Abstract
Eight commonly cultivated and consumed rice varieties of Northern Himalayan regions and a popular high amylose rice variety were characterized at Wx locus and evaluated for resistant starch (RS), in-vitro starch digestibility, predicted glycemic index (pGI), glycemic load (GL) and textural parameters. Cytosine and thymine repeats (CT)n at waxy locus (Wx) showed high association with apparent amylose content (AAC). Both pGI and GL varied substantially within the selected varieties. The pGI was relatively lower in high and intermediate amylose Indica varieties compared to low amylose Japonica ones. However, Koshikari despite being a low amylose variety showed relatively lower pGI and GL, due to its higher RS, dietary fiber, protein and fat content. It was thus presumed that in addition to AAC, RS and other grain components also affect the glycemic response. Inherent resistance to enzymatic hydrolysis was also found to be higher in firm textured and less sticky rice varieties. The genotypes—Lalat, Basmati-1509 and Koshikari, in view of their low to moderate pGI and relatively higher RS content, can be explored in future breeding programmes to develop rice varieties whose consumption will help to prevent hyper/hypo glycemic responses in Northern Himalayan regions, where daily staple diet is rice.
Highlights
The prevalence of type II diabetes is rapidly increasing in all the parts of the world with most severe implications on the low- and middle-income c ommunities[1,2]
As per the classification given by Juliano[26], the Indica varieties namelyShalimar Rice-2, Basmati-1509, China-1007, Chenab, and Jhelum were classified as intermediate amylose type, Lalat as high amylose variety, whereas Japonica varieties—SKUA-402, Koshikari and K-332 were classified as low amylose type
As per WHO39 classification, SR-2, China-1007, Chenab, Jhelum, SKUA-402 and K-332 were classified as high glycemic index (GI) varieties (GI ≥ 70); Basmati-1509 and Koshikari as medium GI varieties (GI = 56–69) and Lalat as low GI variety (GI ≤ 55), All the medium slender, long bold and short bold varieties elicited high GI scores which is in accordance with the results reported by Prasad et al.[15] for popular Indian rice varieties
Summary
The prevalence of type II diabetes is rapidly increasing in all the parts of the world with most severe implications on the low- and middle-income c ommunities[1,2]. Several cohort studies have reported that consumption of more than 300 g/day of white rice increases the risk of type II diabetes by 78%6. There is a scope to screen the commonly consumed rice varieties of Northern Highland Himalayan regions for Wx allele characterization, in-vitro starch digestibility and glycemic index. To the best of our knowledge, rice varieties grown in Northern Highland Himalayan regions have not been tested so far for Wx allele characterization, in-vitro starch digestibility and glycemic index. The present study was conducted with an aim to characterize eight rice varieties commonly cultivated and consumed in Northern Highland Himalayan regions, at waxy locus (Wx) using RM190 and to study the association of amylose content with inherent allelic variation, in-vitro starch digestibility, predicted glycemic index, glycemic load and textural parameters in selected rice varieties
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