Conditions of formation of ochratoxin A in drying, transport and in different commodities

Abstract

The major species of fungi responsible for ochratoxin production (OTA) in a range of commodities are Penicillium verrucosum, Aspergillus ochraceus and Aspergillus section Nigri, especially A. carbonarius. P. verrucosum is particularly important in northern Europe where damp cooler conditions occur and where drying regimes need to be efficient and effective for preventing post-harvest contamination with OTA. A. ochraceus can infect cereals including barley, maize, coffee, cocoa and edible nuts. A. carbonarius has been identified as the key species responsible for OTA contamination of grapes, wine and vine fruits. Recent studies have identified the environmental regimes, especially of temperature and humidity, which are conducive to growth and OTA production by these species pre-and post-harvest and during transport. The optimum and marginal interacting conditions for growth and OTA contamination often vary considerably. This has to be borne in mind when effective preventative management strategies are being implemented. Recent studies with cereals have suggested that isolation frequency can be related to OTA contamination of cereals. A logistical model has been developed and identified that 1000 CFUs g À1 grain of P. verrucosum (CFUs) is the threshold limit at which the probability of exceeding the EU legislative limit of 5 mg kg À1 in cereal grain can be predicted under different storage regimes. Controlled atmospheres >50% C0 2 is required to effectively prevent OTA accumulation in damp cereals. With regard to grapes, preharvest contamination with A. carbonarius has been shown to be a good indicator for regional risk in southern Europe from OTA contamination. The ecological conditions for optimum growth and OTA production have been shown to differ with the optima being 30-35 C and 15-25 C and 0.98-0.99 and 0.93-0.95 water activity, respectively. Studies on vine fruits (drying currants) suggest that OTA contamination and increase contamination levels occur during this drying process of 7-14 days. This will be influenced by prevailing weather conditions and drying rates. Minimizing OTA contamination in these and other commodities including coffee and cocoa require clear guidelines on safe moisture and temperature regimes pre-and post-harvest for the development of effective management strategies based on ecological criteria.

Mycotoxin production by different ochratoxigenic Aspergillus and Penicillium species on coffee- and wheat-based media

“…Wheat is the natural habitat of this species, and the results described here show that apparently the natural environment actively supports OTA biosynthesis by this fungus, comparable with the activation of the biosynthesis by the very supportive YES medium. Aspergilli are not commonly associated with production of important amounts of OTA in wheat at lower temperature (described in Magan and Aldred 2005). However, A. ochraceus BFE635 and A. niger BFE632 produced the highest amounts of OTA (>50 μg OTA/g agar) at 25°C in wheat-based medium.…”

“…Environmental conditions, such as temperature and moisture expressed as water activity (a w ), pH and nutrient content of the matrix, incubation time, and light, are decisive factors for fungal OTA production (Abellana et al 2001;Astoreca et al 2007;Esteban et al 2004;Magan and Aldred 2005;Richter et al 2001;Schmidt-Heydt et al 2010, 2011. Penicillium species are known as OTAproducers in regions with temperate and cold climates.…”

Mycotoxin Contamination of Beverages: Occurrence of Patulin in Apple Juice and Ochratoxin A in Coffee, Beer and Wine and Their Control Methods

“…Grape washing, cooking and pressing can also promote the OTA content drop [53,287]. During vine fruits production, efficient drying and turning over are required because in these stages, moisture and sugar content stimulates Aspergillus section Nigri development and OTA synthesis [288].…”

The effect of dipping pretreatment on ochratoxin A accumulation in sultanas and currants

“…The maximum level of OTA allowed in dried vine fruits in Europe is 10 µg/kg (12). Moreover, Aspergillus niger aggregate and Aspergillus carbonarius have been blamed as the OTA producers in grape and grape-derivatives (13)(14)(15). Astoreca et al (16) reported that, throughout the grape drying process, the biodiversity index showed a decreasing trend because the water activity (Aw) of grape was decreasing and the sugar level was increasing.…”