Pro-oxidant/antioxidant behaviours of ascorbic acid, tocopherol, and plant extracts in n-3 highly unsaturated fatty acid rich oil-in-water emulsions

This study investigated the oxidative stability of n-3 highly unsaturated fatty acid (n-3 HUFA) rich (35% n-3 HUFA) oil-in-water emulsions (10 wt% oil) with commercial antioxidants and natural plant extracts. Ascorbic acid, alpha-tocopherol, and the extracts of Indian gooseberry fruit (Emblica officinalis) (IGFE) and sweet basil leaves (Ocimum basilicum L) (SBLE) were used for the study as antioxidants. The progress of oxidation in the systems was evaluated at 35 C over 120 h against a control (without antioxidant) by monitoring the formation of primary (conjugated dienes) and secondary (volatile carbonyl compounds) oxidation products. Volatile carbonyl compounds were trapped as derivatives of pentafluorophenyl hydrazine and quantified by headspace solid-phase microextraction analysis. About 40 volatile carbonyls were successfully identified by this method. trans,trans-2,4-Heptadienal, trans,cis-2,4-heptadienal, 3,5-octadien-2-one, and 1-penten-3-ol were predominant. The volatile carbonyl compounds and conjugated dienes were formed at low rates in emulsion systems in which alpha-tocopherol and natural plant extracts had been introduced, compared to the control. Emulsion systems containing ascorbic acid showed low stability, as indicated by the oxidation products that were formed at high rates compared to the control. These results indicated that ascorbic acid activated the oxidation reactions in n-3 HUFA rich water emulsions, while natural plant extracts that were rich in polyphenols and alpha-tocopherol were active as antioxidants. The present study further demonstrated the applicability of the polar paradox theory in the determination of stability for n-3 HUFA rich water emulsions with commercial antioxidants and natural plant extracts. (C) 2013 Elsevier Ltd. All rights reserved.