Prevalence of Toxigenic Fungi and Mycotoxins in Arabic Coffee: Protective Effect of Traditional Coffee Roasting, Brewing and Microbial Volatiles
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Like other agricultural crops, fungal infection and synthesis of mycotoxins in coffee leads to significant economic losses. This study is aimed at investigating the prevalence of toxigenic fungi, their metabolites, and the effect of traditional roasting and brewing on ochratoxin A (OTA) and aflatoxins (AFs) contents of naturally contaminated coffee samples. In addition, in vivo biocontrol assays were performed to explore the antagonistic activities of Bacillus simplex 350-3 (BS350-3) on the growth and mycotoxins synthesis potential of Aspergillus ochraceus and A. flavus. The relative density of A. niger, A. flavus, Penicillium verrucosum and A. carbonarius on green coffee bean was 60.82%, 7.21%, 3.09% and 1.03%, respectively. OTA contents were lowest in green coffee beans (2.15 µg/kg), followed by roasted (2.76 µg/kg) and soluble coffee (8.95 µg/kg). Likewise, AFs levels were highest in soluble coffee (90.58 µg/kg) followed by roasted (33.61 µg/kg) and green coffee (9.07 µg/kg). Roasting naturally contaminated coffee beans by three traditional styles; low, medium and high, followed by brewing resulted in reduction of 58.74%, 60.88% and 64.70% in OTA and 40.18%, 47.86% and 62.38% AFs contents, respectively. BS350-3 volatiles resulted in significant inhibition in AFs and OTA synthesis by A. flavus and A. carbonarius on infected coffee beans, respectively. Gas chromatography mass spectrochemistry (GC-MS/MS) analysis of headspace BS350-3 volatiles showed quinoline, benzenemethanamine and 1-Octadecene as bioactive antifungal molecules. These findings suggest that marketed coffee samples are generally contaminated with OTA and AFs; with a significant number of roasted and soluble coffee contaminated at the levels above EU permissible limits for OTA. Further, along with coffee roasting and brewing; microbial volatiles possess a promising potential, which can be optimized to minimize the dietary exposure to mycotoxins.