Effects of different drying methods of Lactarius hatsudake Tanaka on the physicochemical properties, rheology, and bioactivities of its polysaccharides

The drying techniques employed for raw materials critically influence the structural properties of their derived extracts, consequently modulating their biological efficacy. Therefore, this study aims to compare the effect of vacuum freeze drying (VFD) and hot air drying (HD) treatments on the physicochemical properties, rheological properties, and bioactivities of the polysaccharides extracted from Lactarius hatsudake Tanaka (LHP). The results indicated that HD-LHP exhibits a higher glucuronic acid content (13.90 %) and lower molecular weight (1.17 × 10⁷; 1.78 × 10⁴ Da) than VFD-LHP. Additionally, HD-LHP forms a more compact lamellar structure compared to the loose and porous structure of VFD-LHP. The gel characteristics of LHP are further improved by thermal treatment, which is influenced by temperature and concentration but not by pH or ionic concentration (CaCl₂, NaCl). The in vitro bioactivity assays revealed that HD-LHP enhanced antioxidant properties, including higher DPPH⁺, ABTS•⁺, hydroxyl radical scavenging abilities, and greater total reducing power, compared to VFD-LHP. Additionally, HD-LHP was found to effectively suppress tumor cell proliferation by inducing G2 phase cell cycle arrest and promoting apoptosis. Our findings provide preliminary evidence that hot-air drying (HD) may serve as an effective alternative for processing Lactarius hatsudake Tanaka, potentially enhancing its industrial utilization.