Antioxidant Components and Antioxidant Activity of Tibetan Propolis and Its Simulated Digestive Juices

To evaluate the antioxidant activity and potential of propolis, Tibetan propolis and its simulated digestive juice were analyzed for its chemical composition (contents of total phenolics (TPC) and total flavonoids (TFC)), reducing power and antioxidant activity (hydroxyl radical scavenging activity, 1,1-diphenyl-2-picrylhydrazyl (DPPH) assays, metal iron chelating activity and lipid peroxidation inhibition ability). The results showed that the contents of TPC and TFC in Tibetan propolis were 7.02% and 10.05%, respectively. The contents of TPC and TFC in simulated digestive juices were diminished. The contents of TPC and TFC in simulated gastric digestive juices (2 h) were 0.43% and 6.43%, respectively. The contents of TPC and TFC in simulated intestinal digestive juices (2 h) were 0.32% and 5.11%, respectively. The highest values of antioxidant activity was achieved at a concentration of 1 mg/mL, and the values of reducing power, hydroxyl radical scavenging activity, DPPH radical scavenging activity, metal iron chelating activity and lipid peroxidation inhibition ability in Tibetan propolis were 0.35, 96.60%, 92.53%, 19.96% and 97.01%, respectively. Reducing power and DPPH radical scavenging activity of simulated gastric digestive juices exhibited an increasing trend, with respect to the undigested sample. The highest values of reducing power and DPPH radical scavenging activity were 0.39 and 95.69%, respectively. Hydroxyl radical scavenging activity, metal iron chelating activity and lipid peroxidation inhibition ability of simulated gastric digestive juices exhibited a decreasing trend, with respect to the undigested sample. Simulated intestinal digestive had higher hydroxyl radical scavenging rates, metal ion chelation rates and lipid peroxidation inhibition rates than simulated gastric digestive, with highest values of 99.72%, 69.26% and 80.69%, respectively, the reducing power and DPPH radical scavenging rate experienced a decreasing tendency, but the highest DPPH radical scavenging rate remained at 74.74%. All of these suggested that Tibetan propolis had high antioxidant activity. During in vitro digestion, antioxidant indicators significantly changed, but the changing trend of each indicator was inconsistent. Several indicators still performed well. Tibetan propolis can be used as a premium natural antioxidant.