Application of flow cytometry to wine microorganisms

New insights into the roles of fungi and bacteria in the development of medicinal plant

BACKGROUND

The interaction between microorganisms and medicinal plants is a popular topic. Previous studies consistently reported that microorganisms were mainly considered pathogens or contaminants. However, with the development of microbial detection technology, it has been demonstrated that fungi and bacteria affect beneficially the medicinal plant production chain.

AIM OF REVIEW

Microorganisms greatly affect medicinal plants, with microbial biosynthesis a high regarded topic in medicinal plant-microbial interactions. However, it lacks a systematic review discussing this relationship. Current microbial detection technologies also have certain advantages and disadvantages, it is essential to compare the characteristics of various technologies.

KEY SCIENTIFIC CONCEPTS OF REVIEW

This review first illustrates the role of fungi and bacteria in various medicinal plant production procedures, discusses the development of microbial detection and identification technologies in recent years, and concludes with microbial biosynthesis of natural products. The relationship between fungi, bacteria, and medicinal plants is discussed comprehensively. We also propose a future research model and direction for further studies.

Comparison of plate counting with flow cytometry, using four different fluorescent dye techniques, for the enumeration of Bacillus cereus in milk

This study aimed to compare the performance of flow cytometry methods with plate counting for the enumeration of bacteria, using Bacillus cereus as a model organism. It was found that the cFDA-propidium iodide, CellROX™ Green-propidium iodide, and DiOC2 dye techniques had similar accuracy to plate counting, while the SYTO 24-propidium iodide dye technique was not as accurate. The four dye techniques had comparable precision to plate counting, with the CellROX™ Green-propidium iodide dye having the greatest precision. The consistency of the position and shape of the cell clusters on the flow cytometry plots, and the extent of separation of the cell from background clusters, was greatest with the DiOC2 and CellROX™ Green-propidium iodide dyes. Furthermore, the DiOC2 and CellROX™ Green-propidium iodide dyes performed well, even when a sample was measured containing reconstituted whole milk powder at a 10-1 dilution, without the use of sample preparation to specifically remove the milk constituents prior to measurement. Given gating of only one cell cluster was required to be managed with the DiOC2 dye, to determine the viable number of cells, it was found that the DiOC2 dye had the greatest ease-of-use. Overall, results indicated that the DiOC2 dye is an ideal candidate for the enumeration of viable bacteria in dairy samples on a high-throughput, routine basis.

A novel strategy to construct multi-strain starter cultures: an insight to evolve from natural to directed fermentation

Some biotechnological strategies have succeeded in the attempt to imitate natural fermentation, and bioprocesses have been efficiently designed when the product is the result of a unique biological reaction. However, when the process requires more than one biological reaction, few bioprocesses have been successfully designed because the available tools to construct multi-strain starter cultures are not yet well defined. In this work, a novel experimental strategy to construct multi-strain starter cultures with selected native microorganisms from natural fermentation is proposed. The strategy analyses, selects, and defines the number and proportion of each strain that should form a starter culture to be used in directed fermentations. It was applied to evolve natural fermentation to directed fermentation in distilled agave production. The results showed that a starter culture integrated by Kluyveromyces marxianus, Clavispora lusitaniae, and Kluyveromyces marxianus var. drosophilarum in proportions of 35, 32, and 33%, respectively, allows obtaining fermented agave juice containing a 2.1% alcohol yield and a distilled product with a broad profile of aromatic compounds. Hence, the results show, for the first time, a tool that addresses the technical challenge for multi-strain starter culture construction, offering the possibility of preserving the typicity and genuineness of the original traditional product.

