Vanillin
Vanillin is an organic compound with the molecular formula. It is a phenolic aldehyde. Its functional groups include aldehyde, hydroxyl, and ether. It is the primary component of the ethanolic extract of the vanilla bean. Synthetic vanillin is now used more often than natural vanilla extract as a flavoring in foods, beverages, and pharmaceuticals.
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 instead of a methoxy group.
Natural vanilla extract is a mixture of several hundred different compounds in addition to vanillin. Artificial vanilla flavoring is often an ethanol solution of pure vanillin, usually of synthetic origin. Because of the scarcity and expense of natural vanilla, synthetic preparation of artificial vanilla flavoring has long been of interest. The first commercial synthesis of vanillin began with the more readily available natural compound eugenol. 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 guaiacol-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.
Natural 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 Canaan 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. 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.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.
Synthetic history
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. 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 coniferyl alcohol found in pine bark. Tiemann and Haarmann founded a company Haarmann and Reimer and started the first industrial production of vanillin using their process in Holzminden, Germany. In 1876, Karl Reimer synthesized vanillin from guaiacol.By the late 19th century, semisynthetic vanillin derived from the eugenol found in clove oil was commercially available.
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. 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, while approximately 85% is synthesized in a two-step process from the petrochemical precursors guaiacol and glyoxylic acid.
Beginning in 2000, Rhodia began marketing biosynthetic vanillin prepared by the action of microorganisms on ferulic acid extracted from rice bran. This product, sold at USD$700/kg under the trademarked name Rhovanil Natural, is not cost-competitive with petrochemical vanillin, which sells for around US$15/kg. 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. Relatively pure vanillin may be visible as a white dust or "frost" on the exteriors of cured pods of high quality.It is also found in Leptotes bicolor, a species of orchid native to Paraguay and southern Brazil, and the Southern Chinese red pine.
At lower concentrations, vanillin contributes to the flavor and aroma profiles of foodstuffs as diverse as olive oil, butter, raspberry, and lychee fruits.
Aging in oak barrels imparts vanillin to some wines, vinegar, and spirits.
In other foods, heat treatment generates vanillin from other compounds. In this way, vanillin contributes to the flavor and aroma of coffee, maple syrup, and whole-grain products, including corn tortillas and oatmeal.
Production
Natural production
Natural vanillin is extracted from the seed pods of Vanilla planifolia, a vining orchid 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 glucovanillin, its β--glucoside; the green pods do not have the flavor or odor of vanilla. Vanillin is released from glucovanillin by the action of the enzyme β-glucosidase during ripening and during the curing process.
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, 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 -phenylalanine, which is deaminated by phenylalanine ammonia lyase to form t-cinnamic acid. The para position of the ring is then hydroxylated by the cytochrome P450 enzyme cinnamate 4-hydroxylase to create p-coumaric acid. Then, in the proposed ferulate pathway, 4-hydroxycinnamoyl-CoA ligase attaches p-coumaric acid to coenzyme A to create p-coumaroyl CoA. Hydroxycinnamoyl transferase then converts p-coumaroyl CoA to 4-coumaroyl shikimate/quinate. This subsequently undergoes oxidation by the P450 enzyme coumaroyl ester 3'-hydroxylase 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 to give ferulic acid. Finally, vanillin synthase hydratase/lyase catalyzes hydration of the double bond in ferulic acid followed by a retro-aldol elimination to afford vanillin. Vanillin can also be produced from vanilla glycoside with the additional final step of deglycosylation. In the past p-hydroxybenzaldehyde was speculated to be a precursor for vanillin biosynthesis. However, a 2014 study using radiolabelled precursor indicated that p-hydroxybenzaldehyde is not used to synthesise vanillin or vanillin glucoside in the vanilla orchids.Chemical synthesis
The demand for vanilla flavoring has long exceeded the supply of vanilla beans., the annual demand for vanillin was 12,000 tons, but only 1,800 tons of natural vanillin were produced. The remainder was produced by chemical synthesis. Vanillin was first synthesized from eugenol in 1874–75, less than 20 years after it was first identified and isolated. Vanillin was commercially produced from eugenol until the 1920s. Later it was synthesized from lignin-containing "brown liquor", a byproduct of the sulfite process for making wood pulp. Counterintuitively, though it uses waste materials, the lignin process is no longer popular because of environmental concerns, and today most vanillin is produced from guaiacol. Several routes exist for synthesizing vanillin from guaiacol.At present, the most significant of these is the two-step process practiced by Rhodia since the 1970s, in which guaiacol reacts with glyoxylic acid by electrophilic aromatic substitution. The resulting vanillylmandelic acid is then converted by 4-hydroxy-3-methoxyphenylglyoxylic acid to vanillin by oxidative decarboxylation.
Although guaiacol can be obtained by pyrolysis of wood, the type intended for vanillin production is mainly produced by petrochemistry.
Wood-based vanillin
15% of the world's production of vanillin is produced from lignosulfonates, a byproduct from the manufacture of cellulose via the sulfite process. The sole remaining producer of wood-based vanillin is the company Borregaard located in Sarpsborg, Norway. For this kind of use, softwood is preferred because there are more guaiacyl units convertible to vanillin.Early production of wood-based vanillin involved four plants: a sulfite pulp mill, a fermentation plant, a vanillin plant, and a Kraft pulp mill. The sulfite mill provides the brown liquor to the fermentation plant, which makes use of the residual sugar. The spend liquor is sent to the vanillin plant, which uses alkaline oxidation with air at 160–170 °C and 10–12 atm pressure, toluene extraction, and back-extraction with NaOH to obtain a crude sodium vanillate. Addition of sulfurous acid affords easy separation of the soluble sulfide addition compound of vanillin from insoluble impurities such as acetovanillone. The vanillin is extracted, and the remaining liquor is sent to the Kraft mill for burning to recover energy and sodium sulfide, both important for a Kraft mill. This process went out of favor in North America due to the large amounts of caustic liquids that needs to be disposed by the mill at the end: 160 kg for every 1 kg of vanillin produced. The recovery of sodium sulfide also became less and less profitable as the sodium-to-sulfur ratio became more and more unbalanced.
Borregaard is able to keep operating because it runs its own pulp mill. They have improved a process from Monsanto by using ultrafiltration to concentrate the incoming lignosulfonates, which reduces the amount of NaOH used and waste produced. The basic chemistry is unchanged: alkaline oxidation using a metal catalyst such a copper salt. According to Scientific American, vanillin produced this way contains aromatic impurities that add strength and creaminess to its flavor. This is probably due to acetovanillone being present.