LIPID STUDIES ON NICOTIANA TABACUM AND NICOTIANA RUSTICA OF THE FAMILY SOLANACEAE

Lipids of plant origin find applications not only in nutrition but also have been. used in different industries for various purposes. They are used in making lotions, ointments and in a number of pharmaceutical preparations. Keeping in view the vast applications of lipids, an exhaustive study was conducted to investigate' the different lipid classes and their fatty acid composition present in the seed oils of the two Nicotiana species namely Nicotiana tabacum L (which is called generally N. tabacum in the text) and Nicotiana rustica of the plant family Solanaceae. The distribution of fatty acids in the triacylglycerol molecules with the help of pancreatic lipase was also determined. The lipase and phospholipase activities in the seeds at different pH, temperatures and in various solvents were determined. By using Von Rudloffs oxidation technique the positional isomers in octadecenoic acid were found out. The composition of different sterols present in both the species was also determined with the help of gas chromatography.\ud \ud The seeds of N. tabacum and N. rustica were found to contain lipids 41.3% and 36.6%, respectively. The lipids of both the species were separated into different classes by thin layer chromatography. The lipid classes found in N. tabacum were hydrocarbons (1.4%), wax esters (1.7%), sterol esters (2.4%), triacylglycerols (69.3%), free fatty acids (6.2%), l,3-diacylglycerols (4.6%), l,2-diacylglycerols (3.5%), free sterols (2.3%), 2-monoacylglycerols (2.1%), 1-monoacylglycerols (1.8%), phosphatidylethanolamines (1.7%), phosphatidylcholines (0.9%), Iysophosphatidylethanolamines (1.5%) and phosphatidylinositols (0.6%). The lipid classes in N. rustica were found to be the same as in the case of N. tabacum. The percentages of the above mentioned lipids in N. rustica were 1.3%, 1.8%, 2.6%, 64.4%, 9.5%, 5.1%, 4.8%, 2.7%, 1.9%, 1.5%, 1.4%, 1.1%, 0.7% and 1.2%, respectively.\ud \ud Each lipid class except hydrocarbons and free sterols was methylated with BF3-rmethanol reagent and purified to determine the fatty acid composition by gas chromatography. In most of the lipid classes, the fatty acid range was C12:0 - C20:0, showing higher percentage of unsaturated fatty acids as compared to saturated fatty acids.\ud \ud Linoleic acid (C18:21 an essential fatty acid) was found as predominant one in neutral as well as in polar lipids due to the phylogenetic factor of Solanaceae family. Linoleic acid was the main contributor among the unsaturated fatty acids while palmitic acid was the major fatty acid in the saturated fatty acid profile in all the lipid classes of both the species. The other fatty acids found were C12:0, C14:01 C18:01 C18:11 C 18:3 and C20:0 in most of the lipid classes.\ud \ud In order to determine the distribution of fatty acids in the triacylglycerols, this lipid fraction from both species was isolated by preparative thin layer chromatography. The triacylglycerols were fractionated according to their degree of unsaturation by AgN03 -TLC. Triacylglycerols were separated into seven fractions in both species. Each triacylglycerol fraction was hydrolyzed with pancreatic lipase in order to determine the distribution of fatty acids at different positions. The unsaturated C18 acids were found to occupy the 2-position comparatively in higher percentage than the other fatty acids.\ud \ud The lipase and phospholipase extracted from the seed meals of N. tabacum and N. rustica showed maximum activity at pH 6 and 45°C. n-Heptane was found as the best medium amongst the various solvents used for determining the activities of lipase and phospholipase in non aqueous systems