## 3 Results and Discussion
### The Techno-Functional Properties of Proteins
#### 3.2.5 Antioxidant Properties  
In all cases, the ABTS\({}^{+}\) radical scavenging activity of the LPC treated by HIU was bigger than the non-treated LPC (Table 3). The non-treated LPC showed significantly lower antioxidant capacity than the treated proteins. However, the modified proteins extracted at 840 W showed significantly better ABTS\({}^{\bullet\star}\) RSA, reaching the highest antioxidant capacity (from 71 to 96.65%) in the three evaluated times. In the context of ABTS\({}^{\bullet\star}\), the IC\({}_{50}\) value indicates the concentration of an antioxidant needed to scavene 50% of the ABTS radicals present in each system. This value is inversely proportional to the antioxidant activity of a sample. A lower IC\({}_{50}\) value indicates higher antioxidant activity, as it means that a smaller concentration of the sample is required to scavenge the free radicals. The US breaks Van der Waals forces, hydrogen bonds, and other non-covalent bonds of the LPC [45]. The AAA composition showed that the HIU-treated LPC had higher contents of glutamic aspartic and lysine (Table 1). The acidic AAs can donate electrons and act as metal-chelating agents. Likewise, positively charged amino acids, such as lysine, can bind and neutralize negatively charged free radicals [46], which would explain the high antioxidant properties of the modified proteins compared with the controls. The same behavior was observed in lupin-modified proteins [47]. The ultrasonic waves applied during the HIU treatment to proteins break them down into smaller, modified proteins, which often exhibit enhanced antioxidant properties compared to their native proteins [41; 45]. Ultrasonic waves can generate free radicals, which can interact with the protein structure, leading to the exposure of new chemical groups. The size reduction can also modify the content of the different secondary structure portions [41; 45; 48]. In watermelon seed proteins, HIU treatments decreased the proportion of \(\alpha\)-helix and \(\beta\)-turn, increasing the \(\beta\)-sheet proportion [48]. These changes led to the exposure of hydrophobic amino acids, enhancing their ability to interact with and neutralize free radicals [41; 45; 48]. After HIU treatment, the proportion of the identified amino acids increased (Table 2). Some of them have well-demonstrated antioxidant properties, such as methionine (the sulfur atom in its structure can be oxidized, making it a scavenger of ROS), glutamic acid, and aspartic acid (both have carboxylate groups that can chelate metal ions, reducing the oxidative damage caused by metal-catalyzed radical formation) [49]. The increment of the exposition of certain AA residues contributes to the antioxidant activity, without necessarily altering the protein-binding affinity (which the IC\({}_{50}\) measures) [45; 50]. This result may be beneficial in applications where improved antioxidant properties are desired, without compromising the efficiency of inhibition (IC\({}_{50}\)). Even when the proteins have been modified to have a better RSA or exhibit different antioxidant behavior, their efficacy remains stable at certain concentrations. In practical applications, such as in the food or pharmaceutical sectors, this could lead to a more effective antioxidant effect without having to change the dosage, thus maintaining efficacy while improving the health benefits or shelf life of the products [51]. Therefore, these results demonstrated the potential of the HIU as a suitable method for enhancing the release of novel bioactive modified proteins with better antioxidative properties with potential applications in the industrial sector. In addition to this, an economic analysis regarding the use of US has demonstrated its profitability in the food industry [16; 52]. All the assessed properties in this research are linked with the modifications provided by HIU, which generates high-frequency sound waves that create rapid pressure changes in the liquid medium.