Physicochemical, structural, and functional characteristics of protein isolates from New Zealand-grown pea varieties

Abstract

This study provides the first comprehensive structure-function analysis of pea protein isolates (PPIs) derived from three New Zealand (NZ) pea varieties Pizzaz, Yellowstone, and Raider, extracted using a mild alkaline extraction–isoelectric precipitation method (AE-IEP) at pH 8. Results showed that the protein content of the isolates was approximately 90%, and the process yielded a protein recovery of 45-53%. The isolates were also compared with a commercial pea protein isolate (CPPI) for their structure and functionalities. Yellowstone had the highest protein solubility (69%), emulsion capacity (191%), and stability (95%), followed by Pizzaz at neutral pH. Pizzaz had the highest oil-holding capacity (2.4 g g⁻¹). In contrast, CPPI showed less than half the solubility of isolates from the varieties (27.7% vs. 57.2–69.3%). Differential scanning calorimetry and Fourier transform infrared spectroscopy indicated cultivar-specific differences in thermal behaviour and secondary structure. Yellowstone exhibited a lower denaturation peak temperature (93.8 ◦ (ΔH = 26.6 J g⁻¹ ), together with a relatively higher contribution of α C) and moderate enthalpy change -helical structures, consistent with increased molecular flexibility and reduced thermal cooperativity. Small-amplitude oscillatory shear measurements showed higher storage modulus (G ′ ) and lower tan δ for NZ PPIs, particularly Yellowstone, indicating more solid-like, elastic behaviour. Overall, the findings link protein structure to techno-functional performance and show that New Zealand–grown peas, particularly Yellowstone, yield mildly extracted PPIs with improved solubility, emulsification, and rheological properties compared with a commercial isolate. Mild AE–IEP combined with cultivar selection preserves structural integrity while enhancing functionality