The effect of microbial community in the self-induced anaerobic fermentation on the aroma precursor development of geothermal coffee

Abstract

Coffee drying is an important stage for character development of green beans, and it is usually conducted in direct sunlight. Thus, this method is very dependent on the weather conditions. Geothermal drying can be a substitute method to address the limitations of conventional drying. However, geothermal drying is very fast, whereas the translocation of chemical compounds into the green bean is not ideal. Process adjustment was established by applying 5 days of Self-Induced Anaerobic Fermentation (SIAF) without adding water before the geothermal drying, to enhance the sensory quality. The whole process was referred to as ‘geothermal coffee processing’. This study aimed to provide knowledge about the role effect of microorganisms involved in the SIAF on the formation of chemical compounds responsible for the geothermal coffee aroma. Samples were extracted to obtain microbial DNA, which was then analyzed using shotgun metagenomics. The species and microbial enzymes were identified by comparing the Open Reading Frames (ORF) with the databases. Furthermore, non-volatile metabolites in fermented green beans were analyzed using LC-MS/MS. The results showed that Tatumella sp. JGM118, Hanseniaspora uvarum, and Leuconostoc pseudomesenteroides were the dominant species. This microbial community secreted enzymes, such as glycoside hydrolases (GH), transaminases, and L-lactate dehydrogenase, as indicated by their ORFs in the samples. Moreover, these enzymes catalyzed the production of non-volatile metabolites in the coffee beans. The non-volatiles were dominated by chlorogenic acid, amino acids, and carboxylic acids, none of which were detected before SIAF. These metabolites were aroma precursors in the geothermal coffee drink after the roasting process. Therefore, it was confirmed that the microbial community in SIAF contributed to the production of geothermal coffee aroma precursors.