What is Upcycled Salmon? A Guide to This Sustainable Seafood

The fisheries and aquaculture industries are some of the major economic sectors in the world. But these businesses make a lot of waste that needs to be handled properly to keep health and the environment from getting worse. New discoveries in how to use marine waste have shown that fish waste biomass is a great source of biomolecules with high value, such as enzymes, functional proteins, bioactive peptides, and omega-3 rich oils. Because they are green and eco-friendly and cost less than chemical-based processes, enzyme-assisted processes are becoming more popular for recovering these valuable biomolecules. At the moment, most of the commercially available proteases used to get valuable compounds back from fisheries and aquaculture waste are mesophilic and/or thermophilic, which means they need a lot of energy and can cause bad reactions (i.e. e. , oxidation). Cold-adapted proteases, on the other hand, come from cold-water fish species and work at low temperatures but become unstable at higher temperatures. This makes them interesting from both an economic and environmental point of view, as they can be used to recycle fish waste and save a lot of energy. This review gives an overview of cold-adapted proteolytic enzymes from cold-water fish species and talks about the ways they can be used to make fisheries and aquaculture waste useful.

The fisheries and aquaculture industries represent some of the major economic sectors in the world. A recent report from the Food and Agricultural Organization (FAO) said that fish, crustaceans, and mollusks were caught and raised in aquaculture around the world for 177 8 million tons in 2019 and generated USD 406 billion in terms of total first sale value (1). However, 20%E2%80%937% of this global production from fisheries and aquaculture is considered waste and is dumped at sea or in landfills (2%E2%80%934).

Organic wastes from the fishing, aquaculture, and food industries are a big problem around the world because they hurt the economy, society, and the environment. This trash can also help climate change in a small way by releasing greenhouse gases (GHG) when it is thrown away in landfills. For instance, according to a report by Bogner et al. Methane emissions from landfills and wastewater made up almost 90% of waste sector emissions, which was equal to about 18% of the world’s annual anthropogenic methane emissions. Waste valorization is a way to slow down climate change that mostly works because it lowers greenhouse gas (GHG) emissions through recycling, reducing waste, and getting energy back from waste. Several studies have shown that waste from fisheries and aquaculture could be used to make biomolecules like enzymes, functional proteins, bioactive peptides, omega-3-rich oils, and polysaccharides like chitin (8–12). The way these biomolecules are extracted in factories now is not sustainable because they rely too much on harsh chemicals and/or expensive enzyme reactions that use a lot of water and energy and make a lot of waste that needs to be treated before it can be released into the environment (13, 14). Most commercially available enzymes that are used to get valuable compounds out of fish waste work best when they are heated to 50 to 80°C. This temperature range poses a serious safety risk (i. e. , growth of pathogenic micro-organisms) and unfavorable reactions (i. e. , oxidation). By contrast, when used at lower temperatures, their enzyme activity is dramatically reduced. Cold-adapted enzymes, on the other hand, work at temperatures between 0 and 30°C but become unstable above 50°C (15).

Fish viscera is a common waste product from fishing and aquaculture, and it makes up about 5% of a fish’s body weight (16). Fish viscera comprise a number of digestive enzymes including acidic (i. e. , pepsin) and alkaline proteases (i. e. , trypsin, chymotrypsin, and elastase) that are widely used in bioprocessing (16). Also, proteases found in the viscera of cold-water fish have been shown to be able to adapt to cold conditions (17–19). So, using cold-adapted proteases from fish to recycle waste from fisheries and aquaculture could be a long-term way to turn waste into value-added products that would fully utilize the waste and completely eliminate its negative environmental impact. This review’s goal is to give an overall look at cold-adapted proteolytic enzymes from cold-water fish species and to draw attention to the ways they can be used to make fisheries and aquaculture waste useful.

The ways that enzymes adapt to cold temperatures are complicated, but one thing they all have in common is that their molecules are very flexible compared to their mesophilic and thermophilic counterparts, which are less active and more rigid at low temperatures (20–22). It has been suggested that the main structural feature of cold-adapted enzymes is their increased molecular flexibility, which is needed to compensate for the low working temperature. This is currently the most widely accepted theory for cold adaptation (24) However, there is a debate whether the flexibility of cold-adapted enzymes is a global flexibility (i. e. , flexibility throughout the enzyme structure) or a local flexibility (i. e. , distinct regions in the enzyme structure) (22). A smaller number of hydrogen bonds, less densely packed structures, a higher surface hydrophilicity, and an increased number of methionine residues are some of the other things that can be seen in enzymes that have adapted to cold temperatures.

