Linking wine lactic acid bacteria diversity with wine aroma and flavour

Effect of Lactic Acid Fermentation on Volatile Compounds and Sensory Characteristics of Mango (Mangifera indica) Juices

Fermentation is a sustainable bio-preservation technique that can improve the organoleptic quality of fruit juices. Mango juices were fermented by monoculture strains of Lactiplantibacillus plantarum subsp. plantarum (MLP), Lacticaseibacillus rhamnosus (MLR), Lacticaseibacillus casei (MLC), Levilactobacillus brevis (MLB), and Pediococcus pentosaceus (MPP). Volatile compounds were sorbed using headspace solid phase microextraction, separated, and identified with gas chromatography-mass spectrometry. Forty-four (44) volatile compounds were identified. The control, MPP, and MLB had higher amounts of ethyl acetate, ethyl butyrate, 2-hexenal, 2,6-nonadienal, 2,2-dimethylpropanal, β-selinene, γ-gurjunene, α-copaene, and δ-cadinene, while MLC, MLP, and MLR had higher amounts of 2,3-butanedione and a cyclic hydrocarbon derivate. Consumers (n = 80) assessed their overall liking and characterized sensory attributes (appearance, color, aroma, flavor, consistency, acidity, and sweetness) using check-all-that-apply, and penalty analysis (just-about-right). Overall liking was associated with ‘mango color’, ‘pulp’, ‘mango aroma’, ‘sweet’, ‘natural taste’, and ‘mango flavor’ that described the control, MLB, MLC and MPP. Juices MLR and MLP were described as ‘bitter’, ‘sour’, ‘aftertaste’, and ‘off-flavor’. Multivariate analysis revealed relationships between the volatile compounds, mango juices fermented by different lactic acid bacteria, and sensory characteristics. Thus, the type of lactic acid bacteria strains determined the volatile and sensory profile of mango juices.

Advantages and disadvantages of non-starter lactic acid bacteria from traditional fermented foods: Potential use as starters or probiotics

Traditional fermented foods are a significant source of starter and/or non-starter lactic acid bacteria (nsLAB). Moreover, these microorganisms are also known for their role as probiotics. The potential of nsLAB is huge; however, there are still challenges to be overcome with respect to characterization and application. In the present review, the most important steps that autochthonous lactic acid bacteria isolated from fermented foods need to overcome, to qualify as novel starter cultures, or as probiotics, in food technology and biotechnology, are considered. These different characterization steps include precise identification, detection of health-promoting properties, and safety evaluation. Each of these features is strain specific and needs to be accurately determined. This review highlights the advantages and disadvantages of nsLAB, isolated from traditional fermented foods, discussing safety aspects and sensory impact.

Molecular tools for the analysis of the microbiota involved in malolactic fermentation: from microbial diversity to selection of lactic acid bacteria of enological interest

Winemaking is a complex process involving two successive fermentations: alcoholic fermentation, by yeasts, and malolactic fermentation (MLF), by lactic acid bacteria (LAB). During MLF, LAB can contribute positively to wine flavor through decarboxylation of malic acid with acidity reduction and other numerous enzymatic reactions. However, some microorganisms can have a negative impact on the quality of the wine through processes such as biogenic amine production. For these reasons, monitoring the bacterial community profiles during MLF can predict and control the quality of the final product. In addition, the selection of LAB from a wine-producing area is necessary for the formulation of native malolactic starter cultures well adapted to local winemaking practices and able to enhance the regional wine typicality. In this sense, molecular biology techniques are fundamental tools to decipher the native microbiome involved in MLF and to select bacterial strains with potential to function as starter cultures, given their enological and technological characteristics. In this context, this work reviews the different molecular tools (both culture-dependent and -independent) that can be applied to the study of MLF, either in bacterial isolates or in the microbial community of wine, and of its dynamics during the process.

Wine aroma profile modification by Oenococcus oeni strains from Rioja Alavesa region: selection of potential malolactic starters

Previously six selected Oenococcus oeni strains (P2A, P3A, P3G, P5A, P5C and P7B) have been submitted to further characterization in order to clarify their potential as malolactic starters. Laboratory scale vinifications gave an insight of the most vigorous strains: both P2A and P3A strains were able to conclude malolactic fermentation (MLF) in less than 15 days. The remaining strains showed good viability and were able to successfully finish MLF in the established analysis time, except for the strain P5A, which viability was totally lost after inoculation. Also spontaneous fermentation was not initiated. None of the strains was biogenic amine producer; however, P5C strain significantly increased the concentration of volatile phenol-precursor hydroxycinnamic acids after MLF. Regarding the evolution of wine aromatic compounds, main changes were detected for both ethyl and acetate esters after MLF; however, key aromatic compounds including alcohols, terpenes or acids were also found to significantly increase. Principal component analysis classified the strains in two distinct groups, each one correlated with different key volatile compounds. P2A, P3A, P3G and P5C strains were mainly linked to esters, while P7B and the commercial strain Viniflora OENOS showed higher score for diverse compounds as hexanoic acid, β-damascenone, linalool or 2-phenylethanol. These results confirmed the specific impact of each strain on wine aroma profile, which could lead to the production of wines with individual characteristics, in which the reliability and safety of MLF is also ensured.

Utilization of Oenococcus oeni strains to ferment grape juice: Metabolic activities and beneficial health potential

This study aimed to investigate the behavior of Oenococcus oeni MS9 and MS46 strains in sterile grape juice (SGJ, pH 4.0) incubated at 30 °C, in terms of growth and glucose, organic acids and total phenolic compounds utilization. In addition, their antimicrobial activity and the changes in antioxidant properties of fermented juice with selected strain were evaluated. Both strains grew without lag period by ~1.40 log CFU/mL at 12 days with maximum growth rates of about 0.019 h^-1. After this time the MS9 and MS46 strains counts declined by 0.6 log units and remained unchanged respectively. O. oeni MS46 was evaluated in SGJ for low inoculum size (~10⁴ CFU/mL). In this condition it also grew without lag period by 3.11 ± 0.01 log CFU/mL with a μmax of 0.05 h^-1. Glucose and L-malic and citric acids were simultaneously utilized but at different rates and extents, yielding mainly lactic acid with concomitant pH reduction. Acetic acid ranged between 11 and 19 mmol/L. Total phenolic compounds significantly decreased in fermented SGJ with strain MS9 but not MS46. In this last condition, the antioxidant activity increased by 21%. In addition, both O. oeni strains showed antibacterial properties against Escherichia coli 700, Salmonella Typhimurium and Listeria monocytogenes. O. oeni strains, especially MS46, with the ability to growth in SGJ, high malolactic potential and adequate sugars and organic acids profiles from the sensorial viewpoint may be used to ferment grape juice with safer and healthier properties than fresh juice.

