Since people are increasingly conscious of the relationship between diet and health, the consumption of marine-based foods has been growing continuously. Consumers identified seafoods as nutritious and complete foods. Hence, they are perceived them as an excellent source of high quality proteins, valuable lipids with high amounts of PUFA. These compounds are well known to contribute to the enhancement of human health by different alternatives such as reducing the risk of cardiovascular disease, coronary disease and hypertension. Additionally, marine-based food products are easily digested and constitute excellent source of essential minerals. Recently, seafoods have been recognized as nutraceuticals or functional foods. Functional foods, first evolved in Japan in 1980, are defined as foods demonstrating beneficial effect on one or more targeted functions on human organism (Ross, 2000). Marine-based functional foods or nutraceuticals, include omega-3 fatty acids, chitin and chitosan, fish protein hydrolysates, algal constituents, carotenoids, antioxidants, fish bone, shark cartilage, taurine and bioactive compounds (Kadam & Prabhasankar, 2010).
Despite the aforementioned desirable properties, seafood products are highly susceptible to quality deterioration, mainly due to the lipid oxidative reactions, particularly involving polyunsaturated fatty acids (PUFAs). These reactions are enhanced (catalyzed) by the presence of high concentrations of heme and non-heme proteins. These proteins are known to contain iron and other metal ions in their structures (Decker & Hultin, 1992). Moreover, marine-based food quality is highly influenced by autolysis, bacterial contamination and loss of protein functionality (Jeon, Kamil & Shahidi, 2002). More recently, pollution of seafood with different hazardous materials such as refinery, industrial wastes and heavy metals has resulted in elevated concern about the consumption of seafood (Kadam & Prabhasankar, 2010). Additionally, aquaculture industry has increasingly attracted much attention for the intensive farming of fish and shellfish, mainly due to the depleting of wild fish and shellfish stocks worldwide. However, this intensive farming entails several difficulties such as stress, which is the most important factor affecting the immunity system of fish (Ledger, Tucker & Walker, 2002). To address the aforementioned problems, the use of chitosan as protective material appears to be a potential alternative.
In nature, chitosan is found in the cell walls of fungi of the class
Commercially, chitosan is produced from chitin by exhaustive alkaline deacetylation, involving boiling chitin in concentrated alkali for several hours. Because this N-deacetylation is almost never complete, chitosan is classified as a partially N-deacetylated derivative of chitin (Kumar, 2000). From a practical point of view, many of commercial interests and applications of chitosan and its derivatives originate from the fact that this polymer combines several features, such as biocompatibility, biodegradability, nontoxicity and bioadhesion, making it as valuable compound for pharmaceutical (Dias, Queiroz, Nascimento & Lima, 2008), cosmetics (Pittermann, Horner & Wachter, 1997), medical (Carlson, Taffs, Davison & Steward, 2008), food (Shahidi, Kamil & Jeon, 1999; No, Meyers, Prinyawiwatkul & Xu, 2007; Kumar, 2000), textile (El Tahlawy, Bendary, El Henhawy & Hudson, 2005), waste water treatment (Che & Cheng, 2006), paper finishing, photographic paper (Kumar, 2000), and agricultural applications (Hirano, 1996).
Although there have been several prior reviews on the use of chitosan in food applications (No et al., 2007; Shahidi et al., 1999), the use of chitosan in seafood applications, especially its novel application in the form of nanocarriers for bioactive compounds for shelf life extention, has not yet been reported. Recently, a study was published on the use of chitosan nanoparticle for stability enhancement of vitamin C in rainbow trout diet (Alishahi, Mirvaghefi, Rafie-Tehrani, Farahmand, Shojaosadati, Dorkoosh & Elsabee, 2011). Hence, this chapter attempts to survey the applications of chitosan in various fields of marine-based products.
2. Antibacterial activity
The modern era of chitosan research was heralded by publications in the 1990s, that described the antimicrobial potentials of chitosan and its derivatives, exhibiting a wide spectrum of activities against human pathogens and food-borne microorganisms (Chen, Xing & Park & Kong, 2010; No, Park, Lee & Meyers, 2002; Rabea, Badway, Stevens, Smagghe & Steurbaut, 2003: Raafat, Bargen, Haas & Sahl, 2008; Raafat & Sahl, 2009)., The first study reporting antibacterial properties was reported by Allan & Hardwiger (1979). They reported that chitosan showed a broad range of activities and a high inactivation rate against both Gram-positive and Gram-negative bacteria, (Allan & Hardwiger, 1979). However, although several studies have been published in this area, the exact mechanism of the antimicrobial activity of chitosan remains ambiguous.
