Triterpene alcohols, methylsterols, sterols, and fatty acids in five Malagasy legume seed oils

Abstract

This paper reports a study of the chemical composition of the neutral lipids which form 0.8-46.7% of five legumes (Arachis hypogea, Voandzei subterranea, Phaseolus lunatus, Lens esculentus, and Vigna sinensis). Fatty acid profiles revealed that the major acids were palmitic (13.9-31.5%) linoleic (30.9-46.4%), and oleic (5.5-40.0%). Unsaponifiable matter (1.09-3.67%) ,was examined for sterol, 4a-methyl sterol, and triterpene alcohol fractions. @-Sitosterol was the prominent component in four legumes (39.8-79.7%), while stigmasterol (41.7%) was the major component in V. sinensis. Campesterol, stigmasterol, and A5-avenasterol were detected in all samples. Among the 4a-methyl sterol fractions, obtusifoliol (9.5-39.5%), gramisterol (14.7-58.7%), and citrostadienol (8.1-47.6%) were the main components. Cycloartanol (3.0-26.4%), butyrospermol (1.4-59.1%), cycloartenol (1.4-22.4%), 24methylenecycloartano1(0.8-42%), and cyclobranol(1.0-14.4%) were the main compounds of the triterpene alcohol fractions. Leguminous seeds make an important contribution to the diet in many tropical countries. They are used as vegetables and are a good source of protein, lipid, and fatty acids for human nutrition. The fatty acid composition of the endogenous fats plays an important role in determining shelf life, nutrition, and flavor of food products. Although some values have already been presented on numerous foods (Brignoli et al., 1976) and legumes (Exler et al., 1977), data for some tropical vegetable legumes are rarely given. The nature of some Indian legume lipids was investigated by Mahadevappa and Raina (1978). Busson and Bergeret (1958) and Doku et al. (1978) have studied the chemical composition of Voandzei subterranea. A number of some tropical vegetable and subtropical vegetable oils have been analyzed for their unsaponifiable fractions, particularly sterols and methyl sterols. It was shown that campesterol, stigmasterol, @-sitosterol, A5-avenasterol, and Abtigmastenol were common constituents, @-sitosterol being the most prominent in the sterol fraction (Itoh et al., 1974a). Four sterol-containing lipid fractions were isolated from the chloroform-methanol-extracted lipids of cowpea (Vigna uguiculata) by Mahadevappa and Raina (1981). Generally 4a-methyl sterols are minor constituents of the unsaponifiable fractions and their separation from unsaponifiable matter is quite difficult. In common vegetable oils, 4a-methyl sterols were studied by Sawicki and Mordret (1970), Itoh et al. (1974b), and Jeong et al. (1975). Among the important legumes consumed in Madagascar, five of them are used commonly in this country. They are Arachis hypogea (var. Valencia), V. subterranea (or Glycine subterranea), Phaseolus lunatus (var. Inamoenus), Lens esculentus, and Vigna sinensis. Soybeans are becoming an important industrial legume for oil and protein production but are not, at this time, used very much by the population for human nutrition. This paper presents results on these five legumes consumed in Madagascar. This investigation was undertaken to obtain more information on the fatty acid composition