Utjecaj lakaze i polivinilpirolidonana kvalitetu i fenolni sastav vina Laški rizling | Influence of laccase and polyvinylpyrrolidoneon the quality and phenolic composition of Laški Riesling wine

English. Phenolic compounds, with their well known positive effect on human health, are a desirable constituent of wine, however, due to their susceptibility to oxidation, they can negatively affect the color, stability and overall quality of white wines. Sulphur dioxide, the effective antioxidant used for wine browning prevention and stabilization, is avoided cause of possible harmful effect on human health and wine quality. Therefore, other agents such as polyvinylpolypyrrolidone (PVPP) and laccase are used, and investigated as well still , too. PVPP ( a synthetic polymer) binds phenolic compounds and thus prevents their oxidation. In contrast, the enzyme lacase catalyzes the oxidation of phenolic compounds and accelerates the formation of high molecular weight brown polymers which are removed in finalization processes such as ultrafiltration. In this way, the subsequent oxidation of phenolic compounds as well as wine browning and turbidity are prevented. Considering the above facts, the aim of this study was to examine the effectiveness of treatment with PVPP or laccase, combined with ultrafiltration, on the physicochemical properties (contents of ethanol, total extract, volatile and non-volatile acids, pH value, color intensity), sensory quality and the concentration of individual groups of phenolic compounds (flavonoids, neflavonoids, condensed tannins, leukoanthocyanidins) of Laški Riesling white wine. Finalization of untreated (control) wine and wines treated with PVPP or laccase and treated wines was performed by ultrafiltration. The selected experimental conditions were previously tested in laboratory scale and confirmed that colloid content was reduced by treatments with PVPP or laccase. while wine aroma was not significantly impaired. Further, the same treatments were applied in the industrial conditions and according to obtained results they did not significantly affect the basic physicochemical properties, but improved the sensory quality of the treated wines. Therefore, the same treatment conditions were applied in industrial scale and generally did not significantly affect the physico-chemical properties, while the sensory quality of the treated wines were improved. The concentrations of all groups of phenolic compounds and color intensities were reduced in the treated wines when compared to color control wine. The obtained results indicate the suitability of both PVPP and laccase in the processes of stabilization and color preservation of white wine Laški Riesling.

Croatian. Fenolni spojevi su poželjan sastojak vina zbog njihovog dobro poznatog pozitivnog učinka na zdravlje ljudi, međutim zbog podložnosti oksidaciji, mogu negativno utjecati na boju, stabilnost te ukupnu kvalitetu bijelih vina. Sumporni dioksid, učinkovit antioksidans koji se koristi za stabilizaciju i sprječavanje posmeđivanja, izbjegava se zbog mogućeg štetnog utjecaja na zdravlje ljudi i kvalitetu vina. Stoga se koriste i istražuju druga sredstva kao npr. polivinilpolipirolidon (PVPP) i lakaza. PVPP je sintetski polimer koji veže fenolne spojeve i time sprječava njihovu oksidaciju. Nasuprot tome, enzim lakaza katalizira oksidaciju fenolnih spojeva te ubrzava nastajanje visokomolekularnih smeđe obojenih polimera koji se uklanjaju odgovarajućim postupcima filtracije vina. Na taj način se sprječava naknadna oksidacija fenolnih spojeva te posmeđivanje i zamućenje vina. S tim u vezi cilj istraživanja bio je ispitati utjecaj tretmana PVPP-om ili lakazom na fizikalno-kemijska svojstva (udjeli etanola, ukupnog ekstrakta, hlapljivih i nehlapljivih kiselina, pH-vrijednost, intenzitet boje), senzorsku kvalitetu i koncentraciju pojedinih skupina fenolnih spojeva (flavonoidi, neflavonoidi, kondenzirani tanini, leukoantocijani) bijelog vina Laški rizling. Finalizacija netretiranog (kontrolnog) vina i vina tretiranih PVPP-om odnosno lakazom provedena je ultrafiltracijom. Odabrani uvjeti tretmana, provjereni su brzim testiranjem u laboratorijskim uvjetima: aroma je u vinu ostala nepromijenjena, a masena koncentracija koloida je smanjena. Stoga su isti uvjeti tretmana primijenjeni u industrijskom mjerilu te uglavnom nisu značajno utjecali na fizikalno-kemijska svojstva, a poboljšali su senzorsku kvalitetu tretiranih vina. Smanjili su koncentracije svih skupina fenolnih spojeva i rezultirali manjim intenzitetom boje tj. svjetlijom bojom tretiranih od kontrolnog vina. Dobiveni rezultati ukazuju na prikladnost PVPP-a i lakaze u postupcima očuvanja boje i kvalitete bijelog vina Laški rizling.