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In vivo kinetics of β-glucosidase towards glucovanillin and related phenolic glucosides in heat-treated vanilla pod (Vanilla planifolia, Orchidaceae)
Published online by Cambridge University Press: 29 March 2010
Abstract
Introduction. The traditional curing of vanilla pods includes “killing” and sweating steps when pods are exposed to heat (35–65 ℃) for various lengths of time. Although it is known that liberation of vanillin and other phenolics from their non-aromatic glucosides is due to the action of an endogenous β-glucosidase, its in vivo kinetics remained unknown. Materials and methods. Mature green vanilla pods were pretreated for 2 h at 50 ℃, 55 ℃ and 60 ℃, then stored for 118 days at 27 ℃. Phenolic glucosides and their aglycons were extracted at regular intervals during the storage period and analyzed by HPLC. Results and discussion. All phenolic β-glucosides were slowly hydrolyzed during the storage period with production of vanillin, p-hydroxybenzaldehyde, vanillic acid, and other unknown aglycons. Most of the β-glucosidase was heat-denatured by the pretreatment, and analysis of its kinetic parameters showed that it adopts, in vivo, an allosteric mode of functioning with a lower affinity for glucovanillin than in vitro, where it behaves as a Michaelian enzyme. Conclusion. Extensive research is needed to confirm the allosteric mechanism of the vanilla β-glucosidase in vivo.
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- © 2010 Cirad/EDP Sciences
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