| Native casein is recognized as a green and safe material with high nutritional value.Usually,it's applied to deliver nutrients,which is expected to improve the stability and emulsibility of nutrient,and overcome the problems of low bioavailability.So it attracted much attention and it also has a good application prospect.But the poor solubility around isoelectric point limits its widespread applications in the food industry to some extent.However,the Maillard reaction is effective in improving functional property of protein,and it also can avoid the use of synthetic chemical reagents and organic solvents effectively.This method is more safer than other modified methods.In this paper,we based on the effects of different reaction conditions on the grafting degree,browning degree,solubility and emulsifying properties,to select the grafted products with excellent properties.Also,we investigated the effect of grafting reaction on physicochemical properties and structure features of glycosylated casein by using different characterization.At the same time,we prepared copolymer self-assembled nanoparticles using ultrasonic method,studied the assembly mechanism and stability of nanoparticles.It be applied to embed PRP as nano-carrier.Also,the simulative digestive experiment in vitro was carried out,the control release performance of Cas-Ca-PRP-Nanocapsules/Cas-CC-PRP-Nanocapsules was analyzed.First,casein as the basic wall material grafted with two kinds of polysaccharide(carrageenan,carboxymethyl chitosan)by ultrasonic Maillard dry reaction.Preparation process and molecular structure of two kinds of products with excellent properties were studied,the effect of relative humidity,substrate ratio,reaction temperature and time on graft degree between the casein and polysaccharide were explored and the optimum preparation conditions of glycosylated casein were obtained,The optimum substrate ratio of Cas-Ca and Cas-CC are 1:2 and 1:3,respectively,the reaction time are 24h and 36h,respectively,the optimum reaction temperature are all 60?,the reaction humidity are all 79%,and optimal grafting rate reached 78.05%and 79.84%,respectively.SDS-PAGE analysis showed that:In the ultrasonic heat treatment conditions,the original protein bands disappeared and large molecular weight protein bands appeared when glycosylated casein formed.Also,the results of FTIR spectroscopy and fluorescence spectra are in good agreement with SDS-PAGE analysis result,they all proved that Maillard reaction do occurred.Thermogravimetric analysis illustrated thermal stability grafting products were improved significantly,compared to the original protein.Glycation product self-assembly nanoparticles with excellent properties were prepared under conditions of ultrasonic power,and the assembly mechanism and stability of the Cas-Ca-Nanoparticle/Cas-CC-Nanoparticle were explored by studying the influence of different parameter on the particle size and distribution coefficient(PDI).The results showed that assembly of glycosylated casein depend on non-covalent bond,such as hydrophobic force and hydrogen bond and ionic bonding and so on.Besides,glycosylated casein nanoparticle have good stability.Cas-Ca and Cas-CC were used for encapsulating PRP availably and the encapsulation rate reached 87.3%and 82.5%,respectively,the average diameter of nanocapsule were 319.1-371.2 nm and 309.5-385.8 nm,respectively,and polydispersity index was all between 0.15 and 0.37.The PRP and PRP-nanocapsule were stored for six days under the condition of high temperature,illumination,and food additives respectively to observe the PRP retention rate,which can determine the protective effect of nanocapsule on PRP.The results showed that the nanoparticles of glycosylation product can protect and improve its thermal stability effectively.The retention rates of PRP in Cas-Ca-nanocapsule and Cas-CC-nanocapsule were 82.1%and 83.3%respectively after six weeks storage in outdoor light conditions,83.3%and 85.80%respectively after six weeks storage at 25?,and 89.2%and 90.5%respectively after six weeks storage at 4?.The retention rate did not change significantly when sodium benzoate and potassium sorbate were added,The PRP can be protected effectively by Cas-Ca or Cas-CC,which based on theirs antioxygenic property and physical shielding effect.Cas-Ca and Cas-CC are an effective carrier of PRP.And the simulative digestive experiment in vitro was carried out,the control release performance of Cas-Ca-PRP-Nanocapsules and Cas-CC-PRP-Nanocapsules were analyzed.The result show that they all can control release behavior availably.In our study,Cas-Ca and Cas-CC were used as the matrix,and PRP was embedded in the glycosylation product by ultrasonic self-assembly technique.The hydrophobic part of the glycosylation product form capsule core,and hydrophilic part form capsule shell.PRP was embeded in capsule core so as to maximize to solubility and reduce the impact of environmental factors.The digestion behavior was analyzed through in vitro simulative gastrointestinal fluid digestion model.Cas-Ca-nanocapsule and Cas-CC-nanocapsule were disintegrated and released slowly within 3 h under simulated gastric juice conditions,but released rapidly within 1 h in intestinal environments,and the total release rate reached 76.6%and 78.6%,respectively.This is because the PRP could be bound with protein and uniformLy dispersed in simulated gastric fluid,and the rapid release in intestinal juice effectively improved the bioavailability of PRP. |
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