Molecular Plant Breeding 2016, Vol.7, No.30, 1
-
6
1
Review Article
Open
Access
An Insight into the Glycemic Index of Rice
Tripathy Swapan K.
1
, Maharana M.
1
, Ithape Dinesh M.
1
, Mohanty M.R.
2
,
Dash Asit P.
3
, Reshmi Raj K.R.
3
, Ganik N.
3
, Panda S.
4
1 Department of Agricultural Biotechnology, College of Agriculture, OUAT, Bhubaneswar, India
2 Rice Research Station,OUAT, Jeypore, Odisha, India
3 Department of Plant Breeding and Genetics, College of Agriculture, OUAT, Bhubaneswar, India
4 Regional Research Station, Central Zone, OUAT, Bhubaneswar, India
Corresponding author
Molecular Plant Breeding, 2016, Vol.7, No.30 doi
Received: 02 Jun., 2016
Accepted: 14 Jul., 2016
Published: 12 Aug., 2016
Copyright © 2016
Matin et al., This is an open access article published under the terms of the Creative Commons Attribution License, which permits
unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Preferred citation for this article
:
Tripathy S.K., Maharana M., Ithape D.M., Mohanty M.R., Dash A.P., Reshmi R.K.R.A., Ganik N., and Panda S., 2016, An Insight into the Glycemic Index of
Rice, 7(30): 1-6 (doi
Abstract
Glycemic index of rice is a highly complex trait. Rice varieties possessing slowly digestible starch (high amylose) are
potentially characterized to have low glycemic index and can be useful for management of type II diabetes. Understanding genetic
mechanisms underlying starch biosynthesis and metabolism of cooked rice can pave the way for developing efficient breeding and
selection strategy for combining high grain yield with low glycemic index. In this context, reverse genetics can prove useful.
Available rice genome sequence information encoding key enzymes involved in biosynthesis of amylose component of starch can
unravel novel alleles involving single nucleotide polymorphisms (SNPs). A multi-allelic waxygene (Wx) encoding Granule-Bound
Starch Synthase I (GBSS I) enzyme is known to determine amylose content in rice endosperm. Potential molecular markers are now
available to detect GBSS I alleles (SNPs) associated with five classes of amylose (waxy: 0
–
5%, very low: 5
–
12%, low: 12
–
20%,
intermediate: 20
–
25%, and high:25
–
33%). These can be routinely used to assist breeding programme. Besides, the presence of
intra-class variations in amylose content could be attributed to additional regulatory elements or environmental conditions.
Keywords
Glycemic index; amylose content; waxy gene; single nucleotide polymorphisms (SNPs)
Introduction
Rice is the staple food which serves as the chief source of dietary carbohydrates for more than 85% Indian
population. Regular consumption of rice increases the risk of developing type II diabetes due to increased blood
glucose level (Barclay et al., 2008). By 2030, about 330 million people all over the world are expected to be
affected by diabetes and India is certain to have the greatest increase. In India, there are nearly 50 million
diabetics, according to the statistics of the International Diabetes Federation. Presently, nearly one million Indians
die due to diabetes every year. Maintenance of blood glucose level is required for normal brain function. Its build
up
≥
3.3 mmol/l in the blood stimulates brain to signal pancreas for secretion of more insulin to convert excess
sugar into stored fat (Thorens, 2011). But, patients suffering from diabetes fail to secrete required amount of
insulin making them more vulnerable to the dreadful diabetic problems. In this context, brown rice proved to be
protective but not preferred by most consumers for its shorter shelf-life, longer cooking time and unappealing
taste and texture (Zhang et al. 2010). Individuals served with cooked brown rice twice in a week, can reduce their
chances of developing type II diabetes by up to 11%. On the other hand, consumption of white sticky rices
(polished rice) stimulates adverse metabolic affectand increases the risk of acquired blindness, renal failure, colon
cancer and cardiovascular diseases. Therefore, these are unsuitable in a healthy diet.
1 Amylose Content and Glycemic Index (GI)
Carbohydrate component of food is an essential part of our daily nutrition. It serves as the prime source of energy.
Carbohydrate stored in endosperm of rice seed is in form of starch (80-90%). This is made of two polysaccharides
(glucan polymers) i.e., linear amylose and branched amylopectin. Amylose is hard to digest compared with
amylopectin. Therefore, percentage of amylose in total starch, measured as Apparent Amylose Content (AAC), is
the key determinant of rice cooking properties. Based on amylose content, rice varieties are classified as waxy