Metabolic potential of microbial community and distribution mechanism of Staphylococcus species during broad bean paste fermentation

Although the microbial diversity and structure in bean-based fermented foods have been widely studied, systematic studies on functional microbiota and mechanism of community forms in multi-microbial fermentation systems were still lacking. In this work, the metabolic pathway and functional potential of microbial community in broad bean paste (BBP) were investigated by metagenomics approach, and Staphylococcus, Bacillus, Weissella, Aspergillus and Zygosaccharomyces were found to be the potential predominant populations responsible for substrate alteration and flavor biosynthesis. Among them, Staphylococcus was the most abundant and widespread functional microbe, and closely related Staphylococcus species were diverse and ubiquitously distributed, with the opportunistic pathogen S. gallinarum being the most abundant Staphylococcus specie isolated from BBP. To explain the dominance status of S. gallinarum and species distributions of Staphylococcus genus, we tested the effects of abiotic and biotic factors on three Staphylococcus species using a tractable BBP model, demonstrating that adaptation to environmental conditions (environmental parameters and other functional microbes) led to the dominant position and species coexistence of Staphylococcus, and congeneric competition among Staphylococcus species further shaped ecological distributions of closely related Staphylococcus species. In general, this work revealed the metabolic potential of microbial community and distribution mechanism of Staphylococcus species during BBP fermentation, which could help traditional factories to more precisely control the safety and quality of bean-based fermented foods.

Impact of Oral Microbiota on Flavor Perception: From Food Processing to In-Mouth Metabolization

Flavor perception during food intake is one of the main drivers of food acceptability and consumption. Recent studies have pointed to the oral microbiota as an important factor modulating flavor perception. This review introduces general characteristics of the oral microbiota, factors potentially influencing its composition, as well as known relationships between oral microbiota and chemosensory perception. We also review diverse evidenced mechanisms enabling the modulation of chemosensory perception by the microbiota. They include modulation of the chemosensory receptors activation by microbial metabolites but also modification of receptors expression. Specific enzymatic reactions catalyzed by oral microorganisms generate fragrant molecules from aroma precursors in the mouth. Interestingly, these reactions also occur during the processing of fermented beverages, such as wine and beer. In this context, two groups of aroma precursors are presented and discussed, namely, glycoside conjugates and cysteine conjugates, which can generate aroma compounds both in fermented beverages and in the mouth. The two entailed families of enzymes, i.e., glycosidases and carbon-sulfur lyases, appear to be promising targets to understand the complexity of flavor perception in the mouth as well as potential biotechnological tools for flavor enhancement or production of specific flavor compounds.

Improvement of Must Fermentation from Late Harvest cv. Tempranillo Grapes Treated with Pulsed Light

Pulsed light irradiation is a nonthermal technology currently used for the elimination of pathogens from a diverse range of food products. In the last two decades, the results obtained using PL at laboratory scale are encouraging wine experts to use it in the winemaking industry. PL can reduce native yeast counts significantly, which facilitates the use of starter cultures, reducing SO2 requirements at the same time. In this experimental set up, Tempranillo grapes were subjected to pulsed light treatment, and the fermentative performance of non-Saccharomyces yeasts belonging to the species Schizosaccharomyces pombe, Lachancea thermotolerans, Torulaspora delbrueckii, Metschnikowia pulcherrima and Hanseniaspora vineae was monitored in sequential fermentations against spontaneous fermentation and pure culture fermentation with the species Saccharomyces cerevisiae. The experimental analyses comprised the determination of anthocyanin (High performance liquid chromatography with photodiode array detector-HPLC-DAD), polyphenol index and colour (Ultraviolet-visible spectroscopy-UV-Vis spectrophotometer), fermentation-derived volatiles (Gas chromatography with flame ionization detector-GC-FID), oenological parameters (Fourier transform Infrared spectroscopy-FT-IR) and structural damage of the skin (atomic force microscopy-AFM). The results showed a decrease of 1.2 log CFU/mL yeast counts after pulsed light treatment and more rapid and controlled fermentation kinetics in musts from treated grapes than in untreated samples. The fermentations done with treated grapes allowed starter cultures to better implant in the must, although a larger anthocyanin loss (up to 93%) and an increase in hue values (1 unit) towards more yellow hues were observed for treated grapes. The development of biomass was larger in musts from treated grapes. The profile of volatile compounds and oenological parameters reveals that fermentations carried out with untreated grapes are prone to deviations from native microbiota (e.g., production of lactic acid). Finally, no severe damage on the skin was observed with the AFM on treated grapes.

Metabolism Characteristics of Lactic Acid Bacteria and the Expanding Applications in Food Industry

Lactic acid bacteria are a kind of microorganisms that can ferment carbohydrates to produce lactic acid, and are currently widely used in the fermented food industry. In recent years, with the excellent role of lactic acid bacteria in the food industry and probiotic functions, their microbial metabolic characteristics have also attracted more attention. Lactic acid bacteria can decompose macromolecular substances in food, including degradation of indigestible polysaccharides and transformation of undesirable flavor substances. Meanwhile, they can also produce a variety of products including short-chain fatty acids, amines, bacteriocins, vitamins and exopolysaccharides during metabolism. Based on the above-mentioned metabolic characteristics, lactic acid bacteria have shown a variety of expanded applications in the food industry. On the one hand, they are used to improve the flavor of fermented foods, increase the nutrition of foods, reduce harmful substances, increase shelf life, and so on. On the other hand, they can be used as probiotics to promote health in the body. This article reviews and prospects the important metabolites in the expanded application of lactic acid bacteria from the perspective of bioengineering and biotechnology.

