| This study is supported by the school construction project of Jilin Province(sf2017-6-4).Forest frog is an important agricultural and forestry product in Jilin Province,which has both nutritional value and medicinal value.The protein content in the eggs of Rana chensinensis accounts for 16.8% of the egg components.It contains 8 kinds of essential amino acids needed by human body and has anti fatigue and anti-cancer effects.Glycosylation technology is a kind of technical means to change the stability and function of protein purposefully by adding sugar molecules to protein artificially to produce appropriate sugar shape.In this paper,we modified the egg protein of Rana chensinensis(EPR)by glycosylation reaction to study its basic functional characteristics and volatile flavor compounds.Then,the oil loaded curcumin nanoemulsion was prepared by using high quality glycosylated protein as emulsifier,and the basic properties were characterized and the stability of the system was studied.The main research contents include the following three aspects:(1)Extraction,functional analysis and component identification of EPR: the crude EPR was obtained by alkali solution and acid precipitation.The basic functional properties,including solubility,water holding capacity,foaming capacity and emulsifying capacity,were determined by biochemical methods.The results showed that the solubility of EPR was poor,and reached the lowest value at p H = 4.5.When p H > 9 and temperature above 60 ?,the solubility of EPR was significantly enhanced,and the NSI value was above 0.6.The water holding capacity of EPR was good,reaching the optimal value of 5.93 g / g at 40 ?.The water holding capacity of EPR increased at p H far away from the isoelectric point.The emulsifying ability of EPR was better,and the emulsifying stability increased with the increase of concentration.In addition,liquid chromatography-mass spectrometry(LC-MS)was used to determine the protein types.It was found that there were about 425 kinds of proteins / peptides in EPR,which had good homology with bullfrog and Rana chensinensis.Most of the protein types were enzymes,and the molecular weight was mainly between 50 and 200 k Da.(2)The effect of glycosylation on the functional characteristics,structure and flavor of EPR.The solubility of EPR was improved(NSI value was close to 100%)after the reaction with different sugar,and the foaming and emulsification of EPR were improved to some extent.The water holding capacity of glycosylated protein decreased,which was related to the solubility increase caused by the structural change of the protein after glycosylation modification.The functional characteristics of xylose-protein complex were better than that of xylose-protein complex.The results of endogenous fluorescence and Fourier transform the protein structure from the original folding state to the extended state,the ?-fold structure decreases,the protein is unfolded,and the sequence structure is transformed into disordered structure;the chromophore exposure causes fluorescence quenching,and the characteristic peak in the infrared spectrum changes accordingly.In addition,the GC-MS analysis showed that aldehydes were the main contributing substances in the flavor production of EPR.The flavor substances of glycosylated proteins increased from 11 to 46.(3)The preparation,characterization and stability evaluation of curcumin emulsion with xylose-EPR as emulsions: Curcumin emulsion particle size below400 nm,absolute potential greater than 30 m V,PDI dispersion index less than 0.5.Curcumin emulsion shows a typical shear thinning phenomenon and belongs to the category of non Newtonian fluids.The stability of emulsion centrifugation was better when the concentration of EPR was 3% and 5%,and the K value of the centrifugal stability constant was greater than 0.8,and the entrapment rate was above90%.After laser confocal microscopy,the oil droplets of protein in three concentrations of emulsion were very obvious.The particle size of curcumin nanoemulsion rapidly increased to more than 2000 nm near the isoelectric point of p I=4.5,and the potential value approached to 0.The particle size at p H far away from isoelectric point was stable within 500 nm,and the absolute value of the potential was more than 30.Curcumin nanoemulsion showed good thermal stability when treated at 60 ? 100 ? for a short time.In addition,the stability of the emulsion at 3% and 5% concentration was better at 4 temperature.The particle size of the emulsion was less than 550 nm after seven weeks,the absolute value of the potential was greater than 30,the centrifugal stability decreased by 17%,and the entrapment rate was still above 60%.However,at 25 and 37 degrees,the stability of the emulsion decreased significantly with the prolongation of storage time.Conclusion: The EPR has not only high nutritional value,but also good food processing properties.The solubility,foaming and emulsifying properties of glycosylated EPR were superior.Xylose-EPR can effectively encapsulate active components such as curcumin,and shows good stability,which can be used as an important substrate for the research and development of related functional foods. |
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