Six major mechanisms have been proposed in the literature, as follows (Kong et al., 2010; Raafat & Sahl, 2009; Rafaat et al., 2008): (1) the interaction between the positively charged chitosan amine groups and the negatively charged microbial cell membranes, leadingto the leakage of proteinaceous and other intracellular constituents; (2) the activation of several defense processes in the host tissue by the chitosan molecule acting as a water-binding agent and inhibiting various enzymes by blocking their active centers; (3) the action of chitosan as a chelating agent, selectively binding metals and then inhibiting the production of toxins and microbial growth; (4) the formation, generally by high molecular weight chitosan, of an impervious polymeric layer on the surface of the cell, thereby altering cell permeability and blocking the entry of nutrients into the cell; (5) the penetration of mainly low-molecular weight chitosan into the cystosol of the microorganism to bind DNA, resulting in interference with the synthesis of mRNA and proteins; and (6) the adsorption and flocculation of electronegative substances in the cell by chitosan, distributing the physiological activities of the microorganisms, causing their death.. However, it is very important to mention that chitosan is soluble only in acidic media and therefore, the effect of pH on microorganisms must be considered together with the effect of chitosan. Thus, the synergetic effect of chitosan/pH together is probably the most evident explanation of the antimicrobial effect of chitosan.
Complicating the issue, a number of studies aimed at determining the antibacterial activities of chitosan on Gram-positive and Gram-negative bacteria have been reported antithetical outcomes, making their interpretation difficult. More recently, Kong et al. (2010) showed that chitosan and its derivatives are more powerful antibacterial agent against Gram-negative bacteria than against Gram-positive microorganism. Conversely, Raafat and Sahl (2009) reported a study in which they demonstrated that Gram-positive bacteria are more sensitive to the antibacterial effect of chitosan than Gram-negative bacteria. Therefore, the interpretation of the sensitivity of bacteria to chitosan is quite difficult.
To address this problem, Kong et al. (2010) proposed that the variation in the bactericidal efficacy of chitosan arises from different parameters that must be considered when evaluating the antibacterial activity of chitosan. These factors can be categorized into four classes as follows: (1) intrinsic microbial factors, including microbial species and cell age, (2) intrinsic factors of chitosan molecules, namely, the positive charge density, protonation level of the amine group, the chitosan molecular weight and concentration, hydrophilic/hydrophobic characteristics and chelating capacity of the chitosan molecule; (3) its physical state, i.e., either water soluble or solid chitosan; and (4) environmental factors including the ionic strength of the testing medium, pH, temperature and contact time between chitosan and bacterial cells. In addition, it is worth noting that, despite the widely reported antimicrobial properties of chitosan in the literature, the results are mainly based on in vitro experiments. In real-world appliactions, it is important to consider that most foods are complex matrices composed of different compounds (proteins, carbohydrates, lipids, minerals, vitamins, salts and others) and many of them may interact with chitosan to varying levels, possibly leading to a loss or enhancement of its antibacterial activity (Devlieghere, Vermeulen, & Debevere, 2004).
