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New Amylase Inhibitor Present in Corn Seeds Active In Vitro Against Amylase from Fusarium verticillioides

A screening for specific amylase inhibitor levels against amylase from Fusarium verticillioides (Fusarium moniliforme), the most relevant mycotoxigenic fungus in corn, was conducted on 37 corn hybrids. The amylase inhibitor levels in these hybrids ranged from 5.5 to 16.0 amylase inhibitor units per gram of corn (AIU/g) in the MASTER and AG5011 hybrids, respectively. The hybrid with the maximum content of inhibitor was used as the source of this new protein. The inhibitor was partially purified using fractional precipitation, gel filtration on Sephadex G-75 column, high performance liquid chromatography (HPLC) Superose HR 10/30 column, and HPLC anion exchange chromatography, obtaining a 20.7-fold purification. Electrophoresis after denaturing and heating under reductive conditions showed an apparent 23.8 kDa molecular mass and an acidic isoelectric point of 5.4, which differs from previous molecular masses reported for other inhibitors present in corn seeds (14 and 22 kDa). This inhibitor showed activity against amylases from human saliva and pancreas, from the fungi F. verticillioides and Aspergillus flavus, and from the insects Acanthoscelides obtectus, Zabrotes subfasciatus, Tribolium castaneum, and Sitotroga cerealella. The mycoflora found in the corn grain indicated Fusarium sp. as the most prevalent fungi (81.1% of the samples), with a count ranging from 1.5 × 10² to 2.4 × 10⁶ CFU/g of corn. The presence of fumonisins was detected in 21 out of the 37 hybrids studied, ranging from 0.05 to 2.67 μg of FB per gram of corn. No correlation could be established between this amylase inhibitor level in the corn seeds and the presence of Fusarium sp. or with the fumonisin content under the experimental conditions of the test.