# Non-Thermal Technologies in Food Processing: Implications for Food Quality and Rheology
## 3 High-Pressure Processing (HPP)
The flow behaviour of the EWA-BSG solution was adequately described by _Herschel-Bulkley_ and _Carreau_ models. The results showed that the viscoelastic parameters of the storage modulus, loss modulus, tan (\(\delta\)), and low-point stress implied a stronger microstructure at the highest pressure (400 MPa). Furthermore, the effect of high-pressure processing (HPP) on the protein conformation analysis, the microstructure, strength of the pea protein gel, and gel rheology and dissolution were studied based on the high-pressure level, treatment time, protein concentration, and pH [109]. The microstructure study based on scanning electron microscopy (SEM) revealed denser networks with a greater degree of crosslinking for pea protein gels at the higher-pressure level when comparing treatments at 600 MPa vs. 300 MPa at the same pH. The changes in the storage modulus (G\({}^{\prime}\)) and loss modulus (G\({}^{\prime\prime}\)) of a gel system were observed depending on the HPP conditions (pressure level). This indicates the sensitivity of proteins to a pressure variation depending on their types. In a comparative study of 0.8% xanthan gum (XG) or 600 MPa/5 min high-pressure processing (HPP) for the texture modification of lentil protein vegetable purees (10% zucchini, 10% carrots, 2.5% extra virgin olive oil, and 21.8% lentil protein concentrate), it was found that HPP-treated purees showed the highest stiffness (storage modulus), the lowest deformability capacity (yield strain), and the lowest structural stability (yield stress) [110]. In other words, gels obtained by HPP techniques are stronger, while those with hydrocolloids (xanthan gum) are more elastic. However, proteins and polysaccharides are two groups of macromolecules that govern the structure-function properties of foods. In such food systems, gel fabrication by HPP could create microstructures and textures with specific properties depending on the pressure and treatment time. After HPP at a pressure of 300 MPa, the viscosity of milk-gelatin mixtures increased with high milk solid concentrations (15% and 20% \(w/w\)), whereas the viscosity decreased following a further increase in the pressure level to 600 MPa [111]. Based on confocal laser scanning microscopy, ruptured aggregates and phase separation were observed at a higher pressure level. The HPP process is, overall, an excellent process for food preservation and minor undesirable changes in food products are minimal, thus positioning it to be a method of choice in various food matrices [91; 112; 113]. However, certain problems must be considered for the mass application of HPP. Specialty packaging is usually required because HPP must be conducted using flexible, pressure-resistant materials [5]. High energy consumption and high operational costs associated with the special equipment used in HPP also pose financial barriers, thereby creating limitations on implementing it on a large scale in the food industry [114]. Nevertheless, the ongoing advancement of HPP technology means that these operations are more and more optimised for cost and scalability.