STUDIES ON SOME PLANT LIPIDS

Abstract

The thesis on "STUDIES ON SOME PLANT LIPIDS" is divided into two chapters. CHAPTER I : STUDIES ON NEWER OILSEEDS Background and Objective : Vegetable oils, both eaible and nonedible, are in short supply. One way to augment resources is to locate newer oiiseeds. These oilseeds could also be sources of proteins. Analysis of the following 23 newer oilseeds has therefore been undertaken for the first time for seed and oil characteristics, fatty acid composition and amino acid composition : Hibi scus ficulneus, H. surattensis, H. vitifolius, H. hirtus, _H. punctatus, H. zeyl^nicus, _H. micranthus, H. solandra. Sida veronicifolia, S. cordifolia, S_. ovata, S.mvsorensis, S. rhombifolia, Abutilon crispum (Malvaceae); Jatropha pandureaefolia,3. podagarica, Phyllanthus maderaspatensis. Croton sparciflorus (Euphorbiaceae); Trichosanthes nervifolia (Cucurbitaceae); Calotropis gigantea (Asclepiadaceae); Heynea trijuga (Meliaceae); Millingtonia hortensis (Bignoniaceae); Acacia caesia (Leguminosae). Methodology : Official and Tentative Methods of the American Oil Chemists' Society were followed for the determination of moisture, oil, protein and ash contents of the seeds and physico-chemical characteristics of the oils. The oils were examined for ultra violet absorption in carbon tetrachloride, for infrared absorption as liquid films and for proton nuclear magnetic resonance in carbon tetrachloride. The oils as well as the methyl esters were qualitatively examined for the presence of hydroxy, epoxy and cyclopropene fatty acid components by the sulfuric acid turbidity test, Fioriti's picric acid test and the Halphen test, respectively. The oils were converted to methyl esters by treatment with methanoiic sodium methoxide. Cyclopropene and epoxy (ll) fatty acid esters, where present, were estimated by gas-liquid chromatography using methyl heptadecanoate as internal standard after their denvatizations. The cyclopro pene fatty acid methyl esters along with normal fatty acid esters were isolated by thin-layer chromatography and treated with anhydrous methanol saturated with silver nitrate for 20 hr at ambient temperature to convert cyclopropene fatty acids into stable ether and keto derivatives for analysis by gas-liquid chromatography. The epoxy fatty acid methyl esters were isolated by thin-layer chromatography and convert ed to hydroxy-methoxy esters by treatment with methanolic boron trifluonde solution. These were further derivatized to trimethyl silyl ethers by treatment with hexamethyldisilazane and trimethylchlorosilane in pyridine. These derivatives were analyzed by gas chromatography Conjugated fatty acids were identified by infrared, ultra violet and nuclear ( H, C) magnetic resonance spectroscopic techniques as well as by hydrogenation and mass spectrometry of bromomethoxy derivatives of monoenes obtained by partial hydrogenation. Amino acid compositions of the seed meals were analyzed using an Amino Acid Analyzer. Tryptophan was analyzed microbiologically,. Results and Discussion : The oil contents were appreciable (8.8 - 39.5%) and the oils can be extracted with hexane economically. Linoleic acid was predominant (40-70%) in seed oils of A. caesia, 3. pandureaefolia, 3.podagarica, M. hortensis and of the Malvaceae species, linolenic acid (46-64%) in seed oils of P. maderaspatensis and C. sparciflorus and oleic acid in seed oils of C. gigantea (47%) and H. trijuga (81.8%). T. nervifolia seed oils contained high amount (51.7%) of punicic acid. Cyclopropene fatty acids were present (0.6 - 12.5%) in all the seed oils of Malvaceae family studied, while cylopropene (0.2 - 2.7%) and epoxy (0.1 - 0.5%) fatty acids were present in some of the Malvaceae family seed oils. The protein contents were appreciable (11.7 - (ill) 20.0%). Some of the seed proteins are rich in essential amino acids. Conclusions : Some of the plants studied have potential for cultivation or afforestation in view of good oil and protein contents in their seeds. The oils from these seeds could find use in soap, paint and other industries. The deoiled meals of seeds having high protein content could be good sources of animal feed, if toxicity is absent. CHAPTER II : STUDIES ON SELECTED PLANT TISSUES Background and Objective : Although abundant information is available on the storage lipids present in seeds of many plants, information is meagre on the extent, distribution and nature of fatty acids and other lipids in the vegetative tissues. This information may have some bearing on structure of tissues and may provide information on newer sources of hydrocarbons, waxes, sterols, fatty acids and other lipids. The present study is on the separation, identification and estimation of various lipid classes and their component fatty acids present in tissues of the following plants. Edible plants 1. Amaranthus gangeticus Linn. (Amaranthaceae) - leaves. 