Malolactic fermentation (MLF)

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A total of 92 enterococci, isolated from the faeces of minipigs subjected to an in vivo feeding trial, were screened for the production of antimicrobial substances. Bacteriocin production was confirmed for seven strains, of which four were identified as Enterococcus faecalis and three as Enterococcus faecium, on the basis of physiological and biochemical characteristics. The bacteriocins produced by the Ent. faecalis strains showed a narrow spectrum of activity, mainly against other Enterococcus spp., compared with those from the Ent. faecium strains showing a broader spectrum of activity, against indicator strains of Enterococcus spp., Listeria spp., Clostridium spp. and Propionibacterium spp. The bacteriocins of all seven Enterococcus strains were inactivated by alpha-chymotrypsin, proteinase K, trypsin, pronase, pepsin and papain, but not by lipase, lysozyme and catalase. The bacteriocins were heat stable and displayed highest activity at neutral pH. The molecular weight of the bacteriocins, as determined by tricine SDS-PAGE, was approximately 3.4 kDa. Only the strains of Ent. faecalis were found to contain plasmids. PCR detection revealed that the bacteriocins produced by Ent. faecium BFE 1170 and BFE 1228 were similar to enterocin A, whereas those produced by Ent. faecium BFE 1072 displayed homology with enterocin L50A and B.

The atmosphere consists of approximately 21% oxygen (O2). It plays a crucial role in many metabolic and chemical reactions on earth, thus it is of little surprise that it plays a very important role in the winemaking process. Wine can never be completely protected from it. The general use of sulphur dioxide as an anti-oxidant dates back to the early 18th century and the protection of wine from unwanted oxidative spoilage has been recognised . Oxygen can influence the composition and quality of wine drastically, either positively or negatively, and this will be the focus of this review. This review will also focus on the basic steps involved in oxidation, substrates for oxidation in wine and the evolution of wine constituents during the wine production process when in contact with different concentrations of O2. Basic reactions of oxygen in wineOxidation is the process where electron transfer takes place between reductive and oxidative partners. In wine, O 2 is predominantly responsible for this, with it being reduced to certain intermediates and eventually to hydrogen peroxide and then water. Molecular O2 exists as a diradical and is thus in a triplet ground state. This limits the reactivity of O2 and it cannot form bonds by accepting electron pairs. However, the addition of a single electron, originating from reduced transitional metal ions, can overcome this limitation. This leads to an unpaired electron in the resulting negatively-charged superoxide radical, with a second electron transfer resulting in a peroxide anion (Miller et al., 1990;Danilewicz, 2003). This phenomenon results in O2 being involved in various reactions in wine. Substrates for oxidation in winePhenolic molecules originating from grapes can basically be divided into the non-flavonoids and the flavonoids. The nonflavonoids, which are hydroxybenzoic and hydroxycinnamic derivatives, originate from the grape juice, and are normally the principal phenolic molecules in white wines at concentrations ranging from 50-250 mg/L, depending on the cultivar, winemaking techniques, etc. Examples of non-flavonoids are the tartaric esters of caffeic acid, p-coutaric acid and furanic acids. These molecules have been shown to be the main phenolic molecules in white wine that did not receive prolonged periods of skin contact, because they occur at higher concentrations in the grape juice (Margalit, 1997;Monagas et al., 2005).The second main group of grape-derived phenolics is the flavonoids. This group of molecules basically consists of two phenolic rings attached to a pyran ring. The flavanoids have a more complex structure than the non-flavonoids. In a young wine they are normally in a more unpolymerised state, but as wine matures they undergo different polymerisation reactions in which O 2 plays an important role. The most important flavonoids in wine are the anthocyanins, flavanols and flavonols. Anthocyanins occur mainly in the skins of red grape cultivars and are responsible for the colour of red wine. In young red wines their concentrations can range fr...

