Microbiology of the malolactic fermentation: Molecular aspects

Reactive Carbonyl Species Scavenger: Epigallocatechin-3-Gallate

Epigallocatechin-3-gallate (EGCG), a prominent polyphenol found abundantly in tea, has garnered significant attention for its potential in preventing and ameliorating a wide range of diseases. Its remarkable antioxidant properties and ability to capture reactive carbonyl species make it a key player among tea's polyphenolic components. This paper delves into the synthesis and origins of both EGCG and reactive carbonyl species (RCS), emphasizing the toxicity of RCS in various food sources and their formation during food processing. Understanding EGCG's capability to capture and metabolize RCS is crucial for harnessing its health benefits. Thus, this paper explores the underlying mechanisms of EGCG for RCS inhibition and its role in capturing these compounds to generate EGCG-RCS adducts. And the absorption and metabolism of EGCG-RCS adducts is also discussed.

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.

Lactobacillus plantarum, a New Biological Tool to Control Malolactic Fermentation: A Review and an Outlook

Malolactic fermentation (MLF) in wine is an important step in the vinification of most red and some white wines, as stands for the biological conversion of l-malic acid into l-lactic acid and carbon dioxide, resulting in a decrease in wine acidity. MLF not only results in a biological deacidification, it can exert a significant impact on the organoleptic qualities of wine. This paper reviews the biodiversity of lactic acid bacteria (LAB) in wine, their origin, and the limiting conditions encountered in wine, which allow only the most adapted species and strains to survive and induce malolactic fermentation. Of all the species of wine LAB, Oenococcus oeni is probably the best adapted to overcome the harsh environmental wine conditions and therefore represents the majority of commercial MLF starter cultures. Wine pH is most challenging, but, as a result of global warming, Lactobacillus sp. is more often reported to predominate and be responsible for spontaneous malolactic fermentation. Some Lactobacillus plantarum strains can tolerate the high alcohol and SO2 levels normally encountered in wine. This paper shows the potential within this species for the application as a starter culture for induction of MLF in juice or wine. Due to its complex metabolism, a range of compositional changes can be induced, which may positively affect the quality of the final product. An example of a recent isolate has shown most interesting results, not only for its capacity to induce MLF after direct inoculation, but also for its positive contribution to the wine quality. Degrading hexose sugars by the homo-fermentative pathway, which poses no risk of acetic acid production from the sugars, is an interesting alternative to control MLF in high pH wines. Within this species, we can expect more strains with interesting enological properties.

Expanding the biodiversity of Oenococcus oeni through comparative genomics of apple cider and kombucha strains

BACKGROUND

Oenococcus oeni is a lactic acid bacteria species adapted to the low pH, ethanol-rich environments of wine and cider fermentation, where it performs the crucial role of malolactic fermentation. It has a small genome and has lost the mutS-mutL DNA mismatch repair genes, making it a hypermutable and highly specialized species. Two main lineages of strains, named groups A and B, have been described to date, as well as other subgroups correlated to different types of wines or regions. A third group "C" has also been hypothesized based on sequence analysis, but it remains controversial. In this study we have elucidated the species population structure by sequencing 14 genomes of new strains isolated from cider and kombucha and performing comparative genomics analyses.

RESULTS

Sequence-based phylogenetic trees confirmed a population structure of 4 clades: The previously identified A and B, a third group "C" consisting of the new cider strains and a small subgroup of wine strains previously attributed to group B, and a fourth group "D" exclusively represented by kombucha strains. A pair of complete genomes from group C and D were compared to the circularized O. oeni PSU-1 strain reference genome and no genomic rearrangements were found. Phylogenetic trees, K-means clustering and pangenome gene clusters evidenced the existence of smaller, specialized subgroups of strains. Using the pangenome, genomic differences in stress resistance and biosynthetic pathways were found to uniquely distinguish the C and D clades.

CONCLUSIONS

The obtained results, including the additional cider and kombucha strains, firmly established the O. oeni population structure. Group C does not appear as fully domesticated as group A to wine, but showed several unique patterns which may be due to ongoing specialization to the cider environment. Group D was shown to be the most divergent member of O. oeni to date, appearing as the closest to a pre-domestication state of the species.

