## 6 Strategies for Improving Protein Digestibility
### Physical Treatments  
Emerging physical methods, such as high-pressure processing (HPP), ultrasonication, irradiation, and pulsed electric field (PEF), have gained attention for their ability to improve protein digestibility. These techniques disrupt protein structures without using high temperatures, making them ideal for heat-sensitive proteins. This method can unfold proteins and increase enzyme accessibility [153], while ultrasonication breaks protein aggregates into smaller, more digestible fragments. For instance, the high-pressure processing (HPP) of pea protein concentrate (PPC) showed that this treatment enhances gastric proteolysis by inducing structural modifications in proteins [154]. HPP-treated PPC underwent greater proteolysis and exhibited distinct peptide patterns compared to untreated and heat-treated samples. In addition, a study on lupin proteins demonstrated that this treatment could enhance their in vitro digestibility, particularly at higher pressures [155].  
High-intensity ultrasound processing significantly enhances the digestibility of plant proteins by inducing physical and chemical modifications. The fluctuating pressure waves generated during ultrasonication disrupt protein aggregates, alter structural configurations, and expose hydrolytic sites, making proteins more accessible to digestive enzymes [156]. This technology can modify proteins' primary, secondary, tertiary, and quaternary structures, facilitating their enzymatic breakdown [157]. Additionally, ultrasonication helps release proteins from plant matrices and disrupts antinutritional factors that inhibit digestion [158]. By improving the extraction, functionality, and bioavailability of plant proteins, ultrasound processing boosts their digestibility and enhances their overall nutritional profile [157], making it a promising tool for developing plant-based food products.  
Irradiation is a modification technique that uses ionizing radiation, such as gamma rays, X-rays, or accelerated electrons, to alter the properties of food ingredients. Irradiation can enhance the digestibility of plant-based proteins by addressing some of their inherent limitations, such as poor aqueous solubility and the presence of anti-nutritional factors like hemicellulose, lignin, and other poorly digestible polysaccharides [159]. By applying ionizing radiation, proteins can be denatured [160], altering their structure to improve their accessibility to digestive enzymes, thus increasing their bioavailability. This process can also reduce the presence of antinutrients, such as lectins and protease inhibitors, which hinder protein digestion and absorption [161]. Additionally, irradiation can enhance the solubility of plant proteins, making them more easily dispersible in aqueous environments, which is crucial for improving their functionality and digestibility [159].  
Pulsed electric field (PEF) processing is a non-thermal technology that applies short bursts of high voltage to food products, leading to structural modifications in proteins. In soy proteins, PEF treatment can cause the unfolding of protein molecules and the dissociation of subunits, exposing hydrophobic and thiol groups previously buried within the protein structure [162]. These structural changes can enhance the accessibility of proteolytic enzymes during digestion, thereby improving protein digestibility.