Development of a defined autochthonous starter through dissecting the seasonal microbiome of broad bean paste

Bean-based fermentation foods are usually ripened in open environment, which would lead to inconsistencies in flavor and quality between batches. The physicochemical metabolism and microbial community of seasonal broad bean paste (BBP) were compared to distinguish discriminant metabolites and unique taxa, as well as their specific reasons for different flavor and quality in this study. Here, we found that environmental variables led to the seasonal distribution of microbiota, and differential microorganisms further contributed to the inconsistency of flavor quality, in which Lactobacillales was responsible for the higher titratable acid and amino acid nitrogen concentration in winter pei, while Saccharomycetales benefited the formation of volatile flavor substances in autumn pei. Additionally, we compared the effect of different combinations of Lactobacillales with Zygosaccharomyces rouxii on the quality of BBP, and found that W. confusa was more suitable for BBP fermentation rather than T. halophilus in terms of sensory characteristics and physicochemical metabolites.

Bacterial Diversity in Pickled Cowpea (Vigna unguiculata [Linn.] Walp) as Determined by Illumina MiSeq Sequencing and Culture-Dependent Methods

Pickled cowpea (Vigna unguiculata [Linn.] Walp) is a popular fermented vegetable in China that is made by spontaneous fermentation. Prior to this study, little was known about its microbial community. Eighteen pickled cowpea samples were collected in Enshi City, China, in 2018. The bacterial diversity within these samples was evaluated using a combination of high-throughput sequencing (Illumina MiSeq platform) targeting the V3-V4 region of the 16S rRNA gene sequence and culture-dependent methods. A total of 456,318 high-quality 16S rRNA gene sequence reads were obtained, and these reads were clustered into 19,712 OTUs with 97.0% similarity. The core bacterial phyla were Actinobacteria, Bacteroidetes, Proteobacteria, and Firmicutes; the core bacterial genera were Levilactobacillus, Lactiplantibacillus, Companilactobacillus, Pediococcus, Lactobacillus, Weissella, and Pseudomonas. Using the spread-plating method, 39 lactic acid bacteria (LAB) strains were isolated and identified based on the nearly complete 16S rRNA gene sequence. Of these, 37 were identified as Lactiplantibacillus plantarum group, while the other two were classified as Limosilactobacillus fermentum and Lacticaseibacillus rhamnosus. These results indicate a high relative abundance of LAB in traditional pickled cowpea, especially Lactobacillaceae species, which likely contribute to fermentation. This study would provide information on the LAB population of Pickled cowpea and indicated that the Pickled cowpea could be a good source for isolation of lactic acid bacteria.

Integrative Metagenomics-Metabolomics for Analyzing the Relationship Between Microorganisms and Non-volatile Profiles of Traditional Xiaoqu

Xiaoqu, one of three traditional jiuqu in China, is a saccharifying and fermenting agent used in Xiaoqu jiu brewing, with different ingredient compositions and preparation techniques used in various regions. The yield and quality of Xiaoqu jiu are significantly affected by the metabolites and microbiota of Xiaoqu; however, the associated relationship remains poorly understood. This study aimed to analyze this relationship in three typical traditional Xiaoqu from the Guizhou province in China. The non-volatile metabolites of Xiaoqu were detected using gas chromatography time-of-flight mass spectrometry, whereas the classification and metabolic potential of the microbiota were investigated using metagenomic sequencing. Results show that Firmicutes, Proteobacteria, and Actinobacteria represent the dominant bacterial phyla, with Lactobacillus, Bacillus, Acinetobacter, Leuconostoc, and Weissella found to be the dominant bacterial genera. Meanwhile, Ascomycota, Mucoromycota, and Basidiomycota are the dominant fungal phyla with Aspergillus, Saccharomyces, Pichia, Rhizopus, and Phycomyces being the predominant fungal genera. Functional annotation of the microbiota revealed a major association with metabolism of carbohydrates, cofactors, and vitamins, as well as amino acids. A total of 39 significantly different metabolites (SDMs) were identified that are involved in 47 metabolic pathways, primarily that of starch and sucrose; glycine, serine, and threonine; glyoxylate and dicarboxylate; pyruvate; as well as biosynthesis of pantothenate and CoA. Further, based on Spearman's correlation analysis, Aspergillus, Saccharomyces, Lactobacillus, Acetobacter, Weissella, Pantoea, Desmospora, and Bacillus are closely correlated with production of physicochemical indexes and SDMs. Moreover, the metabolic network generated for the breakdown of substrates and formation of SDMs in Xiaoqu was found to primarily center on the metabolism of carbohydrates and the tricarboxylic acid cycle. These results provide insights into the functional microorganisms and metabolic patterns present in traditional Guizhou Xiaoqu and might guide researchers in the production of stable and efficient Xiaoqu in the future.

Biodiversity of Oenological Lactic Acid Bacteria: Species- and Strain-Dependent Plus/Minus Effects on Wine Quality and Safety

Winemaking depends on several elaborate biochemical processes that see as protagonist either yeasts or lactic acid bacteria (LAB) of oenological interest. In particular, LAB have a fundamental role in determining the quality chemical and aromatic properties of wine. They are essential not only for malic acid conversion, but also for producing several desired by-products due to their important enzymatic activities that can release volatile aromatic compounds during malolactic fermentation (e.g., esters, carbonyl compounds, thiols, monoterpenes). In addition, LAB in oenology can act as bioprotectors and reduce the content of undesired compounds. On the other hand, LAB can affect wine consumers’ health, as they can produce harmful compounds such as biogenic amines and ethyl carbamate under certain conditions during fermentation. Several of these positive and negative properties are species- and strain-dependent characteristics. This review focuses on these aspects, summarising the current state of knowledge on LAB’s oenological diversity, and highlighting their influence on the final product’s quality and safety. All our reported information is of high interest in searching new candidate strains to design starter cultures, microbial resources for traditional/typical products, and green solutions in winemaking. Due to the continuous interest in LAB as oenological bioresources, we also underline the importance of inoculation timing. The considerable variability among LAB species/strains associated with spontaneous consortia and the continuous advances in the characterisation of new species/strains of interest for applications in the wine sector suggest that the exploitation of biodiversity belonging to this heterogeneous group of bacteria is still rising.

