https://doi.org/10.15255/KUI.2003.025
Published: Kem. Ind. 53 (11) (2004) 505–516
Paper reference number: KUI-25/2003
Paper type: Review
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Glycerol and Wine Industry. Glycerol Determination in Grape Must and Wine

Đ. Šehović, V. Petravić Tominac and V. Marić+

Abstract

Glycerol is the major fermentation by-product of Saccharomyces cerevisiae, which indirectly contributes to the sensory character of wine.1,2 In dry table wines it is found at concentration of 4-10 gL-1 (Table 1) but occasionally may already be present in grape musts infected by moulds (Botrytis cinerea).3,4 The amount of glycerol formed during fermentation is influenced by several factors, such as grape variety, degree of ripeness, fermentation temperature, SO2 concentration, pH of grape must, nitrogen composition, aeration, yeast strain and inoculation level.5 Glycerol is a nonvolatile compound, but bigger glycerol concentration contributes significantly to the sweetness, body and fullness of wines, although a concentration of 25.8 gL-1 has been proposed as a level at which an increase in viscosity can be perceived.6 For these reasons,glycerol production is one of the desirable features during grape must fermentation. Glycerol is also interesting fermentation by-product as a component which should be considered in the selection of wine yeast strains.23 When grape must or juice is inoculated with S. cerevisiae, ethanol is not immediately produced. Normally, fermentation leads to an excess of energy (ATP) within the cell. This condition will activate enzymes (pyruvate decarboxylase/dehydrogenase19) which consequently causes formation of succinate through the TCA cycle and in turn leads to an excess of reduced respiratory nucleotides. As a consequence the excess NADH is formed (Fig. 1) and used in glycerol production as it can be seen from the pathway of glycerol formation (Fig. 2). Microbiological influence in glycerol formation and consumption (degradation) is observed in wines. It is well established that there is a difference in the amount of glycerol production by various yeast strains during fermentation and this is in correlation with different concentration of glycerol-3-phosphate dehydrogenase in different yeasts.21 The strong conversion of glycerol to dihydroxyacetone by acetic acid bacteria is widely reported.24 This may have an important impact to sensory properties of the wine. Certain lactic acid bacteria can metabolize glycerol by dehydration and also influence on quality of wine. To ensure the quality of wine there are some obligatory analitical methods for the determination of relevant wine constituents, but not for glycerol.28 From the literature can be seen that glycerol in wine is possible to determine in a number of ways but until recently the procedure was time consuming. The old method was to separate, purify and actually weigh the glycerol. In chemical determination most widely is used colorimetric method published by Rebelein in year 1956.30 Enzymatic methods for glycerol determination are more specific than chemical ones. Flow injection analysis (FIA) using glycerol dehydrogenase and fluorometric determination appears especially usefull for reliable routine analyses because it is specific for glycerol and provides results that are unaffected by preliminary treatment, especially when the sugar content does not exceed 5 gL-1 (Fig. 3).34 Also chemiluminometric determination of glycerol by means of glycerol dehydrogenase and NADH oxidase is often used (Fig. 4).34 Gas chromatography determination of glycerol can be made by derivatization of glycerol before analysis to get more volatile compound or very successful by direct analysis of diluted wine samples using Chromosorb 101 column.15 Direct analysis of the major organic compounds, including glycerol, in grape must and wine was performed in many articles (Table 2) using anionic- exchange column system (HPLC) and RI/UV detection. HPLC methods have good possibilities for glycerol determination in combination with other wine constituents such as acids and sugars. Simultaneous determination of sugars, acids and glycerol, was made with fully automated sequential injection system with Fourier transform infrared (FT-IR) detection.57 The detection limit of 0.2 mg mL-1 for analysed compounds demonstrates that flow cell-based FT-IR detection is compatible for practical applications in aqueous phase HPLC. A rapid automated method for wine analysis based upon sequential injection (SI)-FT-IR spectrometry were established by K. Schindler and coworkers.68 In comparison with conventional HPLC, the proposed techniques increase the speed of the analysis. The short analysis time together with high reproducibility make the developed method applicable to process control and screening purposes. Average of standard deviation for glycerol was 0.037 gL-1.68 Application of biosensors for glycerol monitoring during fermentation (Fig. 5)65 is based on an enzymatic reaction catalyzed by glycerol dehydrogenase and spectrofluorometric detection.65 Spectrophotometric determination of glycerol in white and red wines was made using glycerol kinase and glycerol-3-phosphate oxidase (Fig. 6) with 1 % accuracy.73 The optimized biosensors and biosensing systems (Table 3) were used for analysis of glycerol, glucose, and ethanol in wine with detection limit of 0.1-1 m mol L-1 82 for glycerol. The main advantage of probe-type biosensor with flow-through sensors is the availability of former for working, both in batch and in continuous approaches, thus making possible their use for in situ measurements.Their performance can also be automated when included in a dynamic manifold. Adulteration of wine by addition of industrial grade glycerol to wine can be detected by GC/MS determination of typical substances added together with industrial glycerol to wine and this are 3-methoxy-propan-1,2-diol (3-MPD), and/or cyclic diglycerols (CycD).85 Added synthetic glycerol to wine can be determined through isotopic pattern of glycerol. Addition of glycerol from animal sources must be studied through the corresponding 2H-pattern.84

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Keywords

wine, glycerol, glycerol determination