Bleaching with blends of bleaching earth and activated carbon reduces color and oxidation products of carp oil

Abstract

Fish oil is characterized as a rich source of polyunsaturated fatty acids. Bleaching is one of the most important steps in oil refinement. This study evaluated the effect of the bleaching step of carp oil refinement on the total carotenoid content, the TBA value, and the color. The crude oil was obtained by acid silage of carp viscera, and it was refined by the following steps: degumming, neutralization, washing, drying and bleaching. Various percentages of adsorbent to the oil mass (1.4-5.6%, w/w) and of activated carbon to the total adsorbent mass (4-11%, w/w) were used to remove the color and oxidation products. The optimum condition was found with 2% of adsorbent (to the oil mass) and 10% of activated carbon in relation to the total adsorbent mass, showing the lowest losses of carotenoid content (44.4%), and highest decreases of dark oil color (87.5%) and of TBA value (79.7%). In the bleached carp oil, the sum of unsaturated fatty acids was approximately of 67% and the ω-3/ω-6 ratio of 1.22. A kinetic study of the bleaching step to the carotenoid content and TBA values was performed by the models of Brimberg and Langmuir-Hinshelwood, which suitably fit the experimental data. Practical applications: A great number of studies are found in the literature on the pigment adsorption, oxidation products and free fatty acids in the bleaching step of vegetable oils by different adsorbents, however, there is little research that studies this step for fish oil. In this work, the best conditions for the bleaching of carp oil showed greater preservation of carotenoids, reductions in the value of TBA and in the darkening of the oil, resulting in a bleached oil with better quality and oxidative aspect. The neutralized and bleached oils extracted from carp viscera by the acid silage showed ω-3/ω-6 ratios from 1:1.21 to 1:1.22 and these values are in agreement with the literature for oil freshwater fish.