Zygosaccharomyces Rouxii Research Articles

Enhancing nutritional composition and aroma characteristics of kiwifruit wines through indigenous non-Saccharomyces yeast extracellular extract treatment

To unlock the potential of strains for further enhancing the aromatic complexity of kiwifruit wines while avoiding undesirable flavors, indigenous non-Saccharomyces yeast extracellular extract treatment for fermentation was established. The extracellular extract from Zygosaccharomyces rouxii, Pichia kudriavzevii, and Meyerozyma guilliermondii were prepared and supplemented individually or in pairs to the kiwifruit wine fermentation system. Subsequently, the changes in physicochemical properties, antioxidants, and volatile characteristics of kiwifruit wines produced by different protocols were comprehensively evaluated, and the major aroma descriptors affecting sensory acceptability were analyzed by sensory evaluation and partial least squares regression. The results showed that extracellular extract treatment significantly improved the organic acids and monomeric phenols content, antioxidant capacity, and volatiles of kiwifruit wines. Compared to Sc, the increase in esters and alcohols, along with the decrease in aldehydes and acids in Pk-Zr and Mg-Zr, enhanced the aromatic complexity while reduce grassy and fungal flavors, resulting in higher sensory acceptability.

Mechanistic insights into soy sauce flavor enhancement via Co-culture of Limosilactobacillus fermentum and Zygosaccharomyces rouxii

For years, the intricate interactions between microorganisms in fermented food have played a key role in enhancing flavor. Our previous study highlighted that co-culture of Limosilactobacillus fermentum (L. fermentum) and Zygosaccharomyces rouxii (Z. rouxii) could enhance the flavor improvement capability of Z. rouxii in soy sauce fermentation, but the mechanism has been understudied. In this study, gas chromatography-mass spectrometry (GC-MS), GC-MS combined with derivatization (Der-GC-MS) and metabolite addition experiments were employed to elucidate their interaction. The first reason for the enhanced flavor of co-culture was that L. fermentum itself could produce the caramel-like compounds, such as HDMF and 2-furanmethanol. Another important reason was the commensality interaction between L. fermentum and Z. rouxii, where L. fermentum not only grew vigorously, but also significantly promoted the growth of Z. rouxii, mitigating the inhibitory effects of acetic acid on Z. rouxii. Further validation revealed that the metabolites of L. fermentum could stimulate the reproduction of Z. rouxii and increase the synthesis of aroma compounds such as phenylethyl acetate and ethyl acetate. Notably, glycerin and lactic acid emerged as pivotal metabolites facilitating enhanced aroma production. This study offers valuable insights for advancing flavor regulation techniques in soy sauce production.

Regulatory mechanisms of the microbial starter fortification on the community and flavor characteristics in Doubanjiang

Doubanjiang is a special Chinese seasoning paste produced by mixing broad bean paste with chili paste. Besides the antimicrobial substances, such as capsaicin contained in chili, the microbiota and metabolism are directly developed by the stress effect of abiotic factors that periodically change during the fermentation process. The microbial starter is a promising way to improve the quality of Doubanjiang production. In the present study, the regulatory mechanisms of the microbial starters (Tetragenococcus halophilus, Zygosaccharomyces rouxii, and Candida versatilis) were explored by comparing the microbial community, flavor characteristics and their correlation networks between the fortified and control groups. In comparison to the control group, the volatile compound content increased by 30.77%, with notable increases in phenylethyl alcohol, beta-ionone, etc. Conversely, there was a reduction in non-volatile compounds, including reducing sugar, acidity, amino acid nitrogen, and organic acids. The microbial structure underwent a shift, with an increase in the relative abundance of C. versatilis, while Z. rouxii demonstrated no variance and T. halophilus was not detected. The correlations of the specific microbes and certain flavor compounds were modified by the starter (p < 0.05). Notably, the correlation between Enterobacter/Malassezia and 3-furaldehyde was shifted from a negative to a positive conversion. The observed increase in beta-ionone, ethyl phenylacetate, etc., resulted from the synergistic effects, correlated transformations, and reduction of antagonistic interactions. These findings indicate that the starter powerfully regulates the interactions between microbial communities and metabolic networks, thereby provide valuable insights for the improvement of Doubanjiang quality.

