Study on the structural characteristics, in vitro hypoglycemic activity, and regulatory mechanisms of Alpinia oxyphylla polysaccharide in modulating human gut microbiota

This study aimed to systematically compare the structural characteristics, in vitro hypoglycemic activity, and regulatory effects on gut microbiota of Alpinia oxyphylla polysaccharides (AOFP) obtained by three extraction techniques, high‑pressure and high‑temperature (HH), acid‑assisted high‑pressure and high‑temperature (AHP), and Aspergillus niger fermentation (ANF) , to elucidate their structure–activity relationship and gut microbiota regulation mechanisms. By comparing the three types of AOFP (AOFP‑HH, AOFP‑AHP, AOFP‑ANF), we revealed intrinsic associations among structure, activity, and microbiota regulation. The HH method promoted the ordered arrangement of β‑1,3‑glucan chains, forming a semicrystalline state and folded lamellar structures, thereby exhibiting the strongest hypoglycemic activity (α‑amylase inhibition rate: 97.08 %; α‑glucosidase inhibition rate: 59.43 %). The key mechanism lies in the synergy between the integrity of β‑1,3‑glycosidic bonds and the galacturonic acid content (11.74 %); together, they enhance activity through spatial hindrance effects and hydrogen bond networks. On the other hand, the AHP method, due to acid‑induced cleavage of glycosidic bonds, generated amorphous low‑molecular‑weight structures (1.03 kDa), leading to a marked reduction in activity. The ANF method produced medium‑molecular‑weight fragments (1.14 kDa) via enzymatic hydrolysis. In terms of gut microbiota regulation, all AOFPs significantly promoted early butyrate production; notably, the HH group maintained a butyrate concentration of 0.076 mmol/L at 48 h. Each polysaccharide sample specifically increased the Firmicutes and stimulated the proliferation of Ligilactobacillus, thereby improving intestinal barrier function. Interestingly, the ANF group uniquely upregulated the abundance of Fusobacteriota, suggesting potential immunomodulatory capacity. Further analysis indicated that different processing techniques modulate selective microbial metabolic pathways through conformational differences. The AOFP‑HH prepared by the HH method combines high hypoglycemic activity with structural stability, making it an ideal functional food additive. Meanwhile, the distinctive microbiota interaction mechanism exhibited by the ANF method offers novel insights for the development of personalized probiotics. In conclusion, our findings lay a solid theoretical foundation for the precise design of A. oxyphylla polysaccharides and their application in the prevention and treatment of metabolic diseases.