Chapter 13. Morphological, Chemical, Sensory, and Genetic Specificities of Tahitian Vanilla
Sandra Lepers-Andrzejewski, Christel Brunschwig, François-Xavier Collard, and Michel Dron
About the Origin of Vanilla
The Tahitian vanilla plant, which is cultivated in French Polynesia since the nineteenth century, was described for the first time as a new vanilla species in 1933 by J.W. Moore: Vanilla tahitensis. This particular form of vanilla plant, found on trees, in a valley of Faaroa Bay (Raiatea, Society Islands, French Polynesia) is different from all the other cultivated vanilla forms known today. V. tahitensis differs from Vanilla planifolia G. Jacks. [syn. Vanilla fragrans (Salisbury) Ames] in particular by having more slender stems, narrower leaves, longer perianth segments, a lip that is shorter than the sepals, a longer column and shorter pods. For J.W. Moore, V. tahitensis is therefore a new vanilla species, endemical of French Polynesia.
However, the Vanilla genus, although amphitropical, is present as an indigenous species in the Pacific area only in Indonesia and Southeast Asia and is completely absent from the other Pacific islands except when cultivated (Florence and Guérin, 1996). Thus, its origin had to be searched among the various vanilla plants, which were introduced to French Polynesia.
There were at least three introductions of vanilla from various sources between 1848 and 1898 (Chevalier, 1946). The first one dates from 1848. Admiral Hamelin brought to Tahiti V. planifolia Andrews [syns. Vanilla aromatica Swartz and V. fra-grans (Salisbury) Ames] from Manila in the Philippines (Costantin and Bois, 1915; Bouriquet, 1954; Florence and Guérin, 1996). Henry in 1924 noted that some horticultural tests were carried out in Tahiti between 1847 and November 1849; however, no details were given, and he indicated that the vanilla plant brought by Admiral Hamelin in 1848 did flower and produce pods. The seeds of these pods or the horticultural tests could be at the origin of the Tahitian vanilla.
The second introduction of vanilla occurred in 1850 (Costantin and Bois, 1915). French Polynesia received new plants from Paris, sent by Admiral Bonard. There were many V. planifolia plants coming from the botanical garden of Paris and many V. pompona plants from the Antillas (Florence and Guérin, 1996). These two species are still found in French Polynesia. But they are not really cultivated. The weather conditions do not always allow V. planifolia to flower. In addition, V. pompona is only considered as an ornamental plant in French Polynesia.
The third introduction of vanilla plant was by Major Pierre, in 1874, who brought new vanilla plants from Mexico (Costantin and Bois, 1915; Florence and Guérin, 1996). These plants were described as the best vanilla species from Mexico and Bourbon, with broader, thicker, and more round leaves than the vanillas cultivated in French Polynesia, which possess pointed and lanceolate leaves. According to these descriptions, it seems that this third introduction did also correspond to V. planifolia.
According to morphological and historical comparisons, many hypotheses on the origin of Tahitian vanilla were elaborated. According to Portères (1951), the morphology suggests that V. tahitensis was a clonal population resulting from segregations of natural crossings between V. fragrans (Salisbury) Ames (syn. V. planifolia Andrews) and V. pompona Schiede, which was probably already a hybrid of Vanilla odorata Presl. Portères (1953) suggests that this initial hybridization could have occurred in French Guiana or in Reunion Island between V. fragrans and a complex species (V. pompona–V. odorata). However, according to Florence and Guerin, V. tahitensis does not show any intermediate traits that a hybrid between V. planifolia and V. pompona should exhibit. These authors consider V. tahitensis as synonymous of V. planifolia. They do see it as a segregation issued from a small number of introductions. The segregants have brought some variations resulting in traits specifying the Polynesian form.
At present, the origin of Tahitian vanilla is still unknown; nevertheless, morphological diversity exists among the vines encountered in French Polynesia. The most cultivated vanilla vines in French Polynesia are Tahiti and Haapape. The cultivar Haapape was first mentioned in 1914 (Bouriquet and Hibon, 1950). According to C. Henry (1924), Haapape seems to be an inbred of Tiarei, which was described in 1900 (Costantin and Bois, 1915). The cultivar Tiarei was reported as a case of gigantism (Henry, 1924). Comparing the morphological characters, color, and flavor of the beans, the Tiarei form cannot be the result of a cross between a Tahitian vanilla and a vine originating from Mexico. According to Bouriquet and Hibon (1950), the Tiarei cultivar is issued from a somatic mutation or is a spontaneous hybrid of V. planifolia and a Tahitian form.
Biology of the Tahitian Vanilla
Vanilla is mainly propagated by stem cuttings. Seed germination is difficult because it requests a symbiotic fungus: Rhizoctonia. Flowering necessitates approximately 18 months. However, this delay varies with the size of the vine. Cuttings of 20 nodes can flower within less than one year after plantation.
Flowering is induced by a decrease in the temperature (18–19°C) and by drier and sunnier weather during the fresh season. Two flowering periods often occur in a year: the main one is between July and September and another is possible in December–January. The ends of the hanging stems will then dry and 1–3 inflores-cences from 10 to 15 flowers will appear. The flower opens at dawn and fades during the evening. On a single inflorescence only 1–2 flowers open each day.
There is no pollinating insect in French Polynesia and thus pollination, or “ marriage,” is hand-made early in the morning, to prevent pollen becoming too dry to adhere to the stigmata. The marriage is performed according to a common procedure developed in Reunion Island by Edmond Albius (Bouriquet, 1954, see also Chapter 17).
The bean is ripe after nine months. Green until then, the bean starts to yellow and then browns, starting from the heel. This indicates that the bean can be collected and cured.
Curing Process
Thanks to original sensory and physical properties having been retained, the Tahitian vanilla has a unique flavor. In French Polynesia, Tahitian vanilla is nowadays considered as a bona fide source of cultural identity demonstrating the know-how of growers and curers. Polynesians developed a specific curing process based on harvesting pods when fully mature and flavorful, followed by a natural browning enabling the development of the aroma.
For most vanillas cultivated worldwide, notably V. planifolia, ripeness involves dehiscence of the beans. To avoid this phenomenon, clusters of beans are harvested before fully mature; and then ripeness is stopped by a treatment at high temperature. Tahitian vanilla beans rarely develop split ends and they are harvested when fully ripe, with complete aroma potential (Figure 13.1). Natural browning is achieved and allows a complete conversion of glycosylated aroma compounds into corresponding aglycones responsible for the vanilla flavor.
FIGURE 13.1 Mature beans of Tahitian cultivar Haapape, still green or turning brown.
Traditional Polynesian curing involves water loss to concentrate the flavor and to enable a good conservation of the beans. In the course of the curing process, many biochemical reactions (enzymatic and nonenzymatic like oxidative reactions) occur in the vanilla pods, which result in the development of the flavor (Odoux et al., 2006, for more details see Chapters 11 and 12); such biochemical reactions are poorly studied in Tahitian vanilla.
Tahitian curing consists of three main steps that necessitate being very patient and meticulous (Larcher, 1989; Ranadive, 1994):
1. Shade browning After harvest, mature vanilla beans are exposed in the shade until uniform browning and initiation of sweet-scented flavor are attained. Then, they are washed and dried.
2. Sun drying Beans are exposed to sunshine for a few hours a day for several weeks. Their water content drops from 80% to the final moisture content desired (50–55%). When they are exposed to warm temperatures or the sun; water evaporates. Then, while still warm, beans are wrapped in cotton sheets called “faraoiti” and kept in wooden cases overnight to ensure water loss by sweating. The beans become flexible and glossy as their epidermis is increasingly covered with oil. They are massaged one by one, when necessary, to spread and homogenize the seeds lengthwise.
3. Air drying (refining) Beans are finally dried in the shade to homogenize batches and stabilize water content, enabling optimal shelf life.
The curing process allows the development of Tahitian vanilla flavor. The beans become sweet-smelling and rich anise flavored. Their physical properties are also intensified as they show a very attractive oily texture and appearance. The lipid components are involved both in these properties and aroma development because they restrict aroma loss from occurring during the process.
Morphological Specificities and Diversity
Tahitian vanilla is characterized by a more slender stem than V. planifolia or V. pompona with an average stem diameter of 8 mm and internodes of 13 cm length, sometimes very long, up to 19 cm. The leaves are also thinner (Figure 13.2), narrow– oval, lanceolate, gradually become very pointed, 3–7 times longer than their width, dark green in color, not very thick, not or very little in gutter toward the base, 16–25 cm in length, and 2–5 cm broad; the petiole is 15 mm in length on an average, and well canaliculate above.
FIGURE 13.2 Comparison of the size and shape of leaves of V. pompona, V. planifolia, and V. tahitensis cv Haapape (from left to right).
FIGURE 13.3 Comparison of flowers of V. pompona, V. planifolia, and V. tahitensis cv Haapape (from left to right).
