## 1 Introduction
Collagen is an extremely sought-after structural protein, representing up to 30% of total protein content in the skin and bones of all animal species. Due to the many applications in the food, cosmetics, and pharmaceutical industries, the demand for collagen and gelatin has increased globally. Up to 300,000 metric tons of collagen and gelatin are estimated to be produced yearly, with the vast majority coming from bovine and porcine sources. As discussed elsewhere, the cultural and religious implications, as well as the possibility of infectious outbreaks related to these terrestrial sources, may limit their use for collagen production [3; 9; 10; 11]. Thus, reliable alternative sources of collagen would be of great economic potential. Apart from the untapped commercial significance, marine collagen is also of interest due to its unique characteristics. These collagens are easy to extract and exhibit high biocompatibility and negligible biological contaminants and toxins. One must, however, consider the lower denaturation temperatures when compared to mammalian collagens [12]. Currently, collagen is extracted and retrieved from marine sources through a series of common steps, including pre-treatment, extraction, purification, and retrieval. The pre-treatment step entails the removal of non-collagenous proteins, lipid, and mineralized material in the case of bones and scales through chemical treatment [12; 13; 14]. Due to its triple helical structure, collagen is not readily soluble in water and must be solubilized prior to its extraction. Acidic solubilization (ASC) via the use of acetic acid or citric acid is the most common extraction method [12]. Enzymatically solubilized collagen extraction is also commonly utilized, with pepsin being the agent most frequently used. Such proteases aid in the cleavage of the non-helical regions of the collagen structure (telopeptides), increasing solubility and extraction efficiency greatly [15; 16]. Recovery of the solubilized collagen is accomplished via salting out, where the precipitate formed is retrieved via centrifugation or filtration. This is then redissolved in a minimum amount of acetic or citric acid and dialyzed. Further purification steps may be employed. Once a sufficiently clean collagen sample is obtained, this is freeze-dried to obtain the dry collagen sample [15; 17; 18]. Marine-derived oils are some of the most widely used dietary supplements, owing to their high concentrations of n-3 PUFAs, namely, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). These are reported to have cardio-protective functions and to reduce thrombosis risk [19], as well as having anti-aging benefits on brain health and development as well as eye health. In vitro studies show that they may be useful in combating chronic diseases such as diabetes and Alzheimer's [19]. The market value for EPA and DHA is expected to exceed EUR 5.14 billion by 2026 [20; 21]. Depleting marine fisheries resources necessitate alternative ways to produce fish oils that do not include the capture of whole fish for its extraction; therefore, interest in the production of marine oils from the waste material of the fisheries and aquaculture industries has greatly increased. The extraction and concentration of \(\omega\)-3 PUFAs can be achieved in multiple ways [22]. The wet pressing method is the traditional procedure that is employed together with fish meal processing. This process involves the cooking, pressing, and separation (decantation and centrifugation) of the fish tissue. The high temperature and pressure employed may affect the condition of PUFAs in the oil due to hydrolysis and oxidation reactions, and, therefore, this method may not be suitable to produce high-quality EPA and DHA fatty acids destined for human use [23]. Stringent regulations for the production of fish oils in North America and Europe are also pushing for newer technologies that will lead to fish oils richer in uncompromised fatty acids, such as the omega-3 fatty acids mentioned here [20].