Extraction method-dependent structure-function relationships of Astragali complanati semen protein: Implications for its application as a novel plant protein ingredient.

Astragali complanati semen is an underutilized protein-rich plant seed resource. Therefore, the effects of different extraction methods, i.e., ammonium sulfate precipitation (ASP), alkaline extraction (AE), and salt extraction (SE) on the yield, structure, and functional properties of Astragali complanati semen protein (ACSP) were investigated to evaluate its potential for food applications. The findings revealed that AE yielded a protein with a flexible structure, relatively stable conformation, high-purity protein (82.71 ± 0.41%), small particle size (239.50 ± 9.01 nm), and a mild odor. Its foaming capacity exceeded 100% at various pH levels, and its solubility was 87.81 ± 2.84% at pH 11. The least gelling concentration (14%) of AE protein was comparable to that of soy protein, exhibiting 88.54 ± 0.59% DPPH radical scavenging capacity at 2.5 mg/mL, and 52.60 ± 0.83% in vitro protein digestibility. In contrast, ASP exhibited superior foaming ability under acidic conditions, whereas SE yielded a higher amount of protein, with excellent oil-holding (4.91 ± 0.04 g/g) and emulsifying activity. Notably, the solubility of AE protein decreased by approximately 4% after 4 weeks of storage at -20 °C, with low levels of lipid and protein oxidation, demonstrating excellent storage stability. This study provides a theoretical foundation for the potential application of ACSP as a novel plant protein ingredient in the food industry.