Isolation, Identification, and Characterization of Pectinolytic Yeasts for Starter Culture in Coffee Fermentation

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.

The Role of Yeasts in Fermentation Processes

“…To develop these processes in a satisfactory manner, and to preserve/improve the organoleptic properties of coffee, refine its sweetness, control acidity, give them body or add sensory notes (chocolate, caramel, fruits) mucilage should be removed. The process is naturally carried out by the yeasts present in the mixture, although the process can be improved by the addition of appropriate enzymes (polygalacturonase, pectin lyase, pectin methylesterase) [17].…”

“…All these findings highlight the potentiality of this yeast to produce new varieties of beers. Haile et al [17] have explored the possibility to identify and select pectinolytic yeasts that have potential use as a starter culture for coffee fermentation. Almost 30 isolates, eight of them with the ability to produce pectinase enzymes were identified and confirmed by using molecular biology techniques.…”

Evaluation of Multifarious Plant Growth Promoting Trials of Yeast Isolated from the Soil of Assam Tea (Camellia sinensis var. assamica) Plantations in Northern Thailand

“…Pectinase and amylase productions were investigated on pectin agar [ 43 ] and starch agar [ 44 ], respectively. After inoculation, plates were incubated at 30 °C in darkness for 5 days.…”

Coffee and Yeasts: From Flavor to Biotechnology

“…The most important enzymes involved in coffee fermentation are polygalacturonase (PG), pectin lyase (PL) and pectin methylesterase (PME). The time required for this step is a function of the processing methods [29,30]. The selection of microorganism for the fermentation step is based on many criteria, such as PL secretion, production of volatile compounds, the physical and chemical changes and the lack of production of undesirable metabolites [20].…”