Rhizopus sp. as Antagonist Fungi Against Ochratoxin a Production by Aspergillus carbonarius in raw cocoa beans

Abstract

Ochratoxin A (OTA) is produced generally by the mold of the genera Aspergillus in cocoa beans. This study evaluated the antifungal activity of a strain of Rhizopus sp. on an OTA-producing mold and the biocontrol of the toxin production by this species in cocoa. HPLC detected OTA contents in cocoa beans from different post-harvest treatments. Mold species were identified by conventional microbiology and PCR-DGGE methods according to OTA contents. Suspensions calibrated at 106, and 104 conidia.mL-1 of Rhizopus sp. and A. carbonarius were co-inoculated in cocoa pods and incubated for 4 or 8 days in a climatic chamber. The results showed various fungal species of Aspergillus, Aureobasidium, Chrysonilia, Mucor, Penicillium, and Rhizopus. The number of fungal species obtained with PCR-DGGE was higher than that obtained on Petri dishes. Aspergillus carbonarius and A. niger were the main producers of OTA in the samples. The use of plastic crates as fermentation support in the presence of A. Carbonarius promoted a high production of OTA compared to wooden boxes and banana leaves. The co-inoculation of 104 spores.mL-1 of A. carbonarius and 106 spores.mL-1 of Rhizopus led to an OTA content in cocoa of 0.1 µg.kg-1 in 4 days of incubation while in 8 days, this concentration reached 5.6 µg.kg-1. Finally, the co-inoculation of cocoa with 106 spores.mL-1 of A. carbonarius and 104 spores.mL-1 of Rhizopus sp. led in 4 and 8 days of incubation to respective OTA contents of 36.3 and 6.2 µg.kg-1 of cocoa. Rhizopus could inhibit OTA production in cocoa.