Optimisation of soya bean oil bleaching by ultrasonic processing and investigate the physico-chemical properties of bleached soya bean oil

In this study, an ultrasonic bleaching method for soya bean oil under different conditions was optimised by monitoring the reduction of oil-containing colourants. Ultrasonic power, clay content, temperature and time had a significant interaction effect on (P<0.05) the reduction of oil pigments and colourants. Under optimised conditions, red and yellow colour indices in the ultrasound-bleached soya bean oil reduced to 74.44% and 75.55%, and 54.18% and 58.85%, respectively, at amplitudes of 85% and 65%. Carotenoid and chlorophyll concentrations also reduced to 81.19% and 83.62%, and 94.66% and 95.26%, respectively, at 85% and 65% ultrasonic power. The overall contents of sterols and tocopherols decreased using ultrasonic bleaching process compared with the neutralised soya bean oil. Although the peroxide value (PV) of the soya bean oil after ultrasonic and control bleaching reduced, this index was higher in the ultrasonic bleached oil than the control one. The results showed that the ultrasonic bleaching process could be an alternative to the industrial bleaching method as it reduced clay usage, temperature and time of bleaching about 35%, 35% and 10%, respectively.