Oenococcus oeni in Chilean Red Wines: Technological and Genomic Characterization

The presence and load of species of LAB at the end of the malolactic fermentation (MLF) were investigated in 16 wineries from the different Chilean valleys (Limarí, Casablanca, Maipo, Rapel, and Maule Valleys) during 2012 and 2013, using PCR-RFLP and qPCR. Oenococcus oeni was observed in 80% of the samples collected. Dominance of O. oeni was reflected in the bacterial load (O. oeni/total bacteria) measured by qPCR, corresponding to >85% in most of the samples. A total of 178 LAB isolates were identified after sequencing molecular markers, 95 of them corresponded to O. oeni. Further genetic analyses were performed using MLST (7 genes) including 10 commercial strains; the results indicated that commercial strains were grouped together, while autochthonous strains distributed among different genetic clusters. To pre-select some autochthonous O. oeni, these isolates were also characterized based on technological tests such as ethanol tolerance (12 and 15%), SO₂ resistance (0 and 80 mg l⁻¹), and pH (3.1 and 3.6) and malic acid transformation (1.5 and 4 g l⁻¹). For comparison purposes, commercial strain VP41 was also tested. Based on their technological performance, only 3 isolates were selected for further examination (genome analysis) and they were able to reduce malic acid concentration, to grow at low pH 3.1, 15% ethanol and 80 mg l⁻¹ SO₂. The genome analyses of three selected isolates were examined and compared to PSU-1 and VP41 strains to study their potential contribution to the organoleptic properties of the final product. The presence and homology of genes potentially related to aromatic profile were compared among those strains. The results indicated high conservation of malolactic enzyme (>99%) and the absence of some genes related to odor such as phenolic acid decarboxylase, in autochthonous strains. Genomic analysis also revealed that these strains shared 470 genes with VP41 and PSU-1 and that autochthonous strains harbor an interesting number of unique genes (>21). Altogether these results reveal the presence of local strains distinguishable from commercial strains at the genetic/genomic level and also having genomic traits that enforce their potential use as starter cultures.

Effect of Biofilm Formation by Oenococcus oeni on Malolactic Fermentation and the Release of Aromatic Compounds in Wine

The winemaking process involves the alcoholic fermentation of must, often followed by malolactic fermentation (MLF). The latter, mainly carried out by the lactic acid bacterium Oenococcus oeni, is used to improve wine quality when acidity reduction is required. Moreover, it prevents microbial spoilage and improves the wine’s organoleptic profile. Prior observations showed that O. oeni is able to resist several months in harsh wine conditions when adhered on oak barrels. Since biofilm is a prevailing microbial lifestyle in natural environments, the capacity of O. oeni to form biofilms was investigated on winemaking material such as stainless steel and oak chips. Scanning Electron Microscopy and Confocal Laser Scanning Microscopy showed that O. oeni was able to adhere to these surfaces and form spatially organized microcolonies embedded in extracellular substances. To assess the competitive advantage of this mode of life in wine, the properties of biofilm and planktonic cells were compared after inoculation in a fermented must (pH 3.5 or 3.2 and 12% ethanol) The results indicated that the biofilm culture of O. oeni conferred (i) increased tolerance to wine stress, and (ii) functional performance with effective malolactic activities. Relative gene expression focusing on stress genes and genes involved in EPS synthesis was investigated in a mature biofilm and emphasized the role of the matrix in increased biofilm resistance. As oak is commonly used in wine aging, we focused on the O. oeni biofilm on this material and its contribution to the development of wine color and the release of aromatic compounds. Analytical chromatography was used to target the main oak aging compounds such as vanillin, gaiacol, eugenol, whisky-lactones, and furfural. The results reveal that O. oeni biofilm developed on oak can modulate the wood-wine transfer of volatile aromatic compounds during MLF and aging by decreasing furfural, gaiacol, and eugenol in particular. This work showed that O. oeni forms biofilms consisting of stress-tolerant cells capable of efficient MLF under winemaking conditions. Therefore surface-associated behaviors should be considered in the development of improved strategies for the control of MLF in wine.

