Function and regulation of yeast genes involved in higher alcohol and ester metabolism during beverage fermentation

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.

Characterization of volatile compounds and microbial diversity of Arabica coffee in honey processing method based on different mucilage retention treatments

This study combined HS-SPME-GC-MS and high-throughput sequencing to explore how honey-processing methods with varying mucilage retentions impact volatile compounds and microbial communities in green coffee beans. HS-SPME-GC-MS revealed that the RH group (75 % to 80 % mucilage retention) had the highest relative content of volatile compounds. According to rOAV >1, 13 key aroma compounds were identified, contributing to flavors like "mellow" and "fruity". High-throughput sequencing identified seven dominant bacterial genera and four dominant fungal genera, with higher diversity of fungi than bacteria across treatments. Correlation analysis indicated that bacteria and fungi contribute to aroma formation, with bacteria more active in low-mucilage and fungi in high-mucilage treatments. Overall, the RH group was optimal for the aroma quality and bioactivity of green coffee beans. The findings of this research offers insights into aroma compound-microbe interactions in coffee mucilage fermentation, helping coffee producers optimize process parameters for better-quality coffee products.

Refermentation with yeast and lactic acid bacteria isolates: a strategy to improve the flavor of green coffee beans

BACKGROUND

Yeast and lactic acid bacteria (LAB) play an important part in the post-harvest fermentation of coffee. This study applied lab-scale fermentation to commercial green coffee beans using dry coffee pulp as the substrate, with the aim of modifying coffee-bean flavor. In addition to spontaneous fermentation, yeast and LAB isolated from coffee beans and dried coffee pulp were added during fermentation.

RESULTS

Co-inoculation of yeast and LAB showed a significant effect on the chlorogenic acid content after between 24 and 72 h of fermentation. Acetic, citric, malic, lactic, and quinic acids were shown to be affected significantly (P < 0.05) by fermentation and inoculation. Gas chromatography detected that esters, alcohols, aldehydes, furans, and pyrazines were the primary compounds in the coffee beans. Certain volatile groups were present in greater concentrations and broader varieties within the inoculated beans. The highest cupping scores were given to beans that had been co-inoculated with yeast and LAB.

CONCLUSION

Overall, the use of yeasts and LAB starters showed potential to create coffee beverages with desirable characteristics by standardized fermentation. © 2024 Society of Chemical Industry.

Comprehensive analysis of risk factors (methanol, acetaldehyde and higher alcohols) in alcoholic beverages and their reduction strategies: GC-MS analysis and modified activated carbon adsorption and characterization

This study endeavors to examine the levels of risk factors in alcoholic beverages and propose mitigation strategies. GC-MS analysis was utilized to assess risk factors in various distilled-spirits. The content of such risk factors in spirits ranked as follows: vodka ≈ gin < baijiu < whiskey < brandy, and all were adhering to the Chinese national standard. Additionally, a method was refined to alleviate these risks, employing various reagents for activated carbon modification and evaluating their adsorption efficiency for risk factors reduction. Oxalic acid-modified activated carbon exhibited promising adsorption rates for risk factors with acceptable flavor compounds loss, rendering it a prospective solution for health hazard reduction. Characterization via SEM and nitrogen-adsorption-desorption was conducted on the optimal material, complemented by sensory experiments to optimize its application. This study offers valuable insights into the content of risk factors in alcoholic beverages, aiding in improving quality and safety of alcoholic beverages.

Molecular Insights into the Aroma Difference between Beer and Wine: A Meta-Analysis-Based Sensory Study Using Concentration Leveling Tests

Beer and wine are popular beverages with clearly different aroma characters, the molecular background of which has not yet been systematically investigated. A comprehensive literature survey returned 14 845 concentration values obtained from 160 beer and 904 wine samples, covering 42 basic beer and 42 basic wine odorants, among which 40 were common to both beverages. Based on mean concentrations and a comparison with threshold data, 29 beer and 32 wine odorants were finally selected to build aroma base models that reflected the basic olfactory difference between beer and wine. Orthonasal concentration leveling tests applied to groups of odorants with similar odor characteristics finally revealed the crucial role of fruity smelling compounds. When 11 fruity compounds, predominantly esters, in the beer aroma base model were adjusted to the respective concentration levels in the wine aroma base model, the sensory panel no longer described the sample as beer-like but as wine-like.

The correlation between flavor formation and microbial community dynamics during the fermentation of zha cai

BACKGROUND

Zha cai, a pickled vegetable with unique flavors, is produced by fermenting fresh mustard tubers. In this study, the main physicochemical indices and volatile flavor compounds were determined in three fermentation periods. The bacterial and fungal communities in the three fermentation periods of zha cai were also monitored using high-throughput sequencing. Key microbial communities were identified based on significant correlations with flavor substances.

RESULTS

Firmicutes and Proteobacteria were the main bacterial phyla found within the three fermentation periods. Lactic acid bacteria, namely Lactobacillus, was the predominant bacteria found at the genus level. Ascomycetes and Stenotrophomonas were the major fungal phyla found in the three fermentation periods. Yeast, namely Debaryomyces, was the predominant fungus found at the genus level. A total of 42 bacterial genera were negatively correlated with volatile flavor substances of zha cai, and 37 bacterial genera were positively correlated. Meanwhile, a total of 47 genera of fungi were negatively correlated with the volatile flavor substances of zha cai, while 50 genera were positively correlated. Several microbial genera were significantly correlated with volatile flavor compounds, including Lactobacillus, Halomonas, Rhodococcus, and Debaryomyces.

CONCLUSION

This study identified the microbial classes that positively regulate the flavor of zha cai which could provide valuable help for flavor modulation in zha cai production. © 2024 Society of Chemical Industry.

