Effect of irradiation, with and without cooking of maize and kidney bean flours, on porridge viscosity and in vitro starch digestibility

African traditional weaning foods are usually prepared from starchy flours at a total solids content of 50-100gl(-1), giving a viscosity of 1000-3000cP which is consumable by infants. These porridges have very low energy and nutrient densities. Processing to reduce the porridge viscosity and improve the energy and nutrient density may help in solving this problem. Maize, kidney bean and their 70:30 composite flours were irradiated at 0-10kGy at room temperature. Irradiation greatly reduced the viscosity of porridges, probably by starch depolymerisation. Irradiation improved the starch digestibility of raw bean flours, possibly either by inhibiting alpha -amylase inhibitors or by weakening the thick cell walls that enclose the starch granules, thus improving accessibility to enzymes. However, in raw maize, cooked maize and cooked bean flours there was maximum starch digestibility at a dose of 2.5kGy, followed by small but significant decreases in starch digestibility at higher doses, more so in maize than in bean flours. The decrease in digestibility could be due to the formation of inhibitors of amylolytic enzymes (Maillard reactions products) or to the formation of resistant starch. Irradiation doses required to increase the total solids content of traditional maize and/or bean-based weaning porridges to at least 200gl(-1) do not compromise starch digestibility significantly. (C) 2001 Society of Chemical Industry.