The influence of spontaneous microbial fermentation isolates on physicochemical properties and cup quality of wet processed arabica coffee (Coffea arabica)

Abstract

Uganda hardly exports speciality coffee. This is attributed to dependence on spontaneous wet processing which yields inferior quality coffees. This study evaluated the predominant yeasts and bacteria in the spontaneous fermentation of Arabica coffee (Coffea arabica) from Bugisu and their potential use as starter cultures in the wet fermentation of coffee. The isolates were grouped by cell morphology and biochemical features and confirmation done using polymerase chain reaction. Controlled fermentation of pulped Arabica coffee was carried out. Physicochemical changes namely pectin, total soluble sugars, viscosity, hydrogen potential and titratable acidity were monitored in the fermenting mass using standard methods. Fermented coffee beans were dried, roasted and evaluated for cup quality using the Speciality Coffee Association cupping protocol. A total of 130 microbial isolates were obtained on the different growth media. Psuedomonas sp., Paenibacillus campinasensis, Kazachstania exigua and Pichia kudriavzevii, were the predominant species. Mixed cultures significantly (p < 0.05) reduced fermentation period by 30% and attained the highest mean cup score (84 points). Pectin content and pH reduced to 0.00% and 3.85, respectively. Total soluble solids, titratable acidity and absolute viscosity increased to 8.92 oBrix, 3.85 g/L and 88 cP, respectively. There was a strong positive correlation (0.83) between P. kudriavzevii, pH and the cup quality. Processors may use starter cultures to improve on quality of Arabica coffee. •We studied predominant microbes in spontaneous fermented Arabica coffee.•Kazachstania exigua, Pichia kudriavzevii, Psuedomonas sp. and Paenibacillus campinasensi were identified.•Mixed cultures reduced fermentation time and improved cup quality.•Pichia kudriavzevii was positively correlated to pH and cup quality.