Taking into account the above insights about the antibacterial characteristics of chitosan, the following applications of chitosan in seafood products were considered. Due to the high perishability characteristics of marine-based products, there has been an increased interest in the application of chitosan to extend the shelf life of the products. In this context, chitosan has increasingly gained attention as an antibacterial additive in seafood from both seafood processors and consumers, largely due to a desire to reduce the use of synthetic chemicals in seafood preservation. Cao, Xue and Liu (2009) reported that chitosan at 5 g/L extended the shelf life of oyster (
Fish balls have a high water activity and are prone to the growth of microorganisms, with a relatively short shelf life of 4-5 days at a storage temperature of approximately 5 °C. Kok and Park (2007) reported that fish ball shelf life has been increased by adding chitosan which maintained both aerobic and yeast counts at < 1 log CFU/g over 21 days of storage. Kok and Park (2007) also reported that physical state of chitosan is an important parameter for its antibacterial activity. In the dissolved state, chitosan showed excellent antibacterial activity and contributed to the extension of the product shelf life. However, in the study reported by Lopez-Caballero et al. (2005a and b), it was demonstrated that the addition of powdered chitosan to fish patties had no effect on bacterial growth. Roller and Corvill (2000) reported that the spoilage flora was inhibited from log 8 CFU/g in the control sample (without chitosan) to log 4 CFU/g over the 4-week study at 5 °C with the use of chitosan combined with acetic acid in shrimp salad. However, it is important to consider the effect of acetic acid on the ability of chitosan to extend shelf life. Fernandez-Saiz, Soler, Lagaron and Ocio (2010) studied bacterial growth in two conditions. The first one was a fish soup (ANETO ® brand, packaged in TetraBrik ® and fabricated by Jamon Aneto, S. L., Barcelona, Spain). The other medium was a model laboratory growth medium, tryptone soy broth. They reported a significant reduction of the growth of
3. Antioxidant activity
Seafood is considered as excellent sources of functional foods for balanced nutrition favorable for promoting good health. The beneficial health effects of marine foods are ascribed to their lipids, mainly the long-chain omega-3 PUFA such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) (Newton, 2001). However, these valuable compounds in seafood are highly sensitive to oxidative reactions and development of off-flavor even during cold storage (Cadwalladar & Shahidi, 2001). It has been proposed that lipid oxidation in fish and shellfish may be initiated and propagated by a number of mechanisms, namely autooxidation, photosentized oxidation, lipoxygenase, peroxidase and microsomal enzymes (Hsieh & Kinsella, 1989). Additionally, fish and shellfish muscles contain protein-bound iron compounds, for example, myoglobin, hemoglobin, ferritin, transferrin and haemosiderin, as well as other metals. This is a factor that plays an important role in initiating lipid oxidation in marine-based products (Decker & Hultin, 1992). Castell, Maclean and Moore (1965) showed that the relative pro-oxidant activity of metal ions in fish and shellfish muscles decreased in the order of Cu+2> Fe+2> Cd+2> Li+2> Mg+2> Zn+2> Ca+2> Ba+2. The iron-bound proteins and other metal ions may be released during the storage period and can thus activate and/or initiate lipid oxidative reactions (Decker & Hultin, 1992).
Along with the growing consumer demand for seafood devoid of synthetic antioxidants, chitosan has been a booming antioxidant agent in fish and shellfish. The antioxidant activity of chitosans of different viscosities (360, 50 and 14 cP) in cooked, comminuted flesh of herring (
Duan et al. (2009; 2010) showed that the combination of chitosan with modified atmosphere packaging enhanced the lipid stability of lingcod (
4. Bioactive coatings
The modern marine-related food industries are encountering challenges and require for specific alternatives to surmount them. Among these, issues related to seafood packaging for products with a short shelf life are of pivotal importance. Although the utilization of conventional packaging materials such as plastics and their derivatives are effective for seafood preservation, they create serious and hazardous environmental problems, a situation which presents the seafood industry as a source of pollution and social concerns. This problem requires that all stakeholders in this industry and especially scientists specializing in the food engineering and packaging field to seek alternatives to address this serious problem related to the packaging material. A non-negligible aspect, which is the total cost of the final product, is also related to the packaging materials because it is well known that the contribution of the packaging to the product total cost is highly significant. So, the search for more economical packaging materials is a very important subject in the seafood industry (Aider, 2010).
