Development Of A Visual Active Packaging Based On Black Rice Bran Anthocyanin And Its Application In Preservation Of Silvery Pomfret

The visible active packaging was prepared with chitin nanocrystal/gelatin as the fixed matrix and black rice bran anthocyanin extracts as the sensitive p H indicator.In the packaging,food quality can be monitored in real time in order to make customers judge accurately about shelf life of the food,namely a potential freshness indicator.Meanwhile,the packaging has antioxidant and antibacterial properties.Black rice bran anthocyanins（BACNs）were extracted from black rice bran,and chitin nanocrystal（ChNC）was prepared fromα-chitin.The optimal ratio of chitin nanocrystal and gelatin was investigated to prepare a film matrix with strong mechanical property.On this formulation,chitin nanocrystal/gelatin films containing black rice bran anthocyanins（Gel/ChNC-BACNs）of different concentrations were prepared by casting method.The crystal and molecular structure,thermal stability,barrier permeability,mechanical property,oxidation resistance and color responce were analyzed and the optimal concentration of BACNs addition was determined.The specific spoilage organisms（SSOs）in silver pomfret were identified by culture dependent method and high-throughput sequencing technology.The inhibitory effect of Gel/ChNC-BACNs on SSOs was determined.The preservation effect of Gel/ChNC-BACNs films was studied.Freshness detection models were established based on color indice and TVB-N/TBA value.Physical,chemical and microbial properties combined with sensory evaluation on the quality change of silver pomfret during cold storage were investigated.The main results are as follows:（1）The total anthocyanin content was 58.45 mg/g for bran,11.57 mg/g for whole black rice.With solution environment changed from acidic to basic,the color of BACNs solution gradually underwent a change from rose red to light pink,purple and finally to grayish brown.The Chitin nanocrystal with-NH₂ and-COOH on the surface was 100-300 nm in length and 5-10 nm in width.The amino group content and carboxyl group content was 1.58 mmol/g and 0.32 mmol/g respectively,while the degree of deacetylation was 25.43%,showing excellent nano-characteristics,dispersibility and stability.（2）When 40 m L chitin nanocrystal solution and 4%（w/v）gelatin were contained in per 100m L film-forming solution,the tensile strength of Gel/ChNC film was increased by 49.4%compared to pure gelatin film and all properties reached the optimum.On this basis,Gel/ChNC-BACNs was prepared by adding different concentrations of black rice bran anthocyanins.The results of X-ray diffraction and Fourier transform infrared spectroscopy showed that BACNs were successfully immobilized in Gel/ChNC matrix through hydrogen bonds.Scanning and atomic force microscope results showed that BACNs could improve the microstructure of the film by enhancing compatibility.Ultraviolet-visible light barrier property,oxygen and water vapor barrier property,thermal stability and antioxidant property were improved with increasing concentration in BACNs,however tensile strength decreased.When the addition amount of BACNs was 80mg/100 m L FFS,all properties reached the best followed by 40 mg/100 m L FFS.The excessive addition amount would lead to the aggregation of BACNs.Gel/ChNC-BACNs40 and Gel/ChNC-BACNs80 films were both sensitive in color response toward phosphate buffer with significant color changes and easy identification by human eyes.（3）To determine the anti-bioactivity of the obtained film,silver pomfret was used as material fish.The SSOs were screened and identified from silver pomfret stored at 4℃using culture dependent method combined with 16S r DNA sequencing.The SSOs were determined as Psychrobacter sanguinis,Pseudomonas sp.,Acinetobacter schindleri,Hafnia paralvei,Enterobacter cloacae,Escherichia fergusonii,Lysinibacillus boronitolerans and Citrobacter sp..Bacterial phases in different storage periods were analyzed by high-throughput sequencing technology.The results of the end period were similar to those obtained by culture dependent method.With time increasing,the diversity of bacteria decreased with the abundance of SSOs increased.Analysis of total plate count,TVB-N value and yield factor showed that Hafnia paralvei,Psychrobacter sanguinis,Pseudomonas sp.and Macrococcus caseolyticus had the strongest spoilage ability.Bacteriostasis experiments confirmed that Gel/ChNC-BACNs had inhibitory effect on 13 strains of SSOs screened by culture dependent method.（4）Gel/ChNC-BACNs40 and Gel/ChNC-BACNs80 were applied to the preservation trial of silver pomfret（stored at 4℃for 10 days）.With storage,Gel/ChNC-BACNs40 film gradually changed from purple（0d）to dark gray blue（10d）,the b^*value gradually decreased,the a^*value decreased in fluctuation,andΔE continuously increased exceeding 5,which indicated that color parameters could reflect real color change accurately.Gel/ChNC-BACNs80 film was found to have lower sensitivity and low color discrimination than Gel/ChNC-BACNs40.Finally,Gel/ChNC-BACNs40 film was selected to monitor pomfret freshness and a freshness detection model was established.The model of TVB-N andΔE was expressed as y=7.8909e^0.10645x,the model of TBA andΔE was expressed as y=（0.02227-0.0597x+0.0008732x²）^-1,the fitting degree of TVB-N regression model was higher（0.967）that the degree of meat spoilage could be accurately reflected by measuringΔE of the film.Moreover,it was found that Gel/ChNC-BACNs80 film could significantly delay the increase of p H value,total plate count,TVB-N value and TBA value,while significantly delaying the decrease of texture indice and sensory scores.Gel/ChNC-BACNs40 film had slightly weaker preservative effect than Gel/ChNC-BACNs80,indicating that Gel/ChNC-BACNs films could effectively delay protein decomposition and fat oxidation.In synthesis,the freshness could be monitored by visual active packaging.Moreover the shelf life of silver pomfret treated with Gel/ChNC-BACNs40 films could be extended by 2days.Gel/ChNC-BACNs80 films could extend the shelf life of silver pomfret by 2-3 days,although the indicating ability was weaker.