Abstract

Milk thistle, Silybum marianum, is an annual or biennial plant. It has been reported that the extracted oil from milk thistle seed contains essential edible fatty acids. The aim of the present study was to determine the irrigation interval effects on different fatty acids content of milk thistle. Irrigation intervals consisted of D₁ = 5, D₂ = 10, D₃ = 15 days and D₄ = without irrigation. To show the water status of the investigated plants, relative water content of the leaves was measured. Milk thistle seed oil have been used for analysis of physicochemical properties such as oil content and composition using GC (FID). Our results proved that the irrigation intervals had significant effects on all of the studied parameters. The total oil content decreased by 4% due to increasing the water scarcity but the amount of the polyunsaturated fatty acids increased under the drought stress. The highest amount of the polyunsaturated fatty acids: linoleic acid (42.84%) and linolenic acid (0.65%) were measured in D₄ whereas the highest amount of the monounsaturated fatty acids; oleic acid (36.67%) and gadoleic acid (0.57%) have accumulated in D₁. The moisture content of the oil in D₄ decreased until 0.37% and the lowest chlorophyll content, pH, acid value and the highest refract index also were measured in D₄. It has proved that the drought stress increased the quality of milk thistle seed oil. Our results can justify the important value of milk thistle seed oil as an attractive candidate for use in food preparation.

Key words: Milk thistle, seed oil constituents, irrigation interval, essential fatty acids.