Effect of parboiling methods on the physicochemical characteristics and glycemic index of rice varieties

Abstract

The effect of open steaming (HS) and pressure (PP) parboiling on the physicochemical characteristics and glycemic index (GI) of five different Indian rice varieties with varying amylose contents was investigated. Results showed that the severity of processing had a significant effect on the physicochemical properties of rice. PP resulted in reduced whiteness (18.83 ± 0.66 to 26.03 ± 1.27%), increased transparency (1.64 ± 0.05 to 2.05 ± 0.08%), hardness (6.66 ± 0.63 to 7.82 ± 1.19 kg) and equilibrium moisture content (117.59 ± 11.37 to 183.69 ± 39.46%db). PP rice also showed higher cooking time (40.28 ± 0.35 to 59.31 ± 0.69 min), water absorption ratio (4.52 ± 0.06 to 5.23 ± 0.04), and sedimentation volume than HS and non-parboiled counterparts. An increase in parboiling temperature significantly affected the pasting profiles of rice flour. Among the treated samples, the degree of gelatinization was higher for PP rice (70.80 ± 6.83 – 85.24 ± 1.48%). Alkali spreading value explained the lower gelatinization temperature for parboiled rice as compared with the non-parboiled counterpart. Higher amylose content of rice was associated with lower GI values and parboiled rice had a significantly lesser GI. The findings of this study provide insights on rice parboiling methods, particularly for the diabetic population.