Comparing the hierarchy of inter- and intra-species interactions with population dynamics of wine yeast cocultures

In winemaking, the development of new fermentation strategies, such as the use of mixed starter cultures with Saccharomyces cerevisiae (Sc) yeast and non-Saccharomyces (NS) species, requires a better understanding of how yeasts interact, especially at the beginning of fermentation. Despite the growing knowledge on interactions between Sc and NS, few data are available on the interactions between different species of NS. It is furthermore still unclear whether interactions are primarily driven by generic differences between yeast species or whether individual strains are the evolutionarily relevant unit for biotic interactions. This study aimed at acquiring knowledge of the relevance of species and strain in the population dynamics of cocultures between five yeast species: Hanseniaspora uvarum, Lachancea thermotolerans, Starmerella bacillaris, Torulaspora delbrueckii and Sc. We performed cocultures between 15 strains in synthetic grape must and monitored growth in microplates. Both positive and negative interactions were identified. Based on an interaction index, our results showed that the population dynamics seemed mainly driven by the two species involved. Strain level was more relevant in modulating the strength of the interactions. This study provides fundamental insights into the microbial dynamics in early fermentation and contribute to the understanding of more complex consortia encompassing multiple yeasts trains.

Rapid Detection of Brettanomyces bruxellensis in Wine by Polychromatic Flow Cytometry

Brettanomyces bruxellensis is found in several fermented matrices and produces relevant alterations to the wine quality. The methods usually used to identify B. bruxellensis contamination are based on conventional microbiological techniques that require long procedures (15 days), causing the yeast to spread in the meantime. Recently, a flow cytometry kit for the rapid detection (1-2 h) of B. bruxellensis in wine has been developed. The feasibility of the method was assessed in a synthetic medium as well as in wine samples by detecting B. bruxellensis in the presence of other yeast species (Saccharomyces cerevisiae and Pichia spp.) and at the concentrations that produce natural contaminations (up to 10⁵ cells/mL), as well as at lower concentrations (10³-10² cells/mL). Wine samples naturally contaminated by B. bruxellensis or inoculated with four different strains of B. bruxellensis species together with Saccharomyces cerevisiae and Pichia spp., were analyzed by flow cytometry. Plate counts were carried out in parallel to flow cytometry. We provide evidence that flow cytometry allows the rapid detection of B. bruxellensis in simple and complex mixtures. Therefore, this technique has great potential for the detection of B. bruxellensis and could allow preventive actions to reduce wine spoilage.

Multispectral fluorescence sensitivity to acidic and polyphenolic changes in Chardonnay wines - The case study of malolactic fermentation

In this study, stationary and time-resolvedfluorescence signatures, were statistically and chemometrically analyzed among three typologies of Chardonnay wines (A, B and C) with the objectives to evaluate their sensitivity to acidic and polyphenolic changes. For that purpose, a dataset was built using Excitation Emission Matrices of fluorescence (N = 103) decomposed by a Parallel Factor Analysis (PARAFAC), andfluorescence decays (N = 22), mathematically fitted, using the conventional exponential modeling and the phasor plot representation. Wine PARAFAC component C4 coupledwith its phasor plot g and s values enable the description of malolactic fermentation (MLF) occurrence in Chardonnay wines. Such proxies reflect wine concentration modifications in total acidity, malic/lactic and phenol acids.Lower g values among fresh MLF + wines compared to MLF- wines are explained by a quenching effect on wine fluorophores by both organic and phenolic acids.The combination of multispectral fluorescence parametersopens a novel routinely implementable methodology to diagnose fermentative processes.

Development of a flow cytometry-based plating-free system for strain engineering in industrial fungi

