Investigation of Polyphenolic constituents of Diaphragma juglandis Fructus and development of antioxidant instant tea

Abstract

Diaphragma juglandis (D. juglandis) Fructus is a brownish lamellar structure located between walnut kernels. As a traditional Chinese herbal medicine, it exhibits therapeutic effects including spleen-strengthening, kidney consolidation, astringency, diuresis, and heat-clearing. In this study, the polyphenolic constituents of D. juglandis and its functional instant tea were investigated in this study. Three polyphenolic compounds were isolated from 70% ethanol extract of D. juglandis Fructus as 2-methoxy juglone, regiolone and quercetin. The HPLC method was established for determination of the content of quercetin in the instant tea samples under the premise that the methodology was verified to meet the standard requirements. The preparation process of D. juglandis Fructus instant tea was optimized through single factor experiments and Box-Behnken design-response surface methodology and the optimal conditions were determined as follows: feed rate of 10 mL/min, inlet temperature of 151 ℃, and β-cyclodextrin addition of 9%. Then the antioxidant activity of each sample was evaluated using DPPH and ABTS radical scavenging assays. The results showed that the quercetin had significant antioxidant activity. The instant tea group demonstrated superior antioxidant effects compared to the extracts group at 50, 200, and 800 µg/mL (P < 0.001), likely due to the optimized spray-drying process, which might have enhanced the solubility, stability, and bioavailability of the active compounds. The results provided critical foundational data for the deep processing and comprehensive utilization of D. juglandis Fructus.

Keywords

Diaphragma juglandis Fructus / polyphenolic constituents / instant tea / antioxidant / process optimization

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