Formation of <i>N</i>-(Carboxymethyl)fumonisin B₁, Following the Reaction of Fumonisin B₁ with Reducing Sugars

Abstract

The fumonisins are mycotoxins produced by fungi that contaminate primarily corn and are toxic through interruption of intracellular sphingolipid synthesis. Several reports have indicated that fumonisin B1 concentrations decreased when heated in aqueous solutions of reducing sugars. The incubation of fumonisin B1 with d-glucose resulted in the formation of N-(carboxymethyl)fumonisin B1, which was characterized by NMR and electrospray mass spectroscopy. We determined the methylene carbon of the carboxymethyl group is derived from C1 on glucose, while the carbonyl carbon is derived from the C2 of glucose, using 13C glucose. Apparently N-(carboxymethyl)fumonisin B1 arises from Schiff's base formation, Amadori rearrangement to a β-ketoamine, and oxidation with molecular oxygen. N-(Carboxymethyl)fumonisin B1 formation is favored by alkaline conditions (pH >7), requires molecular oxygen, and is catalyzed by several reducing sugars. N-(carboxymethyl)fumonisin B1 was detected in raw corn samples that contained fumonisin B1 (0.5−1.4 ppm) at an average of 4% of the fumonisin B1 levels. Keywords: Fumonisin B1; fumonisins; N-(carboxymethyl)fumonisin B1; detoxification; Amadori rearrangement; Maillard reaction; reducing sugars; mycotoxin