Bio-based material innovation, scales and other fish industry waste to make bio-plastics for food packaging!

World fish production in 2019 is estimated at 177.8 million metric tons and is expected to grow significantly in the future. As widely recognized by the United Nations 2030 Agenda for Sustainable Development and FAO, fisheries and aquaculture play an important role in food security and nutrition. About 70% of fish and seafood are processed before they are sold, resulting in large amounts of solid waste in activities such as decapitation, hulling, de-viscera, defining and scaling, and fillet removal.

Fishery by-products typically include internal organs, muscle tissue, carcasses, heads, fins, skin, scales and bones, which make up about 50 to 75 percent of fresh weight, depending on the species. For example, the processing of shrimp and fillets produces almost 50% and 75% (by weight) of waste. About 20% of fishery by-products are used as low-value ingredients in animal feed, most of which are land filled or incinerated, resulting in environmental, health and economic losses.

Fish waste is therefore a growing problem that requires innovative approaches and solutions. To this end, a number of projects and measures have been adopted globally to prevent food waste. Among them, fish waste as a new raw material for bio-plastics has attracted more and more attention in different application areas (mainly food packaging), with significant economic and environmental advantages.

They can be made into food packaging by recycling several potentially valuable molecules including oils, proteins, colors, bio-active peptides, amino acids, collagen, chitin, gelatin. Packaging is still considered a major segment ofbio-plastics production, accounting for 47% (990,000 tonnes) of the bio-plastics market in 2020. Among these innovative green materials, edible/biodegradable films for food packaging applications have attracted the attention of researchers in academia and industry.

Francesca Rioneto, from the Department of Innovation Engineering at the University of Salento, published in Polymers. The roundup article, titled ‘Recent Applications of Bio-polymers from Fish Industrial Waste in Food Packaging’, summarizes recent advances in the valuation of waste from the fish industry and the potential to reuse these by-products in circular economy approaches for the preparation of bio-plastics for food packaging.

1. Muscle protein
Muscle proteins are divided into three broad categories according to their solubility: myogenic fibrin, sarcoplasmic proteins, and matrix proteins. Myoffibrin is the main component of skeletal muscle, accounting for about 65-75% of total muscle protein. Myoffibrin includes some contractile proteins, such as myosin and actin, regulatory proteins such as protomyosin and troponin, and other secondary proteins. Due to their structure and localization, myoffibrins require denaturing conditions, such as highly ionic strength solutions to be dissolved and extracted.

Proteins are one of the most commonly used bio-materials in the food industry because of their nutritional value, non-toxic, biodegradable and gel-forming ability. In recent years, fish matrix proteins and myogen fibrin have received a lot of attention for their ability to form biodegradable, edible films with good barrier gases, organic volatiles and lipid properties that are insoluble in water but can be dissolved by adjusting the pH of the solution. These films made from fish muscle fibrils or muscle proteins have several advantages:(i) Excellent UV barrier compared to commercial packaging films made of PVC; (ii) good oxygen and carbon dioxide barriers ;(iii) slight transparency; (iv) potential for the production of active packaging.

The main disadvantages that limit the widespread commercial application of these films are rigidity and low mechanical strength, which is further enhanced by the disulfide bonds, hydrogen bonds, and/or electrostatic interactions due to the extensive protein-protein chain interactions in the thin film network. To overcome this problem, high levels of plasticizers (about 40-60%) can be added to biodegradable films to reduce brittleness and increase ductility and toughness by reducing the force between protein-protein chains. Another limitation of fish fibrin membranes is poor water vapor barrier, which is due to the high hydrophilicity of amino acids in proteins and the addition of a large number of hydrophilic plasticizers (such as glycerol and sorbitol) to give the membrane sufficient flexibility . Chemical crosslinking, electron beams, and gamma radiation have been reported to be effective methods for obtaining stronger and less permeable films.

