Mathematical Modeling of pH Variation as a Function of Temperature and Time in Kefir Production
A mathematical model was developed to describe the effect of temperature and fermentation time on the kinetic parameters of pH change by kefir grains yeast population, using whole milk, semi-skimmed milk and skim milk of cows. Fermentation temperature (25–35 ºC), total fat level (3.0, 1.7, 0.15 %) and inoculum level (2%) w/v had simultaneous effects on the acidification process in kefir fermantation. The changes in pH of pasteurized cow milk inoculated with 2 % culture were investigated during fermentation at 25-35 ºC. Measurement of pH change was followed first order kinetics during kefir fermentation. The optimal kinetics model for pH change during fermentation of kefir was the linear mathematical model. Furthermore, statistical analysis indicated that fermentation temperature and time significantly affected pH change of kefir. pH reduction rate of kefir was maximum at semi-skimmed milk (1.7 %) at 35 ºC.
Kefir, pH, Kinetic, Milk Fat, Fermentation, Time
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