Membrane-based Fractionation And Manufacture Of Bovine Milk Bioative Serum Proteins And Casein Micelles

Milk proteins,including whey proteins(WP)and caseins,which have important nutritional and physiological functions and are widely used in the processing of dairy products.Besides the major constituents including ?-lactoglobulin and ?-lactalbumin,WP also contains minor bioactive components such as immunoglobulin(Ig)G,Ig A,Ig M,lactoferrin(LF),lactoperoxidase(LPO)and xanthine oxidase(XO).These bioactive components often are thermal sensitivity.Traditional whey protein ingredients are derived from whey,a by-product of cheese processing,which undergoes multiple heat sterilization treatments during the production and processing process,which can easily lead to the inactivation of bioactive protein.In bovine milk,casein micells is formed by casein combining with mineral salts such as calcium and phosphorus,and the its are easy to form dense flocculation in acidic gastric juice environment,which inhibits protein digestion and degradation.The density of the flocculation structure of casein micelles is related to the amount of calcium ions binding.In this study,fresh cow milk was used as raw material to carry out research on the sterilization process of skimmed milk,the separation and preparation of native bovine whey proteins,and the preparation and digestibility of decalcified casein micelles.First,the effects of different sterilization processes on the quality of skim raw milk was studied.Effects of high-temperature short-time(HTST)pasteurization,microfiltration(MF)with 1.4 or 0.8 ?m pore diameters,and ultraviolet-c(UV-C)irradiation with a coiled tube reactor on the reduction of microorganisms and somatic cells,and the retention of bioactive proteins/enzymes and native serum proteins in skim milk were studied.Bacteria were reduced by 2.3 log using HTST and UV-C,and 3.0 log using MF.Coliforms were not detected after all treatments.Spores were unaffected by HTST,reduced by 0.3 log using UV-C,and not detected after MF.Somatic cells remained unaffected by HTST and UV-C,and were undetectable after MF.Bioactive xanthine oxidase(XO),immunoglobulin G(Ig G),lactoperoxidase(LPO),lactoferrin(LF),Ig M,and Ig A were retained at 87,78,69,57,48,and 41%,respectively,using HTST,and 100% using UV-C and 1.4 ?m MF,while 0.8 ?m MF retained fully the Ig G and LPO,and 93,92,91,and 86% of Ig A,XO,LF,and Ig M.Native serum proteins were retained at 89% using HTST,95% using UV-C,and completely using MF.Carbonyls were increased by26% using UV-C,and sulfhydryls were reduced by 14% using HTST,while both were no significant effect.using MF.Therefore,1.4 ?m microfiltration was selected for further study.Second,whey protein powder with native bioactive ingredients was producted by non-/low-thermal process.Effects of pore diameters(100,50,20 nm),concentration factors(1-8)and processing stages(1-5)on transmission of major serum proteins(?-lactoglobulin and ?-lactalbumin)and minor serum proteins(Ig G,Ig A,Ig M,LF,LPO,XO)during ceramic microfiltration(MF)of skim milk were studied.For MF with 100 and 50 nm pore diameters,the recovery yield of major serum proteins in permeate was 44.3% and 44.1%,while the recovery yield of minor serum proteins was slightly by 0-8% than 50 nm MF.Flux sharply decreased with increasing concentration factor(CF)up to 4,and thereafter remained almost unchanged.,The CF had little effect on the transmission of whey protein.With increasing processing stages,the flux gradually increased,and the recovery yield of whey proteins in the permeate gradually decreased.Compared with spray drying and freeze drying,low-pressure spray drying had less effect on whey protein and can achieve the effect of freeze drying.Finally,the retentate,the casein micelle fraction,produced by the whey separation,which was subjected to ion-exchange treatment to prepare decalcified casein micelle powder,and then the digestibility study is carried out by infant model in vitro.When the calcium of casein micelles was reduced by 36.1%,the structure of casein micelle had basically been dissociated,and the free casein accounts for more than 90% of total casein.With the increase of the decalcification rate,the clot of casein micelle gradually became smaller and the digestibility gradually became better.In summary,raw shim milk was filtered by 1.4 ?m ceramic membrane,the removal efficiency of microorganisms and somatic cells was better than that of HTST treatment,especially,the bioactive proteins/enzymes in milk almost completely retained.Native whey proteins proteins was by small pore-size microfiltration,ultrafiltrationand and low-pressure spray drying,which could significantly protect the active protein content in WP.The casein micelle powder,drvied the by-products of whey protein separation by small-pore microfiltration,was prepared by ion-exchange and spray drying,which can significantly improved digestibility of casein micelle.