Stevia polyphenols: a stable antioxidant that presents a synergistic effect with vitamin C

Stevia leaves have been claimed to possess the highest antioxidant capacity among botanic foods, yet the antioxidant activity has been attributed to the polyphenols from Stevia leaves (PPS). However, most studies about the PPS were based on Stevia extracts that contain abundant polyphenols and flavonoids. The PPS excluded flavonoids were found to possess antioxidant activity similar to that of epigallocatechin gallate, demonstrating stronger hydrophilic antioxidant activity and stability than that of ascorbic acid (VC), vitamin E, or chlorogenic acid under the assayed circumstances. Both of the PPS and their antioxidant activity are very stable in various physical environments, but less stable in the presence of potassium sorbate or sucrose. Moreover the combination of PPS and VC could increase the antioxidant stability of either VC or PPS. Therefore, the PPS have the potential to be a natural, inexpensive, and abundant antioxidant that can be utilized in the pharmaceutical and cosmetics. PRACTICAL APPLICATIONS: The PPS excluded flavonoids were found to possess antioxidant activity similar to that of epigallocatechin gallate, demonstrating stronger hydrophilic antioxidant activity and stability than that of ascorbic acid (VC), vitamin E, or chlorogenic acid under the assayed circumstances. Both of the PPS and their antioxidant activity are very stable in various physical environments, but less stable in the presence of potassium sorbate or sucrose. Moreover the combination of PPS and VC could increase the antioxidant stability of either VC or PPS. Therefore, the PPS have the potential to be a new natural, inexpensive, and abundant antioxidant that can be utilized in the pharmaceutical and cosmetics.