Vanilla - Aldehyde Glycosides

ALDEHYDE GLYCOSIDES

VANILLA

Biological Source

Vanilla (Vanilla Pods) consists of the cured fully grown but unripe fruits of Vanilla fragrans (Salis.), belonging to family Orchidaceae.

Geographical Source

Vanilla fragrans is grown in the woods of eastern Mexico, Reunion (or Bourbon), Mauritius, Seychelles, Madagas-car, Java, Sri Lanka, Tahiti, Guadeloupe, Martinique and Indonesia. It is cultivated in tropical countries where the temperature does not fall below 18°C and where the humidity is high.

The plants are perennial, climbing, dioecious epiphytes attached to the trunks of trees by means of aerial rootlets.

Cultivation and Collection

The plant is usually propagated by means of cuttings and, after two or three years, reaches the flowering stage. The cuttings attach to trees (e.g. Casuarina equisetifolia) where they strike roots on the bark; it continues to bear fruit for 30 or 40 years. The flowers, approximately 30 on each plant, are hand pollinated, thus producing larger and better fruits.

The fruits are collected as they ripen to a yellow colour, 6–10 months after pollination, and are cured by dipping in warm water and repeated sweating between woolen blankets in the sun during the day and packing in wool-covered boxes at night. The characteristic colour and odour of the commercial drug are only developed as a result of enzyme action during the curing. Curing consists of slow drying in sheds with carefully regulated temperatures. This requires about 2 months, during which the pods lose from 70 to 80% of their original weight and take on the characteristic colour and odour of the commercial drug. The pods are then graded, tied into bundles of about 50–75, and sealed in tin containers for shipment.

Characteristics

Vanilla pods are 15–25 cm long, 8–10 mm diameter and somewhat flattened. The surface is longitudinally wrin-kled, dark brown to violet-black in colour, and frequently covered with needle shaped crystals of vanillin (‘frosted’). The fruits are very pliable and have a very characteristic odour and taste.

Chemical Constituents

Green vanilla contains glycosides, namely gluco-vanillin (vanilloside) and glucovanillic alcohol. During the curing these are acted upon by an oxidizing and a hydrolysing enzyme which occur in all parts of the plant. Glucovanillic alcohol yields on hydrolysis glucose and vanillic alcohol; the latter compound is then by oxidation converted into vanillic aldehyde (vanillin). Glucovanillin yields on hydro-lysis glucose and vanillin.

The vanilla species differ in their relative contents of anisyl alcohol, anisaldehyde, anisyl ethers, anisic acid esters, piperonal and p-hydroxybenzoic acid. These minor components, together with the two diastereoisomeric vitispiranes, add to the flavour of the pods.

Uses

Vanilla pods are widely used in confectionery and in perfumery.