Systematic screening of Citri reticulatae pericarpium polysaccharides reveals uronic acid–associated anti-SARS-CoV-2 activity

Citri reticulatae pericarpium (CP), the dried peel of Citrus reticulata Blanco (Rutaceae), is a common traditional Chinese medicine and edible material with effects of regulating Qi, strengthening the spleen, and resolving phlegm. While its flavonoids have been extensively studied, the polysaccharides, which are the major components of its aqueous extract, remain systematically unexplored. In this study, a crude polysaccharide fraction (C142) was extracted from CP and fractionated by DEAE Sepharose™ Fast Flow column to obtain secondary polysaccharides. Analyses showed they had high total carbohydrate and galacturonic acid (19–39%), low protein, molecular weights of 20–25 kDa, main monosaccharides of galactose, galacturonic acid, and arabinose, and both α- and β-glycosidic linkages (FT-IR). Antiviral assays showed that C142, C144, and C146 significantly inhibited SARS-CoV-2 replication: at 1 mg/mL, they reduced viral RNA by over 100-fold, with clear inhibition even at 200 μg/mL, stronger than that of Remdesivir. Higher galacturonic acid content may be associated with antiviral activity, but this relationship is likely influenced by multiple structural and compositional factors. This study elucidates the physicochemical and preliminary structural characteristics of CP polysaccharides, as well as their anti-SARS-CoV-2 properties, linking their uronic acid-rich fractions to CP’s traditional lung-protective effects, providing scientific evidence for CP’s pharmacological material basis and antiviral mechanisms.