Unraveling the complex nexus: Interplay of volatile compounds, free amino acids, and metabolites in oat solid state fermentation

This study delves into the dynamic interplay of volatile compounds, free amino acids, and metabolites, meticulously exploring their transformations during oat fermentation. Analysis via gas chromatography-mass spectrometry (GC-MS) unveiled significant alterations: 72 volatile compounds in unfermented oats (NFO) and 60 in fermented oats (FO), reflecting the profound impact of Saccharomyces cerevisiae TU11 and Lactobacillus plantarum Heal19 on oat constituents. A marked increase in Heptane (5.7-fold) and specific alcohol compounds, like 2-methyl-1-propanol, 3-methyl-1-butanol, and Phenylethyl alcohol in FO samples, while reductions in Hexanal, Hexanoic acid, and Acetic acid were observed. Notably, 4 phenolic compounds emerged post-fermentation, revealing diverse microbial actions in flavor modulation. Orthogonal-partial least squares discriminant analysis (OPLS-DA) indicated a clear separation between NFO and FO, demonstrating distinct volatile compound profiles. Further analysis revealed a noteworthy decrease in all free amino acids except for a significant increase in serine during fermentation. Differential metabolite screening identified 354 metabolites with 219 upregulated and 135 down-regulated, uncovering critical markers like isophenoxazine and imidazole lactic acid. Correlation analyses unveiled intricate relationships between volatile compounds and diverse metabolites, illuminating underlying biochemical mechanisms shaping oat flavor profiles during fermentation.

Volatilome, Microbial, and Sensory Profiles of Coffee Leaf and Coffee Leaf-Toasted Maté Kombuchas

Kombucha is a fermented beverage traditionally made from the leaves of Camelia sinensis. The market has drastically expanded recently, and the beverage has become more elaborated with new, healthy food materials and flavors. Pruning and harvesting during coffee production may generate tons of coffee leaves that are discarded although they contain substantial amounts of bioactive compounds, including those found in maté tea and coffee seeds. This study characterized the changes in volatilome, microbial, and sensory profiles of pure and blended arabica coffee leaf tea kombuchas between 3-9 days of fermentation. Acceptance was also evaluated by consumers from Rio de Janeiro (n = 103). Kombuchas (K) were prepared using black tea kombucha starter (BTKS) (10%), sucrose (10%), a symbiotic culture of Bacteria and Yeasts (SCOBY) (2.5%), and a pure coffee leaf infusion (CL) or a 50:50 blend with toasted maté infusion (CL-TM) at 2.5%. The RATA test was chosen for sensory profile characterization. One hundred volatile organic compounds were identified when all infusions and kombucha samples were considered. The potential impact compounds identified in CL K and CL-TM K were: methyl salicylate, benzaldehyde, hexanal, nonanal, pentadecanal, phenylethyl-alcohol, cedrol, 3,5-octadien-2-one, β-damascenone, α-ionone, β-ionone, acetic acid, caproic acid, octanoic acid, nonanoic acid, decanoic acid, isovaleric acid, linalool, (S)-dihydroactinidiolide, isoamyl alcohol, ethyl hexanoate, and geranyl acetone. Aroma and flavor descriptors with higher intensities in CL K included fruity, peach, sweet, and herbal, while CL-TM K included additional toasted mate notes. The highest mean acceptance score was given to CL-TM K and CL K on day 3 (6.6 and 6.4, respectively, on a nine-point scale). Arabica coffee leaf can be a co-product with similar fingerprinting to maté and black tea, which can be explored for the elaboration of potentially healthy fermented beverages in food industries.

Microbial Community Dynamics and the Correlation between Specific Bacterial Strains and Higher Alcohols Production in Tartary Buckwheat Huangjiu Fermentation

Tartary buckwheat is a healthy grain rich in nutrients and medicinal ingredients and consequently is commonly used for Huangjiu brewing. In order to reveal the correlation between microbial succession and higher alcohols production, in this study, Huangjiu fermentation was conducted using Tartary buckwheat as the raw material and wheat Qu as the starter culture. Microbial community dynamics analysis indicated that the bacterial diversity initially decreased rapidly to a lower level and then increased and maintained at a higher level during fermentation. Lactococcus was the dominant bacteria and Ralstonia, Acinetobacter, Cyanobacteria, and Oxalobacteraceae were the bacterial genera with higher abundances. In sharp contrast, only 13 fungal genera were detected during fermentation, and Saccharomyces showed the dominant abundance. Moreover, 18 higher alcohol compounds were detected by GC-MS during fermentation. Four compounds (2-phenylethanol, isopentanol, 1-hexadecanol, and 2-phenoxyethanol) were stably detected with high concentrations during fermentation. The compound 2-ethyl-2-methyl-tridecanol was detected to be of the highest concentration in the later period of fermentation. Correlation analysis revealed that the generation of 2-phenylethanol, isopentanol, 1-hexadecanol, and 2-phenoxyethanol were positively correlated with Granulicatella and Pelomonas, Bacteroides, Pseudonocardia and Pedomicrobium, and Corynebacterium, respectively. The verification fermentation experiments indicated that the improved wheat Qu QT3 and QT4 inoculated with Granulicatella T3 and Acidothermus T4 led to significant increases in the contents of 2-phenylethanol and pentanol, as well as isobutanol and isopentanol, respectively, in the Tartary buckwheat Huangjiu. The findings benefit understanding of higher alcohols production and flavor formation mechanisms in Huangjiu fermentation.

