Recovery of Flavonoids from Walnuts De-Pellicle Wastewater with Macroporous Resins and Evaluation of Antioxidant Activities In Vitro

Walnut de-pellicle wastewater is rich in polyphenols and flavonoids that are significant to resource and environment. Enrichment and purification of flavonoids from walnut de-pellicle wastewater were investigated by five macroporous resins. As static tests shown, AB-8 resin was the most appropriate, and the adsorption data were fitted to Langmuir and Freundlich isotherms. Meanwhile, dynamic adsorption and desorption tests on packed columns of AB-8 resin were optimized. The optimal adsorption parameters were found to be 0.34 mg/mL, 2.67 bed volume (BV), 7.0, 2 BV/h and 25C for initial concentrations in sample solution, loading amount, pH, flow rate and temperature, respectively. At the same time, the optimal desorption parameters were 80% ethanol each 2 BV. The recovery yield and purity of flavonoids were 81.73 and 61.35%, respectively. The results also indicated that AB-8 resin had pretty good ability to achieve the enrichment of flavonoids from walnut milk wastewater. Furthermore, the antioxidant activities of purified flavonoids were evaluated in vitro, which revealed that the DPPH radical scavenging effect reached 83.47% at the concentration of 120 μg/mL, while the hydroxyl radical scavenging effect increased from 14.01 to 81.62% at different concentrations (0.2–1.6 mg/mL), and the superoxide anion scavenging effect changed from 14.81 to 85.03% at different concentrations (0.1–0.8 mg/mL). Moreover, the reducing ability appeared to be dose dependent of the flavonoids. In a word, the purified flavonoids could be used as a source of potential antioxidant. Practical Applications Traditionally, the walnut de-pellicle wastewater (WDW) rich in a lot of bioactive components is often poured directly to river, which causes serious pollution and the waste of resource. The method of enrichment and separation of flavonoids from WDW can not only improve the utilization of WDW but also create greater economic benefits, which provide some financial support for enterprise wastewater treatment because of the high content of flavonoids extracted from WDW. Meanwhile, the method of enrichment and separation of flavonoids from WDW is in accordance with the principles of green extraction, which makes the best use of renewable walnut resources to achieve a nondenatured and biodegradable extract without contaminants.