Vanillin and
ethylvanillin are used by the food industry; ethylvanillin is more expensive, but has a stronger
note. It differs from vanillin by having an ethoxy group (−O−CH2CH3) instead of a methoxy group (−O−CH3).
Natural
vanilla extract is a mixture of several hundred different compounds in addition to vanillin. Artificial vanilla flavoring is often a solution of pure vanillin, usually of synthetic origin. Because of the scarcity and expense of natural vanilla extract, synthetic preparation of its predominant component has long been of interest. The first commercial synthesis of vanillin began with the more readily available natural compound
eugenol (4-allyl-2-methoxyphenol). Today, artificial vanillin is made either from
guaiacol or
lignin.
Lignin-based artificial vanilla flavoring is alleged to have a richer flavor profile than that from guiacol-based artificial vanilla; the difference is due to the presence of
acetovanillone, a minor component in the lignin-derived product that is not found in vanillin synthesized from guaiacol.[4]
History
Although it is generally accepted that vanilla was domesticated in
Mesoamerica and subsequently spread to the
Old World in the 16th century, in 2019, researchers published a
paper stating that vanillin residue had been discovered inside jars within a tomb in
Israel dating to the 2nd millennium BCE, suggesting the possible cultivation of an unidentified, Old World-endemic Vanilla species in
Canaan since the Middle
Bronze Age.[5][6] Traces of vanillin were also found in wine jars in
Jerusalem, which were used by the
Judahite elite before
the city was destroyed in 586 BCE.[6]
Vanilla beans, called tlilxochitl, were discovered and cultivated as a flavoring for beverages by native Mesoamerican peoples, most famously the Totonacs of modern-day
Veracruz, Mexico. Since at least the early 15th century, the
Aztecs used vanilla as a flavoring for
chocolate in drinks called xocohotl.[7]
Vanillin was first isolated as a relatively pure substance in 1858 by
Théodore Nicolas Gobley, who obtained it by evaporating a vanilla extract to dryness and
recrystallizing the resulting solids from hot water.[8] In 1874, the German scientists
Ferdinand Tiemann and
Wilhelm Haarmann deduced its chemical structure, at the same time finding a synthesis for vanillin from
coniferin, a
glucoside of
isoeugenol found in
pine bark.[9] Tiemann and Haarmann founded a company Haarmann and Reimer (now part of
Symrise) and started the first industrial production of vanillin using their process (now known as the
Reimer–Tiemann reaction) in
Holzminden, Germany. In 1876,
Karl Reimer synthesized vanillin (2) from guaiacol (1).[10]
By the late 19th century, semisynthetic vanillin derived from the eugenol found in
clove oil was commercially available.[11]
Synthetic vanillin became significantly more available in the 1930s, when production from clove oil was supplanted by production from the
lignin-containing waste produced by the
sulfite pulping process for preparing wood pulp for the
paper industry. By 1981, a single pulp and paper mill in
Thorold, Ontario, supplied 60% of the world market for synthetic vanillin.[12] However, subsequent developments in the wood pulp industry have made its lignin wastes less attractive as a raw material for vanillin synthesis. Today, approximately 15% of the world's production of vanillin is still made from lignin wastes,[13] while approximately 85% synthesized in a two-step process from the
petrochemical precursors
guaiacol and
glyoxylic acid.[14][15]
Beginning in 2000,
Rhodia began marketing biosynthetic vanillin prepared by the action of microorganisms on
ferulic acid extracted from
rice bran. At
USD$700/kg, this product, sold under the trademarked name Rhovanil Natural, is not cost-competitive with petrochemical vanillin, which sells for around US$15/kg.[16] However, unlike vanillin synthesized from lignin or guaiacol, it can be labeled as a natural flavoring.
Occurrence
Vanillin is most prominent as the principal flavor and aroma compound in
vanilla. Cured vanilla pods contain about 2% by dry weight vanillin. On cured pods of high quality, relatively pure vanillin may be visible as a white dust or "frost" on the exterior of the pod.
Natural vanillin is extracted from the seed pods of Vanilla planifolia, a
viningorchid native to Mexico, but now grown in tropical areas around the globe.
Madagascar is presently the largest producer of natural vanillin.
