Research On Freshness Indicator Packaging Material Of Salmon Based On Anthocyanin

Salmon will produce volatile amine gas after being contaminated by microorganis-ms which leads to spoilage and quality degradation.Freshness indicative packaging films offered a great perspective to display different colors with the pH changes of packaging environment.Among these freshness pH-indicators,anthocyanins have obvious advantages of innocuity,simple extraction and easily available alternative sources.However,the stability of anthocyanins are affected by several factors such as temperature,light and oxygen.Therefore,in order to solve the unstable problem of anthocyanins as freshness indicators for salmon,anthocyanins were extracted from natural plant materials,and then the structure and stability of anthocyanins were studied.Afterwards,a twin layer freshness indicator film was fabricated.The inner layer used as carrier film of anthocyanin indicator and the outer protective layer used to prevent oxygen.Finally,freshness indicator film was used for freshness monitoring of salmon.The cardinal achievement from this study are summarized as follows:1.Chemical indicators of salmon freshness.The volatile substances produced during salmon storage were analyzed by Gas chromatography-mass spectrometry(GC-MS).Among these volatile substances,trimethylamine served as indicative gas to study the for salmon spoilage process as its concentration would increase during storage.Thereafter,total volatile basic nitrogen value(TVB-N),pH values,total viable count(TVC)and the 2-thiobarbituricacid value(TBA)were studied.The acquired results showed that on the 8th day of storage,the pH value,TBA,TVC,TVB-N of salmon was 6.89,1.13 mg MDA/kg,7.54 lg(cfu/g),and 31.35 mg/100 g,respectively;which exceeded the safety limit of salmon.In conclusion it indicates that salmon spoilage began on the eighth day which provides a strong basis for further research on salmon freshness indicators.2.Study on the structural analysis and stability comparison of anthocyanins from different sources.The different types of natural anthocyanins were extracted from nine plants(Morning glory,Carnation,Black bean,Rose,Grape Skin,Mulberry,Black wolfberry,Purple yam,Blueberry,Red cabbage,Roselle,Purple onion).The sensitivity of extracted anthocyanins with corruptive gases was analyzed.The anthocyanins extracted using(Grape skin,Mulberry,Black wolfberry,Purple yam)were optimized with their components analyzed by HPLC-MS.Grape skin and mulberry anthocyanins were mainly composed of delphinidin-3-glucoside(72.24%)and cyanidin-3-glucoside(59.43%),respectively.Likewise,black wolfberry anthocyanins were mainly contained petunin-3-p-coumarin-glucoside-5-glucoside(78.31%)and Purple yam anthocyanins were contained cyanidin-3-sinapyl-glucosyl(53.93%).Thereafter,the stability of these anthocyanins under different temperature,light,pH value and oxidant were studied and compared.The results of different temperatures showed that the stability of anthocyanins was increased in the order of purple yam > grape skin > mulberry > black wolfberry.The results of different light showed that the stability of anthocyanins was increased as mulberry > grape skin > purple yam > black wolfberry.The stability of anthocyanins under acidic conditions was greater than that of alkaline conditions.The lowest stability was observed for anthocyanin extracted from black wolf-berry.Under the condition of different hydrogen peroxide,the highest stability of anthocyanin was recorded for mulberry anthocyanin,and the lowest stability for anthocyanin extracted from black wolfberry.Hence,the anthocyanins acquired from mulberry were selected to develop pH indicator film to monitor the freshness of salmon.3.Preparation and application of bilayer freshness indicator films incorporated with natural anthocyanins.In this study,chitosan,polyvinyl alcohol,pulullan and sodium alginate were blended with together as outer film,and mulberry anthocyanins and gellan gum were blended as inner film,chitosan/ mulberry bilayer films(CM),polyvinyl alcohol/mulberry bilayer films(PvM),chitosan-polyvinyl alcohol/mulberry bilayer films(CPvM),pulullan/mulberry bilayer films(PM),sodium alginate /mulberry bilayer films(SM),pulullan-sodium alginate/mulberry bilayer films(PSM).The developed films were observed for water vapor permeability,DPPH free radical scavenging capacity,hydrophobicity,sensitivity to trimethylamine and the characterist-ic decaying odor of salmon.Physical and mechanical properties of the films showed that the PSM film had the lowest water-vapor permeability(0.37×10-11 g/(m·s·Pa)and a higher DPPH radical scavenging capacity 90.97%.The drop contact angle is 90.64°,which indicatives of hydrophobic force on the film surface.Fourier transform infrared spectroscopy(FTIR)spectra showed that hydrogen bonds could be formed between the substrates,and the chemical composition remained unchanged.Scanning electron microscope(SEM)images revealed that that CPvM film and PSM film had good compatibility and exhibit uniform composition.The optimal stability of PSM film was recorded when stored for 14 days at 4°C,(35)(36)was 1.01,and the stability of inner film is the lowest,(35)(36)was 3.35.The stability of PSM film was optimal at 25 °C with(35)(36)value 3.59,and the stability of inner film was the lowest,(35)(36)was 9.92.The stability of PSM film was the best at 37°C,(35)(36)was 16.97,and the stability of inner film was the lowest,(35)(36)was 26.45.The sensitivity response of the film to trimethylamine showed that the inner film with single layer structure had the highest sensitivity(70.07%),followed by PSM film(67.42%).The highest sensitivity of the PSM film with 8% dry weight mulberry anthocyanin to trimethylamine was 67.42%.From the results,the PSM film was selected to monitored the freshness of salmon for 10 days.The results showed that the bilayer film could not only be used to indicate the freshness of salmon,but also improve the instability of anthocyanins,which provides reference for the development of an active intelligent packaging film.