Lactic Acid Bacteria in Wine: Technological Advances and Evaluation of Their Functional Role

Currently, the main role of Lactic Acid Bacteria (LAB) in wine is to conduct the malolactic fermentation (MLF). This process can increase wine aroma and mouthfeel, improve microbial stability and reduce the acidity of wine. A growing number of studies support the appreciation that LAB can also significantly, positively and negatively, contribute to the sensorial profile of wine through many different enzymatic pathways. This is achieved either through the synthesis of compounds such as diacetyl and esters or by liberating bound aroma compounds such as glycoside-bound primary aromas and volatile thiols which are odorless in their bound form. LAB can also liberate hydroxycinnamic acids from their tartaric esters and have the potential to break down anthocyanin glucosides, thus impacting wine color. LAB can also produce enzymes with the potential to help in the winemaking process and contribute to stabilizing the final product. For example, LAB exhibit peptidolytic and proteolytic activity that could break down the proteins causing wine haze, potentially reducing the need for bentonite addition. Other potential contributions include pectinolytic activity, which could aid juice clarification and the ability to break down acetaldehyde, even when bound to SO2, reducing the need for SO2 additions during winemaking. Considering all these findings, this review summarizes the novel enzymatic activities of LAB that positively or negatively affect the quality of wine. Inoculation strategies, LAB improvement strategies, their potential to be used as targeted additions, and technological advances involving their use in wine are highlighted along with suggestions for future research.

Secondary Aroma: Influence of Wine Microorganisms in Their Aroma Profile

Aroma profile is one of the main features for the acceptance of wine. Yeasts and bacteria are the responsible organisms to carry out both, alcoholic and malolactic fermentation. Alcoholic fermentation is in turn, responsible for transforming grape juice into wine and providing secondary aromas. Secondary aroma can be influenced by different factors; however, the influence of the microorganisms is one of the main agents affecting final wine aroma profile. Saccharomyces cerevisiae has historically been the most used yeast for winemaking process for its specific characteristics: high fermentative metabolism and kinetics, low acetic acid production, resistance to high levels of sugar, ethanol, sulfur dioxide and also, the production of pleasant aromatic compounds. Nevertheless, in the last years, the use of non-saccharomyces yeasts has been progressively growing according to their capacity to enhance aroma complexity and interact with S. cerevisiae, especially in mixed cultures. Hence, this review article is aimed at associating the main secondary aroma compounds present in wine with the microorganisms involved in the spontaneous and guided fermentations, as well as an approach to the strain variability of species, the genetic modifications that can occur and their relevance to wine aroma construction.

Determination of the microbial communities of Guizhou Suantang, a traditional Chinese fermented sour soup, and correlation between the identified microorganisms and volatile compounds

Guizhou Suantang (GZST), a type of sour soup, is a traditional fermented food that can be classified into Hong Suantang (HST) and Bai Suantang (BST). GZST possesses unique flavors arising from various microbiota in fermentation ecosystems. However, the association between these microbiota and flavors remains poorly understood. Accordingly, this study analyzed the volatile components and microbial communities of GZST via headspace solid-phase microextraction coupled with gas chromatography-mass spectrometry and high-throughput 16S rRNA and internal transcribed spacer sequencing techniques. Results showed that 133 compounds, including alcohols, esters, phenols, hydrocarbons, ketones, aldehydes, nitriles, acids, and sulfides, were identified from GZST. Moreover, principal component analysis found significant variances in the composition of volatile compounds among different samples. The bacterial genus level indicated that all GZST samples were dominated by Lactobacillus. At the fungal genus level, BST was dominated by Pichia, Debaryomyces, Mortierella, unclassified, Meyerozyma, and Dipodascus. Meanwhile, HST was dominated by Pichia, Candida, Kazachstania, Debaryomyces, Archaeorhizomyces, and Verticillium. The potential correlations between microbiota and volatile components were also explored through bidirectional orthogonal partial least squares-based correlation analysis. Nine bacterial genera and eight fungal taxa were identified as functional core microbiota for flavor production on the basis of their dominance and functionality in the microbial community. In addition, excessive Lactobacillus inhibited the formation of certain flavor substances. These findings provided basic data for the isolation, screening, and fermentation regulation of functional microorganisms in GZST. The information provided in this study is valuable for the development of effective strategies for selecting beneficial bacterial and fungal strains to improve the quality of GZST.

Evaluating the influence of simultaneous inoculation of SiO2-alginate encapsulated bacteria and yeasts on volatiles, amino acids, biogenic amines and sensory profile of red wine with lysozyme addition

The influence of the timing of inoculation (sequential and simultaneous alcoholic fermentation (AF)/malolactic fermentation (MLF)) on the chemical and sensory properties of red wines was studied. The impact of the encapsulation of Oenococcus oeni into SiO₂-alginate hydrogel (Si-ALG) and the addition of lysozyme in wines inoculated with encapsulated bacteria were also analysed. There was a significant influence of the timing of inoculation on the volatile composition of the wines just as on the amino acid and biogenic amine content. The wines produced by simultaneous AF/MLF showed the highest contents of some volatile compounds, such as ethyl esters and terpenes, as well as amino acids and tyramine. Bacterial encapsulation affected the volatile and amino acid profile of the wines, while the biogenic amine composition was not modified. The chemical composition of the wines was not altered by the presence of lysozyme. A trained panel did not perceive substantial differences between treatments.

