Review Betalains e emerging prospects for food scientists Florian C. Stintzing * and Reinhold Carle Institute of Food Technology, Section Plant Foodstuff Technology, Hohenheim University, August-von- Hartmann-Straße 3, 70599 Stuttgart, Germany (Tel.: D49 711 459 22314; fax: D49 711 459 24110; e-mail: stintzin@uni-hohenheim.de) Betalains have witnessed swayings of scientific interest in the past 40 years, but only during the past decade research activ- ities in many disciplines dealing with breeding, phytochemi- cal, technological and nutritional aspects have broadened the hitherto narrow view on betalains. The challenge of bring- ing together the knowledge from all these different fields of ex- pertise is considered to be most fruitful. In the present review, the focus will be on the technologically related analytical issues. Introduction As opposed to other pigment classes such as the caroten- oids, chlorophylls and anthocyanins, the betalains have been studied with much less intensity. According to litera- ture, betalains have experienced peaks of scientific atten- tion in the 1960s and 1970s through the impressive phytochemical contributions by Piattelli (1976) in Italy, Dreiding (1961) and Wyler (1969) in Switzerland, Clement, Mabry, Wyler, and Dreiding (1994) and Mabry (1966) in USA, as well as Musso (1979) and Reznik (1975) in Germany. Technological and also nutritional issues were considered in pioneering studies by von Elbe and Goldman (2000) in USA in the 1970s and 1980s, which were the cat- alyst for an extensive breeding programme for red beets conducted by Gabelman and later Goldman (Gaertner & Goldman, 2005; Goldman & Navazio, 2003). In the 1990s research activities were mainly dedicated to biosynthetic aspects both at the Leibniz Institute of Plant Biochemistry in Halle (Saale)/Germany (Strack, Vogt, & Schliemann, 2003) and at the Laboratory of Cellular Phyto- genetics at Lausanne/Switzerland (Zryd & Christinet, 2004). With a focus on food, the scarce attention towards beta- lains may be due to the fact that red beet has long been con- sidered the only edible betalainic source. In the past five to ten years, however, leaf and grain amaranth, cactus fruits, but also coloured Swiss chard and yellow beet have stimu- lated food scientists to study betalains from a technological and nutritional perspective (Stintzing & Carle, 2004, in press). The present overview will discuss selected features of betalain chemistry and their importance to food scientists. Betalains e a bunch of colourful structures To date, the betalains comprise a quite modest number of about 55 structures including the red-violet betacya- nins and the yellow-orange betaxanthins (Stintzing & Carle, in press), while up to 550 anthocyanins have been identified in nature thus far (Andersen & Jordheim, 2006). Although not yet being clarified, the co-occurring betacyanin C 15 -stereoisomers are mainly considered isola- tion artifacts. In contrast, the analogous C 11 -isomers for the betaxanthins have not yet been detected as genuine compounds. Despite this still small number of structures, which is expected to grow, betalains are a matter of fas- cination. In early days erroneously addressed as flavo- cyanins (betaxanthins) and nitrogenous anthocyanins (betacyanins), it was Mabry and Dreiding (1968) who coined the term ‘‘betalain’’ for both pigment types. Only slightly earlier, betanin from red beet was the first betacyanin (Wyler, Mabry, & Dreiding, 1963) and indi- caxanthin from cactus pear the first yellow-orange betax- anthin structurally characterised (Piattelli, Minale, & Prota, 1964; Fig. 1). Although the substitution pattern of betacyanins with respect to sugars and additional acyl- ation resembles part of the structural design of anthocy- anins, distinct differences exist. The uniqueness of betalains is their N-heterocyclic nature with betalamic acid being their common biosynthetic precursor. Aldi- mine formation with cyclo-Dopa yields the betanidin aglycone which is usually conjugated with glucose and sometimes additionally with glucuronic acid, and may also be further modified through aliphatic and aromatic * Corresponding author. 0924-2244/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.tifs.2007.04.012 Trends in Food Science & Technology 18 (2007) 514e525