The antioxidative effect of lipophilized rutin and dihydrocaffeic acid in fish oil enriched milk

The antioxidative effect of phenolipids was evaluated in fish oil enriched milk emulsions as a model for a complex food system. Two different phenolipids modified from dihydrocaffeic acid (with C8 or C18:1) and rutin (with C12 or C16) were evaluated. Both dihydrocaffeate esters and rutin laurate showed significantly better antioxidant properties in milk emulsion compared with the original phenolics.

However, rutin palmitate only performed slightly better as antioxidant than rutin. The results with rutin indicated that a cut‐off effect exists in relation to the alkyl chain length with respect to optimal antioxidant activity in milk emulsions. Thus, the optimal alkyl chain length is at least below 16 carbon atoms, and maybe even less for rutin esters.

For dihydrocaffeate esters it was not possible to conclude on a cut‐off effect in relation to alkyl chain length and antioxidative effect due to the almost similar antioxidant effect of the two phenolipids. However, there was a tendency towards octyl dihydrocaffeate being slightly more efficient than oleyl dihydrocaffeate.

Practical application: The finding that phenolipids are better antioxidants in milk emulsions than the original phenolic acid provides new knowledge that can be used to develop new antioxidant strategies to protect foods against lipid oxidation. However, the results indicate that both optimization of alkyl chain length for each type of phenolic, and optimization for each type of emulsion will be necessary in order to get the best oxidative stability of an emulsion with these phenolipids.

Use of efficient antioxidants may lower the amount of antioxidant needed to protect against lipid oxidation and may in addition decrease the costs.