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Comparison of Lipid Content and Fatty Acid Composition and Their Distribution within Seeds of 5 Small Grain Species



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 to 36.64 compared with 12.15 to 15.61) and lower % of C18:2 (35.69 to 45.44 compared with 50.79 to 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 2 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 pearled kernels. 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.

Practical Application:  This study was the first to document fatty acid distribution across a grain seed. Results provide 2 major reasons for improved oxidative stability of pearled grains: reduced oil content and shift of fatty acids toward more saturated and less unsaturated composition.