Effect of Koji on Flavor Compounds and Sensory Characteristics of Rice Shochu

Koji is an important starter for rice shochu brewing and influences the rice shochu quality. Consequently, we studied the impacts of koji on the flavor compounds and sensory characteristics of rice shochu using molds Aspergillus kawachii SICC 3.917 (A-K), Aspergillus oryzae SICC 3.79(A-O), Aspergillus Niger CICC 2372 (A-N), Rhizopus oryzae CICC 40260 (R-O), and the traditional starter Qu (control). The effects of koji on the aroma components, free amino acids (FAAs), and overall sensory aspects of rice shochu were studied. These findings indicated that koji significantly affected the rice shochu’s quality. The content of total FAAs in rice shochu A-K (30.586 ± 0.944 mg/L) and A-O (29.919 ± 0.278 mg/L) was higher than others. The content of flavor compounds revealed that the aroma of rice shochu with various koji varied greatly from the smells of alcohols and esters. Shochu A-O had a higher concentration of aroma compounds and it exhibited a strong aroma and harmonious taste compared with the others. This research using taste compounds, FAAs, flavor intensity, and partial least squares regression (PLSR) showed that shochu A-O appeared to possess the best sensory qualities, with elevated concentrations of alcohols and sweet FAAs and lesser concentrations of sour FAAs. Therefore, the A-O mold is promising for the manufacture of rice shochu with excellent flavor and sensory characteristics.

Influence of Lactobacillus helveticus ZF22 and TR1-1-3 strains on the aromatic flavor of fermented sausages

In this study, five strains isolated from traditional Inner Mongolian air-dried meat products were used, two Lactobacillus helveticus strains, ZF22 and TR1-1-3, with potent antibacterial activity, acid, salt, and nitrite tolerance, were selected for this study. Lactic acid bacteria (LAB) (Lactobacillus helveticus ZF22 and TR1-1-3) were inoculated into fermented sausages at 10⁷ CFU/g and their volatiles were studied during fermentation and storage. Clustering heat map and principal component analysis (PCA) were used to identify differentiating flavor components in uninoculated and inoculated sausages. The results showed that 72 volatile flavor substances were identified during the fermentation of the fermented sausages and that inoculation with Lactobacillus helveticus ZF22 and TR1-1-3 increased the proportion of acids, ketones and alkanes. Moreover, the clustering heat map demonstrated that esters such as ethyl isobutyrate, ethyl acetate, and ethyl valerate were more abundant in TR1-1-3 and ZF22 than ZR. The PCA analysis showed that the volatile compounds of the three fermented sausages were distributed in separate quadrants, suggesting that the volatile compound compositions of the three fermented sausages differed significantly. Our findings suggest that inoculating fermented sausages with Lactobacillus helveticus TR1-1-3 and ZF22 can improve flavor by enhancing the type and amount of flavor compounds.

Volatile Aroma Compound Production Is Affected by Growth Rate in S. cerevisiae

The initial growth rate of a yeast strain is a key parameter in the production of fermented beverages. Fast growth is linked with higher fermentative capacity and results in less slow and stuck fermentations unable to reach the expected final gravity. As concentrations of metabolites are in a constant state of flux, quantitative data on how growth rate affects the production of aromatic compounds becomes an important factor for brewers. Chemostats allow to set and keep a specific dilution rate throughout the fermentation and are ideal system to study the effect of growth on aroma production. In this study, we ran chemostats alongside batch and fed-batch cultures, compared volatile profiles detected at different growth rates, and identified those affected by the different feeding profiles. Specifically, we quantified six abundant aroma compounds produced in anaerobic glucose-limited continuous cultivations of S. cerevisiae at different dilution rates. We found that volatile production was affected by the growth rate in four out of six compounds assayed, with higher alcohols and esters following opposite trends. Batch and fed-batch fermentations were devised to study the extent by which the final concentration of volatile compounds is influenced by glucose availability. Compared with the batch system, fed-batch fermentations, where the yeast growth was artificially limited by a slow constant release of nutrients in the media, resulted in a significant increase in concentration of higher alcohols, mirroring the results obtained in continuous fermentations. This study paves the way to further process development optimization for the production of fermented beverages. IMPORTANCE The production of fermentation beverages will need to quickly adapt to changes in both the climate and customer demands, requiring the development of new strains and processes. Breakthroughs in the field are hindered by the limited knowledge on the interplay between physiology and aroma compound production in yeast. No quantitative data on how growth rate affects aroma profile is available in the literature to guide optimization of the complex flavors in fermented beverages. In this study, we exploited the chemostat system, alongside with batch and fed-batch cultures, to compare volatile profiles at different growth rates. We identified the aromatic compounds affected by the different feeding profiles and nutrient limitations. Moreover, we uncovered the correlation between yeast growth, esters, and higher alcohols production. This study showcases the potential of the application of feeding profiles for the manipulation of aroma in the craft beverage industry.

The effects of an innovative pulping technique of synchronously pulping and gelatinizing treatment on raw materials properties, oenological parameters, fermentation process, and flavor characteristics of glutinous rice wine

Liquid-state fermentation has been increasingly applied in the industrial glutinous rice wine (GRW) production. However, products brewed by this emerging technique possess some deficiencies in flavor quality. Therefore, this study firstly developed and optimized an innovative pulping technique by the synchronously pulping and gelatinizing treatment (Process I) to improve GRW flavor quality, and then revealed the influences of Process I on raw materials properties, oenological parameters, fermentation process, and flavor characteristics of GRW. Results show that Process I significantly (p < 0.05) enriched the soluble solid and crude protein content of glutinous rice milk by improving gelatinization degree and pulping efficiency, which consequently enhanced the microbial growth, glycolysis, and protein decomposition during the GRW fermentation process. GC-MS analysis shows that Process I sequentially significantly (p < 0.05) enhanced the esterification and Ehrlich or Harrison pathway during the fermentation process. This contributed to a higher content of key ester and alcohol compounds.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10068-022-01119-7.

