Ultrasound-assisted three-phase partitioning produces a pectin-leaning polysaccharide fraction from Idesia polycarpa Maxim cake meal with stable rheology and prebiotic-like potential.

Idesia polycarpa Maxim cake meal (IPMM) is an abundant oil processing by-product that is frequently discarded. In this study, five polysaccharide fractions (IPMPs) were obtained using ultrasound assisted three phase partitioning (UTPP), alkali, citric acid, chelating agent, and enzymatic extraction, and were systematically compared in terms of physicochemical characteristics, rheological behavior, and in vitro fermentation properties. The extraction method markedly affected the composition and functionality of IPMPs. Several conventionally extracted fractions showed glucose-dominant neutral polysaccharide signatures, whereas the UTPP-derived fraction (IPMP-UT) was a pectin-leaning fraction with the highest yield (10.16%), a moderate weight-average molecular weight of 225.84 kDa, elevated uronic acids (40.81%), and pronounced rhamnogalacturonan I (RG-I) features (53.82%). All IPMPs exhibited shear-thinning behavior, while IPMP-UT maintained relatively stable viscosity across broad pH and ionic-strength ranges and displayed the most elastic-dominant viscoelastic profile. During in vitro fecal fermentation, IPMP-UT promoted higher production of straight-chain short chain fatty acids (SCFA) and preferentially enriched SCFA-associated genera, including Dialister, Megasphaera, Prevotella, Faecalibacterium, and Bifidobacterium, while reducing opportunistic taxa such as Escherichia-Shigella and Fusobacterium. Overall, IPMP-UT emerged as the most promising fraction among the tested IPMPs, combining food-relevant rheological stability with stronger microbiota-directed fermentation potential. These findings highlight how extraction-induced structural differences can jointly shape the technological and fermentation-related functions of IPMM polysaccharides, providing a basis for their targeted utilization as multifunctional food ingredients.