Beer fermentation performance and sugar uptake of Saccharomycopsis fibuligera–A novel option for low-alcohol beer

Investigating the role of primary fungi in Huangjiu fermentation: Insights from flavor orientation and synthetic microbiomes

Huangjiu, a traditional alcoholic beverage, presents a complex fermentation ecosystem primarily influenced by specific fungal species. This study utilized a culture-dependent approach and amplicon sequencing to explore fungal community succession during Huangjiu fermentation. Key fungi identified include Saccharomyces cerevisiae, Aspergillus species (flavus, oryzae, niger), Saccharomycopsis fibuligera, Thermomyces lanuginosus, Rhizopus arrhizus, Issatchenkia orientalis, Wickerhamomyces anomalus, and Diutina rugosa. Employing a synthetic microbiome, we developed a dual-strain fermentation system to evaluate the impact of these fungi on Huangjiu's organoleptic properties. Introduction of these fungi significantly altered the flavor profile, enhancing 23 volatile organic compounds (VOCs), with S. fibuligera notably increasing nine distinct VOCs. While molds contributed to bitterness by increasing bitter amino acids, S. fibuligera effectively mitigated these components, enhancing the beverage's alcohol body, smoothness, and balance. These findings provide crucial insights for optimizing Huangjiu fermentation to improve its quality and appeal.

Effect of Non-Saccharomyces Yeasts Derived from Traditional Fermented Foods on Beer Fermentation Characteristics and Flavor Profiles

In recent years, numerous studies have demonstrated that non-Saccharomyces yeasts hold potential for industrial application and aroma generation during fermentation. Non-Saccharomyces wild yeasts can be important tools in the development of new products, and the objective of this work was to obtain and characterize novel yeast isolates for their ability to produce beer. Traditional fermented beverages serve as a vital source of yeast strains that can exhibit unique characteristics during the brewing process. Thus, 22 strains of Saccharomycopsis fibuligera were isolated from traditional fermented foods in this work. Subsequently, through primary and secondary screening, S. fibuligera G02 was identified as a promising candidate for beer brewing, attributed to its advantageous physiological traits and notable potential for beer production. Headspace solid-phase microextraction (HS-SPME) combined with gas chromatography-mass spectrometry (GC-MS) was employed to analyze the volatile flavor substances in beer fermented using the S. fibuligera G02 strain. Chemometric analysis revealed that S. fibuligera G02 had a unique influence on beer aroma. Accordingly, isoamyl alcohol, phenyl-1-ethanol, ethyl acetate, isoamyl acetate, and 4-ethyl guaiacol (4EG) were the key aroma components of S. fibuligera G02. This work provides useful insights into the non-Saccharomyces yeasts to reference the targeted improvement of beer aroma.

Characterization and phylogenetic analysis of the complete mitochondrial genome of Saccharomycopsis fibuligera (lindner) Klocker 1907 (saccharomycetales: saccharomycopsidaceae)

Saccharomycopsis fibuligera (Lindner) Klocker 1907 is frequently employed in the fermentation of metabolites such as citric acid, ethanol, mannitol, and pyruvate. Its heat tolerance and alcohol-producing capabilities during fermentation make it a desirable option for bread and wine production. To date, the mitochondrial genome of S. fibuligera has not been sequenced. In the present study, we obtained the full mitochondrial genome of S. fibuligera, which is 57,302 bp long and has a GC content of 24.40%. This genome contained 14 core protein-coding genes, 3 independent ORFs, 21 intronic ORFs, 25 tRNAs, and 2 rRNA genes. By utilizing the Bayesian inference phylogenetic method, we constructed phylogenetic trees for 24 Saccharomycotina fungi, which indicated that S. fibuligera is closely related to S. capsularis.

Isolation of Saccharomycopsis species from plant material

Saccharomycopsis species are natural organic sulphur auxotrophs. Their genomes do not encode genes for the uptake and assimilation of sulphate and thus these species cannot grow on media lacking e.g. methionine. Due to the similarity between sulphate and selenate, uptake and assimilation of selenate occurs through the same pathway starting from sulphate transporters encoded by the homologs of the SUL1 and SUL2 genes in S. cerevisiae. Lack of these transporters renders Saccharomycopsis species resistant to selenate levels that are toxic to other microorganisms. We used this feature to enrich environmental samples for Saccharomycopsis species. This led to the isolation of S. schoenii, S. lassenensis and a hitherto undescribed Saccharomycopsis species with limited by-catch of other yeasts, mainly belonging to Metschnikowia and Hanseniaspora. We performed growth and predation assays to characterize the potential of these new isolates as predacious yeasts. Most Saccharomycopsis species are temperature sensitive and cannot grow at 37°C; with the exception of S. lassenensis strains. Predation assays with S. schoenii and S. cerevisiae as prey indicated that predation was enhanced at 20°C compared to 30°C. We crossed an American isolate of S. schoenii with our German isolate using marker directed breeding. Viable progeny indicated that both strains are interfertile and belong to the same biological species. S. lassenensis is heterothallic, while S. schoenii and the new Saccharomycopsis isolate, for which we suggest the name S. geisenheimensis sp. nov., are homothallic.

The effect of selected Non-Saccharomyces yeasts and cold-contact fermentation on the production of low-alcohol marula fruit beer

The last decade has seen increased consumer demand for zero and low-alcohol beverages. Cold-contact fermentation (CCF) in combination with non-Saccharomyces can be an effective method for producing low-alcohol fruit beverages with desirable qualities. Thus, the aim of this study was to develop a CCF process to produce low-alcohol marula fruit beer using selected non-Saccharomyces yeasts. The effect of temperature (°C), and time (h) on alcohol (% v/v), pH, total titratable acidity (LAE/mL) and specific gravity (SG) was evaluated using response surface methodology. Sterile marula fruit juice was inoculated with Metschnikowia pulcherrima, Pichia fermentans, or Pichia kluyveri respectively. Higher final SG values were observed for temperatures between 8 °C and 15 °C. Above 15 °C, the SG decreased with an increase in temperature and time. Fermentation at temperatures below 10 °C produced zero to low-alcohol marula fruit beer (0.00-0.20 % v/v) with an attenuation rate above 80 %. This was confirmed by the significance of quadratic models for SG (p ≤ 0.01), and alcohol (p = 0.00) for the three selected yeasts. Overall, P. kluyveri produced the lowest alcohol levels, followed by M. pulcherrima and P. fermentans, respectively. The study confirmed that cold-contact fermentation with non-Saccharomyces yeasts can be an effective biological method to produce low-alcohol marula fruit beer in line with the emerging consumer demand for low-alcohol beverages.