Aspectos microbiológicos, perfil químico e sensorial de cafés fermentados em biorreatores

Abstract

The coffee is one of the most appreciated commodities worldwide, bearing great economic importance in Brazil, the main world producer, and exporter. In the coffee sector, coffee post-harvesting is relevant, once it grants significant impacts, both on the chemical and sensory quality of the beverage. At this stage, the fermentation process takes place, spontaneously, due to microorganisms present in the fruit as well, as in the environment. However, due to the lack of control, new methods for conducting fermentation are necessary for modulation of the sensory profile of the final beverage. The research aimed to investigate the microbial diversity in different fermentations, using the same methodology, chemical, and sensory profiles of fermented coffees, in bioreactors, in three producing regions of Minas Gerais, Brazil. Two cities in Sul de Minas (Carmo de Minas and Três Pontas), one in Matas de Minas (Lajinha), and another one in the Cerrado (Monte Carmelo). Two processes were carried out, natural coffee beans and pulped coffee (PC). The population of bacteria was evaluated by surface plating. The chemical compounds were analyzed through Nuclear Magnetic Resonance (1H NMR). The sensory analysis were conducted by TDS (Temporal Dominance of Sensations). There was a significant difference in population scoring between different times and between. The South de Minas region had higher count during the fermentation. Hanseniaspora opuntiae, Torulaspora delbrueckii, and Pichia kluyvei yeast were detected only in the cities of Carmo de Minas (CM), Três Pontas (TP), Lajinha (LAJ), respectively. In Monte Carmelo (MC), Saccharomyces cerevisiae was detected in vast abundance. The bacterias Zymomonas mobilis and Leuconostoc lactis were detected only in CM. Acinetobacter johnsonii and Enterobacter cloacae were detected only in the TP region. Enterobacter hormaechei was detected only in LAJ. Bacillus cereus only in MC. Hanseniaspora uvarum, Lactobacillus plantarum, Leuconostoc mesenteroides, and Weissella cibaria were detected in all the regions. The chemical composition and the sensory profile were influenced, as the fermentation process changed. The 1H NMR, along with the principal component analysis (PCA), allowed the separation between the green coffee beans fermented in bioreactors and control. The TDS curves varied with the region and the type of post-harvest processing performed. Among the cities studied, in natural coffee in the MC, and the pulped coffee in LAJ, caramel and chocolate attributes were dominant and specific, respectively. The caramel and woody attributes were detected only in MC, in natural coffee, and pulped coffee, respectively. The dominance of the fruity attribute was typical in LAJ, in the natural coffee and in CM and TP in the pulped coffee. The conduction of batch fermentation, closed environment, with oxygen limitation and anaerobiosis, induced by epiphytic microbiota, affected the microbiota and altered the chemical and sensory composition. The microbiota presented different behavior in different varieties. The diversity in each farm indicated a specific microbiota for the geographic region and influenced the flavors. The coffees fermented in bioreactors presented more chemical compounds precursors of flavors, and aromas were correlated with green coffee, and more sensory attributes were perceived to control.