Efficient coffee beans mucilage layer removal using lactic acid fermentation in a stirred-tank bioreactor: Kinetic, metabolic and sensorial studies

Abstract

Post-harvest coffee processing involves a microbial process to remove the mucilage layer adhering to the fruits, prior to storage and transport of the coffee beans. In this study, coffee mucilage removal was done using lactic acid fermentation in a stirred-tank bioreactor (STR). Fermentation assays were done with or without the addition of starter culture (i.e., Lactobacillus plantarum LPBR01), and kinetic parameters, including microbial growth, sugar pulp consumption and metabolite production, were studied. High lactic acid bacteria (reaching 10.7 log CFU/ml at 10 h) were obtained in the STR process with the starter culture, which led to a high lactic acid productivity (0.366 g/l h) and a pH decrease to below 4.0 during the initial 10 h. A temporal analysis using Illumina high-throughput 16S rRNA Gene Sequencing (HTS) showed the Lactobacillus genus's dominance in the inoculation process, as it reached over 88% of read sequences at the end of fermentation, while the Leuconostocaceae family was the dominant bacterial group in the spontaneous treatment. The STR fermentation process led to the production of coffee beans with richer aroma composition and beverages with a notable increase in the sensorial analysis of the coffee beverages compared to those resulting from the conventional process. This new fermentation model can be used to do controlled bean fermentation to supply the coffee industry with homogeneous and high-quality coffee beans.