Using Extracted Sugars from Spoiled Date Fruits as a Sustainable Feedstock for Ethanol Production by New Yeast Isolates.

This study focuses on investigating sugar recovery from spoiled date fruits (SDF) for sustainable ethanol production using newly isolated yeasts. Upon their isolation from different food products, yeast strains were identified through PCR amplification of the D1/D2 region and subsequent comparison with the GenBank database, confirming isolates KKU30, KKU32, and KKU33 as Saccharomyces cerevisiae; KKU21 as Zygosaccharomyces rouxii; and KKU35m as Meyerozyma guilliermondii. Optimization of sugar extraction from SDF pulp employed response surface methodology (RSM), varying solid loading (20-40%), temperature (20-40 °C), and extraction time (10-30 min). Linear models for sugar concentration (R1) and extraction efficiency (R2) showed relatively high R2 values, indicating a good model fit. Statistical analysis revealed significant effects of temperature and extraction time on extraction efficiency. The results of batch ethanol production from SDF extracts using mono-cultures indicated varying consumption rates of sugars, biomass production, and ethanol yields among strains. Notably, S. cerevisiae strains exhibited rapid sugar consumption and high ethanol productivity, outperforming Z. rouxii and M. guilliermondii, and they were selected for scaling up the process at fed-batch mode in a co-culture. Co-cultivation resulted in complete sugar consumption and higher ethanol yields compared to mono-cultures, whereas the ethanol titer reached 46.8 ± 0.2 g/L.

Effect of sequential fermentation with indigenous non-Saccharomyces cerevisiae combinations and Saccharomyces cerevisiae on the chemical composition and aroma compounds evolution of kiwifruit wine

To unlock the potential of indigenous non-Saccharomyces cerevisiae and develop novel starters to enhance the aromatic complexity of kiwifruit wine, Zygosaccharomyces rouxii, Pichia kudriavzevii and Meyerozyma guilliermondii were pairwise combined and then used in sequential fermentation with Saccharomyces cerevisiae. The impact of different starter cultures on the chemical composition and flavor profile of the kiwifruit wines was comprehensively analyzed, and the aroma evolution during alcoholic fermentation was investigated by examining the changes in key volatiles and their loss rates. Compared with Saccharomyces cerevisiae, mixed starter cultures not only improve antioxidant capacity but also increase esters and alcohols yields, presenting intense floral and fruity aromas with high sensory acceptability. The results indicated that sequential inoculation of non-Saccharomyces cerevisiae combination and Saccharomyces cerevisiae promoted the development of volatiles while maintaining the stability of key aroma compounds in the winemaking environment and reducing the aroma loss rates during alcoholic fermentation.

The Diversity of Yeasts in Beekeeping Environments and the Selection of a Culture Starter for the Development of a Mead

The biodiversity of several beekeeping environments and honey samples was studied. The bacterial and yeast counts ranged from 0.00 to 5.19 Log CFU/g and from 0.00 to 3.33 Log CFU/g, respectively, presenting significant differences between the values. Of the honey samples, two of them exceeded the legislative limit established for total aerobic bacteria (5.19 Log CFU/g and 5.03 Log CFU/g). A total of ninety-eight yeast strains were isolated, with eight different species: Candida albicans, Dekkera anomala, Zygosaccharomyces rouxii, Z. mellis, Kazachstania unispora, Meyerozyma guillermondii, Saccharomyces cerevisiae, and S. unisporus. This implies a low microbial biodiversity and a low genetic variability index (D = 0.116 and 6–19%, respectively) due to the large number of genetically identical individuals found in each species. To select the most adequate strains for mead elaboration (with pure and mixed cultures), the fermentation capacity and organoleptic characteristics were studied. The best yeasts were chosen for the “pure culture fermentation” of honey (Saccharomyces spp. M11A2) and for mixed sequential inoculation (K. unispora M17A2). Both of the yeasts were isolated from honey and selected for their high fermentative capacity and resistance to ethanol. The results of the sensory analysis of the meads that were produced, in addition to one commercial product, were compared and indicated that the one inoculated with the pure culture had the best overall impression.