As harvested, the green seed pods contain vanillin in the form of its β-D-
glucoside; the green pods do not have the flavor or odor of vanilla.[29]
After being harvested, their flavor is developed by a months-long curing process, the details of which vary among vanilla-producing regions, but in broad terms it proceeds as follows:
First, the seed pods are
blanched in hot water, to arrest the processes of the living plant tissues. Then, for 1–2 weeks, the pods are alternately sunned and sweated: during the day they are laid out in the sun, and each night wrapped in cloth and packed in airtight boxes to sweat. During this process, the pods become dark brown, and
enzymes in the pod release vanillin as the free molecule. Finally, the pods are dried and further aged for several months, during which time their flavors further develop. Several methods have been described for curing vanilla in days rather than months, although they have not been widely developed in the natural vanilla industry,[30] with its focus on producing a premium product by established methods, rather than on innovations that might alter the product's flavor profile.
Biosynthesis
Although the exact route of vanillin biosynthesis in V. planifolia is currently unknown, several pathways are proposed for its biosynthesis. Vanillin biosynthesis is generally agreed to be part of the
phenylpropanoid pathway starting with L-phenylalanine,[31] which is deaminated by
phenylalanine ammonia lyase (PAL) to form t-
cinnamic acid. The para position of the ring is then
hydroxylated by the
cytochrome P450 enzyme cinnamate 4-hydroxylase (C4H/P450) to create p-
coumaric acid.[32] Then, in the proposed ferulate pathway, 4-hydroxycinnamoyl-CoA ligase (4CL) attaches p-coumaric acid to
coenzyme A (CoA) to create p-coumaroyl CoA.
Hydroxycinnamoyl transferase (HCT) then converts p-coumaroyl CoA to 4-coumaroyl
shikimate/
quinate. This subsequently undergoes oxidation by the P450 enzyme coumaroyl ester 3’-hydroxylase (C3’H/P450) to give caffeoyl shikimate/quinate. HCT then exchanges the shikimate/quinate for CoA to create caffeoyl CoA, and 4CL removes CoA to afford caffeic acid. Caffeic acid then undergoes
methylation by caffeic acid O-
methyltransferase (COMT) to give ferulic acid. Finally, vanillin synthase hydratase/lyase (vp/VAN) catalyzes hydration of the double bond in ferulic acid followed by a retro-aldol elimination to afford vanillin.[32] Vanillin can also be produced from vanilla glycoside with the additional final step of deglycosylation.[29] In the past p-hydroxybenzaldehyde was speculated to be a precursor for vanillin biosynthesis. However, a 2014 study using
radiolabelledprecursor indicated that p-hydroxybenzaldehyde is not used to synthesise vanillin or vanillin glucoside in the vanilla orchids.[32]
Chemical synthesis
The demand for vanilla flavoring has long exceeded the supply of vanilla beans. As of 2001[update], the annual demand for vanillin was 12,000 tons, but only 1,800 tons of natural vanillin were produced.[33] The remainder was produced by
chemical synthesis. Vanillin was first synthesized from eugenol (found in oil of clove) in 1874–75, less than 20 years after it was first identified and isolated. Vanillin was commercially produced from eugenol until the 1920s.[34] Later it was synthesized from lignin-containing "brown liquor", a byproduct of the
sulfite process for making
wood pulp.[12] Counterintuitively, though it uses waste materials, the lignin process is no longer popular because of environmental concerns, and today most vanillin is produced from the
petrochemical raw material
guaiacol.[12] Several routes exist for synthesizing vanillin from guaiacol.[35]
At present, the most significant of these is the two-step process practiced by
Rhodia since the 1970s, in which guaiacol (1) reacts with
glyoxylic acid by
electrophilic aromatic substitution.[36] The resulting
vanillylmandelic acid (2) is then converted by 4-Hydroxy-3-methoxyphenylglyoxylic acid (3) to vanillin (4) by oxidative decarboxylation.[14]
Wood-based vanillin is produced by copper-catalyzed oxidation of the
lignin structures in
lignosulfonates under alkaline conditions[37] and is claimed by the manufacturing company to be preferred by their customers due to, among other reasons, its much lower carbon footprint than petrochemically synthesized vanillin.
Fermentation
The company Evolva has developed a genetically modified microorganism which can produce vanillin. Because the microbe is a
processing aid, the resulting vanillin would not fall under U.S. GMO labeling requirements, and because the production is nonpetrochemical, food using the ingredient can claim to contain "no artificial ingredients".[38]
Using
ferulic acid as an input and a specific non GMO species of Amycolatopsis bacteria, natural vanillin can be produced.
The largest use of vanillin is as a flavoring, usually in
sweet foods. The
ice cream and
chocolate industries together comprise 75% of the market for vanillin as a flavoring, with smaller amounts being used in
confections and
baked goods.[41]
Vanillin is also used in the fragrance industry, in
perfumes, and to mask unpleasant odors or tastes in medicines, livestock
fodder, and cleaning products.[14] It is also used in the flavor industry, as a very important key note for many different flavors, especially creamy profiles such as
cream soda.
