Vanillin, precursor

Validation of the role of femloyl-CoA in the synthesis of the vanillin precursor will be detection of the appropriate intermediates and/or enzyme activities in placental extracts that could account for the production of the predicted levels of capsaicinoids. The presence of low levels of monolignol intermediates could be explained by lignin biosynthesis. An alternate route from phenylalanine to vanillin has been considered by some investigators Orlova et al. [68] demonstrated the role of the benzenoid pathway in petunia flowers for the biosynthesis of phenylpropanoid/benzenoid volatiles. 

In this chapter chemical conversions of natural precursors resulting in flavour chemicals are discussed. The main groups of natural precursors are terpenes for all kinds of terpene derivatives, vanillin precursors like lignin and eugenol, sugars for Maillard-associated flavour chemicals, amino acids and molecules obtained by fermentation or available as residual streams of renewable resources. 

An example of this approach was outlined by Gatfield [65] on the conversion of ferulic acid to vanillin (Figure 9.12). Ferulic is an abundant, inexpensive, natural vanillin precursor recovered from waste streams or from the fermentation of eugenol [87]. While many miCTobial systems have been found that accomplish the desired bioconversion, Gatfield [65] has suggested that Amycolatopsis species is the most efficient providing vanillin concentrations up to lOg/L in a fermentation period of only 36 h [88,89]. This is an excellent yield and few side products were found. 

Capsaicinoids are synthesized by the condensation of vanillylamine with a short chain branched fatty acyl CoA. A schematic of this pathway is presented in Fig. 8.4. Evidence to support this pathway includes radiotracer studies, determination of enzyme activities, and the abundance of intermediates as a function of fruit development [51, 52, 57-63], Differential expression approaches have been used to isolate cDNA forms of biosynthetic genes [64-66], As this approach worked to corroborate several steps on the pathway, Mazourek et al. [67] used Arabidopsis sequences to design primers to clone the missing steps from a cDNA library. They have expanded the schema to include the biosynthesis of the key precursors phenylalanine and leucine, valine and isoleucine. Prior to this study it was not clear how the vanillin was produced, and thus the identification of candidate transcripts on the lignin pathway for the conversion of coumarate to feruloyl-CoA and the subsequent conversion to vanillin provide key tools to further test this proposed pathway. 

Hydroxy-3-methoxy-B-nitrostyrene. A mixture of methylamine hydrochloride (7 g, see precursor section for synthesis) and 10 g of sodium carbonate in 100 ml of methanol is stirred well, filtered, and added to a solution of 219 g of vanillin and 85 ml of nitromethane in 600 ml of ethanol. Keep this solution in the dark at room temp for 71 hours to make the nitrostyrene crystallize out. Filter and wash with cold methanol. Yield 225 grams, nip 166-168°. This and the other two nitriles are reduced by the method listed in the reduction section, JACS, 72, 2781. This reduction can be used to reduce many of the nitro type compounds. 

Labuda IM, Goers KA, Keon KA (1993) Microbial bioconversion process for the production of vanillin. In Schreier P, Winterthaler P (eds) Progress in flavour precursor studies analysis, generation, biotechnology. Proceedings of the international conference, Wuerzburg. Allured, Carol Stream, pp 477-482... 

Eugenol obtained from clove oil is an important precursor for the preparation of vanillin (Scheme 13.10). The reaction consists of two steps. First, eugenol needs to be converted into isoeugenol, which requires alkaline treatment or ruthenium or rhodium catalysis. Second, the isoeugenol is oxidised to vanillin using, for instance, chromic acid. This method results in nature-identical vanillin. 

Tripathi et al. (2002) studied the biotransformation of phenylpropa-noid intermediates — ferulic acid, con-iferyl aldehyde and p-coumaric acid in free and immobilized cell cultures of Haematococcus pluvialis, which accumulated vanilla flavour metabolites - vanillin, vanillic acid, vanillyl alcohol, protocate-chuic acid, p-hydroxybenzoic acid, p-hydroxybenzaldehyde and p-coumaric acid when treated with these precursors, to a range corresponding to vanilla flavour metabolites. 

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). 

