Retention of Lysine in Foods Processed with Microwave and Conventional Heating

The effect of moist and dry heat processing on lysine content of selected foods was investigated. Two moist heat (open and closed vessel) and dry heat (microwave and hot air oven) methods were chosen for processing samples from cereal, oilseed and pulse groups with whey protein concentrate as reference sample. Unheated samples served as controls. The samples were analysed for protein content, available lysine by fluorodinitrobenzene method and for in vitro protein digestibility (IVPD). Results indicated that in moist heat-treated samples lysine retention was between 69 -83%. Dry heat treatment resulted in a greater loss of lysine, which was proportional to the degree of heating. The retention of lysine in dry heat-treated samples ranged from 31 to 65%. All heated samples had higher digestibility than their raw controls. In between methods of heating, the IVPD of dry heat-treated samples were slightly lower than moist heat-treated samples. It can be concluded that heat treatments increase the in vitro digestibility of proteins but lysine content was affected adversely.