The Tahitian vanilla flowers are assembled into an inflorescence. On an average, the inflorescences are 9.2 cm long, greenish, with some parts more yellow than those of V. planifolia (Figure 13.3). The sepals are narrow-oblanceolate, pointed at the base, attenuate-acute at the top, 9–16 mm broad, 55–77 mm long, and nonducted with the back. The petals are also 50–74 mm long, 7–13 mm wide, elliptic, and subacute. The labellum is 46–49 mm in length and funnel-shaped, shows small orange dotted lines on its inner face with a revolute margin, and is fimbriate-crenelated. The Tahitian vanilla fruits, aromatic, are generally indehis-cent contrary to V. planifolia pods.
Today, the main Tahitian vanilla cultivars are Tahiti and Haapape. But local farmers distinguish about 14 cultivars, which differ by the shape, length, and width of the leaves, the size of the flowers, and the size and shape of the beans. The five main cultivated forms are described below and shown in Figures 13.4 through 13.6.
Tahiti
The stem is on an average 8 mm in diameter with internodes of 13 cm length. The leaves are not or very little in gutter toward the base and measure about 18 cm in length, and 3 cm in width with a petiole of 13 mm length. The sepals are 14 × 65 mm on an average, and the petals 11 × 64 mm. The labellum is white with short hairs and dotted lines of dark orange color. The fruit is clear green in color, trigonal and 10–19 cm long (14 cm on an average) and weighs on an average 10.5 g. The pods show little dehiscence with maturity.
Haapape
The stem is larger than “Tahiti,” with, an average diameter of 10 mm and internodes of 16 cm length. The leaves present a gutter, measure about 17 cm in length and 3 cm in width with a petiole of 18 mm length. The flowering is less abundant than “Tahiti,” but the larger flowers of Haapape are easier to marry. The sepals and petals are longer than those of “Tahiti”: an average of about 13 × 70 mm and 10 × 68 mm respectively.
FIGURE 13.4 Plant and leaf shapes of the main Polynesian cultivars of vanilla.
FIGURE 13.5 Color diversity of the labellum of Tahitian vanilla: (a) cultivar Rea rea; (b) cultivar Haapape.
FIGURE 13.6 Variation in size, shape, and color of Tahitian vanilla beans: (a) Tahiti, (b) Haapape, (c) Rea rea, (d) Parahurahu, and (e) Tahiti long. The yellow label is 10 cm long.
The labellum is white, with long hairs and dotted lines of dark orange color. The fruits are of very dark color, rounded, blunt at the end and 13–23 cm long ( average 18 cm) and weigh an average of 16.3 g. The beans are very rarely dehiscent with maturity.
Rea Rea
The stem is thinner, with, an average diameter of 7 mm and relatively short inter-nodes of 13 cm length. The leaves, more oblong than lanceolate, are about 20 cm long, and 4 cm wide with a petiole of 16 mm length. The sepals are about 13 × 62 mm and the petals are 11 × 61 mm. The labellum is white with light orange color dotted lines. The fruits, trigonal, of green–light yellow color, and 11–17 cm long (average 14 cm) and weigh about 9.9 g. The beans are fairly dehiscent with maturity.
Parahurahu
The stem is also thin, measuring an average of 7 mm in diameter with internodes of 14 cm length. Leaves, not or very little in gutter toward the base and present a more apiculate end than pointed and are about 15 cm long and 3 cm wide, with a petiole of 16 mm length. The sepals are about 12 × 63 mm and the petals are about 10 × 61 mm. The labellum is white with white hairs and dotted lines of light orange color. The beans, of dark green color, present the shape of a bludgeon, are 10–18 cm long (14 cm on average) and weigh about 14.1 g. The beans are very rarely dehiscent with maturity.
Tahiti Long
The stem is thin, measuring about 7 mm in diameter with short internodes of 13 cm. The leaves are not or very little in gutter toward the base and are about 15 cm long and 3 cm wide with a petiole of 15 mm length. The flowers are smaller than those of the previous cultivars; the sepals are on average 11 × 59 mm and the petals are 9 × 58 mm. The labellum is white with long hairs and exhibits light yellow dotted lines. The end of the labellum has a thorny form. The fruits, of light green color, are rounded-off, thin, blunt at the end, and 11–24 cm long (average 17 cm) and weigh about 11.1 g. The beans are rarely dehiscent with maturity.
Growers distinguish many other morphological types than those described above. These types differ in the size and width of their leaves and the size, shape, and color of their fruits. These vanilla types are not really cultivated because their fruits do not obey the criteria defined by the regulations (for details, see Chapter 24), but they exhibit a real morphological diversity. Examples: Oviri, which has smaller leaves (14 cm × 3 cm) than “Tahiti” and shorter fruits (11 cm on average); Puroini, which possesses leaves with the shape of a heart; Potiti and “Tahiti” or “Haapape” have the same leave size and shape, but “Potiti” produces very small fruits (average 10 cm). Finally, a “bicolor” (variegated) vanilla plant whose leaves show light yellow stripes is also present in farming systems.
Tahitian vanilla is characterized by a more slender stem than V. planifolia or V. pompona with an average stem diameter of 8 mm and internodes of 13 cm length, sometimes very long, up to 19 cm. The leaves are also thinner (Figure 13.2), narrow– oval, lanceolate, gradually become very pointed, 3–7 times longer than their width, dark green in color, not very thick, not or very little in gutter toward the base, 16–25 cm in length, and 2–5 cm broad; the petiole is 15 mm in length on an average, and well canaliculate above.
FIGURE 13.2 Comparison of the size and shape of leaves of V. pompona, V. planifolia, and V. tahitensis cv Haapape (from left to right).
FIGURE 13.3 Comparison of flowers of V. pompona, V. planifolia, and V. tahitensis cv Haapape (from left to right).
The Tahitian vanilla flowers are assembled into an inflorescence. On an average, the inflorescences are 9.2 cm long, greenish, with some parts more yellow than those of V. planifolia (Figure 13.3). The sepals are narrow-oblanceolate, pointed at the base, attenuate-acute at the top, 9–16 mm broad, 55–77 mm long, and nonducted with the back. The petals are also 50–74 mm long, 7–13 mm wide, elliptic, and subacute. The labellum is 46–49 mm in length and funnel-shaped, shows small orange dotted lines on its inner face with a revolute margin, and is fimbriate-crenelated. The Tahitian vanilla fruits, aromatic, are generally indehis-cent contrary to V. planifolia pods.
Today, the main Tahitian vanilla cultivars are Tahiti and Haapape. But local farmers distinguish about 14 cultivars, which differ by the shape, length, and width of the leaves, the size of the flowers, and the size and shape of the beans. The five main cultivated forms are described below and shown in Figures 13.4 through 13.6.
Tahiti
The stem is on an average 8 mm in diameter with internodes of 13 cm length. The leaves are not or very little in gutter toward the base and measure about 18 cm in length, and 3 cm in width with a petiole of 13 mm length. The sepals are 14 × 65 mm on an average, and the petals 11 × 64 mm. The labellum is white with short hairs and dotted lines of dark orange color. The fruit is clear green in color, trigonal and 10–19 cm long (14 cm on an average) and weighs on an average 10.5 g. The pods show little dehiscence with maturity.
Haapape
The stem is larger than “Tahiti,” with, an average diameter of 10 mm and internodes of 16 cm length. The leaves present a gutter, measure about 17 cm in length and 3 cm in width with a petiole of 18 mm length. The flowering is less abundant than “Tahiti,” but the larger flowers of Haapape are easier to marry. The sepals and petals are longer than those of “Tahiti”: an average of about 13 × 70 mm and 10 × 68 mm respectively.
FIGURE 13.4 Plant and leaf shapes of the main Polynesian cultivars of vanilla.
FIGURE 13.5 Color diversity of the labellum of Tahitian vanilla: (a) cultivar Rea rea; (b) cultivar Haapape.
FIGURE 13.6 Variation in size, shape, and color of Tahitian vanilla beans: (a) Tahiti, (b) Haapape, (c) Rea rea, (d) Parahurahu, and (e) Tahiti long. The yellow label is 10 cm long.
The labellum is white, with long hairs and dotted lines of dark orange color. The fruits are of very dark color, rounded, blunt at the end and 13–23 cm long ( average 18 cm) and weigh an average of 16.3 g. The beans are very rarely dehiscent with maturity.
Rea Rea
The stem is thinner, with, an average diameter of 7 mm and relatively short inter-nodes of 13 cm length. The leaves, more oblong than lanceolate, are about 20 cm long, and 4 cm wide with a petiole of 16 mm length. The sepals are about 13 × 62 mm and the petals are 11 × 61 mm. The labellum is white with light orange color dotted lines. The fruits, trigonal, of green–light yellow color, and 11–17 cm long (average 14 cm) and weigh about 9.9 g. The beans are fairly dehiscent with maturity.
