacillus delbrueckii ssp. bulgaricus) and probiotic bacteria (Lactobacillus acidophilus and Bifidobacterium spp.) during manufacture and refrigerated storage was assessed in yogh urts made with commercial starter cultures. S. thermophilus was most s table in yoghurt, with counts greater than or equal to 10(7) cfu/g thr oughout the storage for all the levels of inoculum. L. delbrueckii ssp . bulgaricus lost viability rapidly to < 10(5) cfu/g after about 20 d storage. L. acidophilus maintained viability to 10(6) cfu/g only up to 20-25 d storage at 4 degrees C, after which counts declined. In three out of four starter cultures, bifidobacteria counts were satisfactory and more stable than for lactobacilli. However, counts of bifidobacte ria declined dramatically during manufacture of yoghurt with the fourt h starter culture. Post acidification was slightly higher in yoghurts prepared with lower levels of inoculum. Associative yoghurt organisms and pH of the yoghurt affected the viability of yoghurt and probiotic bacteria.