Abstract
Small quantities of lipids accumulate in the white rice grains. These are grouped into non-starch lipid and starch lipid fractions that affect starch properties through association with starch. Lysophosphatidylcholine (LPC) and lysophosphatidylethanolamine (LPE) are two major lipid classes in the two fractions. Using high-oleic rice grains, we investigated the fatty-acid composition in flour and starch by LC-MS and evaluated its impact on starch properties. In the wild-type grain, nearly 50% of fatty acids in LPC and LPE were palmitic acid (C16:0), over 20% linoleic acid (C18:2) and less than 10% oleic acid (C18:1). In the high-oleic rice grain, C18:1 increased at the expense of C18:2 and C16:0. The compositional changes in starch lipids suggest that LPC and LPE are transported to an amyloplast with an origin from endoplasmic reticulum-derived PC and PE during endosperm development. The high-dissociation temperature of the amylose-lipid complex (ALC) and restricted starch swelling power in the high-oleic rice starch indicates that the stability of the ALC involving C18:1 is higher than that of C18:2 and C16:0. This study provides insight into the lipid deposition and starch properties of rice grains with optimized fatty-acid composition.
Highlights
Lipids comprise 1–4% of whole grain rice and most of it is concentrated in the bran and embryo while a small amount exists in the starch-rich endosperm
The genotype of the fatty acid desaturase 2 (FAD2)-1 RNA interference (RNAi) backcross population progenies was determined by PCR markers and single-grain total fatty acid (TFA) profiling
As no further segregation was observed in the F4 grains of D5-1, D5-5, D5-7 and D5-8, they were confirmed as a homozygous FAD2-1 down-regulation (FAD2DR) genotype and used for further analyses
Summary
Lipids comprise 1–4% of whole grain rice and most of it is concentrated in the bran and embryo while a small amount exists in the starch-rich endosperm. Total lipids extracted from rice bran consist of 84.9–86.0% triacylglycerols (TAGs), 6.5–6.7% phospholipids (PLs) and 4.2–4.6% free fatty acids (FFAs) [1]. The lipids found in the endosperm can be grouped into starch lipids and non-starch lipids, with the former located inside starch granules and the latter attached to their surface [2,3]. Non-starch lipids are mainly TAGs, PLs, and glycolipids, while starch lipids are mostly lysophospholipids (LPL), mainly lysophosphatidylcholine (LPC) and lysophosphatidylethanolamine (LPE) in addition to FFA [3,4]. LPC and LPE comprise up to 50% of the starch lipid [5]. Amylose is a component of starch with a linear long-chain polysaccharide made of α(1,4)-glucose units with sparse branches linked by the α(1,6)-glucose bonds
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