Author/Authors :
-، - نويسنده Departmant of Food Science, Technology and Engineering, Faculty of Agricultural Engineering and Technology, Agricultural Campus, University of Tehran, P.O. Box 4111, Karaj, I.R. Iran Jalili, Hasan , -، - نويسنده Departmant of Food Science, Technology and Engineering, Faculty of Agricultural Engineering and Technology, Agricultural Campus, University of Tehran, P.O. Box 4111, Karaj, I.R. Iran Razavi, Hadi , -، - نويسنده Departmant of Food Science, Technology and Engineering, Faculty of Agricultural Engineering and Technology, Agricultural Campus, University of Tehran, P.O. Box 4111, Karaj, I.R. Iran Safari, Mohammad
Abstract :
In fermented products containing Bifidobacteria, factors such as organic acid concentration and b-galactosidase activity are important in the development of flavor and texture of final products. Both the process conditions and medium components have significant effects on fluctuation of such factors. The effects of whey permeate powder and yeast extract concentrations, as nitrogen sources was investigated, on metabolic activity of Bifidobacterium animalis subsp. lactis Bb 12 in skim milk based media. Development of organic acids, growth rate and b-galactosidase activity under uncontrolled pH conditions was also monitored. Media with high concentrations of nitrogen sources showed maximum viable counts of B. animalis. The activity of b-galactosidase increased during the logarithmic phase and the initial stage of the stationary phase of growth and then decreased thereafter. Increasing the yeast extract concentration resulted in an increase in the specific sugar consumption rate with concomitant reduction in formation of acetic acid and formic acid. Consequently, the molar ratio of acetic acid to lactic acid was decreased. Using limited amounts of nitrogen sources resulted in more organic acid production in the tested microorganism. During the early hours of fermentation in which the amounts of nitrogen levels were limited, the specific rate of b-glactosidase activity was very high. Therefore, by evaluating the activity of this enzyme we can estimate the amount nutrient components in the medium.The production of succinic acid was observed during logarithmic and stationary phase in all fermentation media. Citric acid that naturally exists in whey and skim milk powder was consumed during the stationary phase of growth by B. animalis and its consumption correlated significantly with the production of succinic acid at this stage.
