The Preparation And Application Of Phosphorylated Polymerized Whey Protein Concentrate As A Fat Replacer

Whey protein applications in food formulation are often used due to its rich nutrition and biological functions.Heat-induced polymerization and phosphorylation have been known to improve the nutritional and functional properties of proteins.This study aimed to prepare phosphorylated polymerized whey protein concentrate(PPWPC)as a novel fat replacer for low-fat dairy product formulation.The combination of heatinduced polymerization and phosphorylation not only improved the functionalities of whey protein,but also controlled the particle size distribution to meet the requirements of being a fat replacer.Further more,the PPWPC improved the texture,sensory properties,nutritional value of low-fat yogurts,which would meet the demands of consumers for functional food with low calories and low-fat content.According to the animal toxicology test,the PPWPC was proved atoxic and suitable to be applied in lowfat dairy production as a food additive.Heating whey protein in alkaline conditions is usually accompanied with the formation of a harmful cross-linking amino acid--lysinoalanine(LAL),which could reduce the protein nutritional value and may cause safety concerns.In order to improve the safety of whey protein,the study investigated the inhibiting effect of sodium tripolyphosphate(STPP)on the formation of LAL,and the results demonstrated that the LAL was an effective inhibitor.The combination of thermal modification and phosphorylation was adopted to produce PPWPC using whey protein concentrate(WPC80)as raw material and STPP as phosphorylation agent,and then the STPP inhibiting effect on LAL was studied,the functional properties(including solubility,water-holding capacity,emulsibility,emulsifying stability and gell viscosity),particle size distribution,toxicological safety,and the application of PPWPC in the low-fat yogurt were also investigated.The specific conclusions are as follows:1.During the thermal polymerization and phosphorylation processes,the extent of phosphorylation was increased with the increase of the STPP content.When the STPP was more than 0.6%(w/w),the extent of phosphorylation seemed to be saturated.Increase the heating temperature(70-85 oC),or prolonging the heating time(5-25 min)properly,would inprove the extent of phosphorylation.When the p H was between 7.5 to 8,the extent of phosphorylation reached its highest.STPP improved the solubility,water-holding capacity,emulsibility,emulsifying stability and gell viscosity of polymerized whey protein significantly(p < 0.05).2.The contents of whey protein and STPP,p H,heating temperature and time affected the particle size distribution of PPWPC.The size distribution of PPWPC met the requirements of being a fat replacer by controlling the reaction conditions.The results showed that higher STPP levels(> 0.5%)or heating for longer time(> 15 min)or at higher p H values(8-8.5)facilitated formation of larger particles(> 10 ?m).The PPWPC in desirable particle size distribution(40% of particles in the range of 1-3 ?m)was obtained by heating the WPC solution(8%,w/v)with appropriate STPP content(0.4%,w/w)at 85°C for 5 min at p H 7.5.The low-fat yogurt incorporated with PPWPC had comparable microstructure,texture characteristics,and sensory properties to the full fat yogurt,but better than the low-fat yogurt with no fat replacer.Results indicated that thermal processing of WPC with STPP can produce aggregates that are suitable to be applied as a fat replacer for low-fat dairy products.3.After investigating the effect of the protein content(8%-10%,w/v),p H(7.5-8.5),heating temperature(70-85oC)and time(5-20 min)on the degree of LAL formation in whey protein concentrate solutions,the results showed that the LAL content was increased significantly(p < 0.05)when the protein concentration,p H,heating temperature and time were increased(> 10 min).However,addition of STPP(~0.6%,w/w)reduced LAL content by 35.5%.The data indicated that STPP could effectively inhibit the LAL formation during thermal treatment of WPC at high p H values.4.The toxicological safety of PPWPC was comprehensively evaluated according to the acute oral toxicity test,genetic toxicity test,and oral toxicity testing for 28 days.The results of acute oral toxicity test showed that no SD rat was dead when the dose reached the maximum value 20 m L/Kg.bw(22g/Kg.bw),and no exceptional cases happened about the body weight,food intake,and clinical manifestation.The results showed that LD50 value was more than 5000mg/Kg.bw,which indicated the PPWPC was non-toxic according to the national standard.The results of Ames test showed that,no matter whether the S9 liver tissue homogenate was added in or not,PPWPC in the range of dose(0.008mg/petri dish~5mg/petri dish)showed no mutagenicity for histidine defect type strain like TA97 a,TA98,TA100,and TA102.The cell micronucleus test results showed that PPWPC did not improve the micronuclei rate of polychromatic erythrocytes of SD rat bone marrow.The results of sperm malformation test demonstrated that PPWPC had no teratogenic effect on SD rat.Therefore,PPWPC was considered as a nontoxic food additive for food production.In conclusion,this study layed the foundation for the preparation,functional properties,toxicology and application of PPWPC as a fat replacer.