THE EFFECT OF HEAT TREATMENT OF MILK UPON THE HYDROLYZABILITY OF LACTOSE BY THE ENZYME LACTASE1

Abstract

Heat treated, condensed skimmilk and nonfat dry milk (NDM) were treated with lactase enzyme obtained from Saccharomyces fragilis. The effect of heat treatment on lactose hydrolysis was determined. Forewarming treatments of 62.8, 68.3, 73.9, 79.5, and 85.0 C resulted in 17, 17, 100, 59, and 156 g, respectively, of lactose hydrolyzed. Concentrates with forewarming treatments of 62.8, 73.9, and 85.0 C for 30 min were given additional heat treatments of 62.8, 73.9, or 85.0 C for 20 min. Activity was lower in all concentrates given the double heat treatment, except those heated at 85.0 C for 20 min after forewarming at 62.8 and 73.9 C. These showed a substantial increase in lactose hydrolysis. Portions of each concentrate, spray dried and reconstituted to 30% total solids, exhibited the same effect on lactose hydrolysis as the original concentrates.Additional studies were conducted with whey and a 5% lactose plus milk salt solution. Results indicated that heating lactose in the presence of milk protein had a great effect on lactose hydrolysis.