Distribution of unusual fatty acids in the mesocarp triacylglycerols of maturing sea buckthorn fruits

Abstract

The pattern of distribution of X-FAs among individual positional species of the X-triacylglycerols (X-TAGs) in the sea buckthorn (Hippophae rhamnoides L.) mesocarp oil by the 80th, 90th, and 105th day after pollination (DAP) was investigated. The X-FAs comprised oleic acid (O) as well as unusual FAs, viz. hexadecenoic (H), palmitolinoleic (Pl), and cis-vaccenic acid (V). During mesocarp growth, the number of X-TAG species decreased dramatically as a result of their metabolism, but their proportion in the total TAGs remained constant. H-TAGs predominating in the oil were similar to total TAGs in their composition and the pattern of their dynamics during maturation. As regards minor Pl-TAGs, there was a tendency for an increase in the level of species including palmitolinoleic acid in the middle (sn-2) position of their molecules. Throughout the entire process of fruit maturation, oleic acid was by 98.0–98.8% concentrated in the sn-2 position of O-TAGs. At the same time, cis-vaccenic acid, a Δ11-positional isomer of oleic acid, was predominantly incorporated in the side positions of V-TAGs, and its 98.1% concentration in these positions was achieved only by the 105th DAP. A virtually absolute selectivity of the distribution of oleic and cis-vaccenic acids in TAGs was found here for the first time. Discussed are the possible physicochemical and biochemical factors of a highly selective incorporation of these FAs in the sea buckthorn TAGs, the pathways of enzymatic biosynthesis of O- and V-TAGs, the metabolic role of discrimination of incorporation of some FA species in the glycerol residue of glycerolipids, and the causes for the disappearance of some TAG species during maturation.