The Role of Yeasts and Lactic Acid Bacteria on the Metabolism of Organic Acids during Winemaking

Effect of Commercial Yeast Starter Cultures on Cabernet Sauvignon Wine Aroma Compounds and Microbiota

Commercial Saccharomyces cerevisiae plays an important role in the traditional winemaking industry. In this study, the correlation of microbial community and aroma compound in the process of alcohol fermentation of Cabernet Sauvignon by four different commercial starters was investigated. The results showed that there was no significant difference in the fermentation parameters of the four starters, but there were differences in microbial diversity among the different starters. The wine samples fermented by CEC01 had higher microbial abundance. GC-MS detected a total of 58 aromatic compounds from the fermentation process by the experimental yeasts. There were 25 compounds in the F6d variant, which was higher than in other samples. The PCA score plot showed that 796 and F15 yeast-fermented wines had similar aromatic characteristic compositions. According to partial least squares (PLS, VIP > 1.0) analysis and Spearman’s correlation analysis, 11, 8, 8 and 10 microbial genera were identified as core microorganisms in the fermentation of 796, CEC01, CECA and F15 starter, respectively. Among them, Leuconostoc, Lactobacillus, Sphingomonas and Pseudomonas played an important role in the formation of aroma compounds such as Ethyl caprylate, Ethyl caprate and Ethyl-9-decenoate. These results can help us to have a better understanding of the effects of microorganisms on wine aroma and provide a theoretical basis for improving the flavor quality of Cabernet Sauvignon wine.

Evaluation of Malolactic Starters in White and Rosé Winemaking of Moschofilero Wines

The aim of the present study was to induce malolactic fermentation (MLF) after alcoholic fermentation (AF) of must of the Moschofilero cultivar, the only ‘gris’ native grape variety that is cultivated in Greece. For this purpose, Oenococcus oeni strains Viniflora® CH16, Viniflora® Oenos and Viniflora® CiNe were inoculated after the completion of AF driven by the Saccharomyces cerevisiae strain UCLM S325. Growth of the aforementioned starter cultures was assessed during fermentation by classical microbiological techniques, and verification of their dominance was performed by (GTG)5 fingerprinting. Assessment of standard enological parameters and colorimetric analysis were performed by established approaches. Identification and quantification of organic acids, ethanol and glycerol was performed by high performance liquid chromatography (HPLC), while the solid-phase microextraction method (SPME), coupled with gas chromatography/mass spectrometry (GC/MS), was employed for the identification and quantification of volatile compounds. Finally, sensory analysis took place according to ISO 13299:2016. The suitability of the starter cultures employed to drive AF and MLF was exhibited; AF and MLF of the white and rosé wines were completed after 15 days. Upon completion of AF, substantial differences were observed in the chemical characteristics of the white and rosé wines, which were also reflected in the balance descriptor. MLF also resulted in significant changes. In all cases total acidity decreased and volatile acidity and pH value increased, while the vanilla and butter descriptors increased. Interestingly, the color intensity of the rosé wines also increased. A series of strain-dependent changes in the chemical composition and sensory analysis of both white and rosé wines was also observed.

Starmerella bacillaris Strains Used in Sequential Alcoholic Fermentation with Saccharomyces cerevisiae Improves Protein Stability in White Wines

Haze can appear in white wines as a result of the denaturation and subsequent aggregation of grape pathogenesis-related (PR) proteins. Yeast cell-wall polysaccharides, particularly mannoproteins, represent a promising strategy to reduce the incidence of this phenomenon. The aim of this study was to evaluate the effects of 13 Starmerella bacillaris strains, in sequential fermentation with Saccharomyces cerevisiae, on wine protein stability of three white wines (Sauvignon blanc, Pinot grigio, and Manzoni bianco). The resulting wines were characterized in terms of their chemical composition, content of PR proteins and polysaccharides, and heat stability. In addition, the mannoprotein fraction was purified from six wines, five produced with S. bacillaris and one with S. cerevisiae EC1118 used as control. Generally, wines produced with S. bacillaris strains were more heat-stable, despite generally containing higher amounts of PR proteins. The increased heat stability of Starmerella wines was attributed to the stabilizing effect resulting from their higher concentrations of both total polysaccharides and mannoprotein fractions. In particular, for the most heat unstable wine (Manzoni bianco), the low MW mannoprotein fraction resulted to be the most involved in wine stability. The ability to produce wines with different heat stability was demonstrated to be strain-dependent and was more evident in the most unstable wines. By reducing fining waste, the use of S. bacillaris as an enological starter can be proposed as a new tool to manage wine protein stability for a more sustainable winemaking.