Correlations between microbiota with physicochemical properties and volatile flavor components in black glutinous rice wine fermentation

Black glutinous rice wine (BGRW) is a popular traditional Chinese rice wine; however, the flavors profiles associated with microbiota changes during its fermentation have not yet been evaluated. In this study, we explored the correlations between microbial communities with physicochemical properties and flavor components during BGRW fermentation. High-throughput sequencing was used to identify the microbial community composition of BGRW at different fermentation stages, and physicochemical properties and volatile flavor compounds (VFCs) were identified via fermentation features testing and headspace solid phase microextraction gas chromatography mass spectrometry. First, we revealed Pantoea and Kosakonia predominated bacterial genera the early stage of BGRW fermentation, Leuconostoc, Pediococcus, Bacillus, and Lactobacillus predominated bacterial genera the later stage, while Rhizopus and Saccharomyces were the predominant fungal genera throughout fermentation. Second, total sugars, titratable acids, pH, ethanol, amino acid nitrogen, and 43 VFCs were detected during fermentation. Twenty-three VFCs were differentially produced according to the linear discriminant analysis effect size method. With the increase of the fermentation time, the kinds and contents of esters and alcohols were also increased, while acids decreased. Moreover, 12 microbial genera, Lactococcus, Pediococcus, Leuconostoc, Lactobacillus, Cronobacter, Pantoea, Weissella, Enterococcus, Rhizopus, Myceliophthora, Cystofilobasidium, and Aspergillus were found to be highly correlated (|ρ| > 0.7 and P < 0.05) with physicochemical properties and VFCs, by redundancy analysis (RDA) and two-way orthogonal partial least squares (O2PLS) analysis. Ultimately, based on the results, a metabolic map of dominant genera in BGRW was established. Our findings provided detailed information on the dynamic changes of physicochemical properties and VFCs and selection of beneficial strains to improve the quality of BGRW.

Assessment of β-D-glucosidase activity and bgl gene expression of Oenococcus oeni SD-2a

Glycosidases enhance flavor during wine-making by mediating the enzymatic release of aroma molecules. In order to better understand the aroma enhancement potential of Oenococcus oeni SD-2a, β-D-glucosidase (βG) activities in the culture supernatant, whole cells, and disrupted cell lysate were assessed at mid log, late log and stationary growth phase. The enzymatic activity was also compared further from cell cultures with 5 different carbon sources (glucose, cellobiose, arbutin, glucose and cellobiose, glucose and arbutin) at late log phase. Correspondingly, expression levels of 3 bgl genes, OEOE-0224, OEOE-1210, and OEOE-1569 were investigated from cell cultures of the 3 growth phases, and the 5 cell cultures with different carbon sources. Finally, the volatile aroma compounds released by O. oeni SD-2a in synthetic wines with natural glycosides were evaluated by GC-MS. Results showed βG of O. oeni SD-2a was not extracellular enzyme, and the location of it didn’t change with the change of growth phase and carbon source studied. βG activities in the whole cells and disrupted cell lysate were similar and constant at the 3 growth phases. As for the carbon sources, βG activities of whole cells and disrupted lysate were positively affected by cellobiose. While arbutin displayed positive and negative effect on βG activity of whole cells and disrupted lysate, respectively. It is probably that bgl genes OEOE-0224 and OEOE-1210 were related to βG activity of SD-2a whole cells, while OEOE-1569 was responsible for βG activity of disrupted lysate. More kinds of volatile compounds and higher total concentration were released by SD-2a in synthetic wine compared with control. Thus, SD-2a showed a great potential for flavor enhancement under wine-like conditions. This study provides more information for further study of βG activity from O. oeni SD-2a.

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

The main role of acidity and pH is to confer microbial stability to wines. No less relevant, they also preserve the color and sensory properties of wines. Tartaric and malic acids are generally the most prominent acids in wines, while others such as succinic, citric, lactic, and pyruvic can exist in minor concentrations. Multiple reactions occur during winemaking and processing, resulting in changes in the concentration of these acids in wines. Two major groups of microorganisms are involved in such modifications: the wine yeasts, particularly strains of Saccharomyces cerevisiae, which carry out alcoholic fermentation; and lactic acid bacteria, which commonly conduct malolactic fermentation. This review examines various such modifications that occur in the pre-existing acids of grape berries and in others that result from this microbial activity as a means to elucidate the link between microbial diversity and wine composition.

The microbial challenge of winemaking: yeast-bacteria compatibility

The diversity and complexity of wine environments present challenges for predicting success of fermentation. In particular, compatibility between yeast and lactic acid bacteria is affected by chemical and physical parameters that are strain and cultivar specific. This review focuses on the impact of compound production by microbes and physical interactions between microbes that ultimately influence how yeast and bacteria may work together during fermentation. This review also highlights the importance of understanding microbial interactions for yeast-bacteria compatibility in the wine context.

A Bottom-Up Approach To Develop a Synthetic Microbial Community Model: Application for Efficient Reduced-Salt Broad Bean Paste Fermentation

Humans have used high salinity for the production of bean-based fermented foods over thousands of years. Although high salinity can inhibit the growth of harmful microbes and select functional microbiota in an open environment, it also affects fermentation efficiency of bean-based fermented foods and has a negative impact on people's health. Therefore, it is imperative to develop novel defined starter cultures for reduced-salt fermentation in a sterile environment. Here, we explored the microbial assembly and function in the fermentation of traditional Chinese broad bean paste with 12% salinity. The results revealed that the salinity and microbial interactions together drove the dynamic of community and pointed out that five dominant genera (Staphylococcus, Bacillus, Weissella, Aspergillus, and Zygosaccharomyces) may play different key roles in different fermentation stages. Then, core species were isolated from broad bean paste, and their salinity tolerance, interactions, and metabolic characteristics were evaluated. The results provided an opportunity to validate in situ predictions through in vitro dissection of microbial assembly and function. Last, we reconstructed the synthetic microbial community with five strains (Aspergillus oryzae, Bacillus subtilis, Staphylococcus gallinarum, Weissella confusa, and Zygosaccharomyces rouxii) under different salinities and realized efficient fermentation of broad bean paste for 6 weeks in a sterile environment with 6% salinity. In general, this work provided a bottom-up approach for the development of a simplified microbial community model with desired functions to improve the fermentation efficiency of bean-based fermented foods by deconstructing and reconstructing the microbial structure and function.IMPORTANCE Humans have mastered high-salinity fermentation techniques for bean-based fermented product preparation over thousands of years. High salinity was used to select the functional microbiota and conducted food fermentation production with unique flavor. Although a high-salinity environment is beneficial for suppressing harmful microbes in the open fermentation environment, the fermentation efficiency of functional microbes is partially inhibited. Therefore, application of defined starter cultures for reduced-salt fermentation in a sterile environment is an alternative approach to improve the fermentation efficiency of bean-based fermented foods and guide the transformation of traditional industry. However, the assembly and function of self-organized microbiota in an open fermentation environment are still unclear. This study provides a comprehensive understanding of microbial function and the mechanism of community succession in a high-salinity environment during the fermentation of broad bean paste so as to reconstruct the microbial community and realize efficient fermentation of broad bean paste in a sterile environment.

