Influence of white light, near-UV irradiation and other environmental conditions on production of aflatoxin B1 by Aspergillus flavus and ochratoxin A by Aspergillus ochraceus.

Abstract

The effects of illumination, near-ultraviolet, incubation temperature pH and some minor elements on the growth rate and production of aflatoxin B1 by A. flavus and ochratoxin A by A. ochraceus were investigated. Aflatoxin B1 and ochratoxin A production was considerably higher in the light than in the dark. The greatest aflatoxin B1 and ochratoxin A production was occurred after 11 days of fermentation with light- and dark-grown cultures at 25 degrees C. The mycelial dry weight was also greater in the light than in the dark for both A. flavus and A. ochraceus. Exposure of conidia to near-UV irradiation increased mycelial dry weight and mycotoxins by both fungi more than white light. The greatest aflatoxin B1 and ochratoxin A was at 25 degrees C with UV-grown culture (24 h exposure) producing a mean of 400 and 260 micrograms/50 ml of medium, respectively. The maximum aflatoxin B1 and ochratoxin A yield was obtained at pH 5.5 and with increasing the initial pH to near neutrality, both mycotoxins yield decreased. Iron, copper and zinc were observed to stimulate aflatoxin B1 and ochratoxin A production and enhanced the growth rate of both A. flavus and A. ochraceus.