Allium genus

Chapters 8-11 are devoted to consideration of two main classes of phytochemicals Chapter 8 centers on organosulfur compounds from the Allium genus, and their role in cancer prevention, while subsequent chapters are devoted to polyphenols and their wide-ranging effects against cancers, cataracts, and cardiovascular disease. Chapter 9 examines the cancer-protective and therapeutic potential of polymethylated flavonoids such as occur in citras, while Chapter 10 summarizes recent cancer chemopievention research in an area particularly relevant to the British and Chinese backgrounds of the editors, notably tea. A much less well-studied area, that of cataracts and their prevention by dietary flavonoids, is presented in Chapter 11. 

Garlic of Allium genus, one of the most widely known spices in the world, is noted for the enzymatic formation of a large amount of organic sulfur compounds when it is crushed. The powerful flavor and possible medical application of the... 

The onion, like the other related vegetables (Allium genus), has long been classified as a member of the Lily family (Liliaceae), but now some botanists place the onion and its close relatives in a new family called the Alliaceae. The common onion is classified as the variety cepa to distinguish it from other varieties of onions such as the shallot, which is the aggregatum variety. Fig. 0-23 shows typical onion bulbs. 

Plants of the genus Allium, e.g. garlic Allium sativum), leek Allium amp-eloprasum), and onion Allium cepa), produce a bewildering variety of sulfur compounds. Selenium analogs for some of these have also been found (Section 11.1.3.6). Much work has focused on garlic (contains more than 100 such materials) and onion.56,66,67 Key compounds for formation of the Allium sulfur-containing secondary metabolites are sulfoxides of cysteine derivatives,... 

Block E (1992) The organosulfur chemistry of the genus Allium - Implications for the organic chemistry of sulfur. Angew Chem Int Edn Engl 31, 1135-1178. 

Thiocarbonyl oxides are a subject of active investigation. The natural occurrence of sulfines and related compounds in plants of the genus Allium (onion, garlic, etc.) is included in a superb and extensive review by Block [91]. Two detailed papers [92, 93] report the isolation of zwiebelanes from onions and their chemical synthesis involving intermediate sulfines produced by oxidation of di-l-propenyl disulfide, subsequent sulfoxide accelerated [3.3] sigmatropic shift and the [2+2] cycloaddition of the C=S and C=S=0 moieties. A further article [94] provides a great deal of information on the mechanism of formation of (Z)-propanethial S-oxide, the lachrymatory factor of the onion, as well as its chemical synthesis and reactions. Techniques of analysis of the volatiles of onions have been further improved [95]. 

Traditional medicine suggests that onions and garlic are good for you and modem chemistry has v, revealed some of the reasons. These bulbs of the genus Allium exhibit some remarkable sulfur chemistry and we will end this chapter with a few examples. Both onions and garlic are almost odourless when whole but develop powerful smells and, in the case of onions, tear gas properties when they are cut. These all result from the action of alliinase enzymes released by cell damage on unsaturated sulfoxides in the bulb. 

Members of the genus Allium (onion, garlic, leeks, etc.) provide a powerful example of an enzyme which distinguishes itself. Though there are hundreds of detectable enzymes occurring naturally in foods, it is difficult to find many examples where an individual enzyme is predominately responsible for a phenomenon. Enzymes and enzyme systems are responsible for the very identity of the food product. It is the enzyme composition that determines the flavor attributes and the textural differences in firmness, as well as the general appearance and color of food items. Table II provides examples of cases where particular changes in food can be primarily ascribed to a specific enzyme or enzyme system. 

Precursors of the Genus Allium to the Flavor of Thermally ] rocessed Allium Vegetables. 53... 

Fenwick GR, Hanley AB. The genus Allium—Part 2. Grit Rev Food Sci Nutr 1985 22 273-377. 

---