VANILLIN PRODUCTION

In 1874, Tiemann and Ha arm ann examined the stmcture of vanillin and reported it to be 3-methoxy-4-hydroxybenzaldehyde. This was not a difficult task because, on treatment with potassium hydroxide, vanillin (1) gave protocatechaic acid [99-50-3] (2), which, in turn, was decarboxylated to catechol [120-80-9] (3) by dry distillation (eq. 1). As both compounds were known at that time, the position of the substituent groups in vanillin was estabHshed. Finally, Reimer synthesized vanillin from guaiacol [90-05-1] and thus proved the identity of its stmcture. In 1894 RhcJ)ne-Poulenc began producing vanillin on an industrial scale. Since then, many other producers have entered into vanillin production, often only to leave it behind. 

Preparation from Waste Sulfite Liquors. The starting material for vanillin production can also be the lignin (qv) present in sulfite wastes from the ceUulose industry. The concentrated mother Hquors are treated with alkaH at elevated temperature and pressure in the presence of oxidants. The vanillin formed is separated from the by-products, particularly acetovanillone, 4-hydroxy-3-methoxyacetophenone, by extraction, distillation, and crystallization. 

Various experiments in Vanilla plant cell cultures, however, gave different results [14-18, 30, 51]. This might be due to the fact that different biosynthetic pathways operate in the beans and in the cell culture. In fact most of the work in cell cultures showed only conversion of non-glucosylated products. Ferulic acid feeding resulted in increased vanillin levels. The fact that the V. planifolia cell cultures do not produce vanillin in any significant amount means that the results from studies using vanilla cell cultures for elucidation of the pathway should be considered with caution. Finally, it cannot be excluded that different pathways may contribute to the vanillin production in the beans. Scheme 9.1 shows that vanillin can be formed through different ways in a complex network of compounds. 

Dignum et al. [8, 10] followed this process in detail on a production site in Bali to measure the various parameters of the processing in order to mimic these in a laboratory model curing system. The parameters are summarised in Table 9.1. On the basis of the observations, a model curing system was set up to study different parameters under controlled conditions and the effect on some enzymes and the vanillin production. 

Since isoeugenol is the important intermediate in the vanillin production from eugenol, the isomerization of eugenol attracted a considerable amount of attention. The first report on the isomerization reaction appeared in 1891, in which Tiemann reported 50% conversion in 24 hours using an ethanolic KOH solution at 80°C [13]. 

In summary, of the alternatives available for introducing a pathway of vanillin production de novo, or for enhancing vanillin production in Vanilla, HCHL presents the most attractive option of generating vanillin from a phenylpropanoid precursor (feruloyl-CoA) naturally present in plants (Whetten and Sederoff, 1995). 

Fargues, C., Mathias, A., and Rodrigues, A., Kinetics of vanillin production from om Krafl lignin oxidation. Industrial Eng Chem Res 1996, 35 (1), 28-36. 

Barghini, P., Di Gioia, D., Fava, F., and Ruzzi, M., Vanillin production using metaboUcally engineered Escherichia coli under non-growing conditions, Microb. Cell Fact., 6, 13, 2007. 

At that time, the price of synthetic vanillin was approximately in the same range, between 180 and 800 dollars per kilogram, as the natural product from vanilla pods. Up to the end of the 1920s, eugenol from dove oil served as the starting material for vanillin production. 

Parpot P, Bettencourt AP, Carvalho AM, Belgsir EM (2000) Biomass conversion attempted electrooxidation of lignin for vanillin production. J Appl Electrochem 30 727-731... 

Brochado, A.R. and Patil, K.R. (2013) Overexpression of O-methyltransferase leads to improved vanillin production in baker s yeast only when complemented with model-guided network engineering. Biotechnol. Bioeng., 110, 656-659. 

Yamada M, Okada Y, Yoshida T, Nagasawa T (2008) Vanillin production using Escherichia coli cells over-expressing isoeugenol monooxygenase of Pseudomonas putida. Biotechnol Lett 30 665-670... 

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