Abstract
A direct steam injection pretreatment was added before the microwave-assisted extraction procedure for the extraction of flavonoids from seeds of Hovenia dulcis Thunb, and the antioxidant activity of flavonoid extracts was determined. Based on the experimental results, the addition of direct steam injection simultaneously increased the extraction yield of total flavonoids compared with direct microwave-assisted extraction, and antioxidant activity of flavonoid extracts obtained by adopting the steam injection pretreatment was higher than that by direct microwave extraction alone. Myricetin was isolated from the flavonoid extracts, and the structure was identified by infrared spectroscopy (IR), electrospray ionization mass spectrometry (ESI-MS), and 1H nuclear magnetic resonance (1H-NMR). Recovery yield of total flavonoids was increased by 11.63% when the direct steam injection pretreatment was added to direct microwave extraction.
Highlights
Myricetin is a popular health food supplement commonly found in tea, berries, fruits, vegetables and medicinal herbs (Ross & Kasum, 2002)
Destruction of H. dulcis cells and tissues resulting from microwave irradiation most probably facilitates mass transfer between flavonoids and the surrounding extractant and subsequently improves the extraction efficiency
The effects of various parameters, including steam injection time, methanol extraction concentration, and ratio of solvent to the material, and extraction temperature on the total flavonoids yield from H. dulcis were determined in this study
Summary
Myricetin is a popular health food supplement commonly found in tea, berries, fruits, vegetables and medicinal herbs (Ross & Kasum, 2002). Finding an alternative source for myricetin production becomes a challenge to meeting this expanding demand. Myricetin is the major flavonoid of the traditional herb, Hovenia dulcis Thunb. Many food products are developed using H.dulcis such as beverages, crispy candy, fruit cakes, biscuits, and tea bags, while the seeds are disposed of as waste during food processing (Wang et al, 2018). Phytochemical investigations of H. dulcis have reported that the seeds have over ten kinds of flavonoids identified to date including myricetin as the major flavonoid (Xu et al, 2013). H. dulcis seeds appeared to be a suitable source of myricetin to increase its production. The extraction method for the seeds needs development as no research on extraction methods has been reported
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