Effects Of Acylation And Enzymatic Hydrolysis On Functional Properties And Antioxidant Activity Of Rapeseed Protein

Nutrition and many functional properties of foods can be improvedby adding plant protein. Rapeseed protein is from rapeseed meal which iseasily prepared by oil extraction of rapeseed. Because of poor solubilityof rapeseed protein in water, its application in foods is limited. Acylationand enzymatic hydrolysis, which can change protein structure, areeffective ways to improve the water-soluble and other functionalproperties and to affect antioxidant activity and other bioactivities ofrapeseed protein.Due to the safety of acetylation and succinylation reagents, methodsof acetylation and succinylation of rapeseed protein and their effects onfunctional properties and antioxidant activity were studied in this paper.Results showed that the solubility of rapeseed protein in water could besignificantly improved by adding5%of anhydrides. The solubility ofacetylated rapeseed is2.8times that of the original protein at pH=7.0, andthe solubility of succinylated protein increased more significantly,reaching8.4times that of the original protein. As increasing the amountof anhydrides to20%, the solubility increased only a little further. Sameresults also showed in oil absorption and emulsification, i.e., small amount of anhydrides in reaction could change the structure of rapeseedprotein, improve its solubility, oil absorption and emulsificationsignificantly, with more effective results for succinylated protein thanacetylated protein in increasing solubility and emulsification. DPPHscavenging rate of rapeseed protein could be improved by acetylation andsuccinylation, with more effective results for succinylated protein. Theamount of anhydrides in reaction had little effect on DPPH scavengingrate.As enzymatic hydrolysis can cut protein molecules to increase thewater solubility, the effects of enzymatic hydrolysis with alcalase onfunctional properties and antioxidant activity of rapeseed protein wereinvestigated. Results showed that water solubility of rapeseed proteincould be significantly improved by enzymatic hydrolysis. The solubilityat pH=7was increased from7.32%for original protein to95.48%forhydrolysed protein at DH of22%. Oil absorption, foamability, emulsionstability and DPPH scavenging rate of rapeseed protein were increased byenzymatic hydrolysis. The enzyme immobilization is an effective methodto improve the utilization of enzyme and it can also cut the productioncosts. As the preparation of immobilized enzyme with gel as an carrier is a new method which has not been reported domestically, we study themethod including etherification, oxidation, immobilization and thehydrolysis of rapseed protein with the immobilized enzyme. NaOHconcentration and temperature are the main factors in etherificationprocess. Alkaline condition was favorable for the reaction between geland glycidol, but by-products would be produced if more alkaline waspresent. At acidic condition there were no reaction between gel andglycidol, so it is necessary to control the pH at etherification. Resultsshowed that the yield of reaction between gel and glycidol at roomtemperature was the highest when the concentration of NaOH was1M.Aldehyde could be produced when o-diol group in etherized gel wasoxidized with NaIO4. Immobilized enzyme could be prepared when thealdehyde reacted with amino group in the enzyme. Stability of theimmobilized enzyme could be improved by reduction reaction withNaBH4. Hydrolysis of rapeseed protein was better with the immobilizedenzyme when it was prepared by reaction between enzyme and gel for15h.In view that acylation and enzymatic hydrolysis both affect thefunctional properties and antioxidant activity of rapeseed protein, it is necessary to study the modification effects with the combination ofenzymatic hydrolysis and acylation. Experiments were carried out in twodifferent procedures: first enzyme hydrolysis then acylation and firstacylation then enzyme hydrolysis. Results showed that, compared withthe single use of acetylation or succinylation, the two combinationprocedures could both improve the functional properties of rapeseedprotein, such as solubility, foamability, emulsion stability and DPPHscavenging rate. The procedure of first acylation then enzyme hydrolysiswas better than the other. The combination procedures had similar effectson functional properties with the single use of enzyme except ofincreasing foamability and DPPH scavenging rate. Acylation changed thestructure of rapeseed protein, which influenced the position of enzymehydrolysis, resulting in different results of the two combinationprocedures.