The way of Qu-making significantly affected the volatile flavor compounds in Huangjiu (Chinese rice wine) during different brewing stages

The volatile flavor compounds of Huangjiu (Chinese rice wine) brewed from different raw materials were obviously different, but there were few studies on the volatile flavor compounds of Huangjiu brewed from different wheat Qu at different brewing stages. In this paper, headspace-solid phase microextraction combined with gas chromatography-mass spectrometry, combined with principal component analysis and sensory evaluation, was used to determine the volatile flavor compounds in Huangjiu brewed from wheat Qu made by hand and wheat Qu made by mechanical. The results showed that there were significant differences in the contents and types of volatile flavor substances in Huangjiu brewed from different wheat Qu at fermentation stages, and the prefermentation and postfermentation Huangjiu samples could be well distinguished from each other. Compared with the Huangjiu brewed from wheat Qu made by mechanical, the Huangjiu brewed from wheat Qu made by hand has stronger aroma and better taste.

A Snapshot of Microbial Succession and Volatile Compound Dynamics in Flat Peach Wine During Spontaneous Fermentation

Flat peaches possess characteristic flavors and are rich in nutrients. The fermentation of flat peaches to produce wine through complex biochemical reactions is an effective method to overcome their seasonal defects. Spontaneously fermented flat peach wine has plentiful and strong flavors, but the microbiota of fermentation are still unknown. In this study, the microbial succession and volatile compound dynamics of spontaneous fermentation in Xinjiang flat peach wine were investigated using high-throughput sequencing (HTS) and headspace solid phase microextraction (HS-SPME) coupled with gas chromatography-mass spectrometry (GC-MS) technology, respectively, to better understand the microbiota involved. Multivariate data analysis was used to predict the relationship between microorganisms and volatile chemicals. The results showed that Kazachstania, Pichia, Aspergillus, Fructobacillus, Leuconostoc, and Lactobacillus were the dominant genera during the spontaneous fermentation of flat peach wine. Furthermore, ethyl hexanoate, 3-hexen-1-yl acetate, ethyl caprate, ethyl caprylate, phenethyl acetate, ethanol, γ-decalactone, decanal, 1-hexanoic acid, and octanoic acid endued flat peach wine with a strong fruity and fatty aroma. The core functional microbiota (primarily consisting of 11 bacterial and 14 fungal taxa) was strongly associated with the production of 27 volatile compounds in the spontaneously fermented flat peach wine, according to multivariate data analysis. Some alcohols and esters were positively linked with the presence of Kazachstania and Pichia. Meanwhile, the presence of Fructobacillus, Leuconostoc, Lactobacillus, and Weissella was significantly correlated with 2-non-anol, ethanol, 3-methyl-1-butanol, octyl formate, isoamyl lactate, and ethyl lactate. This snapshot of microbial succession and volatile compound dynamics provides insights into the microorganisms involved in flat peach wine fermentation and could guide the production of flat peach wine with desirable characteristics.

Screening of Lactiplantibacillus plantarum with High Stress Tolerance and High Esterase Activity and Their Effect on Promoting Protein Metabolism and Flavor Formation in Suanzhayu, a Chinese Fermented Fish

In this study, three Lactiplantibacillus plantarum, namely 3-14-LJ, M22, and MB1, with high acetate esterase activity, acid, salt, and high-temperature tolerance were selected from 708 strains isolated from fermented food. Then, L. plantarum strains MB1, M22, and 3-14-LJ were inoculated at 107 CFU/mL in the model and 107 CFU/g in actual Suanzhayu systems, and the effects during fermentation on the physicochemical properties, amino acid, and volatile substance were investigated. The results showed that the inoculated group had a faster pH decrease, lower protein content, higher TCA-soluble peptides, and total amino acid contents than the control group in both systems (p < 0.05). Inoculation was also found to increase the production of volatile compounds, particularly esters, improve the sour taste, and decrease the bitterness of the product (p < 0.05). L. plantarum M22 was more effective than the other two strains in stimulating the production of isoamyl acetate, ethyl hexanoate, and ethyl octanoate. However, differences were discovered between the strains as well as between the model and the actual systems. Overall, the isolated strains, particularly L. plantarum M22, have good fermentation characteristics and have the potential to become excellent Suanzhayu fermenters in the future.

Downregulation of EHT1 and EEB1 in Saccharomyces cerevisiae Alters the Ester Profile of Wine during Fermentation

EHT1 and EEB1 are the key Saccharomyces cerevisiae genes involved in the synthesis of ethyl esters during wine fermentation. We constructed single (Δeht1, Δeeb1) and double (Δeht1Δeeb1) heterogenous mutant strains of the industrial diploid wine yeast EC1118 by disrupting one allele of EHT1 and/or EEB1. In addition, the aromatic profile of wine produced during fermentation of simulated grape juice by these mutant strains was also analyzed. The expression levels of EHT1 and/or EEB1 in the relevant mutants were less than 50% of the wild-type strain when grown in YPD medium and simulated grape juice medium. Compared to the wild-type strain, all mutants produced lower amounts of ethyl esters in the fermented grape juice and also resulted in distinct ethyl ester profiles. ATF2, a gene involved in acetate ester synthesis, was expressed at higher levels in the EEB1 downregulation mutants compared to the wild-type and Δeht1 strains during fermentation, which was consistent with the content of acetate esters. In addition, the production of higher alcohols was also markedly affected by the decrease in EEB1 levels. Compared to EHT1, EEB1 downregulation had a greater impact on the production of acetate esters and higher alcohols, suggesting that controlling EEB1 expression could be an effective means to regulate the content of these aromatic metabolites in wine. Taken together, the synthesis of ethyl esters can be decreased by deleting one allele of EHT1 and EEB1 in the diploid EC1118 strain, which may modify the ester profile of wine more subtly compared to the complete deletion of target genes.

