Abstract
Fungal infection and synthesis of mycotoxins in coffee leads to significant economic losses. This study aimed to investigate 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 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 at three traditional methods; low, medium and high, followed by brewing resulted in reduction of 58.74% (3.50 μg/kg), 60.88% (3.72 μg/kg) and 64.70% (4.11 μg/kg) in OTA and 40.18% (34.65 μg/kg), 47.86% (41.17 μg/kg) and 62.38% (53.73 μg/kg) AFs contents, respectively. Significant inhibitions of AFs and OTA synthesis by A. flavus and A. carbonarius, respectively, on infected coffee beans were observed in presence of Bacillus simplex BS350-3 volatiles. Gas chromatography mass spectrochemistry (GC-MS/MS) analysis of head-space 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 level of roasted and soluble coffee contaminated above EU permissible limits for OTA. Further, along with coffee roasting and brewing; microbial volatiles can be optimized to minimize the dietary exposure to mycotoxins.
Highlights
Coffee, due to its physiological effects and organoleptic characteristic is widely consumed as non-alcoholic beverage with high economic impact
No fungal colonies were isolated from roasted and soluble coffee samples. This might be associated with the killing of fungal spores during coffee roasting and further sterilized airtight packaging of soluble coffee samples which prevented the fungal contamination
Fungal spore and mycelium are sensitive to coffee roasting temperature, while a significant portion of already synthesized mycotoxins are retained unchanged
Summary
Due to its physiological effects and organoleptic characteristic is widely consumed as non-alcoholic beverage with high economic impact. Prevalence of toxigenic Aspergillus and Penicillium spp., on coffee beans has been reported in coffee growing as well as non-growing parts of the world [3, 4]. These fungal infections at favorable environmental conditions generally leads to the accumulation of mycotoxins [5,6,7]. European Union (EU) has set maximum permissible limit for OTA [9] in roasted (5 μg/kg) and soluble (10 μg/ kg) coffee, while no such regulations exists for green coffee beans [10]. Unlike OTA, there are no set regulations by EU for aflatoxins (AFs) levels in the green, roasted and soluble coffee
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