Isolation, identification and toxigenic potential of ochratoxin A-producing Aspergillus species from coffee beans grown in two regions of Thailand

Abstract

In 2006 and 2007, 32 Thai dried coffee bean samples ( Coffea arabica) from two growing sites of Chiang Mai Province, and 32 Thai dried coffee bean samples ( Coffea canephora var. robusta) from two growing sites of Chumphon Province, Thailand, were collected and assessed for the distribution of fungi with the potential to produce ochratoxin A (OTA). The overall percentage of fungal contamination in coffee was 98% and reduced to 60% after surface disinfection. There were remarkable ecological differences in the composition of ochratoxigenic species present in these two regions. Arabica coffee bean samples from the North had an average of 78% incidence of colonization with Aspergillus of section Circumdati with Aspergillus westerdijkiae and A. melleus as the predominant species. Aspergillus spp. of section Nigri were found in 75% of the samples whereas A. ochraceus was not detected. Robusta coffee beans from the South were 98–100% contaminated with predominantly A. carbonarius and A. niger. A. westerdijkiae was only found in one sample. The diversity of the fungal population was probably correlated with the geographical origin of the coffee, coffee cultivar, and processing method. Representative isolates of section Circumdati (52) and Nigri (82) were examined for their OTA production using HPLC with fluorescence detection. Aspergillus westerdijkiae (42 isolates out of 42), A. steynii (13/13), and A. carbonarius (35/35) in general produced large amounts of OTA, while one isolate of A. sclerotiorum produced intermediate amounts of OTA. 13% of the A. niger isolates produced OTA in intermediate amounts. OTA levels in coffee bean samples were analyzed using the Ridascreen ® OTA ELISA kits. Of the 64 coffee bean samples analyzed, 98% were contaminated with OTA in levels of < 0.6–5.5 µg/kg (Arabica) and 1–27 µg/kg (Robusta). Presence of OTA in representative coffee samples was also confirmed by LC-MS/MS after ion-exchange purification.