Functional Verification of the Citrate Transporter Gene in a Wine Lactic Acid Bacterium, Lactiplantibacillus plantarum

Organic acid metabolism by lactic acid bacteria plays a significant role in improving wine quality. During this process, the uptake of extracellular organic acids by the transporters is the first rate-limiting step. However, up to now, there is very little published research on the functional verification of organic acid transporter genes in wine lactic acid bacteria. In this study, a predicted citrate transporter gene JKL54_04345 (citP) by protein homology analysis was knocked out using a CRISPR/Cas9-based gene-editing system, and then complemented using the modified pMG36e vectors in a major wine lactic acid bacterium, Lactiplantibacillus plantarum XJ25, to verify its function in citrate metabolism for the first time. The results showed that the gene knockout mutant XJ25-ΔcitP lost the ability to utilize citric acid, while the gene complement mutant XJ25-ΔcitP-pMG36ek11-citP fully recovered the ability of citric acid utilization. Meanwhile, citP knockout and complement barely affected the utilization of l-malic acid. These indicated that citP in L. plantarum functioned as a citrate transporter and was the only gene responsible for citrate transporter. In addition, two modified plasmid vectors used for gene supplement in L. plantarum showed distinct transcription efficiency. The transcription efficiency of citP in XJ25-ΔcitP-pMG36ek11-citP mutant was 4.01 times higher than that in XJ25-ΔcitP-pMG36ek-citP mutant, and the utilization rate of citric acid in the former was 3.95 times higher than that in the latter, indicating that pMG36ek11 can be used as a high-level expression vector in lactic acid bacteria.

The Use of γ-Aminobutyric Acid-Producing Saccharomyces cerevisiae SC125 for Functional Fermented Beverage Production from Apple Juice

The development of functional fermented beverages enriched with γ-aminobutyric acid (GABA) has been pursued because of the health benefits of GABA; however, few studies have described GABA production by yeast. Therefore, this study aimed to produce fermented apple beverages enriched with GABA produced by Saccharomyces cerevisiae SC125. Golden Delicious apples were fermented by S. cerevisiae SC125 to produce a novel functional beverage; commercial yeast was used as the control. The GABA, organic acid, and volatile compound content during the fermentation process was investigated by high-performance liquid chromatography and headspace solid-phase microextraction/gas chromatography-mass spectrometry. A yield of 898.35 ± 10.10 mg/L GABA was achieved by the efficient bioconversion of L-monosodium glutamate. Notably, the S. cerevisiae SC125-fermented beverage produced several unique volatile compounds, such as esters, alcohols, 6-decenoic acid, and 3-hydroxy−2-butanone, and showed significantly enhanced contents of organic acids, including malic acids, citric acid, and quinic acid. Sensory analysis demonstrated that the S. cerevisiae SC125-fermented apple beverage had improved aroma, flavor, and overall acceptability. In conclusion, a fermented functional apple beverage containing GABA was efficiently produced using S. cerevisiae SC125.

Application of Chitosan-Lignosulfonate Composite Coating Film in Grape Preservation and Study on the Difference in Metabolites in Fruit Wine

In order to solve the global problem of fruit rotting due to microbial infection and water loss after harvest, which leads to a large amount of food waste, this experiment uses degradable biological composite coating to prolong the preservation period of grapes. Chitosan (CH) and Lignosulfonate (LS) were used as Bio-based film materials, CH films, 1% CH/LS films and 2% CH/LS biomass composite films were synthesized by the classical casting method and applied to grape preservation packaging. Its preservation effect was tested by grape spoilage rate, water loss rate, hardness, soluble solids, titratable acid, and compared with plastic packaging material PE film. At the same time, 1H NMR technology combined with pattern recognition analysis (PCA) and partial least squares discriminant analysis (PLS-DA) was used to determine the nuclear magnetic resonance (NMR) of Cabernet Sauvignon, Chardonnay and Italian Riesling wines from the eastern foothills of Helan Mountain to explore the differences in metabolites of wine. The results of preservation showed that the grapes quality of CH films and 2% CH/LS coating package is better than the control group, the decay rates decreased from 37.71% to 21.63% and 18.36%, respectively, the hardness increased from 6.83 to 10.4 and 12.78 and the soluble solids increased from 2.1 in the control group to 3.0 and 3.2. In terms of wine metabolites, there are similar types of metabolites between cabernet Sauvignon dry red wine and Chardonnay and Italian Riesling dry white wine, but there are significant differences in content. The study found that 2% CH/LS coating package could not only reduce the spoilage rate of grapes, inhibit the consumption of soluble solids and titratable acids, but also effectively extend the shelf life of grapes by 6 days.

