EFFECT OF STEEPING PERIODS ON THE PHYSICO-CHEMICAL, PASTING AND PHYTOCHEMICAL PROPERTIES OF STARCH FROM TWO VARIETIES OF SORGHUM (RED AND WHITE)

Abstract

The effects of steeping periods on the physicochemical, pasting and phytochemical properties of starches from two varieties of sorghum (red and white) were investigated. Sorghum grains steeped for 6, 12, 18 and 24 h with water were processed into starch and sample from unsteeped sorghum served as control. The starch samples were evaluated for proximate composition, mineral composition, amylose content, functional properties, pasting properties and phytochemical components using standard procedure. Moisture content (8.47 to 13.75%), ash content (0.99 to 1.29%), crude fat (4.64 to 8.92%), crude protein (7.76 to 15.82%), fibre (1.05 to 1.63%) and carbohydrate (76.62 to 79.31%). All mineral investigated varied with cultivars and steeping time. Iron content was in the range of (0.87 to 1.29 mg/100 g), magnesium (2.79 to 4.19 mg/100 g), zinc (0.18 to 0.35 mg/100 g), sodium (4.53 to 8.19 mg/100 g), calcium (11.52 to 15.30 mg/100 g), potassium (3.21 to 9.00 mg/100 g) and phosphorous (3.10 to 5.34 mg/100 g). There was decrease in amylose content (23.60 to 18.97%) with increase in steeping time. Water absorption capacity was in the range of (1.71 to 2.81 g/g), oil absorption capacity (1.31 to 1.79 g/g), bulk density (0.61 to 0.75 g/cm3), swelling index (0.71 to 0.99 g/ml), least gelation (14 to 20%), foaming capacity (21.90 to 22.58%) and foaming stability (82.00 to 83.67%). The pasting characteristics varied with cultivars and steeping time. Peak viscosity was in the range of (111.56 to 170.30 RVU), trough (83.55 to 126.85 RVU), breakdown (16.27 to 46.85 RVU), final viscosity (128.21 to 248.55 RVU), setback (55.58 to 125.07 RVU), peak time (4.97 to 6.26 min) and pasting temperature (83.66 oC to 85.95 oC). Phytochemicals investigated varied with cultivars and increased steeping time. Hydrogen cyanide observed was in the range of (1.34 to 1.86 mg/kg), tannin (1.30 to 4.82 mg/g), saponin (6.10 to 13.05 mg/g), oxalate (0.43 to 0.90 mg/g), phytate (2.15 to 9.06 mg/g), cardiac glycoside (9.30 to 13.35 mg/g), terpenoid (13.50 to 18.99 mg/g) and alkaloid (34.10 to 50.31%). There was no significant difference between starches from the two cultivars of sorghum (red and white) in most of the parameters investigated. However, the differences observed in some results could be attributed to isolation method. Steeping of sorghum grains prior to processing into starch could effectively enhance nutritional attributes, functional and pasting properties of sorghum based foods. Mixture of two varieties (red and white) could find applications in food formulation. The effect of steeping on shelf stability on sorghum starch could be further investigated.