Impact of parboiling on nutritionally important starch fractions, pasting properties, and in vitro starch digestibility of rice genotypes

In the present study, comparative evaluation of parboiled and non-parboiled rice genotypes was carried out to assess the variability in grain color, amylose content, nutritionally important starch fractions, and pasting properties along with in vitro starch and protein digestibility. The parboiling process involved steaming of paddy, followed by soaking overnight, and again steaming for a short duration to achieve the desired gelatinization of starch granules. Parboiling decreased the whiteness (~ 1.16-fold) of milled rice, while the amylose content was unaffected. Total starch (TS) and rapidly digestible starch decreased significantly by ~ 1.04- and 1.08-folds (P ≤ 0.05), respectively, while a significant increase of ~ 1.11- and 1.18-folds was observed in slowly digestible starch and resistant starch, respectively. In vitro starch digestibility and predicted glycemic index of parboiled rice decreased significantly. The pasting temperature increased significantly (~ 1.14-fold) with parboiling, while peak viscosity (1.96-fold), breakdown viscosity (3.59-fold), and final viscosity (~ 1.83-fold) decreased due to parboiling. The in vitro protein digestibility of parboiled rice also decreased significantly (~ 1.14-fold) after parboiling. It is therefore concluded that parboiling is a good alternative to conserve and increase nutritional and processing quality of rice.