Development Of Active And Intelligent Film By Using Anthocyanins For Preservation And Detection Of Pork Freshness

Meat is one of the most indispensible food among peoples’ daily life.However,foodborne pathogens contaminated on meat often cause food spoilage leading to economic loss and even food safety issues.Active and intelligent packaging is an innovative packaging technology that allows the product and its environment to interact to extend the product shelf life or monitor the condition of packaged food while tracking the product.Natural anthocyanin extract containing antioxidant,antibacterial activity,and gas-sensitive for meat corruption can be considered as ideal material for active and intelligent packaing.The main research work and conclusion are summarized as follows:1.Study on the activity and gas sensitivity of anthocyanins from different sources.The different species of natural anthocyanins was extracted from nine plants(Black rice,Black bean,Purple potato,Black wolfberry,Blueberry,Mulberry,Rose,Red cabbage,Roselle).All the anthocyanin extracts showing high antioxidant activity,Blueberry pigment reached the highest DPPH radical scavenging activity 81.62%.Escherichia coli and Bacillus subtilis was inhibited by Roselle pigment significantly,which respectively led to the largest inhibition zone 8.90 and 8.38 mm.Rose pigment showed strongest antibacterial activity against Staphylococcus aureus with the largest inhibition zone 11.03 mm.Moreover,Roselle pigment expressed more sensitivity to trimethylamine(TMA)gas,spoiled odor of pork,and showed more stability under storage conditions(4℃ and 25℃)as compared to others.2.Preparation and characterization of active and intelligent films incorporated with natural pigments.In this thesis,chitosan,starch,and polyvinyl alcohol were blended with each other to form film solution,and then incorporated with roselle pigment respectively.Chitosan/starch film(CS),roselle extract/chitosan/starch film(CSE),chitosan/ polyvinyl alcohol film(CP),roselle extract/chitosan/polyvinyl alcohol film(CPE),polyvinyl alcohol/starch film(PS),roselle extract/polyvinyl alcohol/starch film(PSE)were prepared by casting and solvent-evaporation method.Physical and mechanical properties of the films showed that the CS film had the lowest water-vapor permeability(3.39×10-11 g/(m·s·Pa))when it was not incorporated with roselle pigments.CPE film showed strongest antibacterial activity angainst the test bacteria with largest inhibition zone.The antioxidant activity of the films increased significantly with the addition of roselle pigment.The PSE film showed a higher antioxidant activity than others whose DPPH radical scavenging activity reached 95.79%,and furthermore,the incorporation of roselle pigment into PS film led to an increase of elongation at break from 44.15% to 88.16%.PSE film was more sensitive to ammonia gas(NH3),and showed good stability under the conditions of 4℃ and 25℃ with RGB rate of change in about 2% after 16 days’ storage.Fourier transform infrared spectroscopy(FTIR)showed that the incorporation of roselle pigments brought about the interactions between the phenolic component and the film-forming substrate with hydrogen bonds.Significant structural transformation could be observed from scanning electron microscope(SEM).The cross-linking of CSE,CPE film may be interrupted with the incorporation of roselle pigments,while PSE film became more homogeneous and with excellent structural integrity,indicating a high compatibility between the components.3.Study on application of active and intelligent film in Pork.The roselle extract/polyvinyl alcohol/starch films(PSE)were used to preserve pork.The pork stored at 4℃ for 10 days was evaluated for pH,thiobarbituric acid reactive substances(TBARS),total bacterial count(TVC),and total volatile basic nitrogen(TVB-N)parameters.It is found that the roselle pigments released from the PSE film,effectively inhibiting the oxidation of fat and the growth of microorganisms in the pork.PSE film group of pork has the lowest TVC value 6.80(lg CFU/g)after 10 days of storage.According to the results of TVB-N measurement,wrapped in PSE film,the pork was still fresh whose TVB-N value was 15.40 mg/100 g at the 6th day.Our results indicated that the PSE film successfuly extend the shelf life of pork.Moreover,the PSE film was used to discriminate pork freshness grade.The discriminate model was built based on color feature values of the film combined with K-nearest neighbors(KNN)pattern recognition.The results showed that the model combined with fusion color characteristics could effectively discriminate the pork in different freshness,and the discriminating rates for train set and test set were 97.5% and 93.3% respectively.This research indicated that the active and intelligent film incorporated with narural anthocyanin extract was able to keep and detect pork freshness,which may provide a reference for the development of active and intelligent film.