Integrating In-Vitro and In-Vivo Approaches to Understand the Mechanisms of Protein Digestion in Humans

Abstract

ABSTRACT This thesis investigated the digestibility and gastrointestinal responses of chicken versus plant-based chicken analogues through a comprehensive multi-methodological approach. With increasing demand for sustainable protein alternatives, understanding the nutritional equivalence and physiological impact of plant-based meat analogues compared to conventional animal proteins has become crucial. The research presented in this thesis employed three complementary approaches: in vitro digestibility assessment using the standardised INFOGEST protocol, in-vitro MRI-based digestion monitoring, and a randomised crossover human trial. Studies compared chicken (breast and thigh) and plant-based chicken analogues, evaluating protein quality, digestibility, and gastrointestinal responses. In-vitro analysis revealed significant differences in protein quality. Chicken demonstrated superior amino acid profiles with significantly higher levels of indispensable amino acids, compared to plant-based chicken analogues, particularly lysine and methionine. Using the Digestible Indispensable Amino Acid Score (DIAAS), chicken samples achieved excellent protein quality ratings (>100%), while plant-based alternatives scored 52-65%. The degree of protein hydrolysis was substantially higher for chicken (54-60%) compared to plant-based alternatives (20 33%). The in-vitro MRI study employed magnetisation transfer, T1, and T2 relaxation time measurements to monitor protein digestion non-invasively. Chicken proteins exhibited more extensive hydrolysis, demonstrated by elevated T2 values and reduced magnetisation transfer amplitude during simulated digestion. The human crossover trial (n=10) assessed gastrointestinal responses to nutritionally matched chicken and plant-based chicken soups using MRI techniques. Despite similar macronutrient profiles, plant-based chicken soup induced significantly delayed I gastric emptying (26% longer T50 time, p<0.002) and enhanced superior mesenteric artery blood flow (27% increase, p<0.01). However, subjective appetite and satiety ratings remained similar between protein sources. These findings demonstrate that protein source significantly influences digestibility, structural breakdown and gastrointestinal physiology across multiple study models. Chicken protein consistently exhibits a superior amino acid composition and digestibility compared to plant-based analogues, resulting in enhanced protein utilisation and distinct physiological responses. These results emphasise the critical importance of comprehensive protein quality assessment when evaluating plant-based protein analogues.