The genus Hibiscus (Malvaceae) consists of about 200 species, distributed in tropical and subtropical zones, many of which are cultivated as ornamentals. Roselle (Hibiscus sabdariffa L.) is an annual shrub 1.5-2.5 m in height). The calyces contain red pigments and are used for making jelly, jams, beverages, and food colorants in a number of tropical countries (). Roselle has also been used as a source of plant fiber called roselle hemp ().
Due to its widespread use, the red pigments of roselle have been investigated by many researchers since Yamamoto and Oshima first obtained a crystalline anthocyanin, hibiscin (). However, chemical structures of the anthocyanins had not been clarified until Du and Francis () identified delphinidin-3-sambubioside and cyanidin-3-sambubioside as major anthocyanins, and delphinidin-3-monoglucoside and cyanidin-3-monoglucoside as minor pigments. Recently, Pouget et al. () isolated anthocyanins from roselle using HPLC, and detected both delphinidin and cyanidin as anthocyanidins, and glucose, xylose, and fructose as sugar residues. Delphinidin-3-diglucoside and cyanidin-3-diglucoside were identified by Jiang et al. () as major anthocyanins of roselle in addition to delphinidin-3-monoglucoside. These differences in the anthocyanin compositions of roselle may reflect the difference in geographic origin of the plants used in the experiments, because it was reported that the anthocyanin composition was different depending on the geographic strain of the plants, and that Senegalese strain lacked delphinidin glycoside (). The anthocyanin content, however, reached 1.7-2.5% of dry weight of the calyces in all the strains examined (). An efficient method to separate and characterize roselle anthocyanins using HPLC combined with photodiode array detection has recently been established), which may enable further studies on the anthocyanin constituents of roselle from various geographic habitats.
Extraction conditions () and stability () of the roselle anthocyanins have been investigated for application of the pigments as red food colors. In addition, alcoholic extracts of roselle were shown to inhibit the angiotensin I converting enzyme in vitro and to exert an angioprotective effect in rats, apparently due to the presence of anthocyanins and flavones in the extracts ().
Hibiscus sabdariffa L. (roselle) is an annual shrub that accumulates anthocyanin pigments in the calyces, which have been used for making various foods and food colorants.
The in vitro-cultured cells of roselle expressed the ability to produce anthocyanin pigments tentatively identified as cyanidin-3-monoglucoside and cyanidin-3-xylosylglucoside. The clonally selected cell line obtained by combining the microculture of a large number of cell clones and a rapid estimation of anthocyanin content using a microplate reader showed an anthocyanin content exceeding that of the intact calyces.
Anthocyanin production in roselle callus was markedly enhanced by 2,4-D while inhibited by GA. Of the nutritional factors both type and concentration of carbon and nitrogen sources, and phosphate level showed marked effects on both biomass production and anthocyanin biosynthesis. Utilization of the medium optimized for anthocyanin production resulted in 2.5-fold increase in anthocyanin content compared with that of the cells cultured in LS medium.
Cultured roselle cells might potentially be a suitable source for large-scale production of anthocyanin pigments as food colorants when a two-phase culture system is developed.
Selections from the book: “Medicinal and Aromatic Plants V”, 1993.