Effects of parboiling on the starch properties and in vitro digestibility of rice types with different amylose levels

Abstract

The objective of this study was to evaluate the influence of parboiling and polishing on rice grain quality, resistant starch formation, and in vitro digestibility of rice starch. The cultivars “Empasc 104,” “BRS Querência,” and “BRS Pampa” were selected for study based on their amylose content (AC), which ranged from low to high. The physical and chemical properties, viscosity profile, texture, resistant starch content, and in vitro starch digestibility of the different rice cultivars, whole grain or polished, parboiled or unparboiled, were evaluated. The type of processing (non-parboiled or parboiled) was positively correlated with the pasting temperature and chromaticity coordinate b* and negatively correlated with the paste properties: peak and trough viscosities, breakdown, setback, and final viscosity. The reassociation of starch molecules induced resistant starch formation and setback reduction in the “BRS Querência” and “BRS Pampa” grains. Among the cultivars, “BRS Pampa” (high AC) presented elevated resistant starch content and reduced starch digestibility, particularly following parboiling. On the other hand, the “Empasc 104” cultivar (low AC) exhibited the lowest resistant starch content. The highest digestibility was observed in the “BRS Querência” cultivar (intermediate AC). The in vitro digestibility of rice starch was found to be inversely associated with the lipid, ash, and dietary fiber content of the grain. Consequently, parboiling led to increased redness and yellowness values, as well as a modified viscosity profile resulting from partial starch gelatinization. The impact of parboiling on starch digestibility was multifaceted, exhibiting no discernible correlation among the various treatments.