Chitosan and water-soluble chitosan effects on refrigerated catfish fillet quality
Introduction
Chitosan (CH) is a natural carbohydrate polymer obtained by deacetylation of chitin. It is the main component found in the shells of crustaceans such as crab, shrimp, and crawfish (No, Meyers, & Prinyawiwatkul, 2007). Chitin is the second most available biopolymer on earth after cellulose (Shahidi, Arachchi, & Jeon, 1999). Chitin and CH have been used in their native and modified structures in different areas including food, material science, biotechnology, drugs, and pharmaceuticals (Prashanth & Tharanathan, 2007). CH is characterized by its functional groups, an amino group as well as both primary and secondary hydroxyl groups (Furusaki, Ueno, Sakairi, Nishi, & Tokura, 1996). To be characterized as CH instead of chitin, the degree of deacetylation (DD) should be at least 50% and it must be soluble in aqueous acidic solution. However, solubility of CH is a difficult parameter to control, and is related to the degree of acetylation, ionic concentration, pH, type of acid used for protonation, distribution of acetyl groups along the chain, isolation method, and drying conditions (Rinaudo, 2006).
The applicability of CH as a potential food preservative, either alone or in combination with other compounds showed positive results in shelf life extension of various food products (Rhoades & Roller, 2000). Additionally, CH has been applied as a coating material to fresh produce and seafood for prolonging quality (Benhabiles, Drouiche, Lounici, Pauss, & Mameri, 2013; Cao, Xue, & Liu, 2009). CH may extend the shelf life of food, due to its antimicrobial and antioxidant properties. Several investigations reported positive results for CH controlling bacterial growth (Chung et al., 2004; Kok & Park, 2007; Soultos, Tzikas, Abrahim, Georgantelis, & Ambrosiadis, 2008) and lipid oxidation (Jeon, Kamil, & Shahidi, 2002; Kamil, Jeon, & Shahidi, 2002) in pork sausage, fish balls, and fish (cod and herring). CH application in the food industry is limited because of its insolubility in water, high viscosity, and tendency to coagulate with proteins at high pH (Rabea, Badawy, Stevens, Smagghe, & Steurbaut, 2003). Water-soluble chitosan (WSC) can be prepared using acidic or enzymatic degradation of the CH polymer chains to yield low molecular weight CH of higher solubility. The enzymatic process is more desirable than chemical reactions because enzymatic hydrolysis can be controlled more easily compared to the faster rate of chemical reactions (Ilyina, Tikhonov, Albulov, & Varlamov, 2000). WSC has been reported to have antimicrobial (Benhabiles et al., 2012; Qin et al., 2006) and antioxidant (Lin & Chou, 2004) activity.
In 2013, catfish was ranked eighth in the top 10 seafood which Americans consume, and 270 million pounds were processed during 2013 (Hanson & Sites, 2015). Total sales of catfish during 2015 were 361 million dollars. The top 4 states for catfish production in 2016 were Mississippi, Alabama, Arkansas, and Texas, accounting for 96% of the United States total sales (NASS, 2017). Catfish fillets typically have a short shelf life during refrigerated storage, normally <4 days (Marshall & Kim, 1996; Zhuang, Huang, & Beuchat, 1996). The short shelf life is due to three factors: enzymatic autolysis, oxidation, and microbial growth (Ghaly, Dave, Budge, & Brooks, 2010). During fish spoilage, different reactions occur, developing new compounds. Those compounds are responsible for the changes in odor, flavor, and textures of fish meat. The more rapid quality losses are due to lack of chilling coupled with poor storage conditions, distribution, and marketing facilities (Pedrosa & Regenstein, 1988). Utilization of ice and mechanical refrigeration are the most common preservation techniques used to retard microbial and biochemical spoilage of freshly caught seafood (Wilhelm, 1982). Other preservation techniques include adding chemical preservatives such as sodium lactate, propyl gallate, and phosphates (Marshall & Jindal, 1997; Zhuang et al., 1996). However, the use of natural antioxidant and antimicrobial additives has been gaining consumer popularity over synthetic additives (Qiu, Chen, Liu, & Yang, 2014). The objective of this study was to evaluate the quality of refrigerated catfish fillets treated with CH and WSC.
Section snippets
Preparation of water-soluble chitosan and treatments solutions
WSC was produced using medium molecular weight CH, Sigma Aldrich (Saint Louis, MO, USA). Molecular weight of 338 kDa and deacetylation degree of 70.7% were reported for the same CH by Chouljenko, Chotiko, Solval, Solval, and Sathivel (2016b). Enzymatic hydrolysis was carried out with chitosanase from Streptomyces sp. N174 (enzyme activity = 1.67 μmol/sec ml) (EMD Millipore Corp., Billerica, MA, USA) according to the method described by Chouljenko et al. (2016a), and WSC was separated using an
Degree of deacetylation, water solubility, and flow behavior of chitosan and water-soluble chitosan
CH and WSC showed no significant differences in degree of deacetylation (Table 1). DD is an important chemical characteristic of CH linked to the content of free amino groups in the polysaccharide (Li, Dunn, Grandmaison, & Goosen, 1992). The enzymatic hydrolysis of CH led to increased solubility of the biopolymer by nearly 44 times, as seen by the water solubility of WSC (86.7%). Chang, Lin, Wu, and Jane (2015) reported the degradation of CH using cellulase showed low molecular weight and good
Conclusion
Enzymatic hydrolysis of CH produced a WSC with similar DD to the initial material. WSC was less viscous at 5 °C compared to CH, improving its application potential in food systems. WSC was more effective in DPPH inhibition than CH and AA, probably due to its reduction in viscosity. CH and AA treatment controlled the APC during 20 days of refrigerated storage keeping the fish below the spoilage limit, showing effective antibacterial activity for both treatments. Additionally, CH showed a
Conflicts of interest
Declarations of interest: none.
Acknowledgements
This research did not receive any specific grant funding in the public, commercial, or not-for-profit sectors.
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