No abstract

The winemaking sector needs to ensure the microbiological quality of its products to guarantee acceptance and wide commercialization. There are treatments such as high pressure homogenization (HPH) that, apparently, do not affect the final nutritional and sensory food properties. This study is presented to evaluate possibilities of utilizing HPH treatments to reduce the indigenous flora accompanying wine musts, as well as their effects on the fermentative process, oenological parameters, color, aroma, and taste properties. Two different must varieties were used: a white must (Parellada variety) and a red one (Trepat variety). Results showed that the use of HPH at 200 MPa is capable of reducing the microbial load of musts. Residual populations of total bacteria were detected, but neither fungi, nor yeasts, nor lactic acid bacteria were detected after the treatment in either musts. Furthermore, as a result of the decrease of the wild microbiota of the musts, the implantation of the selected yeast for alcoholic fermentation was improved. Sensory assessments of the must and wines showed that there were no significant changes caused by the treatment.

Yeast strains collected from three spontaneous laboratory sourdoughs, prepared over 10 days and using a traditional Spanish protocol, and formulated with (non-essential) different ingredients were identified and described. In addition to wheat flour (Triticum aestivum) and water, organic apples (5 days juice fermented at 40°C), or plain yogurt, or organic white grapes (2 days must fermented at 20°C) were used at the beginning of each sourdough production. One-hundred-eighteen yeast colonies were collected from the different phases of sourdoughs (ingredients preparation, pre-sourdough, and ripe sourdough propagation) using WL agar and Lysine agar media. Yeast isolates were clustered into 8 groups using PCR-RFLP analysis of the 5.8S-ITS rRNA region. One strain of each group was chosen for sequencing to confirm yeast identification at species level. The specifically prepared fruit ingredients, apple and grape, provided diversity of non-Saccharomyces yeast to the respective sourdoughs. The dominant species in the pre-sourdough phase were Meyerozyma guilliermondii for apple sourdough and Hanseniaspora uvarum for grape sourdough. For yogurt sourdough, Saccharomyces cerevisiae was already the dominant yeast in the pre-sourdough phase with a low proportion of Meyerozyma guilliermondii and Wickerhamomyces anomalus. In the three sourdoughs, regardless of the different ingredients used, Saccharomyces cerevisiae was the dominant yeast in the ripe phase.

Ethyl carbamate (EC) is a carcinogenic compound found in fermented food and beverages such as wine. Although its carcinogenic potential in animals is known, information regarding its effects in humans remains insufficient, thus there is increasing interest in its research. EC content is higher in products with high alcohol content and in aged products. The main precursor involved in EC production in wine is urea, which is produced by metabolism of arginine by yeast, but there is also evidence that EC levels can increase after malolactic fermentation (MLF). Some lactic acid bacteria (LAB) can degrade the arginine present in must and wine via the arginine deiminase pathway, producing citrulline and carbamyl phosphate. Both compounds can react with ethanol in acidic conditions and produce EC. Our research group is studying the influence of MLF induced at different points of wine-making on the quality of the resulting wine. Among other parameters, the content of toxic compounds such as EC was evaluated. Results so far indicate that EC levels at the end of MLF were quite low (less than 3 μg/l) in all cases, i.e. below the existing legal limit (e.g. 30 μg/l in Canada). In almost all wines, EC concentrations increased after 8 months of storage as has been described by other authors. In some of the wines in which MLF was carried out by selected LAB, the increase in EC concentration was lower.

The sensory deterioration of wine caused by the formation of volatile phenols (4-ethylphenol and 4-ethylguaiacol) due to the growth of the spoilage yeast Brettanomyces during the winemaking process can cause serious financial loss and problems in export trade barriers. The presence of this microorganism is increasingly common in cellars. Fast, specific and early detection of this yeast during wine production enables the oenologist and producer to take preventive measures before the phenolic aspect appears. Several methods are available for the detection of this yeast species. A new, quick and easy-touse kit based on RT-PCR to detect Brettanomyces has appeared recently on the market. To evaluate the prevalence of this microorganism in our country and the effectiveness of this new technique, we analysed 86 red wines produced and marketed in Spain (commercialised wines or just before being bottled). We compared the results with those obtained with traditional microbial counting on selective medium and with another molecular method based on the amplification of the internal transcribed spacers (ITS1 and ITS2) of the rRNA 5.8S. Fifteen samples (17.4%) were positive for the presence of B. bruxellensis by microbiological plate counting after 5-7 days of incubation and 14 (16.3%) also gave positive results with RT-PCR analysis, after only 7 h. Of 86 wines analysed, 16 (18.6%) were positive with at least one of the methods used.