Fumonisins in corn and their fate during storage and processing

Fumonisin concentrations were determined in twenty corn hybrids, grown in 1996 under irrigated conditions in three different locations of Nebraska. Only five samples contained FB$\sb1$ levels greater than 0.5 $\mu$g/g, and the highest FB$\sb1$ and FB$\sb2$ levels observed were 2.6 $\mu$g/g and 1.0 $\mu$g/g, respectively. No significant $(p \le 0.05)$ increases in either FB$\sb1$ or FB$\sb2$ were observed when the corn was stored for 12 weeks under conditions that did not result in any apparent visual Fusarium mold growth. Experimental dry milling of corn, naturally contaminated with three different levels of fumonisins, resulted in the concentration of fumonisins in bran, germ, and fines. Fumonisins were heat stable to varying degrees during processing of corn-based ingredients. No significant losses of FB$\sb1$ were found when spiked corn masa was fried at 140-170$\sp\circ$C for 0-6 min FB$\sb1$ began to degrade at frying temperatures $\ge$180$\sp\circ$C and times $\ge$8 min. Both the barrel temperature (140-200$\sp\circ$C) and screw speed (40-160 rpm) significantly affected the extent of fumonisin reduction during extrusion cooking of corn grits spiked with FB$\sb1$. The amount of FB$\sb1$ lost from cooking grits ranged from 34-95%. About 46-76% of the spiked FB$\sb1$ was lost when the grits were cooked at temperatures and screw speeds that resulted in acceptable product qualities. Flaking grits containing spiked fumonisin B$\sb1$ (FB$\sb1$) as well as cultured grits containing FB$\sb1$ and FB$\sb2$ were made into corn flakes using a laboratory procedure. Significant decreases in fumonisin levels were observed after cooking of both spiked grits (44.1%) and cultured grits (33.7%, FB$\sb1$; 29.8%, FB$\sb2$). However, toasting was not effective in reducing the fumonisin levels