ABSTRACT Coffee growers use a traditional method of fermentation to remove the cherry pulp surrounding the beans. The aim of this study was to evaluate the microbiological, physicochemical, and sensory aspects of coffee beans fermentation conducted in a controlled yeast bioreactor model (New Brunswick™ BioFlo®). Fermentations were conducted with or without the addition of a selected yeast starter culture (viz., Pichia fermentans YC5.2) and different parameters, including microbial growth, bacterial diversity, inoculum persistence, sugar consumption, and metabolic compounds formation (organic acids, ethanol, and ethyl acetate), were investigated. The chemical composition of resulting fermented coffee beans was assessed by high‐performance liquid chromatography and gas chromatography–mass spectrometry, and sensorial analysis of coffee beverage was performed using the cupping test (SCA – specialty coffee association). The yeast bioreactor model enabled efficient yeast starter culture growth and ethanol (0.136 g/L.h) and ethyl acetate (1.039 mg/L.h) formation. The bacterial population was mainly represented by Pediococcus sp. and Leuconostocaceae family, as revealed by Illumina high-throughput 16S rRNA gene sequencing. The fermentation system also enabled the production of coffee beans with rich aroma composition (including D-Limonene, phenyl-acetaldehyde, and phenylethyl alcohol) and beverages with a remarkable increase in quality compared to the conventional process. With further refinements, the stirred-tank bioreactor (STR) model may be useful in designing novel bioreactors for the optimization of coffee fermentation with starter cultures.

中文翻译：

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在酵母生物反应器模型中进行的咖啡豆发酵的微生物、物理化学和感官研究

摘要 咖啡种植者使用传统的发酵方法去除咖啡豆周围的樱桃果肉。本研究的目的是评估在受控酵母生物反应器模型 (New Brunswick™ BioFlo®) 中进行的咖啡豆发酵的微生物学、物理化学和感官方面。在添加或不添加选定的酵母发酵剂（即发酵毕赤酵母 YC5.2）和不同参数的情况下进行发酵，包括微生物生长、细菌多样性、接种物持久性、糖消耗和代谢化合物形成（有机酸、乙醇, 和乙酸乙酯), 进行了研究。通过高效液相色谱法和气相色谱-质谱法评估所得发酵咖啡豆的化学成分，使用杯测（SCA – 精品咖啡协会）对咖啡饮料进行感官分析。酵母生物反应器模型能够实现高效的酵母发酵剂培养物生长和乙醇 (0.136 g/Lh) 和乙酸乙酯 (1.039 mg/Lh) 的形成。细菌种群主要以片球菌属为代表。Illumina 高通量 16S rRNA 基因测序揭示的明串珠菌科。该发酵系统还能够生产出香气成分丰富的咖啡豆（包括 D-柠檬烯、苯乙醛和苯乙醇）和与传统工艺相比质量显着提高的饮料。随着进一步的改进，搅拌罐生物反应器 (STR) 模型可用于设计新型生物反应器，以优化使用发酵剂培养的咖啡发酵。