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

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.

Comparison of the antioxidant capacity of sesamol esters in gelled emulsion and non-gelled emulsion.

The antioxidant capacity of sesamol esters in gelled emulsion was investigated in comparison with non-gelled emulsion to assess the role of mass transfer on their antioxidant capacity. Initiation phase and propagation phase kinetic parameters of peroxidation was calculated using a sigmoidal model. Sesamol esters showed higher antioxidant activity than sesamol in gelled emulsion and non-gelled emulsion. Sesamyl acetate, sesamyl butyrate, and sesamyl hexanoate had no synergistic effect with sesamol in gelled emulsion, while in non-gelled emulsion sesamyl butyrate exhibited a slight synergistic effect with sesamol. The antioxidant activity of sesamyl acetate and sesamyl hexanoate in non-gelled emulsion samples were higher than those of gelled emulsion samples, while sesamyl butyrate exhibited higher antioxidant activity in gelled emulsion than that of non-gelled emulsion. The cut-off effect hypothesis was observed in gelled emulsion, while this hypothesis was disappeared in non-gelled emulsion. During propagation phase, sesamol esters remained active and exhibited inhibitory effect.

Effect of triacylglycerol structure on the antioxidant activity of γ-oryzanol.

In this study, the triacylglycerol structure of vegetable oils was removed and the effects of this removal were observed on the antioxidant efficiency of γ-oryzanol. A sigmoidal-model was used for calculating kinetic parameters relevant to the initiation and propagation phases during the peroxidation of soybean, corn, sesame, and olive oils as well as their fatty acid methyl esters. Removing the triacylglycerol structure caused an increase in the antioxidant activity of γ-oryzanol (26.49%) by affecting both inhibitory mechanisms, i.e. hydrogen-donating (7.80%) and electron-transfer (14.72%). Unexpectedly, the antioxidant performance of γ-oryzanol continued even when the induction period had ended. During the propagation phase, the highest antioxidant activity was observed in the fatty acid methyl esters of soybean oil (3.86) based on hydroperoxides decomposition. An evaluation of how the endergonic activated complexes formed could indicate that the removal of the triacylglycerol structure increased the effective collisions between the γ-oryzanol molecules and free radicals.

Investigating relationship between water production and interfacial activity of γ-oryzanol, ethyl ferulate, and ferulic acid during peroxidation of bulk oil.

In this study, lecithin (as a surfactant) was added to promote the inhibitory-mechanism of γ-oryzanol, ethyl-ferulate and ferulic acid (based on the interfacial phenomena) so as to inhibit the oxidation of stripped sunflower oil. Monitoring the amount of water production as a byproduct of oxidation showed that the water content of the lipid system increased remarkably through the oxidation progress. Lecithin enhanced the critical concentration of hydroperoxides in reverse micelles, compared to the basic state (14.8 vs. 9.2 mM), thereby improving the hydrogen-donating mechanism of antioxidants. The size of reverse micelles increased progressively during the oxidation, while two breakpoints were pointed out in the micelles growth, i.e. at the end of the initiation and the propagation phases. Based on the kinetic data, ferulic acid showed the highest antioxidant activity (23.4), compared to ethyl-ferulate (15.5) and γ-oryzanol (13.7). Generally, lecithin enhanced antioxidant activity (~ 65%) by improving the interfacial performance of antioxidants.