Aspergilli and ochratoxin A in coffee

Ochratoxin contamination of coffee can be regarded as a post-harvest problem. The diversity and ochratoxin producing potential of Aspergilli in coffee beans depends on a combination of various factors including coffee variety, geographic region, climate, susceptibility to insect pests and processing method. According to recent surveys, the most important ochratoxin producers are A. westerdijkiae and A. niger in Arabica coffee beans, and A. carbonarius in Robusta beans. Optimum water activities and temperatures for growth and ochratoxin production of Aspergillus species were found to be at aw 0.95-0.99 at 24-31 ºC. Some chemicals (caffeine, chlorogenic acid) have inhibiting effect on growth and toxin production of Aspergillus species in coffee. During storage, water activities above 0.80 pose a risk for fungal growth and ochratoxin contamination until roasting. In order prevent the risk of ochratoxin contamination, this critical period need to be minimised to appropriate levels to prevent growth and toxin production. The choice of coffee processing affects ochratoxin content in coffee, while roasting can reduce ochratoxin levels by 30-96% depending on temperature and time of roasting. Coffee contributes only to a small extent to ochratoxin intake of humans in Europe, even if it is prepared from relatively highly contaminated green beans.