New evidence also shows that cold-adapted enzymes usually have a low thermostability level paired with a high specific activity (23) Compared to homologs that are mesophilic or thermophilic, cold-adapted enzymes are less stable at low temperatures (so they don’t freeze) and have a lower activation enthalpy and a more negative activation entropy (25) Also, some proteases that are better at working in cold temperatures have been shown to be more likely to break down on their own than their mesophilic counterparts. This is because they are more efficient at breaking down proteins and less stable at high temperatures (21, 26).

Typical Enzyme Recovery Processes

Separating and purifying enzymes is a complicated process that usually involves using a number of different techniques in a certain order to reach the desired level of purity (61). Of the different ways that have been created to do this, precipitation, aqueous two-phase partitioning, and membrane fractionation are the ones that are used most often.

Proteins, like enzymes, can be precipitated by changing their shapes. This can be done by changing the pH, increasing the ionic strength, or adding solvents that mix with water. Changing the pH of the medium can either make some groups in the protein lose their protons (lower the pH) or gain them back (higher the pH) or cancel out their charges (i.e. neutralize the pH). e. the protein in solution has no net electrical charge because there are an equal number of opposite charges) (62) The latter state refers to the isoelectric point in which the protein has the lowest solubility. We often use precipitation at the isoelectric point to get back proteins (63–68), but not for enzyme isolation because it breaks down proteins irreversibly, which is the biggest problem with isoelectric point precipitation (69).

Adding very large amounts of salt (like sodium chloride, ammonium sulfate, and sodium sulfate) or organic solvents (like methanol, ethanol, butanol, and acetone) can also break up the macrostructures of proteins and enzymes. The large amounts of salt cause protein precipitation through the “salting out” effect. This approach can be used to recover enzymes. In order to get rid of the salts, though, methods like dialysis, gel filtration, or ion exchange chromatography must be used.

Most of the time, adding water-miscible solvents causes precipitation because the polar groups of the protein and the solvent compete with water (62). If you choose to use solvent-based precipitation techniques to get the enzymes back, be careful to extract them at low temperatures, since organic solvents can break down enzymes even at low temperatures (70).

Partition Through Aqueous Two-Phase Systems

In one step, aqueous two-phase partitioning cleans one liquid from another liquid using affinity partitioning. This is usually done by mixing a polymer with another polymer (like dextran or polyethylene glycol) or a polymer with a salt (like phosphate, sulfate, or citrate) and water. In general, polymer/salt based aqueous two-phase systems (ATPS) are better than polymer/polymer based ATPS because they are cheaper and have less viscosity.

As part of downstream processing, ATPS is the first step in isolating and cleaning the material. This is done by getting rid of some impurities and decreasing the working volume. The ATPS process is easy to use and selective, and the phase-forming compounds are cheap and safe, which makes it possible to use ATPS on a large scale (72).

People have said that aquaponic two-phase systems can effectively get enzymes back from fish waste, like the viscera of farmed giant catfish (74, 75) and hybrid catfish (76). ATPS has a lot of potential to clean enzymes better than traditional salt precipitation methods, but it also has some problems that need to be fixed. Firstly, the enzymes still need to be separated from the phase forming reagents after the partition is completed. Additionally, ATPS in industrial settings uses a lot of chemicals, so long-term ways to reuse and/or recycle these chemicals are still needed. Lastly, using inorganic salts causes problems with both disposal and the environment. To solve these problems, new ATPS processes using biodegradable and/or volatile reagents instead of inorganic salts need to be created and improved (72).

Membrane ultrafiltration is a well-established separation process which allows for both purification and concentration (77, 78). Ultrafiltration has routinely been used for the industrial separation and purification of enzymes produced through fermentation (79). When you compare ultrafiltration to other enzyme separation methods, the main benefits are better activity recovery (79) and less denaturation and/or degradation of bio-products (80), since ultrafiltration works under relatively mild temperature and pressure conditions. However, the main problem with ultrafiltration is that the final product can cause the membrane to get clogged up with precipitates (81).

Unfortunately, even though ultrafiltration has many benefits, it has only been used in a few studies to separate and isolate fish proteolytic enzymes (82, 83). Most of the studies looked at how ultrafiltration could be used to separate fish protein hydrolyzates into bioactive peptide fractions.

What is Upcycled Food?