Extraction and characterization of lipophilic extractives from wheat straw. I. Chemical composition

Wheat straw was sequentially extracted with hexane at 70degrees, hexane-chloroform (5/1, v/v) at 60degrees, chloroform at 55, diethyl ether-acetic acid (98/2, v/v) at 30degrees, and methyl tert-butyl ether at 501 for 2 h, respectively. The chemical composition of five lipid classes (free fatty/resin acids, sterols, waxes, sterol esters, and triglycerides) and minor phenolic compounds in the five lipophilic extractives were identified using GC and RPLC. Palmitic acid (C16:0) and myristic acid (C14:0), were found to be the most abundant saturated free fatty acids. while the palmitoleic acid (C16:1) and linoleic acid (C18:2)/oleic acid (C18:1) were identified to be the major unsaturated free fatty acids. Out of the sterols identified, beta-sitosterol and stigmasterol were the major compounds. Palmitic acid palmity ester and palmitic acid oleyl ester were the major components in the class of waxes. Six sterol esters of steryl laurate, steryl myristate, steryl palmitate, steryl heptadecanoate, and steryl oleate were quantitatively determined in all the five lipophilic fractions. Tripalmitin, dipalmitoyl-oleoylglycrol, and triolein were primarily identified in the class of triglycerides. In addition, minor amounts of resin acids (0.21-0.47%), diglycerides (0.11-0.63%), and phenolic substances (0.41-2.76%) were also determined in the extractives.