2. Marine collagen

Collagen is the most common animal protein because it is found in all connective tissue (i.e., skin, bones, ligaments, tendons and cartilage) and interstitial tissues of parenchymal organs

Marine collagen is mainly extracted from fish skins, fish bones, fins, scales or the connective tissue of jellyfish, sea urchins, starfish or sea cucumbers. Fish skins have been used to extract collagen because 70-80% of its dry matter is collagen. In addition, fish scales are another promising and inexpensive source of marine collagen, accounting for about 4% of the total annual weight of fish offal, about 18-30 million tons. Fish scales contain both organic components (collagen, fat, lecithin, hard protein, various vitamins, etc.) and inorganic components (hydroxyapatite, calcium phosphate, etc.).

Compared to mammalian collagen, marine collagen has a comparable or slightly lower molecular weight and a lower denaturation (melting) temperature, which is about 20-35°C for most fish, while collagen values from warm water species are higher. In order to improve thermal stability, suitable cross linking treatments have been studied.

According to Coppola etc., the dry mass of collagen extracted from fish by-products can reach more than 50%. In addition, degreasing during fish processing guarantees no odor or taste. It often takes a long time to extract collagen from fish scales by chemical methods. As a result, researchers are increasingly interested in a suitable process for extracting fish scale collagen.

Compared to mammalian collagen, marine collagen does not have restrictions on use for religious reasons and possible infectious diseases, and at the same time has excellent film-forming capacity, bio-compatibility, low antigenicity, high biodegradability and cell growth potential.This waste has the potential to be developed as an environmentally friendly and low-cost source of collagen with many potential applications as a drug/delivery carrier or wound dressing in various fields such as health food, cosmetics and bio-medicine.Due to its high water absorption capacity, collagen is a good candidate for texturization, thickening, and gel formation. In addition, it has interesting properties related to surface behavior, including emulsion, foam formation, stabilization, adhesion and cohesion, protective colloidal function and film forming ability. Although it has been used as a food additive to improve the rheological properties of foods, marine collagen is not yet fully exploited and its application is much lower than mammalian collagen.

The use of fish collagen film in the packaging industry is limited by some disadvantages, such as low thermal stability and relatively poor mechanical properties. In addition, collagen is a hydrophilic polymer with hydroxyl groups. Therefore, water vapor easily passes through the film. To overcome these limitations, various efforts have been made, including mixing collagen with other biopolymers and several chemical and enzymatic processes. For example, Ahmed et al. using a mixture of collagen and chitosan extracted from leather jacket skins, the bacteriostatic capacity and bacteriostatic activity of the film are enhanced, but the elasticity or brittleness of the film is affected.

3. Fish glue

Gelatin is a denatured protein derived from the partial hydrolysis and heat treatment of collagen. It consists of a set of proteins and poly-peptides of different molecular weights, the composition of which depends mainly on the parent collagen and the extraction procedure . During hydrolysis, the natural molecular bonds between individual collagen chains are broken down, leaving a mixture of single- or multi-stranded poly-peptides, each with an extended left-helix conformation and containing 50-1000 amino acids. Two types of gelatin are obtained by acid hydrolysis and alkali hydrolysis, namely type A and type B.

Due to religious issues and concerns about the health of the spread of disease to humans, the extraction and application of gelatin from fish droppings has aroused widespread interest. Gelatin is an important industrial bio-polymer with significant gelling and film-forming properties that can be used in food, pharmaceutical and other related fields.

Due to its good film-forming properties, low cost, bio-compatibility and biodegradability, fish gelatin has recently been recommended for the preparation of biodegradable films in active food packaging to replace traditional non-biodegradable polymers and other mammalian-based gelatins. By applying heat and mechanical stress in extrusion-based technology, gelatin is easy to process. To increase flexibility, plasticizers are used as internal lubricants, which improve molecular fluidity. Gelatin aqueous solution can be obtained by casting gelatin film. They are odorless, colorless, transparent, water-soluble, and more flexible than other bio-based films used in food packaging. Since the melting point of gelatin is close to body temperature, gelatin-based films can be used to prepare edible films. In addition, fish gelatin has shown great potential as an excellent matrix of bio-active compounds with enhancing functions, such as antioxidants/antibacterial agents.