Edible bio-based films have been investigated for their abilities to avoid moisture or water absorption by the seafood matrix, oxygen penetration to the food matrix, aroma loss and solute transport out of the product (Dutta, Tripathi, Mehrotra & Dutta, 2009). Based on this consideration, one of the most perspective active bio-film is the one based on chitosan. More recently, two review studies have reported the application of chitosan as bioactive film in the food industry (Aider, 2010; Dutta et al., 2009). Chitosan film, like many other polysaccharide based films, tend to exhibit resistance to fat diffusion and selective permeability to gases. However, they have a serious lack in terms of resistance to water and water vapor transmission. This behavior is mainly due to the strong hydrophilic character of these biopolymers, a property that leads to high interaction with water molecules (Bordenave, Grelier, & Coma, 2007). Owing to this, polymer blending or biocomposites and multilayer systems are potential approachs to prepare chitosan based bioactive coatings or films with desirable characteristics. In this context, Ye et al. (2008) stated that since edible film formed by chitosan is brittle and does not have good mechanical properties, coating chitosan onto a plastic film would overcome this problem. These authors have used chitosan-coated plastic films in which they have incorporated five antibacterial agents, namely nisin, sodium lactate (SL), sodium diacetate (SD), potassium sorbate (PS) and sodium benzoate (SB) as a novel antibacterial edible film against
viscoelastic characteristics and temperature dependent viscosity, which allowed uniform glazing on the salmon fillets and prevented rupturing of chitosan glazing during solidification when the glazed fillets were frozen. Therefore, chitosan glazing applied on the surface of the pink salmon fillets might have acted as a barrier between the fillets and the air surrounding, thus slowing down the diffusion of oxygen from the surrounding air into the fillets. Kester and Fennema (1986) reported that chitosan coatings might act as moisture-sacrificing agents of moisture barriers. Thus, moisture loss from the product could be delayed till the moisture contained within the chitosan coating had been evaporated. Sathivel (2005) highlighted that pink salmon fillets coated with chitosan resulted in significantly higher yield, thaw yield, similar drip loss and cook yield, higher moisture content after thawing, less moisture loss than the control samples and somewhat less than protein-coated products. Besides, there were no significant (p < 0.05) effects of coating on color parameters (
5. Effluent treatment
The use of chitosan as a coagulating agent for removing suspended solids from various processing streams has been widely investigated including cheese whey and dairy wash water, in the processing of poultry and seafood products (Kumar, 2000; Savant, 2001; Savant & Torres, 2000; Savant & Torres, 2003; Shahidi et al., 1999). Chitosan at a concentration of 10 mg/L reduced up to 98% the total suspended solids in shrimp processing wastewater (Bough, 1976). Protein recoveries from surimi wash water (SWW) using 150 mg/L chitosan-alginate complex per liter SWW at mixing ratio of 0.2 resulted in 78-94% adsorption after 24 h (Wibowo, 2003). This result was higher than the one obtained by using 50 mg/L, which yielded 81-90 % protein adsorption in the same treatment time (Savant, 2001). These reported findings suggest that reaction time and chitosan concentration play an important role in reducing total suspended solids and lowering solution turbidity. Moreover, the differences in molecular weights (MW) and degree of deacetylation (DD) between chitosan samples could explain the significant differences in protein recovery capacity. At the lowest concentration (20 mg/L SWW) tested in the study reported by Wibowo (2003), the experimental chitosan gave higher protein recovery than a commercial sample, which required a 5-fold higher concentration for the same effectiveness. This finding has commercial implications as it would reduce processing costs and the chitosan content in the solids recovered by the treatment (Wibowo, Velazquez, Savant & Torres, 2007a). If implemented commercially, the chitosan-alginate complex may be an effective alternative not only for the recovering of soluble proteins that would otherwise be discarded into the environment, but also as an economically viable downstream process over expensive, commercial membrane treatments and their limited use due to fouling (Savant, 2001). Surimi wash water protein (SWWP) was precipitated by using a chitosan-alginate complex. The precipitate had a crude protein content of 73.1 % and a high concentration of essential amino acids (3% histidine, 9.4% lysine, 3.7% methionine, and 5.1% phenylalanine). In a rat-feeding trial, SWWP as a single protein source showed higher modified protein efficiency and net protein rations than the casein control. Blood chemistry analysis did not reveal any deleterious effect from the full protein substitution or the chitosan in SWWP (Wibowo, Savant, Gherian, Velazquez & Torres, 2007b; Wibowo, Velazquez, Savant & Torres, 2005). Moreover, Guerrero, Omil, Mendez & Lema (1998) showed that the utilization of chitosan at a concentration of 10 mg/L and pH 7 in the process of coagulation-flocculation followed by centrifugation in fish-meal factory effluents decreased the total suspended solids up to 85%. The most important mechanisms explaining the chitosan effectiveness in seafood plant effluents treatment was mainly attributed to its positive charge and interaction with negatively charged compounds in the effluents such as protein. Furthermore, the hydroxyl groups on the chitosan molecule contribute to increase the precipitation of proteins and other suspended solids in the seafood plant effluents (Savant, 2001; Wibowo et al., 2007a,b).
