Identification and quantitation of lipophilic extractives from wheat straw

The chemical composition of four lipophilic extractives obtained by extract ion with toluene-ethanol (2/1, v/v), toluene-ethanol-methanol (1/1/1, v/v/v ), methyl tert-butyl ether, and chloroform-methanol (2/1,v/v) for 6 h in a Soxhlet extractor, respectively, from wheat straw, has been examined. The i ndividual compounds in five simple lipophilic classes (free fatty and resin acids, sterols, waxes, steryl esters, and mono-, di-, and triglycerides) w ere identified and quantitated by GC on a medium-length capillary column. S tructural characterization and thermal analysis of the extractives was carr ied out by using FTIR, H-1 and C-13 NMR spectroscopy, TGA and DSC analysis. The main groups identified included free fatty acids, sterols, waxes, ster yl esters, and triglycerides, comprising 51.89-72% of the total extractives . Azelaic and maleic acids, ash or salts, and co-extracted polysaccharides consisted of the major non-lipid components together with minor amounts of phenolic compounds (0.48-0.65%). Over all the free fatty acids, the most ab undant saturated fatty acids were palmitic acid (C16:0, 6.51-9.52%), pentad ecanoic acid (C15:0, 5.40-11.00%), and myristic acid (C14:0, 3.91-14.42%), while linoleic acid (C18:2) and/or oleic acid (C18:1, 1.28-2.16%) were the most abundant unsaturated free fatty acids, beta -Sitosterol was a predomin ant compound identified in sterols. The major components in a class of waxe s were determined to be palmitic acid palmity eater and palmitic acid oleyl ester. Five components, steryl laurate, steryl myristate, steryl palmitate , steryl heptadecanoate, and steryl oleate, were identified in a group of s terol esters. Of the triglycerides identified, tripalmitin, dipalmitoyl-ole oylglycrol, and triolein were found in all the extractives. In addition, mi nor amounts of resin acids (0.17-0.46%) and trace quantities of monoglyceri des (0.05-0.10%) and diglycerides (0.10-0.16%) were also determined in the extractives. (C) 2001 Elsevier Science B.V. All rights reserved.