The influence of polyphenol supplementation on ester formation during red wine alcoholic fermentation

Pre-fermentative polyphenol supplementation in industrial scales (100-hL) and simulated fermentation (350 mL clarified juice) were conducted. Results showed that in practical winemaking, adding QCE (quercetin, caffeic acid and ellagic acid) increased acetate concentrations in wines and extra grape seed tannins (T) enhanced the effect of QCE supplementation. In simulated fermentation with clarified juice, the synergy effect of QCE and T was evidenced that ester formation was only promoted through mixed QCET supplementation. Besides, QCE supplementation benefited the formation of 4-vinylcatechol adducted malvidin-3-O-(acetyl/coumaroyl)-glucoside and decreased other anthocyanin derivatives derived from pyruvic acid and acetaldehyde, leading more pyruvic acid and acetaldehyde left in yeast to enhance the metabolic fluxes of esters. Findings manifested the connection between the formation of esters and anthocyanin derivatives during red wine alcoholic fermentation, which would be influenced by the phenolic matrix. This work could provide a perspective in winemaking industry for modulating aroma profile via polyphenol supplementation.

Investigation of Volatile Compounds, Microbial Succession, and Their Relation During Spontaneous Fermentation of Petit Manseng

Petit Manseng is widely used for fermenting sweet wine and is popular among younger consumers because of its sweet taste and attractive flavor. To understand the mechanisms underlying spontaneous fermentation of Petit Manseng sweet wine in Xinjiang, the dynamic changes in the microbial population and volatile compounds were investigated through high-throughput sequencing (HTS) and headspace solid-phase microextraction (HS-SPME) coupled to gas chromatography-mass spectrometry (GC-MS) technology, respectively. Moreover, the relationship between the microbial population and volatile compounds was deduced via multivariate data analysis. Candida and Mortierella were dominant genera in Petit Manseng wine during spontaneous fermentation. Many fermentative aroma compounds, including ethyl octanoate, isoamyl acetate, ethyl butyrate, ethyl decanoate, isoamyl alcohol, ethyl laurate, isopropyl acetate, hexanoic acid, and octanoic acid, were noted and found to be responsible for the strong fruity and fatty aroma of Petit Manseng sweet wine. Multivariate data analysis indicated that the predominant microorganisms contributed to the formation of these fermentative aroma compounds. Hannaella and Neomicrosphaeropsis displayed a significantly positive correlation with the 6-methylhept-5-en-2-one produced. The current results provide a reference for producing Petit Manseng sweet wine with desirable characteristics.

Diversity of Saccharomyces cerevisiae strains associated to racemes of Grillo grape variety

The most important oenological characteristics of high-quality sparkling wines are high content of acidity and low pH. Racemes are late-maturing grapes of Grillo variety characterized by low pH and high content of tartaric and malic acids and, due to their intrinsic characteristics, might represent an interesting technological solution to increase acid quality of base sparkling wine. To this purpose, the use of yeasts able to ferment grape must at very low pH is mandatory for the success of the process. In this work, 261 Saccharomyces cerevisiae isolated from spontaneous vinifications of Grillo grape racemes were subject to intraspecific characterization by interdelta analysis which evidenced a total population consisting of 82 strains which were screened for their basis of technological traits including SO2 and alcohol tolerance, flocculence, growth at low temperatures and qualitative features such as H2S production. A total of 11 strains with interesting technological performance in vitro were inoculated into musts obtained from racemes of Grillo grape variety and microfermentation were monitored. For the first time an ecological investigation of yeast associated to raceme grapes has been carried out and provided an innovative strategy to improve the acidity of a Sicilian sparkling base wine from Grillo grape variety.

GAT1 Gene, the GATA Transcription Activator, Regulates the Production of Higher Alcohol during Wheat Beer Fermentation by Saccharomyces cerevisiae

Uncoordinated carbon-nitrogen ratio in raw materials will lead to excessive contents of higher alcohols in alcoholic beverages. The effect of GAT1 gene, the GATA transcription activator, on higher alcohol biosynthesis was investigated to clarify the mechanism of Saccharomyces cerevisiae regulating higher alcohol metabolism under high concentrations of free amino nitrogen (FAN). The availability of FAN by strain SDT1K with a GAT1 double-copy deletion was 28.31% lower than that of parent strain S17, and the yield of higher alcohols was 33.91% lower. The transcript levels of the downstream target genes of GAT1 and higher alcohol production in the double-copy deletion mutant suggested that a part of the effect of GAT1 deletion on higher alcohol production was the downregulation of GAP1, ARO9, and ARO10. This study shows that GATA factors can effectively regulate the metabolism of higher alcohols in S. cerevisiae and provides valuable insights into higher alcohol biosynthesis, showing great significance for the wheat beer industry.

Metabolic, Organoleptic and Transcriptomic Impact of Saccharomyces cerevisiae Genes Involved in the Biosynthesis of Linear and Substituted Esters

Esters constitute a broad family of volatile compounds impacting the organoleptic properties of many beverages, including wine and beer. They can be classified according to their chemical structure. Higher alcohol acetates differ from fatty acid ethyl esters, whereas a third group, substituted ethyl esters, contributes to the fruitiness of red wines. Derived from yeast metabolism, the biosynthesis of higher alcohol acetates and fatty acid ethyl esters has been widely investigated at the enzymatic and genetic levels. As previously reported, two pairs of esterases, respectively encoded by the paralogue genes ATF1 and ATF2, and EEB1 and EHT1, are mostly involved in the biosynthesis of higher alcohol acetates and fatty acid ethyl esters. These esterases have a moderate effect on the biosynthesis of substituted ethyl esters, which depend on mono-acyl lipases encoded by MGL2 and YJU3. The functional characterization of such genes helps to improve our understanding of substituted ester metabolism in the context of wine alcohol fermentation. In order to evaluate the overall sensorial impact of esters, we attempted to produce young red wines without esters by generating a multiple esterase-free strain (Δatf1, Δatf2, Δeeb1, and Δeht1). Surprisingly, it was not possible to obtain the deletion of MGL2 in the Δatf1/Δatf2/Δeeb1/Δeht1 background, highlighting unsuspected genetic incompatibilities between ATF1 and MGL2. A preliminary RNA-seq analysis depicted the overall effect of the Δatf1/Δatf2/Δeeb1/Δeht1 genotype that triggers the expression shift of 1124 genes involved in nitrogen and lipid metabolism, but also chromatin organization and histone acetylation. These findings reveal unsuspected regulatory roles of ester metabolism in genome expression for the first time.

