Study of Oxidative Stability of Sardine Oil in the Presence of Antioxidants

Abstract

The Indian sardine fish (Sardinella longiceps) oil is highly valued for its affordability and abundance as a source of n-3 polyunsaturated fatty acids (n-3 PUFA), which includes the beneficial eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). These compounds have positive effects on the prevention and treatment of various health conditions, such as coronary, neuromuscular, immunological, and allergic disorders. However, it is important to note that the n-3 PUFA contains many -C=C- double bonds, which are susceptible to oxidation due to their low bond dissociation energies (80kcal/mol). This oxidation process produces primary (hydroperoxide) and secondary oxidation (aldehydes and ketones) products that can result in an unpleasant taste. The extrinsic and intrinsic factors that contribute to the oxidation process, such as light, temperature, degree of saturation, free fatty acids, phospholipids, and pigments, leading to a decline in the nutritional value of the oil. Antioxidants are substances present in natural and synthetic forms and prevent several oxidation processes by various antioxidant mechanisms, such as free radical scavenging, metal chelating, and singlet oxygen quenching. A comprehensive study was conducted, and a tailor-made strategy was developed for one-factor at-a-time analysis that utilizes thirteen natural and synthetic antioxidants from various classes with different mechanisms with 0.9mM at 25°C under darkness in the presence of air for 50 days to maintain the oxidative stability of the oil. catechin, sinapic acid, caffeic acid, resveratrol, quercetin, and vanillic acid were found to be highly effective factors in preventing oxidation. A full factorial design (24) was utilized to choose a combination of natural antioxidants (catechin, resveratrol, sinapic acid, and vanillic acid) and synthetic antioxidants (TBHQ, BHA, and BHT) which exhibit interactive effects and response surface modelling (RSM) was used to identify the optimal concentration of the selected antioxidant mixture, which exhibits the synergistic effect. Natural antioxidants, catechin and resveratrol at 0.5mM and 0.625mM, respectively and synthetic antioxidants, TBHQ and BHT at 0.18mM and 0.18mM, respectively exhibited a strong synergistic effect. The kinetic and thermodynamic study of synthetic antioxidant (TBHQ and BHT) combination at several temperatures (25, 35, and 45°C) shows that the decomposition follows a zero-order reaction irrespective of the presence/absence of antioxidants, their concentrations, and storage temperatures. The thermodynamic analysis revealed that the formation of peroxides in the sardine oil is an endothermic, endergonic, and non-spontaneous reaction at ambient temperature.