Inline control of yoghurt fermentation process using a near infrared light backscatter sensor

In industrial yoghurt production, continuous process monitoring using pH meters is a cumbersome and non-appropriate technique. The objective of this study was to evaluate the suitability of an optical sensor as a new method for the inline control of yoghurt fermentation. Tests were conducted with three fat and three inulin concentrations and fermentation was monitored simultaneously using an inline light backscatter sensor, pH-meters and a rheometer. A mathematical model that correlates the near infrared light backscatter ratio with the pH, at real time during milk fermentation, was developed. The model was calibrated and successfully validated at the different experimental conditions, predicting the evolution of pH from 5.2 to 4.6 with determination coefficient values higher than 0.993 and standard error of prediction values between 0.02 and 0.11 pH units. The results demonstrated that this is a promising method for the inline control of pH in industrial yoghurt production.