ABSTRACT
The free amino acid contents of onions vary considerably, with both arginine and glutamic acid being abundant. Nonstructural carbohydrate accounts for the major portion of the dry weight of onions and comprises free sugar, trisaccharides, and polysaccharides. Onion and garlic skins, and probably those of other alliums, are good sources of pectin. Despite the fact that the anthocyanins of red onions were first investigated more than 50 years ago, there is relatively little known about their composition. J. Kiviranta et al. have found the total content of flavonols in the edible portion of a red onion to be double that of a yellow variety. Extracts of the colored outer skins of onions have been shown to contain protocatechuic acid, phloroglucinol, pyrocatechol, and methyl esters of protocatechuic acid and phloroglucinol carboxylic acid. In common with many other species, garlic, onion, and other alliums possess well-defined antioxidant activity.