Comparative metabolic profiling to investigate the contribution of O. oeni MLF starter cultures to red wine composition

In this research work we investigated changes in volatile aroma composition associated with four commercial Oenococcus oeni malolactic fermentation (MLF) starter cultures in South African Shiraz and Pinotage red wines. A control wine in which MLF was suppressed was included. The MLF progress was monitored by use of infrared spectroscopy. Gas chromatographic analysis and capillary electrophoresis were used to evaluate the volatile aroma composition and organic acid profiles, respectively. Significant strain-specific variations were observed in the degradation of citric acid and production of lactic acid during MLF. Subsequently, compounds directly and indirectly resulting from citric acid metabolism, namely diacetyl, acetic acid, acetoin, and ethyl lactate, were also affected depending on the bacterial strain used for MLF. Bacterial metabolic activity increased concentrations of the higher alcohols, fatty acids, and total esters, with a larger increase in ethyl esters than in acetate esters. Ethyl lactate, diethyl succinate, ethyl octanoate, ethyl 2-methylpropanoate, and ethyl propionate concentrations were increased by MLF. In contrast, levels of hexyl acetate, isoamyl acetate, 2-phenylethyl acetate, and ethyl acetate were reduced or remained unchanged, depending on the strain and cultivar evaluated. Formation of ethyl butyrate, ethyl propionate, ethyl 2-methylbutryate, and ethyl isovalerate was related to specific bacterial strains used, indicating possible differences in esterase activity. A strain-specific tendency to reduce total aldehyde concentrations was found at the completion of MLF, although further investigation is needed in this regard. This study provided insight into metabolism in O. oeni starter cultures during MLF in red wine.

Changes in sour rotten grape berry microbiota during ripening and wine fermentation

This study investigated the microbiota of sour rotten wine grapes and its impact on wine fermentations. Yeasts, lactic acid bacteria (LAB) and acetic acid bacteria (AAB) were enumerated and identified on sound and sour rot grapes during the ripening stage. The alteration of the ecological balance induced by sour rot was particularly evidenced by the unequivocal increase of yeast and AAB counts on rotten grapes, since the beginning of ripening. Yeast and AAB species diversity in rotten grape samples were much higher than those found in sound grapes. LAB populations were low detected from both healthy and sour rotten grapes. The yeast species Issatchenkia occidentalis, Zygoascus hellenicus and Zygosaccharomyces bailii and the AAB species Gluconacetobacter hansenii, Gluconacetobacter intermedius and Acetobacter malorum, were recovered from damaged grapes and resulting grape juices in the winery. Acetobacter orleaniensis and Acetobacter syzygii were only recovered from sour rotten grapes. Dekkera bruxellensis and Oenococcus oeni were only recovered after wine fermentation induced by starter inoculation, irrespective of grape health, probably originating from cellar environment. After malolactic fermentation, racking and sulphur dioxide addition the only remaining species were the yeast Trigonopsis cantarellii and Saccharomyces cerevisiae, independently of the grape health status.

Expression of the malolactic enzyme gene (mle) from Lactobacillus plantarum under winemaking conditions

Malolactic fermentation (MLF) plays an important role in the production of wine, especially red wines, resulting in microbial stability, deacidification, as well as contributing to the aroma profile. MLF can be influenced by a number of factors. In this study, the influence of pH and ethanol on expression of the structural malolactic enzyme gene (mle) from Lactobacillus plantarum was investigated in a synthetic wine media, as well as in wine using quantitative PCR. Expression of mle was shown to be inducible by the presence of malic acid, with increased expression in the middle of MLF. Expression of mle was also shown to be increased at low pH values and decreased in the presence of ethanol. This indicates the role of MLF in acid tolerance and the negative impact of ethanol on the completion of MLF. The results therefore provide further evidence that L. plantarum should be applied as co-inoculation for MLF where alcohol will initially not have a negative impact on the malic acid degradation.