Adaptation and Validation of a Modified Broth Microdilution Method for Screening the Anti-Yeast Activity of Plant Phenolics in Apple and Orange Juice Models.

Yeasts are the usual contaminants in fruit juices and other beverages, responsible for the decrease in the quality and shelf-life of such products. Preservatives are principally added to these beverages to enhance their shelf-life. With the increasing consumer concern towards chemical food additives, plant-derived antimicrobials have attracted the attention of researchers as efficient and safer anti-yeast agents. However, the methods currently used for determining their anti-yeast activity are time- and material-consuming. In this study, the anti-yeast effect of plant phenolic compounds in apple and orange juice food models using microtiter plates has been evaluated in order to validate the modified broth microdilution method for screening the antimicrobial activity of juice preservative agents. Among the twelve compounds tested, four showed a significant in vitro growth-inhibitory effect against all tested yeasts (Saccharomyces cerevisiae, Zygosaccharomyces bailii, and Zygosaccharomyces rouxii) in both orange and apple juices. The best results were obtained for pterostilbene in both juices with minimum inhibitory concentrations (MICs) ranging from 32 to 128 μg/mL. Other compounds, namely oxyresveratrol, piceatannol, and ferulic acid, exhibited moderate inhibitory effects with MICs of 256-512 μg/mL. Furthermore, the results indicated that differences in the chemical structures of the compounds tested significantly affected the level of yeast inhibition, whereas stilbenes with methoxy and hydroxy groups produced the strongest effect. Furthermore, the innovative assay developed in this study can be used for screening the anti-yeast activity of juice preservative agents because it saves preparatory and analysis time, laboratory supplies, and manpower in comparison to the methods commonly used.

Preparation of plant-derived compounds/chitosan/gelatin antifungal film and investigation of its control effect on Zygosaccharomyces rouxii contamination in concentrated apple juice

The purpose of this work is to develop a plant-derived compounds (PDCs)/chitosan (CS)/gelatin (GL) packaging lining film with high inhibitory activity against the contamination of Zygosaccharomyces rouxii in concentrated apple juice. The PDCs with high anti-Z. rouxii activity were selected from 19 PDCs for pairwise combining, and the combination with synergistic anti-Z. rouxii effect was selected to prepare nanoemulsion. Then, the effect of PDCs emulsion on mechanical and anti-Z. rouxii properties of CS/GL film was investigated. Finally, the prepared PDCs/CS/GL film was used as packaging lining to explore the preservation effect on concentrated apple juice. The results showed that the combination of trans-cinnamaldehyde and geraniol (4:6, v/v) presented the highest synergistic anti-Z. rouxii effect (the value of fractional inhibitory concentration index equaling 0.25). Addition of trans-cinnamaldehyde-geraniol nanoemulsion reduced mechanical properties of CS/GL film, but improved anti-Z. rouxii activity. The CS/GL film containing 1.5 % (v/v) trans-cinnamaldehyde-geraniol nanoemulsion showed high anti-Z. rouxii activity and did not affect the quality of concentrated apple juice, which could be used as a packaging lining for preservation of concentrated apple juice. The PDCs/CS/GL packaging lining film prepared in this work not only presented an enduring and effective inhibitory effect on Z. rouxii contamination in concentrated apple juice, but also avoided the influences of trans-cinnamaldehyde and geraniol on the quality of concentrated apple juice, which provided a new idea for the development of food preservation packaging film.