Influence of fermentation temperature and yeast type on the chemical and sensory profile of handcrafted beers

BACKGROUND

Various physicochemical parameters, the polyphenolic content, the volatile fraction as well as the sensory profile of beers were studied using five different yeast strains (three top-fermentation and two bottom-fermentation) and two different fermentation temperatures (12 and 18 °C) for each of them.

RESULTS

The results indicated that at lower fermentation temperatures, the yeast strain factor was less significant for the various physicochemical parameters considered. The polyphenolic content increased as the fermentation temperature decreased, and significantly higher amounts of tyrosol were found in the samples fermented at 12 °C. However, the volatile content increased for beers fermented at 18 °C, these beers being better evaluated from the sensory point of view.

CONCLUSIONS

No clear relationship was observed between the temperature used and the type of yeast, with more complex aroma and sensory profiles being found in beers fermented at higher temperatures, using yeasts that are supposedly suitable for use at lower temperatures. © 2020 Society of Chemical Industry.

The Use of Non-Saccharomyces Yeast and Enzymes in Beer Production

The objective of this paper was to test the potential of selected non-Saccharomyces strains for beer production, by using Saccharomyces cerevisiae as a control sample. For some of variants brewing enzymes were added to wort to increase the content of fermentable sugars. The non-Saccharomyces yeasts differed in the fermentation process rate. The basic beer physiochemical parameters were assessed, including: alcohol content, extract, free amino nitrogen, sugars, acidity, colour, and the profile of volatile compounds and metal ions. The use of enzymes caused an increase in alcohol and fusel alcohols concentration in beers obtained. Total acidity, free amine nitrogen content, colour and sugar content indicated that the tested non-Saccharomyces yeast allowed obtaining beers with the proper analytical parameters.

Effect of the Deletion of Genes Related to Amino Acid Metabolism on the Production of Higher Alcohols by Saccharomyces cerevisiae

The higher alcohols produced by Saccharomyces cerevisiae exert remarkable influence on the taste and flavour of Chinese Baijiu. In order to study the regulation mechanism of amino acid metabolism genes on higher alcohol production, eight recombinant strains with amino acid metabolism gene deletion were constructed. The growth, fermentation performance, higher alcohol production, and expression level of genes in recombinant and original α5 strains were determined. Results displayed that the total higher alcohol concentration in α5ΔGDH1 strain decreased by 27.31% to 348.68 mg/L compared with that of α5. The total content of higher alcohols in α5ΔCAN1 and α5ΔGAT1 strains increased by 211.44% and 28.36% to 1493.96 and 615.73 mg/L, respectively, compared with that of α5. This study is the first to report that the CAN1 and GAT1 genes have great influence on the generation of higher alcohols. The results demonstrated that amino acid metabolism plays a substantial role in the metabolism of higher alcohols by S. cerevisiae. Interestingly, we also found that gene knockout downregulated the expression levels of the knocked out gene and other genes in the recombinant strain and thus affected the formation of higher alcohols by S. cerevisiae. This study provides worthy insights for comprehending the metabolic mechanism of higher alcohols in S. cerevisiae for Baijiu fermentation.

Effect of Fungi on Metabolite Changes in Kimchi During Fermentation

The purpose of this study is to investigate the effect of fungi on kimchi metabolites during fermentation. A gas chromatography-mass spectrometry (GC-MS) based metabolite profiling approach in combination with principal component analysis (PCA) is performed to differentiate metabolites produced by fungi or bacteria. To avoid bacterial growth, kimchi is treated with 100 μg/mL of ampicillin every three days from 30 to 50 days of fermentation. The relative content of the major fungi at 50 days of fermentation, between the control group and the ampicillin treatment group, was not significantly different. The administration of ampicillin changed the metabolites in kimchi by affecting the growth of kimchi bacteria. Based on the pattern of change of each metabolite, the changed metabolites are grouped into four categories: (1) metabolites produced or consumed by fungi, (2) metabolites involving both fungi and bacteria, (3) metabolites produced or consumed by bacteria, and (4) metabolites of undetermined origin. Alanine, thymine, galacturonic acid, and malonic acid can be regarded as the metabolites produced by fungi between 30 and 50 days of fermentation. In contrast, malic acid, oxaloacetic acid, galactitol, glucose, and mannitol are presumed to be the metabolites mainly consumed by fungi. This study is meaningful as the first study conducted by inhibiting growth of bacteria to identify the metabolites contributed by fungi or bacteria in the kimchi fermentation process. These results could be used to make customized kimchi that controls the production of desired metabolites by selectively controlling the formation of microbial communities in the kimchi industry.

