Although resveratrol (3,5,4′-trihydroxy-stilbene) is one of the most studied natural product because of its biological properties such as antioxidant or anticancer, its low water solubility and stability (influenced by pH, light and increased temperature), as well as its propensity to oligomerize, limit its bioavailability and applications in nutraceutic, cosmetics or pharmaceutical industries. Besides, resveratrol production at the multigram scale through vine cell culture is limited by the tedious extraction of pure resveratrol from the bioconversion medium due to its complexation by cyclodextrins, the latter being used as elicitors in the bioproduction process. In this work, we have been able to overcome all these drawbacks by performing a single organic solvent-free enzymatic α-glycosylation directly from the βcyclodextrin-resveratrol complex in water using β-cyclodextrin as glycoside-donor. The combined effects of five parameters (CGTase amount, cyclodextrin amount, cyclodextrin/resveratrol ratio, pH, and temperature) were studied by design of experiments (DoE) to maximize the glycosylation yield. The optimal setting point of parameters was obtained by response surface methodology (RSM). After optimization, an efficient α-glycosylation was performed being obtained 35% of molar yield. The major glycosidestwo monoglycosides: 3-O-α-D-glucosyl-resveratrol and 4′-O-α-D-glucosyl-resveratrol and two diglycosides: 3-O-α-D-maltosyl-resveratrol and 4′-O-α-D-maltosyl-resveratrolwere characterized using a hyphenated liquid chromatography-solid phase extraction-nuclear magnetic resonance system, then separated and purified using centrifugal partition chromatography (CPC). Their antiradical properties, as well as that of their crude mixture, were evaluated through DPPH analysis. Results confirmed that the position 4′−OH is the best position for the glycosylation to maintain the highest antiradical properties.

The O-glycosylation of resveratrol increases both its solubility in water and its bioavailability while preventing its oxidation, allowing a more efficient use of this molecule as a bioactive ingredient in pharmaceutical and cosmetic applications. Resveratrol O-glycosides can be obtained by enzymatic reactions. Recent developments have made it possible to selectively obtain resveratrol α-glycosides from the β-cyclodextrin–resveratrol complex in water with a yield of 35%. However, this yield is limited by the partial hydrolysis of the resveratrol glycosides produced during the reaction. In this study, we propose to intensify this enzymatic reaction by coupling the enzymatic reactor to a membrane process. Firstly, membrane screening was carried out at the laboratory scale and led to the choice of a GE polymeric membrane with a cut-off of 1 kDa. This membrane allowed the retention of 65% of the β-cyclodextrin–resveratrol complex in the reaction medium and the transfer of 70% of the resveratrol α-O-glycosides in the permeate. In a second step, this membrane was used in an enzymatic membrane reactor and improved the yield of the enzymatic glycosylation up to 50%.