Reinforcement of pea protein isolate gels through NaCl-assisted pea protein fibril formation at acidic pH

Alternative protein foods with desirable textural properties are of wide interest. Here we investigated the potential to improve pea protein isolate (PPI) gel strength by the addition of pea protein fibrils (PPF). Firstly, optimal conditions for PPF production were investigated, in particular whether the presence of salt (0.15 M NaCl) improved fibril quality when generated under acidic conditions. Pea protein fibrils were prepared in either water (PPFW) or 0.15 M NaCl (PPFS) at pH 2. Fibrils were formed when PPI proteins were hydrolyzed, unfolded, and aggregated into a fibrillar structure as determined by TEM, particle size analysis, CD, and SAXS. AFM-IR confirmed their long, thin morphology and revealed differences in the secondary structures composition of PPFS and PPFW, with high β-sheet content and increased aggregation observed when adjusted to pH 7. Rheological examination of gels formed from either PPI or PPF individually showed very weak gel strengths at 60 °C. Fibrils mixed with PPI at either pH 2 (native fibril-forming condition) or pH 7 (typical for food applications) at a 1:1 ratio formed strong elastic gels. The highest value of the elastic modulus (Gʹ ∼ 30 kPa) resulted from PPFS forming a scaffold network for PPI entrapment at pH 2. The viscoelastic material response of all the gels is well described by the Scott Blair model for a critical gel. Analysis of the resulting model parameters indicated a strong and rigid network formed between PPI and PPFS at pH 2, consistent with an open, highly connected network of rigidly bonded flocs. SEM images showed dense interconnected networks with protein aggregates of PPI within a continuous fibrillar matrix. Overall, the incorporation of PPF formed in the presence of salt into PPI gels could significantly enhance the textural properties of pea protein. • Pea protein fibrils formed in both Milli-Q water and 0.15 M NaCl solution at pH 2. • AFM-IR, SAXS, and TEM confirm fibril formation and β-sheet-rich morphology. • pH adjustment to seven promoted aggregation and loss of fibrillar form. • Salt-induced pea protein fibrils at pH 2 enhanced PPI gel strength (G′∼30 kPa). • Scott-Blair model supports a critical-gel network reinforcement mechanism.