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Exopolysaccharide production by lactic acid bacteria is beneficial in the dairy and oat-based food industries and is used to improve the texture of the fermented products. However, β-D-glucan–producing bacteria are considered spoilage microorganisms in alcoholic beverages because their secreted exopolysaccharides alter the viscosity of cider, wine, and beer, rendering them unpalatable. The plasmidic glycosyltransferase (gtf) gene of the Pediococcus parvulus 2.6 strain isolated from ropy cider has been cloned and sequenced, and its GTF product was functionally expressed in Streptococcus pneumoniae. The GTF protein, which has glycosyltransferase activity, belongs to the COG1215 membrane-bound glycosyltransferase family, and agglutination tests revealed that the enzyme enables S. pneumoniae to synthesize β-D-glucan. PCR amplification and Southern blot hybridization showed that the gtf gene is also present at different genomic locations in the β-d-glucan producers Lacto-bacillus diolivorans G77 and Oenococcus oeni I4 strains, also isolated from ropy cider. A PCR assay has been developed for the detection of exopolysaccharide-producing bacteria. Forward and reverse primers, included respectively in the coding sequences of the putative glycosyltransferase domain and the fifth trans-membrane segment of the GTF, were designed. Analysis of 76 ropy and nonropy lactic acid bacteria validated the method for specific detection of β-d-glucan homopolysaccharide producer Pediococcus, Lactobacillus, and Oenococcus strains. The limit of the assay in cider was 3 × 102 CFU/ml. This molecular method can be useful for the detection of ropy bacteria in cider before spoilage occurs, as well as for isolation of new exopolysaccharide-producing strains of industrial interest.

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Aims:  To study the influence of medium constituents on growth, and exopolysaccharide (EPS) production by a strain of Oenococcus oeni. The structure of one of the EPSs has also been characterized. Methods and Results:  EPS concentration was estimated by the phenol/sulfuric acid method. After purification and fractionation of crude EPSs, the sugar composition was determined by GLC‐MS of the TMS methyl glycosides. The major polysaccharide is 2‐substituted‐(1–3)‐β‐d‐glucan. This structure was determined by methylation analysis and conventional 1H‐ and 13C‐nuclear magnetic resonance spectroscopy. In addition, O. oeni synthesized two heteropolysaccharides, although a lesser proportion, constituted by galactose and glucose, and one of them also showed rhamnose. The sugar source has a clear influence on growth and EPS synthesis, and EPS production was not enhanced by adding ethanol or increasing the nitrogen source. EPS biosynthesis starts in the exponential growth phase, and continued during the stationary growth phase. Conclusions:  Higher EPS yields were obtained on cultures grown on glucose + fructose. O. oeni produces a β‐glucan, as the predominant EPS, and it is also able to produce two heteropolysaccharides. Significance and Impact of the Study:  This work provides a better understanding of EPS synthesis by O. oeni and shows the first EPS structure described for this species.

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The aim of this study was to evaluate the influence of two factors -pressing (with either a traditional or a pneumatic press) and vat material (stainless steel and chestnut wood) -on the global parameters and volatile and acidic compounds of ciders throughout their fermentation in relation to micro-organism levels. A complete factorial design with two factors was applied and the samples were taken at five stages of cider fermentation. In each stage, 21 parameters were measured by standard methods, HPLC, GC, and enzymatic and microbiological techniques. Analysis of variance investigated the effect of pressing, vat types and replication of the measures on analytical and microbiological composition of the ciders. The results obtained for the different parameters indicated that the pneumatically pressed cider, fermented in a stainless steel vat, developed alcoholic and malolactic fermentations more slowly, and the decrease in phenolic compounds was also slower than it was for the traditionally pressed cider fermented in a wooden barrel. These differences influenced the composition of the cider.