Abstract
The aromatic expression of wines can be enhanced by the addition of specific glycosidases, although their poor stability remains a limitation. Coimmobilization of glycosidases as cross-linked enzyme aggregates (combi-CLEAs) offers a simple solution yielding highly stable biocatalysts. Nevertheless, the small particle size of combi-CLEAs hinders their recovery, preventing their industrial application. Encapsulation of combi-CLEAs of glycosidases in alginate beads and in polyvinyl alcohol is proposed as a solution. Combi-CLEAS of β-d-glucosidase and α-l-arabinofuranosidase were prepared and encapsulated. The effects of combi-CLEA loading and particle size on the expressed specific activity (IU/gbiocatalyst) of the biocatalysts were evaluated. Best results were obtained with 2.6 mm diameter polyvinyl alcohol particles at a loading of 60 mgcombi-CLEA/gpolyvinyl alcohol, exhibiting activities of 1.9 and 1.0 IU/gbiocatalyst for β-d-glucosidase and α-l-arabinofuranosidase, respectively. Afterwards, the stability of the biocatalysts was tested in white wine. All the encapsulated biocatalysts retained full activity after 140 incubation days, outperforming both free enzymes and nonencapsulated combi-CLEAs. Nevertheless, the alginate-encapsulated biocatalysts showed a brittle consistency, making recovery unfeasible. Conversely, the polyvinyl-encapsulated biocatalyst remained intact throughout the assay. The encapsulation of combi-CLEAs in polyvinyl alcohol proved to be a simple methodology that allows their recovery and reuse to harness their full catalytic potential.
Highlights
Research over the last decades has revealed that much of the aromatic expression of wines is due to the enzymatic-mediated release of flavor compounds, namely monoterpenes [1,2]
The βG specific activity obtained in this study at 60 mgcombi-cross-linked enzyme aggregates (CLEA)/gPVA is nearly two times higher, while almost the same ARA specific activity was achieved in both works
The 2.8 mm alginate biocatalyst produced at 20 mgcombi-CLEA/galginate and the 2.6 mm polyvinyl alcohol (PVA) biocatalyst encapsulated at 40 mgcombi-CLEA/gPVA were selected for evaluating their stability
Summary
Research over the last decades has revealed that much of the aromatic expression of wines is due to the enzymatic-mediated release of flavor compounds, namely monoterpenes [1,2]. The enzymatic hydrolysis of these glycosides involves a two-step cascading reaction process where the diglycosidic bond is cleaved first by enzymes such as α-L-arabinofuranosidase (ARA), α-L-rhamnosidase (RAM) and β-D-apiosidase (API), resulting in the release of the monoterpenyl β-D-glucoside moiety which is hydrolyzed in a second step by β-D-glucosidase (βG) releasing the aromatic monoterpene [4,5]. This enzymatic process is extensively applied nowadays in industrial winemaking during the maturation stage, using commercial preparations of soluble enzymes that contain mainly ARA, RAM and βG activities [6]. Enzyme immobilization provides solutions to these limitations by linking or containing the enzymes into a carrier, allowing to recover the biocatalyst and increase its stability [7,8]
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