Enzymatic Modification And Emulsifying Properties Of Sugar Beet Pectin

Sugar beet pectin (SBP) is a polysaccharide derived from sugar beet pulp. SBP hasexcellent emulsifying properties except the relatively poor long-term stability ofemulsions stabilized by SBP, particularly at high temperature. This has restricted theapplication of SBP in the food industry. It is possible to use horseradish peroxidase andlaccase to cross-link SBP molecule and improve its emulsion stability by increasingmolecular weight. The present study investigated the effect of different factors (pH,H2O2, temperature and enzyme dosage) on the viscosity of SBP during modification andestablished the optimal conditions for modification. The molecular characteristics andemulsifying properties of modified SBP were investigated. The results were as follows:1. pH, H2O2concentration and HRP dosage were important factors influencing theenzymatic modification of SBP using HRP. The viscosity of HMSBP (HRP-modifiedSBP) reached a maximal value at pH6.5and1.0mM H2O2. The viscosity andmolecular weight (Mw) of HMSBP increased with increasing HRP dosage. A maximumMwof1.86×106Da, which was twice the initial Mw, was obtained at0.005U/mL HRP,meanwhile remaining good solubility. The optimal modification conditions of SBP byHRP were therefore pH=6.5, H2O2=1.0mM and HRP dosage=0.005U/mL.2. pH, temperature and laccase dosage were critical factors influencing theenzymatic modification of SBP using laccase. The viscosity of LMSBP(laccase-modified SBP) reached a maximal value at pH6.5and50oC. The viscosity andMwof LMSBP increased with increasing laccase dosage. A maximum Mwof5.74×106Da, which was26times than initial Mw, was obtained at0.0033U/mL laccase,meanwhile remaining good solubility. The optimal modification conditions of SBP bylaccase were pH=6.5, temperature=50oC and laccase dosage=0.0033U/mL.3. The droplet size of emulsions prepared by control SBP and HMSBP increasedcontinuously with storage time. The rate of droplet size growth was reduced withincreasing HRP dosage for HMSBP. HMSBP also demonstrated increased ability ofdelaying emulsion creaming. This indicated that modificatioin by HRP improved theemulsion stability of SBP. The modulus of MCT/water interface adsorbed with HMSBPwas increased with increasing HRP dosage.4. Compared with the relatively fast development of droplet size in emulsionsstabilized with control SBP, the emulsions stabilized with LMSBP had nearlyunchanged droplet size during storage. This is an indication of dramatical improvementof emulsion stability by modifying SBP with laccase. The modulus of MCT/waterinterface adsorbed with LMSBP was increased with increasing laccase dosage.5. Relative to HMSBP, LMSBP had better ability of stabilizing oil in wateremulsions. This was attributed to higher Mwand larger size of SBP modified by laccase,which formed a thicker interface layer around oil droplets, providing more effectivesteric stabilization to prevent droplet coalescence and flocculation.