Recent technical advances regarding filamentous fungi have accelerated the engineering of fungal-based production and benefited basic science. However, challenges still remain and limit the speed of fungal applications. For example, high-throughput technologies tailored to filamentous fungi are not yet commonly available for genetic modification. The currently used fungal genetic manipulations are time-consuming and laborious. Here, we developed a flow cytometry-based plating-free system to directly screen and isolate the transformed protoplasts in industrial fungi Myceliophthora thermophila and Aspergillus niger. This system combines genetic engineering via the 2A peptide and the CRISPR-Cas9 system, strain screening by flow cytometry, and direct sorting of colonies for deep-well-plate incubation and phenotypic analysis while avoiding culturing transformed protoplasts in plates, colony picking, conidiation, and cultivation. As a proof of concept, we successfully applied this system to generate the glucoamylase-hyperproducing strains MtYM6 and AnLM3 in M. thermophila and A. niger, respectively. Notably, the protein secretion level and enzyme activities in MtYM6 were 17.3- and 25.1-fold higher than in the host strain. Overall, these findings suggest that the flow cytometry-based plating-free system can be a convenient and efficient tool for strain engineering in fungal biotechnology. We expect this system to facilitate improvements of filamentous fungal strains for industrial applications. KEY POINTS: • Development of a flow cytometry-based plating-free (FCPF) system is presented. • Application of FCPF system in M. thermophila and A. niger for glucoamylase platform. • Hyper-produced strains MtYM6 and AnLM3 for glucoamylase production are generated.

Different Wines from Different Yeasts? "Saccharomyces cerevisiae Intraspecies Differentiation by Metabolomic Signature and Sensory Patterns in Wine"

Alcoholic fermentation is known to be a key stage in the winemaking process that directly impacts the composition and quality of the final product. Twelve wines were obtained from fermentations of Chardonnay must made with twelve different commercial wine yeast strains of Saccharomyces cerevisiae. In our study, FT-ICR-MS, GC-MS, and sensory analysis were combined with multivariate analysis. Ultra-high-resolution mass spectrometry (uHRMS) was able to highlight hundreds of metabolites specific to each strain from the same species, although they are characterized by the same technological performances. Furthermore, the significant involvement of nitrogen metabolism in this differentiation was considered. The modulation of primary metabolism was also noted at the volatilome and sensory levels. Sensory analysis allowed us to classify wines into three groups based on descriptors associated with white wine. Thirty-five of the volatile compounds analyzed, including esters, medium-chain fatty acids, superior alcohols, and terpenes discriminate and give details about differences between wines. Therefore, phenotypic differences within the same species revealed metabolic differences that resulted in the diversity of the volatile fraction that participates in the palette of the sensory pattern. This original combination of metabolomics with the volatilome and sensory approaches provides an integrative vision of the characteristics of a given strain. Metabolomics shine the new light on intraspecific discrimination in the Saccharomyces cerevisiae species.

Toxicity of Carbon Nanomaterials-Towards Reliable Viability Assessment via New Approach in Flow Cytometry

The scope of application of carbon nanomaterials in biomedical, environmental and industrial fields is recently substantially increasing. Since in vitro toxicity testing is the first essential step for any commercial usage, it is crucial to have a reliable method to analyze the potentially harmful effects of carbon nanomaterials. Even though researchers already reported the interference of carbon nanomaterials with common toxicity assays, there is still, unfortunately, a large number of studies that neglect this fact. In this study, we investigated interference of four bio-promising carbon nanomaterials (graphene acid (GA), cyanographene (GCN), graphitic carbon nitride (g-C₃N₄) and carbon dots (QCDs)) in commonly used LIVE/DEAD assay. When a standard procedure was applied, materials caused various types of interference. While positively charged g-C₃N₄ and QCDs induced false results through the creation of free agglomerates and intrinsic fluorescence properties, negatively charged GA and GCN led to false signals due to the complex quenching effect of the fluorescent dye of a LIVE/DEAD kit. Thus, we developed a new approach using a specific gating strategy based on additional controls that successfully overcame all types of interference and lead to reliable results in LIVE/DEAD assay. We suggest that the newly developed procedure should be a mandatory tool for all in vitro flow cytometry assays of any class of carbon nanomaterials.

