Untangling the interplay between food microstructure, mechanical properties, macrostructural breakdown and in vitro gastric protein digestion

With the growing global population and environmental challenges, developing a sustainable food system is essential. Protein digestibility plays a crucial role in determining the nutritional value of food, particularly in plant-based meat analogues (PBMAs), which often have low digestibility due to unbalanced amino acid composition and anti-nutritional factors. This thesis investigates the interplay between food microstructure, mechanical properties, oral breakdown, and in vitro gastric protein digestion using both static and dynamic digestion models. - The study began with model whey protein gels to examine how microstructure and mechanical properties affect protein digestion. Gels with different microstructures but similar mechanical properties were tested, revealing that microstructure independently influences digestion. Homogeneous gels displayed the highest digestion rates, while bi-continuous gels were least digestible. Increasing gel stiffness reduced digestion rates in homogeneous gels but had no effect in protein-continuous gels. Additionally, increasing surface area improved digestion efficiency, but the extent depended on microstructure. - Next, in vivo mastication experiments evaluated how chewing alters digestion outcomes. Despite significant macrostructural breakdown, microstructural effects persisted. Bi-continuous gels showed the greatest increase in protein digestion, likely due to their high pepsin partition coefficient at the gel-gastric juice interface. These findings suggest that food structure continues to influence digestion even after substantial oral processing. - The research then shifted to textured vegetable proteins (TVPs), a key ingredient in PBMAs, to explore how structural properties impact digestion. Eight TVPs with varying structural properties, such as surface area, porosity, pore size, and wall density, were tested. Larger surface area and pore size enhanced digestion, while higher wall density inhibited it. We concluded that in addition to macroscopic surface area, pore-related, rather than wall-related properties were primary structural properties influencing in vitro gastric protein digestion of TVPs and TVP-based patties. This indicates that modifying macroscopic structural properties can improve protein digestibility. - Further studies using static and dynamic digestion models (NERDT) investigated the effects of mechanical properties and bolus particle size on PBMA digestion. Two commercial patties were analyzed, showing that bolus particle size had a primary impact on dynamic in vitro gastric protein digestion of PMBA patties. We concluded that bolus particle size, rather than mechanical properties, primarily impact dynamic gastric protein digestion. Specifically, Model PBMAs confirmed smaller bolus particles facilitate dynamic in vitro gastric protein digestion by accelerating gastric emptying and modulating intragastric pH.- Overall, this thesis highlights the intricate relationships between food structure, mastication, and protein digestibility. Findings underscore the importance of considering both micro- and macroscopic food structures when designing plant-based foods to optimize protein availability. The importance of in vivo mastication or realistic mastication simulation prior to in vitro gastrointestinal digestion is also highlighted. Future research should explore how these principles apply to specific populations, such as infants and the elderly, to improve dietary protein utilization.