Cheese Whey Protein Recovery By Polymerase Catalysis Coupling With Ultrafiltration And Membrane Fouling Mechanism Research

Dairy industry processing waste water recycling has not only limited to the traditional chemical method and the single membrane collection technology.The application of multiple technologies is the future development direction of the food industry.Although a series of ultrafiltration,nanofiltration and reverse osmosis equipments have constantly been used around the world,but due to the membrane fouling,high membrane cleaning frequency,and short service life of polyethersulfone membrane,which have greatly increased the production cost.This made many companies hesitate to use the membrane filtration.So the effective processing method is of great significance to improve protein recovery,reduce the pollution of the membrane,prolong membrane operation time and decrease the production cost for membrane technology.This study is to investigate whey protein aggregation by enzyme which could improve protein recovery rate,membrane flux and reduce the pollution of the membrane.Based on this study,the enzyme was covalently immobilized on the modified PES membrane surface to build enzyme membrane reactor(EMR).The membrane fouling model,interaction energy analysis and fractal theory were used to analysis the mechanism of membrane fouling.The characteristic and utilization of the membrane recovery whey protein were investigated in the study.There were four polymerases i.e.Horseradish peroxidase,Tyrosinase(EC 1.14.18.1),Laccases(EC 1.10.3.2)and transglutaminase(EC 2.3.2.13),which could catalyze different whey protein cross-linking.Single enzyme and combined enzyme were used to catalyze whey protein cross-linking coupling ultrafiltration.The relationship between protein aggregation and protein recovery rate and VCF was analyzed.The results showed that the single TG enzyme and combined enzyme(TG and tyrosinase)catalysis protein aggregate had higher protein recovery rate than control.The rodlike structure of TG catalysis protein could form loose cake on membrane surface making permeate flux increased through protein shape and membrane resistance and permeate relationship analysis.Then the relation between TG enzyme catalysis condition and filtration efficiency was determined.It was found that the optimal conditions for protein recovery involved catalyzing whey protein cross-linking with TG(40 U/g whey proteins)at 40 °C for 60 min at p H 5.0.Under these conditions,relative permeate flux was increased by 30~40%,the protein recovery rate,rejection rate was increased by 20% and lactose rejection rate was decreased by 10% compared to the sample without enzyme treatment(control).The total resistance and cake resistance were decreased at p H 5.0 enzyme catalysis condition.This was mainly due to the increased particle size and decreased zeta potential.This also made the membrane running time extended 10 h.There is no active bond to graft enzyme on the PES membrane surface.Therefore,the PES membrane surface was modified by MA firstly.This made the membrane surface had active bond to gaft enzyme such as carboxyl or ketone.Then the membrane was modified by MES,EDC and NHS to graft enzyme.The modified PES membrane surfaces were analyzed by FTIR and XPS to confirm that transglutaminase was successfully immobilized onto the membrane.The optimal condition of transglutaminase immobilization was 20 U/ml enzyme concentration and p H 5.0.The immobilized TG had high affinity to the substrate according to the kinetic parameters.It can retained 50 % activity after 20 days storage.When the tranmembrane pressure was increased to 0.2 MPa,the enzyme activity could still keep a certain activity.The water contact angle of transglutaminase immobilized membrane was obviously decreased,indicating that the hydrophilic of transglutaminase immobilized membrane and anti-protein fouling ability were improved.The membrane flux sharply decreased after transglutaminase immobilization.Therefore,increasing the molecular weight cut off of PES membrane to 30 k Da for immobilizing enzyme.Enzyme membrane reactor(EMR)can achieve enzyme catalysis and filtration separation simultaneously,and at the same time the immobilized enzyme realize the enzyme recycling in EMR.Based on the above research,enzyme membrane reactor was used to recycle enzyme and made the recovery rate increased to 85%.The membrane pore resistance was decreased by 80%,respectively.The membrane resistance and membrane fouling model analysis results showed that the standard filtration model could fit whey protein pure PES membrane filtration and enzyme membrane filtration without catalysis well.This means that a lot of protein was blocking the membrane pore making membrane permeate flux decreased and forming membrane irreversible pollution.Interaction energy analysis results showed that the attractive energy was very high during whey protein pure membrane filtration leading to the protein aggregate and deposit on the membrane surface forming membrane fouling.The repulsive energy was very higher between aggregation protein and enzyme membrane than attractive energy.So the protein deposition on membrane surface and membrane fouling was decreased.Fractal and collapse theory were used to describe the effect of protein shape and size on the porosity and permeate flux so as to control membrane fouling during whey protein filtration and improve membrane operation efficiency.Adopting the thermophilic streptococcus Sp1.1 and Bulgaria 34.5 two strains of lactobacillus strains for fermentation,the effect of different stabilizers and fermentation processes on protein beverage stability were investigated.The results showed that sodium phosphate and sodium pyrophosphate had no significant influence on the stability of whey fermented beverages.Two stabilizers XD2159 and XD2135 can better maintain the stability of whey fermented beverages.The deposition rate,particle size and Zeta potential of the final product were total reduced when 0.3% of stabilizer XD2159 added with a homogeneous pressure 200 bar before fermentation and homogeneous pressure of 150 bar after fermentation.Furthermore,when stabilizer XD2135 added 0.3% before fermentation,fermentation homogeneous pressure before 200 bar and homogeneous pressure of 150 bar after fermentation,no significant final product particle size reduced.However,Zeta potential decreased significantly.This meant that the electrostatic repulsion was increased.Therefore,the final product precipitation rate was reduced.Enzyme membrane reactor of concentrated protein liquid in spray drying,low protein nutrition powder,its nutrition and physical and chemical properties are studied.It was found that the enzyme cross-linked low protein nutrition powder has good emulsifying property and lower foaming property.Furthermore,the enzyme cross-linked low protein nutrition powder has good digestibility in vitro.