Research On Wheat Gluten Modified By Sodium Sulfite And Alcalase

The compound modification of pretreatment and enzymolysis became a newstudying focus because of certain limitations in enzymatic modification of wheatgluten. Sodium sulfite, as a reducing agent, is able to interrupt the disulfide bondsof proteins resulting in looseness of the protein structure. The functional characteristics ofwheat gluten would substantially improve by enzymatic modification with sodiumsulfite pretreatment. But little research was done about this at present. Based onthat, effects of sodium sulfite pretreatment and sodium sulfite-Alcalase modificationon the functionality of wheat gluten were studied and then optimized the optimaltechnological parameters. The structural changes of proteins in the process ofmodification and the biological functionality of the enzymatic hydrolysate werealso investigated. The results suggested that:(1) Sodium sulfite pretreatment noteworthily improved the functionality of wheatgluten. Solubility increased from5.46%to28.14%with0.8mg/g sodium sulfite,pretreating for20min under70℃. Meanwhile, emulsifying properties and foamingproperties were improved markedly. Under these conditions, pretreated wheatgluten was also modified with Alcalase and obtained optimal process parameters asfollows: enzymolysis time28min, amounts of Alcalase0.50%, enzymolysis pHvalue9, enzymolysis temperature60℃. On this condition, validation test showedthat: solubility was48.32%, emulsifying activity and emulsion stability were42.5%and40.27%respectively, and foamability and foaming stability were106.24%and59.5%individually.(2) Proteins structure has changed greatly after sodium sulfite pretreatment andsodium sulfite-Alcalase modification. After sodium sulfite pretreatment, thesulphydryl contents of wheat gluten, gliadin and glutenin increased observablywhile the disulfide bonds decreased. Among them, the sulphydryl contentsincreased from14.75μmol/g to41.29μmol/g, while disulfide bonds contentsreduced from42.35μmol/g to28.35μmol/g in wheat gluten. Scanning electronmicroscope showed that the structures of three kinds of proteins became loose andfragmental structure increased. After compound modification, sulphydryl anddisulfide bond contents in unit mass of proteins reduced, protein surfaces were seriously eroded, holes and fragmental structures further increased. SDS-PAGErevealed that: after pretreatment, less than40KDa of wheat gluten and lowmolecular weight glutenin increased, but the relative molecular weight change ofgliadin was not significant. The relative molecular weights of three proteins were allreduced by compound modification.Fourier-transform infrared spectroscopy showed that: wheat gluten mainly wasβ-sheet structure. The β-turns decreased3.23%and random coil increased about2.33%by sodium sulfite pretreatment, α-helix decreased slightly and random coilincreased by compound modification. For gliadin, the β-turns and β-sheet decreasedby6.03%and9.35%respectively after pretrearment, and both were increased to acertain extent after compound modification. The random coil increased and thendescended. There were hardly any β-turns in glutenin. Α-helix and β-sheet declinedby3.32%and11.53%, individually, after pretreatment. After compound modification,the α-helix further decreased, β-sheet and β-turns increased modestly, the changetrend of random coil in both glutenin and gliadin was equal.(3) The antioxidant activities of products modified by sodium sulfite-Alcalasewere investigated, such as hydroxyl radical scavenging activity, superoxide radicalscavenging activity, reducing power and Fe2+chelating activity. Results showedthat the antioxidant activities were enhanced with the increase of the sampleconcentration, and the smaller relative molecular weight, the higher the antioxidantactivity. Escherichia coli (E.coli) and Staphylococcus aureus (S.a) were inhibited tosome extent by the products of compound modification. The antibacterial activitywas positively associated with sample concentration, whereas was negativelycorrelated with the relative molecular weight. In addition, the inhibition wasstronger in E.coli than in S.a.