Process Flavour Chemistry

Process flavourings are more related to cooking than to chemical synthesis. The reactions that occur are chemically very complex with hundreds of volatiles and nonvolatiles being formed. The final process flavouring is defined by the sum of the sensory effects of all aroma-active volatiles and taste-active compounds. 

Model reaction trials and modem analytical methods (gas chromatography/mass spectrometry (GC/MS), gas chromatography/olfactometry (GC/0)) permitted the identification of key mechanisms responsible for flavour generation in process flavourings and some of the most important ones are detailed below. Often chemically complex precursor raw materials (vegetables such as onions, spices, yeast extracts, animal products) are used. Research work on these complex reactions is rare but necessary and allows the discovery of new key odorants and formation pathways. For example, Widder and co-workers [13] discovered a new powerful aroma compound, 3-mer-capto-2-methylpentan-l-ol in a complex process flavour based on onion. 

The basic reactions contributing to thermal flavour generation are the Maillard reaction, Strecker degradation, lipid oxidation and thiamin degradation. Interaction of products formed by these different mechanisms additionally leads to further flavour components. 

In 1912 Maillard was the first scientist who studied the reaction between glucose 

Without any doubt the Maillard reaction and the Strecker reaction play an outstanding role in thermal aroma generation [ 15-20] and in particular in process flavourings. 

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PLS does not appear to have been applied to QSAR of flavours, and although much process has been made in the field of flavour chemistry, a greater insight into odour quality could be derived by the concept of applying many physico-chemical descriptors to the appropriate molecules. 

A complete understanding of the flavour chemistry and biochemistry of volatile components of fruits and vegetables is important in order to improve the flavour quality of fresh and processed produce that complies with the consumer needs for better quality vegetable and fruit products. 

Volatile flavour ptrofile changes in selected field pea cultivars as affected by crop year and processing. Food Chemistry, Vol. 124, No.l, pp. 326-335, ISSN 0308-8146 Barra, A., Baldovini, N., Loiseau, A. M., Albino, L., Lesecq, C., Lizzani Cuvelier, L. (2007). 

Alkylcatechols are important as chemicals and chemical intermediates in the fine chemistry industry for the synthesis of flavouring agents, agricultural chemicals and pharmaceuticals [1]. 3-methyl catechol has a special value from the industrial point of view. Previously y-alumina was found to be an effective catalyst for the gas-phase methylation of catechol with methanol [2]. The process can be schematically presented as ... 

J. Kerler, and C. Winkel, The basic chemistry and process conditions underpinning reaction flavour production, in Food Flavour Technology, A. J. Taylor (ed), Sheffield Academic Press, Sheffield, 2002, 27-59. 

L. P. Christensen M. Edelenbos S. Kreutzmann, Fruits and Vegetables of Moderate Climate. In Flavours and Fragrances Chemistry, Bio processing and Sustainability R. G. Berger, Ed. Springer-Verlag Berlin, 2007 pp 135-187. 

Chemical Changes In Food during Processing T. Richardson and J. W. Finley, Ed. AVI Westport, Connecticut, 1985 514 pp. Chemistry of Heterocyclic Compounds In Flavours and Aromas G. Vernln, Ed. Ellis Norwood, Ltd. Chichester, 1982 375 pp. Umaml A Basic Taste Y. Kawamura and M. R. Rare, Ed. Marcel Dekker, Inc. New York, 1987 649 pp. 

Schieberle, P, Hofmann, T., Identification of the key odorants in processed ribose-cysteine Mad-lard mixtures by instrumental analysis and sensory studies. In Flavour Science. Recent Developments, 8th Weurman Flavour Research Symposium (Taylor, A.J., Mottram, D.S., eds.), Royal Society of Chemistry, Cambridge, pp 175-181, 1996... 

Biotechnology has had a significant effect on the flavour industry but two factors have limited its application to fragrance. The first is cost, as biotechnological processes are usually quite expensive. The second is selectivity. Individual enzymic reactions are very selective, but biochemical redox reactions require expensive co-factors and so the usual technique is to run whole cell fermentations so as to allow the cell s chemical factory to recycle the co-factors. However, the cell does much chemistry in addition to the reaction we wish it to do and the result is a horrendous effluent problem. In flavours, the problem is often simpler as the whole cell, e.g. a yeast cell, can be used as the product. 

In this chapter, perfumery is used as an example of discovery chemistry but the basic underlying principles are the same as those in discovery of novel molecules for applications including pharmaceuticals, flavour ingredients, adhesives, lubricants and so on. The first part of the chapter outlines these basic principles and serves as an introduction for any area of discovery chemistry. The second part of the chapter uses fragrance ingredients as an example of the discovery process. 

Lindsay, R.C. 1994. Flavour of fish, in Seafoods Chemistry, Processing Technology and Quality, Shahidi, F. and Botta, J. R., Eds., Blackie Academic Professional, London, Chapter 6, 75. 

The 2001 Australian Science Festival in Canberra featured almost 200 events. The only ones with a chemical flavour were part of the Gourmet Science series that included the chemistry of beer, of wine, of cheese and of coffee. They were highly popular events with a general public audience and dealt with chemical reactions and processes with some practical tasting along the way. Other kinds of chemical presentations were absent, unless we include bubble shows and the like which incorporate a little chemistry in their explanations. 

In the early years of their use, plastics were regarded as essentially unreactive materials and there was a widespread ignorance of the chemistry of the materials and of the variety of compounds used in their manufacture. A decade or so ago, reports of adverse reactions arising from the use of plastics in a number of applications began to appear. These included problems of colour modification, flavour and odour taint of packaged food, and also unforeseen biological effects due to the use of plastics in the construction of medical appliances. Health problems associated with vinyl chloride processing led to the... 

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