The Interaction Between Purple Sweet Potato Pigment And Gluten Protein And Its Application

Natural plant anthocyanins have been used to adjust the structure and nutritional value of cereal products.However,due to the complexity of the food system,the different pH environments of different types of food affect the physical and chemical properties of the mixed biologically active substances.Therefore,studying the interaction between anthocyanins and protein under different pH systems and exploring its influence on protein structure is of great significance for the development of polyphenol-protein complexes as functional foods in the future industrial applications.In this paper,the interactions between gliadin/glutenin（Gli/Glu）and cyanidin/peonidin（in purple sweet potato pigment）were studied by ultraviolet spectroscopy and fluorescence quenching method under different pH conditions.Included fluorescence quenching mechanism,number of binding sites,binding force,binding constant and thermodynamic parameters,etc.,The changes of Gli/Glu surface hydrophobicity and influence on the conformation of gluten（WG）were also analyzed.Lastly,Single factor experiments and response surface optimization experiments were performed,optimized process parameters of 40%purple sweet potato flour nutrition fresh noodles were obtained.The main summary is as follows:（1）Firstly,fluorescence spectroscopy was mainly used to analyze the intermolecular interactions between Gli/Glu and cyanidin-3-O-glucoside（C3G）in different pH conditions（2.3,4.6,6.0）.Ultraviolet spectroscopy to assist in judging the mechanism of fluorescence quenching.The results showed that the interactions of Gli/Glu and C3G mainly existed in static quenching mechanism,which were spontaneous reaction（ΔG<0）,and the binding site（n）were close to 1,the product had good stability.The UV spectrum results showed an increase in absorbance and red shift of the maximum absorption peak,indicated that Gli and Glu with C3G could cause changes in the microenvironment of amino acid residues.The hydrophobicity of the protein surface（H₀）presented downward trend in the three different pH conditions.According to the analysis of binding force and thermodynamics,at pH 2.3,the binding force of Gli and C3G was mainly the hydrophobic interaction ofΔH>0 andΔS>0,while at pH 4.6 and 6.0,the hydrogen bond or van der Waals force is the main driving force of the interaction.Through SDS-PAGE electrophoresis experiment,it was judged that the combination of WG and C3G did not form covalent complex.The increase ofβ-turn content and the decrease of random coil content were obtained in Fourier infrared spectroscopy（FTIR）,the conformation of WG changes from disorder to order.Scanning electron microscopy（SEM）results showed that the pore size of the WG was significantly reduced and more compact after adding C3G.（2）Secondly,the interaction mechanism of Gli/Glu with peonidin-3-O-glucoside（P3G）and influence on the secondary structure of WG were studied at pH 2.3,4.6 and 6.0.According to the Stern-Volmer equation,C3G and Gli have both dynamic quenching and static quenching mechanisms at pH 2.3,and the binding force was mainly hydrophobic.The quenching mechanism with Glu was static quenching mechanism,which was the non-covalent force of hydrogen bond and van der Waals force.At pH 4.6 and 6.0,the fluorescence quenching mechanism of Gli/Glu with P3G was static quenching.Van’t Hoff equation and thermodynamic equation showed that under different pH conditions,P3G and Gli/Glu wereΔG<0 spontaneous reaction,non-covalent crosslinking is dominant,forming about 1:1 complex.The H₀ of Gli and Glu decreases,and the secondary structure of WG is that theα-helix content decreases and theβ-turn content increases.SEM observed that the microstructure of WG has changed,the pores are small and dense,forming a honeycomb shape,and the protein network skeleton is significantly improved.（3）Finally,the effects of four kinds of noodle improvers including gluten,salt,sodium alginate and VC on the quality of 40%fresh purple potato noodles were studied.The results showed that,based on the single factor test results,the optimum process parameters were obtained by Box-Behnken response surface optimization experiment.Combined with the feasibility of practical operation,the additive amounts of gluten,salt,sodium alginate and VC for noodles were determined at 5%,2%,0.6%and 0.4%,respectively.