Protein digestibility of textured wheat protein (TWP)-based meat analogs: (II) Effects of sodium tripolyphosphate

In this study, the effects of adding sodium tripolyphosphate during the extrusion of textured wheat protein (TWP)-based meat analogs were investigated. Five TWPs (TWP-C0, TWP-C0.10, TWP-C0.25, TWP-C0.50, and TWP-C0.75) were prepared with sodium tripolyphosphate concentrations of 0%, 0.10%, 0.25%, 0.50%, and 0.75%, respectively. The fibrous structure of TWPs was analyzed by determining their textural properties, degree of texturization, microstructure, and protein bonds. When the concentration of sodium tripolyphosphate increased from 0% to 0.75%, the fibers in TWPs became more regular and finer with smaller pores, the degree of texturization increased from 2.10 ± 0.09 to 2.73 ± 0.07, and the proportions of solubilized protein from the breaking of hydrophobic bonds and disulfide bonds increased from 2.06 ± 0.14% and 1.38 ± 0.11% to 3.42 ± 0.12% and 1.74 ± 0.05%, respectively. The results of particle size, soluble nitrogen content, and free amino acids of samples during digestion indicated that the disintegration rate and protein digestibility of TWPs increased with the increase in the concentration of sodium tripolyphosphate. After gastrointestinal digestion, the total free amino acids released in TWP-C0, TWP-C0.10, TWP-C0.25, TWP-C0.50, and TWP-C0.75 were 391.5 ± 2.2, 403.9 ± 1.5, 430.0 ± 3.6, 473.8 ± 2.9 and 485.3 ± 5.73 mg/10 g digesta, respectively. Sodium tripolyphosphate may improve the protein digestibility of TWPs by forming a finer fibrous structure with a more unfolded protein structure and more hydrophobic groups being exposed to enzymes.