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 apparatu s consists of an electrochemical flow-through wall-jet cell assembled with a platinum sensor covered with the immobilized lactate oxidase en zyme and connected to an amperometer. This system was used to monitor the concentration of L-lactic acid produced by lactose fermentation ca talyzed by selected starters during cheese manufacture. Lactate was de tected in the range (5 x 10(-6))-(1 x 10(-4)) mol/L with a detection l imit 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 the rmophilus. Real time analysis of lactate allowed a control of the curd -ripening evolution at different pasteurization temperatures of the mi lk. Values of lactic acid were compared with pH variation during the p rocess. This method proved to be more sensitive than the pH measuremen t procedure for the control of the continuous production of lactic aci d particularly near the ''stretching point'' when very slight pH varia tions were observed.