A cytofluorimetric analysis of a Saccharomyces cerevisiae population cultured in a fed-batch bioreactor

The yeast Saccharomyces cerevisiae is a reference model system and one of the widely used microorganisms in many biotechnological processes. In industrial yeast applications, combined strategies aim to maximize biomass/product yield, with the fed-batch culture being one of the most frequently used. Flow cytometry (FCM) is widely applied in biotechnological processes and represents a key methodology to monitor cell population dynamics. We propose here an application of FCM in the analysis of yeast cell cycle along the time course of a typical S. cerevisiae fed-batch culture. We used two different dyes, SYTOX Green and SYBR Green, with the aim to better define each stage of cell cycle during S. cerevisiae fed-batch culture. The results provide novel insights in the use of FCM cell cycle analysis for the real-time monitoring of S. cerevisiae bioprocesses.

Two-Dimensional Cytometry Platform for Single-Particle/Cell Analysis with Laser-Induced Fluorescence and ICP-MS

A two-dimensional cytometry platform (CytoLM) with high sensitivity and high temporal resolution is developed for single-particle and single-cell sampling and analysis. First, a Dean flow-assisted vortex capillary cell sampling (VCCS) unit confines the sample stream in curved flow and drives to focus and align the particles or cells in a small probe volume. By coupling VCCS to a laser-induced fluorescence (LIF) detector with data acquisition and processing capability, a high-throughput single-particle/cell analysis system (VCCS-LIF) was established. The particle analysis throughput of 119.42/s and a detection recovery of 78.20 ± 1.75% were achieved at a density of 9.16 × 10⁴/mL for fluorescent particles, and the cell analysis throughput is 48.20/s at a density of 1.5 × 10⁵/mL. Second, the CytoLM platform is constructed by hyphenating VCCS-LIF with inductively coupled plasma mass spectrometry (ICP-MS). In the analysis of HepG2 cells by Ag⁺ incubation and AO staining, 10,760 fluorescence bursts and 3068 MS events were observed in 240 s. Invalid signals due to undispersed cells were controlled at 3.80% for LIF and 1.01% for MS, with a proportion of effective signal of >96.20%. After peak identification and integral processing of the original data, the statistical results including peak area, height, width, and spacing are obtained concurrently and the information on concentration and elemental quantification of single cells is evaluated. CytoLM facilitates high-throughput, multi-dimensional, and multi-parameter characterization of particles and cells, and it may provide vast potential in life science analysis.

The ecology of wine fermentation: a model for the study of complex microbial ecosystems

The general interest in microbial ecology has skyrocketed over the past decade, driven by technical advances and by the rapidly increasing appreciation of the fundamental services that these ecosystems provide. In biotechnology, ecosystems have many more functionalities than single species, and, if properly understood and harnessed, will be able to deliver better outcomes for almost all imaginable applications. However, the complexity of microbial ecosystems and of the interactions between species has limited their applicability. In research, next generation sequencing allows accurate mapping of the microbiomes that characterise ecosystems of biotechnological and/or medical relevance. But the gap between mapping and understanding, to be filled by "functional microbiomics", requires the collection and integration of many different layers of complex data sets, from molecular multi-omics to spatial imaging technologies to online ecosystem monitoring tools. Holistically, studying the complexity of most microbial ecosystems, consisting of hundreds of species in specific spatial arrangements, is beyond our current technical capabilities, and simpler model systems with fewer species and reduced spatial complexity are required to establish the fundamental rules of ecosystem functioning. One such ecosystem, the ecosystem responsible for natural alcoholic fermentation, can provide an excellent tool to study evolutionarily relevant interactions between multiple species within a relatively easily controlled environment. This review will critically evaluate the approaches that are currently implemented to dissect the cellular and molecular networks that govern this ecosystem. KEY POINTS: • Evolutionarily isolated fermentation ecosystem can be used as an ecological model. • Experimental toolbox is gearing towards mechanistic understanding of this ecosystem. • Integration of multidisciplinary datasets is key to predictive understanding.

