DPPH radical scavenging and mixture effects of plant o‐diphenols and essential oil constituents

Abstract

A series of natural compounds were examined for potential synergistic and antagonistic antiradical activities. Four natural o‐diphenolic compounds, namely quercetin, rutin, (+)‐catechin, and rosmarinic acid as well as five common essential oil components: thymol, carvacrol, thymoquinone, p‐cymene, and γ‐terpinene were studied individually and in binary, ternary, and quaternary mixtures against DPPH•. The antiradical activities of the individual compounds were quantified according to the number of radicals scavenged per molecule of antioxidant and the EC50 parameter. Also, the different reaction patterns resulting to different stoichiometries are discussed. In binary and higher systems an additive effect was observed with any combination of the o‐diphenols. The monoterpenoid phenols carvacrol and thymol presented low DPPH radical scavenging activity and antagonistic interactions with the o‐diphenols, partially attributed to equilibrium phenomena. The rest essential oil components were inactive and did not interfere in the overall antiradical activity of any combination.Practical applications: Plant extracts can be used as antioxidants for lipid foods or combined with essential oils that provide antimicrobial protection. They contain a variety of active compounds, which might interact and affect the overall antioxidant activity. The present work examines the radical scavenging activity of the basic constituents of extracts, essential oils, and their mixtures. The results could have an impact on the production of natural antioxidants, since a cost effective industrial process involves the recovery of a multicomponent fraction rather than the isolation of single antioxidants. Also, they can be useful to estimate the antiradical activity of multicomponent herbal supplements.The antiradical activities of o‐diphenols commonly found in natural extracts (quercetin, rutin, (+)‐catechin, and rosmarinic acid) and essential oil components (thymol, carvacrol, thymoquinone, p‐cymene, and γ‐terpinene) were studied individually and in binary, ternary, and quaternary mixtures. An additive effect was observed with any combination of the o‐diphenols. Among the essential oil components, the monoterpenoid phenols carvacrol and thymol presented low DPPH radical scavenging activity and antagonistic interactions with the o‐diphenols partially attributed to equilibrium phenomena, while the rest were inactive and did not interfere in the overall antiradical activity of any combination.