In vivokinetics of β-glucosidase towards glucovanillin and related phenolic glucosides in heat-treated vanilla pod (Vanilla planifolia, Orchidaceae)

Abstract

Introduction . The traditional curing of vanilla pods includes “killing” and sweating steps when pods are exposed to heat (35–65 °C) 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 °C, 55 °C and 60 °C, then stored for 118 days at 27 °C. 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 . (Resume d'auteur)