Abstract
In this study, the ultra-high pressure extraction (UHPE) conditions for obtaining the maximum flavonoid yield from Xinjiang jujube (Ziziphus jujuba Mill.) leaves (XJL) were optimized by response surface methodology (RSM). Box–Behnken design (BBD) was applied to evaluate the effects of four variables (extraction temperature, pressure, time and liquid-to-solid ratio) on flavonoid yield. The results showed that the optimal flavonoid yield (25.45 ± 0.21 mg/g) was derived at 50.0 °C, 342.39 MPa, 11.56 min, and a liquid-to-solid ratio of 43.95 mL/g. Eight compounds were tentatively identified and quantified as kaempferol and quercetin glycosides with UPLC-ESI-MS. Compared to ultrasound-assisted extraction (UAE), UHPE can obtain higher concentrations of total flavonoids and stronger DPPH and ABTS radical-scavenging activities in a much shorter time. Therefore, UHPE is an alternative to UAE for obtaining flavonoids from XJL, which may be an optional method for large-scale industrial flavonoid extraction from XJL.
Highlights
Ziziphus jujuba Mill., a plant belonging to the family Rhamnaceae, is an important economic crop in East Asia
Jujube is an important fruit in China and has attracted significant interest because of its common consumption as food, a food additive, as a flavoring and in traditional Chinese medicine (TCM) [1,2]
Jujube-leaf green tea extracts can inhibit human hepatocellular carcinoma cells via activating AMP-activated protein kinase (AMPK) [9], and an unidentified β-D-glucosidase inhibitor exists in jujube leaf extract [10]
Summary
Ziziphus jujuba Mill., a plant belonging to the family Rhamnaceae, is an important economic crop in East Asia. Chinese jujube can be traced back 4000 years, with over 700 subspecies used during thousands of years of cultivation in the temperate and subtropical areas of the Northern Hemisphere [1]. Jujube is an important fruit in China and has attracted significant interest because of its common consumption as food, a food additive, as a flavoring and in traditional Chinese medicine (TCM) [1,2]. The jujube leaf, which is the main byproduct of jujube, has been used in TCM for thousands of years (i.e., to improve sleep, to nourish the heart and soothe the nerves, and to reduce hemorrhaging and diarrhea) [3,4,5,6]. Jujube-leaf green tea extracts can inhibit human hepatocellular carcinoma cells via activating AMP-activated protein kinase (AMPK) [9], and an unidentified β-D-glucosidase inhibitor exists in jujube leaf extract [10]
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