Abstract
Recently, studies on theabrownins (TBs), the main bioactive polymeric pigments found in dark tea, have received increasing attention for its health effects. Thus far, information on their structural characteristics is unclear. In the present study, theabrownins were isolated from single species Eurotium cristatum PW-1-fermented loose tea and their structural and hypolipidemic characteristics were studied for the first time. The theabrownins were fractionated by their molecular weights and were then analyzed. Ultraviolet–visible spectrophotometry (UV-Vis) and Flourier transformation infrared spectroscopy (FT-IR) showed that they were polymerized phenolic substances containing abundant hydroxy and carboxyl groups. All theabrownin samples exhibited hypolipidemic activity in high-fat zebrafish; among which TBs-10-30k sample, decreased lipid level in high-fat zebrafish to 51.57% at 1000 μg/mL, was most effective. It was found that TBs-10-30k was a type of amorphous and thermostable polymer with slice shape and smooth surface under scanning electron microscope (SEM). Atomic force microscope (AFM) analysis showed that it had island-like structure because of aggregation of theabrownin molecules. Pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) analysis further showed that the main pyrolytic products of TBs-10-30k were hexadecanoic acid (33.72%), phenol (14.90%), and eicosane (12.95%), indicating TBs-10-30k was mainly composed of phenols, lipids, saccharides, and proteins. These results not only facilitate subsequent identification of theabrownins, but also provide insights into the applications of theabrownins in functional foods.
Highlights
In addition to water, tea is one of the most popular beverages consumed worldwide because of its many health-promoting benefits, such as antioxidation, anticancer, anti-inflammatory, and hypolipidemic activities [1,2,3]
Fractionated by ultrafiltration centrifugation through microseps, theabrownins were separated into four fractions with different molecular weights
The results indicated the abundance of aromatic C=C content in theabrownins as the π–π* transitions in substituted benzenes or polyphenols occurred in the wavelength region [25]
Summary
Tea is one of the most popular beverages consumed worldwide because of its many health-promoting benefits, such as antioxidation, anticancer, anti-inflammatory, and hypolipidemic activities [1,2,3]. In the past few years, studies have provided important information on the functions and bioactivities of theabrownins, demonstrating that they can inhibit the activity of α-glucosidase in vitro, decrease blood glucose levels and increase glucose tolerance in mice under hyperglycemic stress [7]. They exhibit anti-osteoporotic [8], anti-tumor [9,10,11], and hypolipidemic effects in vitro and in vivo [12,13,14,15]. Because of their condensed nature, the molecules of theabrownins cannot be separated by chemical methods, the structural characteristics of theabrownins remain unclear, their applications remain limited
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