Impact of pH on the structure and foaming properties of pea protein isolate: Structure – function relationship

Pea has attracted interest as a sustainable protein source, but its application in the food industry as a functional agent faces inherent limitations due to limited scientific knowledge, especially concerning to the specific protein structure-function relationship.  This study explores the relationship between pH-induced structural changes, interfacial properties and the resulting foaming behaviour of pea protein isolate (PPI). Understanding these interactions is crucial for the development of sustainable pea protein-based products.

The PPI structure was determined at four pH conditions (native: 7.5, 7, 5 and 3) by using Fourier transform mid-infrared and fluorescence spectroscopy. The interfacial tension and viscosity properties were examined using a drop tensiometer and rheometer, respectively. The foaming properties of PPI were studied using Foamscan.

Results showed pH-dependent trends with significant differences. Indeed, Foamscan analysis revealed that lower pH values, particularly pH 3, positively influenced foaming properties resulting in an improved foaming capacity (1.27) directly associated with: i) an increase of α-helix level (10.53%), ii) a decrease of aggregates content (15.23%), iii) a higher surface hydrophobicity (3.44.10³ FI/g.µm) and iiii) reduced surface tension (54.98 mN/m), facilitating the incorporation of air. While pH 3 resulted in a higher foaming capacity, the highest foam stability was observed at pH 5 (94.29%). One explanation could be ascribed to the presence of larger protein aggregates (16.15%) at pH 5 which formed thicker and more viscous films around the air bubbles improving gas bubbles retention, suggesting a complex relationship between structural elements and distinct foaming. All the investigated parameters showed no significant differences between the native and pH 7. From the obtained results, high correlations could be noted between the structure determined at the molecular level, and surface and foaming properties highlighting the structure-function relationship and its importance for understanding and optimizing the foaming properties of PPI.