Parahurahu
The stem is also thin, measuring an average of 7 mm in diameter with internodes of 14 cm length. Leaves, not or very little in gutter toward the base and present a more apiculate end than pointed and are about 15 cm long and 3 cm wide, with a petiole of 16 mm length. The sepals are about 12 × 63 mm and the petals are about 10 × 61 mm. The labellum is white with white hairs and dotted lines of light orange color. The beans, of dark green color, present the shape of a bludgeon, are 10–18 cm long (14 cm on average) and weigh about 14.1 g. The beans are very rarely dehiscent with maturity.
Tahiti Long
The stem is thin, measuring about 7 mm in diameter with short internodes of 13 cm. The leaves are not or very little in gutter toward the base and are about 15 cm long and 3 cm wide with a petiole of 15 mm length. The flowers are smaller than those of the previous cultivars; the sepals are on average 11 × 59 mm and the petals are 9 × 58 mm. The labellum is white with long hairs and exhibits light yellow dotted lines. The end of the labellum has a thorny form. The fruits, of light green color, are rounded-off, thin, blunt at the end, and 11–24 cm long (average 17 cm) and weigh about 11.1 g. The beans are rarely dehiscent with maturity.
Growers distinguish many other morphological types than those described above. These types differ in the size and width of their leaves and the size, shape, and color of their fruits. These vanilla types are not really cultivated because their fruits do not obey the criteria defined by the regulations (for details, see Chapter 24), but they exhibit a real morphological diversity. Examples: Oviri, which has smaller leaves (14 cm × 3 cm) than “Tahiti” and shorter fruits (11 cm on average); Puroini, which possesses leaves with the shape of a heart; Potiti and “Tahiti” or “Haapape” have the same leave size and shape, but “Potiti” produces very small fruits (average 10 cm). Finally, a “bicolor” (variegated) vanilla plant whose leaves show light yellow stripes is also present in farming systems.
Chemical Composition of Tahitian Vanilla
Tahitian vanilla is very different from other vanillas cultivated in the world, particularly when compared to V. planifolia because of its subtle flavor and rich anise fragrance, and the glossy and flexible aspect of its beans.
To characterize the originality of Tahitian vanilla, methods were developed at the laboratory of the “Etablissement Vanille de Tahiti” to analyze its chemical composition, especially the molecules of interest–namely, aroma compounds and fatty acids.
Aroma Composition of Tahitian Vanilla
An Original Aroma Composition
Thanks to their sensory properties, vanilla pods are mostly studied for their aroma compounds. The first comprehensive work on vanilla volatiles was carried out in 1976 by Klimes and Lamparsky, who identified, by gas chromatography (GC)–mass spectrometry (MS), 169 compounds in V. planifolia.
Then, several studies of Tahitian vanilla aroma composition highlighted its originality compared to V. planifolia by the presence of major phenolic compounds, including the widely mentioned anisyl compounds present in higher amounts, and less frequently the presence of minor compounds. The different studies of Tahitian vanilla describe the aroma as composed of the following molecules (see Table 13.1 for chemical structure) whose contents differ from V. planifolia as detailed later.
Ten major phenolic compounds are listed below:
a. Vanillin, p-hydroxybenzaldehyde, vanillic acid, and p-hydroxybenzoic acid (Fayet et al., 1987; Ranadive, 1992; Langella et al., 2003) usually quantified in V. planifolia to authenticate natural vanilla.
b. Four anisyl compounds characteristic of Tahitian vanilla: i. Anisyl alcohol and anisic acid, which are with vanillin the most concentrated compounds in Tahitian vanilla beans. They have been identified by GC–MS (Adedeji et al., 1993), confirming previous works (Shiota and Itoga, 1975; Lhuguenot, 1978; Tabacchi et al., 1978; Rey et al., 1980; Purseglove et al., 1981; Larcher, 1989; Hartman, 2003). ii. p-Anisaldehyde (Tabacchi et al., 1978) and methyl anisate (Shiota and Itoga, 1975; Adedeji et al., 1993; Lechat-Vahirua and Bessiere, 1998; Sostaric et al., 2000), which are less concentrated.
c. Other phenolic compounds in nonnegligible amounts: protocatechualde-hyde, protocatechuic acid, syringic acid, and p-hydroxybenzyl alcohol (Fayet et al., 1987).
Minor components with various chemical functions:
d. Aromatic esters: anisyl acetate, anisyl formate, and methyl cinnamate (Shiota and Itoga, 1975; Adedeji et al., 1993; Sostaric et al., 2000; Hartman, 2003).
e. Other phenolic compounds (Shiota and Itoga, 1975; Scharrer, 2002).
f. Aldehydes, ketones, and lactones: 2,4-decadienal, 3-methylpentanal, 2-methyl-2-pentanone, 1-methoxy-2-propanone, isovaldehyde, and gamma nonalactone (Adedeji et al., 1993; Lechat Vahirua and Bessiere, 1998; Scharrer, 2002).
g. Monoterpenes (α-pinen, β-pinen, limonen, linalool, terpinen-4-ol, and α-terpineol (Scharrer, 2002).
h. Aliphatic esters (for instance, ethyl hexanoate, ethyl nonanoate, and ethyl decanoate) (Sostaric et al., 2000).
i. Heterocyclic compounds, aliphatic acids, and alcohols (Fayet et al., 1987).
j. Derivatives of anisyl compounds (Da Costa and Pantini, 2006).
TABLE 13.1 Major Aroma Molecules Identified and Quantified in Tahitian Vanilla
Family
Molecule Name
Used
R1
R2
R3
R4
Vanillyl
Vanillyl alcohol
Van_alc
CH2OH
OCH3
OH
H
Vanillin
Van
COH
OCH3
OH
H
Vanillic acid
Van_ac
COOH
OCH3
OH
H
p-Hydroxybenzyl
p-Hydroxybenzyl alcohol
Phb_alc
CH2OH
H
OH
H
p-Hydroxybenzaldehyde
Phb
COH
H
OH
H
p-Hydroxybenzoic acid
Phb_ac
COOH
H
OH
H
Methyl p-hydroxybenzoate
Me_paraben
COOCH3
H
OH
H
Anisyl
Anisyl alcohol
Anis_alc
CH2OH
H
OCH3
H
Anisaldehyde
Anis_ald
COH
H
OCH3
H
Anisic acid
Anis_ac
COOH
H
OCH3
H
Methyl anisate
Me_anis
COOCH3
H
OCH3
H
Protocatechuyl
Protocatechualdehyde
Pro_ald
COH
OH
OH
H
Protocatechuic acid
Pro_ac
COOH
OH
OH
H
Isovanillyl
Isovanilline
Isovan
COH
OH
OCH3
H
Others
Syringic acid
—
COOH
OCH3
OH
OCH3
The presence of piperonal (heliotropin) as a characteristic constituent of Tahitian vanilla has been a matter of debate for a long time. Definitively Joulain et al. (2007) showed that the supposed characteristic odorant constituent of Tahitian vanilla was p-anisaldehyde and that piperonal was present in Tahitian vanilla but only as a trace element as well as in V. planifolia, confirming previous works (Tabacchi et al., 1978; Ehlers et al., 1994; Lechat-Vahirua and Bessiere, 1998).
At the laboratory of the “Etablissement Vanille de Tahiti,” the high flavored, original and pervasive flavor of the Tahitian vanilla was highlighted by the high-pressure liquid chromatography (HPLC) analysis of the major aroma phenolic compounds. The work focused on the role of the curing process in the development of a unique flavor, and on the aroma composition of some Polynesian cultivars.
More than 300 samples of Tahitian cured vanilla beans were analyzed from three successive annual harvests (2005, 2006, and 2007). Cured beans of Tahitian vanilla are rich in overall aroma compounds with an average of 4.6% of dry matter compared to 2.1–4.2% for V. planifolia. Moreover, the aroma composition of Tahitian vanilla is more different, with a smaller contribution of vanillin to the overall flavor (30% v. 80% for V. planifolia). Whereas its vanillin level is of less influence (1.2% as it reaches 1.7–3.5% for V. planifolia), Tahitian vanilla contains higher amounts of ani-syl molecules (2.1% and less than 0.05% for V. planifolia) and p-hydroxybenzalde-hyde. The most concentrated anisyl molecules are anisyl alcohol and anisic acid (respectively, 1.35% and 0.75% of dry matter); p-anisaldehyde and methyl anisate represent about 200 ppm each, whereas they are only at trace levels in V. planifolia.
Evolution of Aroma Compounds during the Curing Process
Many factors influence the flavor of Tahitian vanilla, such as genetic, agronomic, climatic, and transformation criteria. In fact, the highly valued flavor of Tahitian vanilla becomes more and more intense during the curing process. Nevertheless, if vanilla pods undergo a water loss when exposed to the sun, some aroma compounds are also evaporated and the batches of pods generate a pleasant vanilla flavor. Research on vanilla aroma in French Polynesia focuses on phenolic compounds that contribute to the overall flavor. Fourteen “aroma compounds” from an ethanolic Soxhlet extract were assessed by HPLC during the curing process (see Table 13.1).
