Mild alkaline extraction improves recovery, modulates structure, and enhances bioactivities of Siraitia grosvenorii polysaccharides in vitro

This study investigated whether mild alkaline extraction could improve the recovery of Siraitia grosvenorii polysaccharides and modulate structural features associated with their in vitro bioactivities. Single-factor experiments and Box-Behnken optimization identified 0.25 mol/L NaOH, 30 °C, 2 h, and a solid-to-liquid ratio of 1:10 as the selected extraction condition. AE-SGP was characterized by PMP-HPLC, HPGPC-RID, FT-IR, and NMR, whereas AE-SGP and WE-SGP were compared for purified fraction yield and in vitro bioactivities. The purified AE-SGP fraction yield was 2.95%, which was 1.74-fold that of WE-SGP. The post-dialysis AE-SGP fraction had an estimated dextran-equivalent apparent Mw of 6.4 × 10⁴ Da and contained Glc, Ara, Gal, GalA, Rha, and GlcA at a molar ratio of 45.87:20.29:19.82:6.99:4.99:2.04. Spectroscopic analysis detected acidic and ester-related structural features. AE-SGP showed lower apparent IC ₅₀ values for α-amylase and yeast-derived α-glucosidase and a lower EC ₅₀ for ABTS⁺ scavenging than WE-SGP. These combined characteristics were associated with the stronger in vitro responses of AE-SGP and support the high-value utilization of S. grosvenorii polysaccharides.