Abstract
There is a growing interest in developing protein-rich plant-based foods with tailored texture and digestion profiles; however, little is known about how protein incorporation and structural construction affect these characteristics. This PhD thesis investigates the effects of increasing levels of pea protein isolate (PPI) incorporation on the structural and textural properties, alongside in vitro starch and protein digestibility of a vegan pasta food model. Two processing methods were used for structuring the food model, namely (1) conventional pasta making, and (2) 3D printing with variable infill densities to modify the 3D structure of pasta.
In conventional pasta, PPI incorporation (0–35% w/w) disrupted the gluten network, transitioning the protein structure to a denser configuration characterized by less organized clumps. At low PPI levels (<15% w/w), texture profile analysis revealed reduced hardness and cohesiveness, while higher PPI incorporation (≥15% w/w) promoted globular aggregation, increasing hardness but decreasing springiness and chewiness. Sensory evaluation showed PPI-incorporated pasta was perceived as less firm but more brittle, resulting in reduced chewing duration before swallowing. The in vivo oral processing study demonstrated smaller bolus particles of PPI-incorporated pasta, thus improving the accessibility of protein and starch to digestive enzymes. This subsequently increased the rate and amount of protein and starch hydrolysis during in vitro digestion. The disrupted gluten network also improved starch gelatinisation during thermal processing, further improving starch digestibility.
From a rheological perspective, PPI incorporation improved the 3D printing performance of wheat-based inks by improving key viscoelastic properties, as evidenced by notably increasing the storage modulus (G'), loss modulus (G"), and complex modulus (G*), while extending the linear viscoelastic region (LVR). The PPI-incorporated inks also exhibited superior shear-thinning behaviour (flow index n < 0.2 at 15-25% (w/w) PPI) and demonstrated enhanced self-supporting capacity after extrusion, as indicated by their high post-shear viscosity. These rheological modifications were related to better printing fidelity, with optimal results achieved using a formulation containing 25% PPI (dry weight) at a 1:1 water-to-dry ingredient ratio.
Increasing the infill densities (reducing void spaces) of 3D printed pasta enhanced the hardness, cohesiveness, and chewiness measured through texture profile analysis, leading to longer chewing durations for swallowing. The prolonged chewing of high-infill samples improved oral breakdown, yielding smaller bolus particles that elevated the rate of in vitro protein digestion, and increased the amount of starch hydrolysis during the oral phase through extended α-amylase interaction. In comparison, when the in vivo oral breakdown was conducted for a controlled/fixed chewing duration of 29 seconds, no clear reduction in particle size or accelerated in vitro protein/starch digestion rates was observed on high-infill samples. The total amounts of protein and starch being hydrolysed during digestion were kept constant, regardless of the oral breakdown and chewing duration, suggesting the overall bioaccessibility of protein and starch was not influenced by infill densities.
By strategically altering texture through PPI substitution and infill density modulation during 3D printing, this research provides a foundation for designing functional foods with tailored digestion kinetics to meet specific nutritional and sensory needs. This study also bridges the gap between in vitro digestion and in vivo oral processing by incorporating human oral processing, highlighting the important role of oral breakdown on the subsequent protein and starch digestion profiles.