Chen, C.-Y.O., J.B. Blumberg, 2008. In vitro activity of almond skin polyphenols for scavenging free radicals and inducing quinone reductase. J. Agr. Food Chem. 56:4427-4434.
Almond skins are rich in polyphenols (ASP) that may contribute to these almond oxidant defense benefits. The in vitro effect of ASP extracted with methanol (M) or a gastrointestinal juice mimic (GI) alone or in combination with vitamins C (VC) or E (VE) (1-10 µmol/L) on scavenging free radicals and inducing quinone reductase (QR) were tested to assess their potential mechanisms of action. Flavonoid profiles from ASP-M and -GI extracts were different from one another. ASP-GI was more potent in scavenging HOCl and ONOO- radicals than ASP-M. In contrast, ASP-M increased and ASP-GI decreased QR activity in Hepa1c1c7 cells. Adding VC or VE to ASP produced a combination-and dose-dependent action on radical scavenging and QR induction. In comparison to their independent actions, ASPM plus VC were less potent in scavenging DPPH, HOCl, ONOO-, and O2 – •. However, the interaction between ASPGI plus VC promoted their radical scavenging activity. Combining ASP-M plus VC resulted in a synergistic interaction, inducing QR activity, but ASP-GI plus VC had an antagonistic effect. On the basis of their total phenolic content, the measures of total antioxidant activity of ASP-M and -GI were comparable. Thus, in vitro, ASP act as antioxidants and induce QR activity, but these actions are dependent upon their dose, method of extraction, and interaction with antioxidant vitamins.