Semi-dynamic in vitro digestion of alternative proteins: structural insights and peptidomics

This study investigates the in vitro digestive fate of various alternative plant proteins. We used a combination of INFOGEST semi-dynamic in vitro digestion model, particle sizing, confocal laser scanning microscopy, zeta-potential, circular dichroism, Fourier Transform Infrared spectroscopy, peptidomics analysis and in silico bioactivity predictions to provide a comprehensive understanding of the microstructural and digestive fate of soy protein isolate (SPI), pea protein isolate (PPI), potato protein isolate (PoPI), spirulina protein concentrates (SpPC) and hemp protein isolate (HPI). Buffering capacity, zeta potential and particle size distribution of alternative proteins significantly affected the protein digestibility and consequently, gastric emptying. Furthermore, the presence of cell wall components in SpPC, impacted gastric digestibility. Findings suggest that protein secondary structure contributed to differences in the extent of digestion; the higher content of α-helix correlated with the high digestibility of SPI, PPI and PoPI, while higher proportions of β-sheet correlated with lower digestibility of HPI. Peptidomics analysis revealed that the SpPC released the highest number of peptides whilst HPI produced fewest peptides after gastrointestinal digestion. In silico bioactivity predictions highlighted angiotensin-converting enzyme (ACE) inhibition, antioxidant and dipeptidyl peptidase (DPPIII and IV) inhibition as the dominant bioactivities, irrespective of the types of alternative proteins tested. Overall, alternative proteins from different sources demonstrated diverse digestive fate and proteolysis profiles, largely dictated by their structural properties.