Transfer kinetics of labeled aroma compounds from liquid media into coffee beans during simulated wet processing conditions

Self-induced anaerobiosis fermentation in coffees inoculated with yeast: Effect on key enzymes of the germination process and its relationship with the decrease in seed germination

Our objective was to monitor the main enzymes of coffee germinal metabolism and chemical composition during Self-Induced Anaerobiosis Fermentation (SIAF) with yeasts (Saccharomyces cerevisiae (CCMA0543), Candida parapsilosis (CCMA0544) and Torulospora delbrueckii (CCMA0684)) evaluating their relationship with seed germination. The starter cultures were assessed by qPCR. The organic acids were analyzed by liquid chromatography. Catalase (CAT), Esterase (EST), Alcohol dehydrogenase (ADH), and Isocitrate Lyase (ICL) enzyme activity was confirmed by the presence of sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-Page) gel bands. The formation of a white halo confirmed the activity of the enzyme endo-β-mannanase, and its quantification was performed using the diameter of the halo of both the samples and the standard curve. At the end of the fermentation process, S. cerevisiae and T. delbrueckii presented the highest populations (>7 log10 cells/g). Succinic acids (average -1.11 g/kg) were consumed during SIAF. Lactic acid increased after 180 h in coffees fermented by the SIAF method (average 3.57 g/kg). CAT and EST showed high activity in the conventional process. ADH activity was detected in both processes after 180 h of the SIAF method. Yeast inoculation during the SIAF method increased the activity of ICL andshowed more intense activity in the first 96 h of fermentation, especially the pulped coffee. Endo-β-mannanase activity was intense during conventional coffee processing (9.89-10.99 pmol/min/g). Natural processing tends to preserve a higher percentage of viable seeds. Therefore, the processing and fermentation methods impact seed quality differently.

Exploring Microbial Influence on Flavor Development during Coffee Processing in Humid Subtropical Climate through Metagenetic-Metabolomics Analysis

Research into microbial interactions during coffee processing is essential for developing new methods that adapt to climate change and improve flavor, thus enhancing the resilience and quality of global coffee production. This study aimed to investigate how microbial communities interact and contribute to flavor development in coffee processing within humid subtropical climates. Employing Illumina sequencing for microbial dynamics analysis, and high-performance liquid chromatography (HPLC) integrated with gas chromatography-mass spectrometry (GC-MS) for metabolite assessment, the study revealed intricate microbial diversity and associated metabolic activities. Throughout the fermentation process, dominant microbial species included Enterobacter, Erwinia, Kluyvera, and Pantoea from the prokaryotic group, and Fusarium, Cladosporium, Kurtzmaniella, Leptosphaerulina, Neonectria, and Penicillium from the eukaryotic group. The key metabolites identified were ethanol, and lactic, acetic, and citric acids. Notably, the bacterial community plays a crucial role in flavor development by utilizing metabolic versatility to produce esters and alcohols, while plant-derived metabolites such as caffeine and linalool remain stable throughout the fermentation process. The undirected network analysis revealed 321 interactions among microbial species and key substances during the fermentation process, with Enterobacter, Kluyvera, and Serratia showing strong connections with sugar and various volatile compounds, such as hexanal, benzaldehyde, 3-methylbenzaldehyde, 2-butenal, and 4-heptenal. These interactions, including inhibitory effects by Fusarium and Cladosporium, suggest microbial adaptability to subtropical conditions, potentially influencing fermentation and coffee quality. The sensory analysis showed that the final beverage obtained a score of 80.83 ± 0.39, being classified as a specialty coffee by the Specialty Coffee Association (SCA) metrics. Nonetheless, further enhancements in acidity, body, and aftertaste could lead to a more balanced flavor profile. The findings of this research hold substantial implications for the coffee industry in humid subtropical regions, offering potential strategies to enhance flavor quality and consistency through controlled fermentation practices. Furthermore, this study contributes to the broader understanding of how microbial ecology interplays with environmental factors to influence food and beverage fermentation, a topic of growing interest in the context of climate change and sustainable agriculture.

Unlocking the Aromatic Potential of Native Coffee Yeasts: From Isolation to a Biovolatile Platform

Postharvest processing of coffee has been shown to impact cup quality. Yeasts are known to modulate the sensory traits of the final cup of coffee after controlled fermentation at the farm. Here, we enumerated native coffee yeasts in a Nicaraguan farm during dry and semidry postharvest processing of Arabica and Robusta beans. Subsequently, 90 endogenous yeast strains were selected from the collected endogenous isolates, identified, and subjected to high-throughput fermentation and biovolatile generation in a model system mimicking postharvesting conditions. Untargeted volatile analysis by SPME-GC-MS enabled the identification of key aroma compounds generated by the yeast pool and demonstrated differences among strains. Several genera, including Pichia, Candida, and Hanseniaspora, showed both strain- and species-level variability in volatile generation and profiles. This fermentation platform and biovolatile database could represent a versatile opportunity to accelerate the development of yeast starter cultures for generating specific and desired sensory attributes in the final cup of coffee.

Understanding the Effects of Self-Induced Anaerobic Fermentation on Coffee Beans Quality: Microbiological, Metabolic, and Sensory Studies

In this study, an investigation of the microbial community structure and chemical changes in different layers of a static coffee beans fermentation tank (named self-induced anaerobic fermentation-SIAF) was conducted at different times (24, 48, and 72 h). The microbial taxonomic composition comprised a high prevalence of Enterobacteriaceae and Nectriaceae and low prevalence of lactic acid bacteria and yeast, which greatly differs from the traditional process performed in open tanks. No major variation in bacterial and fungal diversity was observed between the bottom, middle, and top layers of the fermentation tank. On the other hand, the metabolism of these microorganisms varied significantly, showing a higher consumption of pulp sugar and production of metabolites in the bottom and middle layers compared to the top part of the fermentation tank. Extended processes (48 and 72 h) allowed a higher production of key-metabolites during fermentation (e.g., 3-octanol, ethyl acetate, and amyl acetate), accumulation in roasted coffee beans (acetic acid, pyrazine, methyl, 2-propanone, 1-hydroxy), and diversification of sensory profiles of coffee beverages compared to 24 h of fermentation process. In summary, this study demonstrated that SIAF harbored radically different dominant microbial groups compared to traditional coffee processing, and diversification of fermentation time could be an important tool to provide coffee beverages with novel and desirable flavor profiles.