Physical, functional, pasting and thermal properties of flours and starches of six Nigerian rice cultivars

Abstract

Physical, functional, pasting and thermal properties of flours and starches of six Nigerian rice cultivars (Faro 21, 40, 44, 46, 52, and 55) were investigated. Starches showed higher CIE L (96.37–99.81) value than flours (81.09–90.03). Water (122.64–143.35%) and oil (59.97–72.98%) absorption capacities varied significantly among the cultivars. Starch yield varied between 41.21 and 52.57%, with Faro 52 showing higher yield. Starch granules were small and polyhedral shaped, with average length and width of 5.37–9.25 and 3.94–6.94 μm, respectively. The Faro 40 (5.49) and Faro 55 (2.80) exhibited highest and lowest swelling power, respectively at 60 °C. The Faro 52 (2376.0 cP) and Faro 44 (3988.5 cP) flours showed highest and lowest peak viscosities, respectively. Amylose content of the rice starches varied from 20.68 (Faro 40) to 25.95 (Faro 55). Peak viscosity of starches (4893–6080 cP) was higher than flours, and increased in the order: Faro 52 < Faro 21 < Faro 40 < Faro 55 < Faro 44 < Faro 46. The FTIR spectroscopy of starches identified most of the α-1 → 4 glucosidic linkages within spectral absorption bands of 1149.55–1023.00 cm−1. Thermal properties of the rice starches ranged: gelatinization onset To (50.8–68.8 °C), gelatinization peak, Tp, (78.7–93.7 °C), glass transition temperature Tg (35.2–50.2 °C), gelatinization conclusion Tc, (116.4–127.6 °C), gelatinization enthalpy, ΔHG (7.58–17.35 J/g) and peak height index, ΔHG/(Tp − To) (0.26–1.64). This study provides knowledge for the utilization of flours and starches isolated from Nigerian rice cultivars that would be relevant for the postharvest value addition chain.