Enzymatic hydrolysis method for development of low glycemic index rice flour from temperate grown rice (var. Jehlum): Numerical optimization, rheological and spectroscopic characteristics

This study aimed at optimizing process protocols for development of low glycemic index (GI) rice flour (LGIRF) by employing enzymatic hydrolysis method using central composite rotatable design (CCRD). LGIRF was evaluated for pasting, farinographic, spectroscopic and microbiological attributes. Independent variables for optimization included concentrations of α-amylase (0.02–0.12 %), glucoamylase (0.02–0.24 %), as well as the incubation temperature (55–80°C). Resistant starch (RS), glycemic index (GI) and glycemic load (GL) were investigated as response variables. The optimum conditions for development of LGIRF with better quality were- α-amylase concentration of 0.040 %, glucoamylase concentration of 0.070 % and an incubation temperature of 60 °C. The results of mineral analysis revealed significantly (p < 0.05) lower levels of boron, potassium, zinc, phosphorus, magnesium, and manganese in LGIRF, while iron and copper were significantly higher. The viscosity profile as evident from pasting profile and farinographic characteristics of LGIRF were significantly (p < 0.05) lower than native rice flour. ¹H NMR and ¹³C NMR spectroscopic studies showed an increase in flexible starch segments and a decrease in amorphous portion of starch LGIRF, along with chemical shift alterations in carbons 1 and 4. Free fatty acids and total plate count were significantly (p < 0.05) higher in LGIRF although was within limits.