Technological Improvements on FML in the Chianti Classico Wine Production: Co-Inoculation or Sequential Inoculation?

Winemaking variables and techniques are known to affect the composition of wines. To obtain a rapid and safe fermentation course, with a reduced risk of proliferation of unwanted microbial species, frequent recourse is made to the use of selected microorganisms, which can greatly simplify the complex management of the fermentation process. In particular, selected strains of lactic acid bacteria are used, which are much more sensitive than yeasts to the operating conditions of the medium. In this regard, the overall aim of this research was to verify whether the early inoculation of homolactic acid bacteria for hexoses (Lactobacillus plantarum) carried out after 24 h, compared with that of saccharomycetes operating alcoholic fermentation, could be advantageous compared with a traditional innoculation with a different heterolactic bacterial strain for hexoses (Oenococcus oeni) operated at the end of alcoholic fermentation. The grape variety chosen was Sangiovese, the protagonist of Tuscan oenology. The evaluation focused on different aspects such as the management of winery operations, and the quality and longevity of the product; was carried out in all phases of winemaking; and analysed both from a chemical and sensory point of view.

New Isolated Autochthonous Strains of S. cerevisiae for Fermentation of Two Grape Varieties Grown in Poland

Many commercial strains of the Saccharomyces cerevisiae species are used around the world in the wine industry, while the use of native yeast strains is highly recommended for their role in shaping specific, terroir-associated wine characteristics. In recent years, in Poland, an increase in the number of registered vineyards has been observed, and Polish wines are becoming more recognizable among consumers. In the fermentation process, apart from ethyl alcohol, numerous microbial metabolites are formed. These compounds shape the wine bouquet or become precursors for the creation of new products that affect the sensory characteristics and quality of the wine. The aim of this work was to study the effect of the grapevine varieties and newly isolated native S. cerevisiae yeast strains on the content of selected wine fermentation metabolites. Two vine varieties—Regent and Seyval blanc were used. A total of 16 different yeast strains of the S. cerevisiae species were used for fermentation: nine newly isolated from vine fruit and seven commercial cultures. The obtained wines differed in terms of the content of analyzed oenological characteristics and the differences depended both on the raw material (vine variety) as well as the source of isolation and origin of the yeast strain used (commercial vs. native). Generally, red wines characterized a higher content of tested analytes than white wines, regardless of the yeast strain used. The red wines are produced with the use of native yeast strains characterized by higher content of amyl alcohols and esters.

Enhancing Ethanol Tolerance via the Mutational Breeding of Pichia terricola H5 to Improve the Flavor Profiles of Wine

Although using non-Saccharomyces yeasts during alcoholic fermentation can improve the wine aroma, most of them are not ethanol tolerant; therefore, in 2017, this study screened 85 non-Saccharomyces yeasts isolated and identified from 24 vineyards in seven Chinese wine-producing regions, obtaining Pichia terricola strain H5, which displayed 8% ethanol tolerance. Strain H5 was subjected to ultraviolet (UV) irradiation and diethyl sulfate (DES) mutagenesis treatment to obtain mutant strains with different fermentation characteristics from the parental H5. Compared with strain H5, the UV-irradiated strains, UV5 and UV8, showed significantly higher ethanol tolerance and fermentation capacity. Modified aroma profiles were also evident in the fermentation samples exposed to the mutants. Increased ethyl caprate, ethyl caprylate, and ethyl dodecanoate content were apparent in the UV5 samples, providing the wine with a distinctly floral, fruity, and spicy profile. Fermentation with strain UV8 produced a high ethyl acetate concentration, causing the wine to present a highly unpleasant odor. To a certain extent, UV irradiation improved the ethanol tolerance and fermentation ability of strain H5, changing the wine aroma profile. This study provides a theoretical basis for the industrial application of non-Saccharomyces yeasts that can improve wine flavor.

