Influence of amylose content on phenolics fortification of different rice varieties with butterfly pea (Clitoria ternatea) flower extract through parboiling

Abstract

Milled rice of different rice varieties (waxy, low-, and high-amylose) were evaluated on the impacts of amylose content on phenolic fortification with butterfly pea extract through parboiling. The total flavonoid content (TFC), total phenolic content (TPC), antioxidant activities, histology, microstructure, and physiochemical properties of the fortified rice were compared with positive (parboiled rice) and negative (raw rice) controls. TFC, TPC and antioxidant activities of all rice varieties significantly reduced with parboil treatment and restored when fortified with butterfly pea extract. Increment of TFC, TPC and antioxidant activities showed strong negative Pearson correlation with amylose content (r = −0.839 to −0.996, p < 0.05). The microstructure of the parboiled and fortified rice grains revealed apparent porous structure with reduction in amylose content suggesting the role of amylopectin in the uptake of flavonoid compounds. The fixation of phenolic compounds due to gelatinization was apparent in FTIR spectra at 3400-3200 cm−1 which demonstrate dependency on amylose content. Amylose content negatively influenced reduction of bulk density and cooking time, as well as increment of water absorption capacity of rice grain and hardness of the cooked rice due to parboiling treatment. In conclusion, low amylose milled rice is recommended for maximum phenolic fortification via parboiling method.