Abstract: Hops soft resin contains three homologues of β-acids: co-, n- and ad-lupulone, and the ratio among these homologues varies depending on hops varieties. In this experiment, five β-acid homologue mixtures were obtained from the crude β-acid from hops by crystallization, and their antioxidant activity in vitro were investigated comparatively by measuring the inhibitory activity against xanthine oxidase, 1,1-diphenyl-2-picrylhydrazyl (DPPH) and OH radical scavenging activity, total antioxidant activity and inhibition zone diameter. The results showed that the antioxidant activity of these β-acid homologue mixtures were significantly different. Among them, the 1:4 mixture of co-lupulone with n-lupulone + ad-lupulone possessed the strongest antioxidant activity, indicating that the antioxidant activity of n-lupulone + ad-lupulone was stronger than that of co-lupulone. At high concentrations (≥ 40.00 mg/L), mixtures with higher proportion of co-lupulone had stronger antibacterial activity. The antibacterial activity of all samples except the 1:4 mixture of co-lupulone with n-lupulone + ad-lupulone at a concentration of 160.00 mg/L was similar to or even stronger than that of amoxicillin. The sample with the highest proportion of n + ad-lupulone showed the lowest minimum inhibitory concentration (5.00 mg/L) against Staphylococcus aureus. In addition, although the minimum inhibitory concentrations of all samples against Escherichia coli were equally 10.00 mg/L, this one exhibited a bigger diameter of inhibition zone.

Key words: hops; soft resin; β-acid homologues; antioxidant activity; antibacterial activity