Biocontrol of Aflatoxins B1,B2,G1,G2, and Fumonisin B1 with 6,7-Dimethoxycoumarin, a Phytoalexin from Citrus sinensis

Abstract

Phytoalexins (stress-induced compounds) from Citrus sinensis cultivar Valencia were screened for antifungal and anti-mycotoxic activity against a test organism (Cladosporium cladosporoides) and mycotoxin-producing fungi Fusarium verticillioides and Aspergillus parasiticus. The active compound, a member of the coumarin family of compounds, has antifungal and antimycotoxic activities and was chemically identified. High-performance liquid chromatography results indicated that Valencia oranges contain a trace amount (0.36 μg/g) of scoparone in untreated fruit, but concentrations increased in UV-irradiated fruit (15.2 μg/g). Infection with Penicillium digitatum, a natural spoilage mold of citrus fruit, caused a 35.51-μg/g increase in the phytoalexin. UV absorption, infrared absorption, and 1H nuclear magnetic resonance spectroscopy revealed that this phytoalexin is identical to 6,7-dimethoxycoumarin. This is the first report indicating that the stress-induced compound, 6,7-dimethoxycoumarin, isolated from P. digitatum–infected Valencia fruit confers resistance against the mycotoxigenic fungi A. parasiticus and F. verticillioides and causes a reduction in production of fumonisin B1 and aflatoxins G1,G2,B1, and B2.