Synergistic and antagonistic co-antioxidant effects of flavonoids with trolox or ascorbic acid in a binary mixture

Ethanol organosolv lignin as a substitute for commercial antioxidants, focusing on the structural properties and synergistic effect with myricetin

Lignin has potential as a substitute for natural antioxidants in cosmetics and food industries due to its radical scavenging ability and price competitiveness. The antioxidant activity of lignin depends on its structural properties, and they accordingly have synergy with natural antioxidants. Based on the structural characteristics, the antioxidant activity of ethanol organosolv lignin (EOL) and synergy with myricetin were investigated. The phenolic-OH content was a predominant factor in the antioxidant activity of EOL, and EOL-H with a higher phenolic-OH content and lower IC₅₀ value (0.17 mg/mL) covered a wide synergy range of 1:32-2:1 (EOL:myricetin). The synergistic effect was verified by comparing predicted and actual values based on ESR analysis, and the phenolic-OH ratio (>0.4) of myricetin and EOL for the synergy was suggested. In this respect, the results highlight the potential of lignin with high phenolic-OH content as a substitute for commercial antioxidants with superior activity and broad synergy ranges.

Recent advances in the antioxidant activity and mechanisms of chalcone derivatives: a computational review

In this review, we have reported the antioxidant mechanisms and structure-antioxidant activity relationship of several chalcone derivatives, investigated in the recent past, based on the density functional theory (DFT) calculations, considering free radical scavenging and metal chelation ability. The antioxidant mechanisms include hydrogen atom transfer (HAT), sequential proton loss electron transfer (SPLET), single electron transfer followed by proton transfer (SET-PT), sequential proton loss hydrogen atom transfer (SPLHAT), sequential double proton loss electron transfer (SdPLET), sequential triple proton loss double electron transfer (StPLdET), sequential triple proton loss triple electron transfer (StPLtET), double HAT, double SPLET, double SET-PT, triple HAT, triple SET-PT, triple SPLET, proton-coupled electron transfer (PCET), single electron transfer (SET), radical adduct formation (RAF) and radical adduct formation followed by hydrogen atom abstraction (RAF-HAA). Furthermore, solvent effects have also been considered using different solvation models. The feasibility of scavenging different reactive oxygen and nitrogen species (ROS/RNS) has been discussed considering various factors such as the number and position of hydroxyl as well as methoxy groups present in the antioxidant molecule, stability of the species formed after scavenging reactive species, nature of substituent, steric effects, etc. This review opens new perspectives for designing new compounds with better antioxidant potential.

A Modification of the ABTS• Decolorization Method and an Insight into Its Mechanism

A modification of the ABTS• decolorization assay for plate readers is presented. In our modification, 200 µL of ABTS solution of absorbance 1.0 at 734 nm was added with an antioxidant and decreased absorbance resulted. For comparison of antioxidant activities in the kinetic assay of absorbance decrease, concentration dependence of absorbance decrease and of area under curve are recommended. “Fast” and “slow” antioxidants were distinguished: while the reactions of “fast” antioxidants ABTS• were completed within seconds, the reactions of “slow” antioxidants were not finished after 6 min. We recommend reaction time of 60 min for assays of such antioxidants, blood plasma and plant extracts. Sub-additive interactions between some antioxidants (ascorbate and Trolox, hispidulin and Trolox, and glutathione and ascorbate) were found in the ABTS• decolorization; possible reasons for such interactions are discussed.