Modeling and Optimizing Biocontrol in Wines: pH as a Modulator of Yeast Amensalism Interaction

The control of spoilage yeasts in wines is crucial to avoid organoleptic deviations in wine production. Traditionally, sulfur dioxide (SO2) was used to control them; nevertheless, SO2 influence on human health and its use is criticized. Biocontrol emerges as an alternative in wine pre-fermentation, but there is limited development in its applicability. Managing kinetics is relevant in the microbial interaction process. pH was identified as a factor affecting the interaction kinetics of Wickerhamomyces anomalus killer biocontrol on Zygosaccharomyces rouxii. Mathematical modeling allows insight into offline parameters and the influence of physicochemical factors in the environment. Incorporating submodels that explain manipulable factors (pH), the process can be optimized to achieve the best-desired outcomes. The aim of this study was to model and optimize, using a constant and a variable pH profile, the interaction of killer biocontrol W. anomalus vs. Z. rouxii to reduce the spoilage population in pre-fermentation. The evaluated biocontrol was W. anomalus against the spoilage yeast Z. rouxii in wines. The kinetic interactions of yeasts were studied at different pH levels maintained constant over time. The improved Ramón-Portugal model was adopted using the AMIGO2 toolbox for Matlab. A static optimization of a constant pH profile was performed using the Monte Carlo method, and a dynamic optimization was carried out using a method based on Fourier series and orthogonal polynomials. The model fit with an adjusted R2 of 0.76. Parametric analyses were consistent with the model behavior. Variable vs. constant optimization achieved a lower initial spoilage population peak (99% less) and reached a lower final population (99% less) in a reduced time (100 vs. 140 h). These findings reveal that control with a variable profile would allow an early sequential inoculation of S. cerevisiae. The models explained parameters that are difficult to quantify, such as general inhibitor concentration and toxin concentration. Also, the models indicate higher biocontrol efficiency parameters, such as toxin emission or sensitivity to it, and lower fitness of the contaminant, at pH levels above 3.7 during biocontrol. From a technological standpoint, the study highlights the importance of handling variable profiles in the controller associated with the pH management actuators in the process without incurring additional costs.

Simultaneous inoculation of non-Saccharomyces yeast and lactic acid bacteria for aromatic kiwifruit wine production

To further explore strain potential and develop an aromatic kiwifruit wine fermentation technique, the feasibility of simultaneous inoculation by non-Saccharomyces yeast and lactic acid bacteria was investigated. Lacticaseibacillus paracasei, Lactiplantibacillus plantarum, and Limosilactobacillus fermentum, which have robust β-glucosidase activity as well as good acid and ethanol tolerance, were inoculated for simultaneous fermentation with Zygosaccharomyces rouxii and Meyerozyma guilliermondii, respectively. Subsequently, the chemical compositions and sensory characteristics of the wines were comprehensively evaluated. The results showed that the majority of the simultaneous protocols effectively improved the quality of kiwifruit wines, increasing the content of polyphenols and volatile compounds, thereby enhancing sensory acceptability compared to the fermentation protocols inoculated with non-Saccharomyces yeast individually. Particularly, the collaboration between Lacp. plantarum and Z. rouxii significantly increased the diversity and content of esters, alcohols, and ketones, intensifying floral and seeded fruit odors, and achieving the highest overall acceptability. This study highlights the potential significance of simultaneous inoculation in kiwifruit wine production.

