Enhanced antioxidant activity of aqueous phase bio-oil by hydrothermal pretreatment and its structure-activity relationship

Abstract

The antioxidant activity and the structure-activity relationship of aqueous phase bio-oil (APBO), obtained from hydrothermal treatment (HTT) combined with pyrolysis of biomass, have been investigated in this study. HTT increased the relative content of phenolic compounds and reduced the relative content of acids. Phenolic compounds possessed as the dominant chemical components in APBO, representing up to 61.68 %. 2-methoxyphenol (guaiacol) and its derivatives were the major components of phenolic compounds. HTT promoted the antioxidant activity of APBOs and APBO-180 showed higher antioxidant activity than that of commercial chemical antioxidant (butylated hydroxyl toluene) with IC50 values of 0.402 mg/mL of reducing power, 0.132 mg/mL of DPPH free radical scavenging capacity and 0.405 mg/mL of hydroxyl free radical scavenging capability. The antioxidant activity of APBO was affected by its chemical composition. Phenols exhibited a promotion effect on antioxidant activity, while acids showed an inhibition effect. In addition, the substituent structure of phenols played a key role in antioxidant activity. Phenols with the shorter carbon side chain showed higher antioxidant activity (e.g. 2-methylphenol>2-methoxyphenol, 4-methyl-2-methoxyphenol>4-ethyl-2-methoxyphenol). This study suggested that APBO could be developed as the natural feed additives or alternative antioxidant, providing a new strategy for efficient utilization of APBO.