In relation to the drying process, there is a subsequent loss of aromatic molecules. When beans are dried to 38% moisture content, they lose approximately one-third of their aroma potential, from 6.5% to 4.6% of dry weight. However, given that the loss of water is more important than the loss of aroma compounds, their concentration per gram of fresh weight actually increases during the curing period.
Differences in volatility between aroma compounds and oxidation reactions occurring in the beans (from alcohol to aldehyde and then to acid function) involve diverse changes of molecule concentrations (see Figure 13.7). The highly concentrated vanillin and anisyl alcohol undergo a significant decrease, whereas vanillic acid and anisaldehyde concentrations increase because of their production due to the oxidation of previous major compounds (respectively, vanillin and anisyl alcohol).
FIGURE 13.7 Evolution of major aroma compounds of Tahitian vanilla during the curing process. Variation in content of the compounds is indicated as a percentage of initial content.
The moisture content has an influence on the flavor composition: drying favors accumulation of acid molecules (anisic acid and p-hydroxybenzoic acid) and decrease of the ratio of anisyl alcohol and vanillin (Figure 13.8). The odor-active compound p-anisaldehyde is a key component of the original Tahitian vanilla flavor, as its concentration doubles during the curing process. Since moisture content produces some effect on aroma quality, it is very important to provide details of moisture content when describing vanilla beans composition (Collard, 2007).
The curing process of Tahitian vanilla is a subtle compromise between optimal drying and conservation of aroma compounds. This results in an original aroma composition.
FIGURE 13.8 Aroma composition of Tahitian vanilla pods for different moisture contents (80%, 60%, and 40%). See Table 13.1 for complete names of molecules.
Tahitian Vanilla Cultivars Show Various Aroma Compositions
Tahitian vanilla develops an exotic flavor compared to other vanillas. There is an intra-tahitensis diversity with various cultivars and nuanced flavors.
In Tahitian vanilla, there is a morphological diversity, which is confirmed by different chemical compositions. A study was carried out based on aroma quality of uncured beans of five cultivars of importance in French Polynesia (the most cultivated Tahiti and Haapape, Rea rea, Parahurahu, and Tahiti long).
Each cultivar develops its own aroma characteristics. Table 13.2 shows that the overall aroma amount differs from one cultivar to another and that some molecules are discriminating as they contribute to structure groups by statistical analysis. Performing a factorial discriminant analysis shows very good correspondence between the observed classification obtained with aroma variables and naturally occurring cultivars (see Figure 13.9) (Collard et al., 2006).
FIGURE 13.9 2D plot of fi ve cultivars of uncured Tahitian vanilla beans in factorial discriminant analysis using aroma compounds (see Table 13.2) as variables.
Among Polynesian cultivars, Parahurahu is very specific with a significantly lower overall amount, a lower amount of vanillyl molecules and a higher level of anisic acid. The cultivar Rea rea demonstrates a remarkably lower amount of p-hydroxybenzaldehyde and a higher amount of vanillyl compounds, and it differs from the group formed by Tahiti, Haapape, and Tahiti long, all of which show quite similar aroma compositions. Beans of Tahiti long are characterized by a high amount of p-hydroxybenzaldehyde. Tahiti and Haapape are the cultivars that have the most similar aroma compositions, although Tahiti is richer in overall aroma and vanillyl compounds, and Haapape contains relatively more p-hydroxybenzyl and anisyl components.
TABLE 13.2 Aroma Content (ppm) of Five Cultivars of Tahitian Vanilla (Uncured Beans) Quantified by HPLC at the “Etablissement Vanille de Tahiti”
Molecule*
Parahurahu
Rea rea
Tahiti long
Haapape
Tahiti
No. of samples
18
13
15
23
110
Van_alc
243a
909e
407b
514c
614d
Van
806a
17,718c
11,732b
13,337b
20,184d
Van_ac
87a
316e
177b
197c
227d
Phb
2504c
352a
4221d
2621c
2081b
Phb_ac
7101c
4932a
7275c
7202c
6007b
Anis_alc
7156a
13,108b
16,397c
20,158d
21,117d
Anis_ald
46a
65b
71b
82b
65b
Anis_ac
16,026c
4896a
8103b
8736b
7907b
Pro_ald
1101a
1421b
2585c
2758c
2628c
Pro_ac
220b
216b
219b
188ab
169a
Σ Van
1137a
18,943c
12,316b
14,048b
21,025c
Σ Phb
9605c
5284a
11,496d
9823c
8088b
Σ Anis
23,228b
18,069a
24,571b
28,976c
29,088c
TOTAL
35,290a
43,933b
51,186c
55,793d
60,998e
Averages with the same letter within rows are not significantly different (p < 0.05).
* See Table 13.1 for complete names of the molecules.
The aroma composition can explain the original flavor of Tahitian vanilla and show slight differences between the main cultivars. As seen before, the originality of Tahitian vanilla is not only due to its flavor but also due to its oily texture.
Fatty Acid Composition of Tahitian Vanilla
The fatty acid composition has been a topic of interest to better understand the physical and sensory properties of Tahitian vanilla, which is oilier (see the section on Sensory Properties).
Some previous chemical studies of vanilla beans related to the presence of fatty acids or fatty acid derivatives. The major components identified were oleic or palm-itic acid (Purseglove et al., 1981; Adedeji et al., 1993; Lechat-Vahirua and Bessiere, 1998). A comprehensive study of the lipidic fraction of three vanilla bean species V. tahitensis, V. planifolia, and Vanilla madagascariensis by GC revealed discriminating fatty acid compositions, with a predominance of linoleic acid among 31 fatty acids in every species (Ramaroson-Raonizafinimanana, 1988). Moreover, many additional lipidic components were identified: phytosterols (Ramaroson-Raonizafinimanana et al., 1998), hydrocarbons (Ramaroson-Raonizafinimanana et al., 1997), and two new product families: long-chain γ-pyrones (Ramaroson-Raonizafinimanana et al., 1999) and long-chain β-diketones (Ramaroson-Raonizafinimanana et al., 2000).
At the “Etablissement Vanille de Tahiti,” work on the lipid extract aims at characterizing Tahitian vanilla and its different cultivars by the fatty acid composition. Derivatives of fatty acids are analyzed by HPLC. About 10 fatty acids were identified and the identification was confirmed by GC for a few of them (Brunschwig et al., 2007). Six common fatty acids coming from primary metabolites such as triglycerides were quantified: linolenic 18:3, linoleic 18:2, palmitic 16:0, oleic 18:1, stearic 18:0, and erucic 20:1 acids. Four very-long-chain monounsaturated fatty acids, rarely found in plants, were identified in vanilla beans: nervonic (24:1), ximenic (26:1), octacosen-19-oïc acid (28:1), and lumequeic (30:1) acids. These fatty acids derive from secondary metabolites (supposed β-diketones) and their composition may be much more variable than that of the primary metabolites (Ramaroson-Raonizafinimanana, 1988).
The fatty acid composition demonstrates that Tahitian vanilla is richer in fatty acids and that it could discriminate Polynesian cultivars. Cured Tahitian vanilla beans have an average fatty acid content higher than other vanillas in the world (an average of 2.5% of dry matter compared to 1.2–2.4%), which may explain the attractive glossy and oily aspect of the pods (Brunschwig et al., 2007). Tahitian vanilla beans contain mainly polyunsaturated fatty acids (with a preponderance of linoleic acid from 55% to 65%) and monounsaturated fatty acids (from 20% to 30%) with a remarkable content of monounsaturated long-chain fatty acids (5%–13%), and not much of saturated fatty acids (about 15%). These data consolidate the data of Ramaroson-Raonizafinimanana et al. (1988).
TABLE 13.3 Fatty Acid (FA) Composition (%) of Lipid Extract from Different Cultivars of Tahitian Vanilla (Uncured Beans)
Parahurahu
Tahiti long
Haapape
Tahiti
V. tahitensis*
No. of samples
8
6
8
8
1
16:0–palmitic
9.8a
10.4a
9.4a
9.6a
8.2
18:0 + 20:1 stearic + eructic
3.9a
4.4b
3.9a
4.7b
3.6
18:1ω9–oleic
15.7a
17.5b
15.2a
15.3a
12.9
18:2ω6–linoleic
53.9a
58.1b
63.7d
61.2c
67.4
18:3ω3–linolenic
3.7b
2.8a
2.5a
2.2a
1.3
Total common FA
87.0a
93.2b
94.7c
93.0b
93.3
24:1ω9–nervonic
6.6c
3.5b
2.4a
3.5b
4.5
26:1ω9–ximenic
2.0c
1.3b
0.9a
1.3b
1.0
28:1ω9–octasen-19oïc
2.1b
1.1a
1.0a
1.2a
0.6
30:1ω9–lumequeic
2.2b
0.9a
0.9a
1.0a
0.5
Total long-chain FA
12.9c
6.8b
5.2a
7.0b
6.7
Saturated FA
13.7a
14.8a
13.3a
14.3a
11.8
Monounsaturated FA
28.6d
24.3c
20.4a
22.3b
19.5
Polyunsaturated FA
57.6a
60.9b
66.2d
63.4c
68.6
Unsaturated FA
86.2a
85.2a
86.6a
85.7a
88.2
Total (ppm)
9147a
12,950b
16,978b
14,152b
—
Averages with the same letter within rows are not significantly different (p < 0.05).
