Mycotoxin Production and Prevention of Afl atoxin Contamination in Food and Feed (2007)

CONTENTS 27.1 Introduction ............................................................................................................................. 457 27.2 Signifi cance of Mycotoxin Contamination ............................................................................. 45827.2.1 Mycotoxins and Afl atoxins ....................................................................................... 458 27.2.2 Health Risk, Food Safety, and Economic Impact of Afl atoxin Contamination .......... 45827.3 Afl atoxin Biosynthesis ............................................................................................................ 459 27.3.1 Afl atoxin Biosynthetic Pathways and Enzymes ....................................................... 459 27.3.2 Afl atoxin Biosynthetic Pathway Genes .................................................................... 460 27.3.3 Afl atoxin Biosynthetic Pathway Gene Clusters ........................................................ 460 27.3.4 Regulation of Afl atoxin Biosynthesis ....................................................................... 46127.4 Factors Affecting Afl atoxin Formation ................................................................................... 461 27.4.1 Nutritional Factors .................................................................................................... 461 27.4.2 Environmental Factors .............................................................................................. 462 27.4.3 Developmental Factors ............................................................................................. 462 27.4.4 Stress Factors and Antioxidation .............................................................................. 46227.5 Strategies in Preventing Afl atoxin Contamination ................................................................. 463 27.5.1 Biological Control by Nontoxigenic Aspergillus fl avus Strain ................................. 463 27.5.2 Host Resistance Through Crop Breeding and Genetic Engineering ........................ 464 27.5.3 Crop Genomics for Improving Host Resistance in Corn, Cotton, and Peanuts ....... 464 27.5.4 Gene Profi ling Through Aspergillus fl avus Genomics ............................................. 46527.6 Summary and Prospects ......................................................................................................... 466 References .......................................................................................................................................... 46627.1 Introduction Afl atoxins are the most prominent groups of mycotoxins. They are known as the most toxic and most potent carcinogens naturally produced by fungal molds, mainly Aspergillus fl avus and Aspergillus parasiticus. Over 40 years of research and investigations generated a wealth of publications on fungal biology, toxicology, and toxin biosynthesis. In this review, only the most pertinent aspects on afl atoxin biosynthesis and prevention are discussed. In deciphering the afl atoxin biosynthetic pathway, signifi cant progress has been made in the last decade.1-3 A complete afl atoxin biosynthetic pathway gene cluster consisting of 29 genes has been cloned.4,5 Details of these genes and their encoded enzymes as well as the regulation of gene expression have been reported.3 Sterigmatocystin (ST) or dihydrosterigmatocystin(DHST), the penultimate precursor of afl atoxins, is produced by several species including A. versicolor and A. nidulans.6 ST and DHST are toxic and and carcinogenic. They share strikingly similar common biochemical pathway, homologous genes, and regulatory mechanism to afl atoxin synthesis in A. fl avus.5 The ST biosynthetic pathway and genes are discussed as well.