Optimized Extraction of Phenolics from Jujube Peel and Their Anti-inflammatory Effects in LPS-Stimulated Murine Macrophages

The extraction of phenolics from jujube peel (PJP) was optimized using response surface methodology (RSM). A Box-Behnken design was utilized to analyze the effects of NaOH concentration, temperature, and extraction time on the total phenolic content (TPC). The results showed that RSM could be an adequate approach for modeling the extraction of PJP. The optimal extraction condition for the highest TPC was obtained with 3.4 M NaOH concentration for 67 min at 50 °C. Not only PJP but also phenolics from the jujube seed (PJS) contain considerable amounts of phenolics, particularly flavonoids. Quercetin and galangin were found to be the predominant phenolics. PJP markedly down-regulated the levels iNOS and COX-2 proteins in macrophages by inhibiting the activation of NF-κB through interfering with the MAPK signaling pathways. Compared to PJS, PJP presented higher anti-inflammatory activities, reflecting increased amounts of TPC and total flavonoid content (TFC). These findings suggest that PJP could be a potential source of anti-inflammatory agents.