Abstract
In Colombia, coffee growers use a traditional method of fermentation to remove the cherry pulp surrounding the beans. This process has a great influence on sensory quality and prestige of Colombian coffee in international markets, but has never been studied. Here we use an Illumina-based amplicon sequencing to investigate bacterial and fungal communities associated with spontaneous coffee-bean fermentation in Colombia. Microbial-derived metabolites were further analysed by high–performance liquid chromatography and gas chromatography–mass spectrometry. Highly diverse bacterial groups, comprising 160 genera belonging to 10 phyla, were found. Lactic acid bacteria (LAB), mainly represented by the genera Leuconostoc and Lactobacillus, showed relative prevalence over 60% at all sampling times. The structure of the fungal community was more homogeneous, with Pichia nakasei dominating throughout the fermentation process. Lactic acid and acetaldehyde were the major end-metabolites produced by LAB and Pichia, respectively. In addition, 20 volatile compounds were produced, comprising alcohols, organic acids, aldehydes, esters, terpenes, phenols, and hydrocarbons. Interestingly, 56 microbial genera, associated with native soil, seawater, plants, insects, and human contact, were detected for the first time in coffee fermentation. These microbial groups harbour a remarkable phenotypic diversity and may impart flavours that yield clues to the terroir of Colombian coffees.
Highlights
In Colombia, coffee growers use a traditional method of fermentation to remove the cherry pulp surrounding the beans
Coffee is classified into two main categories according to the postharvest processing technology used to remove the outer layers adhered to the fruits: ‘natural coffee’, produced from coffee beans processed on the farm by the simple method of sun-drying, known as dry processing; and ‘washed coffee’, produced from coffee beans that undergo a relatively complex series of steps, including depulping, fermentation, and sun-drying, known as wet processing[3,4]
For the first time, the great diversity of bacteria and yeasts harboured in the most traditional method of coffee fermentation in the world
Summary
In terms of time, temperature, and exchange of water; spontaneous development of microorganisms can be better managed to minimize any adverse impacts on coffee quality[4]. Due to the high quality of ‘washed coffee’ produced in the Colombia, nowadays, fermentation process is a subject of worldwide interest[3,5] Countries such as Brazil, Guatemala, Honduras, and Ecuador export, annually, tons of coffee beans classified as ‘washed coffee’. For the first time, the great diversity of bacteria and yeasts harboured in the most traditional method of coffee fermentation in the world. These core microbiomes have strong influence on the metabolites produced during the fermentation and may impact the chemical composition of Colombian coffees
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