Flavour precursors

Kubec R, Svobodova M and Velisek J (2000), Distribution of 5-alk(en)ylcysteine sulfoxides in some Allium species. Identification of a new flavour precursor S-ethylcysteine sulfoxide (ethiin) , JAgric Food Chem, 48, 428-433. 

Scheme 7.3 Enzymatic production of sulfur-containing flavour compounds in Allium species from amino acid flavour precursors, a S-Alk(en)yl cysteine sulfoxides and b (+)-S-l-propenyl cysteine sulfoxide (isoalliin) P-5 -Ppyridoxal-5 -phosphate...

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... 

Schieberle P (1993) In Progress in Flavour Precursor Studies (Schreier P, Winterhalter P, eds.) Allured Publishing Corporation, Carol Stream, IL, USA, pp 343-360. 

Albrecht W, Heidlas J, Schwarz M, Tressl R (1992) In Flavour Precursors (Teranishi R, Takeoka GR, Guntert M, eds.) American Chemical Society, Washington, DC, pp 46-58. 

Graf S, Knorr D (1993) Multiple shoot cultures of Mentha canadensis for biotechnological production of flavours. In Schreier P, Winterhalter P (eds) Progress in flavour precursor studies, vol 4. Carol Stream Allured Publishers, p 471... 

Abbott, N.A., Coombe, B.G. Williams, P.J. (1991). The contribution of hydrolyzed flavour precursors to quahty differences in Shiraz juice and wines an investigation by sensory descriptive analysis. Am. J. Enol. Vitic., 42, 167-174. 

Boido, E., Uoret, A., Medina, K., Carrau, E Delia Cassa, E. (2002). Effect of [J-glycosidase activity of Oenococcus oeni on the glycosylated flavour precursors of Tannat wine during mal-olactic fermentation. J. Agric. Food Chem., 50, 2344-2349. 

Francis, I.L., Sefton, M.A., Williams. P.J. (1992). Sensory descriptive analysis of the aroma of hydrolysed flavour precursor fractions from Semilion, Chardonnay, and Sauvignon Wane grape juices. J. Sci Food Agric., 59, 511-520. 

Tominaga, T., Peyrot de Gachons. C. Dubourdieu, D. (1998). A new type of flavour precursors in Vitis vinifera L. cv. Sauvignon Wane S-cysteine conjugates. J. Agric. Food Chem., 46, 5215-5219. 

Williams, P. J., Erancis, l.L. Black. S. (1996). Changes in concentration of juice and must glycosides, including flavour precursors, during primary fermentation. In T. Henick-Kling Wolf, T. (Eds.), Proceedings of the IVth International Symposium on cool climate viticulture and enology (pp. V1-5-V1-9). Rochester, NY. 

Wakabayashi, H., Wakabayashi, M., Engel, K.H. (2003). (i-lyase-catalysed-transformations of sulphur-containing flavour precursors. In J.L. Lequere P. Etievant (Eds.), Flavour Research at the Dawn of the Twenty First Century (pp. 350-355). Paris Tec Doc. 

Garegg, P J, Oscarson, S, Ritzen, H, Partially esterified sucrose derivatives synthesis of 6-0-acetyl-2, 3,4-tri-0-[(5)-3-methylpentanoyl]sucrose, a naturally occurring flavour precursor of tobacco, Carbohydr. Res., 181, 89-96, 1988. 

In the case of salami, starter cultures can be cultivated on meat substrate and freeze-dried, where they remain active at a large rate. The storable culture substrate is added to the salami raw mixture to start the desired ripening process. Depending on process course, it can already contain flavour or flavour-precursors which contribute to accelerating the ripening process. 

Table 2.10 shows that the isolation and purification of naturally occurring flavour chemicals and extracts from animal and plant raw materials is most important for the preparation of natural flavours. About 75% of the commercially used flavours come from such natural sources. Physico-chemical reactions of typical flavour precursors may also lead to natural flavouring substances when mild conditions ( kitchen technology ) are applied. In addition, natural flavour chemicals may be prepared by biotechnological processes. This chapter outlines the most important biotechnical manufacturing techniques. 

The chemical transformation of flavour precursors by micro-organisms (biotransformation)... 

It is the role of technical bioreactors in such advanced systems to create a specifically defined environment for the biochemical reaction system producing or modifying flavour substances. The most important purpose of such bioreactors is the well controlled combination of food raw material and flavour precursor, respectively, with the biological reaction centres. It also provides the means for survival and maintenance of the centre s metabolic activity. Presently there is laboratory and partially also industrial experience with mostly all kinds of different micro-organisms and isolated biocatalysts ... 

Fig. 2.66 Biotransformation of a flavour precursor into a flavour product by enzymes in a membrane reactor...

As shown above flavour substances may be mobilized by destruction of cells and framing structures of plants and by extraction of flavour materials dissolved in the plant juices. In addition, flavour precursors may also be liberated from covalent bonds [18a], The majority of these bonds are glycosidic links of flavour chemicals to molecular or particulate plant components. The enzymes used for cleavage of these bonds (p-glycosidases) tend to form equilibria of bound and free forms. 

The same holds for products from animal cell cultures where even less results are available. With animal cell cultures especially enzymes are accessible which may be used for biotransformations of flavour precursors. Compared to the progress in the production of pharmaceutical substances from animal cell cultures it is only a question of time when processes are developed which allow the economical production of flavour chemicals not yet accessible by other routes. Quick progress is expected, among others, for sweeteners, bitter substances, essential oils, fruity flavours and vegetable flavours from cell cultures. 

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