Study on the color effects of (-)-epigallocatechin-3-gallate under different pH and temperatures in a model beverage system

The effects of pH (2.2–8.0) and temperature (25–100 °C) on the instrumental color of a model beverage containing (−)-epigallocatechin-3-gallate (EGCG) were investigated. As the pH and temperature increased, the lightness ( L *) decreased while the redness and yellowness ( a* and b* , respectively) increased. Using spectral scanning, it was possible to verify that color changes might be related to the structural rearrangement of the EGCG aqueous solution in the system under alkaline and heating conditions. There were 6 key substances identified in the EGCG solutions, among which (2R)-2-Hydroxy-3-(2,4,6-trihydroxyphenyl)-1-(3,4,5-trihydroxyphenyl)-1-propanone 2- O -gallate ( m/z 473.0720) and theacitrin C/dehydrotheasinensin AQ ( m/z 911.1340) were identified as key coloring substances. Color changes did not decrease antioxidant activity of the beverage model. These results provide new insights on the mechanism of color change during storage of green tea beverages, and enable the understanding of key contributors to the browning of infusions color in tea beverages for the first time.