Presence of lactic bacteria in the air of a winery during the vinification period

In this paper we have studied the presence and evolution in the winery air of the lactic bacteria responsible for malolactic fermentation. Sampling took place during the winemaking process (between September 2007 and July 2008) in a winery from the Rioja appellation in Spain. The results obtained indicated that the presence of these microorganisms in the atmosphere was detected when grapes were entering the winery, while malolactic fermentation was taking place, and when liquid containing bacteria was manipulated. The species and clones of the lactic bacteria identified were also related to those present in the vinification tanks at any given stage of the process.

Malolactic fermentation by Streptococcus mutans

Streptococcus mutans and certain other oral lactic-acid bacteria were found to have the ability to carry out malolactic fermentation involving decarboxylation of L-malate to yield L-lactic acid and concomitant reduction in acidity. The activity was inducible by L-malate in S. mutans UA159 growing in suspensions or biofilms. The optimal pH for the fermentation was c. 4.0 for both suspensions and biofilms, although the pH optimum for malolactic enzyme in permeabilized cells of S. mutans UA159 was close to 5.5. Although malate did not serve as a catabolite for growth of S. mutans, it did serve to protect the organism against acid killing and to maintain ATP pool levels during starvation. Alkalinization associated with malolactic fermentation resulted in pH rise or increased need to add standardized HCl solution to maintain a set pH value in pH-stat experiments. The net conclusion is that malate has the potential to be effective for alkalinization of dental plaque, although the fermentation is sensitive to fluoride and triclosan, which are commonly added to oral care products.

Use of lemon extract to inhibit the growth of malolactic bacteria

The potential use of lemon extract as a natural preservative to inhibit the growth of Oenococcus oeni and Lactobacillus plantarum, microorganisms involved in the malotactic fermentation of wine, was studied. Growth tests were run at 30 degrees C using laboratory media. Carbon dioxide concentration in the vial headspace was used as metabolic activity index of the investigated microorganisms. The MIC and the noninhibiting concentration (NIC) were calculated for each microorganism. Results suggest that lemon extract was active on each phase of the growth cycle for the tested microorganisms. It was also shown that lemon extract exhibits a nonlinear dose-related inhibitory effect on microbial growth. In particular, the active compound could be added at concentrations slightly higher than the NIC levels in order to appreciably slow down the microbial growth rate as well as to reduce the maximum microbial growth level.

Environmental stress response in wine lactic acid bacteria: beyond Bacillus subtilis

Lactic acid bacteria (LAB) constitute a heterogeneous group of bacteria that are traditionally used to produce fermented foods. The industrialization of food transformations has increased the economical importance of LAB, as they play a crucial role in the development of the organoleptic and hygienic quality of fermented products. However, the strains selected for industrial purposes, should tolerate adverse conditions encountered in industrial processes, either during starter handling and storage (freeze-drying, freezing, or spray-drying) or during food processing in which abiotic stresses such as heat, cold, acidity, and high concentration of NaCl or ethanol are common. Wine LAB have to deal with several stresses including an acidic pH, a high alcoholic content, non optimal growth temperatures, and growth-inhibitory compounds such as fatty acids and tannins, originated from yeast and bacteria metabolism. Wine LAB have developed several mechanisms to escape or to tolerate wine conditions. They carry out a malolactic fermentation in this stressful environment. In addition to the regulation of the expression of specific genes, bacteria have evolved adaptive networks to face the challenges of a changing environment and to survive under conditions of stress. The so called Global Regulatory Systems control the simultaneous expression of a large number of genes in response to a variety of environmental stress factors. CIRCE sequences able to bind the HrcA repressor, sigma(B) dependent promoters and CtsR regulatory elements have been observed in several genes identified from wine LAB. Improved knowledge of regulators and a better understanding of LAB stress responses could constitute a basis of comparison with the well known model microorganisms, Escherichia coli and Bacillus subtilis. Moreover, it can provide an important insight into improving current industrial starter strains.

Evolution of malolactic bacteria and biogenic amines during spontaneous malolactic fermentations in a Greek winery

AIMS

To study the population dynamics of indigenous malolactic bacteria in a Greek winery and to examine their potential to produce detrimental levels of biogenic amines (BA) under winemaking conditions.