Using immediate precursors of desired food aroma compounds also increased metabolite yields. For example, by applying ferulic acid to cultured Vanilla planifolia cells, vanillin concentration could be enhanced as compared to untreated cells. Vanilla concentration was also increased in green vanilla bean extracts when the cells were treated with 3-glucosidase. 

Vanilla is one of the most important food flavors (37). Sahai et al. (38) suggested that ferulic acid is an immediate precursor to vanillin and vanillic acid, two key components of vanilla flavor (38). Applying a 1 mM ferulic acid solution to Vanilla planifolia callus increased vanillin concentration, as compared to the untreated samples (Table VI). Concentration of key vanilla flavor components... 

Table VI. Production of vanillin in Vanilla planifolia callus cultures as affected by precursor treatment with ferulic acida...

Alkylarylethers have pleasant odors and flavours which made them valuable for the perfume and fragrance industries. They are also important precursors of agrochemicals, pharmaceuticals, antioxidants, etc. (32). Thus, anisole which results from phenol methylation is a precursor of Parsol, a solar protector (paragraph 14.2.). Vanillin results from gai acol transformation (3, 32) ... 

On reduction with sodium borohydride, product II yielded a pair of radioactive products that were tentatively identified as 2-deoxy-L-Zyxo-hexose and 2,6-dideoxy-L-arafeino-hexose. This result, together with the chromatographic properties of II, and its reaction on chromatograms with vanillin-perchloric acid to give a blue color, are consistent with the structure of 2,6-dideoxy-L-Zyxo-hexos-4-ulose (20) for II. This structure is also consistent with the concept that II (20) is, very probably, the precursor of III (19). 

The onset of the industrial production of essential oils can be dated back to the first half of the 19 century. After the importance of single aroma chemicals was recognised in the middle of the century, efforts were started to isolate such compounds from corresponding natural resources for the first time. This was soon followed by the synthesis of aroma chemicals. In this context, the most important pioneers of synthetic aroma chemicals have to be mentioned, such as methyl salicylate [1843], cinnamon aldehyde [1856], benzyl aldehyde [1863] and vanillin [1872], as they constitute the precursors of a rapidly growing number of synthetically produced (nature-identical) aroma chemicals in the ensuing years. 

Labuda, I.M., Keon, K.A., and Goers, S.K. Microbial Bioconversion Process for the Production of Vanillin. In Progress in Flavour Precursor Studies (Schreier, P. and Winterhalter, P. eds.). Allured Publishing, pp. 477-482 (1993)... 

Reactivity and selectivity observed for furan derivatives have been extended to aromatic phenols. The most interesting results have been obtained for the hydro-xymethylation of guaiacol with formaldehyde leading to pura-hydroxymethyl-guaiacol, the precursor for vanillin [11]. Use of H-Mordenite type catalyst with an Si to A1 ratio of 18, low temperature (40 °C), and well-defined conditions led to very good results-33 % conversion with 98 % alcohol selectivity can be obtained and para selectivity of 83 % [12] (Eq. 4). 

Later, Tressl et al. (1976) also proceeded to the thermic degradation (2 h, 200 JC) of ferulic acid (H.87) and identified the same phenols as Fiddler et al., plus 4-isopropylguaiacol and vanillin alcohol (4-hydroxy-3-methoxybenzenemethanol) which have not been found in coffee. For isoeugenol (H.38), the formula is written as the (E)-( trans -) isomer, but nothing was specified in the text. Tressl et al. (1976) also published the results of thermal decomposition of cinnamic, p-coumaric (H.84) and sinapic (H.90) acids. Many of the simple phenols (and other aromatic compounds) formed have also been identified in roasted coffee volatiles. A thermic fragmentation of quinic acid (E.62) has shown that simple acids, phenols and polyphenols originate from this precursor (Tressl et al., 1978a). 

Friedrich (1976) suggested formation by methylation of protocatechuic aldehyde (H.55), the corresponding glycoside being the immediate precursor. Tressl et al. (1976, 1979b) identified vanillin as a thermal decomposition product of ferulic acid (H.87), formed by oxidation of 4-vinylguaiacol (H.36). 

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