In vivo kinetics of [bêta]-glucosidase towards glucovanillin and related phenolic glucosides in heat-treated vanilla pod (Vanilla planifolia, Orchidaceae)

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 . (Résumé d'auteur

Influence du procédé de dépulpage de la drupe de Coffea arabica L. sur la fermentation

Au cours du traitement de postrécolte du café Arabica, l'eau utilisée a une influence directe sur les paramètres physico-chimiques, microbiologiques et biochimiques de la fermentation. Elle intervient lors du dépulpage et du transport des drupes dépulpées jusqu'à la cuve de fermentation, solubilise alors les sucres simples du mucilage, ralentit la croissance microbienne et en conséquence l'acidification du milieu fermentaire. Le dépulpage et le transport du café avec ou sans eau ne modifient pas la composition biochimique du café vert. Par ailleurs, les propriétés organoleptiques à la tasse ont été jugées identiques. Les technologies moins polluantes, dépulpage et transport sans eau des drupes dépulpées, permettent aux producteurs de contrôler la durée et l'acidité produite. En revanche, il est nécessaire de réduire le temps de fermentation car le pH devient plus rapidement acide. Des durées prolongées pourraient provoquer des surfermentations et développer des mauvais goûts. (Résumé d'auteur

kinetics of β-glucosidase towards glucovanillin and related phenolic glucosides in heat-treated vanilla pod (

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

Anatomy, histochemistry and biochemistry of glucovanillin, oleoresin and mucilage accumulation sites in green mature vanilla pod (

Introduction. Mature green vanilla pods accumulate 4-O-(3-methoxy-benzaldehyde)-β-D-glucoside (glucovanillin), which, upon hydrolysis by an endogenous β-glucosidase, liberates vanillin, the major aroma component of vanilla. Sites of storage of glucovanillin in the pod have been controversially reported for decades; we aim, using precise and widely accepted technical terminology, to clarify this controversy by providing an anatomical, histochemical and biochemical evidence-based picture of glucovanillin accumulation sites. The pod also synthesizes an oleoresin and a mucilage of unknown constitutions; we report here their localization and structures. Materials and methods. The pod anatomy was examined by light and epifluorescence microscopy. A protocol was established allowing fine hand-dissection of diverse anatomical parts of the pod (mesocarp, placentae, trichomes, intralocular interstitial cell-free region and seeds). Glucovanillin and γ-pyranones were extracted and analyzed by HPLC, while the structures of the mucilaginous polysaccharides were determined after permethylation. Results and discussion. Glucovanillin is essentially stored in the placentae (92%) and marginally in trichomes (7%); traces were measured in the mesocarp and intralocular interstitial cell-free medium. Trichomes store massive amounts of a fluorescing oleoresin (44%) rich in alkenylmethyldihydro-γ-pyranones and synthesize a mucilage made of a glucomannan and a pectic polysaccharide carrying monomeric arabinose and galactose side-chains. Conclusion. To date, the physiological roles of glucovanillin, long-chain pyranones, and mucilage remain unknown

Fate of proanthocyanidins and anthocyanins along fermentation of cocoa seeds (Theobroma cacao L.)

Condensed tannins, also called proanthocyanidins, play a substantial role in the sensory characteristics of chocolate. Little is known about their fate along fermentation. In the present study, location and behavior of tannins in the cotyledons and testae of cocoa seeds are studied during fermentation by light and transmission electron microscopy. Tannins along with anthocyanosides were also measured. Tannins are located in special tanniferous cells from both cotyledons and testae of native seeds. The most striking phenomena occurring during fermentation are an almost complete disappearance of the testa tannins and, in the cotyledons, a translocation without losses of the tannins from the tanniferous cells towards surrounding tissues. Quantitative analyses confirm these observations and show that little oxidation of the cotyledonary tannins occurs. The anthocyanosides from the cotyledons completely disappear. It is assumed that this translocation could hinder proteolysis of the cotyledon proteins by formation of resistant tannin-protein complexes

A new technique for visualizing proanthocyanidins by light microscopy

International audienceWe describe a new technique for visualizing proanthocyanidin-containing elements in plant tissues. Our innovation is the fixation of condensed tannins with an exogenous protein prior to alcohol dehydration. In this way, tannins do not undergo partial solubilization during the dehydration sequence and appear as sharply contoured globules of various diameters