Microbiological, physicochemical and sensory studies of coffee beans fermentation conducted in a yeast bioreactor model

Mass Transfer Kinetics of Nonvolatile Compounds into Coffee Beans during Wet Processing: Study at the Laboratory Scale and in Real Conditions Using Two Yeast Strains

“…During fermentation, lactic acid was detected in the beans from 12 h, and its concentration increased continuously due to the transfer phenomena from the mucilage to the coffee bean and accumulation into the bean to reach 0.14 ± 0.006 and 0.1 ± 0.007 mg/g at 36 h, respectively, for the fermentation with LSCC2 and the control and 0.026 ± 0.009 mg/g for the fermentation with LSCC3 at 24 h. These observations are consistent with the results obtained by other researchers. In their study on the crucial role of yeast in wet fermentation, Elhalis et al reported that lactic acid was detected only from 16 h in the coffee beans during spontaneous fermentation (with yeast), while it was detected only after 24 h during fermentation where the yeasts had been inhibited by the addition of Natamycin, with the concentration of lactic acid 3 times lower in fermentation without yeast than that recorded with spontaneous fermentation after 36 h. Moreover, Zhang et al and De Carvalho Neto et al reported that the maximum lactic acid concentration produced outside the coffee beans was reached around 16 h of fermentation. Accordingly, the transfer kinetics of lactic acid in real conditions went through two phases depending on the external concentration.…”

“…Moreover, the acidification process promotes the pectin breakdown, contributing to the mucilage removal and facilitating the drying of the bean. , It could also modify Maillard reaction pathways during roasting, influencing the production of volatiles . Indeed, lactic acid is an important compound for coffee bean fermentation; its presence improves the texture of the final beverage. , The modulation of the concentration of this organic acid in the coffee bean depends on the inoculated strain and on the fermentation duration for optimal transfer.…”

“…First, a latency phase could be observed by an organic acid production with no transfer into the coffee beans. During this phase, the concentration of lactic acid produced outside coffee beans could increase progressively 11 and could modify progressively the physicochemical structure of the coffee bean. 30 Moreover, Chetschik et al 35 have shown that organic acids play an important role in modifying the permeability of the beans to the transfer of certain molecules.…”

“…8 Indeed, lactic acid is an important compound for coffee bean fermentation; its presence improves the texture of the final beverage. 11,36 The modulation of the concentration of this organic acid in the coffee bean depends on the inoculated strain and on the fermentation duration for optimal transfer.…”

“…First, the skin and pulp of the cherries are removed mechanically; then, the depulped beans are fermented to degrade the mucilage layer via microbiological activity; and finally, the beans are sundried . It has been shown that controlled fermentation helps improve the sensory quality of coffee. , The use of microbial starters can show a different behavior depending on the coffee variety and processing method, resulting in beverages with different and positive sensory characteristics , due to the extracellular enzymes and organic acids produced by yeast fermentation. Hameed et al, Lee et al, and Martinez et al ,, assumed that the yeast metabolism can lead to the hydrolysis of mucilage macromolecules, generating important aroma precursors, such as reducing sugars, amino acids, and organic acids, which could penetrate the coffee beans and reappear after roasting and brewing in the form of volatile and nonvolatile compounds that have a major influence on sensory and organoleptic properties.…”