Screening of Anti-fungal Bacillus Strains and Influence of their Application on Cocoa Beans Fermentation and Final Bean Quality

Abstract

Aims: Contamination with filamentous fungi reduces the quality of cocoa beans and poses a health risk for consumers due to the potential accumulation of mycotoxins. The aim of this study was to develop antifungal Bacillus cultures for cocoa beans fermentation. Methods and Results: Antifungal activity of 7 Bacillus isolates was investigated using overlay technique. Solid culture media inoculated with bacterial and fungal isolates were cultivated under aerobic conditions at 30 ºC for 5 days.  The Bacillus strain with strong antifungal activity was studied and inoculated to 18 kg box fermentations cocoa beans in Cote d'Ivoire in three time-independent replications each including a spontaneous control fermentation. The comparison of inoculated and spontaneous fermentation processes revealed that the Bacillus thuringiensis strain ATCC 10792 don't affected the fermentation process and cocoa bean quality. The anti-fungal in vivo assays revealed that the Bacillus thuringiensis strain ATCC 10792 completely inhibited growth of all fungi on the surface of cocoa beans. The result showed that sensory evaluation of chocolates is not significant differences for all treatment. The sensory evaluation of control and chocolates made from the inoculated cocoa beans with Bacillus showed excellent sensory quality, demonstrating that Bacillus thuringiensis strain ATCC 10792 did not affect aroma, texture and appearance of chocolate. Conclusion: From this study, it is revealed that the addition of Bacillus thuringiensis strain ATCC 10792 during fermentation cocoa beans suppress fungal growth and improve the quality of cocoa beans. Therefore, the anti-fungal culture Bacillus thuringiensis strain ATCC 10792 is recommended for future applications and its capacity to limit fungal growth during industrial-scale cocoa bean fermentation should be investigated in further studies.