Abstract

Dietary polyphenols like epigallocatechin-3-gallate (EGCG)—which represents the most abundant flavan-3-ol in green tea—are subject of several studies regarding their bioactivity and health-related properties. On many occasions, cell culture or in vitro experiments form the basis of published data. Although the stability of these compounds is observed to be low, many reported effects are directly related to the parent compounds whereas the impact of EGCG degradation and autoxidation products is not yet understood and merely studied. EGCG autoxidation products like its dimers theasinensin A and D, “P2” and oolongtheanin are yet to be characterized in the same extent as their parental polyphenol. However, to investigate the bioactivity of autoxidation products—which would minimize the discrepancy between in vitro and in vivo data—isolation and structure elucidation techniques are urgently needed. In this study, a new protocol to acquire the dimers theasinensin A and D as well as oolongtheanin is depicted, including a variety of spectroscopic and quadrupole time-of-flight high-resolution mass spectrometric (qTOF-HRMS) data to characterize and assign these isolates. Through nuclear magnetic resonance (NMR) spectroscopy, polarimetry, and especially circular dichroism (CD) spectroscopy after enzymatic hydrolysis the complementary atropisomeric stereochemistry of the isolated theasinensins is illuminated and elucidated. Lastly, a direct comparison between the isolated EGCG autoxidation products and the monomer itself is carried out regarding their antioxidant properties featuring Trolox equivalent antioxidant capacity (TEAC) values. These findings help to characterize these products regarding their cellular effects and—which is of special interest in the flavonoid group—their redox properties.

Highlights

  • Green or black tea undergoes an increasing popularity all over the world

  • The chromatographic separation which is shown in this study does not mark the first analytical method to separate the described compounds, but it is the first preparative isolation procedure published in literature to yield multiple autoxidation products

  • The degradation and autoxidation of EGCG and flavonoids similar to EGCG in buffer to theasinensins and oolongtheanin digallate is known to occur [15, 23], but it is not used as point of origin for theasinensin isolation with these specific incubation parameters and a dedicated sample preparation method before

Read more

Summary

Introduction

Green or black tea undergoes an increasing popularity all over the world. With billions of cups drunken daily, tea is the second most popular beverage following water [1]. On-going food trends often feature tea or tea components. Several teas such as the Japanese Matcha tea can be used in so-called “superfoods” which are widely used in modern food recipes, for instance in green smoothies, home-made iced tea, or ice cream. The high consumption of tea and its presence in new superfood-type edibles carries emerging questions. 1 3 Vol.:(0123456789) OH OH HO O OH. Chemical Formula: C22H18O11 Exact Mass: 458.0849 u OH HO HO B'

Methods
Results
Conclusion
Full Text
Published version (Free)

Talk to us

Join us for a 30 min session where you can share your feedback and ask us any queries you have

Schedule a call