Oenological Characterization of Native Hanseniaspora uvarum Strains

The utilization of native yeast strains associated with a distinct terroir for autochthonous grape types represents a novel trend in winemaking, contributing to the production of unique wines with regional character. Hence, this study aimed to isolate native strains of the yeast H. uvarum from the surface of various fruits and to characterize its fermentation capability in Prokupac grape must. Out of 31 yeasts, 8 isolates were identified as H. uvarum. The isolates were able to grow at low (4 °C) temperatures, SO2 concentrations up to 300 ppm and ethanol concentrations up to 5%. Additionally, they provided a good profile of organic acids during the microvinification of sterile grape must. Although the content of acetic acid (0.54–0.63 g/L) was relatively high, the sniffing test proved that the yeast isolates developed a pleasant aroma characterized as fruity. All H. uvarum isolates produced twice the concentration of glycerol compared to commercial wine yeast Saccharomyces cerevisiae, contributing to the fullness and sweetness of the wine. The results for pure and sequential fermentation protocols confirmed that the selected S-2 isolate has good oenological characteristics, the capability to reduce the ethanol content (up to 1% v/v) and a potential to give a distinctive note to Prokupac-grape wines.

Use of Non-Saccharomyces Yeast Co-Fermentation with Saccharomyces cerevisiae to Improve the Polyphenol and Volatile Aroma Compound Contents in Nanfeng Tangerine Wines

This study attempted to improve the polyphenol and volatile aroma compound contents in Nanfeng tangerine wines using non-Saccharomyces yeast and Saccharomyces cerevisiae. The effects of fermentation with pure cultures of Candida ethanolica, Hanseniaspora guilliermondii and Hanseniaspora thailandica, as well as in sequential and mixed inoculations (1:1 or 1:100 ratio) with S. cerevisiae in Nanfeng tangerine wines were evaluated. C. ethanolica was found to produce the most polyphenols (138.78 mg/L) during pure fermentation, while H. guilliermondii produced the most volatile aroma compounds (442.34 mg/L). The polyphenol content produced during sequential fermentation with S. cerevisiae and H. guilliermondii (140.24 mg/L) or C. ethanolica (140.21 mg/L) was significantly higher than other co-fermentations. Meanwhile, the volatile aroma compounds were found to be more abundant in S. cerevisiae/H. guilliermondii mixed fermentation (1:1 ratio) (588.35 mg/L) or S. cerevisiae/H. guilliermondii sequential fermentation (549.31 mg/L). Thus, S. cerevisiae/H. guilliermondii sequential fermentation could considerably boost the polyphenol and volatile aroma component contents in Nanfeng tangerine wines. The findings of this study can be used to drive strategies to increase the polyphenol content and sensory quality of tangerine wines and provide a reference for selecting the co-fermentation styles for non-Saccharomyces yeast and S. cerevisiae in fruit wine fermentation.

Effects of sequential inoculation of Lachancea thermotolerans and Oenococcus oeni on chemical composition of spent coffee grounds hydrolysates

Spent coffee grounds (SCG) disposal is an environmental problem. These residues from coffee brewing and instant coffee production have potential to produce novel alcoholic beverages. SCG valorization through sequential alcoholic and malolactic fermentation was investigated using a yeast, Lachancea thermotolerans Concerto and a lactic acid bacterium (LAB), Oenococcus oeni Lalvin 31 in this study. Our results showed that sequential inoculation prevented early death of yeast confronted when simultaneous inoculation was adopted, allowing for growth and persistence of both yeast and LAB till the end of fermentation. Adequate ethanol production (4.91 ± 0.13 %, v/v) with low residual sugar content was also attained. In addition, relatively lower levels of acetic, lactic, and succinic acids were produced by sequential inoculation than that of simultaneous inoculation. Furthermore, SCG hydrolysates fermented via sequential inoculation had the widest variety of volatiles (e.g. esters and ketones). Overall, our results indicated that sequential inoculation of L. thermotolerans and O. oeni in SCG hydrolysates might be a way to develop novel beverages with pleasant flavor profiles.

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L. thermotolerans and O. oeni were used in spent coffee grounds (SCG) hydrolysates fermentation.

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Sequential inoculation of O. oeni prevented early yeast cell death.

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Sequential inoculation produced desired content of ethanol.

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Sequential inoculation generated and/or retained the widest variety of volatiles.

