Application Of κ-carrageenan Composite Films In Freshness Monitoring And Preservation Of Marine Fish

Freshness is one of the most important quality indicators of marine fish,which plays a decisive role in the value of marine fish.In recent years,the freshness monitoring and preservation of aquatic products through intelligent active packaging has become a research hotspot.Smart packaging provides food quality information to consumers by monitoring the changes of microenvironment within the packaging,and active packaging can prolong the shelf life of food by releasing functional components.In this paper,κ-carrageenan(CAR)was used as film-forming substrate.Grape skin extract(GSE)and nano-silver(Ag NPs)were used as functional components to construct a highly stable freshness indicator film;potassium sorbate(PS)and D-sodium erythorbate(SE)were used to prepare an cling film for fish quality retaining.They were used to freshness monitoring and preservation of marine fish.The main research contents are as follows.1.Development of highly stable color indicator films based on CAR,Ag NPs,GSE for fish freshness assessment.Six kinds of color indicator films were fabricated by p H indicators(red grape skin extract and purple sweet potato extract)and film-forming substrates(quaternary ammonium chitosan,Color Catcher cellulose paper and κ-carrageenan).The CAR/GSE film with the most rapid response was selected for the follow-up study through ammonia sensitivity experiments and sea bass freshness indication experiments.Color indicator films for fish freshness were fabricated by incorporating κ-carrageenan(CAR)polymer with red grape skin extract(GSE)as a p H-sensing agent and silver nanoparticles(Ag NPs)as an antimicrobial agent.Anthocyanins in GSE exhibited distinguished p H responsive color changes.GSE and Ag NPs were well compatible with CAR with intramolecular interactions,approved by scanning electron microscopy(SEM),Fourier transform infrared spectroscopy(FTIR)and X-ray diffraction(XRD)analysis,thermogravimetric analysis(TGA)and differential scanning calorimetry(DSC).GSE-containing films displayed distinguished color changes in response to p H variations and volatile ammonia.Enhanced UV blocking ability and strong antioxidant activity were revealed for GSE included films without sacrificing the physicochemical properties of the CAR film.Films containing Ag NPs showed improved mechanical strength and strong antimicrobial ability against both Escherichia coli and Staphylococcus aureus.The CAR/Ag NPs/GSE film displayed a distinctive color change corresponding to changes in the total volatile basic nitrogen(TVB-N)of fish during storage.In addition,the CAR/Ag NPs/GSE film showed excellent color stability to consecutive UV exposure and its storage time at 25 ℃ is expected to be at least 240 days,which indicates that it has high potential as an intelligent food freshness indicator film.2.Development of a packaging film by incorporating CAR with PS,and SE for retaining quality of fish fillet.PS has been known as an antibacterial food additive and SE has been known for its antioxidant activity.PS and SE were incorporated with CAR to develop a cling packaging film for fish preservation.CAR film,CAR/PS film,CAR/SE film and CAR/PS/SE film were prepared.FTIR and XRD results showed good compatibility between the filmforming materials.The mechanical properties results showed little difference in mechanical strength among these cling films.The transmittance test showed that the addition of SE reduced the UV transmittance and oxygen permeability of CAR-based cling films,and significantly improved the antioxidant activity of the films.Furthermore,cling film was applied to sea bass skin-packaging and the influence of different types of cling films on the preservation of sea bass was evaluated.The results showed that fish packaged with CAR/PS/SE film had slower bacterial proliferation rate and lower TVB-N level than other groups.Sensory evaluation shows that the overall quality index increased by 235% using the CAR/PS/SE packaging film.Therefore,the constructed CAR/PS/SE cling film can slow down the spoilage process of fish fillets and improve their quality,exhibiting great potential for skinpackaging of marine fish.