PHYSICOCHEMICAL PROPERTIES, IN-VITRO STARCH AND PROTEIN DIGESTIBILITY AND SENSORY ACCEPTABILITY OF MILLET-SOYBEAN SNACK

Abstract

The physicochemical properties, in-vitro starch and protein digestibility, sensory acceptability and storage life stability of home-processed millet and soybean snack were investigated in this research. Pearl millet (Pennisetum glaucum) and soybean (Glycine max) were processed into flour and the flours were composited into blends in the following ratios: 90/10, 80/20, 70/30, 60/40, and 50/50 (millet/soybean; w/w). The 100% millet flour was used as the control. The various flour blends were used for the preparation of snacks using an appropriate ingredient formulation ratio. The protein content of the blends increased steadily with increasing content of soybean flour (15.88% in 90:10 to 20.89% in 50:50) while carbohydrate decreased (64.82% in 90:10 to 51.86% in 50:50). Water absorption capacity of flour blends showed that the control sample had the highest value (7.8%) while the 90:10 ratio had the lowest (4.4%). Particle size distribution of the flour blends showed the mean mass size of the flour ratios to be between 309.65 μm and 504.21 μm. Bulk density of snack showed a progressive increase from 0.58 g/ml in the 100:0 ratio to 0.74 g/ml in the 50:50 ratio of snack sample. Hardness of snack increased with increasing content of soybean flour (0.66 Nm2 – 2.56 Nm2). The result of anti-nutritional factors showed that trypsin inhibitor, tannin and heamaglutinin increased progressively from 100:0 ratio of snack sample to 50:50 ratio (53.55 TIU/mg – 60.26 TIU/mg; 18.63 mg/g – 30.35 mg/g and 35.25 HU/mg – 37.92 HU/mg respectively). The in-vitro starch digestibility of the snack showed digestibility to be decreasing with increasing content of soybean flour (0.28 mg/g in 100:0 to 0.10 mg/g in 50:50 ratio) while the in-vitro protein digestibility increased with an increase in soybean flour content (0.15 mg/g in 100:0 to 0.41 mg/g in 50:50). Snack made from 100% millet flour was more generally accepted in the sensory evaluation than those made from the various blends (p<0.05) because it was scored the highest in all the sensory attributes of taste, texture, flavour, appearance and overall acceptability. Storage stability study (10 days) of the snack showed that thiobarbituric acid value (0.003 TBA/g - 0.029 TBA/g), acid value (0.76 meq/g - 3.22 meq/g) and peroxide value (0.26 mgKOH/g - 0.85 mgKOH/g) increased as the period of storage increased for all the snack samples while there was a decrease in the values as soybean ratio increased. The storage stability of the snacks was assessed to be acceptable for all snack samples up to a period of 10days. It may be concluded that although the snack from 100% millet flour had the highest sensory scoring in terms of most sensory qualities; yet, the snack containing 50:50 formulation of millet-soybean exhibited the highest protein digestibility (0.41 mg/g) and moderate oiliness index (6.9 cm).