Physiochemical Properties and Effects of Addition of Some Natural Antioxidants on Shelf Life of Sunflower and Soybean Oils

Abstract

The aim of this work was to investigate the effect of addition of natural antioxidants , Sesame oil and dichloromethane ( DCM ) extract of ginger roots , at different concentrations (0,200 ,300 , 400 ,500 and 600 ppm each separately) , to the shelf life (150 days) of edible oils ( refined sunflower oil and crude soybean oil), at room temperature (28° C ). It is found that ginger roots were found to consist from 12.5% moisture, 5.98% ash, 3.24% protein, 21.5% carbohydrate, 1.5% oil content and 56.86% fiber. Their main elements determined by atomic absorption spectrophotometry were found to be calcium 111.23 ppm , iron 15.24 ppm , zinc 10.96ppm , and sodium 10.92ppm as well as small amount of copper 0.65ppm , manganese 11.03 ppm , lead 0.27 ppm and chromium 0.02ppm ; however aluminum was not detected. Fatty acids of oils under study (sesame, sunflower, soybean, ginger oil and dichloromethane extract) were determined by GC-MS. The effective use of antioxidants in edible oils was investigated by determining the changes in the physiochemical properties of edible oil such as peroxide value, iodine value, acidity, viscosity, refractive index and colour intensity through the period of storage. Among these physiochemical properties, only peroxide and iodine values were found to be the useful in determining the extent of deterioration of the quality and nutritional value between treated and untreated edible oils with natural antioxidants during different times of the storage period . The activity of antioxidant was determined by 2, 2-diphenylpicrylhydrazyl (DPPH) free radical scavenging assay. In comparison with 94.7% for the standard propyl gallate , it gave up to 80% for DCM extract from ginger roots and down to 4.0% for crude sesame oil.