Search

The sensorial characteristics of the wines produced with Muscat grapes are related to the level of terpene alcohols, so an improvement of such a level is expected as a result of hydrolytic processes conducted by Hanseniaspora. The aim of this work was to select and identify new strains for this purpose. In a second step, the strains were assayed to evaluate their oenological abilities. H. uvarum H107 and H. vineae G26 and P38 were proven to be good candidates to be used in commercial vinification processes to enhance wine properties. Wine inoculated with yeasts showed an increase in the level of aromatic compounds. [ABSTRACT FROM AUTHOR]

Aims: The purification and biochemical properties of the 1,4-β-xylosidase of an oenological yeast were investigated. Methods and Results: An ethanol-tolerant 1,4-β-xylosidase was purified from cultures of a strain of Pichia membranifaciens grown on xylan at 28°C. The enzyme was purified by sequential chromatography on DEAE cellulose and Sephadex G-100. The relative molecular mass of the enzyme was determined to be 50 kDa by SDS-PAGE. The activity of 1,4-β-xylosidase was optimum at pH 6·0 and at 35°C. The activity had a Km of 0·48 ± 0·06 mmol l-1 and a Vmax of 7·4 ± 0·1 μmol min-1 mg-1 protein for p-nitrophenyl-β-d-xylopyranoside. Conclusions: The enzyme characteristics (pH and thermal stability, low inhibition rate by glucose and ethanol tolerance) make this enzyme a good candidate to be used in enzymatic production of xylose and improvement of hemicellulose saccharification for production of bioethanol. Significance and Impact of the Study: This study may be useful for assessing the ability of the 1,4-β-xylosidase from P. membranifaciens to be used in the bioethanol production process. [ABSTRACT FROM AUTHOR]

The article presents a study which analyzed aroma compounds of wines resulting from fermentation of sterile grape musts from Monastrell variety inoculated with pure and mixed cultures of apiculate and Saccharomyces yeasts. Gas chromatography with flame ionization and mass spectrometry were used. The initial presence of apiculate yeasts in fermentations improved the production of some compounds and in general, increased the higher alcohol and acid total amounts.

The capacity of four isolates belonging to the Gibberella fujikuroi complex to produce fumonisin B1 and fumonisin B2 when grown in liquid medium supplemented with one sugar and one amino acid at various concentration levels has been investigated. The sugars used for supplementing the medium were glucose, fructose, rhamnose, sucrose, maltose, and trehalose at 5, 10 or 20 g/l. The amino acids used were serine, threonine, glutamic acid, aspartic acid, valine, isoleucine, methionine, glycine, alanine, and cystine at 1 or 10 g/l. Fumonisins were extracted from culture filtrates, purified by SAX column and determined by reversed-phase C18 HPLC with fluorescence detection of the o-phthaldialdehyde derivatives. Two isolates produced very low concentrations of fumonisins with all sugars. The remaining isolates provided increased contents of fumonisins when sugar level increased. Concerning the amino acids, production of fumonisins was also dependent on the isolate, although at 1 g/l, the production of fumonisins was greater than at 10 g/l. The results indicate that the sugar-amino acid-isolate combination is basic in fumonisin biosynthesis and that the particular behaviour of each isolate in the different nutritional conditions may constitute a piece of interesting information in the fields of the Taxonomy, Physiology and Toxicology of these fungi. This is the first report on the influence of the carbon and nitrogen sources on fumonisin production by isolates of the G. fujikuroi complex.

Various liquid chromatographic methods used in the analysis of mycotoxins (zearalenone, trichothecenes and fumonisins) produced by Fusarium species were compared in this work. The results demonstrate the suitability of modern clean-up procedures employing multifunctional MycoSep and immunoaffinity columns although these methods are more expensive than conventional methodologies for clean-up. HPLC with both fluorescence and photodiode array detection is a suitable technique for the analysis of toxic secondary metabolites produced by Fusarium species; different derivatisation strategies have been studied to improve the sensitivity of the technique because of the low concentration of these metabolites in contaminated food. The utility of the proposed methodology was assessed in cereal cultures of various Fusarium strains.

Toxigenic isolates of Fusarium sporotrichioides were tested for the production of type A trichothecenes (T-2 toxin, HT-2 toxin, diacetoxyscirpenol and neosolaniol) when grown on three substrates (maize, rice and wheat) under various conditions of temperature and water activity in the laboratory for 3 weeks. Trichothecenes were determined by high-performance liquid chromatography with fluorescence detection, after derivatisation with coumarin-3-carbonyl chloride. This is the first time this analytical method has been applied to an extensive study of trichothecene accumulation. With minor exceptions, greater trichothecene production occurred when samples were incubated at 20 degrees C and moistened with 35% water (water activity 0.990) although incubation conditions affected the substrates studied in different ways. No correlation between the different pairs of trichothecenes was found except for neosolaniol and diacetoxyscirpenol (r=0.56). Principal component analysis results show that the data points can be grouped in three rough clusters related to cereal type, which points out that the composition of these cereals can influence the production of type A trichothecenes.

Twenty nine isolates of Fusarium spp. (twenty four of them belonging to the Gibberella fujikuroi complex) isolated from banana and corn from different geographical regions were analyzed for their ability to produce fumonisins B1 and B2 and for genetic relatedness using random amplified polymorphic DNA (RAPD) and restriction analysis of PCR amplification products of the 5.8s ribosomal DNA-intervening internal transcribed spacer regions (ITS I-5.8S-ITS II). For RAPD analysis, six of twenty oligonucleotide primers were selected after testing with five Fusarium spp. isolates and used to characterize 24 additional isolates. DNA fragments from the 29 isolates of Fusarium spp., which were approximately 560 bp, were amplified with the universal primers ITS1 and ITS4. The restriction enzymes HaeIII, MboI, HpaII and MspI were useful for distinguishing the isolates. The RAPD analysis permitted to find interspecific differences among the isolates of Fusarium spp., between isolates with low and high capacity of fumonisin production and among isolates from different hosts. The restriction fragment length polymorphism (RFLP-PCR) analysis permitted to distinguish among different species of Fusarium. In combination with morphological analysis, the results of this research may find an application for the diagnosis of unknown Fusarium spp. and, particularly, for the characterization of fumonisin-producing isolates, which may be very useful in the food technology field.

The glycosides in mono-, di- and trihydroxylated terpene and norisoprenoid alcohols and also those in the related shikimate pathway have been isolated on C18 reversed-phase cartridges and then fractionated into classes of different polarity at increasing percentages of methanol. The benzyl alcohol glycosides are the most polar, while those of terpene monohydroxylated alcohols and geranic acid are the least polar. The terpene diols, linalool furanoid and pyranoid oxides and also norisoprenoid precursors show intermediate polarity and separate into well defined fractions according to their polarity.

Volatile substances of wines obtained by fermentation of musts from 'Monastrell' grapes (Alicante, Spain) was studied for yeast isolated from such musts. The results of the statistical treatment performed show the importance of yeasts of low fermentative power, particularly Kloeckera apiculata, in the production of volatile substances. Saccharomyces cerevisiae var. chevalieri was found to be the most important yeast of high fermentative power.