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.
Keywords: Glutamine transaminase; Lactobacillus bulgaricus; Microencapsulated; Phosphorylated; Walnut isolate protein.
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