Isolation of pea protein-polysaccharide natural mixtures and physicochemical properties investigation

Proteins and polysaccharides are two essential nutrients in the human food system that can significantly influence their structural and functional properties. Pea protein-polysaccharide natural mixtures (PPMs, namely PPM1, PPM2, PPM3 and PPM4) were extracted from defatted pea powder through different extraction processes. PPM1 is derived from the supernatant of a neutral aqueous solution of defatted pea flour. The precipitate is subjected to alkaline dissolution at pH 9.0, yielding a supernatant and a precipitate (PPM3). A portion of the supernatant is lyophilized to produce PPM2, while another portion undergoes acid precipitation at pH 4.0 to yield PPM4. The protein and soluble polysaccharide content, SDS-PAGE of protein, solubility, thermal property, water and oil holding capacity, emulsion properties and foaming properties of these mixtures were examined in this work. The results indicate that PPM1 and PPM2 contain significantly higher (p < 0.05) soluble polysaccharide contents compared to PPM3 and PPM4. The SDS-PAGE analysis of PPMs reveals distinct variations in protein composition during the various extraction processes. Notably, PPM1, PPM2 and PPM4 demonstrated a gradual decrease in solubility from pH 2.0 to 4.0, followed by an increase from pH 4.0 to 10.0. However, the solubility of PPM3 rose as the pH increase from 2.0-10.0. FTIR analysis suggests that PPM2 is dominated in beta-sheet, PPM1 and PPM4 were primarily composed of random coil; additionally, a high content of beta-sheet and beta-turn is observed in PPM3. Furthermore, PPM2 demonstrates the highest (p < 0.05) denaturation temperature of 98.19 degrees C compared to W1(70.7 degrees C), W3(77.74 degrees C), and W4(72.28 degrees C). PPM1 exhibits the best WHC and OHC relative to other PPMs. PPM1, PPM2 and PPM4 exhibited the better emulsifying property (p < 0.05) than PPM3. At pH levels ranging from 2.0 to 10.0, PPM1 and PPM2 displayed significantly higher (p < 0.05) foaming capacity and foam stability than both PPM3 and PPM4. Especially for PPM1, which presented the highest (p < 0.05) foaming capacity across the pH range of 2.0-10.0. This work provides valuable insights into the properties of PPMs and will be beneficial for expanding their application respect in food industry.