GROWTH BEHAVIOR OF SOME LACTIC ACID BACTERIA IN STIRRED YOGHURT WITH SOME NATURAL SWEETENERS

L. bulgaricus NRRL B-548, S. thermophilus NRRL B-512, L. reuteri NRRL B-14171 and L. johnsonii B-2178 were examined for their growth activity in skim milk containing (7% w/v) six different natural sweeteners (sucrose, glucose, fructose, honey, cane molasses and dibis). The growth activity were monitored by determining the pH and OD at 0, 4, 8, 24 h interval L. bulgaricus displayed the highest growth activity throughout the incubation period followed by S. thermophilus. While L. reuteri and L. johnsonii showed the slowest growth activity in skim milk with the natural sweeteners. Regarding the effect of the different sweeteners, dibis and molasse improved the growth and acid production of L. bulgaricus. While glucose affected the acid production of S. thermophilus and the pH values were the least (4.25) after 24 h of incubation, however no significant differences in the OD value were observed. The different types of sweeteners were not stimulatory or inhibitory to L. reuteri or L. johnsonii. There was a decline in the viable counts of all of the examined  microorganisms with different rates during the refrigerated storage. However their populations were still above 5 log cycles especially when dibis was used. Stirred yoghurt was manufactured from sweetened buffaloes' milk, L. reuteri or L. johnsonii were used as adjunct, the stirred yoghurt was analyzed physiochemically and evaluated organoleptically. Yoghurt manufactured by L. johnsonii gained the highest score especially with dibis, molasse or honey.