Investigation of Soybean Oil Bleaching by Using Walnut Shell

In this research, the application of walnut shell ash, as an adsorbent for soybean oil bleaching, has been investigated. Therefore, neutralized soybean oil was bleached with 1 and 2% of walnut shell ash as well as commercial bleaching earth. Then, a series of chemical tests such as amounts of carotenoids, chlorophylls, peroxide value, and free fatty acid content of bleached oils and oil retention of adsorbents were determined. The results indicated that bleaching with 2% walnut shell ash reduced carotenoids and chlorophyll contents up to 37.46 and 33.4%, respectively. Moreover, the red and yellow colors reduced in the oil bleached with 2% walnut shell ash and reached to 1.23 and 50 Lovibond, respectively. The oil retention by walnut shell ash (36.99%) was significantly lower than commercial bleaching earth (45.33%). Therefore, as a food waste, walnut shell ash can be used alone or in combination with acid activated earths or activated carbons for oil bleaching as a low cost adsorbent.