Advances in the control of lipid peroxidation in oil-in-water emulsions: kinetic approaches†

Large efforts have been, and still are, devoted to minimize the harmful effects of lipid peroxidation. Much of the early work focused in understanding both the lipid oxidation mechanisms and the action of antioxidants in bulk solution. However, food-grade oils are mostly present in the form of oil-in-water emulsions, bringing up an increasing complexity because of the three-dimensional interfacial region. This review presents an overview of the kinetic approaches employed in controlling the oxidative stability of edible oil-in-water emulsions and of the main outcomes, with particular emphasis on the role of antioxidants and on the kinetics of the inhibition reaction. Application of physical-organic chemistry methods, such as the pseudophase models to investigate antioxidant partitioning, constitute a remarkable example on how kinetic methodologies contribute to model chemical reactivity in multiphasic systems and to rationalize the role of interfaces, opening new opportunities for designing novel antioxidants with tailored properties and new prospects for modulating environmental conditions in attempting to optimize their efficiency. Here we will summarize the main kinetic features of the inhibition reaction and will discuss on the main factors affecting its rate, including the determination of antioxidant efficiencies from kinetic profiles, structure-reactivity relationships, partitioning of antioxidants and concentration effects.

Antioxidant properties of extract combination of Coccinia grandis and Blumea balsamifera: An in vitro synergistic effect

Introduction: As single extracts, Coccinia grandis and Blumea balsamifera have been known to have potent antioxidant activities. However, the synergistic antioxidant effect of the combination of these plant extracts was unknown. In this study, the combination of C. grandis and B. balsamifera extracts was investigated for its antioxidant and synergistic properties. Methods: Separately, C. grandis and B. balsamifera leaves were extracted with ethanol. After evaporation, the thick extracts were assayed for their total phenolic content (TPC) and total flavonoid content (TFC). The antioxidant properties of single and combined extracts were measured using the molybdenum(VI) reducing power, ferric reducing antioxidant power (FRAP), 2,2-diphenyl-1-picrylhydrazyl (DPPH), and 2,2-azino-bis-3-ethylbenzothiazoline-6-sulfonic acid (ABTS) methods. The possible synergism effect was evaluated using the checkerboard method and the combination index values were also calculated. Results: The TPC and TFC of the B. balsamifera extracts were much greater than that of C. grandis extract. In the molybdenum(VI) reducing power and FRAP assay, the reducing power of the extract combination increased as B. balsamifera extract concentration increased (P < 0.05). In the ABTS+ and DPPH radical scavenging assays, B. balsamifera extract demonstrated a higher antioxidant activity than C. grandis extract (P < 0.05). When combined, increasing the concentration of B. balsamifera caused an increase in the radical scavenging activity (P < 0.05). Synergism was observed in the combination of the extracts with low concentration ratios. Conclusion: In this study, we showed that the combination of C. grandis and B. balsamifera leaf extracts possessed synergistic antioxidant properties.

Characterization of phenolic compounds and antioxidative potential of pot-pollen produced by stingless bees (Tetragonula biroi Friese) from the Philippines

Eight pot-pollen samples produced by Philippine stingless bees (Tetragonula biroi Friese) were analyzed for the antioxidant composition and capacity. The methanolic extracts showed values of 7.95-24.75 mg GAE/g, 16.13-35.04 mg QE/g, and 0.19-0.74 mg CGE/g for total phenolics, flavonoids, and anthocyanins, respectively. All pot-pollens contained substantial amounts of rutin (0.471-1.547 mg/g), quercetin glucoside (1.427-3.390 mg/g), other flavonol glycosides, and hydroxycinnamic acids. Additionally, pollen samples contained 24-methylenecholesterol and Δ5-avenasterol as dominant phytosterols. Antioxidant activities based on ferric ion reducing antioxidant power (FRAP), DPPH^• , and ABTS^•+ scavenging activities, and lipid peroxidation (LPO) inhibition showed a high correlation with phenolic and flavonoid contents, except for LPO inhibition. Results suggested that there might be synergistic effects among antioxidants. Summing up, this study revealed that T. biroi Friese pot-pollen can be used as a food supplement with high nutraceutical potential. PRACTICAL APPLICATIONS: The recognition of Tetragonula biroi Friese pot-pollen as a nutraceutical product is strongly limited because its bioactive properties are not well-studied compared to other bee pollens. The results showed a rich occurrence of compounds with antioxidative effects like flavonoids and sterols. Antioxidant activities except lipid peroxidation inhibition revealed a high correlation with analyzed ingredients and shown interactions indicated that there might be synergistic effects among antioxidants.