2. Peucedanum graveolens Linn. (Umbelliferae) - leaves and stems. 3. Mentha arvensis Linn. (Labiatae) - leaves and stems. 4. Colocasia esculenta Schott. (Araceae) - leaves and leaf stalks. Non-edible plants 5. Eichhornia crassipes Soims. (Pontederiaceae) - roots, leaf stalks, leaves and flowers. (iv) 6. Caiotropis gigantea Linn. (Asclepiadaceae) - leaves. 7. Nefumbo nueifera Gaertn. (Nymphaeaceae) - leaves. Methodology : The plant tissues were dipped in hot water to inactivate the lipases. The lipids were extracted with chloroform: methanol and purified according to Folch. The lipids were separated on a silicic acid column using chloroform, acetone and methanol. The chloroform eiuate contained the nonpolar lipids from which pigments were separat ed by passing through a charcoal-Ceiite column. The acetone fraction contained glycolipids and the methanol fraction phospholipids. Preparative thin-layer chromato graphy on Silica gel Gusing a solvent system of petroleum ether: diethyl ether: acetic acid (90:10:1) separated the nonpolar lipids into various sub-classes. Di- and monoacylglycerols which were not resolved in this system were separated by using petroleum ether: diethyl ether: acetic acid (60:40:1). Each lipid class was estimated by gravimetry . The glycoiipid classes were separated on SilicagelG using chloroform: methanol: acetic acid: water (170:24:25:4). The glycoiipid classes were quantified by estimation of either their carbohydrate moieties using the anthrone reagent or fatty acid moieties by gas chromatography using methyl heptadecanoate as internal standard. The phos pholipid classes were separated on Silica gel G layers using chloroform:acetone:methanol: acetic acid: water (30:40:10:10:5). The phospholipid classes were quantified either by spectrophotometry after colour development with ammonium molybdate and elon reagent or by gas chromatography of fatty acids as methyl esters using methyl hepta decanoate as internal standard. Lipid classes were identified using authentic samples as reference compounds and by spraying with the following group-specific spray reagents: concentrated sulfuric acid-acetic acid (1:1) for sterols, Dragendorff reagent for choline group, ninhydrin for free amino group, periodate-Schiff reagent for vicinal hydroxyl group, a-naphthol for sugar and ammonium molybdate-perchloric acid for phosphate( v) containing lipids. Acyl lipids, except free fatty acids and ester waxes, were converted to methyl esters by treatment with methanoiic sodium methoxide. Free fatty acids were converted to methyl esters with diazomethane in methanol-diethyl ether. Ester waxes were saponified and the liberated fatty acids were esterified. The methyl esters were qualitatively and quantitatively examined by silica gel and argentation thin-layer chromatography and by gas chromatography. Results and Discussion : Leaves contained more lipids than the other tissues (leaf stalks, stems, roots. flowers) of ail the plants studied. The lipid class composition varied with tissue. Pigments, acylglycerols and sterols were the major nonpolar lipids. Monogalactosyldiglycendes were the predominant glycosides in leaves, leaf stalks and stems except in the leaves of P. graveolens while digalactosyldiglycendes were predominant in the roots and flowers of E. crassipes and leaves of P.graveolens. Phosphatidylglyceroi, phosphatidylcholine and phosphatidylethanolamine were the chief components of phospholipids in different tissues of different plants studied. The major fatty acids were linolenic, linoleic and palmitic and their proportions varied from tissue to tissue. Conclusions : Edible leaves contained appreciable quantities of lipids, rich in essential fatty acids. Nonedible leaves could be a good source of lipids and perhaps could be a source of carbon in the production of methane gas.