Antifungal effects of three natural branched medium-chain fatty acids and their potential as fumigants against Aspergillus flavus in stored peanut seeds

The contamination of peanuts with aflatoxins predominantly produced by Aspergillus flavus poses a worldwide threat to both food safety and agricultural economies. Antifungal compounds from natural sources may offer a safe and effective alternative strategy to control A. flavus in peanuts. We evaluated the contact and fumigant antifungal effects of three natural branched medium-chain fatty acids (branched-MCFAs), ( E )-2-methyl-2-pentenoic acid, 2-methylhexanoic acid, and 2-methylheptanoic acid against A . flavus relative to their straight-chain isomers and sorbic acid a commonly used preservative. In vitro experiments showed that the inhibitory effects of these three branched-MCFAs on A. flavus were stronger than their straight-chain isomers and sorbic acid. In addition, fumigant effects of the branched-MCFAs were more effective than their direct contact inhibitory effects against the growth of A. flavus . 2-Methylhexanoic acid, 2-methylheptanoic acid, and ( E )-2-methyl-2-pentenoic acid showed significant fumigant activity, with the minimum inhibitory concentration (MIC) values of 0.10, 0.10, and 0.12 g/l air, respectively. Fumigation of these branched-MCFAs also significantly slowed the growth of A. flavus in peanut seeds, and completely inhibited A. flavus growth at 2.0 g/l air. After 24 h of fumigation exposure to the branched-MCFAs, the fumigated A. flavus on medium or peanut seeds was re-incubated to observe whether the A. flavus could continue to grow, and the results revealed that the in vitro and in vivo minimum fungicidal concentrations (MFC) were 0.15 and 2.5 g/l air, respectively. This study indicated that these three natural branched-MCFAs have strong antifungal fumigation activity with application potential in protecting peanut seeds from A. flavus contamination during storage.