Apple Pomace as a Sustainable Substrate in Sourdough Fermentation

Innovations range from food production, land use, and emissions all the way to improved diets and waste management. Global apple production has amounted to over 87 million tons/year, while 18% are processed, resulting in 20-35% (apple fruit fresh weight) apple pomace (AP). Using modern AP management, integrated knowledge in innovative fermentation demonstrates opportunities for reducing environmental pollution and integration into a circular economy. With this association in view, integrating AP flour during sourdough fermentation increases the nutritional value, highlighting a new approach that could guide innovative fermented foods. In this study, the wheat flour (WF) and AP flour were mixed at different ratios, hydrated with water (1:1 w/v), and fermented using a selective culture of Fructilactobacillus florum DSM 22689 and baker's yeast (single and co-culture). Sourdough fermentation was monitored and analyzed for 72 h. Results suggested that AP may be an important source of organic acids and fermentable sugars that increase nutritional sourdough value. AP flour addition in WF had a positive effect, especially in fermentations with 95% WF and 5% AP, mainly in co-culture fermentation.

An Integrative View of the Role of Lachancea thermotolerans in Wine Technology

The interest in Lachancea thermotolerans, a yeast species with unusual characteristics, has notably increased in all ecological, evolutionary, and industrial aspects. One of the key characteristics of L. thermotolerans is the production of high quantities of lactic acid compared to other yeast species. Its evolution has mainly been driven by the influence of the environment and domestication, allowing several metabolic traits to arise. The molecular regulation of the fermentative process in L. thermotolerans shows interesting routes that play a complementary or protective role against fermentative stresses. One route that is activated under this condition is involved in the production of lactic acid, presenting a complete system for its production, showing the involvement of several enzymes and transporters. In winemaking, the use of L. thermotolerans is nowadays mostly focused in early–medium-maturity grape varieties, in which over-ripening can produce wines lacking acidity and with high concentrations of ethanol. Recent studies have reported new positive influences on quality apart from lactic acid acidification, such as improvements in color, glutathione production, aroma, malic acid, polysaccharides, or specific enzymatic activities that constitute interesting new criteria for selecting better strains. This positive influence on winemaking has increased the availability of commercial strains during recent years, allowing comparisons among some of those products. Initially, the management of L. thermotolerans was thought to be combined with Saccaharomyces cerevisiae to properly end alcoholic fermentation, but new studies are innovating and reporting combinations with other key enological microorganisms such as Schizosaccharomyces pombe, Oenocous oeni, Lactiplantibacillus plantarum, or other non-Saccharomyces.

Effect of Different Winemaking Conditions on Organic Acids Compounds of White Wines

Organic acids represent naturally occurring compounds that are found in many types of food and beverages, with important functions in defining products' final quality. Their proportions in wine are dependent on grape composition and winemaking conditions (temperature, pH levels, oxygen, and carbon dioxide concentration). Therefore, this article studied the influence of different fermentation conditions (200 hL tanks vs. 50 L glass demijohns) and various yeasts on the evolution of the main organic acids during alcoholic fermentation of "Aligoté" wines. The fermentation lasted 22 days and samples were collected daily. Laboratory analyses were quantified according to the International Organization of Vine and Wine recommendations. High-performance liquid chromatography for the identification and quantification of organic acids was used. The data showed the important effect of winemaking conditions on sugar consumption, density or acidity values, and sensory characteristics. Significant differences in organic acid concentrations (especially for tartaric acid) were obtained for all variants, depending on the fermentation conditions, inoculated yeast and the sampling moment. The quantities of most of the identified organic acids were generally significantly increased when glass vessels were used, compared to those fermented in tanks. Most organic acids concentrations were favored by lower pH and showed higher values at lower temperatures.

The changes of physicochemical properties, antioxidants, organic, and key volatile compounds associated with the flavor of peach (Prunus cerasus L. Batsch) vinegar during the fermentation process

