## 6 Strategies for Improving Protein Digestibility
### Thermal Processing  
Numerous studies have focused on improving plant protein quality through food processing techniques, particularly thermal techniques. These methods aim to enhance plant-based protein sources' nutritional, functional, and sensory properties. Some of the common thermal processing techniques include cooking [110; 116], autoclaving [133], microwave [134], and extrusion [135]. Heat denatures protein structures, making them more accessible to digestive enzymes. Additionally, thermal processing can reduce or eliminate anti-nutritional factors such as trypsin inhibitors and tannins, which otherwise hinder protein digestion. However, excessive heating should be avoided, as it may lead to the formation of undesirable compounds like Maillard reaction products, which can reduce protein quality. For instance, in vitro and in vivo studies have demonstrated that wet sorghum cooking significantly decreases its protein digestibility [136]. In contrast, this effect is not observed in maize, where cooking has only a minimal impact on protein digestibility [137]. The reduced digestibility of sorghum protein is primarily attributed to the formation of enzymatically resistant protein polymers during cooking, caused by disulfide bonding between \(\beta\) and \(\gamma\)-kafirins and matrix proteins [136]. These disulfide crosslinks limit the access of proteolytic enzymes to the more abundant and digestible \(\alpha\)-kafirin found at the core of the protein body, which may explain the observed reduction in digestibility [138]. Autoclaving improves the protein digestibility of beans by reducing antinutritional factors and modifying the structural properties of the seeds [139]. The process significantly decreases the content of trypsin inhibitors, which are known to interfere with protein digestion, thus enhancing the accessibility of proteins to digestive enzymes. In addition, autoclaving enhances the protein digestibility of soybeans by effectively inactivating antinutritional factors such as trypsin inhibitors, which interfere with enzymatic protein breakdown [107]. The high temperature and pressure conditions during autoclaving denature the proteins, making their structure more accessible to digestive enzymes. This process also reduces the presence of other compounds, like lectins, that impair nutrient absorption, thereby increasing protein bioavailability. As a result, autoclaving transforms soybeans into a more digestible and nutritionally valuable food ingredient, suitable for direct consumption and use in various food formulations. Microwave treatment can enhance protein digestibility because it modifies enzyme function, leading to improved protein-protease interactions. Microwaves influence enzyme activity through four key mechanisms [134]. Microwave treatment enhances protein digestibility through several mechanisms: (1) It denatures thermally unstable enzymes, rendering them inactive; (2) it induces molecular rearrangement and protein unfolding, making specific regions of the protein more accessible to enzymatic hydrolysis; (3) it reduces the particle size of treated protein, increasing surface area and exposing more cleavage sites for protease activity; and (4) it promotes the development of proteins with a high zeta potential, stabilizing the protein suspension, preventing aggregation in water, and increasing the availability of sites for protein-protease interaction [140; 141]. A study on the effects of extrusion demonstrated that this processing method can significantly improve protein digestibility by altering both the secondary and tertiary structures of plant proteins [142]. Extrusion reduces the \(\alpha\)-helix/\(\beta\)-sheet ratio in the protein's secondary structure, decreasing disulfide bonds and hydrophobic interactions in the tertiary structure. These structural modifications make the proteins more accessible to digestive enzymes, promoting their digestion and absorption. [PERSON] et al.