Structural modification of Abelmoschus esculentus (L.) Moench polysaccharides by partial hydrolysis on the antioxidant and immune-enhancing activities

• Four polysaccharides from Okra were extracted, purified, and structurally modified. • Hydrolyzed fractions (AP2-HS1, HS2, HS3) exhibited distinct molecular weights. • AP2 and its derivatives enhance the immune-enhancing activity of AP2s. • AP2-HS1 exhibits the strongest effect as a new polysaccharide immunopotentiator. • AP2s showed antioxidant activity by scavenging DPPH, ABTS⁺, and •OH radicals. In this study, Abelmoschus esculentus (L.) Moench polysaccharides (APs) were prepared by mild acid extraction and ethanol precipitation, followed by purification with ion-exchange chromatography on a DEAE Sepharose Fast Flow column. The crude polysaccharides (AP-Crude) were purified to obtain AP2. The backbone of AP2 mainly consists of (1→4)-linked galactose, (1→4)-linked glucose, (1→2,4)-linked rhamnose, and (1→2)-linked rhamnose residues, with terminal glucose and galactose units. AP2 was further modified by hydrolysis (HS), producing the derivatives AP2-HS1, AP2-HS2, and AP2-HS3, with average molecular weights of 182.5 × 10 3 , 107.2 × 10 3 , 52.6 × 10 3 , and 19.8 × 10 3 g/mol, respectively. The immune-enhancing effects of AP2 and its derivatives were evaluated, showing significant increases in NO and PGE 2 production. Interestingly, AP2-HS1exhibited greater immune-enhancing potential than the other fractions. AP2-HS1 also upregulated the expression of COX-2, iNOS, TNF-α, IL-1β, and IL-6 by promoting phosphorylation of ERK, JNK, p38, and p65. Additionally, AP2 and its derivatives enhanced radical scavenging activity against DPPH, ABTS⁺, and •OH. These results demonstrate that all polysaccharides possess antioxidant activity and activate macrophages through the MAPK and NF-κB pathways. Overall, partial hydrolysis effectively enhanced the antioxidant and immunomodulatory functions of AP2, with AP2-HS1 showing the strongest potential as a macrophage-activating immunomodulator.