Effect of temperature and inoculum concentration on prediction of both gelation time and cutting time. Cottage cheese-type gels

Prediction of gelation and cutting times were investigated under conditions used in cottage cheese processing. Effect of temperature and inoculum concentration on predictions was analyzed using a factorial design. Culture growth was monitored using a pH-meter, an oscillatory rheometer and a light (880 nm) backscatter sensor. Gelation time determined by oscillatory rheometry was predicted by the equation tgel=β1t2mintgel=β1t2min (determination coefficient, R2=0.988R2=0.988 and standard error of prediction, SEP=11.3 min), where β1β1 was the regression coefficient and t2 min was the time to the first minimum of the second derivative of the light backscatter ratio. Cutting time was set as the time when gel pH reached 4.8 and predicted using the equation tcut*=β0+β1t2max2(R2=0.987,SEP=14.7min), where β0β0 and β1β1 were regression coefficients and t2 max 2 was the second maximum of the second derivative of the light backscatter ratio. The inclusion of an acidification term in the cutting time prediction model reduced the SEP to 7.9 min. These results demonstrated that, when the acidification rate varied, accurate cutting time prediction of cottage cheese required the inclusion of reference pH values.