Download Enhancement of antioxidant properties of tea extract and cellular

 BIOL6001 Presentation Skills and Research Seminars in Biological Sciences
(Food and Nutritional Science Module)
Enhancement of antioxidant properties of tea extract and cellular uptake of tea
flavonoids by lactic acid bacterial fermentation
Presenter: ZHAO Danyue (PhD Year 4)
Supervisor: Prof. N. P. Shah
Date: 30th October 2015 (Friday)
Time: 10:30 am*
*This seminar will start immediately after the first seminar (scheduled for 10:00 am)
Venue: Rm. 6S-13, Kadoorie Biological Sciences Building, HKU
Tea has been a popular health-promoting beverage worldwide and a fascinating field of research for
decades. Tea flavonoids (TFLs), the major phenolic components in tea, have been reported to
exhibit high antioxidant, anti-microbial, anti-carcinogenic and anti-inflammatory activities in vitro
and in vivo. Fermentation with lactic acid bacteria (LAB) is considered as a simple and valuable
biotechnology for improving the safety, nutritional and sensory properties of various food products.
This project aimed to examine the potential of LAB fermentation to enhance the stability and
cellular uptake of TFLs, the overall antioxidant activity of tea extracts (TEs), and the protective
effect of TEs against oxidative stress in human colon cell lines. Following LAB fermentation of
TEs or tea phenolic mixture (TPM), variations in phenolic compositions and phenolic compounds
accumulated in Caco-2 monolayers after tea treatment were characterized by LC-MS/MS. Effect of
tea sample pre-treatment in combating H2O2–induced oxidative damage to cells was evaluated by
addressing cellular ROS level, expression of intracellular detoxifying enzymes and mitochondria
membrane potential (Δψm). Resistance to oxidative DNA damage and effect on endogenous DNA
repair in CCD 841 cells were studied using single cell gel electrophoresis (alkaline Comet assay).
Results showed significant increase in DPPH and hydroxyl radical scavenging activity, and cellular
antioxidant activity of tea samples after fermentation, particularly evident for black tea, which was
in alignment with the extensive metabolism of phenolic profile by LAB and elevation in total
phenolic content compared with non-fermented samples. In addition, higher amount of TFLs from
fermented TEs was taken up by Caco-2 monolayers, with the major constituents being catechins,
gallic acid, quercetins and kaempferols. The loss of cell viability and Δψm was largely restored by
pre-incubating cells with tea samples, especially for the fermented samples. The fermented tea
samples also exerted marked impact on DNA repair activity, resulting in significantly less strand
breaks and purine oxidation in H2O2–stressed CCD 841 cells. Our findings indicate that LAB
fermentation can be an efficient way to stabilize TFLs during food processing, to enhance TFL
bioavailability and to protect colon cells from oxidative damage. All are welcome!