Green approaches for dietary fibre-rich polysaccharide production from the cooking liquid of Adzuki beans: Enzymatic extraction combined with ultrasonic or high-pressure homogenisation

This research follows the current trend of food waste valorisation via green approaches. The structural and functional characteristics of active polysaccharides from the cooking liquid of Adzuki beans were examined, filling an existing knowledge gap. Enzymatic extraction (EE) followed by ultrasonic modification (UM) or high-pressure homogenisation modification (HM) were effective in producing dietary fibre-rich polysaccharide products: EU-P and EH-P (total dietary fibre: 86.3% and 82.4% dry weight (DW); insoluble/soluble dietary fibre ratio: 2.21 and 2.10; protein: 1.26% and 1.09% DW; Lipid: 1.50% and 1.94% DW, respectively). Both contained Rha, Gal, Glu, Ara, Xyl and GlcNAc, and had statistically identical total phenolic content (0.33% DW) and particle size (1000–1032 nm) and very similar DPPH scavenging activities. EU-P and EH-P exhibited good capacities for water-holding (10.15 and 8.34 g/g), oil-holding (15.48 and 15.57 g/g), cholesterol-adsorption (17.34 and 18.41 mg/g at pH 2; 29.47 and 29.72 mg/g at pH 7) and nitrite-adsorption (285.31 and 296.44 μg/g at pH 2; 141.39 and 122.95 μg/g at pH 7). EH-P had a lower molecular weight (Mw 68420 Da; Mn 21350 Da; Mw/Mn 3.20), lower thermal stability, higher viscosity at shear rates above 1 s−1, higher emulsifying capacity, and comparable and lower emulsion stability at 1% and 2% concentrations, respectively, compared with EU-P (Mw 102101 Da; Mn 24810 Da; Mw/Mn 4.11). EE was effective in loosening the compact polysaccharide-based polymeric network via cleaving glycosidic and peptide bonds in the samples. Subsequent UM or HM further facilitated depolymerisation then re-assembly of some EE-disintegrated fragments to form new networks/structures.