Optimization of Phenolic Compound Extraction from Supercritical Fluid Extraction Residues of Fraxinus mandshurica Leaf and Evaluation of Anti-inflammatory Activity

Abstract

This study investigated the optimization of phenolic compound recovery from Fraxinus mandshurica leaves residues generated by supercritical fluid extraction (SFE) to promote the sustainable use of resources. Using Box–Behnken design under response surface methodology, the optimal extraction conditions were determined to be an extraction temperature of 64.3 °C, an extraction time of 12.6 h, and an ethanol concentration of 76.3%. Under these conditions, the experimental yields of total polyphenol content and total flavonoid content were 63.41 ± 3.05 mg GAE/g and 5.12 ± 0.12 mg QE/g, respectively. These results showed high reliability, with relative errors below 10%. Biological analysis using RAW 264.7 cells revealed that the optimized extract exhibited non-toxicity up to a concentration of 125 µg/mL. At a treatment concentration of 62.5 µg/mL, it inhibited the production of nitric oxide and tumor necrosis factor-alpha (TNF-α) 38.0% and 15.8%, respectively, under inflammatory conditions induced by lipopolysaccharide (LPS). These results demonstrate that SFE residues from F. mandshurica leaves, which were previously considered waste, can be effectively upcycled into high-value functional materials for use in the pharmaceutical and food industries.