Non-Saccharomyces Yeasts and Organic Wines Fermentation: Implications on Human Health

A relevant trend in winemaking is to reduce the use of chemical compounds in both the vineyard and winery. In organic productions, synthetic chemical fertilizers, pesticides, and genetically modified organisms must be avoided, aiming to achieve the production of a “safer wine”. Safety represents a big threat all over the world, being one of the most important goals to be achieved in both Western society and developing countries. An occurrence in wine safety results in the recovery of a broad variety of harmful compounds for human health such as amines, carbamate, and mycotoxins. The perceived increase in sensory complexity and superiority of successful uninoculated wine fermentations, as well as a thrust from consumers looking for a more “natural” or “organic” wine, produced with fewer additives, and perceived health attributes has led to more investigations into the use of non-Saccharomyces yeasts in winemaking, namely in organic wines. However, the use of copper and sulfur-based molecules as an alternative to chemical pesticides, in organic vineyards, seems to affect the composition of grape microbiota; high copper residues can be present in grape must and wine. This review aims to provide an overview of organic wine safety, when using indigenous and/or non-Saccharomyces yeasts to perform fermentation, with a special focus on some metabolites of microbial origin, namely, ochratoxin A (OTA) and other mycotoxins, biogenic amines (BAs), and ethyl carbamate (EC). These health hazards present an increased awareness of the effects on health and well-being by wine consumers, who also enjoy wines where terroir is perceived and is a characteristic of a given geographical area. In this regard, vineyard yeast biota, namely non-Saccharomyces wine-yeasts, can strongly contribute to the uniqueness of the wines derived from each specific region.

Effect of Co-Inoculation of Candida zemplinina, Saccharomyces cerevisiae and Lactobacillus plantarum for the Industrial Production of Negroamaro Wine in Apulia (Southern Italy)

The employment of multi-species starter cultures has growing importance in modern winemaking for improving the complexity and wine attributes. The assessment of compatibility for selected species/strains at the industrial-scale is crucial to assure the quality and the safety associated with fermentations. An aspect particularly relevant when the species belong to non-Saccharomyces, Saccharomyces spp. and malolactic bacteria, three categories with different biological characteristics and oenological significance. To the best of our knowledge, the present report is the first study regarding the utilization of a combined starter culture composed of three strains of non-Saccharomyces, Saccharomyces cerevisiae and Lactobacillus plantarum for production of wine at the industrial scale. More in-depth, this work investigated the oenological potential of the autochthonous characterized strains from the Apulian region (Southern Italy), Candida zemplinina (syn. Starmerella bacillaris) 35NC1, S. cerevisiae (NP103), and L. plantarum (LP44), in co-inoculation following a complete scale-up scheme. Microbial dynamics, fermentative profiles and production of volatile secondary compounds were assessed in lab-scale micro-vinification tests and then the performances of the mixed starter formulation were further evaluated by pilot-scale wine production. The above results were finally validated by performing an industrial-scale vinification on 100HL of Negroamaro cultivar grape must. The multi-starter formulation was able to rule the different stages of the fermentation processes effectively, and the different microbial combinations enhanced the organoleptic wine features to different extents. The findings indicated that the simultaneous inoculation of the three species affect the quality and quantity of several volatile compounds, confirming that the complexity of the wine can reflect the complexity of the starter cultures. Moreover, the results underlined that the same mixed culture could differently influence wine quality when tested at the lab-, pilot- and industrial-scale. Finally, we highlighted the significance of employment non-Saccharomyces and L. plantarum, together with S. cerevisiae, autochthonous strains in the design of custom-made starter culture formulation for typical regional wine production with pronounced unique quality.

Influence of must yeast-assimilable nitrogen content on fruity aroma variation during malolactic fermentation in red wine

This study assessed the impact of must yeast-assimilable nitrogen (YAN) content and lactic acid bacteria (LAB) strains used for malolactic fermentation (MLF) on the formation of substituted esters, as well as the corresponding precursors (substituted acids), to investigate the modulation of fruity expression in red wines. In microvinification experiments, a Merlot must was fermented with an initial YAN content of 111 mg/L, or supplemented up to 165 and 220 mg/L. Two Oenococcus oeni LAB strains were used for MLF. Analytical methods were used to quantify substituted esters, as well as the corresponding acids, including, any enantiomeric forms. YAN supplementation of the must significantly increased concentrations of substituted esters of short- and branched-chain alkyl fatty acids produced during alcoholic fermentation (AF) (up to 67% in samples with the highest nitrogen content) and substituted esters of hydroxycarboxylic acids generated during MLF (up to 58% in samples with the highest nitrogen content). YAN supplementation in the must did not affect substituted acid formation during AF. After MLF, short- and branched-chain alkyl fatty acid levels increased in wines made from musts with the highest nitrogen content (up to 56% in samples with the highest nitrogen content), whereas concentrations of hydroxycarboxylic acids increased (up to 55%) independently of the initial YAN content, highlighting the important role of MLF. (2S)-2-hydroxy-4-methylpentanoic acid was only found in wines after malolactic fermentation, suggesting different pathways for each enantiomer and opening up new prospects for the study of bacterial metabolisms. Moreover, sensory profiles revealed a significant increase in black-berry- and jammy-fruit aromas during MLF and a strong positive correlation between these aromas and the production of substituted esters following must nitrogen supplementation and MLF. Aromatic reconstitutions revealed that variations in the concentrations of substituted esters after MLF impacted the fruity aroma of red wines.