Potential application of yeasts from Ecuadorian chichas in controlled beer and chicha production

The potential of yeasts isolated from traditional chichas as starter cultures, either for controlled production of the native beverage or for industrial beer production, has been investigated. Three S. cerevisiae strains and one T. delbrueckii strain isolated from four different Ecuadorian chichas were compared to ale and lager beer strains with respect to fermentation performance, sugar utilisation, phenolic off-flavour production, flocculation and growth at low temperature. Fermentations were performed in 15 °P all-malt wort and in a model chicha substrate at 12 °C and 20 °C. Tall-tube fermentations (1.5 L) were also performed with both substrates to assess yeast performance and beer quality. Among the strains tested, only one Ecuadorian S. cerevisiae strain was able to ferment the wort sugars maltose and maltotriose. Fermentations with all Ecuadorian strains were poor in wort at 12 °C relative to 20 °C, but were similar in model chicha substrate at both temperatures. The aromatic profile was different between species and strains. These results indicate the potential of yeasts derived from traditional Andean fermented beverages for commercial applications. One of the chicha strains demonstrated traits typical of domesticated brewery strains and could be suitable for ale fermentation, while the other strains may have potential for low-alcohol beer or chicha production.

Molecular profiling of beer wort fermentation diversity across natural Saccharomyces eubayanus isolates

The utilization of S. eubayanus has recently become a topic of interest due to the novel organoleptic properties imparted to beer. However, the utilization of S. eubayanus in brewing requires the comprehension of the mechanisms that underlie fermentative differences generated from its natural genetic variability. Here, we evaluated fermentation performance and volatile compound production in ten genetically distinct S. eubayanus strains in a brewing fermentative context. The evaluated strains showed a broad phenotypic spectrum, some of them exhibiting a high fermentation capacity and high levels of volatile esters and/or higher alcohols. Subsequently, we obtained molecular profiles by generating 'end-to-end' genome assemblies, as well as metabolome and transcriptome profiling of two Patagonian isolates exhibiting significant differences in beer aroma profiles. These strains showed clear differences in concentrations of intracellular metabolites, including amino acids, such as valine, leucine and isoleucine, likely impacting the production of 2-methylpropanol and 3-methylbutanol. These differences in the production of volatile compounds are attributed to gene expression variation, where the most profound differentiation is attributed to genes involved in assimilatory sulfate reduction, which in turn validates phenotypic differences in H2 S production. This study lays a solid foundation for future research to improve fermentation performance and select strains for new lager styles based on aroma and metabolic profiles.

Study of the Enzymatic Capacity of Kluyveromyces marxianus for the Synthesis of Esters

Recently, biotechnological opportunities have been found in non-Saccharomyces yeasts because they possess metabolic characteristics that lead to the production of compounds of interest. It has been observed that Kluyveromyces marxianus has a great potential in the production of esters, which are aromatic compounds of industrial importance. The genetic bases that govern the synthesis of esters include a large group of enzymes, among which the most important are alcohol acetyl transferases (AATases) and esterases (AEATases), and it is known that some are present in K. marxianus, because it has genetic characteristics like S. cerevisiae. It also has a physiology suitable for biotechnological use since it is the eukaryotic microorganism with the fastest growth rate and has a wide range of thermotolerance with respect to other yeasts. In this work, the enzymatic background of K. marxianus involved in the synthesis of esters is analyzed, based on the sequences reported in the NCBI database.

Differential Analysis of Proteins Involved in Ester Metabolism in two Saccharomyces cerevisiae Strains during the Second Fermentation in Sparkling Wine Elaboration

The aromatic metabolites derived from yeast metabolism determine the characteristics of aroma and taste in wines, so they are considered of great industrial interest. Volatile esters represent the most important group and therefore, their presence is extremely important for the flavor profile of the wine. In this work, we use and compare two Saccharomyces cerevisiae yeast strains: P29, typical of sparkling wines resulting of second fermentation in a closed bottle; G1, a flor yeast responsible for the biological aging of Sherry wines. We aimed to analyze and compare the effect of endogenous CO2 overpressure on esters metabolism with the proteins related in these yeast strains, to understand the yeast fermentation process in sparkling wines. For this purpose, protein identification was carried out using the OFFGEL fractionator and the LTQ Orbitrap, following the detection and quantification of esters with gas chromatograph coupled to flame ionization detector (GC-FID) and stir-bar sorptive extraction, followed by thermal desorption and gas chromatography-mass spectrometry (SBSE-TD-GC-MS). Six acetate esters, fourteen ethyl esters, and five proteins involved in esters metabolism were identified. Moreover, significant correlations were established between esters and proteins. Both strains showed similar behavior. According to these results, the use of this flor yeast may be proposed for the sparkling wine production and enhance the diversity and the typicity of sparkling wine yeasts.

[Synthesis and regulation of flavor compounds derived from brewing yeast: fusel alcohols]

Among the main beer components, fusel alcohols are important because of their influence on the flavor of the final product, and therefore on its quality. During the production process, these compounds are generated by yeasts through the metabolism of amino acids. The yeasts, fermentation conditions and wort composition affect fusel alcohols profiles and their concentrations. In this review, we provide detailed information about the enzymes involved in fusel alcohols formation and their regulation. Moreover, we describe how the type of yeast used, the fermentation temperature and the composition of carbohydrates and nitrogen source in wort, among other fermentation parameters, affect the biosynthesis of these alcohols. Knowing how fusel alcohol levels vary during beer production provides a relevant tool for brewers to achieve the desired characteristics in the final product and at the same time highlights the aspects still unknown to science.

Increase ethyl acetate production in Saccharomyces cerevisiae by genetic engineering of ethyl acetate metabolic pathway

Ethyl acetate has attracted much attention as an important chemical raw material and a flavor component of alcoholic beverages. In this study, the biosynthetic pathway for the production of ethyl acetate in Chinese liquor yeast was unblocked. In addition to engineering Saccharomyces cerevisiae to increased intracellular CoA and acetyl-CoA levels, we also increased the combining efficiency of acetyl-CoA to ethanol. The genes encoding phosphopantothenate-cysteine ligase, acetyl-CoA synthetase, and alcohol acetyltransferase were overexpressed by inserting the strong promoter PGK1p and the terminator PGK1t, respectively, and then combine them. Our results finally showed that the ethyl acetate levels of all engineering strains were improved. The final engineering strain CLy12a-ATF1-ACS2-CAB2 had a significant increase in ethyl acetate yield, reaching 610.26 (± 14.28) mg/L, and the yield of higher alcohols was significantly decreased. It is proved that the modification of ethyl acetate metabolic pathway is extremely important for the production of ethyl acetate from Saccharomyces cerevisiae.

