Abstract
This experiment was carried out to identify and select pectinolytic yeasts that have potential use as a starter culture for coffee fermentation during wet processing. The coffee fruit was fermented for 48 h at 28 °C and a sample was taken from the fermented solution and spread onto yeast extract-peptone-dextrose agar (YPDA) media and incubated at 28 °C. A total of 28 yeasts were isolated, eight of which had the ability to produce pectinase enzymes. The species of those eight yeasts were molecularly identified and confirmed. These yeasts are Wickerhamomyces anomalus (strain KNU18Y3), Saccharomycopsis fibuligera (strain KNU18Y4), Papiliotrema flavescens (strain KNU18Y5 and KNU18Y6), Pichia kudriavzevii (strain KNU18Y7 and KNU18Y8), and Saccharomyces cerevisiae (strain KNU18Y12 and KNU18Y13). The pectin degradation index of S. fibuligera (strain KNU18Y4), W. anomalus (strain KNU18Y3), and P. flavescens (strain KNU18Y6) were higher compared to the others, at 178%, 160%, and 152%, respectively. The pectinase enzyme assays were made on two growth media: coffee pulp media (CPM) and synthetic pectin media (SPM). S. fibuligera (strain KNU18Y4) and W. anomalus (strain KNU18Y3) had great potential in producing polygalacturonase (PG) and pectin lyase (PL) compared to others in both media. However, S. cerevisiae strains (KNU18Y12 and KNU18Y13) produced higher pectin methylesterase (PME). Using MEGA 6 software, the phylogenetic trees were constructed to determine the evolutionary relationship of newly identified yeasts from our experiment and previously published yeast species. The sequences of the yeasts were deposited in the National Center for Biotechnology Information (NCBI) database.
Highlights
Coffee is one of the essential worldwide commodities, next to crude oil
The ultimate objectives of this experiment were to isolate, identify, and characterize pectinolytic yeasts. We evaluated their efficiencies in producing PG, pectin lyase (PL), and pectin methylesterase (PME) using the synthetic pectin media (SPM) and the coffee pulp-culture media (CPM)
The fermentation of coffee cherries was done for 48 h with yeasts and other microorganisms that naturally existed on the coffee fruit
Summary
Coffee is one of the essential worldwide commodities, next to crude oil. Coffee is the major export commodity of around 60 tropical and subtropical countries [1,2]. Ethiopia is the origin of arabica coffee, and as such, has a long tradition of roasting and drinking this deeply cultural non-alcoholic beverage. Brazil ranks as the leading producer and exporter of arabica coffee, followed by Indonesia, Ethiopia, Philippines, Mexico, Vietnam, and 40 other countries [3]. The coffee fruit is processed using various methods: wet processing, dry processing, and semi-dry processing. During the wet-processing method, the pulp is mechanically separated from fully ripe coffee cherries. The fruit is collected and naturally fermented following the process of removal of mucilage by placing it in a fermentation tank and submerging in water for at least 6–24 h [4]
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