* GC quantitation (Ramaroson-Raonizafinimanana, 1988).
The cultivars from French Polynesia show quite different fatty acid compositions, as illustrated by Table 13.3. The intra-tahitensis chemodiversity is highlighted by a factorial discriminant analysis, showing that Parahurahu is very specific with a significantly higher content of monounsaturated long-chain fatty acids (especially nervonic acid) and linolenic acid (Figure 13.10).
FIGURE 13.10 2D plot of four cultivars of uncured Tahitian vanilla beans analyzed in factorial discriminant analysis using fatty acids as variables (see Table 13.3).
The other cultivars have similar compositions with slight variations: Tahiti shows a greater amount of stearic acid, Tahiti long is distinguishable by its significantly higher oleic acid content, and Haapape is the oiliest among Polynesian cultivars.
The chemodiversity of Polynesian cultivars is underlined as well by aroma diversity as by fatty acids.
Conclusion
Tahitian vanilla beans have a specific aroma and fatty acid composition. The most original cultivar is Parahurahu, which contains a relatively high level of anisyl molecules and a low amount of vanillyl compounds, as well as a very high level of monounsaturated long-chain fatty acids.
The vanillas most cultivated in French Polynesia, namely Tahiti and Haapape, have homogeneous aroma and lipid characteristics. Their aroma composition and high fatty acid content explain, respectively, their subtle sensory properties and their attractive physical aspect.
Tahitian vanilla is very different from other vanillas cultivated in the world, particularly when compared to V. planifolia because of its subtle flavor and rich anise fragrance, and the glossy and flexible aspect of its beans.
To characterize the originality of Tahitian vanilla, methods were developed at the laboratory of the “Etablissement Vanille de Tahiti” to analyze its chemical composition, especially the molecules of interest–namely, aroma compounds and fatty acids.
Aroma Composition of Tahitian Vanilla
Thanks to their sensory properties, vanilla pods are mostly studied for their aroma compounds. The first comprehensive work on vanilla volatiles was carried out in 1976 by Klimes and Lamparsky, who identified, by gas chromatography (GC)–mass spectrometry (MS), 169 compounds in V. planifolia.
Then, several studies of Tahitian vanilla aroma composition highlighted its originality compared to V. planifolia by the presence of major phenolic compounds, including the widely mentioned anisyl compounds present in higher amounts, and less frequently the presence of minor compounds. The different studies of Tahitian vanilla describe the aroma as composed of the following molecules (see Table 13.1 for chemical structure) whose contents differ from V. planifolia as detailed later.
Ten major phenolic compounds are listed below:
a. Vanillin, p-hydroxybenzaldehyde, vanillic acid, and p-hydroxybenzoic acid (Fayet et al., 1987; Ranadive, 1992; Langella et al., 2003) usually quantified in V. planifolia to authenticate natural vanilla.
b. Four anisyl compounds characteristic of Tahitian vanilla: i. Anisyl alcohol and anisic acid, which are with vanillin the most concentrated compounds in Tahitian vanilla beans. They have been identified by GC–MS (Adedeji et al., 1993), confirming previous works (Shiota and Itoga, 1975; Lhuguenot, 1978; Tabacchi et al., 1978; Rey et al., 1980; Purseglove et al., 1981; Larcher, 1989; Hartman, 2003). ii. p-Anisaldehyde (Tabacchi et al., 1978) and methyl anisate (Shiota and Itoga, 1975; Adedeji et al., 1993; Lechat-Vahirua and Bessiere, 1998; Sostaric et al., 2000), which are less concentrated.
c. Other phenolic compounds in nonnegligible amounts: protocatechualde-hyde, protocatechuic acid, syringic acid, and p-hydroxybenzyl alcohol (Fayet et al., 1987).
Minor components with various chemical functions:
d. Aromatic esters: anisyl acetate, anisyl formate, and methyl cinnamate (Shiota and Itoga, 1975; Adedeji et al., 1993; Sostaric et al., 2000; Hartman, 2003).
e. Other phenolic compounds (Shiota and Itoga, 1975; Scharrer, 2002).
f. Aldehydes, ketones, and lactones: 2,4-decadienal, 3-methylpentanal, 2-methyl-2-pentanone, 1-methoxy-2-propanone, isovaldehyde, and gamma nonalactone (Adedeji et al., 1993; Lechat Vahirua and Bessiere, 1998; Scharrer, 2002).
g. Monoterpenes (α-pinen, β-pinen, limonen, linalool, terpinen-4-ol, and α-terpineol (Scharrer, 2002).
h. Aliphatic esters (for instance, ethyl hexanoate, ethyl nonanoate, and ethyl decanoate) (Sostaric et al., 2000).
i. Heterocyclic compounds, aliphatic acids, and alcohols (Fayet et al., 1987).
j. Derivatives of anisyl compounds (Da Costa and Pantini, 2006).
| Family | Molecule Name | Used | R1 | R2 | R3 | R4 |
|---|---|---|---|---|---|---|
| Vanillyl | Vanillyl alcohol | Van_alc | CH2OH | OCH3 | OH | H |
| Vanillin | Van | COH | OCH3 | OH | H | |
| Vanillic acid | Van_ac | COOH | OCH3 | OH | H | |
| p-Hydroxybenzyl | p-Hydroxybenzyl alcohol | Phb_alc | CH2OH | H | OH | H |
| p-Hydroxybenzaldehyde | Phb | COH | H | OH | H | |
| p-Hydroxybenzoic acid | Phb_ac | COOH | H | OH | H | |
| Methyl p-hydroxybenzoate | Me_paraben | COOCH3 | H | OH | H | |
| Anisyl | Anisyl alcohol | Anis_alc | CH2OH | H | OCH3 | H |
| Anisaldehyde | Anis_ald | COH | H | OCH3 | H | |
| Anisic acid | Anis_ac | COOH | H | OCH3 | H | |
| Methyl anisate | Me_anis | COOCH3 | H | OCH3 | H | |
| Protocatechuyl | Protocatechualdehyde | Pro_ald | COH | OH | OH | H |
| Protocatechuic acid | Pro_ac | COOH | OH | OH | H | |
| Isovanillyl | Isovanilline | Isovan | COH | OH | OCH3 | H |
| Others | Syringic acid | — | COOH | OCH3 | OH | OCH3 |
The presence of piperonal (heliotropin) as a characteristic constituent of Tahitian vanilla has been a matter of debate for a long time. Definitively Joulain et al. (2007) showed that the supposed characteristic odorant constituent of Tahitian vanilla was p-anisaldehyde and that piperonal was present in Tahitian vanilla but only as a trace element as well as in V. planifolia, confirming previous works (Tabacchi et al., 1978; Ehlers et al., 1994; Lechat-Vahirua and Bessiere, 1998).
At the laboratory of the “Etablissement Vanille de Tahiti,” the high flavored, original and pervasive flavor of the Tahitian vanilla was highlighted by the high-pressure liquid chromatography (HPLC) analysis of the major aroma phenolic compounds. The work focused on the role of the curing process in the development of a unique flavor, and on the aroma composition of some Polynesian cultivars.
More than 300 samples of Tahitian cured vanilla beans were analyzed from three successive annual harvests (2005, 2006, and 2007). Cured beans of Tahitian vanilla are rich in overall aroma compounds with an average of 4.6% of dry matter compared to 2.1–4.2% for V. planifolia. Moreover, the aroma composition of Tahitian vanilla is more different, with a smaller contribution of vanillin to the overall flavor (30% v. 80% for V. planifolia). Whereas its vanillin level is of less influence (1.2% as it reaches 1.7–3.5% for V. planifolia), Tahitian vanilla contains higher amounts of ani-syl molecules (2.1% and less than 0.05% for V. planifolia) and p-hydroxybenzalde-hyde. The most concentrated anisyl molecules are anisyl alcohol and anisic acid (respectively, 1.35% and 0.75% of dry matter); p-anisaldehyde and methyl anisate represent about 200 ppm each, whereas they are only at trace levels in V. planifolia.
Many factors influence the flavor of Tahitian vanilla, such as genetic, agronomic, climatic, and transformation criteria. In fact, the highly valued flavor of Tahitian vanilla becomes more and more intense during the curing process. Nevertheless, if vanilla pods undergo a water loss when exposed to the sun, some aroma compounds are also evaporated and the batches of pods generate a pleasant vanilla flavor. Research on vanilla aroma in French Polynesia focuses on phenolic compounds that contribute to the overall flavor. Fourteen “aroma compounds” from an ethanolic Soxhlet extract were assessed by HPLC during the curing process (see Table 13.1).
