The Color of Cowpea Boiling Extract and Identification of Cowpea Peel and Cowpea Boiling Extract Anthocyanin Pigments (Studies on the color of sekihan with the Cowpea Part 1)

Sekihan is a Japanese traditional food that is usually cooking to steam glutinous rice with adzuki beans or cowpea beans and those boiling extract. We describe identification of cowpea peel anthocyanin and cowpea boiling extract antocyanin, and the effects of heating time on the color of cowpea boiling extract. Cowpea peel anthocyanins were identified to be cyanidin 3 -glucoside , delphinidin 3 -glucoside and acylated delphinidin type pigment. The cowpea boiling extract anthocyanins were almost the same pigments as cowpea peel anthocyanins. The absorption of cowpea boiling extract increased in 440~600nm as the longer heating time. Especially, the absorption in 487nm increased conspicuously. The anthocyanin concentration of cowpea boiling extract increased until heating for 15 min.. Then, that decreased by heating for 30 min.. Compared with the cyanidin 3 - glucoside solution (0.12mg in lOOmü of Mcllvain buffer, pH 6.4), the cowpea boiling extract seemed a far dark color (V, a*, b' values), and had a very high value at 531nm (absorbance at Amax-visible of anthocyanin). This result shows that the color of cowpea boiling extract is not created only with the anthocyanin and made by the interpositions of other components.