OTA-producers in coffee
What organisms are involved in the production of OTA in coffee?
As noted above, certain fungi have ecological associations with certain crop plants, and some processing or storage conditions favour specific fungi - hence certain crops have a tendency to contain particular mycotoxins and not others. Coffee is no exception.
Neither of the OTA-producing species of Penicillium (P. verrucosum and P. nordicum) have been isolated from coffee. P. brevicompactum is common in coffee and is in the same group as the two producing species, but is not an OTA-producer. For coffee, three species or groups of species, all in the genus Aspergillus, are of possible significance:
1. A. niger complex (there is no consensus on speciation in A. niger-like fungi) is by far the most common, particularly in Coffea caneophora (robusta), but OTA production is rare and usually feeble. One study revealed only one producer amongst the seventy isolates tested;
Aspergillus niger - Click here to enlarge
2. A. carbonarius is generally rare, but there is some evidence that it can be relatively common in certain locations. Most isolates seem to be capable of OTA production in significant amounts, though over a restricted range of environmental conditions;
Aspergillus carbonarius - Click here to enlarge
3. A. ochraceus and related fungi are well distributed in coffee production systems and because OTA production is common (about 80% of isolates readily produce OTA), it comprises the most important OTA-producing species in coffee.
Aspergillus ochraceus - Click here to enlarge
(diminutive conidial head - 10 µ radius)
OTA contamination of coffee has been shown to be primarily a post-harvest problem. Basically, adequately controlling the water available in coffee that could support mould growth and mycotoxin contamination during the post-harvest handling of coffee is the best way to avoid OTA contamination.