No abstract

Alliums have been grown for many centuries for their characteristic, pungent flavor and medicinal properties. The present review, which includes references published up to the middle of 1984, is primarily concerned with the chemical composition, flavor, and physiological properties of these crops, their extracts, and processed products. Special emphasis is placed upon the relationship between the organoleptically and biologically active components of onion and garlic. Following a brief historical introduction, current production of commercially important alliums is described and their botanical origins and interrelationships are explained. Following consideration of the major economic diseases and pests of alliums, the agronomic, husbandry, and practices associated with their cultivation are described, particular emphasis being placed upon the storage and processing of onion and garlic. The detailed, overall chemical composition and nutritional value of members of the genus Allium are presented in Section 7; after an outline of the origin and nature of flavor components and precursors, the flavor volatiles of individual members are presented. The effects of agronomic, environmental, and processing practices on chemical and flavor content and quality are considered in Section 9. The following section deals critically with the human and animal studies which have been conducted into the medical and therapeutic properties of alliums, emphasis being placed upon the studies into the antiatherosclerotic effect of onion and garlic and their essential oils. After a study of antimicrobial properties of alliums and their effects on insects and animals, an overview is presented which highlights unexplored or inadequately studied areas and suggests rewarding areas for future research.

Allium is a genus of some 500 species belonging to the family Liliaceae. However only a few of these are important as food plants, notably onion, garlic, chive, leek, and rakkyo. Such plants have been used for many centuries for the pungency and flavoring value, for their medicinal properties, and, in some parts of the world, their use also has religious connotations. The flavors of members of the genus Alliums, in addition to having certain characteristics, are also complex, being derived enzymically from a number of involatile precursors. In addition to there being variation of flavor between different alliums, there are also considerable changes that occur as a result of cooking and processing. Of course, these are of importance to the consumer and food technologist-processor. The review will introduce the subject by an historical perspective and will set this against data on the present cultivation and usage of commercially cultivated alliums. The chemical composition of these plants will be discussed, emphasis being given to nonvolatile constituents which are, perhaps, less often considered. Discussion of the volatile constituents, which will include mention of the methods currently used for their analysis and for the determination of "flavor strength", will be mainly concerned with literature taken from the last 5 years. In considering the extent and nature of allium cultivation and processing, factors affecting the nutritional value and quality will be highlighted. The medicinal properties of garlic and onion oils have been much studied over the last decade and the review will include critical assessment of this area and also will touch on the more general properties (antimicrobial, antifungal, antibacterial, and insecticidal) of these oils. Finally mention will be made of the antinutritional, toxic, or otherwise undesirable effects of alliums, for example, as inadvertent components of animal diets, tainting of milk and other food products. It is our intention to review the literature up to mid-1984.

The hydrolysis of (I) proceeds via the isothiocyanate (II) yielding (III) and (IV).