Exploring the diversity and role of microbiota during material pretreatment of light-flavor Baijiu

Baijiu (Chinese liquor) is a type of traditional distilled alcoholic beverage produced through spontaneous solid-state fermentation with sorghum as the primary material. Material processing, including sorghum soaking, steaming and cooling which is carried out in an open environment, is an integral part of Baijiu manufacturing. However, the microbiota involved in material pretreatment and its associate with the alcoholic fermentation is unclear. This research is aimed to exploring the diversity and role of microbiota during material pretreatment of light-flavor Baijiu. Results showed that Cyanobacteria, Epicoccum, and Cladosporium predominated in the sorghum at the beginning of soaking. Lactobacillus and Pichia became the predominant bacterial and fungal genera by the end of soaking. With the dynamics of microbiota, the pH declined sharply and the categories and concentration of volatile flavors such as alcohols, esters, acids, phenols, ketones, and aldehydes increased. Correlation analysis indicated that Lactobacillus and Pichia showed positive correlation with various flavors during soaking. Furthermore, SourceTracker analysis revealed that the microbiota involved during cooling processing was an important source of the Lactobacillus during fermentation of light-flavor Baijiu. This study illustrates the role of microbiota during material pretreatment and the association with alcoholic fermentation, which contributes to reveal the mechanism of Baijiu manufacturing.

Co-Existence of Inoculated Yeast and Lactic Acid Bacteria and Their Impact on the Aroma Profile and Sensory Traits of Tempranillo Red Wine

This study investigates the effects of simultaneous inoculation of a selected Saccharomyces cerevisiae yeast strain with two different commercial strains of wine bacteria Oenococcus oeni at the beginning of the alcoholic fermentation on the kinetics of malolactic fermentation (MLF), wine chemical composition, and organoleptic characteristics in comparison with spontaneous MLF in Tempranillo grape must from Castilla-La Mancha (Spain). Evolution of MLF was assessed by the periodic analysis of L-malic acid through the enzymatic method, and most common physiochemical parameters and sensory traits were evaluated using a standardized sensory analysis. The samples were analyzed by GC/MS in SCAN mode using a Trace GC gas chromatograph and a DSQII quadrupole mass analyzer. Co-inoculation reduced the overall fermentation time by up to 2 weeks leading to a lower increase in volatile acidity. The fermentation-derived wine volatiles profile was distinct between the co-inoculated wines and spontaneous MLF and was influenced by the selected wine bacteria used in co-inoculation. Co-inoculation allows MLF to develop under reductive conditions and results in wines with very few lactic and buttery flavors, which is related to the impact of specific compounds like 2,3-butanedione. This compound has been also confirmed as being dependent on the wine bacteria used.

Transcriptional Regulator AcrR Increases Ethanol Tolerance through Regulation of Fatty Acid Synthesis in Lactobacillus plantarum

Lactobacillus plantarum is a versatile bacterium with significant adaptability to harsh habitats containing excessive ethanol concentrations. It was found that the L. plantarum NF92-TetR/AcrR family regulator, AcrR, significantly enhanced the growth rate of this lactic acid bacterium in the presence of ethanol. Through screening 172 ethanol-resistant related genes by electrophoretic mobility shift and quantitative reverse transcription-PCR (RT-qPCR) assays, six genes were identified to be regulated by AcrR under ethanol stress. Among these was a gene coding for a 3-hydroxyacyl-ACP dehydratase (fabZ1) regulated by AcrR under ethanol stress. AcrR regulated fabZ1 under ethanol stress by binding to its promoter, P _fabZ1 DNase I footprinting analysis indicated that there were two specific AcrR binding sites on P _fabZ1 RT-PCR results showed fabZ1 could cotranscribe with its downstream 12 genes and conform a fatty acid de novo biosynthesis (fab) gene cluster under the control of P _fabZ1 Both RT-qPCR of the fab gene cluster in acrR knockout and overexpression strains and fatty acid methyl ester analysis of the acrR knockout strain showed that AcrR could promote fatty acid synthesis in L. plantarum NF92. Membrane fluorescence anisotropy analysis of acrR knockout and overexpression strains showed that AcrR could increase membrane fluidity under ethanol stress. Thus, AcrR could regulate fatty acid synthesis and membrane fluidity to promote the adaption of L. plantarum NF92 to a high ethanol concentration.IMPORTANCE Ethanol tolerance is essential for L. plantarum strains living in substances with more than 9% ethanol, such as wine and beer. The details regarding how L. plantarum adapts to ethanol are still lacking. This study demonstrates that AcrR regulates the de novo synthesis of fatty acids in L. plantarum adapting to toxic levels of ethanol. We also identified the ability of the TetR/AcrR family regulator to bind to the fatty acid biosynthesis gene promoter, P _fabZ1 , in L. plantarum and defined the binding sites. This finding facilitates the induction of the adaptation of L. plantarum strains to ethanol for food fermentation applications.