In relation to the drying process, there is a subsequent loss of aromatic molecules. When beans are dried to 38% moisture content, they lose approximately one-third of their aroma potential, from 6.5% to 4.6% of dry weight. However, given that the loss of water is more important than the loss of aroma compounds, their concentration per gram of fresh weight actually increases during the curing period.
Differences in volatility between aroma compounds and oxidation reactions occurring in the beans (from alcohol to aldehyde and then to acid function) involve diverse changes of molecule concentrations (see Figure 13.7). The highly concentrated vanillin and anisyl alcohol undergo a significant decrease, whereas vanillic acid and anisaldehyde concentrations increase because of their production due to the oxidation of previous major compounds (respectively, vanillin and anisyl alcohol).
FIGURE 13.7 Evolution of major aroma compounds of Tahitian vanilla during the curing process. Variation in content of the compounds is indicated as a percentage of initial content.
The moisture content has an influence on the flavor composition: drying favors accumulation of acid molecules (anisic acid and p-hydroxybenzoic acid) and decrease of the ratio of anisyl alcohol and vanillin (Figure 13.8). The odor-active compound p-anisaldehyde is a key component of the original Tahitian vanilla flavor, as its concentration doubles during the curing process. Since moisture content produces some effect on aroma quality, it is very important to provide details of moisture content when describing vanilla beans composition (Collard, 2007).
The curing process of Tahitian vanilla is a subtle compromise between optimal drying and conservation of aroma compounds. This results in an original aroma composition.
FIGURE 13.8 Aroma composition of Tahitian vanilla pods for different moisture contents (80%, 60%, and 40%). See Table 13.1 for complete names of molecules.
Tahitian vanilla develops an exotic flavor compared to other vanillas. There is an intra-tahitensis diversity with various cultivars and nuanced flavors.
In Tahitian vanilla, there is a morphological diversity, which is confirmed by different chemical compositions. A study was carried out based on aroma quality of uncured beans of five cultivars of importance in French Polynesia (the most cultivated Tahiti and Haapape, Rea rea, Parahurahu, and Tahiti long).
Each cultivar develops its own aroma characteristics. Table 13.2 shows that the overall aroma amount differs from one cultivar to another and that some molecules are discriminating as they contribute to structure groups by statistical analysis. Performing a factorial discriminant analysis shows very good correspondence between the observed classification obtained with aroma variables and naturally occurring cultivars (see Figure 13.9) (Collard et al., 2006).
FIGURE 13.9 2D plot of fi ve cultivars of uncured Tahitian vanilla beans in factorial discriminant analysis using aroma compounds (see Table 13.2) as variables.
Among Polynesian cultivars, Parahurahu is very specific with a significantly lower overall amount, a lower amount of vanillyl molecules and a higher level of anisic acid. The cultivar Rea rea demonstrates a remarkably lower amount of p-hydroxybenzaldehyde and a higher amount of vanillyl compounds, and it differs from the group formed by Tahiti, Haapape, and Tahiti long, all of which show quite similar aroma compositions. Beans of Tahiti long are characterized by a high amount of p-hydroxybenzaldehyde. Tahiti and Haapape are the cultivars that have the most similar aroma compositions, although Tahiti is richer in overall aroma and vanillyl compounds, and Haapape contains relatively more p-hydroxybenzyl and anisyl components.
| Molecule* | Parahurahu | Rea rea | Tahiti long | Haapape | Tahiti |
|---|---|---|---|---|---|
| No. of samples | 18 | 13 | 15 | 23 | 110 |
| Van_alc | 243a | 909e | 407b | 514c | 614d |
| Van | 806a | 17,718c | 11,732b | 13,337b | 20,184d |
| Van_ac | 87a | 316e | 177b | 197c | 227d |
| Phb | 2504c | 352a | 4221d | 2621c | 2081b |
| Phb_ac | 7101c | 4932a | 7275c | 7202c | 6007b |
| Anis_alc | 7156a | 13,108b | 16,397c | 20,158d | 21,117d |
| Anis_ald | 46a | 65b | 71b | 82b | 65b |
| Anis_ac | 16,026c | 4896a | 8103b | 8736b | 7907b |
| Pro_ald | 1101a | 1421b | 2585c | 2758c | 2628c |
| Pro_ac | 220b | 216b | 219b | 188ab | 169a |
| Σ Van | 1137a | 18,943c | 12,316b | 14,048b | 21,025c |
| Σ Phb | 9605c | 5284a | 11,496d | 9823c | 8088b |
| Σ Anis | 23,228b | 18,069a | 24,571b | 28,976c | 29,088c |
| TOTAL | 35,290a | 43,933b | 51,186c | 55,793d | 60,998e |
Averages with the same letter within rows are not significantly different (p < 0.05).
* See Table 13.1 for complete names of the molecules.
The aroma composition can explain the original flavor of Tahitian vanilla and show slight differences between the main cultivars. As seen before, the originality of Tahitian vanilla is not only due to its flavor but also due to its oily texture.
The fatty acid composition has been a topic of interest to better understand the physical and sensory properties of Tahitian vanilla, which is oilier (see the section on Sensory Properties).
Some previous chemical studies of vanilla beans related to the presence of fatty acids or fatty acid derivatives. The major components identified were oleic or palm-itic acid (Purseglove et al., 1981; Adedeji et al., 1993; Lechat-Vahirua and Bessiere, 1998). A comprehensive study of the lipidic fraction of three vanilla bean species V. tahitensis, V. planifolia, and Vanilla madagascariensis by GC revealed discriminating fatty acid compositions, with a predominance of linoleic acid among 31 fatty acids in every species (Ramaroson-Raonizafinimanana, 1988). Moreover, many additional lipidic components were identified: phytosterols (Ramaroson-Raonizafinimanana et al., 1998), hydrocarbons (Ramaroson-Raonizafinimanana et al., 1997), and two new product families: long-chain γ-pyrones (Ramaroson-Raonizafinimanana et al., 1999) and long-chain β-diketones (Ramaroson-Raonizafinimanana et al., 2000).
At the “Etablissement Vanille de Tahiti,” work on the lipid extract aims at characterizing Tahitian vanilla and its different cultivars by the fatty acid composition. Derivatives of fatty acids are analyzed by HPLC. About 10 fatty acids were identified and the identification was confirmed by GC for a few of them (Brunschwig et al., 2007). Six common fatty acids coming from primary metabolites such as triglycerides were quantified: linolenic 18:3, linoleic 18:2, palmitic 16:0, oleic 18:1, stearic 18:0, and erucic 20:1 acids. Four very-long-chain monounsaturated fatty acids, rarely found in plants, were identified in vanilla beans: nervonic (24:1), ximenic (26:1), octacosen-19-oïc acid (28:1), and lumequeic (30:1) acids. These fatty acids derive from secondary metabolites (supposed β-diketones) and their composition may be much more variable than that of the primary metabolites (Ramaroson-Raonizafinimanana, 1988).
The fatty acid composition demonstrates that Tahitian vanilla is richer in fatty acids and that it could discriminate Polynesian cultivars. Cured Tahitian vanilla beans have an average fatty acid content higher than other vanillas in the world (an average of 2.5% of dry matter compared to 1.2–2.4%), which may explain the attractive glossy and oily aspect of the pods (Brunschwig et al., 2007). Tahitian vanilla beans contain mainly polyunsaturated fatty acids (with a preponderance of linoleic acid from 55% to 65%) and monounsaturated fatty acids (from 20% to 30%) with a remarkable content of monounsaturated long-chain fatty acids (5%–13%), and not much of saturated fatty acids (about 15%). These data consolidate the data of Ramaroson-Raonizafinimanana et al. (1988).
| Parahurahu | Tahiti long | Haapape | Tahiti | V. tahitensis* | |
|---|---|---|---|---|---|
| No. of samples | 8 | 6 | 8 | 8 | 1 |
| 16:0–palmitic | 9.8a | 10.4a | 9.4a | 9.6a | 8.2 |
| 18:0 + 20:1 stearic + eructic | 3.9a | 4.4b | 3.9a | 4.7b | 3.6 |
| 18:1ω9–oleic | 15.7a | 17.5b | 15.2a | 15.3a | 12.9 |
| 18:2ω6–linoleic | 53.9a | 58.1b | 63.7d | 61.2c | 67.4 |
| 18:3ω3–linolenic | 3.7b | 2.8a | 2.5a | 2.2a | 1.3 |
| Total common FA | 87.0a | 93.2b | 94.7c | 93.0b | 93.3 |
| 24:1ω9–nervonic | 6.6c | 3.5b | 2.4a | 3.5b | 4.5 |
| 26:1ω9–ximenic | 2.0c | 1.3b | 0.9a | 1.3b | 1.0 |
| 28:1ω9–octasen-19oïc | 2.1b | 1.1a | 1.0a | 1.2a | 0.6 |
| 30:1ω9–lumequeic | 2.2b | 0.9a | 0.9a | 1.0a | 0.5 |
| Total long-chain FA | 12.9c | 6.8b | 5.2a | 7.0b | 6.7 |
| Saturated FA | 13.7a | 14.8a | 13.3a | 14.3a | 11.8 |
| Monounsaturated FA | 28.6d | 24.3c | 20.4a | 22.3b | 19.5 |
| Polyunsaturated FA | 57.6a | 60.9b | 66.2d | 63.4c | 68.6 |
| Unsaturated FA | 86.2a | 85.2a | 86.6a | 85.7a | 88.2 |
| Total (ppm) | 9147a | 12,950b | 16,978b | 14,152b | — |
Averages with the same letter within rows are not significantly different (p < 0.05).
