The Aggregation Behavior And Functional Properties Of Fish Scale Collagen Regulated By Heat Assisted Ionic Liquids

Fish scales are rich in collagen.Extraction of collagen from fish scales has important research significance because it can effectively solve the problems of collagen source and environmental pollution.Natural collagen cannot exhibit good functional properties due to large molecular aggregates and poor solubility.In this work,collagen was extracted from fish scales.Then heat treatment and ionic liquid were used to modify the collagen.The relationship between the structure and functional properties of collagen aggregates were explored.This work will provide theoretical guidance for the preparation of active proteins with different functional properties.The main results are as follows:(1)Collagen was extracted from Tilapia scales by different methods.The structure of collagen was analyzed by SDS-PAGE and X-ray diffraction.Furthermore,the emulsion activity and stability were investigated.The extraction yield obtained by ultrasonic and enzymatic methods were 79.53% and 82.23%,respectively,which were higher than those of other methods.SDS-PAGE analysis revealed that ultrasound did not alter the subunits composition of collagen.However,drastic change could be observed in the structure of collagen extracted by high temperature and enzymatic method.X-ray diffraction of collagen showed that the structure of collagen was destroyed to some extent after extraction by various methods.However,collagen extracted by acid and ultrasound were relatively stable and had good emulsification activity.(2)The effects of different ionic liquids,ultrasound-assisted ionic liquids and heat-assisted ionic liquids on collagen aggregation were investigated.The structure of regenerated collagen was also analyzed.Results showed that 1-butyl-3-methylimidazolium chloride and 1-butyl-2.3-dimethylimidazolium chloride could significantly promote the dissolution of collagen at the concentration of 5%.Heat-assisted ionic liquids promoted collagen dissolution more than ionic liquids and ultrasonic-assisted ionic liquids.The solubility of regenerated collagen could be up to 62% by heat-assisted 1-ethyl-3-methylimidazolium pretreatment,which was significantly higher than control collagen(12.37%)(P<0.05).The regenerated collagen particle size was significantly reduced after heat-assisted ionic liquid pretreatment than heat treatment alone.It showed that ionic liquid could prevent excessive re-aggregation of collagen.SDS-PAGE and infrared spectroscopy showed that the regenerated collagen was type ? collagen.However,during the regeneration process,the hydrogen bonds between the molecules were reconstructed to form new aggregates.(3)The functional properties of regenerated collagen were determined.The relationship between functional properties and aggregated state were investigated.Results showed that the enzymolysis of the regenerated collagen was improved by the heat-assisted 1-butyl-3-methylimidazolium hexafluorophosphate,1-butyl-3-methylimidazolium tetrafluoroborate,1-ethyl-3-methylimidazolium chloride and 1-butyl-2.3-dimethylimidazolium chloride pretreatments.The antioxidant activity of enzymatic hydrolysate was related to the type of ionic liquid.The drastic increase in emulsification stability of regenerated protein were observed during pretreatment of heat-assisted 1-ethyl-3-methylimidazolium chloride and 1-butyl-2.3-dimethylimidazolium chloride,and their indexes were 182.30 and 170.46,increased by 49.97% and 40.22% than the control(P<0.05).The strength of the regenerated collagen gels were 811.66 g cm and 802.05 g cm after heat-assisted 1-ethyl-3-methylimidazole chloride and 1-butyl-2.3-dimethylimidazolium chloride pretreatments,which increased by 118.28% and 115.68% in respect to the control collagen.The water absorption and oil absorption of regenerated collagen was reduced after heat-assisted ionic liquid pretreatments.The foamability of regenerated collagen was improved by the heat-assisted ionic liquid pretreatments.