## 1 Introduction  
In recent years, ultrasonic pulses have been used as an environmentally-friendly technology to improve the functional properties of vegetable and animal proteins by altering their hydrogen bonds and hydrophobic interactions, as well as by disrupting their molecular conformation through cavitation, heating, dynamic agitation and shear stress [1]. Additionally, this technology has been used in green chemistry as a tool for the extraction of functional compounds with an improved yield, short time, low cost, and less solvent [2]. Ultrasound consists of an acoustic wave with a frequency greater than 20 kHz that is undetectable to the human ear and which spreads in a medium; the application of ultrasound can be classified into two major groups: low-intensity and high-intensity ultrasound. High-intensity ultrasound (HIU) consists of low frequency (20-100 kHz), and a high power (>1 W/cm\({}^{2}\)) is preferred since it provokes more substantial effects on a substrate [3]. The ultrasound mechanism of action is based on the passage of waves that create regions of high and low pressure; this variation in acoustic pressure is directly proportional to the amount of energy applied to the system [3]. The propagation of high-intensity ultrasound in a liquid induces a series of compressions and decompressions, causing molecular displacement by disrupting dipole-dipole, hydrogen bonding, and other weaker interactions. The conventional process of extracting gelatin from tilapia skin consists of the thermal denaturation of the collagen that, in its native form, is found as a triple helix of polypeptide chains. The acid and alkali chemical treatments remove the soluble proteins. Finally, the heat treatment interrupts intramolecular interactions, thus causing the triple helix to open and exposing the hidden hydrophobic groups towards the inside of the helix. The high-intensity ultrasonic treatments that are applied to the system energy disrupt weak intramolecular interactions, and this causes changes in the conformation of the protein by the splitting of the polypeptide chains. High-intensity ultrasound pulses have been tested for collagen extraction at an industrial level, and favorable results were obtained because it was possible to minimize the extraction time (from 24 to 3 h) and acid concentration (from 0.5 to 0.05 M) while obtaining twice the yield compared to the conventional method. The industrial system for this process consists of a collagen separation device (where ultrasound is generated and collagen is separated from the sample), a cooling unit, sample supply, a discharge pipe, and circulation pump [2]. Among the most relevant findings about the effect of HIU on proteins is the increase in the solubility of protein suspensions, which is considered to be one of the main requirements during the improvement of the other functional and biological properties of proteins; however, not using proper power and time conditions can lead to the denaturation of proteins due to the overexposure of hydrophobic residues [1; 4; 5]. Other studies have found that ultrasonic treatments reduce the size of proteins [6], and cavitation can promote the deployment of proteins, causing the exposure of hydrophobic and electrostatic regions; therefore, the capacity of the proteins to interact with oil in an emulsion can be improved [7]. Additionally, according to some findings, pulsed ultrasound increases sulfhydryl groups and hydrophobicity due to the unfolding of the secondary structure of the protein [8; 9]. HIU also affects the secondary and tertiary structure of quinoa proteins, changes which result in an increase in solubility and particle size, improving the protein's potential in the food industry [10]. In addition to their functional properties, proteins have also been used as a source of molecules with biological activity, with antioxidant activity being one of the most studied [11]. Ultrasound has also been used as a pretreatment during protein hydrolysis to improve the bioactivities of hydrolyses [12].