The pH-neutral cell supernatant of Enterococcus faecalis BFE 1071, isolated from the feces of minipigs in Göttingen, inhibited the growth of Enterococcus spp. and a few other gram-positive bacteria. Ammonium sulfate precipitation and cation-exchange chromatography of the cell supernatant, followed by mass spectrometry analysis, yielded two bacteriocin-like peptides of similar molecular mass: enterocin 1071A (4.285 kDa) and enterocin 1071B (3.899 kDa). Both peptides are always isolated together. The peptides are heat resistant (100°C, 60 min; 50% of activity remained after 15 min at 121°C), remain active after 30 min of incubation at pH 3 to 12, and are sensitive to treatment with proteolytic enzymes. Curing experiments indicated that the genes encoding enterocins 1071A and 1071B are located on a 50-kbp plasmid (pEF1071). Conjugation of plasmid pEF1071 to E. faecalis strains FA2-2 and OGX1 resulted in the expression of two active peptides with sizes identical to those of enterocins 1071A and 1071B. Sequencing of a DNA insert of 9 to 10 kbp revealed two open reading frames, ent1071A and ent1071B, which coded for 39-and 34-amino-acid peptides, respectively. The deduced amino acid sequence of the mature Ent1071A and Ent1071B peptides showed 64 and 61% homology with the ␣ and ␤ peptides of lactococcin G, respectively. This is the first report of two new antimicrobial peptides representative of a fourth type of E. faecalis bacteriocin.Bacteriocins are ribosomally synthesized bacteriostatic or bactericidal proteins and peptides which are produced by a number of gram-positive and gram-negative bacteria. By definition these proteins exhibit a relatively narrow spectrum of antimicrobial activity and are in general active only against bacteria closely related to the producer strain (18). The bacteriocins of lactic acid bacteria were classified by Klaenhammer (18) into four groups. Most of the bacteriocins isolated so far belong to class I or class II. Class I bacteriocins, named lantibiotics, are small (Ͻ5-kDa) membrane-active peptides which contain posttranslationally modified amino acid residues. Nisin is the best-studied lantibiotic (31). Class II bacteriocins are unmodified, heat-stable, low-molecular-mass (Ͻ10-kDa), membrane-active peptides, usually characterized by a G-G-Xaa where Xaa is any amino acid, processing site, in the bacteriocin precursor. The class II bacteriocins are divided into three subgroups; IIa comprises peptides that contain a Y-G-N-G-V-Xaa-C motif near their N termini (Listeria-active peptides), e.g., pediocin PA-1 (22) and sakacin A (12); IIb comprises twopeptide bacteriocins, e.g., lactococcin G (25) and brochocin-C (23); and IIc comprises thiol-activated peptides, which require reduced cysteine residues for activity, e.g., lactococcin B (39).To date, six bacteriocins of Enterococcus faecalis have been described (7,10,17,19,34,35,40), of which only three types have been biochemically and genetically characterized. A hemolysin/bacteriocin, encoded on a 58-kbp conjugative plasmid (pAD1) and origin...

Wine comprises a complex microbial ecology of opportunistic microorganisms, some of which could potentially induce spoilage and result in consequent economic losses under uncontrolled conditions. Yeasts of the genus Brettanomyces, or its teleomorph Dekkera, have been indicated to affect the chemical composition of the must and wine by producing various metabolites that are detrimental to the organoleptic properties of the final product. These yeasts can persist throughout the harsh winemaking process and have in recent years become a major oenological concern worldwide. This literature review summarises the main research focus areas on yeasts of the genera Brettanomyces and Dekkera in wine. Specific attention is given to the spoilage compounds produced, the methods of detection and isolation from the winemaking environment and the factors for controlling and managing Brettanomyces spoilage.

Lactobacillus kunkeei is an inhabitant of fructose-rich niches and is a potential member of the fructophilic lactic acid bacteria. In the present study, the phylogenetic and biochemical characteristics of the type strain and eight isolates of L. kunkeei, originating from wine, flowers and honey, were studied. The nine isolates, including the type strain, formed a well-defined phylogenetic subcluster based on the analysis of 16S rRNA gene sequences. The subcluster was not closely related to other subclusters in the Lactobacillus phylogenetic group. Biochemically, the eight new isolates showed typical fructophilic characteristics. The eight isolates grew poorly on glucose, but grew well on fructose. Good growth on glucose was only recorded in the presence of electron acceptors. The type strain of L. kunkeei differed from the other isolates only on the basis of poor growth on fructose. Although they belong to a group of obligately heterofermentative lactic acid bacteria, all nine isolates, including the type strain, produced almost equimolar amounts of lactic acid and acetic acid and very little ethanol from glucose. Eight of the isolates can thus be regarded as typical 'obligately' fructophilic lactic acid bacteria. Although the type strain of L. kunkeei was phenotypically slightly different from the other isolates, it possessed several important fructophilic characteristics. On the basis of the evidence gathered in this study, the type strain of L. kunkeei is recognized as a member of the 'obligately' fructophilic lactic acid bacteria.