The Physicochemical Properties Of EGCG-Gelatin Composite Film And Its Mechanism In The Maintenance Of The Tilapia Fillets Quality During Chilled Storage

Gelatin is a water-soluble protein with good gel forming,thickening and water binding and film forming property.The main sources of gelatin are skin and bone of mammals.In recent years,fish skin and bone has attracted wide attention as a new source of gelatin extraction material.The(-)-epigallocatechin gallate(EGCG)is an active component of green tea,which has strong free radical scavenging and antimicrobial activity.In this study,EGCG and gelatin were crosslinked into a new type of composite composite film at low temperature for the preservation of tilapia fillets.And the effects of composite film on improving quality,changing the microbial composition and prolonging shelf life of tilapia were explored.The main contents and results are as follows:1.The effects of EGCG on the mechanical,bioactivities,cross-linking and release properties of gelatin filmThe gelatin solution was mixed with EGCG(1%-5%)at room temperature and degassed by ultrasonic.After that,the gelatin and EGCG was crosslinked at 4? for 12 h to formate composite film.The properties of composite composite film were determined.The composite films exhibited excellent antioxidant and antibacterial activities against Staphylococcus aureus and Escherichia coli when the content of EGCG was higher than 3%.With the increasing content of EGCG(1%to 5%),higher denaturation temperature(66.5 to 84.6?)and bloom strength(609.3 to 1114.7 g)and denser microstructure suggested the existence of cross-linking bonds in the composite films.The infrared spectroscopy,protein pattern and release property of EGCG showed that hydrogen bonds were the main driving force for cross-linking of the composite film.The release of EGCG from the composite film system was described and two compounds were cross-linked via hydrogen bonds.The peak of the release was observed at 13 h in all groups.Then the speed decreased and remained relatively stable for more than 300 h.The effects of EGCG on the mechanical,antioxidative,antimicrobial,cross-linking and release properties of gelatin film were evaluated.2.Effect of EGCG-gelatine composite film formation on the tilapia fillets quality during chilled storageFresh tilapia fillets were treated with EGCG,gelatin and composite films and were packaged in vacuum at 4?.The freshness of the fillets was measured every 3 days.EGT delayed the change of mechanical properties(springiness&hardness)and colour of fish fillets and decayed the oxidation of fat and protein in fish fillets.Compared with the control group,EGT samples had lower K values(74%in 18 d)and biogenic amines(39 mg/kg for putrescine and 50 mg/kg for cadaverine)at the end of storage.With the prolongation of storage time,the microstructures of fish fillets changed,and EGT inhibited the increase of muscle fiber gap.The electronic nose analysis showed that EGT changed the aroma composition of fish fillets.According to sensory evaluation,the shelf life of tilapia fillets was extended 6 days in EGT group.Therefore,EGT improved the quality of cryopreserved tilapia fillets which was mainly due to the delayed oxidation of protein and fat.3.Effect of EGCG-gelatine composite film formation on the tilapia fillets microbial composition during chilled storageChanges in microbial composition of fish fillets treated with EGT were studied during storage by plate counting and high-throughput sequencing.The results of plate counting showed that the colony values of psychrophilic bacteria,thermophilic bacteria,Aeromonas,Pseudomonas and H2S-producing bacteria in EGT group were lower than those in control group.The results showed that the growth and reproduction of bacteria were inhibited by composite composite film.The results of high throughput sequencing showed that the microbial species of tilapia fillets decreased with the increase of storage time.The number of microorganisms at each taxonomic level in EGT samples was the smallest at 0 d(phylum:13;taxa:25;order:40;family:53;genus:75,species:39).The number and relative abundance of microorganisms in EGT group were lower than those in CON,and the relative abundance of Aeromonas and Acinetobacter in deteriorated samples was reduced by EGT(21 d).Therefore,EGT changed microbial composition and inhibited the growth and reproduction of spoilage bacteria.