## 3 Results and Discussion
### Field Experiment
In immature coffee treatments, a pH higher than 4.5 was reported, which may be attributed to the insufficient development of _P. acidilactici_. Ethanol and ethyl acetate were the major volatile compounds detected during fermentation processes (Figure 2). Interestingly, combined inoculations with _P. acidilactici_ and _P. fermentans_ resulted in a significant increase in the production of these metabolites when compared to pure cultures and a spontaneous process. The higher values of ethanol (27.04 and 14.8 umol/L) and ethyl acetate (1.63 and 1.21 umol/L) were reached after 24 h of ripe and immature combined fermentations, respectively. Figure 1: Pulp sugar consumption, organic acid production, and pH monitoring of inoculated (pure culture with _Pichia fermentans_, pure culture with _Pediococcus acidilactici_, and combined fermentation with _P. fermentans_ and _P. acidilactici_) and spontaneous fermentation of ripe (**A**) and immature (**B**) coffee fruits. The significance of the results was assessed using an ANOVA with [PERSON]’s post-hoc test at \(p<0.05\). Different lowercase letters (a, b, c, d, e, f) indicate significant differences within the same process (ripe and immature coffee beans) over fermentation time. This agrees with the findings of [PERSON] et al. (2018) and [PERSON] et al. (2018) that demonstrated an increase of ethyl- and acetate esters as a result of the co-inoculation of LAB and yeasts in wine fermentation. The significant sugar consumption and lactic acid, ethyl acetate, and ethanol production in treatments with combined inoculations indicated an ecological interaction between these two microbial groups. The complex nature of this interaction is highlighted by the observations that (i)the autolysis of yeasts release nutrients, such as amino acids, polysaccharides and riboflavin, favorable for bacterial growth, and that (ii) the acidification of the fermentation media by LAB creates a prone environment for yeast development ([PERSON], 2016; [PERSON], 2016). These positive interactions have been shown to promote desired sensory attributes in wine, sourdough, and yogurt. However, information about these mechanisms in coffee fermentation is scarce ([PERSON], 2016). Other minor volatile compounds that increased during the fermentation processes were 1-decanol, ethyl-acetaldehyde, and hexyl acetate (Figure 2). Yeast and lactic acid bacteria generate ethyl-acetaldehyde by a condensation reaction between fatty acids and an alcohol molecule ([PERSON], 2016), while 1-decanol can be derived from amino acid catabolism via the Ehrlich pathway ([PERSON], 1984; [PERSON] et al., 2018). The presence of higher concentrations of linalool using immature fruits can be associated with the inferior maturation stage of the coffee beans, since this compound has been considered a volatile marker of coffee beverages produced from immature fruits ([PERSON], 2016). Figure 2: Concentration of volatile compounds produced in the course inoculated (pure culture with _P. fermentatus_, pure culture with _P. acidilactici_, and combined fermentation with _P. fermentatus_ and _P. acidilactici_) and spontaneous fermentation of ripe (**A**) and immature (**B**) coffee fruits. The significance of the results was assessed using an ANOVA with [PERSON]’s post-hoc test at _p_\(<\) 0.05. Different lowercase letters (a, b, c, d, e, f) indicate significant differences within the same process (ripe and immature coffee beans) over fermentation time.