Development of novel refining techniques and enzymatic synthesis of antioxidant esters for improving the oxidative stability of sardine oil

Abstract

The growing market for n-3 polyunsaturated fatty acids (PUFA) has lead to the increasing amount of research in fish oil as they are excellent sources of n-3 PUFA. However, the highly unstable nature of these compounds has to be addressed. Hence, the present work deals with improving the stability of Indian sardine oil obtained from the western coastal region. This study aimed at developing novel refining strategies for removing impurities that caused poor stability and quality. Novel technologies involving simultaneous degumming and deacidification and membrane assisted free fatty acid removal were employed in the present work to eliminate the impurities in crude sardine oil that might increase the rate of oxidation. A novel degumming method involving triethanolamine resulted in simultaneous degumming and deacidification with phospholipid reduction from 303 ppm to 37 ppm, while the free fatty acids were reduced from 3.75% to 1.21%. Further removal of impurities was done by membrane assisted deacidification followed by bleaching using activated charcoal, resulting in refined sardine oil. The n-3 PUFA content in sardine oil was retained without much loss The best and convenient method for improving the oxidative stability of fish oils is by adding antioxidants which delays the oxidation process. In the current study, several natural antioxidants were studied for their effect in reducing the oxidation process in Indian sardine oil. Quercetin, rutin, gentisic acid and caffeic acid showed maximum effect in imparting oxidative stability. Further, the effect of antioxidants in stabilizing sardine oil in the presence of metal ions and trace water were tested. Though the effectiveness of antioxidants was not affected when sardine oil possessed trace metals, their efficiency reduced drastically with increase in trace water levels. Considering the relatively high antioxidant activity of rutin in Indian sardine oil and the complex heterogeneous nature of the oil, rutin was enzymatically modified toimprove its solubility in oil. It was identified that rutin was more effective during oxidation of refined sardine oil, whereas rutin ester showed higher activity in sardine oil containing trace water indicating the importance of antioxidant polarity and oil heterogeneity.