Antiviral activity of a hot water extract of black soybean against a human respiratory illness virus

Significant antiviral activity against respiratory illness viruses has been found in a hot-water extract of black soybean. This black soybean extract showed significant antiviral activity against human adenovirus type 1 and coxsackievirus B1 in a dose-dependent manner, while the hot-water extract from common yellowish soybean showed only weak activity. The antiviral activity could not be extracted from the black soybean by 70% aqueous ethanol, suggesting that saponin in the seed did not contribute to this activity. The antiviral activity was only recovered from cotyledons and not from seed coats with the hot water, showing that the activity was distributed in the cotyledons and that antocyanins in the black soybean seed coats did not contribute to the antiviral activity. The antiviral compound(s) in the black soybean was partially purified by up to 166 times by a combination of gel filtration, reversed phase HPLC, and ion-exchange HPLC. The partially purified antiviral compound showed hydrophilic and anionic properties, and a maximum absorption at 260 nm, suggesting that this antiviral fraction may contain a phenyl group(s). On the other hand, an amino acid analysis with the acid hydrolyzate and a neutral sugar analysis showed that the antiviral compound from black soybean might not be a polypeptide or glycoconjugate bearing neutral sugar(s).