Lipids of plant origin find. application not only as the nutritive value but also have been used for therapeutic purposes since time immemorial. They are used in the treatment of leprosy, as cathartics, insects sprays, suppositories, antibiotics and as excipient in intramuscular .injections. They are also used in making lotions, ointments and other pharmaceutical preparations. Similarly the seeds kernels of Citrullus uulgaris (watermelon vern. tarbooz) have been used by the people of subcontinent as an important member out of four called "Chahar Maghaz" as brain tonic. Its fruit is used as purgative and its juice is taken as cathartic and antiseptic in typhus fever, diuretic and stomachic, for blood purification, as aphrodisiac and is also used in intestinal inflammation. The second species, Citrullus colocynthis (Colocynth vern."tumma") is used as important medicine by the local physicians in their concoctions in the form of its leaves, roots, whole fruit, pulp, seeds and seed oil. It is used for the treatments' of various ailments as purgative, anathematic, antipyretic .and carminative. It cures tumours, ascites, leucoderma, ulcer, asthma, bronchitis, urinary discharges jaundice, enlarged spleen, constipation atrophy of the foetus, rheumatic pains, snake bites and scorpion stings.
Keeping in view the vast medicinal properties of these two species, it is intended to study the chemistry of one of the major component known as lipid and lipid metabolism during the course of germination. The distribution of fatty acids in the triacylglycerol molecules of the two species were determined for their structure elucidation. The activity of lipase and phospholipase procured from the defatted seed meal were' also studied under various parameters.
The lipids were classified qualitatively and quantitatively by thin layer and gas chromatographies. The neutral lipids identified were hydrocarbons, wax esters, triacylglycerols (the main constituent), free fatty acids, 1,3-diacylglycerols, 1,2-diacylglycerols, glycolipids, fatty alcohols, sterols, 2-monoacylglycerols, and I-monoacylglycerols. The polar lipids found were monogalactosyldiacylglycerols, phosphatidylethanolamines, phosphatidylcholines, lysophosphatidylethanolamines, lysophosphatidylcholines and phosphatidylinositols. The amount of polar lipids was very low (3.0%) as compared to neutral lipids (97.0%).
All the classified lipids except hydrocarbons, sterols and fatty alcohols were methylated, extracted and then purified by TLC. The methyl esters thus obtained were characterized by gas chromatography for their fatty acid composition. In all the lipid classes, the fatty acid range was (CI2:0 - C20:0) showing higher percentage of unsaturated fatty acids as compared to saturated fatty acids.
Linoleic acid (C18:2, an essential fatty acid) has been found as predominant one in neutral as well as in polar lipids due to the phylogenetic factor of this family. C18:2 was the main contributor among the unsaturated fatty acids while C16:0 was the major fatty acid in saturated fatty acid profile in all the lipid classes. The other fatty acids found were C12:0, C12:1, C14:0, C14:1, C16:1, C18:0, C18:l, Cl8:3, and C20:0,
The total neutral lipids decreased while polar lipids increased as the germination proceeds from resting seeds to 30 mm root length, which might be due to the continuous increase of lipase activity and gradual decrease of phospholipase activity. During germination saturated fatty acids increase except lauric acid whereas unsaturated fatty acids decrease, this shows the interconversion of unsaturated fatty acids to saturated fatty acids.
The triacylglycerols were fractionated by argentation TLC depending upon their degree of unsaturation. The composition and the nature of fatty acids of these fractions at their a, a' and β positions were determined by the use of pancreatic lipase and GLC. The unsaturated C18 acids occupied the β-position depending upon the comparatively higher percentage of the respective acid.
The lipase and phospholipase extracted from the defatted seed meal of both the species, showed maximum activity at pH 7 (at 40°C) in an aqueous media