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.

The terroir of Brazilian Coffea canephora: Characterization of the chemical composition.

FTIR spectroscopy and multivariate analysis were used in the chemical study of the terroirs of Coffea canephora. Conilon coffees from Espírito Santo and Amazon robusta from Matas of Rondônia, were separated by PCA, with lipids and caffeine being the markers responsible for the separation. Coffees from Bahia, Minas Gerais, and São Paulo did not exhibit separation, indicating that the botanical variety had a greater effect on the terroir than geographic origin. Thus, the genetic factor was investigated considering the conilon and robusta botanical varieties. This last group was composed of hybrid robusta and apoatã. The DD-SIMCA favored the identification of the genetic predominance of the samples. PLS-DA had a high classification performance regarding the conilon, hybrid robusta, and apoatã genetic nature. Lipids, caffeine, chlorogenic acids, quinic acid, trigonelline, proteins, amino acids, and carbohydrates were identified as chemical markers that discriminated the genetic groups.

Microbiomes associated with Coffea arabica and Coffea canephora in four different floristic domains of Brazil.

Brazilian coffee production relies on the cultivation of Coffea arabica and Coffea canephora. Climate change has been responsible for the decreasing yield of the crops in the country yet the associated microbial community can mitigate these effects by improving plant growth and defense. Although some studies have tried to describe the microorganisms associated with these Coffea species, a study that compares the microbiome on a wider spatial scale is needed for a better understanding of the terroir of each coffee planting region. Therefore, our aim was to evaluate the microbial communities harbored in soils and fruits of these Coffea species in four Brazilian floristic domains (Amazon, Atlantic Forest Caatinga, and Cerrado). One hundred and eight samples (90 of soil and 90 of fruits) were used in the extraction and sequencing of the fungal and bacterial DNA. We detected more than 1000 and 500 bacterial and fungal genera, respectively. Some soil microbial taxa were more closely related to one coffee species than the other species. Bacillus bataviensis tends to occur more in arid soils from the Caatinga, while the fungus Saitozyma sp. was more related to soils cultivated with C. arabica. Thus, the species and the planting region (floristic domain) of coffee affect the microbial composition associated with this crop. This study is the first to report microbial communities associated with coffee produced in four floristic domains that include sites in eight Brazilian states. Data generated by DNA sequencing provides new insights into microbial roles and their potential for the developing more sustainable coffee management, such as the production of biofertilizers and starter culture for fermentation of coffee cherries.

SHS-GC-MS applied in Coffea arabica and Coffea canephora blend assessment.

Considering the great economic significance of Coffea arabica (arabica) associated with the lower production cost of C. canephora (conilon), blends of these coffees are commercially available to reduce costs and combine sensory attributes. Thus, analytical tools are required to ensure consistency between real and labeled compositions. In this sense, chromatographic methods based on volatile analysis using static headspace-gas chromatography-mass spectrometry (SHS-GC-MS) and Fourier transform infrared (FTIR) spectroscopy associated with chemometric tools were proposed for the identification and quantification of arabica and conilon blends. The peak integration from the total ion chromatogram (TIC) and extracted ion chromatogram (EIC) was compared in multivariate and univariate scenarios. The optimized partial least squares (PLS) models with uninformative variable elimination (UVE) and chromatographic data (TIC and EIC) have similar accuracy according to a randomized test, with prediction errors between 3.3% and 4.7% and Rp2 > 0.98. There was no difference between the univariate models for the TIC and EIC, but the FTIR model presented a lower performance than GC-MS. The multivariate and univariate models based on chromatographic data had similar accuracy. For the classification models, the FTIR, TIC, and EIC data presented accuracies from 96% to 100% and error rates from 0% to 5%. Multivariate and univariate analyses combined with chromatographic and spectroscopic data allow the investigation of coffee blends.

Multivariate calibration applied to study of volatile predictors of arabica coffee quality.

The chemical complexity of coffee influences the sensory evaluation of the beverage, the main method used to define the quality of the coffee. In view of the subjectivity that method offers, we propose the association of an instrumental method with multivariate calibration (PLS and GA-SVR) to predict the quality of arabica coffee as support for sensory analysis. Arabica coffee samples were submitted to sensory evaluation using the Specialty Coffee Association (SCA) protocol and HS-SPME-GC/MS analysis. The models presented RMSEp results from 0.20 to 0.25, within the evaluation range the quality levels of sensory attributes (0.25). For the fragrance/aroma attribute, a value of R2p equal to 0.8503 was reached. 15 volatile compounds were identified as responsible for predicting the quality of arabica coffee, among which, 1-nonadecene was first reported as an impact compound in the prediction of important sensory attributes.

Evaluation of genetic divergence of coffee genotypes using the volatile compounds and sensory attributes profile.

