Extraction Optimization and Antioxidant Activity of Bound Polyphenols in Bamboo Shoot Dietary Fiber

To investigate the optimal extraction process, component composition and antioxidant activity of bound polyphenols in bamboo shoots dietary fiber (BSDF), the extraction time, extraction temperature, alkali concentration and liquid-to-material ratio on the extraction yield were researched in this paper. Thereafter, the extraction process of bound polyphenols in BSDF was optimized by Box-Behnken response surface experiment based on single-factor experiments. The components of bound polyphenols were preliminarily identified and the antioxidant activity such as ABTS cation radicals, DPPH radicals, superoxide anion radicals and hydroxyl radicals were investigated. The results showed that alkali concentration of 9 mol/L, extraction temperature of 40 °C, extraction time of 4 h and liquid-to-material ratio of 20:1 mL/g were the optimal condition. Under this condition, the predicted extraction amount of bound polyphenols in BSDF was 27.95 mg GAE/g BSDF while the actual extraction amount was 26.68±0.73 mg GAE/g BSDF, with a prediction accuracy of 95.46%. There were 12 polyphenolic components including sinapic acid, gallic acid, ferulic acid, and coumaric acid were preliminarily identified by ultra performance liquid chromatography-triple quadrupole mass spectrometer. The free radical scavenging rate of polyphenols extract initially increased and then gradually stabilized with the increase of mass concentration. The scavenging rates of ABTS cation radical, superoxide anion radical and hydroxyl radical reached 73.24%, 59.92% and 51.41% with mass concentration of 3.0 mg/mL, respectively. The scavenging rate of DPPH radical reached 76.79% when the concentration was 1.25 mg/mL. The scavenging rate of each group was less than that of ascorbic acid solution of the same mass concentration. The results can provide theoretical reference for the development and utilization of polyphenols in BSDF.