INACTIVATION OF LACTOCOCCUS-LACTIS SSP LACTIS C2 AND ALKALINE-PHOSPHATASE DURING SPRAY-DRYING

Bacteria dispersed in condensed skim milk were spray dried using five different outlet-air temperatures. Powder samples were analyzed for survival and lactic acid production. Inactivation resulted from dehydration, and exposure to heat during drying. A mathematical model of thermal inactivation of alkaline phosphatase was used to analyze thermal inactivation of the bacteria during drying. Most thermal inactivation was predicted to occur in a critical period of 10 to 20 ms and 70% to 85% solids content. In the absence of relevant experimental data, a procedure was proposed for an order-of-magnitude estimate of overall inactivation to candidate bacteria during spray drying. It utilized predictions of thermal inactivation from the model, pasteurization data from the literature, and estimates of dehydration inactivation from survival after freezing and freeze drying.