D-Arabitol production by a high arabitol-producing yeast, Zygosaccharomyces sp. Gz-5 isolated from miso.

d-Arabitol, an alternative sweetener to sugar, has low calorie content, high sweetness, low glycemic index, and insulin resistance-improving ability. In this study, d-arabitol-producing yeast strains were isolated from various commercial types of miso, and strain Gz-5 was selected among these strains. Phylogenetic tree analysis of the internal transcribed spacer sequence revealed that strain Gz-5 was distinct from Zygosaccharomyces rouxii, a major fermenting yeast of miso. The strain, identified as Zygosaccharomyces sp. Gz-5, grew better than other Z. rouxii in 150g/L NaCl and produced 114g/L d-arabitol from 295g/L glucose in a batch culture for 8 days (0.386g/g-consumed glucose). In a fed-batch culture, the yeast produced 133g/L d-arabitol for 14 days, and the total d-arabitol amount increased by 1.75-fold. These results indicated that Zygosaccharomyces sp. Gz-5, a non-genetically modified strain, has excellent potential for the industrial production of d-arabitol.

Unconventional Yeasts Isolated from Chilean Honey: A Probiotic and Phenotypic Characterization.

This study explores the potential probiotic properties of yeasts isolated from various Chilean honeys, focusing on Ulmo, Quillay, and Mountain honeys. Six yeast strains were identified, including Zygosaccharomyces rouxii, Candida sp., Schizosaccharomyces pombe, Rhodosporidiobolus ruineniae, Clavispora lusitaniae, and Metschnikowia chrysoperlae. Phenotypic characterization involved assessing their fermentative performance, ethanol and hops resistance, and cross-resistance. Ethanol concentration emerged as a limiting factor in their fermentative performance. The probiotic potential of these yeasts was evaluated based on resistance to high temperatures, low pH, auto-aggregation capacity, survival in simulated in vitro digestion (INFOGEST method), and antimicrobial activity against pathogens like Escherichia coli, Staphylococcus aureus, and Salmonella enteritidis. Three yeasts, Zygosaccharomyces rouxii, Schizosaccharomyces pombe, and Metschnikowia chrysoperlae, exhibited potential probiotic characteristics by maintaining cell concentrations exceeding 106 CFU/mL after in vitro digestion. They demonstrated fermentative abilities and resistance to ethanol and hops, suggesting their potential as starter cultures in beer production. Despite revealing promising probiotic and technological aspects, further research is necessary to ascertain their viability in producing fermented foods. This study underscores the innovative potential of honey as a source for new probiotic microorganisms and highlights the need for comprehensive investigations into their practical applications in the food industry.

Wine Barrel Biofilm as a Source of Yeasts with Non-Conventional Properties.

This study investigated the main microbial groups characterizing the interior surface of oak barrels from different years (1890, 1895, 1920, 1975, 2008) used in the production of vino cotto. The yeasts were characterized for the following properties: γ-aminobutyric acid (GABA) production, antioxidant activity, air-liquid interfacial biofilm formation, and anthocyanin adsorption capacity. Community-level physiological profile analysis revealed that the microbial communities inside the barrels used the tested carbon sources in different manners. The following yeast species were identified: Millerozyma farinosa, Zygosaccharomyces bisporus, Wickerhamiella versatilis, Zygosaccharomyces bailii, Starmerella lactis-condensi, and Zygosaccharomyces rouxii. All the strains were able to produce GABA, and S. lactis-condensi, Z. bisporus and Z. rouxii were the highest producers (more than 600 mg/L). The Z. rouxii and Z. bailii strains showed the highest antioxidant activity. Only seven strains out of ten M. farinosa formed air-liquid interfacial biofilm. None of the M. farinosa strains adsorbed anthocyanins on their cell wall. The other strains adsorbed anthocyanins in a strain-dependent way, and the highest adsorption was observed for the W. versatilis strains. The yeasts isolated in this study could be used to increase the functional properties and the quality of fermented foods and beverages.

Overexpression of the FBA and TPI genes promotes high production of HDMF in Zygosaccharomyces rouxii.

