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Opis: Conventionally, alcoholic fermentation in the production of wine is performed by yeast species Saccharomyces cerevisiae. There are numerous starters available, however due to the growing demand for wines with specific characteristics, other Saccharomyces and non-Saccharomyces species are being investigated for potential use as starters. [1]. Yeast selection has involved the development of techniques for detecting strains that might improve wines in terms of aroma, structure, colour and other technological properties [2]. Colour of the wine can be affected as some metabolites produced by yeast during fermentation may react with grape anthocyanins to produce highly stable pyranoanthocyanins. For the facilitation of formation of vinylphenolic pyranoanthocyanins, yeast strains with high hydroxycinnamate decarboxylase activity are used (HCDC). The mechanism of reaction is decarboxylation of hydroxycinnamic acids and formation of vinylphenols that condense with grape anthocyanins and form stabile vinyphenolic pyranoanthocyanin adducts [3]. It has been demonstrated that some non-Saccharomyces strains (Pichia guillermondii, Schizosaccharomyces pombe) have positive HCDC activity and they can produce vinylphenolic pyranoanthocyanins in higher concentrations than S. cerevisiae. A simple way of determining whether the yeast strain has HCDC activity or not, is the use of fermentation media with the addition of hydroxycinnamic acids, such as p-coumaric acid. The degradation of p-coumaric acid and transformation into 4-vinylphenol (and possibly in 4-ethylphenol) can be checked by LC-DAD. Most of the published data has been done on smaller number of strains. The goal of our work was to develop simple method for the screening of Slovenian in-house yeast collection, comprising of native isolates that mostly originated from Vipava valley and Karst region, and therefore try to determine strains with high HCDC activity. These strains can be used for wine fermentations in order to produce more stable pyranoanthocyanins; which is especially important in wines that has less anthocyanin concentration already from the grape, such as Pinot Noir. 103 different yeast strains belonging to 28 species were selected for the assessment of HCDC activity. In some cases the difference in p-coumaric acid metabolism rate between two strains exceeded 90%. All tested S. paradoxus strains showed higher than 40% degradation rate of p-coumaric acid. HCDC activity of S. cerevisiae strains which is the species most commonly used in fermentation, varied between 5.1 and 66.1%. The commercial strains tested, FPC and EC118 showed 43.9 and 21.5% conversion rate, respectively. It was observed that some native strains had higher HCDC activity than commercial tested ones. Three strains produced vinylphenol in concentration higher than 50 ppm, two of them being P. guillermondii and another strain being S. paradoxus (Sut85). In general strain with high HCDC activity also produced high concentration of 4-vinylphenol. The results showed that HCDC activity is highly strain dependent, which correlates with the literature data available. The proposed method is very simple and does not require special sample preparation prior to HPLC analysis. Furthermore, the proposed fermentations in deep-well microtiter plates allow the screening of high number of strains. The method could be used for routine screening, to determine which strain has high HCDC activity and produces high concentration of vinylphenols and can therefore be used in future for determination of strains ability to synthesize vinylphenolic pyranoanthocyanins.
Najdeno v: osebi
Ključne besede: yeast, hydroxycinnamate decarboxylase, 4-vinylphenol
Objavljeno: 18.06.2018; Ogledov: 2816; Prenosov: 0
Polno besedilo (4,46 MB)

Najdeno v: osebi
Ključne besede: yeast, Saccharomyces, non-Saccharomyces, wine colour, pyranoanthocyanins
Objavljeno: 20.12.2019; Ogledov: 2161; Prenosov: 0
Polno besedilo (1,01 MB)

Opis: This work focuses on assessing the analytical capabilities of a new photothermal lens method based on the self-mixing effect to reliably measure metallic traces in water-ethanol solutions. We compare it with the conventional thermal lens scheme, considering the low detection limit and versatility. A theoretical model is presented to describe the laser power variations as a function of the photothermal parameters of the analyzed sample. The experimental results demonstrate that the laser intensity variations, induced by the external optical feedback, are governed by the photothermal lens effect. Measurements of Fe(II)-1,10-phenanthroline in water–ethanol solutions show a favourable correspondence and agreement with the theory. The low detection limits obtained by the two analytic techniques also agree very well. Nevertheless, our instrument presents advantages regarding compactness and simplicity, suggesting that this platform could be potentially useful as a robust analytical tool for metallic trace detection. In addition, calibration of the method is performed by measuring the so-called self-mixing constant.
Najdeno v: osebi
Ključne besede: thermal lens, photothermal spectroscopy, self-mixing effect, trace detection
Objavljeno: 05.04.2019; Ogledov: 2158; Prenosov: 0
Polno besedilo (715,09 KB)

Najdeno v: osebi
Ključne besede: thermal lens spectrometry, nanobodies, fluobodies, cyanobacteria
Objavljeno: 18.11.2019; Ogledov: 2357; Prenosov: 92
Polno besedilo (15,09 KB)

Opis: Biogenic amines are naturally occurring compounds that have been reported in variety of food, such as fish, meat, cheese, vegetables, and wines. When biogenic amines are formed by microorganisms such as lactic acid bacteria (LAB) they may have adverse effect on human health. The most common biogenic amines found in foodstuff are histamine, tyramine, putrescine and cadaverine. LAB are used as starters in the production of several foods and beverages. In wines they are used in malolactic fermentation, where the conversion of malic acid to lactic acid occurs. The aim of this work was to determine biogenic amine-forming capacity of indigenous LAB strains isolated from grapes which were PCR positive and screening medium positive for biogenic amines. Three methods for the confirmation of LAB biogenic amine-forming potential were developed and compared: HPLC-DAD and TLC methods both using derivatization agent dansyl chloride and enzymatic method using horseradish peroxidase (HRP) and diamine oxidase (DAO) enzymes. The applicability of methods was tested on the three known biogenic amine-producing LAB strains: 0006, 9809, 9906 (IOEB, France). The limit of detection (LOD) of the methods was <1 mg/L for HPLC-DAD, 5 mg/L for TLC and 25 mg/L for enzymatic method. Although the LODs between the proposed methods differed, all of the three methods confirmed BA-forming potential of the three strains. Furthermore, the proposed methods were applied for the analysis of three indigenous strains: MKBT-282 (BA+), MKBT-307 (BA-) and MKBT-325 (BA+). The positive or negative BA-forming potential was confirmed with all of the three proposed methods.
Najdeno v: osebi
Ključne besede: lactic acid bacteria, biogenic amines, histamine, grape
Objavljeno: 10.07.2020; Ogledov: 1558; Prenosov: 0
Polno besedilo (225,99 KB)