METHODS AND RESULTS

Although the wines studied were of different vintage, grape variety and enological characteristics, molecular typing of malolactic bacteria revealed only a low number of strains within the single-species populations of Oenococcus oeni that developed during spontaneous fermentations. Strain MF1, originating primarily from the vineyards surrounding the winery invariably predominated in almost all samples. HPLC analysis showed a slight increase in the BA, putrescine, tyramine and phenylethylamine after malolactic conversion, while histamine, methylamine and ethylamine remained unaffected. No correlation could be established between the BA profiles and the bacterial compositions or the amino acid concentrations in wine samples studied.

CONCLUSIONS

A certain regional bacterial flora is established in the winery that prevails in spontaneous malolactic fermentations (MLF) irrespective of the wine characteristics. In all cases, the BA content of the wines after malolactic conversion was within enologically acceptable levels.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first report on the malolactic bacteria occurring naturally in spontaneous MLF in Greek red wines and a preliminary assessment of their impact on wine safety in relation to BA.

Metabolic engineering of malolactic wine yeast

Malolactic fermentation is essential for the deacidification of high acid grape must. We have constructed a genetically stable industrial strain of Saccharomyces cerevisiae by integrating a linear cassette containing the Schizosaccharomyces pombe malate permease gene (mae1) and the Oenococcus oeni malolactic gene (mleA) under control of the S. cerevisiae PGK1 promoter and terminator sequences into the URA3 locus of an industrial wine yeast. The malolactic yeast strain, ML01, fully decarboxylated 5.5 g/l of malate in Chardonnay grape must during the alcoholic fermentation. Analysis of the phenotype, genotype, transcriptome, and proteome revealed that the ML01 yeast is substantially equivalent to the parental industrial wine yeast. The ML01 yeast enjoys 'Generally Regarded As Safe' status from the FDA and is the first genetically enhanced yeast that has been commercialized. Its application will prevent the formation of noxious biogenic amines produced by lactic acid bacteria in wine.

Lactic acid bacteria associated with wine grapes from several Australian vineyards

AIMS

The detection and isolation of lactic acid bacteria by enrichment methods from wine grapes cultivated in vineyards located in New South Wales, Australia.

METHODS AND RESULTS

Enrichment cultures in de Man, Rogosa and Sharpe (MRS) broth, MRS + ethanol (5%), MRS broth supplemented with 15% (v/v) tomato juice (MRST), pH 5.5 and 3.5 and autoenrichment in grape juice homogenate were used to detect lactic acid bacteria on wine grapes. Bacteria were isolated from enrichment cultures by plating onto MRS and MRST agar and identified by 16S rDNA sequence analysis and phenotypical methods. A molecular method, PCR-denaturing gradient gel electrophoresis (DGGE) was also used to examine the bacteria that developed in enrichment cultures. Species of Lactobacillus, Enterococcus, Lactococcus and Weissella were detected in enrichments by plating and PCR-DGGE. Other bacteria (Sporolactobacillus, Asaia, Bacillus ssp.) were also found in some enrichment cultures. The principal malolactic bacterium, Oenococcus oeni, was not isolated.

CONCLUSIONS

The incidence and populations of lactic acid bacteria on wine grapes were very low. Damaged grape berries showed a greater presence of these bacteria than undamaged berries. The diversity of bacterial species isolated from the grapes was greater than those previously reported and represented both lactic acid bacteria and nonlactic acid bacteria. Some of these bacteria (i.e. Lactobacillus lindneri, Lactobacillus kunkeei) could be detrimental to wine production. Oenococcus oeni was not found on grapes, but its recovery could be obscured by overgrowth from other species.

SIGNIFICANCE AND IMPACT OF THE STUDY

Lactic acid bacteria are significant in wine production because they conduct the malolactic fermentation and cause stuck or sluggish alcoholic fermentation and wine spoilage. This study investigates wine grapes as a potential source of these bacteria.

