# Non-Thermal Technologies in Food Processing: Implications for Food Quality and Rheology
## 3 High-Pressure Processing (HPP)
For this reason, food processing using HPP can become a sustainable and flexible solution for liquid and solid foods. HPP-treated mango pulp, for instance, retains its natural viscosity, while protein denaturation during HPP processing can improve the meltability of cheeses and related products [92; 96]. Studies have shown that pressures between 400 and 600 MPa can induce up to 30-50% denaturation of whey proteins, which contributes to a smoother texture in dairy products [102]. For example, the study by [PERSON] et al. [103] found that HPP(600 MPa for 5 min) led to a significant denaturation of \(\beta\)-lactoglobulin (about 41-59%) and a slight denaturation of \(\alpha\)-lactalbumin (6%) in milk, leading to the disruption of casein micelle disruption. Apart from contributing to a smoother texture in dairy products, the HPP-induced disruption of casein micelles has been found to alter the optical characteristics of milk, including its turbidity and lightness [96]. Additionally, the cold gelation induced by HPP on some protein systems allows for creating new textures in foods such as high-protein gels or low-fat spreads [104]. This is useful in the reduction of the fat content in meat products while maintaining or even enhancing their functional and textural properties. The relationship between these structural modifications and rheological behaviour is important. Higher viscosity in liquid and semi-solid foods, such as fruit pures and dairy products, is a result of the increased water-binding capacity brought on by pressure-induced protein unfolding and polysaccharide interactions [105]. Improved gelation from HPP-induced denaturation improves the firmness, elasticity, and cohesiveness of foods high in protein, such as meat and cheese. For example, regulated protein denaturation in dairy products enhances the meltability and spreadability, thereby improving the mouthfeel [80]. The high-pressure treatment promotes the formation of a stronger gel structure, which reduces the fat content without compromising the sensory qualities. This is usually achieved by the structural modification of proteins, which induces changes in myofibrillar protein gelation, one of the most important factors affecting the final texture and mouthfeel of products such as sausages [106]. Through these interrelated adjustments, HPP balances viscosity, firmness, and spreadability to maximise the product quality while also altering the microstructure and regulating the final rheological characteristics. The new microstructure developed after HPP treatment enhances the water-binding capacity of these products, improving the juiciness, firmness, and overall acceptability. Through these changes, the manufacturers are enabled to design low-fat meat products possessing the required texture and sensorial quality to meet the growing consumer demand for healthier alternatives without compromising the product quality [106]. In several food products, the presence of proteins and or polysaccharides can affect the texture, microstructure, shelf life, thickening, and stability because of gelling. The rheology of these components can be affected by the pressure level during HPP. In a pioneering study, the rheological characterisation of a selected allergenic protein after HHP processing was investigated via the modelling of the rheological behaviour [107]. The results showed that viscosity is increased as the processing pressure levels increase (600, 700, and 800 MPa) and the treatment time increases (15 and 25 min). Based on the _[PERSON]_ rheological model, the flow consistency index (\(K\)) of a Bovine Serum Albumin solution increases with the increasing pressure levels, treatment times, and protein concentration, whereas the protein solution processed at pressure levels above 600 MPa demonstrated a characteristic behaviour of a pseudoplastic fluid. A study of the effect of pH and HPP on the rheological properties of egg white albumin and basil seed gum (EWA-BSG) mixtures has been reported for pressure levels of 0, 200, and 400 MPa [108].