Peach is a delicious food preferred by consumers and widely used in the manufacture of peach juice, peach juice concentrate, peach jam, dried fruit, puree, etc. Alternatively, peach can be used in the production of vinegar. In this study, peach vinegar was produced as an alternative to other industrial products produced from peach. In this study, it was determined that the TPC content and ORAC value of peach vinegar were higher than those of peach juice and peach wine. In addition, the major contributor compounds to the aroma profiles of the samples were the γ-decalactone, linalool, and geraniol compounds for the peach juice; the ethanol, ɣ-decalactone, phenylacetic acid, acetic acid, 2-phenylethanol, ethyl decanoate, the linalool, and the decanoic-acid for the peach wine; and the ɣ-decalactone, phenylacetic acid, acetic-acid, phenethyl-acetate, and isovaleric acid for the peach vinegar. It is thought that the results of this study will pave the way for the widespread production of vinegar from peach, which has positive effects on health, is rich in volatile aroma components, and has a high potential to be preferred. Furthermore, this study is the first detailed study so far on peach vinegar. PRACTICAL APPLICATIONS: In this study, it was aimed to produce vinegar as a new and alternative foodstuff product from peach fruit which was normally processed as fresh or/ dried fruit, fruit juice, puree, and canned fruit by the industry. An alternative idea was created for the use of peach fruit, which has a short shelf life. In the study, the antioxidant capacity, organic compounds, and volatile compounds associated with aroma profile of peach vinegar during the fermentation process were determined. Moreover, the changes of these compounds were monitored during the fermentation process. The results of the study are a guide for the usability of peach fruit as a raw material in the production of peach vinegar, which has potentially positive effects on health, is rich in volatile aroma components, and has a high potential to be preferred. Furthermore, this study is the first detailed study on peach vinegar.

Investigation of the possibility of fermentation of red grape juice and rice flour by Lactobacillus plantarum and Lactobacillus casei

The aim of the current study was to evaluate the possibility of the bacterial growth and substrate metabolism during the fermentation of red grape juice and the mixture of red grape juice and rice flour solution using Lactobacillus plantarum and Lactobacillus casei. In recent years, cereal-based beverages have been used as functional compounds such as antioxidants, dietary fiber, minerals, probiotics, and vitamins in diets. In this research, fermentation of red grape juice (media 1) and 1:1 mixture of red grape juice and rice flour solution (media 2) by two strains of gram positive and homofermentative lactic acid bacteria: L. plantarum and L. casei (individually and mixed) was examined. Fermentation was carried out at 37°C for 48 hr. Microbial population, pH, acidity, sugar, and organic acid metabolism were measured during the fermentation period. Data showed that in media 2 fermented with mixed culture of both L. plantarum and L. casei, acidity and microbial population increased sharply at the initial stages of fermentation, and the most percentage of lactic acid production occurred. Red grape juice fermented with mixture of L. plantarum and L. casei showed the most sugar consumption (p < .05). Results indicated that the use of the mixture of red grape juice and rice flour solution can be a proper substrate for producing lactic acid.

Potential for Lager Beer Production from Saccharomyces cerevisiae Strains Isolated from the Vineyard Environment

Saccharomyces pastorianus, genetic hybrids of Saccharomyces cerevisiae and the Saccharomyces eubayanus, is one of the most widely used lager yeasts in the brewing industry. In recent years, new strategies have been adopted and new lines of research have been outlined to create and expand the pool of lager brewing starters. The vineyard microbiome has received significant attention in the past few years due to many opportunities in terms of biotechnological applications in the winemaking processes. However, the characterization of S. cerevisiae strains isolated from winery environments as an approach to selecting starters for beer production has not been fully investigated, and little is currently available. Four wild cryotolerant S. cerevisiae strains isolated from vineyard environments were evaluated as potential starters for lager beer production at laboratory scale using a model beer wort (MBW). In all tests, the industrial lager brewing S. pastorianus Weihenstephan 34/70 was used as a reference strain. The results obtained, although preliminary, showed some good properties of these strains, such as antioxidant activity, flocculation capacity, efficient fermentation at 15 °C and low diacetyl production. Further studies will be carried out using these S. cerevisiae strains as starters for lager beer production on a pilot scale in order to verify the chemical and sensory characteristics of the beers produced.

Optimization of Electrotransformation Parameters and Engineered Promoters for Lactobacillus plantarum from Wine

Robust and versatile promoters for Lactobacillus plantarum found in wine are necessary gene expression tools for genetic research involving wine stress. We optimized the electrotransformation parameters for L. plantarum XJ25 isolated from wine and engineered five promoters based on the promoter P₂₃; these promoters showed significantly different transcriptional activities under nonstress conditions. The activities of these promoters in vivo and the resulting growth burden to the host strain under different wine stresses were also evaluated. A range of colors (from white to dark pink) of the developing colonies with the plasmid pNZ8148 carrying an X-mCherry expression cassette, namely, P₂₃-mCherry, trcP₂₃-mCherry, P_OL1-mCherry, P_OL2-mCherry, P_OL3-mCherry, or P_OL4-mCherry, were analyzed. The applicability of the optimized electrotransformation parameters and synthetic promoters with different activities were also verified in several L. plantarum strains. Therefore, the optimized electrotransformation and these characterized promoters were determined to be suitable for applications in wine research in the future.

