Starches in Rice: Effects of Rice Variety and Processing/Cooking Methods on Their Glycemic Index

Abstract

Rice is a fundamental food source for more than fifty percent of the world's population, significantly contributing to human nutrition and food security. Like other cereal grains, rice is rich in starch, although it also contains protein, vitamins, and minerals. Regular consumption of white rice has been reported to be positively associated with the increased risk of type 2 diabetes in rice-consuming countries due to the high glycemic index (GI) of white rice. However, the nutritional value and health effects of rice differ markedly depending on the variety and are influenced by processing methods, cooking styles employed, and the presence of other food components/ingredients. Therefore, this review examines the chemical compositions, starch structures, and glycemic indices of different rice types and the impact of processing techniques and genetic mutation on starch's structure, amylose content, and GI. The interactions between rice starch and other food components, such as proteins, lipids, dietary fibers, and polyphenols, and their impact on the digestibility and GI of rice starch are also discussed. The purpose of this comprehensive review is to elucidate the strategies that can improve the nutritional advantages of rice and mitigate health issues, such as obesity, diabetes, and inflammation, linked to the long-term consumption of rice.

Keywords: cooking methods; gene mutation; glycemic index; rice processing; rice types; starch composition; starch structure; starch–ingredient interaction.

Figure 1

Molecular structure of amylose and amylopectin.

Figure 2

Representative types of rice. White, brown, and black rice fall into the groups Japonica and Indica. The red rice belongs to Indica due to its non-sticky nature. The glutinous rice was placed into the Japonica group due to its low amylose content and sticky nature.

Figure 3

Granular structures of native rice starches from different rice varieties or cultivars to show the amylose/amylopectin ratios.

Figure 4

Proposed mutation in rice plant genes by reducing SIIIa and BEIIb levels and forming high RS rice genotypes with low GI. AGPase (ADP-glucose pyrophosphorylase) and GBSSI (granule-bound starch synthase I) play important roles in the formation of amylose and amylopectin synthesis enzymes, including AGPase (ADP-glucose pyrophosphorylase), (SSs) starch synthases, (BEs) branching enzymes, (DBEs), (SSIIIa) debranching enzymes, and starch synthase IIIa (a major isoform of SSIII). Through mutation in plant genes, amylose content increases with increasing AGPase and GBSSI enzymes while decreasing the large branching of amylopectin by reducing the starch synthase IIIa and branching enzymes (DBEs).

Figure 5

Schematic diagram of the impact of different processing methods on the starch properties and glycemic index of rice starches. Blue color revealed starch granule and layer structure. The green color indicated starch crystal structure, while amylose appeared in a sea green color and amylopectin was represented in a dark pink color.