The quality of the coffee beverage is related to the chemical, physical, and sensory attributes of the coffee beans that vary with the geographic location of the crop, genetic factors, and post-harvest processing. So, the objective of this study was to evaluate the genetic divergence of 27 genotypes of Coffea canephora using the volatile compounds and sensory attributes profile to select genotypes that produce a coffee beverage with high sensory quality. This genetic diversity was estimated from the Euclidean distance matrix using non-standard data and the Unweighted Pair-Group Method Using Arithmetic Averages (UPGMA). The 2-furyl-methanol, 4-ethenyl-2-methoxyphenol, furfural, 5-methylfurfural, methylpyrazine, and 2,6-dimethylpyrazine were predominating volatile compounds in the genotypes. The sensory attributes had a positive Pearson's correlation with the total score. The volatile compounds had a different relative contribution to the genetic divergence between the genotypes of C. canephora. The 4-ethenyl-2-methoxyphenol, 2-furyl-methanol, and furfural were volatile compounds that most contributed to the formation of the groups in the UPGMA dendrogram. The relative contribution of sensory attributes to dissimilarity among genotypes was 6.42% to 20.20%. Therefore, this study verified the relative contribution of volatile compounds, in specially 4-ethenyl-2-methoxyphenol, 2-furyl-methanol, and furfural, and sensory attributes (flavor, mouthfeel, and bitterness/sweetness) to the genetic divergence between the genotypes of the three clonal varieties. Thus, this work points out compounds that positively contribute to the sensory quality of the Conilon coffee beverage.

Effects of environmental factors on microbiota of fruits and soil of Coffea arabica in Brazil.

In recent years, several studies have been developed to understand the impact of fermentation on the final quality of coffee and have indicated that postharvest processing could be a determinant of quality. However, a trend has appeared as a scientific counterpoint, indicating that the interactions between soil, fruit, altitude, and slope exposures with respect to the Sun are important to understand the behavior of the microbiome in coffee. Studies on the microbiota of coffee have addressed its role during the fermentation process, however the knowledge of indigenous microorganisms harbored in fruits and soil of coffee trees growing in fields are essential, as they can contribute to fermentation. Therefore, the aim of this work was to evaluate the influence of topographic and edaphic factors on the bacterial and fungal communities present in the soil and in the fruits of Coffea arabica trees. Samples of fruits and soil were collected from different growing areas at different altitudes and soil conditions. The microbial DNA was extracted and sequenced. The results showed the contribution of environmental factors in the structure of bacterial and fungal communities. The richness, evenness and diversity of the mycobiome and bacteriome were higher in the soil than in the fruits, independent of altitude. In addition, coffee trees at higher altitudes tended to have more bacteria shared between the soil and fruits. The co-occurrence/co-exclusion network showed that bacteria-bacteria connections were greater in higher altitudes. On another hand, fungi-fungi and fungi-bacteria connections were higher in low altitudes. This was the first study that evaluates in deep the influence of environmental factors in the microbiota habiting fruits and soil coffee trees, which may affect the coffee beverage quality.

New propositions about coffee wet processing: Chemical and sensory perspectives.

The interactions between edaphoclimatic factors, forms of processing, drying, storage and roasting, directly affect the sensorial results. This study applied four forms of wet-processing in six different altitude strata, aiming to potentiate the final quality of the drink. The final quality of the coffees was measured using the sensory technique and HS-SPME-GC/MS analyses. Results indicate that the use of starter culture in the fermentation phase constitutes a relevant alternative for lower-altitude zones, and that spontaneous fermentations have a higher potential of sensorial results at above 900 m. In the sequence, the volatile compounds were affected according to the type of processing and the altitude. The compounds in general that contributed the most to the formation of the math models were: 2-furylmethanol, octadecanal, 2-acetyl-3-methylpyrazine, 2,3-Dihydro-3,5-dihydroxy-6-methyl-4H-pyran-4-one (DDMP) and caffeine. The positive effects of the fermentation corroborate with new sensory routes, modification of the flavor and volatile compounds, consequently, generating new fermentation strategies.

Very beyond subjectivity: The limit of accuracy of Q-Graders.

When it comes to the sensory analysis of specialty coffees, it is necessary to discuss the protocol of tests of the Specialty Coffee Association (SCA) and the formation of Q-Graders as reliable parameters in the sensory analysis. However, the training of these Q-Graders and the use of the SCA protocol has generated discussions in the scientific community and demonstrated the importance of talking about the level of professional precision as well as the use of the protocol. This study sought to understand the relation of accuracy and efficiency of the Q-Graders and protocol in the sensory analysis of coffees. Three experiments were carried out to evaluate and test the hypotheses regarding the level of precision in relation to the shift, the number of samples and the judgment abilities of Q-Graders due to the quality of the specialty coffee and nonspecialty coffee. These three experiments were performed by seven Q-Graders in an isolated environment during three consecutive days with 137 specialty coffee samples and 7 nonspecialty coffee samples as defined by the SCA. The results indicate that the Q-Graders present high precision when evaluating excellent and outstanding coffees, as defined by the SCA. In addition, the effect of the shift did not exert fatigue on the Q-Graders. However, evaluation errors were made by the Q-Graders on very good coffee (77.00-80.00 points), which are considered as nonspecialty by the SCA, thus allowing a more in-depth discussion on what would be the boundary between a specialty and nonspecialty coffee. PRACTICAL APPLICATIONS: The article deals with the sensory evaluation process of coffees, and it has great importance to teaching and research institutions in Brazil, the largest producer, largest exporter and the country with the highest concentration of coffee scholars in the world. The article focuses on a new approach and a new way of looking at the sensory evaluation process of coffees, using the methodology of the Specialty Coffee Association to analyze the accuracy and efficiency of the Q-Graders.