Starch and thermal treatment, important factors in changing detectable fumonisins in maize post-harvest.

The drying process is commonly applied to maize grain to guarantee a safe storage. Different temperature can be considered in commercial plants, but below 100°C is suggested, and consequently the exposure time is defined. Two different conditions were tested (70°C x 24 hours and 95°Cx 9 hours) on 6 maize hybrids collected in 2010 in Italy. Maize samples were analysed from a biological and a chemical point of view; in particular, fungal incidence, kernel chemical composition (proteins, fat, starch) and free and hidden forms of fumonisins (FBs) were investigated pre- and post-drying treatments. Drying treatments confirmed their importance in reducing fungal incidence. In particular, both temperature x time combination were able to reduce more than 85% of Fusarium spp. incidence. In general, both free and total FBs increased after drying, especially at 70°C for 24 hours exposure. Regarding chemical composition, proteins and starch resulted unvaried, while fat content had a mean decrement of 26% and 14% after treatment at 70°C x 24 hours and 95°C x 9 hours, respectively. A possible retrogradation of starch, and in particular amylose, after heating has been proposed in this study; these changes seemed to be strongly related to the changes in detectable fumonisin. This study confirms the variation in detectable FBs occurring after the drying treatment. Therefore, the quantification of fumonisin contamination after the post-harvest treatments is strongly suggested to avoid maize contaminated above the legal limit to enter the food/feed chain.