Comparative study of the nutritive value of casein heated by microwave and conventionally

Abstract The objective of this study was to compare the net protein utilisation, digestibility and biological value of casein solution heated by microwave or conventionally, ie on an electrically heated plate. Portions (500 ml) of an aqueous solution of casein (100 g litre−1) were heated to a temperature of 80°C and subsequently kept at 80± 5°C for 2 min. The heating times of microwave and conventional heating were the same. Additional portions were subjected to a so‐called abused treatment consisting of repeating the normal microwave or conventional heat treatment three times. Next, the nutritive value of heated and unheated casein was determined in a 10‐day feeding study with Wistar rats. The net protein utilisation, digestibility and biological value of unheated casein were 61.1, 100 and 61%, respectively. Comparable values were obtained for casein heated by microwave or conventionally. These results did not therefore indicate any decrease in nutritive quality of the protein by microwave heating or conventional heating under simulated household conditions.