The effect of transglutaminase and ultrasound pre-treatment on the structure and digestibility of pea protein emulsion gels

This study examines the effects of ultrasound and transglutaminase pre-treatments on the structure, rheological properties, and digestibility of emulsion gels made from pea protein isolate and concentrate. Pre-treatments enhanced the elasticity and deformation resistance of gels made from pea protein isolate, with the combination of both treatments yielding the highest storage modulus. In contrast, emulsion gels from pea protein concentrate showed a more complex response, with untreated samples exhibiting higher storage modulus. These differences reflect variations in gelation behaviour between isolates and concentrates, likely due to differences in composition and extraction processes. Protein digestibility, assessed using the o-phthalaldehyde assay, showed significant differences between pre-treatments, but the impact was less pronounced compared to the difference between gels made from isolate and concentrate. Gels made from pea protein isolate had a hydrolysis degree of 77 %, while those from pea protein concentrate had 48 %, with this difference mainly attributed to the higher amounts of starch and fiber in the concentrate, which affected both the gel structure and digestibility. Nuclear magnetic resonance-based metabolomics revealed lower glucose release in transglutaminase-treated gels made from pea protein concentrate and lower glycine release from ultrasound and transglutaminase-treated gels made from pea protein isolate during gastric digestion. However, no significant differences were observed after intestinal digestion, indicating no major limitations in nutrient release due to processing. Overall, these findings highlight the role of protein source and processing methods in influencing rheological properties and nutrient bioavailability in protein systems.