Linking gene expression and oenological traits: Comparison between Torulaspora delbrueckii and Saccharomyces cerevisiae strains

Wine fermentations typically involve the yeast Saccharomyces cerevisiae. However, many other yeast species participate to the fermentation process, some with interesting oenological traits. In this study the species Torulaspora delbrueckii, used occasionally in mixed or sequential fermentation with S. cerevisiae to improve wine sensory profile, was investigated to understand the physiological differences between the two. Next generation sequencing was used to characterize the transcriptome of T. delbrueckii and highlight the different genomic response of these yeasts during growth under wine-like conditions. Of particular interest were the basic differences in the glucose fermentation pathway and the formation of aromatic and flavour compounds such as glycerol, esters and acetic acid. Paralog genes were missing in glycolysis and glycerol biosynthesis in T. delbrueckii. Results indicate the tendency of T. delbrueckii to produce less acetic acid relied on a higher expression of alcoholic fermentation related genes, whereas acetate esters were influenced by the absence of esterases, ATF1-2. Additionally, in the Δbap2 S. cerevisiae strain, the final concentration of short branched chain ethyl esters (SBCEEs) was related to branched chain amino acid (BCAA) uptake. In conclusion, different adaption strategies are apparent for T. delbrueckii and S. cerevisiae yeasts, an understanding of which will allow winemakers to make better use of such microbial tools to achieve a desired wine sensory outcome.

Microbial acidification, alcoholization, and aroma production during spontaneous lambic beer production

Acidic beers, such as Belgian lambic beers and American and other coolship ales, are becoming increasingly popular worldwide thanks to their refreshing acidity and fruity notes. The traditional fermentation used to produce them does not apply pure yeast cultures but relies on spontaneous, environmental inoculation. The fermentation and maturation process is carried out in wooden barrels and can take up to three years. It is characterized by different microbial species belonging to the enterobacteria, acetic acid bacteria, lactic acid bacteria, and yeasts. This review provides an introduction to the technology and four fermentation strategies of beer production, followed by the microbiology of acidic beer production, focusing on the main microorganisms present during the long process used for the production of Belgian lambic beers. © 2018 Society of Chemical Industry.

Exploring the impacts of postharvest processing on the aroma formation of coffee beans - A review

The aim of this review is to describe the volatile aroma compounds of green coffee beans and evaluate sources of variation in the formation and development of coffee aroma through postharvest processing. The findings of this survey showed that the volatile constituents of green coffee beans (e.g., alcohols, aldehydes, and alkanes) have no significant influence on the final coffee aroma composition, as only a few such compounds remain in the beans after roasting. On the other hand, microbial-derived, odor-active compounds produced during removal of the fruit mucilage layer, including esters, higher alcohols, aldehydes, and ketones, can be detected in the final coffee product. Many postharvest processing including drying and storage processes could influence the levels of coffee aroma compositions, which remain to be elucidated. Better understanding of the effect of these processes on coffee aroma composition would assist coffee producers in the optimal selection of postharvest parameters that favor the consistent production of flavorful coffee beans.

[Synthesis and regulation of flavor compounds derived from brewing yeast: Esters]

During brewing process yeast produce more than 500 chemical compounds that can negatively and positively impact beer at the organoleptic level. In recent years, and particularly thanks to the advancement of molecular biology and genomics, there has been considerable progress in our understanding about the molecular and cellular basis of the synthesis and regulation of many of these flavor compounds. This article focuses on esters, responsible for the floral and fruity beer flavor. Its formation depends on various enzymes and factors such as the concentration of wort nutrients, the amount of dissolved oxygen and carbon dioxide, fermentation temperature and mainly the genetics of the yeast used. We provide information about how the esters originate and how is the impact of different fermentative parameters on the final concentrations of these compounds and the quality of the end product.

Impact of coculturing Bifidobacterium animalis subsp. lactis HN019 with yeasts on microbial viability and metabolite formation

AIMS

To evaluate the impact of coculturing Bifidobacterium animalis subsp. lactis HN019 with yeasts on microbial viability and metabolite production.

METHODS AND RESULTS

Monocultures and bacteria-yeast cocultures of B. lactis HN019 and 10 different yeast strains belonging to different species in skim milk media were fermented at 37°C. The presence of yeasts enhanced the growth rate and metabolic activities of B. lactis HN019, which might be attributed to their antioxidative properties. The viability of yeasts, when cocultured with bifidobacteria, was either unaffected or suppressed, depending on the strain. When the B. lactis HN019 monoculture and cocultures with Saccharomyces cerevisiae EC-1118, Pichia kluyveri FrootZen and Kluyveromyces lactis KL71 were fermented to pH 4·7, there were no significant differences in their organic acid composition. On the other hand, cocultures produced significantly higher quantities of alcohols and/or esters than the monoculture. Coculturing B. lactis HN019 with yeasts did not improve the viability of the probiotic during storage at 10°C for 8 weeks, as the bifidobacteria itself demonstrated satisfactory survival in the fermented SMM.

CONCLUSIONS

Coculturing B. lactis HN019 with yeasts accelerated the growth of the bifidobacteria and increased the production aroma-active volatile metabolites.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study demonstrates the potential of utilizing specific yeast species as starter or adjunct cultures to simultaneously improve the growth of fastidious bifidobacteria and modulate the organoleptic properties of fermented food products.