The effect of gallic acid (GA) on the redox state of hemoglobin (Hb) and the structural mechanism upon the Hb− GA interaction were investigated. Results indicated that GA exhibited antioxidant and pro-oxidant effects on Hb, which depended on its concentration and the redox state of Hb. The antioxidant capacity of GA contributed to the inhibition of free iron release from Hb. GA could bind to the central cavity of Hb and interacted with the heme moiety through direct hydrophobic contacts as indicated by docking analysis, but GA did not disrupt the heme structure. Conversely, GA increased the compactness of the Hb molecule and might narrow the crevice around the heme pocket, which contributed to the inhibition of Hb autoxidation and the free iron release. Results provided significant insights into the interaction of GA with redox-active Hb, which is beneficial to the application of GA in relative meat and blood products.

The oxidation and color stability of porcine hemoglobin (Hb) in the presence of tea polyphenols (TP), as well as the mechanism, were investigated using the methods of color and oxidation analyses, ultraviolet‐visible and fluorescence spectroscopy. Results indicated that TP interacted with the tryptophan and tyrosine residues of Hb through inserting into its hydrophobic pocket. This interaction showed a concentration‐dependent effect on Hb, which might lead to completely opposite results. The presence of TP (16 mg/L) disrupted Hb (16 mg/L) structure, and the exposure of heme iron facilitated the oxidation and discoloration of Hb. However, a lower level of TP should not break Hb structure but could work as an antioxidant and restrain the formation of methemoglobin. Consequently, TP (1.6 mg/L) considerably maintained the redness of Hb (16 mg/L, P < 0.05) when stored at pH 7.4 and 25 °C for 72 hr. Results may provide scientific information for the proper use of TP in blood and meat products. Practical Application Proper utilization of tea polyphenols (TP) in food products is beneficial to improve antioxidant capacity and nutrition quality of food. We proved that it was potential to corporate TP into blood and meat products to prevent discoloration and oxidative deterioration.