Determination of antifungal volatile organic compounds of upland rice vinegar and their inhibition effects on Aspergillus flavus in dried chili pepper

Determination of volatile organic components (VOC) produced in high acid upland rice vinegar was conducted using GC-MS. Acetic acid and ethyl acetate at 9.11% and 2.69% (v/v), respectively, were major VOC found in the vinegar while the others were isobutyl acetate, isobutyl alcohol, isoamyl acetate, isoamyl alcohol, phenethyl acetate and phenethyl alcohol. Subsequently, vinegar and VOC were tested, in vitro, for their inhibition on conidia germination of 103 conidia/mL of Aspergillus flavus. The exposure with 10% (v/v) of vapor-phase vinegar and pure acetic acid completely inhibited the germination of conidia with 30 min exposure, while VOC mixture of 9.11% (v/v) acetic acid, 0.08% (v/v) isoamyl alcohol, 0.45% (v/v) phenethyl alcohol and 0.01% (v/v) isobutyl alcohol with 45 min exposure could achieve the same target. Then, vinegar vapor was tested on the inhibition of conidia germination and aflatoxin production of A. flavus during 90 d subsequent storage of dried chili pepper. Complete inhibition of conidia germination and aflatoxin production were achieved with the 40 min exposure of 1.04 +/- 0.03 mmol/L of vaporized vinegar. Our results showed that fumigation of upland rice vinegar containing antifungal VOC is a simple and an economical method for commercial preservation of dried chili pepper. Upland rice vinegar is a novel bio-fumigant for prevention of mycotoxin production in dried food and feed products during storage.

Automated summary

The determination of volatile organic components (VOC) in high acid upland rice vinegar was conducted using GC-MS. The major VOC found in the vinegar were acetic acid and ethyl acetate. In vitro experiments showed that vapor-phase vinegar and pure acetic acid completely inhibited the germination of Aspergillus flavus conidia. A VOC mixture containing acetic acid, isoamyl alcohol, phenethyl alcohol, and isobutyl alcohol achieved the same result with longer exposure. Vaporized vinegar at a specific concentration was able to inhibit conidia germination and aflatoxin production of A. flavus during long-term storage of dried chili pepper. These findings suggest that upland rice vinegar containing antifungal VOC can be used for commercial preservation of dried chili pepper and other food products.