The water resistance is improved by laminating the fish gelatin film with a moisture-resistant biodegradable polymer in a multi-layer film with a moisture and oxygen barrier layer optimized for specific packaging and conditions. Matutsch etc. With montmorillonite sodium plasticizing gelatin as the inner layer, cross-linked dialdehyde starch and plasticizing gelatin film as the outer layer, three layers of gelatin film were hot pressed. Since the individual layers can interact with each other with strong hydrogen bonds, multi-layer membranes exhibit compact and uniform micro-structures. The same authors also prepared a multi-layer structure in which poly-lactic acid film acts as an outer layer with higher water vapor permeability than other commercial polymers such as high-density polyethylene or polyvinyl chloride.

Another promising way to improve the barrier properties, mechanical properties and thermal properties of fish glue for food packaging is based on cross linking. In particular, as Garavand etc. reviewed, naturally based crosslinkers have attracted more attention in order to consider environmental and health concerns as well as economic issues. Liguori etc. developed a protocol for cross linking fish gelatin with citric acid. Heat treatment in the presence of reducing sugars (called the Maillard reaction) has been shown to lead to cross linking processes and altered network structures. Recently, Maroufi etc. demonstrated the chemical cross linking of fish gelatin with the aldehyde group of K-carrageenan.

4. Application of chitosan in food packaging

Chitin, the second most abundant bio-polymer in nature after cellulose, is a linear polymer, a polysaccharide, located in the fungal cell wall and in plankton, crustaceans and insect exoskeleton, in the form of orderly crystalline microfibers that produce about 100 billion tons of chitin per year.

The bio-compatible, non-toxic and bio-functional properties of chitin and chitosan bio-polymers make them potentially suitable for food packaging applications. In particular, chitosan bio-polymers extracted from shrimp are pre-determined as generally recognized as Safe (GRAS). Chitosan, on the other hand, is much cheaper compared to other bio-polymers. Nevertheless, the excellent properties of chitosan make it more suitable for food packaging applications. For example, it was successfully proposed to extend the shelf life of bread because it was shown to delay the return of starch by preventing microbial growth.

Tyliszczak etc. demonstrated that chitosan films can also preserve strawberries. In addition, Zakaria etc. demonstrated that chitosan membranes inhibit changes in the physical properties of vegetables. Chitosan can also be used to produce food wrapper coated with it, thereby delaying the growth of microorganisms. The strategy for improving the performance of chitosan films for food packaging is almost identical to that used for fish gelatin films. In fact, the development of polymer blends represents an effective way to improve mechanical properties and reduce water solubility and water vapor permeability. Several polysaccharides have been added to chitosan for the production of mixed films with enhanced final properties for food applications. Among them, due to its low cost, wide availability and biodegradability, starch is one of the most common polysaccharides proposed for the production of chitosan-based biofilms.

Chitosan/starch films show reduced bacterial adhesion, excellent antioxidant activity and increased water vapor barrier properties on packaging, thus demonstrating their potential suitability for specific applications. Several scientists have studied the possibility of preparing a cellulose/chitosan mixture to improve the mechanical properties of pure chitosan .

Fish industrial waste shows great potential as a new raw material for bio-polymer production and can be used in different application areas, mainly food packaging. The value-added utilization of fish waste has economic advantages because it helps to reduce the cost of safe waste disposal and generates additional value by recycling several molecules that may be valuable. In addition, the added value of fish by-products brings a number of environmental advantages that come from reduced land filling, incineration and disposal, which constitute a serious waste of resources, as well as substitution from fossil-based polymers. In this way, the recycling of fishery waste can have a positive impact on ecosystems and the financial viability of fisheries. Its impact is expected to increase in the coming years.

The main contribution of this review is to show that all fisheries by-products can potentially be used to develop bio-refining technologies compared to classic petroleum refineries associated with carbon-based greenhouse gas emissions. As shown, fibro-fibrin, collagen, gelatin, chitin, chitosan from muscles, visceral, skin, scales, fins or crustacean shells has been shown to meet the technical requirements of a new generation of packaging, called smart packaging, which involves the interaction between packaging and food or food inside the packaging atmosphere. The future market prospects can be expected!