Recovery of Proteins from Squid By-Products with Enzymatic Hydrolysis and Increasing the Hydrolysate’s Bioactivity by Maillard Reaction

A review on the processing of functional proteins or peptides derived from fish by-products and their industrial applications

To understand the production and characteristics of protein hydrolysates pertaining to individual fish species, we selected and analyzed the most important commercial fish species according to the market value based on the Statistics on International Exports of Fishery Commodities by Food and Agriculture Organization. Accordingly, salmon, shrimp, cod, tuna, squid, and herring are marine species with high global value. Peptides obtained from their by-products were predominant in hydrophobic amino acids such as alanine, phenylalanine, methionine, proline, valine, tyrosine, tryptophan, leucine, and isoleucine. Bioactive peptides are short with a length of 2-20 amino acids. They remain inactive when they are within their parent proteins. Low molecular weight (0.3-8 kDa) peptides from hydrolyzed protein are easily digestible, readily absorbed by the body and are water-soluble. The hydrophobic nature contributes to their bioactivity, which facilitates their interactions with the membrane lipid bilayers. Incomplete hydrolysis results in low yields of hydrophobic amino acids. The glycosylation type of the resulting peptide fragment determines the different applications of the hydrolysate. The degree of conservation of the glycosidic residues and the size of the peptides are influenced by the method used to generate these hydrolysates. Therefore, it is crucial to explore inexpensive novel methodologies to generate bioactive peptides. According to the current studies, a unified approach (in silico estimation coupled with peptidomics) can be used for the identification of novel peptides with diverse physiological and technological functions. From an industrial perspective, the reusability of immobilized enzymes and membrane separation techniques (e.g., ultrafiltration) on marine by-products can offer low operating costs and higher yield for large-scale production of bioactive peptides. This review summarizes the production processes and essential characteristics of protein hydrolysates from fish by-products and presents the advances in their application.

Formation of Oxidative Compounds during Enzymatic Hydrolysis of Byproducts of the Seafood Industry

There is a significant potential to increase the sustainability of the fishing and aquaculture industries through the maximization of the processing of byproducts. Enzymatic hydrolysis provides an opportunity to valorize downstream fish industry byproducts for the production of protein hydrolysates (FPH) as a source of bioactive peptides (BAP) with health benefits. Deteriorative oxidative reactions may occur during the enzymatic hydrolysis of byproducts, influencing the safety or bioactivities of the end product. Lipid oxidation, autolysis mediated by endogenous enzymes in viscera, protein degradation, and formation of low-molecular-weight metabolites are the main reactions that are expected to occur during hydrolysis and need to be controlled. These depend on the freshness, proper handling, and the type of byproducts used. Viscera, frames, trimmings, and heads are the byproducts most available for enzymatic hydrolysis. They differ in their composition, and, thus, require standardization of both the hydrolysis procedures and the testing methods for each source. Hydrolysis conditions (e.g., enzyme type and concentration, temperature, and time) also have a significant role in producing FPH with specific structures, stability, and bioactivity. Protein hydrolysates with good safety and quality should have many applications in foods, nutraceuticals, and pharmaceuticals. This review discusses the oxidative reactions during the enzymatic hydrolysis of byproducts from different fish industry sectors and possible ways to reduce oxidation.

Transformation of Seafood Side-Streams and Residuals into Valuable Products

Seafood processing creates enormous amounts of side-streams. This review deals with the use of seafood side-streams for transformation into valuable products and identifies suitable approaches for making use of it for different purposes. Starting at the stage of catching fish to its selling point, many of the fish parts, such as head, skin, tail, fillet cut-offs, and the viscera, are wasted. These parts are rich in proteins, enzymes, healthy fatty acids such as monounsaturated and polyunsaturated ones, gelatin, and collagen. The valuable biochemical composition makes it worth discussing paths through which seafood side-streams can be turned into valuable products. Drawbacks, as well as challenges of different aquacultures, demonstrate the importance of using the various side-streams to produce valuable compounds to improve economic performance efficiency and sustainability of aquaculture. In this review, conventional and novel utilization approaches, as well as a combination of both, have been identified, which will lead to the development of sustainable production chains and the emergence of new bio-based products in the future.

Quality improvement of shrimp ( Litopenaeus vannamei ) during refrigerated storage by application of Maillard peptides/water‐soluble chitosan coating

We investigated the effect of squid Maillard peptides (SMPs) on the shelf life and quality of shrimp for 20 days. Water‐soluble chitosan coatings incorporated with SMPs (SMPs + chitosan) were applied to shrimp under chilled conditions. Untreated samples were used as control, along with samples treated with water‐soluble chitosan and SMPs alone. The pH increase was observed in all samples, as well as increased total plate count, total volatile basic nitrogen, peroxide value, and thiobarbituric acid index. However, these indexes in the SMPs + chitosan group were lower than the other three groups, which suggested SMPs + chitosan might play a role in retarding quality loss of shrimp, and there might be a combined effect between water‐soluble chitosan and SMPs. Based on hardness, springiness, and sensory evaluation, shrimp coated with SMPs + chitosan was the best preserved, with a shelf life of 16 days but only 8–12 days for other samples. The present work demonstrates the effectiveness of SMPs + chitosan, offering a promising alternative to inhibit microbial growth and lipid oxidation on shrimps during refrigerated storage.

Functional and Bioactive Properties of Peptides Derived from Marine Side Streams

In fish processing, a great amount of side streams, including skin, bones, heads and viscera, is wasted or downgraded as feed on a daily basis. These side streams are rich sources of bioactive nitrogenous compounds and protein, which can be converted into peptides through enzymatic hydrolysis as well as bacterial fermentation. Peptides are short or long chains of amino acids differing in structure and molecular weight. They can be considered as biologically active as they can contribute to physiological functions in organisms with applications in the food and pharmaceutical industries. In the food industry, such bioactive peptides can be used as preservatives or antioxidants to prevent food spoilage. Furthermore, peptides contain several functional qualities that can be exploited as tools in modifying food ingredient solubility, water-holding and fat-binding capacity and gel formation. In the pharmaceutical industry, peptides can be used as antioxidants, but also as antihypertensive, anticoagulant and immunomodulatory compounds, amongst other functions. On the basis of their properties, peptides can thus be used in the development of functional foods and nutraceuticals. This review focuses on the bioactive peptides derived from seafood side streams and discusses their technological properties, biological activities and applications.

Aquaculture and its by-products as a source of nutrients and bioactive compounds

Underutilized marine resources (e.g., algae, fish, and shellfish processing by-products), as sustainable alternatives to livestock protein and interesting sources of bioactive compounds, have attracted the attention of the researchers. Aquatic products processing industries are growing globally and producing huge amounts of by-products that often discarded as waste. However, recent studies pointed out that marine waste contains several valuable components including high-quality proteins, lipids, minerals, vitamins, enzymes, and bioactive compounds that can be used against cancer and some cardiovascular disorders. Besides, previously conducted studies on algae have shown the presence of some unique biologically active compounds and valuable proteins. Hence, this chapter points out recent advances in this area of research and discusses the importance of aquaculture and fish processing by-products as alternative sources of proteins and bioactive compounds.