The impact of phosphates on the fibrous structure formation of textured wheat gluten

Plant protein-based meat analogs have attracted attention as alternatives to meat products. To improve the fibrous structure of textured wheat gluten (TWG), different phosphates (sodium tripolyphosphate, sodium pyrophosphate, and sodium hexametaphosphate) were added to wheat gluten at different concentrations (0%, 0.25%, 0.5%, 1%, and 2%) during extrusion cooking. Analysis of the morphological characteristics showed the positive effect of sodium tripolyphosphate on the formation of the fibrous structure of TWG. The textural properties and degree of fibrous structure of TWG significantly improved with sodium tripolyphosphate treatment. Higher specific mechanical energy and lower bulk density were observed in the TWG treated with sodium pyrophosphate than in the control. The sodium dodecyl sulfate (SDS)-extractable protein results showed that sodium tripolyphosphate promoted the extent of gluten polymerization, but the other two phosphates had negative effects. The increased thermal stability of the sodium tripolyphosphate treatment group indicated stronger bonds conformation. The β-sheets content increased with sodium tripolyphosphate treatment. X-ray photoelectron spectroscopy results showed that the phosphate group was successfully introduced into the TWG treated with sodium tripolyphosphate via a phosphorylation reaction. The decrease in elastic modulus and viscous modulus observed with sodium tripolyphosphate treatment was related to changes in surface charges and the water layer of protein, which were affected by PO43−. Thus, sodium tripolyphosphate is a promising candidate that can be used for the improvement of the fibrous structure of TWG.