Winemaking Biochemistry and Microbiology: Current Knowledge and Future Trends

The fermentation of grape must and the production of premium quality wines are a complex biochemical process that involves the interactions of enzymes from many different microbial species, but mainly yeasts and lactic acid bacteria. Yeasts are predominant in wine and carry out the alcoholic fermentation, while lactic acid bacteria are responsible for malolactic fermentation. Moreover, several optional winemaking techniques involve the use of technical enzyme preparations. Considerable progress has been made recently in understanding the biochemistry and interactions of enzymes during the winemaking process. In this study, some of these recent contributions in the biochemistry of winemaking are reviewed. This article intends to provide an updated overview (including works published until December, 2003) on the main biochemical and microbiological contributions of the different techniques that can be used in winemaking. As well as considering the transformations that take place in traditional winemaking, the production of special wines, such as sparkling wines, 'sur lie' wines, and biologically aged wines, are also studied.

Nucleotide sequence analysis of pRS2 and pRS3, two small cryptic plasmids from Oenococcus oeni

Nucleotide sequence analysis of two cryptic plasmids, pRS2 (2544 bp) and pRS3 (3948 bp), from Oenococcus oeni revealed the presence in both of three major open reading frames with significant similarity to other small cryptic plasmids from O. oeni. The results suggest that those plasmids could be separated into two subfamilies, one represented by pLo13 and pRS3, the other represented by pOg32, pRS1, and pRS2.

Biogenic amines in wines: role of lactic acid bacteria

Biogenic amines have undesirable physiological effects when absorbed at too high a concentration. Several kinds of food and beverages contain biogenic amines. Lactic acid bacteria can decarboxylate amino acids. Since winemaking involves the growth of lactic acid bacteria for malolactic fermentation, biogenic amines may occur. However, not all bacterial strains carry these activities. In the same wine-producing area, some wines may contain very low amounts of biogenic amines while others may have relatively large quantities. It is now possible to detect the presence of undesirable histamine-producing strains by PCR test or DNA probe based on the presence of the gene encoding histidine decarboxylase. Other strains have the ornithine and/or tyrosine decarboxylase. When biogenic amine-producing strains are present, the winemaker is encouraged to inoculate selected malolactic starters to replace the indigenous microflora.

Kinetics, stereospecificity, and expression of the malolactic enzyme

Mass spectrometric measurement of carbon dioxide production was used to study malolactic fermentation (MLF) in Lactobacillus collinoides isolated from cider. The kinetics and stereospecificity of the malolactic enzyme (MLE) were studied, and the stoichiometry of the reaction sequence was investigated. The optimum pH for activity of the MLE was 4.9. MLF was more rapid (in both intact cells and cell extracts) when L-malic acid was used than when D-malic acid or the racemic mixture was added. The enzyme was found to be constitutively present in L. collinoides. Addition of L-malic acid (37 mM) to the growth medium resulted in increased MLE activity; addition of the D isomer alone or the racemic mixture resulted in lower activities. Addition of the main sugars in apple juice (fructose, sucrose, and glucose) to the growth medium in the presence of malic acid repressed production of MLE to similar extents in all three cases; in the absence of malic acid, instead of inhibiting MLF, addition of sugars to the growth medium somewhat increased the residual MLE activity.

Presence and analysis of large plasmids in Oenococcus oeni

The use of a large-scale isolation technique to screen 30 Oenococcus oeni strains for extrachromosomal DNA led to the finding of large plasmids (ca. 40 kb) in most of the strains as well as the finding of small plasmids (2.5 to 4.5 kb) in 6 of the strains. The circular nature of the large plasmids was assessed by electrophoresis in ethidium bromide continuous gradient gels and the different conformations of these elements could be distinguished by three run types of pulsed-field gel electrophoresis (PFGE). Southern hybridization with PFG-electrophoresed DNA also suggested that the low extraction yields of these probably low-copy-number plasmids could be related to the generation of the OC conformation resulting from nicking during cell lysis. The results seem to indicate that the occurrence of large plasmids in O. oeni may be more frequent than is usually considered, although their presence is difficult to ascertain. Furthermore, spontaneous curing of these elements might occur. In fact, plasmid pOg25 (37 kb) was eventually not detected by DNA-DNA hybridization in its original host strain.