PHYSICOCHEMICAL PROPERTIES OF CHEMICALLY INTERESTERIFIED VEGETABLE OILS

Interesterification is an alternative to partial hydrogenation that helps to manufacture products of a variety of melting properties. When the process is applied to different blends of vegetable oils, redistribution of fatty acids between and within triacyglycerol occurs that changes the physical properties especially the melting characteristics of the vegetable oil blends. For chemical interesterification process, unrefined vegetable oils (soybean oil and cottonseed oils) were obtained from the local industry (United Industries Faisalabad, Pakistan). Different blends of soybean and cottonseed oils were prepared ranging from 100% soybean oil to 100% cottonseed oil in 25% increments (w/w) with different ratios of (100% : 0%, 75% : 25%, 50% : 50%, 25% : 75%, 0% : 100%) respectively. The blended oil portions (500mL) were neutralized and dried. For chemical interesterification sodium methoxide was used as catalyst. At the end of reaction, the catalyst was inactivated and reaction was stopped by the addition of citric acid solution and at the end by the addition of warm water (70-80°C). Interesterified oils were bleached by heating them to 110°C and mixing with bleaching earth and then the hot interesterified oils were filtered and cooled. Physico-chemical properties (refractive index, specific gravity, colour, melting point, free fatty acids, iodine value, peroxide value, saponification value and rancidity) and sensory evaluation (appearance, odor and overall acceptability) of the final product was conducted at 0, 15 and 30 days of interval. The results revealed that refractive index, specific gravity, color, melting point, free fatty acids value, peroxide value and saponification value increased while iodine value decreased with the passage of time. Further studies showed that storage had a highly significant effect on color, melting point, free fatty acids value, iodine value, peroxide value and saponification value. The effect of storage was non-significant for parameters like specific gravity and refractive index.