Novel Methods to Manipulate Autolysis in Sparkling Wine: Effects on Yeast

Sparkling wine made by the traditional method (Méthode Traditionelle) develops a distinct and desirable flavour and aroma profile attributed to proteolytic processes during prolonged ageing on lees. Microwave, ultrasound and addition of β-glucanase enzymes were applied to accelerate the disruption of Saccharomyces cerevisiae, and added to the tirage solution for secondary fermentation in traditional sparkling winemaking. Scanning electron microscopy and flow cytometry analyses were used to observe and describe yeast whole-cell anatomy, and cell integrity and structure via propidium iodide (PI) permeability after 6-, 12- and 18-months post-tirage. Treatments applied produced features on lees that were distinct from that of the untreated control yeast. Whilst control yeast displayed budding cells (growth features) with smooth, cavitated and flat external cell appearances; microwave treated yeast cells exhibited modifications like 'doughnut' shapes immediately after treatment (time 0). Similar 'doughnut'-shaped and 'pitted/porous' cell features were observed on progressively older lees from the control. Flow cytometry was used to discriminate yeast populations; features consistent with cell disruption were observed in the microwave, ultrasound and enzyme treatments, as evidenced by up to 4-fold increase in PI signal in the microwave treatment. Forward and side scatter signals reflected changes in size and structure of yeast cells, in all treatments applied. When flow cytometry was interpreted alongside the scanning electron microscopy images, bimodal populations of yeast cells with low and high PI intensities were revealed and distinctive 'doughnut'-shaped cell features observed in association with the microwave treatment only at tirage, that were not observed until 12 months wine ageing in older lees from the control. This work offers both a rapid approach to visualise alterations to yeast cell surfaces and a better understanding of the mechanisms of yeast lysis. Microwave, ultrasound or β-glucanase enzymes are tools that could potentially initiate the release of yeast cell compounds into wine. Further investigation into the impact of such treatments on the flavour and aroma profiles of the wines through sensory evaluation is warranted.

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.

Synergistic effects of Lactobacillus plantarum and Staphylococcus carnosus on animal food components

Introduction. Various cultures of microorganisms have recently been used to accelerate technological processes. In this regard, it appears highly relevant to study the action of beneficial microorganisms on the components of food systems. Study objects and methods. The study objects included a model mixture of beef muscle and pork fat tissue with 2% salt, as well as a model protein. Lactobacillus plantarum and Staphylococcus carnosus were used in an amount of 1×107 CFU/g of raw material. The compositions of free amino and fatty acids, carbohydrates, and other components were analyzed by liquid and gas chromatography with mass-selective detection. Results and discussion. We studied the effect of L. plantarum and S. carnosus on protein, lipid, and carbohydrate components of food systems based on animal raw materials. We found that the combined effect of the cultures was by 25% as effective as their individual use at 4×109 CFU/kg of raw material. The three-week hydrolysis of proteins to free amino acids was almost a third more effective than when the cultures were used separately. The synergistic effect of L. plantarum and S. carnosus on fat components was not detected reliably. Free monosaccharides formed more intensively when the cultures were used together. In particular, the amount of free lactose almost doubled, compared to the cultures’ individual action. Conclusion. We described culture-caused quantitative changes in the main components of animal-based food systems: amino acids, fatty acids, carbohydrates, and basic organic compounds. Also, we identified substances that can affect the taste and aroma of final products when the cultures are used together or separately. These results make it possible to obtain products with a wide variety of sensory properties.

Survival and metabolism of hydroxycinnamic acids by Dekkera bruxellensis in monovarietal wines