4-Hydroxy-2,5-dimethyl-3 (2H)-furanone (HDMF) is widely used in the food industry as a spice and flavoring agent with high market demand. In this study, fructose-1,6-bisphosphate aldolase (FBA) and triose phosphate isomerase (TPI) were overexpressed in Zygosaccharomyces rouxii in the form of single and double genes, respectively, via electroporation. High-yield HDMF-engineered yeast strains were constructed by combining the analysis of gene expression levels obtained by real-time fluorescence quantitative PCR technology and HDMF production measured by HPLC. The results showed that there was a significant positive correlation between the production of HDMF and the expression levels of the FBA and TPI genes in yeast; the expression levels of the FBA and TPI genes were also positively correlated (p < 0.05). Compared with the wild type (WT), the engineered strains F10-D, T17-D, and TF15-A showed marked increases in HDMF production and FBA and TPI gene expression (p < 0.05) and exhibited great genetic stability with no obvious differences in biomass or colony morphology. In addition, the exogenous addition of d-fructose promoted the growth of Z. rouxii. Among the engineered strains, when fermented in YPD media supplemented with d-fructose for 5 days, TF15-A (overexpressing the FBA and TPI genes) generated the highest HDMF production of 13.39 mg/L, which is 1.91 times greater than that of the wild-type strain. The results above indicated that FBA and TPI, which are key enzymes involved in the process of HDMF biosynthesis by Z. rouxii, positively regulate the synthesis of HDMF at the transcriptional level. d-fructose can be used as a precursor for the biosynthesis of HDMF by engineered yeast in industrial production.

Construction of a Zygosaccharomyces rouxii strain overexpressing the QOR gene for increased HDMF production.

4-Hydroxy-2,5-dimethyl-3(2H)-furanone (HDMF) is a flavor compound widely found in natural products and is used in food as a flavor-enhancing agent. Quinone oxidoreductase (QOR) was verified as a key enzyme to synthesize HDMF in strawberry, while its impact on HDMF production by Zygosaccharomyces rouxii was still unknown. The QOR gene was cloned and overexpressed in Z. rouxii, and its impact on HDMF production by Z. rouxii was then further analyzed. At the same time, it is expected to obtain engineered strains of Z. rouxii with high HDMF production. The results showed that the engineered strains of Z. rouxii exhibit different levels of QOR gene expression and HDMF production; among them, the QOR6 strain exhibiting the highest gene expression level and HDMF production was named as ZrQOR. The HDMF production of the ZrQOR strain was significantly higher than that of wild-type Z. rouxii at 3 and 5 days of culture, with 1.41-fold and 1.08-fold increases, respectively. At 3 days of fermentation, the highest HDMF yield of ZrQOR strain was obtained (2.75 mg/L), 2 days ahead of the reported highest HDMF production by Z. rouxii. At 3, 5, and 7 days, QOR gene expression was 4.8-fold, 3.3-fold, and 5.6-fold higher in the ZrQOR strain than in the wild-type Z. rouxii, respectively. Therefore, overexpression of the QOR gene facilitates HDMF synthesis. The genetic stability of the 0-20 generation ZrQOR strain was stable, and there was no significant difference in colony shape, QOR expression, or HDMF production compared to the wild type. In this study, the genetic engineering Z. rouxii strain was used to improve HDMF production. This research has laid the groundwork for further industrial production of HDMF via microbial synthesis.

Characterization of the effect of non-Saccharomyces cerevisiaes on the non-volatile constituents and volatile profiles of low-alcoholic pomegranate beverages

