Comparison of lipid content and fatty acid composition and their distribution within seeds of 5 small grain species

Authors: Liu, Keshun

Submitted to: Journal of Food Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/23/2010
Publication Date: 2/5/2011
Citation: Liu, K. 2011. Comparison of lipid content and fatty acid composition and their distribution within seeds of 5 small grain species. Journal of Food Science. 76(2):C334-C342.

Interpretive Summary: For the majority of the world population, cereal-based foods constitute the most important source of energy and nutrients. Because of heterogeneous distribution of nutrients throughout a seed, several processing methods, such as roll milling, de-germinating, and pearling, have been used to remove germ and/or outer layers of cereal grains. The processes reduce undesirable components while improve certain characteristics of remaining kernels. Equally important is that germ and bran fractions removed from grains generally have special end-use values. Compared to starch and protein, the content of lipids in most cereals is relatively low (about 3%). Their contribution toward the nutritional value as well as storage stability of cereal-based food or feed, however, is important. Therefore, various studies have been carried out to document the content and fatty acid composition of lipids in whole as well as several structural parts of grains. However, research on distribution of lipid content across a cereal seed has been limited, while none has reported on distribution of fatty acid composition within a cereal grain. The objective of this study was to meet this need by comparing lipid content, fatty acid composition and their distribution patterns within a seed among grain species. Comparison is necessary among grains simply because the distribution of lipids among structural parts is known to vary with grain species. Thus, distribution patterns in the content and fatty acid composition of lipids within a seed are expected to be different among grain species. Such information would be valuable for those who study or use cereals grains or materials made of them for improving nutritional values, storage stability, or general quality. The significance of the present study lies in that it was the first time to provide information about lipid and fatty acid distributions within a kernel of 5 small grain species (barley, oats, rice, sorghum and wheat). Results show that from outer surface to inner core of seeds, the content and fatty acid composition of lipids varied. In general, oil content decreased, while C16:0 and C18:0 increased, C18:1 and C18:3 decreased, and C18:2 changed slightly. This new finding points out two reasons of improved oxidative stability for pearled kernels: reduced oil content and shifting fatty acids toward more saturated and less unsaturated composition.

Technical Abstract: Barley, oats, rice, sorghum, and wheat, each with two genotypes, were sequentially abraded by an electric seed scarifier. The pearling fines (PF) and pearled kernels (PK) at each cycle were analyzed for lipid (mostly nonpolar) content and fatty acid (FA)composition. The oil content in whole or dehulled grains ranged from 2.18% of a wheat variety to 6.38% of an oat line. Compared with barley and wheat, rice, oat and sorghum had higher relative % of C18:1 (31.60-36.64 compared with 12.15-15.61) and lower % of C18:2 (35.69-45.44 compared with 50.79-61.50). The relationship between oil content in PF and the cumulative level of surface removal essentially describes the distribution pattern of oil content within a seed. Barley, rice, and sorghum had a similar distribution pattern, characterized by a rapid rate of decreasing for the first few outer layers and then by gradual decrease to a flat value toward the inner core. In contrast, distribution within oats was characterized by a gradual reduction in oil content across the seed. The distribution of oil within wheat fell between the former two types. For all 10 grains, from seed surface to inner core, C16:0 and C18:0 increased, C18:1 and C18:3 decreased, and C18:2 changed slightly, providing a new reason for improved oxidative stability for PK. The differences in the changing intensity of FA composition among grain species correspond to those in oil distribution within a seed, while varietal difference in distribution patterns of content and FA composition of lipids within a species was insignificant.