ENHANCEMENT OF β-GALACTOSIDASE ACTIVITY OF LACTIC ACID BACTERIA IN FERMENTED CAMEL MILK
It is known that, the main problem associated with the production of fermented camel milk is the lower growth rate of lactic acid bacteria which caused many quality problems in the final product. The aim of this research was to enhance of β-galactosidase enzymatic activity of Lactobacillus delbrueckii ssp. bulgaricus DSMZ 20081, Streptococcus thermophilus ATCC 19258 and Lactobacillus acidophilus DSMZ 20079 by cell-rupture method to release their intracellular β-galactosidase and used the ruptured cell cultures as the source of the β-galactosidase enzyme. The results show that the bacterial growth rate in fermented camel milk made by using mixed cells of L. delbrueckii ssp. bulgaricus, S. thermophilus and L. acidophilus was 2 h faster than whole cells of the same strains. Moreover, the significant (P<0.05) faster dropping in pH-value to about 4.6 was observed in fermented camel milk made by using mixed cells of S. thermophilus, L. acidophilus and L. delbrueckii ssp. bulgaricus it was 4.65±0.02, 4.64±0.01and 4.63±0.01 during 4 h of fermentation time, respectively. Furthermore, the highest significance (P<0.05) activity of β-galactosidase was obtained during 4 h of fermentation in all fermented camel milk made by using mixed cells of L. delbrueckii ssp. bulgaricus, L. acidophilus and S. thermophilus it was about 1.97±0.12, 1.77±0.06 and 1.70±0.01 IU/ml, respectively. On the other hand, more rapid and efficient utilization of lactose was observed in fermented camel milk made by using mixed cells of S. thermophilus, L. acidophilus and L. delbrueckii ssp. bulgaricus during the first 2 h of incubation time and the higher degree of lactose hydrolysis reached the maximum approximately 37.69, 38.39 and 40.56 % at the end of 10h of incubation time, respectively. The present results revealed that enhance of microbial growth rate in fermented camel milk can be simultaneously achieved by a suitable rupture-cell method.