6. Gelling enhancer
Surimi is a refined fish protein product prepared by washing mechanically deboned fish to remove blood, lipids, enzymes and sarcoplasmic protein. The myofibrillar proteins are concentrated in the resulting product and form an elastic gel when solubilized with NaCl and heated (Mao & Wu, 2007). Gel forming properties of myofibrillar proteins are quickly lost by degradation by the action of endogenous proteolytic enzymes if fish is not processed into surimi immediately. The utilization of frozen fish flesh for surimi production is unsuitable due to the rapid loss of protein functionality by freeze denaturation. High quality surimi is produced from fresh, unfrozen fish. Thus, processing at sea has been required in order to obtain high quality surimi. However, the cost of the processing at sea is much higher compared to the land-base processing (Lanier, Manning, Zetterling & Macdonald, 1992). In order to prepare a strong and elastic gel from fish species with low commercial value, low quality surimi is produced onshore with the aid of gel-forming biopolymers such as starch. In this way, chitosan is a good option to be incorporated into the products to improve their techno-functional quality (Kataoka, Ishizaki, & Tanaka, 1998; Mao & Wu, 2007; Li & Xia, 2010). Overall, gel-forming ability of surimi depends on both intrinsic and extrinsic factors, namely fish species, physio-chemical properties of muscle proteins, the presence of endogenous enzymes such as proteinase amd transglutaminase, and the conditions used in the product processing (Benjakul, Visessanguan, Phatchrat & Tanaka, 2003). The strength of gels prepared from low quality walleye Pollock (
Nowadays, the value of functional foods and bioactive compounds are increasing due to the awareness and consciousness of people about it. Despite this fact, many of these compounds are so much sensitive to environmental factors such as oxygen, light, and temperature. In addition, being incorporated into foods and drugs in delivery systems, these bioactive components are hydrolyzed by harsh conditions in the gastrointestinal tracts (Alishahi et al., 2011). Schep, Tucker, Young, Ledger and Butt (1999) stated that many of oral delivery systems of bioactive compounds in aquaculture met the three major barriers through the gastrointestinal tract, involving the enzymatic barriers from the host luminal and membrane bound enzymes, immunological cells present within both the enterocytes and underlying connective tissue and the physical barrier of the epithelial cells. Based on this consideration, the encapsulation of bioactive compounds and functional foods could be a promising way to overcome these problems. Encapsulation is a process in which thin films, generally of polymeric materials, are applied to little solid particles, liquids or gas droplets. This method is used to entrap active components and release them under controlled conditions (Deladino, Anbinder, Navarro & Martino, 2008). Several materials have been encapsulated for the use in the food industry such as vitamins, minerals, antioxidants, colorants, enzymes and sweeteners (Shahidi & Han, 1993). Chitosan can act as an encapsulating agent because of its non-toxicity, biocompatibility, mucus adhesiveness and biodegradability (Alishahi et al., 2011: Kumar, 2000). Recently, Alishahi et al. (2011) showed that chitosan/vitamin C nanoparticle system successfully increased the shelf life and delivery of vitamin C during 20 days storage of rainbow trout. They showed that shelf life of vitamin C significantly (p < 0.05) increased in rainbow trout feed till 20 days at ambient temperature, while the control which was feed by vitamin C alone, drastically lost its vitamin C content during few days at ambient temperature. Moreover, the controlled release behavior of vitamin C, in vitro and in vivo, showed that vitamin C was released in the gastrointestinal tract of rainbow trout in the controlled manner (up to 48 h) and chitosan nanoparticles could well maintain vitamin C against harsh conditions, acidic and enzymatic hydrolysis, in the gastrointestinal tract of rainbow trout. Also, Alishahi et al. (2011) showed that the chitosan nanoparticles containing vitamin C could significantly (p < 0.05) induce the non-specific immunity system of rainbow trout, as compared with the control. RajeshKumar, VenKatesan, Sarathi, Sarathbabu, Thomas and Anver Basha (2009) demonstrated that chitosan nanoparticles are able to encapsulate DNA and then favorably incorporated into shrimp feed to protect them from white spot syndrome virus. Their results showed that these nanoparticles increased the survival rates of shrimp against white spot syndrome during 30 days post-treatment. Likewise, RajeshKumar, Ishaq Ahmed, Parameswaran, Sudhakaran, Sarath Babu and Sahl Hameed (2008) incorporated chitosan nanoparticles containing DNA vaccine into Asian sea bass (Lates calcarifer) feed. Their results indicated that the sea bass orally vaccinated with chitosan-DNA (pVAOMP38) complex showed moderate protection against experimental
Chitosan, a deacetylated derivative of chitin, has attracted a great attention in the seafood industry due to its non-toxicity, biodegradability, biocompatibility and mucus adhesiveness properties. Chitosan has different characteristics such as antibacterial, antioxidant, film-forming ability, gel enhancer, encapsulating capacity, tissue engineering scaffold, wound dressing, and coagulating agent. Upon knowing these, chitosan could successfully be incorporated into seafood products for both seafood quality and human health enhancement. Regarding its outstanding characteristics, chitosan would be used as functional ingredients in marine-based products and it merits further researches in the future.