Introduction. During maturation, vanillin is accumulated in green vanilla beans as glucovanillin; it is hydrolyzed to free vanillin by endogenous glucosidases during curing and gives the characteristic flavor of vanilla. The objective of our study was to investigate methods of curing that could greatly reduce the time to complete the process and yield cured beans that retain high concentrations of vanillin and other flavor compounds with high sensory quality rating. Materials and methods. Mature green beans were obtained from a commercial grower (Cairns, Queensland, Australia). One batch of beans was continuously sweated at 35 °C at high relative humidity (RH) for 12 d. Two further batches were blanched in water at 67 °C for 3 min, and then sweated at 45 °C at high RH for 4 d or at 35 °C for 5 d. The beans were sweated until they turned brown. Three methods of drying were evaluated: a heat pump dryer at 40 °C and RH 15%, tunnel dryer at 60 °C and RH 20%, and tunnel dryer at 60 °C and RH 10%. Vanillin was extracted from powdered samples of beans with n-pentane and dichloromethane (1:1 v/v) and assayed by HPLC. Glucovanillin was measured as total vanillin after acid hydrolysis of powdered samples of beans. Results and discussion. About 90% of the glucovanillin was converted to vanillin in non-blanched beans continuously sweated at 35 °C, but there was only 70% conversion in beans blanched at 67 °C for 3 min and sweated at 45 °C for 4 d or at 35 °C for 5 d. The sensory quality of cured beans was assessed by untrained panelists. Profiling showed that the beans sweated continuously at 35 °C had superior aroma compared with beans blanched in hot water and sweated at 45 °C or at 35 °C but the appearance of non-blanched beans was less attractive. Conclusion. The study revealed that a mild hot water blanching treatment followed by sweating at 35–45 °C and rapid drying is required to produce cured beans with excellent appearance and attractive aroma.

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.

Introduction. Mature green vanilla pods accumulate 4-O-(3-methoxy-benzaldehyde)-β-D-glucoside (glucovanillin), which, upon hydrolysis by an endogenous b-glucosidase, liberates vanillin, the major aroma component of vanilla. Little is known on the spatial distribution of aroma-generating phenolics, and the enzymes responsible for their liberation (β-glucosidase) and oxidation (peroxidase). We report here quantitative data with respect to these three components in relation to the anatomy of the pod. Furthermore, the spatial progression of oxidation is shown. Materials and methods. Mature green vanilla pods were analyzed for their contents of phenolics (HPLC), and β-glucosidase and peroxidase activities by spectrophotometric techniques using p-nitrophenyl glucoside and vanillin as substrates, respectively. Lipids were examined under fluorescence microscopy after Nile red staining. Oxidation development was observed on transverse slices of pods. Results and discussion. Phenolics, and β-glucosidase and peroxidase activities showed gradients of increasing-decreasing concentrations from the stem to the blossom end of pods. The β-glucosidase activity is distributed in between the placentae, mesocarp, and trichomes in a [7 / 2 / 1] proportion while that of peroxidase shows a [38 / 1] ratio in the mesocarp and placentae, and was absent from trichomes. Oxidation begins from the blossom end in the placentae, progressively invading the mesocarp and moving towards the stem end. Conclusion. The green mature vanilla pod is spatially heterogeneous for its phenolics, and β-glucosidase and peroxidase activities, its placentae playing an important role in the liberation of vanillin and its subsequent oxidation.

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.

Introduction. The heat treatments applied to vanilla beans (Vanilla planifolia G. Jackson) during processing have various objectives, which include encouraging the hydrolysis of the glucosylated precursors of the aroma components by one (or several) endogenous glucosidase(s). The glucosides of the vanilla bean. Fifteen glucosides have been identified in the green fruit, of which glucovanillin is the most abundant. It can reach concentrations of up to 15% of fruit dry matter about 30 weeks after pollination, and represents the main form of accumulation of vanillin. β-D-glucosidase(s) of the vanilla bean. A β-D-glucosidase from the vanilla bean was purified and characterised. However, several glucosidases may exist and have yet to be studied. The glucosidase activity seems to be very unstable during the heat treatments. This raises questions about the process of glucoside hydrolysis during vanilla curing. Compartmentation between the glucosidase activity and glucosides in the vanilla bean. After various debates, it now appears that glucovanillin and glucosidase activity largely occur in the bean’s placental region. Their respective cellular localisation has yet to be determined. However, numerous elements support the hypothesis that enzymatic hydrolysis is regulated by a cellular compartmentation that differs between enzyme and substrate. Conclusion. A great deal of research work still needs to be conducted on the glucosides and glucosidase(s) of the vanilla bean. It would be particularly interesting to further our understanding of what occurs during the enzymatic hydrolysis of aroma precursors during curing.