Parboiling of pigmented and non-pigmented Philippine rice (Oryza sativa L.) cultivars: Textural properties and carbohydrate quality

Abstract

Parboiling improves rice carbohydrate quality, which is beneficial for diabetes management in Asia. However, parboiling drastically alters cooked rice texture, making it unappealing for Filipinos, who generally prefer tender cooked rice. The present work evaluated the carbohydrate quality and cooked rice hardness of nine local pigmented and non-pigmented rice varieties as affected by parboiling and cooking treatments. The amylose content (AC), retrogradation potential (RP), and resistant starch (RS) content were determined, and the samples with the highest RS were further investigated for their thermal properties and starch morphology. Results showed that parboiling increased RS level by as much as five-fold, particularly in the red rice Minaangan, which had intermediate AC and the highest RP (2,822 cP) among the samples. The highest RS, 2.71 ± 0.02 g/100 g, was recorded in parboiled NSIC Rc 222 cooked at 1:2.5 (rice:water). It also produced soft cooked rice, which was significantly better than its non-parboiled counterpart. High proportion of water needed to gelatinise parboiled non-pigmented NSIC Rc 222 was due to higher starch crystallinity as indicated by its gelatinisation enthalpy and intact starch granule. In conclusion, parboiling and cooking at appropriate rice:water ratio of NSIC Rc222 and Minaangan could deliver healthier cooked rice with Filipino preferred textural quality.