Effect of roasting on the nutritional quality of finger millet

Abstract

Samples of finger millet (Eleucine coracana) Seremi 2 variety were roasted with and without conditioning. Roasting was done at 70, 80, 90 and 100 0 C for 4, 5, 7 and 9 minutes. The control was unroasted millet. The roasted millet samples were milled into flour and porridge prepared. Proximate composition, Viscosity, in vitro protein digestibility and mineral extractability of flours and the porridge were determined. Protein, carbohydrate, fibre, ash, calcium, iron, were done before and after treatment so as to determine the effect of the treatment on proximate composition of finger millet. Proximate composition also helped in calculation of protein digestibility and mineral extractability. In vitro protein digestibility was determined by the pepsin method of Hamaker et al as described by Duodu (2000). This was done to simulate digestibility of protein by pepsin in humans so as to determine the degree of digestion of the treated millet hence answering objective three of the research. Mineral content i.e., calcium was determined using flame photometer, iron using atomic absorption spectrophotometer and extractability on the other hand was determined by the HCl method as described by Mbithi-Mwikya et al., (2000). Viscosity was determined using a method described by Mbithi- Mwikya with some modification using a viscometer. It was important to determine viscosity because viscosity has a bearing on energy intake. Highly viscous foods have low energy while food of low viscosity has more nutrients. It was thus imperative to determine viscosity in the millet porridge since porridges are most weaning foods The in vitro protein digestibility and mineral extractability in this study increased with increases in roasting time and temperature. The digestibility increased by 18 % - 48 % and 65 % - 66 % in uncooked unconditioned and conditioned roasted finger millet respectively. Porridge viscosity decreased with increasing roasting time and temperature. Viscosity decreased by 47 % – 70 % and 51 % - 71 % in conditioned and unconditioned roasted finger millet respectively. Iron extractability increased by 48 % - 55 % and 50 % - 55 % in conditioned and unconditioned roasted finger millet respectively. Calcium extractability increased by 8.8 % to 12 % and 5.7 % to 7.1 % in conditioned and unconditioned roasted finger millet respectively. Roasting did not affect the proximate composition (P<0.05). Conditioning did not influence the effect of roasting on protein digestibility, mineral extractability and viscosity (P> 0.05) The results indicate that roasting is a technology that can be used to improve the energy density and nutrient availability from millet and can be potentially used at industrial scale.