The Combined Use of Lachancea thermotolerans and Lactiplantibacillus plantarum (former Lactobacillus plantarum) in Wine Technology

Most commercialized red wines are produced through alcoholic fermentation performed by yeasts of the Saccharomyces genus, and a second fermentation performed by lactic bacteria of the Oenococus oeni species once the first is completely finished. However, the classical process can suffer complications, of which the risks can increase in grape juices with high contents of sugar and pH. Due to climate change, these situations are becoming more common in the winemaking industry. The main risks in those scenarios are alcoholic-fermentation stops or sluggish and undesirable bacteria development while alcoholic fermentation is not finished yet and wine still contains residual sugars. The study propose a novel alternative that offers a solution or reduces the risk of those scenarios while increasing acidity, which is another serious problem of warm viticulture regions. The alternative consists of the combined use of Lachancea thermotolerans to reduce the pH of musts that suffer from a lack of acidity, Lactiplantibacillus plantarum (formerly Lactobacillus plantarum) to achieve malic acid stability during the first stages of alcoholic fermentation, and Saccharomyces bayanus to complete the alcoholic fermentation in difficult wines of high potential alcohol degree of over 15% (v/v). The new proposed biotechnology produced wines with higher final concentrations in lactic acid, glycerol, color intensity, ethyl lactate and 2-phenyl ethyl acetate in 2.39 g/L, 0.52 g/L, 21%, 48% and 37% respectively than the classical methodology where Saccharomyces genus performs alcoholic fermentation and later Oenococus oeni performs malolactic fermentation. Additionally, the new alternative produced wines with lower concentration in ethanol, pH, acetic acid, ethyl acetate, diacetyl and 1-propanol in 0.37% (v/v), 0.26, 0.08 g/L, 22%, 69% and 28% respectively than the classic method.

Fungal diversity and occurrence of mycotoxin producing fungi in tropical vineyards

Grapevine cultivars are distributed worldwide, nevertheless the fermentation of its grape berries renders distinct wine products that are highly associated to the local fungal community. Despite the symbiotic association between wine and the fungal metabolism, impacting both the terroir and mycotoxin production, few studies have explored the vineyard ecosystem fungal community using both molecular marker sequencing and mycotoxin production assessment. In this study, we investigated the fungal community of three grapevine cultivars (Vitis vinifera L.) in two tropical vineyards. Illumina MiSeq sequencing was performed on two biocompartments: grape berries (GB) and grapevine soil (GS); yielding a total of 578,495 fungal internal transcribed spacer 1 reads, which were used for taxonomic classification. GB and GS fungal communities were mainly constituted by Ascomycota phylum. GS harbors a significant richer and more diverse fungal community than GB. Among GB samples, Syrah grape berries exclusively shared fungal community included wine-associated yeasts (e.g. Saccharomycopsis vini) that may play key roles in wine terroir. Mycotoxin production assessment revealed the high potential of Aspergillus section Flavi and Penicillium section Citrina isolates to produce aflatoxin B1-B2 and citrinin, respectively. This is the first study to employ next-generation sequencing to investigate vineyard associated fungal community in Brazil. Our findings provide valuable insights on the available tools for fungal ecology assessment applied to food products emphasizing the coexistence between classical and molecular tools.

Regulatory Mechanisms of L-Lactic Acid and Taste Substances in Chinese Acid Rice Soup (Rice-Acid) Fermented With a Lacticaseibacillus paracasei and Kluyveromyces marxianus

Rice-acid has abundant taste substances and health protection function due to the various bioactive compounds it contains, including organic acids. L-lactic acid is the most abundant organic acid in rice-acid, but the regulatory mechanisms of L-lactic acid accumulation in rice-acid are obscure. In this study, we analyzed the dynamic changes in organic acids and taste substances in rice-acid in various fermentation phases and different inoculation methods. We identified the key genes involved in taste substance biosynthesis by RNA-Seq analysis and compared the data of four experimental groups. We found that the interaction of the differences in key functional genes (L-lactate dehydrogenase and D-lactate dehydrogenase) and key metabolism pathways (glycolysis, pyruvate metabolism, TCA cycle, amino acid biosynthesis, and metabolism) might interpret the accumulation of L-lactic acid, other organic acids, and taste substances in rice-acid fermented with Lacticaseibacillus paracasei. The experimental data provided the basis for exploring regulatory mechanisms of taste substance accumulation in rice-acid.

