RESUMO
Higher alcohol formation by yeast is of great interest in the field of fermented beverages. Among them, medium-chain alcohols impact greatly the final flavour profile of alcoholic beverages, even at low concentrations. It is widely accepted that amino acid metabolism in yeasts directly influences higher alcohol formation, especially the catabolism of aromatic and branched-chain amino acids. However, it is not clear how the availability of oxygen and glucose metabolism influence the final higher alcohol levels in fermented beverages. Here, using an industrial Brazilian cachaça strain of Saccharomyces cerevisiae, we investigated the effect of oxygen limitation and glucose pulse on the accumulation of higher alcohol compounds in batch cultures, with glucose (20 g/l) and leucine (9.8 g/l) as the carbon and nitrogen sources, respectively. Fermentative metabolites and CO2 /O2 balance were analysed in order to correlate the results with physiological data. Our results show that the accumulation of isoamyl alcohol by yeast is independent of oxygen availability in the medium, depending mainly on leucine, α-keto-acids and/or NADH pools. High-availability leucine experiments showed a novel and unexpected accumulation of isobutanol, active amyl alcohol and 2-phenylethanol, which could be attributed to de novo biosynthesis of valine, isoleucine and phenylalanine and subsequent outflow of these pathways. In carbon-exhausted conditions, our results also describe, for the first time, the metabolization of isoamyl alcohol, isobutanol, active amyl alcohol but not of 2-phenylethanol, by yeast strains in stationary phase, suggesting a role for these higher alcohols as carbon source for cell maintenance and/or redox homeostasis during this physiological phase.
Assuntos
Bebidas Alcoólicas/microbiologia , Álcoois/metabolismo , Meios de Cultura/metabolismo , Aromatizantes/metabolismo , Glucose/metabolismo , Leucina/metabolismo , Oxigênio/metabolismo , Saccharomyces cerevisiae/metabolismo , Bebidas Alcoólicas/análise , Álcoois/análise , Brasil , Fermentação , Aromatizantes/análise , Nitrogênio/metabolismo , Proteínas de Saccharomyces cerevisiae/genética , Proteínas de Saccharomyces cerevisiae/metabolismoRESUMO
The distilled spirit made from sugar cane juice, also known as cachaça, is a traditional Brazilian beverage that in recent years has increased its market share among international distilled beverages. Several volatile compounds produced by yeast cells during the fermentation process are responsible for the unique taste and aroma of this drink. The yeast Dekkera bruxellensis has acquired increasing importance in the fermented beverage production, as the different metabolites produced by this yeast may be either beneficial or harmful to the end-product. Since D. bruxellensis is often found in the fermentation processes carried out in ethanol fuel distillation in Brazil, we employed this yeast to analyse the physiological profile and production of aromatic compounds and to examine whether it is feasible to regard it as a cachaça-producing microorganism. The assays were performed on a small scale and simulated the conditions for the production of handmade cachaça. The results showed that the presence of aromatic and branched-chain amino acids in the medium has a strong influence on the metabolism and production of flavours by D. bruxellensis. The assimilation of these alternative nitrogen sources led to different fermentation yields and the production of flavouring compounds. The influence of the nitrogen source on the metabolism of fusel alcohols and esters in D. bruxellensis highlights the need for further studies of the nitrogen requirements to obtain the desired level of sensory compounds in the fermentation. Our results suggest that D. bruxellensis has the potential to play a role in the production of cachaça.