Additionally, vanillin can be used as a general-purpose stain for visualizing spots on
thin-layer chromatography plates. This stain yields a range of colors for these different components.
Vanillin–HCl staining can be used to visualize the localisation of tannins in cells.
Vanillin is becoming a popular choice for the development of bio-based plastics.[42]
Manufacturing
Vanillin has been used as a chemical intermediate in the production of
pharmaceuticals,
cosmetics, and other
fine chemicals.[43] In 1970, more than half the world's vanillin production was used in the synthesis of other chemicals.[12] As of 2016, vanillin uses have expanded to include
perfumes, flavoring and aromatic masking in medicines, various consumer and cleaning products, and
livestock foods.[44]
Adverse effects
Vanillin can trigger
migraine headaches in a small fraction of the people who experience migraines.[45]
Some people have
allergic reactions to vanilla.[46] They may be allergic to synthetically produced vanilla but not to natural vanilla, or the other way around, or to both.[47]
Vanilla orchid plants can trigger
contact dermatitis, especially among people working in the vanilla trade if they come into contact with the plant's sap.[47] An allergic contact dermatitis called vanillism produces swelling and redness, and sometimes other symptoms.[47] The sap of most species of vanilla orchid which exudes from cut stems or where beans are harvested can cause moderate to severe dermatitis if it comes in contact with bare skin. The sap of vanilla orchids contains
calcium oxalate crystals, which are thought to be the main causative agent of contact dermatitis in vanilla plantation workers.[48][49]
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Lampman, Gary M.; Jennifer Andrews; Wayne Bratz; Otto Hanssen; Kenneth Kelley; Dana Perry; Anthony Ridgeway (1977). "Preparation of vanillin from eugenol and sawdust". Journal of Chemical Education. 54 (12): 776–778.
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Vreuls, René J. J.; van der Heijden, Arnold; Brinkman, Udo A. Th.; Adahchour, Mohamed (1999). "Trace-level determination of polar flavour compounds in butter by solid-phase extraction and gas chromatography–mass spectrometry". Journal of Chromatography A. 844 (1–2): 295–305.
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^According to
Esposito 1997, blind taste-testing panels cannot distinguish between the flavors of synthetic vanillin from lignin and those from guaicol, but can distinguish the odors of these two types of synthetic vanilla extracts. Guaiacol vanillin, adulterated with acetovanillone, has an odor indistinguishable from lignin vanillin.
^According to
Hocking 1997, synthetic vanillin was sold commercially in 1874, the same year Tiemann and Haarmann's original synthesis was published. Haarmann and Reimer, one of the corporate ancestors of the modern flavor and aroma manufacturer Symrise, was in fact established in 1874. However,
Esposito 1997 claims that synthetic vanillin first became available in 1894 when Rhône-Poulenc (since 1998,
Rhodia) entered the vanillin business. If the former claim is correct, the authors of the latter article, being employees of Rhône-Poulenc, may have been unaware of any previous vanillin manufacture.
^Carrero Gálvez, Miguel (1994). "Analysis of polyphenolic compounds of different vinegar samples". Zeitschrift für Lebensmittel-Untersuchung und -Forschung. 199: 29–31.
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S2CID91784893..
^Dignum 2001 reviews several such proposed innovations in vanilla processing, including processes in which the seed pods are chopped, frozen, warmed by a heat source other than the sun, or crushed and treated by various enzymes. Whether or not these procedures produce a product whose taste is comparable to traditionally prepared natural vanilla, many of them are incompatible with the customs of the natural vanilla market, in which the vanilla beans are sold whole, and graded by, among other factors, their length.
^Sinha, A. K.; Sharma, U. K.; Sharma, N. (2008). "A comprehensive review on vanilla flavor: Extraction, isolation and quantification of vanillin and others constituents". International Journal of Food Sciences and Nutrition. 59 (4): 299–326.
doi:
10.1080/09687630701539350.
PMID17886091.
S2CID37559260.
^Saint Denis, M.; Coughtrie, M. W.; Guilland, J. C.; Verges, B.; Lemesle, M.; Giroud, M. (Dec 1996). "Migraine induced by vanillin". Presse Méd. 25 (40): 2043.
PMID9082382.
^Meyer, H.J.; Norris, D.M. (17 July 1967). "Vanillin and Syringaldehyde as Attractants for Scolytus multistriatus (Coleoptera: Scolytidae)". Annals of the Entomological Society of America. 60 (4): 858–859.
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