The effects of yeasts involved in the fermentation of Coffea arabica in East Africa on growth and ochratoxin A (OTA) production by Aspergillus ochraceus

The effects of Pichia anomala, Pichia kluyveri and Hanseniaspora uvarum predominant during coffee processing on growth of Aspergillus ochraceus and production of ochratoxin A (OTA) on malt extract agar (MEA) and on coffee agar (CA) were studied. The three yeasts were able to inhibit growth of A. ochraceus when co-cultured in MEA and CA. Growth inhibition was significantly higher on MEA than on CA. Furthermore, P. anomala and P. kluyveri were found to have a stronger effect on growth of A. ochraceus than H. uvarum. The three yeasts were able to prevent spore germination of A. ochraceus in yeast glucose peptone (MYGP) broth. In yeast-free supernatant of MYGP broth after an incubation period of 72 h, spores of A. ochraceus were able to germinate with very short germ tubes, but further development of the germ tubes was inhibited. The three yeasts decreased the pH of MYGP broth from 5.6 to a range of 4.4–4.7, which was found to have no effect on spore germination of A. ochraceus.P. anomala, P. kluyveri and H. uvarum were able to prevent production of OTA by A. ochraceus when co-cultured on MEA. On CA medium, P. anomala and P. kluyveri prevented A. ochraceus from producing OTA. H. uvarum did not affect production of OTA by A. ochraceus on CA medium.