Study On The Preparation,Multilevel Structure And Functional Properties Of Bitter Apricot Kernel Gluten-Sugar Conjugates

Bitter apricot kernel is an excellent resource for both medicine and food,and its protein and amino acid species are complete,which can be used as a plant protein resource with high edible value.At present,the deep processing and comprehensive utilization degree of bitter apricot kernel is low in China,and most of them are still sold in the form of raw materials.There are few large-scale bitter apricot kernel protein processing enterprises and the technical strength of enterprises is limited,which has not fully utilized its protein resources advantages.In order to guide the functional properties of protein products to be more diversified and characteristic,protein modification technology was used to enable the widely and friendly application of bitter apricot kernel protein.In this study,bitter apricot kernel gluten(AKG)was used as raw material,monosaccharide(glucose)and polysaccharides(sodium alginate,dextran and chitosan)were used as different sugar substrates,and the process of preparing high solubility protein-sugar covalent complexes was optimized by glycosylation modification method,the conjugates of molecular conformation,microstructure,functional properties and antioxidant properties were analyzed.The main research results are as follows:(1)The bitter apricot kernel gluten was extracted by the Osborne method,and the dry and wet glycosylation were compared with degree of grafting,browning degree and solubility as evaluation indicators,and the wet glycosylation method was selected for modification.Using single factor and response surface,the preparation process of glucose-gluten covalent complex was determined as follows:reaction temperature was 63?,reaction time was 0.6 h,pH was 9.4,protein-sugar ratio was 1?2,and the solubility of glucose-protein conjugate was 96.24%.(2)AKG was modified by polysaccharides with different charge types.Single factor and response surface tests were used to determine the optimal process parameters as follows:reaction temperature was80?,reaction time was 4 h,pH was 9.0,protein-sugar ratio was 1?1,and the solubility of sodium alginate-protein conjugate was 88.58%.Reaction temperature was 60?,reaction time was 1.5 h,pH was10.0,protein-sugar ratio was 3?1,and the solubility of dextran-protein conjugate was 95.23%.Reaction temperature was 65?,reaction time was 1.5 h,pH was 10.0,protein-sugar ratio was 2?1,and the solubility of chitosan-protein conjugate was 92.53%.(3)The multilevel structure of the covalent complexes was observed by fluorescence spectroscopy,fourier infrared spectroscopy,scanning electron microscopy and SDS-PAGE.After the glycosylation reaction,the polarity of the environment in which AKG is located changes,and the groups in the protein molecules undergo vibrational energy level transitions,the conformation and microstructure of the protein changes accordingly.(4)Compared with AKG,the solubility,emulsification activity index,emulsification stability and foaming property of the conjugates were improved in different degrees after glycation treatment,but the foaming stability was decreased on average,while the water holding and oil holding properties of the modified products did not change significantly overall.The antioxidant capacity of the grafted products on DPPH free radical and ABTS~+free radical and reducing ability were increased significantly(P<0.05).