To create the low-alcoholic beverages with excellent nutritional properties and flavor qualities, pomegranate juice was fermented with 16 strains of non-Saccharomyces yeasts from 9 species without added sugar. The effects of different yeasts on the non-volatile constituents (vitamins, organic acids, polyphenols), volatile compounds and sensory characteristics of the fermented beverages were comprehensively evaluated. The study revealed that non-Saccharomyces fermentations resulted in a higher abundance of polyphenols compared to the pomegranate juice and S. cerevisiae WLS21 (Sc21). The monomer phenols in Meyerozyma guilliermondii 12 (Mg12) were approximately twice the total of CK and 1.3 times of Sc21. Moreover, they led to a higher concentration of volatile compounds than the pomegranate juice. A total of 94 volatile compounds were identified in the pomegranate fermented beverages. In contrast to S. cerevisiae, Wickerhamomyces anomalus 1-1 and 10 (Wa1-1, Wa10), Pichia kudriavzevii 8 (Pk8) and Mg12 resulted in more acetate esters, and Zygosaccharomyces rouxii IFO 1130 and 53 (Zr1130, Zr53) yield higher levels of ethyl esters. A total of 40 volatiles with a relative odour activity value (rOAV) of ≥ 0.1 were identified, of which 14 were selected for principal component analysis (PCA). The sensory analysis confirmed that Zr1130, Zr53, Wa1-1, Wa10 and Pk8 strains exhibited superior aroma generation compared to Sc21. Furthermore, the partial least-squares regression (PLSR) analysis revealed that cherry, red fruits, black currant, citrus fruits, raspberry, black berry, pineapple, floral, sour and alcoholic odours had a significantly positive impact on the overall acceptability of the fermented beverages.

High Glucose Is a Stimulation Signal of the Salt-Tolerant Yeast Zygosaccharomyces rouxii on Thermoadaptive Growth.

The salt-tolerant yeast Zygosaccharomyces rouxii is a typical aroma-producing yeast used in food brewing, but its mechanism of high temperature tolerance is still unclear. In this study, the response mechanism of Z. rouxii to glucose under high temperature stress at 40 °C was explored, based on the total synthetic lowest-nutrient medium. The results of the growth curves and scanning electron microscopy showed that high glucose was necessary for Z. rouxii to restore growth under high temperature stress, with the biomass at 300 g/L of glucose (OD600, 120h = 2.44 ± 0.26) being 8.71 times higher than that at 20 g/L (OD600, 120h = 0.28 ± 0.08). The results of the transcriptome analysis, combined with RT-qPCR, showed that the KEGG analysis of differentially expressed genes was enriched in pathways related to glucose metabolism, and high glucose (300 g/L) could effectively stimulate the gene expression of glucose transporters, trehalose synthesis pathways, and xylitol synthesis pathways under a high temperature, especially the expression of the glucose receptor gene RGT2 (up-regulated 193.7 times at 12 h). The corresponding metabolic characteristics showed that the contents of intracellular metabolites, such as glucose (Cmax, 6h = 6.50 ± 0.12 mg/g DCW), trehalose (Cmax, 8h = 369.00 ± 17.82 μg/g DCW), xylitol (Cmax, 8h = 1.79 ± 0.27 mg/g DCW), and glycerol (Cmax, 8h = 268.10 ± 44.49 μg/g DCW), also increased with time. The accumulation of acetic acid, as the main product of overflow metabolism under high temperature stress (intracellular Cmax, 2h = 126.30 ± 10.96 μg/g DCW; extracellular Cmax, 12h = 499.63 ± 27.16 mg/L), indicated that the downstream glycolysis pathway was active. Compared with the normal physiological concentration of glucose, a high glucose concentration can effectively stimulate the gene expression and metabolism of salt-tolerant Z. rouxii under high-temperature conditions to restore growth. This study helps to deepen the current understanding of the thermoadaptive growth mechanism of salt-tolerant Z. rouxii.

