The Onion Family
Garlic and Other Alliums. The Lore and the Science
Eric Block
RSC Publishing, Cambridge, UK, 2009, 474pp (HB) ISBN 9780854041909
Reviewed by Jim Hanson
This is a fascinating book written by an authority on the chemistry of the edible alliums, which include garlic, onions, leeks and chives. True to its subtitle, the lore and the science , the book contains much more than just the sulfur chemistry of garlic and its relatives.
The first two chapters are devoted to a historical introduction to the botany of the edible alliums and to their role in literature and the arts.
The next two chapters 'unpeel' the chemistry of onions, garlic and other edible alliums. This is an area to which the author has made many contributions over the last 40 years. The title of the first of these chapters Chemistry 101 indicates that the chemistry is presented at a level which is easy to understand. Together with the chapter entitled Chemistry in the salad bowl there is much on the sulfur chemistry of the pungent and lachrymatory compounds in alliums. This complex story of the reactions of allyl sulfides and sulfoxides, particularly allicin, is told from first hand experience and given a historical perspective. The title of one section 'Allicin in Wonderland' epitomises the complexity of the topic.
The final two chapters deal with alliums in folk medicine and in the garden, including their use in protecting other plants from predatory attack. Much has been written concerning the health benefits of garlic and onions. Here the evidence is evaluated in a critical and balanced manner. The quotation in the heading of one section that 'the plural of anecdote is not data' summarises the author's approach.
The book concludes with a very extensive bibliography, tables of the constituents of alliums and their biological activity and rare historical drawings of alliums.
The book is well written and up-to-date, including references to papers published in 2008 and 2009. The experimental evidence supporting the structural conclusions is discussed in detail and the underlying physical principles of some of the instrumental methods are described in an approachable manner.
I can thoroughly recommend this book not just to natural product chemists but also to all those who have grown these plants in the garden or enjoyed eating them. It contains many anecdotes and quotations to enliven a chemist's dinner party.
Chemistry World, 2010, 7(2), p. 62
The Appeal of Alliums
Reviewed by Meriel Jones
What would our meals be like without garlic and onions? World cuisine would be much poorer, and chemists would have missed out on a fascinating array of organic sulphur compounds. For these vegetables are not shy members of the food chain. Their immediately recognisable odours evoke memories and can make a pungent statement that is rarely welcome if the garlic from a romantic evening meal lingers on the breath.
Indeed, applying the word ‘vegetable’, with its connotation of quiet passivity, seems almost inappropriate. The alliums, including garlic, onion, leeks, chives and spring onions, have international roles. They are big agribusiness, with onions alone covering 2.7m ha in over 175 countries. In a bizarre twist, import quotas to protect European garlic farmers against the dominant world producer, China, have resulted in lucrative garlic smuggling. Onions have provided the name for cultural icons, including the domes of Russian Orthodox churches and a web-based satirical magazine, the Onion. Finally, I am sure that no one has escaped recommendation of onion soup or garlic capsules as the ‘guaranteed’ cure for all manner of ailments.
This book by Eric Block is a synthesis of his four decades of distinguished work with alliums. Having started his career as a natural products chemist in the 1960s, his research into organic sulphur chemistry – the basis of the smells – led him to these plants. Once garlic or onion tissue is damaged, enzymes act on odourless chemical precursors to yield the first of hundreds of volatile odour compounds.
These include the eye-watering lachrymatory factor from onions, as well as zwiebelanes, cepaenes, ajoene and others. Their diversity, and the fact that many contain exotic and unstable chemical configurations, has provided decades of scientific enquiry exploiting every new development in analytical technology. Block’s account of this ever-increasing knowledge is accessible and will even entertain readers without a deep knowledge of chemistry.
However, he does not stop there. Around two thirds of the book is devoted to other aspects, from cultural to medical. There are plenty of well-chosen, high quality colour illustrations, ranging from onions painted by Renoir to the life-cycle of the leek moth. The numerous claims for health benefits get a thorough evaluation, from the baseless recommendation of garlic juice as a treatment for tuberculosis to the tentative evidence that it may reduce the risk of stomach cancer and benefit those with cardiovascular disease. The natural roles for the volatile odours are in the constant war between the alliums and their pests and his account of this is truly fascinating. Block may look at the world through garlic-tinged lenses, but in this book he is very good at getting readers to see it his way.
Chemistry & Industry, 2010, February, p. 26
