Optimization And Physicochemical Properties Of Corn Starch Prepared By Extrusion Pretreatment Combined With L-cysteine

The application of corn starch involves many food processing industries,such as starch sugar,modified starch,engineering food,fermentation technology,etc.In the processing and application of starch,the purity and extraction rate of starch determine the quality and production efficiency of the product,while the crystal structure and the proportion of amylose branch chain of corn starch determine the application range of corn starch.The traditional preparation method of corn starch is wet grinding process,soaking in 0.2-0.3%sulfurous acid solution for 45-60 h to destroy the compound structure of starch and protein in corn grains.Current studies have shown that the internal binding mode of maize is mainly through the disulfide bond of protein,in addition,there are a variety of interaction forces,such as hydrogen bond,hydrophobic force,electrostatic force,etc.The traditional wet milling process only destroys the disulfide bond,so the efficiency of starch separation is relatively low and the soaking time is long.Therefore,the extrusion technology combined with L-cysteine was studied to destroy multiple interactions between starch and protein,improve the traditional process,accelerate the release of starch particles,and provide a theoretical basis for a new environmental protection extraction process.The main contents of this study are as follows:Using extrusion combination technology of preparation of corn starch,l-cysteine of extrusion temperature,material moisture,screw speed,adding amount of l-cysteine,soaking temperature and soaking time for single factor experiment,starch extraction yield as reference index,on the basis of single factor experiment,using four factors three levels of response surface optimization of extraction process.The results showed that the optimal conditions of extrusion combined with L-cysteine were as follows:extrusion temperature 45?,extrusion moisture50%,screw rotation speed 220 r/min,L-cysteine content 0.8%,immersion temperature 50?,immersion time 12 h.Under these conditions,the extraction yield of starch was 92.88%±0.28%,starch purity was 94.77%±0.38%,protein content was 0.70%±0.08%,and immersion time was12 h.Compared with the traditional process,the extraction rate of starch increased by 1.42%and the soaking time was shortened by 36 h.This process can effectively shorten the time and improve the production efficiency.With the use of environmentally friendly soaking agent,it is an environment-friendly preparation process with no pollution to the environment.The effects of extrusion combined with L-cysteine(ELP)on the structure of corn protein were studied.FT-IR analysis showed that extrusion could destroy the secondary structure of protein and break the hydrogen bond.L-cysteine introduced new functional groups and changed the structure of corn protein.Scanning electron microscopy(SEM)showed that the protein particles were destroyed by extrusion and formed large flocculent.Chromatic aberration analysis showed that extrusion could destroy protein structure and release zeaxanthin,resulting in yellowish protein color.DSC results showed that the extruder protein would recombine to form a more compact structure and increase the enthalpy of?H.The structure and physicochemical properties of traditional process(CS),extrusion combined with H₂SO₃(EHS)and extrusion combined with L-cysteine(ELS)starch were compared.FT-IR results showed that extrusion did not destroy the chemical structure of starch.Scanning electron microscopy(SEM)and polarized light microscopy(PLM)showed that some starch particles appeared cracks and grooves on the surface of ELS and EHS compared with CS.XRD patterns showed that all three starches were typical A-type.The average grain size ELS<EHS<CS was obtained by particle size distribution analysis.The hydrolysis degree of starch in the process of separation was different with different extraction processes.The analysis of physical and chemical properties showed that the dissolution and swelling ability of ELS and EHS was higher than CS,while the freeze-thaw stability was lower than CS.RVA results showed that the peak viscosity of starch could be decreased by extrusion,EHS<ELS<CS.DSC data analysis showed that there was no significant change in thermal characteristics,and the double helix structure and crystal structure were not damaged.The results of in vitro digestion test showed that part of resistant starch could be changed into fast digestible starch by extrusion,and the content of resistant starch was CS>ELS>EHS.