* GC quantitation (Ramaroson-Raonizafinimanana, 1988).
The cultivars from French Polynesia show quite different fatty acid compositions, as illustrated by Table 13.3. The intra-tahitensis chemodiversity is highlighted by a factorial discriminant analysis, showing that Parahurahu is very specific with a significantly higher content of monounsaturated long-chain fatty acids (especially nervonic acid) and linolenic acid (Figure 13.10).
FIGURE 13.10 2D plot of four cultivars of uncured Tahitian vanilla beans analyzed in factorial discriminant analysis using fatty acids as variables (see Table 13.3).
The other cultivars have similar compositions with slight variations: Tahiti shows a greater amount of stearic acid, Tahiti long is distinguishable by its significantly higher oleic acid content, and Haapape is the oiliest among Polynesian cultivars.
The chemodiversity of Polynesian cultivars is underlined as well by aroma diversity as by fatty acids.
Conclusion
Tahitian vanilla beans have a specific aroma and fatty acid composition. The most original cultivar is Parahurahu, which contains a relatively high level of anisyl molecules and a low amount of vanillyl compounds, as well as a very high level of monounsaturated long-chain fatty acids.
The vanillas most cultivated in French Polynesia, namely Tahiti and Haapape, have homogeneous aroma and lipid characteristics. Their aroma composition and high fatty acid content explain, respectively, their subtle sensory properties and their attractive physical aspect.
Sensory Properties
The sensory properties of Tahitian vanilla are unique. They are often analyzed either by sensory evaluation or by GC-O. These two techniques respectively (i) describe the overall flavor of vanilla and (ii) determine odor-active compounds contributing to the overall vanilla flavor.
Sensory Evaluation
The sensory properties of vanilla beans are primarily due to volatile constituents, but some nonvolatile compounds such as lipids may play a role in modifying the flavor perception (Purseglove et al., 1981). Their odor impact has not yet been well elucidated, but during the curing process, they fix some volatiles and restrict their release out of vanilla pods.
In sensory analysis, Tahitian vanilla is described as showing distinctive flowery, fragrant, perfumed, anise, almond, and cherry notes. The beans are also characterized by a shallow vanilla character as well as weaker phenolic, woody, balsamic, and smoky notes than V. planifolia (Ranadive, 1994, 2006; Petitdidier, 2005).
But there is no clear relationship between these sensory properties and the quantitative analytical parameters (as described in the section “Chemical Composition of Tahitian Vanilla”). For V. planifolia, high vanillin contents, which are indicators of quality, do not necessarily imply good sensory properties. In fact, due to a high odor threshold, some major compounds quantified in vanilla beans are not directly linked to the sensory properties of the extracts since minor compounds are involved in the overall vanilla flavor (Ranadive, 2006; Gassenmeier et al., 2008). That is why a GC-O analysis was performed.
GC-O Analysis
To describe the overall vanilla flavor, recent studies took into account the olfactory impact of compounds by GC-O and not only their concentration in the pods (Scharrer, 2002; Black, 2005; Perez-Silva et al., 2006). Compounds like anisaldehyde and ani-syl alcohol account in great part for the characteristic flavor of Tahitian vanilla and are essential to the anise, sweet notes (www.flavornet.org). Some other compounds, such as aromatic anisyl esters (methyl anisate is present at 200 ppm in Tahitian vanilla), could have an olfactory impact on the overall aroma. Thus, a work on Tahitian vanilla enables the identification of 276 components. Among them, some minor specific anisyl molecules are scented and described as “anise, cherry, sweet” (Da Costa and Pantini, 2006).
Some phenolic compounds identified in Tahitian vanilla were found to be aroma-active by GC-O in V. planifolia beans (vanillin, vanillyl alcohol, p-hydroxybenzaldehyde, p-hydroxybenzyl alcohol, anisyl alcohol, and methyl cinnamate). Sweet, woody, balsamic, spicy, vanilla-like, and toasted notes were attributed to these compounds. Moreover, minor compounds present at less than 2 ppm have been found to contribute to the overall vanilla flavor, such as aldehydes, which were seen with green, oily, and herb-like floral notes, and aliphatic acids, which were described as having sour, buttery, and oily notes (Perez-Silva et al., 2006).
These studies have highlighted the specific anise flavor of Tahitian vanilla known as unique in the global market and considered as a luxury product.
The sensory properties of Tahitian vanilla are unique. They are often analyzed either by sensory evaluation or by GC-O. These two techniques respectively (i) describe the overall flavor of vanilla and (ii) determine odor-active compounds contributing to the overall vanilla flavor.
Sensory Evaluation
The sensory properties of vanilla beans are primarily due to volatile constituents, but some nonvolatile compounds such as lipids may play a role in modifying the flavor perception (Purseglove et al., 1981). Their odor impact has not yet been well elucidated, but during the curing process, they fix some volatiles and restrict their release out of vanilla pods.
In sensory analysis, Tahitian vanilla is described as showing distinctive flowery, fragrant, perfumed, anise, almond, and cherry notes. The beans are also characterized by a shallow vanilla character as well as weaker phenolic, woody, balsamic, and smoky notes than V. planifolia (Ranadive, 1994, 2006; Petitdidier, 2005).
But there is no clear relationship between these sensory properties and the quantitative analytical parameters (as described in the section “Chemical Composition of Tahitian Vanilla”). For V. planifolia, high vanillin contents, which are indicators of quality, do not necessarily imply good sensory properties. In fact, due to a high odor threshold, some major compounds quantified in vanilla beans are not directly linked to the sensory properties of the extracts since minor compounds are involved in the overall vanilla flavor (Ranadive, 2006; Gassenmeier et al., 2008). That is why a GC-O analysis was performed.
GC-O Analysis
To describe the overall vanilla flavor, recent studies took into account the olfactory impact of compounds by GC-O and not only their concentration in the pods (Scharrer, 2002; Black, 2005; Perez-Silva et al., 2006). Compounds like anisaldehyde and ani-syl alcohol account in great part for the characteristic flavor of Tahitian vanilla and are essential to the anise, sweet notes (www.flavornet.org). Some other compounds, such as aromatic anisyl esters (methyl anisate is present at 200 ppm in Tahitian vanilla), could have an olfactory impact on the overall aroma. Thus, a work on Tahitian vanilla enables the identification of 276 components. Among them, some minor specific anisyl molecules are scented and described as “anise, cherry, sweet” (Da Costa and Pantini, 2006).
Some phenolic compounds identified in Tahitian vanilla were found to be aroma-active by GC-O in V. planifolia beans (vanillin, vanillyl alcohol, p-hydroxybenzaldehyde, p-hydroxybenzyl alcohol, anisyl alcohol, and methyl cinnamate). Sweet, woody, balsamic, spicy, vanilla-like, and toasted notes were attributed to these compounds. Moreover, minor compounds present at less than 2 ppm have been found to contribute to the overall vanilla flavor, such as aldehydes, which were seen with green, oily, and herb-like floral notes, and aliphatic acids, which were described as having sour, buttery, and oily notes (Perez-Silva et al., 2006).
These studies have highlighted the specific anise flavor of Tahitian vanilla known as unique in the global market and considered as a luxury product.
Genetic Specificity
Genetic Relationship between Tahitian Vanilla and Other Cultivated Vanilla Species
In order to determine if Tahitian vanilla was genetically different from the other cultivated vanilla species, a comparative study of the genetic diversity was carried out. This project involved the Bureau des Ressources Génétiques (BRG), the Centre de Cooperation Internationale en Recherche Agronomique pour le Développement (CIRAD), the Etablissement Vanille de Tahiti, the University of Reunion Island, and the Institut de Biotechnologie des Plantes (IBP) (Andrzejewski et al., 2006; Duval et al., 2006). Cultivated species V. planifolia (47 samples), V. pompona (6 samples), and Polynesian cultivars (6 samples) from Reunion Island, Central America, and French Polynesia, and 35 related species from Thailand, Brazil, Guiana, Cameroun, and botanical gardens were analyzed. The amplification fragment length polymorphism (AFLP) pattern of each sample was compared with other samples and the data were used to calculate dissimilarities between the samples according to the Sokal and Michener index. The structure of the genetic tree represented the species delimitation with a high level of accuracy (bootstraps of 100%). This study indicated that Tahitian vanilla is genetically very distinct from other cultivated or wild vanilla species.
