Recent clinical studies indicated that mulberry tea showed to suppress postprandial hyperglycemia. Its mechanism is suspected due to inhibition of intestinal α-glucosidase activity. Mineral treated water may change physico-chemical properties. In particular, brewing mulberry tea with mineral treated water may increase the inhibitory activity of hot water extract. In present study, we have demonstrated oxidation-reduction potential (ORP) and α-glucosidase inhibitory activity of mineral treated water, tap water and various mineral water on the market. Mineral treated water showed the lowest ORP value (205 mV) and tap water showed higher ORP value (558-620 mV) . Moderate ORP values were observed for mineral water on the market. The hot water extract using mineral treated water indicated the strongest α-glucosidase inhibitory activity. The hot water extract using tap water showed weak inhibitory activity. Moderate inhibitory activities were also observed for mineral water on the market. The contents of phenols and saponins of hot water extract by mineral treated water were higher than those of the extract by tap water. These observations indicate that mineral treated water increases extractability of inhibitory substances from mulberry tea.

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