Phosphorylated modification of walnut protein isolate: structural characteristics, functional properties and...

This study examined the effect of sodium tripolyphosphate (STP) on the modification of walnut protein isolate (WPI) at different concentrations. The phosphorylated walnut protein isolate (STP-WPI) has improved surface hydrophobicity, solubility, water-holding and oil-holding properties over WPI. FTIR results showed that phosphorylation decreased the α-helix and β-folding content of the protein, and increased β-turns and random curls, which allowed the conformational structure of WPI to be revealed; the phosphorylation treatment resulted in the blue-shift of the maximum emission in the endogenous fluorescence spectrum (from 360 to 358 nm); SEM observation revealed that the structure of WPI was smooth and compact, while the surface of STP-WPI particles was rough. Transglutaminase was employed to cross-link STP-WPI as a wall material for embedding Lactobacillus bulgaricus. In vitro simulated gastrointestinal digestion revealed that microcapsules with STP-WPI as the wall material provided a slow-release mechanism for Lactobacillus bulgaricus. The release of Lactobacillus bulgaricus in continuous simulated gastrointestinal fluid digestion exceeded 6.0 log cfu/g, effectively resisting the erosion of the gel matrix by pepsin and gastric juice, preventing premature release in simulated gastric fluid, and ensuring gradual release upon reaching the intestine.