Alternaria mycotoxins and its incidence in fruits and vegetables

Abstract

Alternaria is a ubiquitous fungal genus, widely distributedin the environment and a range of different habitats. It includes both plantpathogenic and saprophytic species, which can affect crops in the field orcause post-harvest spoilage of plant fruits and kernels. Numerous Alternaria species cause damage toagricultural products including cereal grains, fruits and vegetables, and areresponsible for severe economic losses worldwide. MostAlternaria species have the abilityto produce a variety of secondary metabolites, which may play important rolesin plant pathology as well as food quality and safety. Alternariol (AOH),alternariol monomethyl ether (AME), tenuazonic acid (TeA), tentoxin (TEN) andaltenuene (ALT) are considered the main Alternariacompounds thought to pose a risk to human health. However, food-borne Alternaria species are able to producemany additional metabolites, whose toxicity has been tested incompletely or nottested at all. Both alternariols are mutagenic and their presence in cerealgrain has been associated with high levels of human esophageal cancer in China.TeA exerts cytotoxic and phytotoxic properties, and is acutely toxic in differentanimal species, causing hemorrhages in several organs. The possible involvementof TA in the etiology of onyalai, a human hematological disorder occurring inAfrica, has been suggested. Altertoxins (ALXs) have been found to be morepotent mutagens and acutely toxic to mice than AOH and AME. Other metabolites,such as TEN, are reported to be phytotoxins, and their toxicity on animals hasnot been demonstrated up to now. Vegetablefoods infected by Alternaria rot areobviously not suitable for consumption. Thus, whole fresh fruits are notbelieved to contribute significantly with Alternariatoxins to human exposure. However, processed vegetable products may introduceconsiderable amounts of these toxins to the human diet if decayed or moldyfruit is not removed before processing. Thetaxonomy of the genus is not well defined yet, which makes it difficult toestablish an accurate relationship between the contaminant species and theirassociated mycotoxins. Great efforts have been made to organize taxa intosubgeneric taxonomic levels, especially for the small-spored, food associatedspecies, which are closely related and constitute the most relevant foodpathogens from this genus.Severalcrops of agricultural value are susceptible to infection by different Alternaria species and can contribute tothe entry of Alternaria mycotoxins inthe food chain. The distribution of Alternariaspecies was studied in different commodities grown in Argentina. These foodpopulations were characterized through a polyphasic approach, with specialinterest in their secondary metabolite profiles, to understand their fullchemical potential. Alternariaspecies associated with tomato, bell pepper, blueberry, apples and wheatcultivated in Argentina showed a surprisingly high metabolomic andmycotoxigenic potential. The natural occurrence of Alternaria toxins in these foods was also investigated. The resultshere presented will provide background for discussion on regulations for Alternaria toxins in foods.