Identification and quantitation of lipophilic extractives from wheat straw

The chemical composition of four lipophilic extractives obtained by extraction 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 individual compounds in five simple lipophilic classes (free fatty and resin acids, sterols, waxes, steryl esters, and mono-, di-, and triglycerides) were identified and quantitated by GC on a medium-length capillary column. Structural characterization and thermal analysis of the extractives was carried 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, steryl 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 abundant saturated fatty acids were palmitic acid (C16:0, 6.51-9.52%), pentadecanoic 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 predominant compound identified in sterols. The major components in a class of waxes were determined to be palmitic acid palmity ester and palmitic acid oleyl ester. Five components, steryl laurate, steryl myristate, steryl palmitate, steryl heptadecanoate, and steryl oleate, were identified in a group of sterol esters. Of the triglycerides identified, tripalmitin, dipalmitoyl-oleoylglycrol, and triolein were found in all the extractives. In addition, minor amounts of resin acids (0.17-0.46%) and trace quantities of monoglycerides (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.