Structure–antioxidant activity relationships of gallic acid and phloroglucinol

Gallic acid and phloroglucinol are the main phenolic compounds of the pistachio green hull (Pistachia vera) extract. The anti-radical and -peroxide activities of gallic acid and phloroglucinol were compared through DPPH radicals scavenging, bleaching of β-carotene (BCB), and Rancimat assays. The gallic acid molecules (log P =  − 0.46) with an electron-donating carboxylate anion had significantly higher radical scavenging activities than phloroglucinol molecules (log P = 1.38) in DPPH (IC50 = 30.53 vs. 45.72 μM), BCB (IC50 = 43.66 vs. 66.15 μM), and Rancimat (OSI = 4.89 vs. 2.26 h) assays. The combinational kinetic model was successfully used for the determination of kinetic parameters, such as induction period (IP), the maximum concentration of lipid hydroperoxides (PVmax), and critical reverse micelle concentration (CMC) in soybean oil triacylglycerols (TAGs) peroxidized at 60 °C. The kinetics parameters, antioxidant effectiveness (F), and activity (AA) revealed gallic acid had the highest inhibitory effect during TAGs peroxidation due to the improved interfacial performance. Gallic acid and phloroglucinol were able to protect TAGs against peroxidation (IP = 388.34–816.21 vs. 25.53–122.4 h) in terms of the extent of their participation in the main reaction of chain termination and pro-oxidative side reactions of chain initiation, and anti-oxidative side reactions of chain propagation.