Cooking, sensory and in-vitro digestibility characteristics of rice as affected by rice-water ratio and karaya gum concentration

Cooked rice has high starch digestibility. Prolonged and excess consumption of polished rice has been associated with the incidence of diabetes amongst rice eating populations. Therefore, researchers are working on extensively to devise strategies that could retard digestion of cooked rice. Keeping this fact into consideration, four rice cultivars (SR-4, K-39, Mushq Budij and Zhag) grown in Kashmir were milled and cooked with varying concentrations (0, 2.5 and 5.0% w/w, rice basis) of karaya gum at different rice-water ratios (1:10 and 1:1.8). The prepared rice samples were evaluated for cooking and sensory properties, in-vitro digestibility and structural characteristics. Cooking of rice with karaya gum (2.5–5.0%) at large rice-water ratio (1:10) increased minimum cooking time (19.0–25.0 min) and water uptake ratio (3.23–4.69) of samples. Also, rice cooked in excess water had better sensory acceptability scores than those cooked in less water. At large rice-water ratio, Zhag rice prepared with karaya gum (2.5%) had acceptable hardness and flavour scores. With increase in gum concentration, the equilibrium starch hydrolysis percentage (C_∞) and estimated glycemic index (eGI) scores of cooked rice decreased, irrespective of cultivars and rice-water ratio. Maximum reduction in C_∞ was observed for Mushq Budij rice (85.20%) prepared with karaya gum (5.0%) at large rice-water ratio (1:10). Fourier transform infrared spectra of gum cooked rice samples revealed shifting of peak at 3250.0 cm⁻¹ to higher intensities indicating hydrogen bonding interaction of starch and gum. From X-ray diffraction studies, the highest relative crystallinity (16.20%) was observed for rice prepared with 5.0% gum concentration. Therefore, cooking of rice with karaya gum at large rice–water ratio can be considered to slow down starch hydrolysis process of cooked rice.