Aflatoxigenic Fungi and Aflatoxins in Portuguese Almonds

1. Introduction

Almond tree, Prunus dulcis (Miller) D.A. Webb, synonym Amygdalus communis L., is a cultivated tree originating from wild trees from Central Asia, which is currently dispersed throughout the world. The almond tree is adapted to dry and hot climates, and for that reason it is mainly established in Mediterranean countries (Portugal, Spain, Italy, and France) and others with similar climatic characteristics, like USA (specifically California), Australia, South Africa, Chile, and Argentina. In Portugal, almonds are produced mostly in the northeast region of Trás-os-Montes and in the southernmost region of Algarve. The region of Trás-os-Montes integrates one Protected Designation of Origin (Denominação de Origem Protegida, DOP), DOP Douro. Even though Portugal is responsible for only 0.5% of almond’s worldwide production (http://faostat.fao.org/, accessed 10.09.2011), the culture represents significant cultural and economic incomes for local populations, since, under the traditional culturing methods, no major inputs are made other than harvest. Also, Portuguese almonds are usually exported as high-value product to other European countries such as Spain, France, and Germany.

Aflatoxins (AFs) are a group of mutagenic, teratogenic, and immunosuppressive mycotoxins that include the most widely studied aflatoxins B₁ (AFB₁), B₂ (AFB₂), G₁ (AFG₁), and G₂ (AFG₂). AFB₁ is considered the most carcinogenic compound naturally produced [1]. These mycotoxins are produced as secondary metabolites mostly by some species belonging to Aspergillus section Flavi when growing on a variety of food products. Tree nuts are among the commodities with moderate-to-high risk of AF contamination, since they are generally produced under environmental conditions which also favour growth of aflatoxigenic fungi and toxin production [2]. All over the world, almond producers are greatly affected by the economic impact of AF contamination. In 2009, the Rapid Alert System for Food and Feed (RASFF) reported a total of 669 alerts or notifications for mycotoxins, of which 95% were for AFs, mostly from nuts, nut products, and seeds (81%). Among these, 55 notifications (8.6%) were on almonds, mainly from USA and a few from Australia [3].

Knowledge of the structure of Aspergillus section Flavi communities of a given area is helpful in devising AF control strategies. Regarding the distribution and economic importance of aflatoxigenic species, only species belonging to Aspergillus