Antioxidant activity of water extract from bamboo by high-temperature and high-pressure steam treatment

The antioxidant activity of water extract from bamboo by high-temperature and high-pressure steam treatment was analyzed. Bamboo was decomposed by high-temperature and high-pressure steam treatment, and more decomposition products were extracted with water extraction. The maximum antioxidant activity, i.e., EC 50 = 0.127 mg/mL, and the maximum flavonoid content, i.e., 3.94 mg-quercetin equiv./g-dry weight bamboo, of water extract were obtained at a treatment pressure of 30 atm for a steaming time of 5 min. Compared with the untreated sample, they showed about 4.16 times higher of antioxidant activity and 6.02 times higher of flavonoid content. The maximum total polyphenol content, i.e., 35.7 mg-catechin equiv./g-dry weight bamboo, of water extract was obtained at 25 atm for 5 min. Compared with the untreated sample, it showed 6.69 times higher of total polyphenol content. The water extract from bamboo by high-temperature and high-pressure steam treatment was fractionated by high-performance liquid chromatography (HPLC). The structure of the fraction showing the highest antioxidant activity in the fractionated extract was determined. It had a structure having two highly reactive phenolic hydroxyl groups. The two phenolic hydroxyl groups reacted with reactive oxygen species (ROS) to cause a reduction reaction, thereby exhibiting antioxidant activity. Graphical abstract