"Alkanet color", natural food color, is described as ethanol extract of Alkanet (Anchusa officinalis L.) root in the "Lists of Existing Food Additives in Japan". In our ongoing study to evaluate its quality and safety as a food additive, main pigments in Alkanet color were investigated. Five pigments were isolated from Alkanet color by HPLC. They were identified as 5, 8-Dihydroxy-2-(l-hydroxy-4-methyl-3-pentenyl)-1, 4-naphthalenedione (DHMPN), and acetyl-, isobutyryl-, 3, 3-dimethylacryloyl- and isovaleryl- derivatives of DHMPN by NMR and HR-TOFMS. The optical isomers, alkannin and shikonin, were separated from DHMPN by chiral phase HPLC. The result of analysis showed that the component ratio of shikonin and alkannin in DHMPN was 88 to 12. The specific rotation of four esterified derivatives of DHMPN suggested that configuration in each pigment was shikonin type. Furthermore, some commercially available standards of "shikonin" contain both optical isomers in various proportions.
