# Extraction of Novel Bioactive Peptides from Fish Protein Hydrolysates by Enzymatic Reactions
## 1 Introduction  
Over the years, the steep rise in the world population has created immense pressure on the extraction of natural resources [1, 2, 3, 4, 5], including an overburden on the agricultural and food sector to feed people with stable nutritional diets [6, 7, 8]. Therefore, there is an urgent need to manage waste in a manner that solves the issues of food scarcity, food insecurity, and environmental pollution. The sustainable development goals of the United Nations propose to take stringent actions in the form of research and government policies to create a balance in these sectors. In the global trade setting, fish and marine products are considered highly perishable commodities and are commonly processed to maintain their nutritional components. In 2020, the global production of capture and aquaculture recorded that 157 million tons (89%) were utilized for human consumption, 20 million tons (16%) wereutilized for non-food uses, others were utilized as fish meal and fish silage (81%), and the remaining amount unaccounted for went to waste [9]. Due to the worldwide abundance of fish, it is considered one of the main protein sources for human consumption. A wide variety of products can be derived from fish, but most of the time, the fish byproducts are shown the least attention. Most fish products that are fresh and of optimum quality are high-priced commodities [10]. On the other hand, underutilized and abundant species are commonly subjected to traditional preservation techniques, which include salting, drying, and smoking, which lead to diversified product forms across continents and other parts of the world. These processing methods produce byproducts in high quantities, mainly composed of heads, fins, guts, and bones, and are often discarded as waste materials and thrown into landfills, oceans, and rivers [11]. The increasing demand for value-added products has led to a high production of fish waste that needs more attention to mitigate its negative effects on the environment [12; 13]. The disposal of agro-fishey waste biomass accounts for 50% of the global aquaculture and processing industry production, and has been considered a global problem [14]. Significant actions are needed on the valorization of fish byproducts to improve the waste management and proper disposal of these fish scraps. The fish biomass including the skin, bones, head, and viscera are considered processing wastes produced by seafood processing activities which result in negative environmental and economic impacts [15]. However, fishery byproducts and discards are good sources of bioactive compounds and have a high potential for food applications and other industrial uses. At present, there is a growing interest in the utilization of fish wastes and discards that are generated from fishing activities and production [16], and most of them are considered not fit for human consumption. Fish protein hydrolyses (FPH) are one of the high-quality products that can be derived from fish muscle protein. These are made from fish or fish byproducts by hydrolyzation, which yields a mixture of broken proteins and smaller compounds of peptides and amino acids [17]. The hydrolysis methods that are usually employed to extract fish proteins are chemical, microbial, and enzymatic processes. The chemical methods employ the use of alkalis and other solvents. However, in the recent past, deep eutectic solvents have also been recognized as \"green\" solvents for extracting novel proteins from fish discards such as skin, scales, bones, and viscera in an economical manner [18; 19]. On the other hand, the enzymatic processes usually involve using pure commercial proteolytic enzymes. FPH is known to contain bioactive peptides and exhibit biological activities such as antioxidant and antimicrobial activities, angiotensin-I converting enzyme (ACE) inhibition, calcium-binding capacity, dipeptidyl peptidase (DPP)-IV inhibition, immunomodulation, and antiproliferative activity (Figure 1) [20].