Volatile phenols in wines are responsible for unpleasant aromas, which negatively affect the quality of the wine. These compounds are produced from the metabolism of hydroxycinnamic acids, mainly by the yeasts Brettanomyces/Dekkera. Relevant data, potentially useful to support decisions on how to manage the risk of contamination of wines by Brettanomyces/Dekkera, according to the grape varieties used in the vinification, is important to the wine industry. Therefore, the aim of this work was to evaluate the survival and the metabolism of hydroxycinnamic acids by Dekkera bruxellensis in monovarietal wines. Yeast growth and survival were monitored in fifteen wines, five from each of the grape varieties Touriga Nacional, Cabernet Sauvignon and Syrah, inoculated with a strain of D. bruxellensis. Yeast culturable populations of 10⁷ CFU mL^-1 were reduced to undetectable numbers in 24 h in all wines. Plate counts of 10⁴-10⁶ CFU mL^-1 were, however, detected after 48 h in most of Touriga Nacional and Cabernet Sauvignon wines and later in Syrah. Viability measurement by flow cytometry showed that a significant part of the populations was in a viable but non-culturable state (VBNC). The time required for the recovery of the culturable state was dependent on the wine, being longer on Syrah wines. Besides the production of ethylphenols, the metabolism of hydroxycinnamic acids by VBNC cells led to the accumulation of vinylphenols at relatively high levels, independently of the grape variety. The flow cytometry methodology showed a higher survival capacity of D. bruxellensis in Touriga Nacional wines, which corroborates with the higher amounts of volatile phenols found on this variety.

Monitoring the Functionality and Stress Response of Yeast Cells Using Flow Cytometry

Throughout fermentation, yeast faces continuously changing medium conditions and reacts by adapting its metabolism. The adaptation is a critical process and is dependent on the accurate functioning of the cell. A stable membrane potential, which is, among other roles, responsible for protecting the yeast from low pH, is an important attribute for evaluating functionality. Other factors are storage products such as glycogen, trehalose, and neutral lipids, as well as mitochondrial activity and the integrity of the DNA. These parameters can be complemented by the analysis of viability, cell cycle, intracellular pH, and reactive oxygen species in the cell. The correlation of all these factors provides valuable information for evaluating the performance of a yeast population during fermentation. In order to demonstrate the analytical capabilities of flow cytometry, a Saccharomyces cerevisiae yeast strain was observed in a modified growth medium for 384 h (16 days). The results confirm observations made with other methods and reports from the literature. However, with flow cytometry, it is possible to gain deeper insight into stress response and adaptation behavior of yeast at a cellular level. The causality from the formation of oxygen-radicals to cell death, for example, can be shown, as well as the dependency of the intracellular pH on the stability of the membrane. The proposed bio-monitoring system has the potential to provide applicable information as a process control tool for wineries.

Yeast-Yeast Interactions: Mechanisms, Methodologies and Impact on Composition

During the winemaking process, alcoholic fermentation is carried out by a consortium of yeasts in which interactions occurs. The consequences of these interactions on the wine matrix have been widely described for several years with the aim of controlling the winemaking process as well as possible. In this review, we highlight the wide diversity of methodologies used to study these interactions, and their underlying mechanisms and consequences on the final wine composition and characteristics. The wide variety of matrix parameters, yeast couples, and culture conditions have led to contradictions between the results of the different studies considered. More recent aspects of modifications in the composition of the matrix are addressed through different approaches that have not been synthesized recently. Non-volatile and volatile metabolomics, as well as sensory analysis approaches are developed in this paper. The description of the matrix composition modification does not appear sufficient to explain interaction mechanisms, making it vital to take an integrated approach to draw definite conclusions on them.

A simple procedure for detecting Dekkera bruxellensis in wine environment by RNA-FISH using a novel probe

Dekkera bruxellensis, considered the major microbial contaminant in wine production, produces 4-ethylphenol, a cause of unpleasant odors. Thus, identification of this yeast before wine spoilage is crucial. Although challenging, it could be achieved using a simple technique: RNA-FISH. To reach it is necessary to design probes that allow specific detection/identification of D. bruxellensis among the wine microorganisms and in the wine environment and, if possible, using low formamide concentrations. Therefore, this study was focused on: a) designing a DNA-FISH probe to identify D. bruxellensis that matches these requirements and b) determining the applicability of the RNA-FISH procedure after the end of the alcoholic fermentation and in wine. A novel DNA-FISH D. bruxellensis probe with good performance and specificity was designed. The application of this probe using an in-suspension RNA-FISH protocol (applying only 5% of formamide) allowed the early detection/identification of D. bruxellensis at low cell densities (5 × 10² cell/mL). This was possible by flow cytometry independently of the growth stage of the target cells, both at the end of the alcoholic fermentation and in wine even in the presence of high S. cerevisiae cell densities. Thus, this study aims to contribute to facilitate the identification of D. bruxellensis before wine spoilage occurs, preventing economic losses to the wine industry.

