Yeasts are essential for mucilage degradation of coffee beans during wet fermentation

Abstract

During wet fermentation, mucilage layers in coffee cherries must be removed completely. To explain mucilage degradation, several controversial hypotheses have been proposed. The aim of this work was to improve our understanding of the kinetics of mucilage breakdown. Pulped coffee beans were wet fermented with seven different treatments for 36 h. Endogenous bacteria and yeasts are selectively suppressed, and pectinases or lactic acid are added. They also involve maintaining the beans at pH 7 throughout fermentation and using spontaneous fermentation without additives as a control. During spontaneous fermentation, yeast and lactic acid bacteria were detected and significantly increased to 5.5 log colony‐forming units (CFU)/mL and 5.2 log CFU/mL, respectively. In the first 12 h of fermentation, there was a significant degree of endogenous pectinolytic activity, which resulted in partly destroyed beans in the absence of microorganisms. By adding pectinase and lactic acid to the fermentation mass, the breakdown process was accelerated in less than 8 h. When yeast was present throughout the fermentation, complete degradation was achieved. Bacteria played no critical role in the degradation. Klebsiella pneumoniae and Erwinia soli were found in a lower population and showed weaker pectinolytic activities compared to Hanseniaspora uvarum and Pichia kudriavzevii. During wet fermentation, mucilage degradation appears to be mediated by endogenous enzymes at the early stage, whereas microbial contributions, mainly yeasts, occur subsequently. H. uvarum and P. kudriavzevii may be promising candidates to be tested in future studies as coffee starter cultures to better control the mucilage degradation process.

Effects of cherries Sanitization methods and fermentation times on quality parameters of coffee beans

“…Likewise, the effect of fermentation time, especially long times, in coffee beans subjected to wet processing, with or without control of variables such as temperature, pH and the microbiota present in the fermenting coffee mass, on the kinetics has been evaluated. Of mucilage removal, the behavior of the microorganisms that participate in this stage (identification/presence/absence/counts), and on quality parameters of the coffee bean or the fermenting mass such as the content of different organic acids, sugars, alcohols, content humidity and final sensory profile in cup [ 23 , [26] , [27] , [28] , [29] ]. These studies have shown various results of interest where they show variability in the quality of the coffee bean depending on the fermentation conditions, especially the time used, the spontaneity or control of the process and the microbiota present at this stage.…”