New Insights Into Cinnamoyl Esterase Activity of Oenococcus oeni

Some strains of Oenococcus oeni possess cinnamoyl esterase activity that can be relevant in the malolactic stage of wine production liberating hydroxycinnamic acids that are precursors of volatile phenols responsible for sensory faults. The objective of this study was to better understand the basis of the differential activity between strains. After initial screening, five commercial strains of O. oeni were selected, three were found to exhibit cinnamoyl esterase activity (CE+) and two not (CE-). Although the use of functional annotation of genes revealed genotypic variations between the strains, no specific genes common only to the three CE+ strains could explain the different activities. Pasteurized wine was used as a natural source of tartrate esters in growth and metabolism experiments conducted in MRS medium, whilst commercial trans-caftaric acid was used as substrate for enzyme assays. Detoxification did not seem to be the main biological mechanism involved in the activity since unlike its phenolic cleavage products and their immediate metabolites (trans-caffeic acid and 4-ethylcatechol), trans-caftaric acid was not toxic toward O. oeni. In the case of the two CE+ strains OenosTM and CiNeTM, wine-exposed samples showed a more rapid degradation of trans-caftaric acid than the unexposed ones. The CE activity was present in all cell-free extracts of both wine-exposed and unexposed strains, except in the cell-free extracts of the CE- strain CH11TM. This activity may be constitutive rather than induced by exposure to tartrate esters. Trans-caftaric acid was totally cleaved to trans-caffeic acid by cell-free extracts of the three CE+ strains, whilst cell-free extracts of the CE- strain CH16TM showed significantly lower activity, although higher for the strains in experiments with no prior wine exposure. The EstB28 esterase gene, found in the genomes of the 5 strains, did not reveal any difference on the upstream regulation and transport functionality between the strains. This study highlights the complexity of the basis of this activity in wine related O. oeni population. Variable cinnamoyl esterases or/and membrane transport activities in the O. oeni strains analyzed and a possible implication of wine molecules could explain this phenomenon.

Different forms of nitrogen application affect metabolite patterns in grapevine leaves and the sensory of wine

The quality of grapevine berries, must and wine is influenced by environmental and viticultural inputs and their complex interactions. Aroma and flavour are decisive for quality and are mainly determined by primary and secondary metabolites. In particular, phenolic compounds contribute to berry and wine quality. The influence of various nitrogen forms on i) the composition of phenolic compounds in leaves and wine and; ii) the resulting wine quality were studied in a vineyard system. Must and wine quality was evaluated by chemical analysis and sensory testing. Metabolomic profiling was also performed. Aroma and sensory profile were significantly changed by the application of nitrogen in contrast to no nitrogen fertilisation. The levels of 33 metabolites in leaves and 55 metabolites in wine were significantly changed altered by fertilisation with the various nitrogen forms. In leaves, more metabolites were increased by the use of calcium nitrate or ammonium but were decreased by the use of urea. In terms of wine, the used nitrogen forms decreased more metabolites compared with no fertilisation.

Looking at the Origin: Some Insights into the General and Fermentative Microbiota of Vineyard Soils

In winemaking processes, there is a current tendency to develop spontaneous fermentations taking advantage of the metabolic diversity of derived from the great microbial diversity present in grape musts. This enological practice enhances wine complexity, but undesirable consequences or deviations could appear on wine quality. Soil is a reservoir of important microorganisms for different beneficial processes, especially for plant nutrition, but it is also the origin of many of the phytopathogenic microorganisms that affect vines. In this study, a meta-taxonomic analysis of the microbial communities inhabiting vineyard soils was realized. A significant impact of the soil type and climate aspects (seasonal patterns) was observed in terms of alpha and beta bacterial diversity, but fungal populations appeared as more stable communities in vineyard soils, especially in terms of alpha diversity. Focusing on the presence and abundance of wine-related microorganisms present in the studied soils, some seasonal and soil-dependent patterns were observed. The Lactobacillaceae family, containing species responsible for the malolactic fermentation, was only present in non-calcareous soils samples and during the summer season. The study of wine-related fungi indicated that the Debaryomycetaceae family dominates the winter yeast population, whereas the Saccharomycetaceae family, containing the most important fermentative yeast species for winemaking, was detected as dominant in summer.

Yeast prion-based metabolic reprogramming induced by bacteria in fermented foods

Microbial communities of yeast and bacterial cells are often observed in the manufacturing processes of fermented foods and drinks, such as sourdough bread, cheese, kefir, wine and sake. Community interactions and dynamics among microorganisms, as well as their significance during the manufacturing processes, are central issues in modern food microbiology. Recent studies demonstrated that the emergence of a yeast prion termed [GAR+] in Saccharomyces cerevisiae is induced by coculturing with bacterial cells, resulting in the switching of the carbon metabolism. In order to facilitate mutualistic symbiosis among microorganisms, this mode of microbial interaction is induced between yeasts and lactic acid bacteria species used in traditional sake making. Thus, yeast prions have attracted much attention as novel platforms that govern the metabolic adaptation of cross-kingdom ecosystems. Our minireview focuses on the plausible linkage between fermented-food microbial communication and yeast prion-mediated metabolic reprogramming.

Effect of mixed species alcoholic fermentation on growth and malolactic activity of lactic acid bacteria

In recent years, there is an increasing interest from the winemaking industry for the use of mixed fermentations with Starmerella bacillaris (synonym Candida zemplinina) and Saccharomyces cerevisiae, due to their ability to modulate metabolites of oenological interest. The current study was carried out to elucidate the effect of this fermentation protocol on the growth and malolactic activity of lactic acid bacteria (LAB) used for malolactic fermentation (MLF) and on the chemical and volatile profile of Nebbiolo wines and their chromatic characteristics. To this end, two LAB species, namely Lactobacillus plantarum and Oenococcus oeni, were inoculated at the beginning and at the end of the alcoholic fermentation (AF) performed by pure and mixed yeast using the abovementioned yeasts. The different yeast inoculation protocols and the combination of species tested influenced greatly the interactions and behavior of the inoculated yeasts and LAB during AF and MLF. For both LAB species, inoculation timing was critical to how rapidly MLF started and finished. Fermentation inoculated with L. plantarum, at the beginning of the AF, completed MLF faster than those inoculated with O. oeni. The presence of Starm. bacillaris in mixed fermentation promoted LAB growth and activity, in particular, O. oeni. Furthermore, LAB species choice had a greater impact on the volatile and chromatic profile of the wines than inoculation time. These findings reveal new knowledge about the importance of LAB species choice and inoculation time to ensure fast MLF completion and to improve wine characteristics in mixed fermentation with Starm. bacillaris and S. cerevisiae.