Researchers Discover Thermotolerant Yeast Strains Produced During Coffee Fermentation that May Benefit Specialty Production – CoffeeTalk

The study conducted at Maestra Chela Farm in Volcancito, Boquete, Panama, investigated the fermentation of hand-picked Catuaí coffee fruits at an altitude of 1,575 meters. The process included depulping the fruits mechanically, fermenting the beans for 30 hours using a local artisanal method, and maintaining an ambient temperature between 17 and 20 degrees Celsius. Biomass temperatures were monitored to assess fermentation conditions.

Sixty samples of ten beans each were taken from five 17-kilogram bags at various time intervals: before depulping, immediately after, and then at 8, 16, and 30 hours. Samples designated for DNA barcoding were frozen, while those for live culture were processed promptly. Thermotolerant yeast isolates were selected by incubating plates at 43 degrees Celsius, the maximum temperature noted for yeast growth in prior studies. The culture media used included YPD, yeast-malt, and Sabouraud dextrose agar, each augmented with antibiotics to inhibit bacterial growth. The yeast-malt medium yielded the highest diversity, with 51% of isolates, followed by Sabouraud (39%) and YPD (10%).

In total, the study recovered 80 thermotolerant yeast morphotypes, leading to the identification of 32 distinct operational taxonomic units (OTUs) within the Ascomycota phylum. Phylogenetic analysis confirmed five clades associated with the genera Clavispora, Nakaseomyces, Meyerozyma, Candida, and Pichia. Temporal dynamics were observed, with Clavispora and Meyerozyma predominant in early fermentation, while Pichia became the dominant isolate by the 30-hour mark, constituting 56% of the sequences.

The results were notable in comparison to previous studies that found significantly fewer species diversity. This finding may relate to the higher incubation temperature capturing yeasts that lower temperatures missed. Despite the high diversity, three genera—Pichia, Nakaseomyces, and Candida—comprised 86% of isolates, indicating many species-level taxa exist within a limited number of higher taxonomic groups.

Three specific strains advanced to starter culture trials: two isolates of P. kudriavzevii and one strain of Clavispora. They were cultured at 43 degrees Celsius and used to inoculate depulped Catuaí beans. Sensory evaluation followed Specialty Coffee Association criteria, where trained tasters assessed multiple attributes. The Clavispora and one P. kudriavzevii strain were promising as starter cultures owing to their favorable influence on coffee characteristics as indicated in the evaluations. The authors highlight that Clavispora can metabolize various sugars and tolerate fermentation, while Pichia possesses well-established fermentation characteristics.

The research highlights significant implications for small coffee producers in Panama, emphasizing that temperature-adapted isolation protocols can streamline the process of starter culture selection. The unexpected diversity noted in this study suggests previous lower-temperature studies may have missed many thermotolerant taxa, enriching the understanding of yeast biodiversity in coffee fermentation.

Read More @ Bioengineer