Nutritional aspects of thermal and irradiation processing of peanut kernels and their oil

Abstract

Dry heating at 100°C or 120°C for up to an hour, autoclaving at 121°C for 30 min and exposure to γ-irradiation up to 800 krad could not secure complete inactivation of trypsin inhibitor activity (TIA) of peanut kernels. Roasting at 160°C for 1 h completely inactivated TIA. Either dry heating or moist heat increased the in-vitro digestibility of peanut protein as the temperature and/or time of heating increased. γ-irradiation increased protein digestibility with increasing irradiation dose up to 350 krad then gradually declined upon using higher doses. Increasing either the roasting temperature or exposure time achieved a slight decrease in acid value accompanied by an increase in peroxide value and a noticeable decrease in iodine value of peanut oil. Accordingly, optimum roasting procedure was found to be 140°C for not more than 30 min. Whereas autoclaving of peanut did not cause any marked changes in oil properties, γ-irradiation decreased the peroxide value without causing noticeable changes in iodine value. Successive heating of peanut oil at 180°C for up to 60 h caused a gradual increase in both refractive index and flow time. Although the peroxide value increased gradually during the first 8 h, it began to decrease thereafter. Also, a slight increase in acid value was noticed. Oxidized fatty acids increased with increasing heating time while iodine value gradually decreased at 180°C for up to 60 h.