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Abstract
A rapid analytical procedure, which enables convenient quantitative determination of individual components in rice straw lipophilic extractives, has been developed in this study. The method comprises a Soxhlet extraction with toluene–ethanol (2 : 1, v/v), chloroform, petroleum ether, dichloromethane, or hexane, silylation, and gas chromatography on a medium-length capillary column. The chemical composition of five lipophilic extractives has been examined. Free fatty/resin acids, sterols, waxes, steryl esters, and triglycerides were identified as the major five classes of lipids. Over all the free fatty acids, the most abundant free fatty acids were palmitic acid (C16 : 0, 3.82–8.11%), linoleic acid (C18 : 2) and/or oleic acid (C18 : 1, 1.22–3.35%), hexadecenoic acid (C16 : 1, 1.36–2.96%), and heptadecanoic acid (C17 : 0, 0.86– 1.50%). β-Sitosterol and stigmasterol were the predominant components identified in a class of sterols, comprising over 90% of the total sterols. Palmitic acid palmity ester and palmitic acid oleyl ester were the major components analyzed in a group of waxes. The steryl esters identified were composed mainly of steryl palmitate, steryl oleate, steryl myristate, steryl heptadecanoate, and steryl laurate. Of the triglycerides identified, triolein was the dominant compound. Tripalmitin and dipalmitoyl-oleoylglycerol were also found in small amounts in this class of lipids. Diglycerides accounted for only minor amounts (0.19–0.33%) of the total extractives.
ACKNOWLEDGMENTS
The authors are grateful for the financial support of this research from China National Science Funds for Distinguished Young Scholars (No. 30025036) and for general research (No. 39870645).