Structural, rheological, and tribological behavior of flaxseed protein concentrates: Effect of warm-water and enzymatic demucilaging.

This study aimed to investigate the effect of two demucilaging approaches (i.e., warm water and enzymatic method) on the structural, rheological, and tribological properties of flaxseed protein. The chemical composition, color, molecular weight, secondary structure, rheological, and tribological properties of flaxseed protein concentrate were analyzed. Results showed that flaxseed protein concentrate (FPC) with higher protein content (66 g/100 g) was obtained by demucilaging flaxseed with warm water. In contrast, FPC with higher total phenolic content (45 mg GAE/g protein) and relatively lower protein content (45 g/100 g) was acquired by enzymatic treatment, which contributed to a darker green color. Compared to the enzymatic treatment of FPC (EFPC), the warm water treatment of FPC (WFPC) consisted of a larger proportion of high molecular weight protein subunits. Circular dichroism spectra demonstrated that WFPC had a lower proportion of α-helix but a higher ratio of β-sheet compared to EFPC. In addition, WFPC solutions exhibited shear-thinning behavior, while EFPC showed Newtonian fluid behavior, indicating that lower mucilage residues existed in EFPC compared to WFPC. The tribological behavior, which mimics the oral lubrication property of a product, was studied at 37 °C with/without the addition of artificial saliva. EFPC showed a higher friction coefficient (CoF) than that of WFPC, which suggested that WFPC had a smooth oral lubrication property. CoF was decreased appreciably in both samples by the addition of simulated saliva. Overall, demucilaging with warm water is more practical than enzymatic treatment for maintaining high protein content, preserving the molecular structure, and achieving smooth oral lubrication.