Interaction and complex formation of sonicated soluble lentil protein and Tremella fuciformis polysaccharide

Proteins' physicochemical and structural properties critically affect their interactions with polysaccharides. The effect of ultrasound treatment (0–40 min) on the physicochemical properties of soluble lentil proteins (LPs) was investigated. The interaction between LPs (ultrasound-treated for different times, U0-LP, U5-LP, and U40-LP) and Tremella fuciformis polysaccharides (TPS) under different pHs, biopolymer mixing ratios, and total biopolymer concentrations was studied. With the sonication duration increasing, decreased intrinsic fluorescence, higher zeta potential values, and increased hydrophilicity were observed for the sonicated LP samples. The molecule weight of LPs remained unchanged, and their secondary structure changes were independent of the sonication duration. The soluble LPs:TPS complexes and insoluble complex coacervates formed at pH 6.5 (pHc) and pH 6.0 (pH ɸ1), respectively, regardless of the mixing ratio and the LP type. The maximum formation of insoluble LPs:TPS complex coacervates (pHopt) occurred at the biopolymer mixing ratio of 4:1 at pH 3.0, 2:1 at pH 3.0, and 2:1 at pH 3.5 for the U0-LP:TPS, U5-LP:TPS, and U40-LP:TPS systems, respectively. The pHɸ1 and pHopt of all the three LPs:TPS systems shifted to higher pH values as the total biopolymer concentration increased. With the greatest dynamic quenching constants (Ksv) and binding site (n) values, U40-LP exhibited the strongest binding affinity with TPS. This was consistent with the highest viscosity of their mixture solution under pHs greater than pHopt. The overall results suggest that ultrasound-treated proteins showed a stronger electrostatic interaction with TPS compared to untreated proteins.