Procedure to Reduce Sulphite in Wine with Anion-exchange Resin

HORÁK, M., HÍC, P., TOMÁNKOVÁ, E., BALÍK, J.: Procedure to reduce sulphite in wine with anion-exchange resin. Acta univ. agric. et silvic. Mendel. Brun., 2012, LX, No. 8, pp. 79–86 The aim of this experiment was to eliminate SO2 ions present in wine using the anion-exchanger resins. To compare the eff ectiveness, 2 following strongly basic anion-exchange resin were used. When activated, the sodium bicarbonate solution (activation solution I) is used to prevent parallel reduction of sulphites, tartates and malates, so the anion-exchange resins were activated in two-step activation. In the second step, it was immersed into a mixture of malic acid and tartaric acid (1:1). A er the application of anex into wine, the content of total SO2 was reduced to 97–201 mg.L −1 (depending on the amount of anex added into the wine sample). According to our expectations, the variants with anion-exchange resin activated only with bicarbonate solution, the tartrates and malates were signifi cantly reduced. If the anion-exchange resin was activated with a two-steps activation, the tartaric acid and malic acid were reduced in the range of ± 0.13 g.L−1. This phenomenon was strongly refl ected at the anion-exchanger Aqua Osmotic 02. The changes in antioxidant content were not aff ected by the type of anion-exchange resin, the method of activation, or an amount of used anion-exchanger. The color parameters of wine, expressed by the L * a * b *, were not signifi cantly aff ected by the eff ects of anion-exchange resin use. sulphites, sulfur dioxide, anion exchanger, wine Sulphur dioxide plays an important role in the wine-making technology. To eliminate changes caused by oxidative processes and an eventual refermentation of wine, it is necessary to stabilise it with some preservative preparations. Sulphur dioxide is one of them because it is capable to bind labile oxygen molecules dissolved in the solution; this means that it shows a reductive action and prevents the occurrence of both enzymatic and non-ezymatic oxidation (FARKAŠ, 1983; STEIDL, 2002). Therefore it acts as an antioxidant in wine (RIBÉREAU-GAYON et al., 2000). In wine, sulphur dioxide not only plays an reductive role but it also inhibits activities of yeasts (above all of those that are not able to synthetisize thiamin, which is split by SO2 to ineffi cient compounds), bacteria and other microorganisms (VELÍŠEK, 2002). In wine, SO2 can be present in two forms, viz. as free and bound sulphur. In wine, sulphurous acid (H2SO3) originates from a reaction of sulphur dioxide with water. Under the eff ect of wine pH, sulphurous acid is dissociated to sulphurous (SO3 2−) and hydrogen sulphurous (HSO3 −) ions, which then represent the free form of SO2 in wine. In an acid environment (i.e. with pH 3–4), hydrogen sulphites are predominating (TOIT et al., 2005). The remaining SO2 is bound to acetaldehyde, pyruvic acid, ketoglutaric acid, sugars, quinone, anthocyanins and other compounds (STEIDL, 2002; VELÍŠEK, 2002; OUGH, AMERINE, 1988). However, an antiseptic eff ect shows only a part of free SO2 and this is usually denoted as “active sulphur dioxide“ (FARKAŠ, 1983). When applying SO2 to wine it is necessary to count with a certain amount of SO2 which is produced by yeast during the fermentation, this amount does not usually exceed the value of 10 mg.L−1 (RIBÉREAUGAYON et al., 2000). If the amount of SO2 applied to wine during the fermentation is too high, it can lead to the suppression or discontinuation of fermentation and subsequently to wine fl avor deterioration, or to the allergy symptoms in sensitive people (AGARD et al., 1998). 80 M. Horák, P. Híc, E. Tománková, J. Balík Sulphites, as allergenic compounds, are subjected to hygienic control and must be declared on the label only in case that their concentration in the product exceeds the level of 10 mg.L−1. In the Czech Republic, the content of total SO2 in wine is specifi ed in the Council Regulation (EC) No. 479/2008 and the Commission Regulation (EC) No. 606/2009. In white and rosé wines, the admissible maximum is 200 mg.L−1 while in red quality and cabinet wines with the content of residual sugar up to 5 g.l−1, the approved maximum is 150 mg.L−1. As far as other kinds of wine are concerned, the maximum admissible limits of SO2 are defi ned in special regulations. In practice, it can sometimes happen that this allowed limit is exceeded. In such a case, thre are several methods how to remove the excessive SO2 from wine. The simplest method is to mix the over-sulphurised wine with another that does not contain SO2 (or only a low level of this compound). The bubbling of over-sulphurised wine with gaseous oxygen can release a part of SO2 into the atmosphere; this treatement, however, is associated with a risk of occurrence of negative oxidative processes. This method, however, enables to remove free SO2 and only a minimum amount of its bound form. Another method of removal of sulphites from wine represents the vacuum heating of wine in a special apparatus so that the excessive SO2 is volatilised. In this case, however, there is a risk of the loss of aromatic compounds and of ethanol (FARKAŠ, 1983). The application of resins used in the food industry represents another possibility how to decrease the content of excessive SO2 in wine. As mentioned above, the anex is an anion-exchange resin. This high-molecular-weight substance is a polymer showing a suffi cient porosity and most frequently is based on styrenes, polyacrylates, phenolformaldehyde resins etc. The basic anex skeleton bears functional (charged) groups that can be dissociated in aqueous medium (MARHOL, 1976). Anions remaining in the solution must be balanced with those that are released from it. In case that the amount of anex is exhausted, it can be regenerated by means of adding the solution of another anion (JELÍNEK et al., 2009). However, when applying the aforementioned resins into wine, not only a decrease in the content of sulphites but also of acids and other qualitative components of wine can take place. The ratio of reduced anions is infl uenced above all by their concentration in wine and by their affi nity to the applied resin (HÜBNER et al., 2006). MATERIAL AND METHODS Preparation of anion-exchange resin The capacity to decrease the content of total SO2 was studied with two resins that are normally used in the food industry. The fi rst one was a strongly basic anion-exchange resin IMAC HP555 with quartenary ammonium groups; the divinylbenzene and styrene copolymers of this resin were of the type I (hereina er mentioned only as HP555) while the second one was a part of the fi ll of the anionexchanger Aqua Osmotic 02 that is used for making of demineralised water by means of the system catex-anex (hereina er mentioned only as Aqua Osmotic 02). Resins were acitivated in a two-step system. Before activating anion exchangers were washed 3 times with distilled water. In the fi rst step, resins were activated by means of immersion into a 10-percent sodium bicarbonate solution (the activation solution I) for a period of 24 hours. Therea er, they were carefully rinsed with distilled water untill the moment when pH of the mixture of anex and disitlled water reached the value 7.0. In the second step, it was immersed into the activation solution II for a period of another 24 hours. The activation solution II was a mixture of malic acid and tartaric acid (1:1); the total concentration of both acids in the solution was 50 g.L−1. In the fi nal stage of the activation process, resins were immersed into distilled water so that the residues of the activation solution II could be washed away from the anex surface. The last rinsing was performed only once because we did not want to wash away those anions of both acids that were bound on the anexfunctional groups. To be able to carry out a mutual comparison of results, anexes activated in the same manner were used (i.e. by means of their immersion into a 10-percent solution of sodium bicarbonate for a period of 24 hours. Each sample anion exchange resin was investigated in 3 repetitions, each sample analysis was performed 3 times.