A study of the influenza virus infection inhibitory activity of blueberry and natsuhaze (Vaccinium Oldhamii) fruits

Herein, we report on the anti-influenza virus infection inhibitory activity of blueberries and related fruits. We investigated IFV infection inhibitory activity of 39 species of berry fruits using cultured cells. As a result, Elliot, which is a Northern High Bush blueberry, and rabbit eye blueberry varieties have high levels of IFV infection inhibitory activity. It was also revealed that wild blueberries, Natsuhaze (Vaccinium oldhamii) and Bilberry have very high activity. In addition, we confirmed that there was a good correlation between IFV inhibitory activity and total polyphenol content of the berries. Based on these results, we investigated the components involved in the infection inhibitory activity of the Natsuhaze berries. As a result of fractionation of the fruit extract of Natsuhaze using synthetic adsorption resin, fractions with ethanol concentrations of 30, 40, and 50% showed high levels of IFV infection inhibitory activity, and were found to contain polyphenols other than anthocyanin. Those fractions were then analyzed by HPLC, and three characteristic peaks were found. These peaks had IFV infection inhibitory activity and, when analyzed by ESI-LC/MS, these fractions were found to contains contained procyanidin B2 and ferulic acid derivatives, respectively. In addition, the IFV infection inhibitory activity of berry fruits was examined by against various IFV types, which revealed that the IFV infection inhibiting activity of the berry fruit is dependent on the virus type and strain. On the other hand, it was confirmed that the IFV infection inhibiting activity of Natsuhaze fruit is maintained even after heat treatment, and candy containing 1% dry Natsuhaze fruit powder has high IFV infection inhibitory activity. This study revealed that it is possible to develop processed products making use of the IFV infection inhibitory activity of blueberries and Natsuhaze fruit.