Curd-ripening evaluation by flow injection analysis of L-lactic acid with an electrochemical biocell during mozzarella cheese manufacture

A flow injection analysis procedure was used for the determination of L-lactic acid during the production of mozzarella cheese. The apparatus consists of an electrochemical flow-through wall-jet cell assembled with a platinum sensor covered with the immobilized lactate oxidase enzyme and connected to an amperometer. This system was used to monitor the concentration of L-lactic acid produced by lactose fermentation catalyzed by selected starters during cheese manufacture. Lactate was detected in the range (5 x 10(-6))-(1 x 10(-4)) mol/L with a detection limit of 2 x 10(-6) mol/L. L-Lactate has been measured in raw milk and during the manufacture of cow and water buffalo mozzarella cheese. The starter used was a commercially available strain of Streptococcus thermophilus. Real time analysis of lactate allowed a control of the curd-ripening evolution at different pasteurization temperatures of the milk. Values of lactic acid were compared with pH variation during the process. This method proved to be more sensitive than the pH measurement procedure for the control of the continuous production of lactic acid particularly near the ''stretching point'' when very slight pH variations were observed.