抄録
Few papers have reported on the phenolic compounds in Azuki beans. In addition, these data can not be compared with each other because the extraction methods used in these studies are quite different. Therefore, we conducted comparative studies to find out the suitable method for extracting phenolic compounds with methanol qauntitatively from seed coats and cotyledons of the beans. The differences of content within seed coats and cotyledons were also studied. The results obatained were summarized as follows;
1. The most suitable extraction from seed coats was obtained with 50% aqueous methanol at 90°C for 30 minutes with three replications. The contents of each compound were estimated at 17.0 mg D-catechin equivalent/g beans for phenolic compounds,6.68 mg/g beans for chlorogenic acid and 17.3Absorbance at 540 nm in 10ml of n-Butanol: conc HCl (5: 1) solution/g beans for proanthocyanidin, respectively.
2. The most suitable extraction from cotyledons was obtained with 70% aqeuous methanol at 90°C for 30 minutes with the same replications as seed coats. The contents of each compound were estimated at 2.05 mg D-catechin equivalent/g beans for phenolic compounds,0.367mg/g beans for chlorogenic acid and 0.213 Absorbance at 540nm in 10ml of n-Butanol: conc HCl (5: 1) solution/g beans for proanthocyanidin, respectively.
3. The percentages of soluble proanthocyanidins in cotyledons at extraction temperatures of 25°C and 90°C were very low compared with those of seed coats, and lowered slightly at extraction temperature of 90°C. It was suggested from the data obtained that proanthocyanidins reacted with the proteins in the cotyledon, and formed insoluble complexes during extraction.
4. It was found that 89% of the phenolic compound,94.8% of the chlorogenic acid and 96.8% of the proantocyanidins in the whole bean were contained in the seed coats, but very low in cotyledons.
5. The above results provide very useful information for chemical investigations of phenolic compounds and for understanding the mechanism of Ann particle formation in Azuki beans.
