Effects of temperature on fusaria and Fusarium mycotoxins during short‐term storage of maize kernels (Zea mays)

Abstract

In three trials freshly harvested maize kernels (Zea mays) of different moisture contents (MC) (19%, 24%, 27%) were stored at 20°C, 25°C, 30°C, and 37°C for 3, 6, and 10 days and changes in the percentages of Fusarium‐infected kernels and in the concentrations of the mycotoxins nivalenol (NIV) and deoxynivalenol (DON) measured. The effects of storage varied with the initial Fusarium infections and moisture content as well as with time and temperature. In the grain of 19% MC, F. subglutinans was the dominant Fusarium species and initially infected 16% of kernels, while the NIV + DON concentration was below 0.2 mg/kg. Neither the percentage of Fusarium infection nor the toxin concentration changed greatly at any temperature during the storage period, although the proportion of F. subglutinans increased at 30°C and 37°C. In the harvest sample of 24% MC, F. graminearum was the dominant Fusarium species on day 0 and infected 26% of kernels. The total content of NIV plus DON was less than 0.5 mg/kg. By day 10 during storage at 20–30°C the infection rate of F. graminearum rose to 42–60% and NIV + DON concentration to over 2 mg/kg. At 37°C F. graminearum was no longer recovered by day 6 and NIV + DON concentration was unchanged from the initial level. In the harvest sample of 27% MC, F. graminearum was dominant and initially infected 80% of the kernels. The initial NIV + DON concentration was 2 mg/kg. At 20–30°C the infection rates did not materially change but toxin content rose to c. 6 mg/kg by day 10. At 37°C F. graminearum was no longer recoverable at day 10 while the NIV + DON concentration remained at the original level. Visual inspection of the incubated samples showed visible mould growth about the grains in samples incubated for 10 days at 37°C for the 24% MC sample or for 6–10 days at all temperatures in for the 27% MC sample. The incidence of Penicillium was favoured by storage, and at 37°C the predominant fungus found at day 10 was Penicillium (19% MC and 27% MC samples) or Aspergillus (24% MC sample).