Abstract
In grapes, monoterpenes and norisoprenoids are in the form of non-volatile compounds, flavourless glycosides which could enhance the aroma of wines after its hydrolysis using β- glucosidases enzymes. It is known that the use of immobilised enzymes offers advantages such as reusability and easy recuperation. In this study, a commercial β-glucosidase was immobilised by absorption in sodium alginate. Biotechnological characteristics and terpen hydrolysis (hydrolysis aroma precursors) in muscat wines were studied after treatment with both free and immobilised commercial β- glucosidase with two different concentrations. It was revealed that both forms shared an optimal pH (4.5) and a maximum temperature (64°C), even an increment on the activity between 40and 60°C. A similar Km value has been determined while Vmax from the immobilised enzyme was higher than the free (3.35 and 2.52 μmol min–1 mg–1, respectively). Additionally, the immobilised enzyme showed a better hydrolytic activity during 24 h, and its reusability has been proven. Regarding enzymatic hydrolysis in grape must, the best results were observed for the highest concentration of free β-glucosidase although glucose release was also determined for the immobilised enzyme along the days. In contrast, maximum activity was reached by the immobilised β-glucosidase in less time but in no case equalled the free ones. Finally, volatile compound liberation in wines treated with free or immobilised enzymes was analysed using HRGC-MS. Liberation for both enzymes and the greatest concentrations of some volatiles were detected when a double dose of the free β-glucosidase was used. Nevertheless, the wines treated with the immobilised β-glucosidase showed a high concentration of some volatile compounds such as nerol or geraniol.
Highlights
Monoterpenes and norisoprenoids from grapes are important aroma compounds, which improve flavour in wines, especially white wine
At the lowest temperatures (13–25◦C), the immobilised β-glucosidase presented better hydrolysis capability no significant differences were found between both enzymes at those temperatures
An increment in both activities was detected at a temperature range of 4064◦C, and the maximum significant activity was reached at 64◦C for both enzymes
Summary
Monoterpenes and norisoprenoids from grapes are important aroma compounds, which improve flavour in wines, especially white wine. Reports indicate that not all glycosides are present in all grape varieties and that concentrations vary across them (Bayonove et al, 1993) In this way, Muscat, Gewürztraminer, Riesling, or Sauvignon Blanc are varieties with higher concentrations in these compounds. Grapes include compounds called “aroma precursors,” the most active of which are glycosides—mostly linalool, nerol, and geraniol (Alem et al, 2018). These compounds are usually present in two fractions: (i) a free fraction, which contributes directly to must aroma, and (ii) a bound fraction, which forms non aromatic glycosides (these glycosides may later release their aromatic load). The release of glycosidically bound aroma compounds by acid or enzyme treatment can enhance the total aroma of processed fruit products and aroma wines (Arévalo-Villena et al, 2006a)
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