Measurement of pH at high temperature in milk protein solutions

This study determined the changes in the chemical properties of milk protein ingredients during heat-treatment, with a focus on the in-situ measurement of pH. Milk protein concentrate, micellar casein concentrate, sodium caseinate and whey protein isolate powders were rehydrated in either distilled water or lactose-free simulated milk ultra-filtrate (SMUF). Protein dispersions were heated from 25 to 120 °C before cooling to 25 °C in a custom-engineered hermetically sealed cell, fitted with a pH probe. The direct measurement of pH was successfully performed at temperatures >100 °C, addressing a significant gap in the current literature where pH values are rarely, if ever, carried out at in-process temperatures. This novel approach for measuring pH at high temperature has potential as a laboratory based analytical tool or as a critical control point during industrial high temperature processing.