| Whiteleg shrimp (Litopenaeus vannamei) is one of the largest amounts in aquaculture production of the three excellent shrimp species in the world. Whiteleg shrimp is rich in nutrition with high consuming demands. This species was introduced into China in early1990s, and China has become the largest producing country nowadays. However, whiteleg shrimp is a kind of perishable food in the processes of fishing, transportation, processing and storage. When it gets spoilage, the flesh tissue will become very soft accompanied and high protease activities, as well as rapid autolysis and reduce of freshness. Chitosan with safety and significant antimicrobial properties can be easily obtained. Therefore, this study investigated the effects of nanoparticle chitosan on the quality changes of postharvest whiteleg shrimp during storage at4℃using normal chitosan coating as a reference. Meanwhile, acute toxicity of chitosan nanoparticles in vivo was observed by zebrafish model. The aim of this study is to evaluate the safety of nanoparticle chitosan and explore the application for preversation in whiteleg shrimp. The main results are as follows:1. Chitosan nanoparticles were prepared by ionic cross-linking chitosan with sodium tripolyphosphate (STPP). The indexes, such as concentration of chitosan solution, concentration of STPP solution, chitosan and multi-mass ratio of STPP and the pH value of reaction, affecting preparation of nanoparticles were well studied. The optimal conditions of chitosan nanoparticles preparation is as bellows:chitosan concentration of0.5mg/mL, STPP concentration of lmg/mL, the mass ratio of chitosan and STPP at2.5:1, pH value of3.4. Chitosan nanoparticles were characterized by scanning electron microscopy, transmission electron microscopy and FT-IR analysis. The result shows that the average diameter of the nanoparticles is less than100nm, evenly distributed and stable.2. Effects of chitosan coatings on quality changes of whiteleg shrimp were studied during10-day storage at4℃. Groups of treatment1(T-1), treatment2(T-2) and control were treated with carboxymethyl chitosan coating, chitosan nanoparticle coating and deionised water, respectively. The lowest pH values (P<0.05) were observed in T-2on days6,8and10. Chitosan coatings significantly decreased (P<0.05) total volatile basic nitrogen (TVB-N) amounts and K values on the same sampling day except day0and the lowest showed in T-2. Lower thiobarbituric acid (TBA) value (P<0.05) and higher inosinic acid (IMP) content (P<0.05) were obtained in the groups of T-2than those of the control on day10. On day10, the highest hardness and springiness (P<0.05) and lowest total viable counts (TVC) were obtained in T-2followed by T-1(P<0.05). Similarly, sensory scores were8.0,4.0and2.3in T-2, T-1and control, respectively. It is suggested that chitosan nanoparticles coating exhibited better effect on quality maintenance and shelf life extension of shrimp.3. Using normal chitosan as reference, the acute toxicity test of chitosan nanoparticles in zebrafish embryos was performed. It can be observed that both normal and nano chitosan had teratogenic effect on zebrafish embryos, including axial malformations (AM), pericardial edema (PE), yolk sacedema (YES), and uninflated swim bladder (USB). The malformation of zebrafish embryos induced bychitosan depended on concentration and exposure duration. The results show that LC50of chitosan nanoparticles was280mg/L at96hpf and270mg/L at120hpf, and for normal chitosan, LC50was257mg/L at both96hpf and120hpf. The TC50of chitosan and chitosan nanoparticles were257mg/L and137mg/L, respectively. Thus, the values of LC50and TC50of chitosan nanoparticles were both higher than that of normal chitosan.4. The normal chitosan at higher concentrations (300mg/L and400mg/L) will significantly reduce the hatching rate of zebrafish embryos at72hpf, while chitosan nanoparticles cause no significant effect. Both normal and nano chitosan will delay zebrafish embryos hatch and played a concentration-dependent manner. The final hatch ratio of zebrafish supplemented by chitosan nanoparticles was significantly higher than that of normal chitosan at the incubation of120h. There was no effect of nanoparticle on heart rate of zebrafish larvae, however, at the high concentration of normal chitosan (100mg/L-300mg/L), the heart rate of zebrafish larvae decreased. The effect of both nano and normal chitosan on body length only happened at high concentrations (200mg/L and300mg/L), and also showed concentration-dependent. The two solutions had no effect on weight of zebrafish larvae.5. In order to study the neurological effects of chitosan nanoparticles on zebrafish larvae, the behavior of zebrafish larvae were examined behavior including light stimulation and vitality test after exposure to low concentrations (10mg/L,20mg/L,30mg/L and40mg/L) of chitosan nanoparticles. The swimming speed of zebrafish larvae in each group suddenly increased from light into the dark at the concentrations of20mg/L,30mg/L and40mg/L. The result of vitality test showed that larvae swimming speed of10mg/L and20mg/L group was no difference compared with the control group, while the larvae swimming speed of30mg/L and40mg/L group was significantly higher than that of control group (p<0.01). |
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