Tahitian vanilla was also compared with several wild or cultivated species of Vanilla from Central America in collaboration with the Riverside University (Lubinsky et al., 2008). The putative origin of the Tahitian vanilla was assessed. Patterns of DNA sequences from the nuclear internal transcribed spacer (ITS) and chloroplast genomes were compared between Polynesian cultivars and samples collected in the tropical forest of Central America: V. planifolia, V. odorata, V. insig-nis, V. pompona, and a few other species. These data indicated that the two genetically closest species to Tahitian vanilla were V. planifolia and V. odorata and thus indicated that these two species are closely related to the ancestors of the Tahitian vanilla. This study favors the hypothesis of Porteres (1951) who assumed that Tahitian vanilla resulted from hybridization between V. planifolia and another hybrid involving V. odorata.
Polynesian Genetic Diversity
At the same time, the genetic diversity among Polynesian cultivars was also analyzed. The morphological diversity observed among Tahitian vanilla, which allowed local growers to distinguish 14 cultivars, was related to genetic diversity. This genetic diversity was due to a variation at the level of the DNA sequences highlighted by the comparison of AFLP patterns between the different cultivars. AFLP patterns were defined by the presence or absence of each of the 529 tested AFLP markers. The comparison of these AFLP patterns indicated that in spite of the genetic diversity existing within Tahitian vanilla, all the accessions are gathered and form only one monophyletic group (Andrzejewski et al., 2006; Figure 13.11). Genetic diversity is weak (maximum distance between accession = 0.091) but coherent for a plant that is propagated by stem cutting and not by sexual reproduction. For some cultivars, many AFLP patterns were observed, indicating that diversity was underestimated by the growers and that new cultivars had to be defined.
FIGURE 13.11 Diversity structure of 42 cultivated vanilla and Vanilla bahiana accessions and detailed relationships of the Polynesian accessions derived from neighbor joining trees using the distance matrix of Sokal and Michener (529 variables and 1000 bootstraps).
Some others cultivars were not discriminated by their AFLP pattern; this was the case of Tahiti and Haapape. Their morphological differences were unambiguous; nevertheless, their genetic diversity has been found to be only the consequence of the number of copies of each AFLP marker. For this reason, cytogenetic analyses were developed.
As previously described for V. planifolia by Nair and Ravindran (1994), all the cells of a single root do not present the same chromosome value for Tahitian vanilla. We also observed these variations for the accessions of V. planifolia and V. pompona. Three ploidy levels were observed among the Polynesian accessions. The chromosome counts for numerous metaphase plates of root tips, and the genome size measurements by flow cytometry were concordant. Three groups were distinguished:
1. A diploid group (2×) with chromosome number ranging from 22 to 31 and with a genome size from 4.87 to 5.80 pg. These characteristics concerned the majority of the Polynesian cultivars: Tahiti (Figure 13.12), Rea rea, Parahurahu, Oviri, Paraauti, Potiti, Puroini, Pupa, Popoti, and Poura.
2. A triploid group (3×) for which the chromosome number varies from 33 to 41. This group contains two sterile vanilla plants called “Haapape sterile” showing abnormal flower physiology (absence of pollen and autoincompatibility).
3. A tetraploid group (4×) where the number of chromosomes and the genome size are twice as high as in the first group (43–56 chromosomes and genome size of 10.10–10.89 pg). The following are the cultivars: Haapape, Ofe ofe, Tiarei, and Tahiti long.
FIGURE 13.12 Metaphase plates of (a) cultivar Tahiti with 24 chromosomes and (b) cultivar Haapape with 52 chromosomes.
Genetic Relationship between Tahitian Vanilla and Other Cultivated Vanilla Species
In order to determine if Tahitian vanilla was genetically different from the other cultivated vanilla species, a comparative study of the genetic diversity was carried out. This project involved the Bureau des Ressources Génétiques (BRG), the Centre de Cooperation Internationale en Recherche Agronomique pour le Développement (CIRAD), the Etablissement Vanille de Tahiti, the University of Reunion Island, and the Institut de Biotechnologie des Plantes (IBP) (Andrzejewski et al., 2006; Duval et al., 2006). Cultivated species V. planifolia (47 samples), V. pompona (6 samples), and Polynesian cultivars (6 samples) from Reunion Island, Central America, and French Polynesia, and 35 related species from Thailand, Brazil, Guiana, Cameroun, and botanical gardens were analyzed. The amplification fragment length polymorphism (AFLP) pattern of each sample was compared with other samples and the data were used to calculate dissimilarities between the samples according to the Sokal and Michener index. The structure of the genetic tree represented the species delimitation with a high level of accuracy (bootstraps of 100%). This study indicated that Tahitian vanilla is genetically very distinct from other cultivated or wild vanilla species.
Tahitian vanilla was also compared with several wild or cultivated species of Vanilla from Central America in collaboration with the Riverside University (Lubinsky et al., 2008). The putative origin of the Tahitian vanilla was assessed. Patterns of DNA sequences from the nuclear internal transcribed spacer (ITS) and chloroplast genomes were compared between Polynesian cultivars and samples collected in the tropical forest of Central America: V. planifolia, V. odorata, V. insig-nis, V. pompona, and a few other species. These data indicated that the two genetically closest species to Tahitian vanilla were V. planifolia and V. odorata and thus indicated that these two species are closely related to the ancestors of the Tahitian vanilla. This study favors the hypothesis of Porteres (1951) who assumed that Tahitian vanilla resulted from hybridization between V. planifolia and another hybrid involving V. odorata.
Polynesian Genetic Diversity
At the same time, the genetic diversity among Polynesian cultivars was also analyzed. The morphological diversity observed among Tahitian vanilla, which allowed local growers to distinguish 14 cultivars, was related to genetic diversity. This genetic diversity was due to a variation at the level of the DNA sequences highlighted by the comparison of AFLP patterns between the different cultivars. AFLP patterns were defined by the presence or absence of each of the 529 tested AFLP markers. The comparison of these AFLP patterns indicated that in spite of the genetic diversity existing within Tahitian vanilla, all the accessions are gathered and form only one monophyletic group (Andrzejewski et al., 2006; Figure 13.11). Genetic diversity is weak (maximum distance between accession = 0.091) but coherent for a plant that is propagated by stem cutting and not by sexual reproduction. For some cultivars, many AFLP patterns were observed, indicating that diversity was underestimated by the growers and that new cultivars had to be defined.
FIGURE 13.11 Diversity structure of 42 cultivated vanilla and Vanilla bahiana accessions and detailed relationships of the Polynesian accessions derived from neighbor joining trees using the distance matrix of Sokal and Michener (529 variables and 1000 bootstraps).
Some others cultivars were not discriminated by their AFLP pattern; this was the case of Tahiti and Haapape. Their morphological differences were unambiguous; nevertheless, their genetic diversity has been found to be only the consequence of the number of copies of each AFLP marker. For this reason, cytogenetic analyses were developed.
As previously described for V. planifolia by Nair and Ravindran (1994), all the cells of a single root do not present the same chromosome value for Tahitian vanilla. We also observed these variations for the accessions of V. planifolia and V. pompona. Three ploidy levels were observed among the Polynesian accessions. The chromosome counts for numerous metaphase plates of root tips, and the genome size measurements by flow cytometry were concordant. Three groups were distinguished:
1. A diploid group (2×) with chromosome number ranging from 22 to 31 and with a genome size from 4.87 to 5.80 pg. These characteristics concerned the majority of the Polynesian cultivars: Tahiti (Figure 13.12), Rea rea, Parahurahu, Oviri, Paraauti, Potiti, Puroini, Pupa, Popoti, and Poura.
2. A triploid group (3×) for which the chromosome number varies from 33 to 41. This group contains two sterile vanilla plants called “Haapape sterile” showing abnormal flower physiology (absence of pollen and autoincompatibility).
3. A tetraploid group (4×) where the number of chromosomes and the genome size are twice as high as in the first group (43–56 chromosomes and genome size of 10.10–10.89 pg). The following are the cultivars: Haapape, Ofe ofe, Tiarei, and Tahiti long.
FIGURE 13.12 Metaphase plates of (a) cultivar Tahiti with 24 chromosomes and (b) cultivar Haapape with 52 chromosomes.
Conclusion
The originality of Tahitian vanilla is due to its morphology, its texture, and the aromatic content of its pods. These characteristics are indeed related to genotype. They are also influenced by geographical areas of cultivation. For example, beans of Tahitian vanilla produced and cured in French Polynesia are different from those produced in other countries. The rare and highly considered gourmet French Polynesian spice results from a combination of the factors the soil, the climate, and also the Polynesian people, who carefully produce and cure the vanilla beans.
Acknowledgments
The authors thank Dr. S. Siljak-Yakovlev (Univ. Paris Sud) and Dr. S.C. Brown (CNRS Gif sur Yvette) for their help in cytogenetic analysis and for their interest and support to Tahitian vanilla genome studies, and J. Foster for his invaluable comments on the manuscript.
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