Processing techniques and microbial fermentation on microbial profile and chemical and sensory quality of the coffee beverage

Exploring the microbiome of coffee plants: Implications for coffee quality and production

Coffee stands as one of the world's most popular beverages, and its quality undergoes the influence of numerous pre- and post-harvest procedures. These encompass genetic variety, cultivation environment, management practices, harvesting methods, and post-harvest processing. Notably, microbial communities active during fermentation hold substantial sway over the ultimate quality and sensory characteristics of the final product. The interaction between plants and microorganisms assumes critical significance, with specific microbes assuming pivotal roles in coffee plant growth, fruit development, and, subsequently, the fruit's quality. Microbial activities can synthesize or degrade compounds that influence the sensory profile of the beverage. However, studies on the metabolic products generated by various coffee-related microorganisms and their chemical functionality, especially in building sensory profiles, remain scarce. The primary aim of this study was to conduct a literature review, based on a narrative methodology, on the current understanding of the plant-microorganism interaction in coffee production. Additionally, it aimed to explore the impacts of microorganisms on plant growth, fruit production, and the fermentation processes, directly influencing the ultimate quality of the coffee beverage. Articles were sourced from ScienceDirect, Scopus, Web of Science, and Google Scholar using specific search terms such as "coffee microorganisms", "microorganisms-coffee interactions", "coffee fermentation", "coffee quality", and 'coffee post-harvest processing". The articles used were published in English between 2000 and 2023. Selection criteria involved thoroughly examining articles to ensure their inclusion was based on results about the contribution of microorganisms to both the production and quality of the coffee beverage. The exploration of microorganisms associated with the coffee plant and its fruit presents opportunities for bioprospecting, potentially leading to targeted fermentations via starter cultures, consequently generating new profiles. This study synthesizes existing data on the current understanding of the coffee-associated microbiome, its functionalities within ecosystems, the metabolic products generated by microorganisms, and their impacts on fermentation processes and grain and beverage quality. It highlights the importance of plant-microorganism interactions in the coffee production chain.

Functioning of Saccharomyces cerevisiae in honey coffee (Coffea canephora) and their effect on metabolites, volatiles and flavor profiles

Post-harvesting and microbial activity of coffee play a critical role in the metabolites and the sensory quality of the brew. The pulped natural/honey coffee process is an improvised semi-dry technique consisting of prolonged fermentation of depulped coffee beans excluding washing steps. The starter culture application in coffee industry plays an important role to enhance the cup quality. This work focuses on the fermentation of pulped natural/honey Robusta coffee with a starter culture (Saccharomyces cerevisiae MTCC 173) and the identification of fermentation patterns through 1H NMR, microbial ecology, volatomics and organoleptics of brew. Fermentation was accelerated by yeast populace (10 cfu log/mL) for 192 h. Principal compound analysis performed on 1H NMR led to the investigation of metabolites such as sugars, alkaloids, alcohols, organic acids and amino acids. Detection of some sugars and organic acids represented that the starter cultures imparted few metabolic changes during the process. A major activity of sugars in fermentation with 83.3 % variance in PC 1 and 16.7 % in PC 2 was observed. The chemical characteristics such as carbohydrates (41.88 ± 0.77 mg/g), polyphenols (34.16 ± 0.79 mg/g), proteins (58.54 ± 0.66 mg/g), caffeine (26.54 ± 0.06 mg/g), and CGA (21.83 ± 0.04 mg/g) were also evaluated. The heatmap-based visualization of GC-MS accorded characterization of additional 5 compounds in treated (T) coffee contributing to sweet, fruity and caramelly odor notes compared to untreated (UT). The sensory outlines 72.5 in T and 70.5 in UT scores. Preparation of honey coffee with Saccharomyces cerevisiae is the first report, which modulated the flavor and quality of coffee.

Use of microencapsulated starter cultures by spray drying in coffee under self-induced anaerobiosis fermentation (SIAF)

Using starter culture in liquid form is not economically viable in the coffee fermentation process. This work aimed to compare the fermentative performances of fresh and microencapsulated yeasts in coffee under self-induced anaerobic fermentation (SIAF). The inoculum permanence was monitored, and sugars, alcohols, acids, and volatile compounds were analyzed by chromatography. In addition, sensory analysis was performed on roasted beans. After 180 h of fermentation in the natural process, microencapsulated Torulaspora delbrueckii (MT) (7.97 × 107 cells/g) showed a higher population thanfresh Torulaspora delbrueckii (FT) (1.76 × 107 cells/g). The same acids and volatile compounds were detected in coffees with fresh and microencapsulated yeast. However, the yeast state influenced the concentration of the compounds. In pulped coffee, the coffee inoculated withmicroencapsulated Saccharomyces cerevisiae (MS) obtained the highest concentration of alcohols, esters, pyrazines, and others compared with fresh Saccharomyces cerevisiae (FS), with an increase of up to 47%. Furthermore, the coffee inoculated with MT obtained the highest concentration in almost all chemical classes in both processes compared with FT. These differences ranged up to 55%. Regarding sensory analysis, coffees inoculated with MS showed dominant notes of fruity, caramel, and nuts in the natural process. Otherwise, in pulped process, coffees inoculated with MT showed caramel, honey, and nuts. Therefore, the microencapsulated yeasts were metabolically active and may be considered with commercial potential. Considering the parameters analyzed, the most suitable yeast for natural and pulped processing would be MS and MT, respectively.