Influence of Glutathione on Yeast Fermentation Efficiency under Copper Stress

Copper in grape musts can influence the fermentation efficiency of Saccharomyces cerevisiae during winemaking. The present study revealed the impact of glutathione addition on yeast strains with variable copper sensitivity. The antioxidant glutathione increased yeast vitality and fastened sugar metabolism at copper concentrations up to 0.39 mM. A significant accumulation of acetaldehyde at high copper concentrations was mitigated by the addition of 20 mg L^-1 glutathione. Low recovery of glutathione added implicated a complexation of both compounds. Specific alcohol dehydrogenase (ADH) activity was inhibited or reduced in the enzyme extracts of the copper-stressed yeast cells. The activity was restored in fermentations with glutathione at a copper concentration of 0.16 mM. At low copper concentrations, glutathione decreased ADH activity presumably due to complexation of essential copper amounts. Results provide important information on the use of glutathione as an antioxidant in winemaking to counteract negative effects of copper-rich musts on copper-sensitive yeast strains.

Flow Cytometry: Evolution of Microbiological Methods for Probiotics Enumeration

GOALS

The purpose of this trial was to verify that the analytical method ISO 19344:2015 (E)-IDF 232:2015 (E) is valid and reliable for quantifying the concentration of the probiotic Lactobacillus rhamnosus GG (ATCC 53103) in a finished product formulation.

BACKGROUND

Flow cytometry assay is emerging as an alternative rapid method for microbial detection, enumeration, and population profiling. The use of flow cytometry not only permits the determination of viable cell counts but also allows for enumeration of damaged and dead cell subpopulations. Results are expressed as TFU (Total Fluorescent Units) and AFU (Active Fluorescent Units). In December 2015, the International Standard ISO 19344-IDF 232 "Milk and milk products-Starter cultures, probiotics and fermented products-Quantification of lactic acid bacteria by flow cytometry" was published. This particular ISO can be applied universally and regardless of the species of interest.

STUDY

Analytical method validation was conducted on 3 different industrial batches of L. rhamnosus GG according to USP39<1225>/ICH Q2R1 in term of: accuracy, precision (repeatability), intermediate precision (ruggedness), specificity, limit of quantification, linearity, range, robustness.

RESULTS

The data obtained on the 3 batches of finished product have significantly demonstrated the validity and robustness of the cytofluorimetric analysis.

CONCLUSIONS

On the basis of the results obtained, the ISO 19344:2015 (E)-IDF 232:2015 (E) "Quantification of lactic acid bacteria by flow cytometry" can be used for the enumeration of L. rhamnosus GG in a finished product formulation.

Fluorescence microscopy to monitor wine malolactic fermentation

Malolactic fermentation (MLF) is a natural and biological deacidification of wines and a required step for making premium red wines. MLF is carried out by lactic acid bacteria (LAB) that are present in the fermenting wines. Currently, real-time control of MLF is an issue of great interest as the classical plate count technique for assessing bacterial populations requires long incubation times that are not compatible with a tight control of MLF. The aim of this study was to apply fluorescence microscopy and the bacteria staining kit Live/Dead BacLight™ to quantify viable LAB populations in red wines undergoing MLF. This method proved to be a fast and reliable culture-independent method to monitor wine MLF. Moreover, comparison of bacterial population data obtained by fluorescence microscopy and classical plate counts of LAB populations allowed discriminating a population of fully active and culturable cells, from total viable cells that include cells in an intermediate unculturable state.