The Modification of Coffee Beans Through a Combination of Microbial and Enzymatic Processes

Fermentation with various microorganisms modifies the quality of coffee. In animal-digested coffee, enzymatic activity also affects coffee characteristics. However, limited information is available on in vitro coffee modification employing both mechanisms simultaneously in controlled conditions. In this study, robusta green beans were modified with selected bacterial species (<i>Bacillus subtilis</i>, <i>Gluconobacter</i> sp., <i>Lactiplantibacillus plantarum</i>) and pepsin, which was introduced at the soaking or fermentation stage. The characteristics of green and roasted coffee were analyzed, including the amount of basic aroma precursors, antioxidant activity, acrylamide concentration and volatile organic compound (VOC) content. The number of bacterial cells increased by 1.95-2.64 logCFU/mL during the modification process; pepsin addition did not affect their growth significantly. The use of acid-producing bacteria (APB) resulted in higher consumption of sucrose but also in greater retention of bioactive compounds and higher antioxidant activity. The acrylamide content in fermented and roasted beans was below 10 μg/100 g dry matter; the lowest values were reported after modification with <i>L. plantarum</i>. The combination of tested bacterial and enzymatic processes changed the content and composition of VOCs. Further research should focus on sensory attributes as the result of the combined modification process.