Structure-Function Relationships of Alpinia oxyphylla Fruit Polysaccharides via Different Extraction Methods: IL-22 Pathway Activation Mediates Enhancement of Intestinal Barrier Protection by Ultrasound Extraction

The bioactivity of Alpinia oxyphylla fruit polysaccharides (AFP) is closely linked to their extraction-determined structural properties. This study systematically compared three extraction methods (ultrasound-assisted enzymatic (AFP-UE), pure ultrasound (AFP-U), and hot water (AFP-H)) for their efficiency in extracting AFP and influencing their structural features and intestinal barrier protective effects. Although AFP-UE yielded the highest extraction efficiency (4.75%) and exhibited predominantly a neutral arabinogalactan, it was AFP-U (comprises mixed rhamnogalacturonan-I and homogalacturonan domains alongside notable glucan motifs) that demonstrated the most potent intestinal barrier protection in a dextran sulfate sodium (DSS)-induced zebrafish colitis model. At 50 μg/mL, AFP-U significantly reduced the pro-inflammatory cytokine TNF-α, while upregulating anti-inflammatory cytokine IL-4, tight junction protein ZO-1, and mucin 2. Mechanistically, AFP-U is very likely to mainly alleviated oxidative stress and promoted intestinal barrier repair primarily by activating the IL-22 pathway, as evidenced by enhanced IL-22/IL-10 expression and suppression of IL-22 Receptor Subunit Alpha-2 (IL-22RA2). These findings highlight the critical role of extraction methods in shaping polysaccharide structure and bioactivity, positioning pure ultrasound extraction as a green and efficient strategy for producing functional polysaccharides with enhanced gastrointestinal health benefits.