Characterisation of flavour profiles and microbial communities of fermented peppers with different fermentation years by combining flavouromics and metagenomics

The changes in flavours, volatile aromas and microbial communities of fermented peppers with different fermentation years and their relationships were investigated in this study. Results indicated a gradual increase in organic acids during fermentation, whereas free amino acids and capsaicinoids reached stability after 1 year of fermentation. Overall, the analysis detected 340 volatile compounds in fermented peppers and regarded 69 of them as differential compounds. Peppers fermented for 2 (FY2) and 4 years (FY4) possessed a greater number of differential volatiles with large odour activity values, thus endowing them with more favourable flavours. Hence, metagenomic analysis compared their microbial communities and functional annotations. Results revealed that Lactiplantibacillus plantarum and Zygosaccharomyces rouxii were the dominant bacterium and fungus, and metabolism was the main Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway in FY2. Correlation analysis demonstrated that Hyphopichia, Kazachstania and Clavispora were highly positively correlated with 12 key aroma flavours.

Effects of co‐fermentation of high‐yield ester Zygosaccharomyces rouxii and Saccharomyces cerevisiae on the quality of rice wine

AbstractBackgroundAt present, rice wine has the characteristics of fast fermentation, energy saving, and simple production due to the addition of commercial Saccharomyces cerevisiae. However, this kind of fermented rice wine has the disadvantages of single flavor and weak taste. To address this concern, the combination of Saccharomyces cerevisiae and non‐Saccharomyces yeast has been identified as an effective approach to enhance the quality of fermented rice wine. This research aims to further enhance the ethyl ester and higher alcohol components of rice wine by utilizing the co‐fermentation method of high‐yield ester Zygosaccharomyces rouxii and Saccharomyces cerevisiae, thereby increasing the aroma complexity of rice wine.ResultsAccording to the fermentation performance and gas chromatography–mass spectrometry (GC–MS) analysis, it was found that S. cerevisiae GJM and Z. rouxii SC01 have a strong metabolic ability for glucose and sucrose. Furthermore, the crucial alcohols such as isobutanol, isoamyl alcohol, and phenylethyl alcohol increased by 85%, 29%, and 138%, respectively, when compared to single S. cerevisiae GJM. Additionally, the ethyl acetate and phenylethylene acetate were increased by 1.35 and 1.45 times, respectively, when compared to single S. cerevisiae GJM. These findings were comparable with the results of sensory evaluation and electronic nose analysis, where the fruit flavor score and the content of mellow substances were found to be higher.ConclusionThese findings suggest that the co‐fermentation of S. cerevisiae and high‐yield ester Z. rouxii has the potential to enhance the quality and diversity of aroma in liquid rice wine.

The Hydrophilic C-terminus of Yeast Plasma-membrane Na+/H+ Antiporters Impacts Their Ability to Transport K+

Yeast plasma-membrane Na+/H+ antiporters (Nha/Sod) ensure the optimal intracellular level of alkali-metal cations and protons in cells. They are predicted to consist of 13 transmembrane segments (TMSs) and a large hydrophilic C-terminal cytoplasmic part with seven conserved domains. The substrate specificity, specifically the ability to recognize and transport K+ cations in addition to Na+ and Li+, differs among homologs. In this work, we reveal that the composition of the C-terminus impacts the ability of antiporters to transport particular cations. In the osmotolerant yeast Zygosaccharomyces rouxii, the Sod2-22 antiporter only efficiently exports Na+ and Li+, but not K+. The introduction of a negative charge or removal of a positive charge in one of the C-terminal conserved regions (C3) enabled ZrSod2-22 to transport K+. The same mutations rescued the low level of activity and purely Li+ specificity of ZrSod2-22 with the A179T mutation in TMS6, suggesting a possible interaction between this TMS and the C-terminus. The truncation or replacement of the C-terminal part of ZrSod2-22 with the C-terminus of a K+-transporting Nha/Sod antiporter (Saccharomyces cerevisiae Nha1 or Z. rouxii Nha1) also resulted in an antiporter with the capacity to export K+. In addition, in ScNha1, the replacement of three positively charged arginine residues 539–541 in the C3 region with alanine caused its inability to provide cells with tolerance to Li+. All our results demonstrate that the physiological functions of yeast Nha/Sod antiporters, either in salt tolerance or in K+ homeostasis, depend on the composition of their C-terminal parts.