1. in Houben-Weyl, Methoden der Organischen Chemie (Edit.: ), Georg Thieme, Stuttgart, Vol. E 7a, p. 30, 1991
2. Handbuch der Naturfarbstoffe, Ecomed, Landsberg, 1993
3. The chemistry of anthocyanins, anthocyanidins and related flavylium salts
4. (a) DOS 2352112 (1973).