Assessment of alcoholic native yeasts isolated from the fermentation of wet processed coffee (Coffea arabica)

Abstract

Biofuels produced from waste biomass are the best alternative to fossil fuels; however, considering that bioethanol production occurs due to fermentation, the yield should be improved during this stage by incorporating microorganisms that can increase yields in the conversion of carbohydrates present in the residue to ethanol. Therefore, native yeasts were isolated and identified from natural fermentation of coffee cherries (Coffea arabica) from Chiapas, Mexico, and then, evaluated the yield of ethanol. First, a morphological study was conducted in which yeast-like microorganisms were isolated from plates with a YPDA culture medium, taking into account their texture, surface, margin, elevation, and color. In total, 15 isolates with macroscopic and microscopic characteristics typical of yeasts were obtained. Subsequently, biochemical tests were conducted to evaluate the fermentative capacity of the strains; simple sugars such as glucose, fructose, sucrose, lactose, and xylose were tested in a liquid medium composed of 0.3% yeast extract, 0.5% peptone, and 2% simple sugar. The mixture was incubated for 48 h at room temperature. The strains fermented with the aforementioned sugars were subjected to a qualitative iodoform test to confirm the presence of ethanol in the medium, identifying the best M2A and M2B strains with yields of 3.7 and 18 g/L, respectively. The M2A strain corresponded to Wikerhamomyces anomalus, and the M2B strain corresponded to Pichia kudriavzevii. To summarize, native yeasts represent a biological alternative to the production of bioethanol, which guarantees the conversion of the sugars present in the substrate to ethanol.