Winemaking Characteristics of Red-Fleshed Dragon Fruit from Three Locations in Guizhou Province, China

The aim of this study was to identify the locations and harvest months in Guizhou province, China, producing the most suitable red dragon fruit (Hylocereus polyrhizus) for winemaking. Fruit from Guanling, Luodian and Zhenfeng counties was harvested separately from successive fruit cycles in August, September and October, respectively. The key traits measured were fruit weight, pulp yield, soluble solids content, and titratable acid. Wine characteristics measured were alcohol content, total carbohydrates, titratable acidity, volatile acidity, and betacyanin content. The overall suitability of fruit from each location for winemaking was evaluated using a multi-factor, unweighted, scorecard. On that basis, fruit from Guanling county harvested in August was the most suitable. Fruit from Luodian, and Zhenfeng was most suitable when harvested in August and September, and September, respectively. These results provide a preliminary guide for the sourcing of red dragon fruit from Guizhou for wine production.

The Use of Yeast Mixed Cultures for Deacidification and Improvement of the Composition of Cold Climate Grape Wines

Interest in the use of non-Saccharomyces yeast in mixed cultures is increasing due to the perceived improvement in the quality and complexity of the resulting wines. The aim of the study was to determine the ability of monocultures and mixed yeast cultures for deacidification and improvement of the composition of cold climate grape wines. Fermentation of grape musts with increased total acidity was carried out with the use of monocultures of Saccharomyces cerevisiae MH020215 (Sc), Zygosaccharomyces bailii 749 (Zb) and Metschnikowia pulcherrima MG970690 (Mp), and their mixed cultures, inoculated simultaneously and sequentially. Oenological parameters, organic acids and volatile compounds profiles of obtained wines were characterized. The fermentation kinetics and analytical profiles of the obtained wines showed that the use of mixed yeast cultures contributed to the reduction of volatile acidity and acetic acid content in the wines, as well as obtaining a favorable aromatic profile of the wines. The dominant higher alcohols in all wines were 2-methyl-1-propanol, 3-methyl-1-butanol and 2-methyl-1-butanol. Significantly higher amounts of the first two compounds were found in wines obtained with M. pulcherrima MG070690, both in monoculture and in mixed cultures. The monocultures of M. pulcherrima MG070690 (Mp) compared with Z. bailli 749 (Zb) synthesized higher levels of esters in wines, including ethyl acetate, ethyl propionate, isobutyl acetate, ethyl pyroracemate and isoamyl acetate.

Influence of L. thermotolerans and S. cerevisiae Commercial Yeast Sequential Inoculation on Aroma Composition of Red Wines (Cv Trnjak, Babic, Blatina and Frankovka)

Even though Saccharomyces cerevisiae starter cultures are still largely used nowadays, the non-Saccharomyces contribution is re-evaluated, showing positive enological characteristics. Among them, Lachancea thermotolerans is one of the key yeast species that are desired for their contribution to wine sensory characteristics. The main goal of this work was to explore the impact of L. thermotolerans commercial yeast strain used in sequential inoculation with S. cerevisiae commercial yeast on the main enological parameters and volatile aroma profile of Trnjak, Babić, Blatina, and Frankovka red wines and compare it with wines produced by the use of S. cerevisiae commercial yeast strain. In all sequential fermented wines, lactic acid concentrations were significantly higher, ranging from 0.20 mg/L in Trnjak up to 0.92 mg/L in Frankovka wines, while reducing alcohol levels from 0.1% v/v in Trnjak up to 0.9% v/v in Frankovka wines. Among volatile compounds, a significant increase of ethyl lactate and isobutyl acetate, geraniol, and geranyl acetate was detected in all wines made by use of L. thermotolerans. In Babić wines, the strongest influence of sequential fermentation was connected with higher total terpenes and total ester concentrations, while Trnjak sequentially fermented wines stood up with higher total aldehyde, volatile phenol, and total lactone concentrations. Control wines, regardless of variety, stood up with higher concentrations of total higher alcohols, especially isoamyl alcohol. The present work contributed to a better understanding of the fermentation possibilities of selected non-Saccharomyces strains in the overall red wine quality modeling.