126 BOOK REVIEWS

FLAVOR CHEMISTRY: TRENDS AND DEVELOPMENTS, edited by Roy Teranishi, Ron G. Buttery and Fereidoon Shahidi. No. of pages: viii + 246. ACS Symposium Series 388. ISBN 0-8412-1 570-7. Price: US $ 52.95. American Chemical Society, Washington DC (1989).

This book represents the proceedings of a symposium sponsored by the Division of Agricultural and Food Chemistry at the Third Chemical Congress of North America (195th National Meeting of the American Chemical Society) held in Toronto, Ontario, Canada, 5-1 1 June 1988. Despite the venue the authors of eight of the eighteen chapters came from outside the American continent. In his introductory overview Roy Teranishi pointed out that the public has an unbased fear of ‘chemicals’ and ‘synthetics’ and an unbased confidence in ‘natural’ compounds. However, the ( U S ) Food and Drug Administration definition of natural flavours con- tains the phrase ‘or fermentation products thereof‘ which allows some flavours produced by biotechnology to be labelled as ‘natural flavours’. In addition, this chapter contains an extensive bibliography of reviews of flavour chemistry.

Eight chapters make up the section on the formation of flavour compounds. The first, by Tress1 and his co- workers from Berlin, deals with the biosynthesis of chiral flavour and aroma compounds in plants and micro- organisms, especially pineapple and baker’s yeast. The second, by Dirinck, De Pooter and Schamp, reports on aroma development in ripening apples where ester for- mation parallels the respiratory climacteric. P. I. Wil- liams and Australian colleagues describe non-volatile conjugates of secondary metabolites which are precur- sors of the flavours which differentiate between Chardon- nay, Sauvignon Blanc and Semillon grapes by examination of the volatiles produced by hydrolysis with either glycosidase or acid at pH 3.2. Kobayashi found that sotolon, 4,5-dimethyl-3-hydroxy-2(5H)-furanone, was the flavour impact compound in raw cane sugar and molasses at a concentration of about 1 ppm: it was also important in the flavour of botrytized wine but produced an off-flavour in sake. The role of oxidative processes in the formation and stability of fish flavours was reviewed by Karahadian and Lindsay carefully differentiating be- tween the enzymatic and autoxidative pathways which produce volatiles from fish lipids. The effect of the amino acid and sugar on the kinetics of the formation of pyrazines was studied by Leahy and Reineccius who found the reaction to be pseudo zero order. The forma- tion and aroma of not only pyrazines but also pyridines, thiazoles, oxazoles and trithiolanes in foods, especially fried chicken and potatoes, was discussed by Ho and Carlin. In the chapter on the production of natural flavours by biotechnological processes Armstrong, Gil- lies and Yamazaki point out that at present only GRAS substrates and GRAS micro-organisms can be used but

approval of organisms produced by rDNA techniques would greatly expand this approach. Meanwhile, fermen- tation with Candida utilis in an iron-limited medium can lead to the formation of acetaldehyde and ethyl acetate while the immobilized lipase from C. cylindracae can be used for the synthesis of esters such as ethyl butyrate.

In the first of four chapters on perception, Boudreau reports on the neurophysiology and stimulus chemistry on the cat, dog, rat and goat, and finds considerable differences between the species. The temporal aspects of flavour are emphasized by Overbosch and Soeting who describe a method for mass spectroscopic breath-by- breath analysis. Pickenhagen reviews the different odour impressions of enantiomers of chiral flavouring com- pounds and reports the synthesis and sensory properties of ( + )(S)-muscone, ( + )-Ambrox, and ( + )(R)-a- damascone. The role of free amino acids and peptides in the taste of food is discussed by Kato, Rhue and Nishi- mura. Most amino acids have taste ~ bitter, sweet, sour or umani - but the concentration in food is often below the taste threshold. However, they show a synergistic effect so together they play an important role in the flavour of foods.

The final section deals with specific flavours. Mooker- jee and his co-workers found considerable differences between the volatiles given off by living herbs and spices and those found after picking and drying. Yellow tea rose, peach, spearmint, peppermint, rosemary, thyme and coriander are some of the species studied. Shahidi re- viewed the flavour of cooked meats. Raw meat contains few volatile substances but on cooking hundreds of volatile compounds are formed: the range depending on the species. Many volatiles are produced from lipids but in nitrite-cured meat there are few volatile carbonyl compounds. Twenty-six compounds were identified in the headspace of black truffles by Talou, Delmes and Gaset. None of these compounds individually had much truffle aroma but a mixture of these compounds was judged similar to that of fresh black truffles. Fresh tomato volatiles were studied further by Buttery, Teran- ishi, Flath and Ling. Among the unusual compounds found p-damascenone and 1-nitro-2-phenylethane are important contributors to fresh tomato aroma. In the last paper Takeoka and colleagues studied the volatile con- stituents of pineapple, 80 % of which are esters. In terms of odour units, methyl 2-methylbutanoate, ethyl 2-meth- ylbutanoate, ethyl acetate, ethyl hexanoate and ethyl butanoate are the most important volatile components.

In conclusion, this is a valuable collection of papers which well illustrates the state-of-the-art in flavour studies. It can be recommended to all flavour chemists and technologists most of whom will find something useful and informative between its covers.

ROGER STEVENS Threlkeld