Combinatorial Interactions of Essential Oils Enriched with Individual Polyphenols, Polyphenol Mixes, and Plant Extracts: Multi-Antioxidant Systems

With the aim to develop essential oil (EO) multi-antioxidant systems, combinatorial interactions of selected phenol and terpene-rich EOs (from Pimento Berry, Ceylon Cinnamon, Clove, Sage, White thyme; Oregano) enriched with individual polyphenols, crude plant extracts, and mixtures of their major polyphenols were investigated using single electron transfer (SET)-based DPPH and hydrogen atom transfer (HAT)-based ORAC assays. Polyphenols that enriched Eos the most favorably were rosmarinic acid (IC(50) of 0.0891–0.1448 mg enriched EO/mg DPPH; 5772–17,879 µmol TE/g enriched EO) and quercetin (IC(50) of 0.0682–0.1060 mg enriched EO/mg DPPH; Trolox Equivalents (TE) of 9776–14,567µmol /g enriched EO), whereas p-coumaric acid (IC(50) of 0.1865–1.1424 mg enriched EO/mg DPPH; 7451.00–11,588 µmol TE/g enriched EO) and rutin hydrate (IC(50) of 0.1140–0.3112 mg enriched EO/mg DPPH; 2298–6227 µmol TE/g enriched EO) were the least favorable. Enrichments with polyphenol mixes and crude extracts exhibited synergistic and additive effects in the SET-based DPPH assay. In the HAT-based ORAC assay, EO enrichments with crude extracts exhibited more additive effects, as well as less antagonistic effects, than enrichments with their major polyphenol mixes, revealing the significant contributions of minor compounds. EOs enriched with crude green tea and apple extracts exhibited synergistic or additive effects, whereas EOs enriched with grape seed and rosemary extracts exhibited equal antagonistic effects. Predictive models were developed to explain the variability between the observed and predicted antioxidant activities of enriched EOs.