Effect of time and temperature on lactic acid fermentation of a white wheat flour-yoghurt mixture

A white wheat flour-yoghurt mixture was fermented by its indigenous microfl ora at different temperatures (20 to 40 degrees C) and for different times (0 to 42 h). Response surface methodology was applied to find a quadratic e quation showing the relationship between the pH and the acidity of the mixt ure and the fermentation time and temperature. Setting the first derivative of the quadratic equations to zero and solving for the time gives the dura tion of the lag phase period. When the temperature was increased from 20 to 40 degrees C, the fermentation time to attain a pH of 4.0 was reduced by a pproximately 5 times from 24.1 to 5.2 h and the lag phase period (no net ch ange in pH) was reduced from 19.8 to 3.6 h. The activation energy (E-a) was 10.4 J/mol.