Antioxidant functions of caffeic acid and allylpyrocatechol in supramolecular oxidation of bulk oil: Role of acidic group in the mass transfer network

Abstract

Antioxidant activities of caffeic acid (CFA) and allylpyrocatechol (APC) were measured in bulk oil and in emulsion (oil/water) to evaluate the effects of the carboxylic group on the antioxidant function. As an emulsifier, polyglycerol polyricinoleate (PGPR) was added to the bulk oil to assist in promoting the interfacial activity of antioxidants. The antioxidant activity of CFA in the bulk oil was 186.5% higher than that of APC. In the emulsion, however, APC showed 150.3% higher antioxidant activity. PGPR showed a synergistic effect on CFA (>31%) and APC (<18%) which arose from organizing and supporting the formation of oxidation-microreactors. Water molecules were generated as an oxidation byproduct throughout the oxidation course, and they facilitated the formation of supramolecular structures. Polar imbalance became more prominent in the molecular structure of CFA, due to the presence of the carboxyl group, thereby increasing the effective collisions between the antioxidant molecules and free radicals.