Characterization and application of betalain pigments from plants of the Amaranthaceae Yi-Zhong Cai a , Mei Sun b and Harold Corke a * & a Department of Botany, The University of Hong Kong, Pokfulam Road, Hong Kong, China (Tel.: C852 22 99 0314; fax: C852 28 58 3477; e-mail: hcorke@yahoo.com) b Department of Zoology, The University of Hong Kong, Pokfulam Road, Hong Kong, China The colored vegetative tissues of plants in the family Amaranthaceae contain various betalain pigments and are often produced in high biomass, and therefore, attract interest as potential alternatives to the well-known betalains from beet roots. We attempted a comprehensive systematic study, including selection of betalain-producing genotypes and species, extraction, identification and quantification of betalains, determination and evaluation of physicochemical properties and antioxidant activity; and pigment utilization in certain food systems. The results demonstrated high potential for Amaranthus pigments for use as natural food colorants. Introduction There has been an increasing trend towards replace- ment of synthetic colorants by natural pigments in the last 20 years, because of natural pigments’ safety and health benefits, and strong consumer demand for more natural products (Boyd, 1998; Jackman & Smith, 1996). Although natural pigments are generally less stable and have higher cost than synthetic colorants, their development and utilization is attracting more and more attention. Well-known betacyanins from red beet (Beta vulgaris) have been extensively used in the food industry worldwide for many years (von Elbe & Goldman, 2000). Moreover, recent studies have shown that beet betacya- nins can be classified as dietary cationized antioxidants (Kanner, Harel, & Granit, 2001). With sustainably increasing markets for natural colorants, it is worthwhile to search for and develop new or alternative sources of natural colorants. Betalains are of great taxonomic significance in higher plants. The presence of betalains in members of the order Caryophyllales has been an important criterion for their classification. The presence of betalains and anthocyanins is mutually exclusive in the angiosperms (Strack, Steglich, & Wray, 1993; Stafford, 1994), i.e. betalains and anthocyanins have never been reported in the same plants (Francis, 1999). Betalains are water-soluble nitrogenous pigments. They can be divided into two major structural groups, the red to red-violet betacyanins (Latin Beta, beet and Greek kyanos, blue color) and the yellow betaxanthins (Latin Beta and Greek xanthos, yellow). Betacyanins can be further classified by their chemical structures into four kinds: betanin-type, amaranthin-type, gomphrenin-type and bougainvillein-type (Strack et al., 1993). So far it has been found that betalains in nature comprise approximately 50 red betacyanins and 20 yellow betaxanthins (Francis, 1999). Common beets usually contain both red betacyanins (consisting of 75–95% betanin) and yellow betaxanthins (w95% vul-gaxanthin I), in various ratios depending on cultivar (Francis, 1999; Piattelli, 1981). Betalains occur only in the plants from 10 families of the order Caryophyllales (old name: Centrospermae), such as the family Amaranthaceae which includes several important genera, i.e. Amaranthus, Celosia, Gomphrena, and Iresine (Benson, 1957; Bhattacharyya & Johri, 1998). Amaranth is a rediscovered ‘new’ crop. It was an ancient crop that was under cultivation 5000–7000 years ago as a staple food of the ancient Aztecs (Lehmann, 1994). It is still cultivated as a minor crop in Central and South America and some areas of Asia and Africa. Grain amaranth (Amaranthus) has developed worldwide as a new crop over the past 20 years, with good nutritional quality, strong tolerance to stress conditions (drought, Trends in Food Science & Technology 16 (2005) 370–376 Review 0924-2244/$ - see front matter q 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.tifs.2005.03.020 * Corresponding author.