Preparation Of Polyphenol Modified Gelatin Complex And Its Application In Emulsion

Gelatin is an important natural amphiphilic macromolecule,which can be obtained by hydrolyzing collagen.Due to its unique functional characteristics,excellent biocompatibility and biodegradability,gelatin has been widely explored and applied in the fields of food,pharmacy,bioimaging and tissue engineering.As far as we know,the functional properties of gelatin determine the quality and shelf life in food,and the cross-linking reaction between protein molecules is a method to improve the functional properties of protein.Polyphenols can induce covalent cross-linking reaction of protein.Therefore,in this paper,polyphenol-gelatin covalent modifier was prepared by polyphenol-protein covalent modification reaction,and its structure and functional properties were characterized,and it was applied to the emulsion system.Then we extracted gelatin from the spine of silver carp,and finally modified the extracted gelatin with polyphenol,characterized its structure and applied it into emulsion.The results are as follows:(1)In this chapter,the polyphenol-gelatin cocomplex was prepared by alkali treatment method,and the commercial bovine bone gelatin(BBG),commercial fish skin gelatin(CFG)and commercial pig skin gelatin(PSG)were modified by selecting two kinds of polyphenol tannic acid(TA)and caffeic acid(CA).The structure was characterized by SDS-PAGE,ATR-FTIR,scanning electron microscope(SEM),and the prepared polyphenol-gelatin covalent complex was prepared into emulsion,which was observed by digital camera and optical microscope.The results of sodium dodecyl sulfonatepolyacrylamide gel electrophoresis and UV absorption spectrum showed that polyphenols could successfully induce covalent crosslinking reaction of commercial gelatin.The modification degree of BBG-TA(59.39± 1.47 mg/g)and PSG-TA(64.71 ± 0.35 mg/g)was higher than that of CFG-TA(51.07 ± 0.26 mg/g),indicating that the type of gelatin affected the binding amount of polyphenols.In addition,the modification degree of BBG-TA and PSG-TA was higher than BBG-CA(39.44 ± 0.43 mg/g)and PSG-CA(49.22 ± 1.08 mg/g),indicating that TA was higher than CA.The structure and function of the modified gelatin were changed,for example,the β-angle content of TA modified gelatin increased,the α-helix content of CA modified gelatin decreased,the isoelectric point and gel strength of gelatin decreased,but the microstructure became more dense,and the in vitro oxidation resistance was improved.In addition,the in vitro antioxidant activity of TA modified tannic acid-gelatin covalent complex was higher than that of caffeic acid-gelatin covalent complex.In addition,due to the different sources of gelatins,the decrease and increase of their functional properties are different.Fish oil-loaded polyphenol-gelatin covalent complex emulsion was prepared by modifying the covalent complex successfully,and the storage changes of the emulsion after freezing treatment,heat treatment and polyphenol-gelatin covalent complex emulsion containing different concentrations of sodium chloride at room temperature were discussed.We found that after the emulsion was frozen for 24 hours,the stability of BBG and PSG modified polyphenol-gelatin covalent emulsion by TA/CA was worse than that of pure gelatin,and the emulsion effect of CFG-TA/CA covalent emulsion was better than that of CFG.After heat treatment,it was found that the emulsion prepared by gelatin-polyphenol covalent complex after heat treatment at 55℃ and 85℃,after stored at room temperature for 28 days,the emulsification degree increased compared with the emulsion prepared by pure gelatine after heat treatment,and the stability of the emulsion was reduced by the degree of emulsification.In addition,the fish oil emulsion stabilized by polyphenol-gelatin covalent complex has poor stability compared with the emulsion prepared by pure gelatin.When a certain amount of sodium chloride is added,the emulsification degree of the fish oil emulsion stabilized by polyphenol-gelatin covalent complex decreases and the stability of the emulsion is improved.(2)To investigate the effects of pepsin on structure and function of silver carp spine bones gelatin(PEHGs)and its application in emulsion.The structure of the gelatin was characterized by SDS-PAGE,ATR-FTIR and AFM,and the gelatin was prepared into emulsion,which was observed by digital camera and optical microscope.The molecular weight of PEHGs extracted from the spine of silver carp is mainly less than 5KDa,and the yield is 12.6%-13.3%.They can self-assemble into p H-stable nanoparticles.The results showed that there was no significant relationship between enzyme/bone ratio and protein secondary structure percentage,water holding capacity(WHC),oil holding capacity(FBC),emulsifying activity index(EAI)and emulsifying stability index(ESI)during the hydrolysis of gelatin nanoparticles from silver carp vertebrae.With the decrease of the enzyme/bone ratio,the number and size of nanoparticles increased,and the turbidity and gel strength increased.In addition,the obtained PEHG could stably load the fish oil emulsion,and the initial droplet size of the emulsion decreased with the decrease of the enzyme/bone ratio,and the emulsion stability increased.After 28 days of storage at 4℃,a low index value of <11% was observed.It can be seen that PEHGs has good emulsifying stability and can be better applied in emulsion.(3)In this chapter,polyphenol-silver carp spine bones gelatin covalent complex was prepared.TA was used to modify a silver carp spine gelatin(PEHG6)extracted from the experiment in the previous chapter to explore the structural and functional properties of the covalent complex and study its application in the emulsion.In accordance with the characterization method of polyphenol-gelatin covalent complex modified by different kinds of polyphenols on three commercial gelatins in Chapter 2,we can conclude that TA can successfully covalently cross-link with PEHG6,and the modification degree is(103.23± 2.5 mg/g).The structure and functional properties of the modified PEHG6 changed,for example,the isoelectric point decreased,the solution precipitated at p H 5.0,the gel strength decreased from 313.6 ± 9.8 g to 266.9 ± 2.5g,and the microstructure became denser.In vitro antioxidant activity was increased compared with PEHG6.The stability of the emulsion prepared by PEHG6-TA covalent complex decreases after freezing treatment and heat treatment.In addition,the fish oil emulsion stabilized by PEHG6-TA covalent complex has a lower stability than the emulsion prepared by PEHG6.After adding a certain amount of sodium chloride and storing it at room temperature for 28 days,it is observed that the emulsification range of the emulsion decreases and the emulsion has a better stability,which is of great significance.