Interfere With Casein For The Formation Of Whey Protein Concentrate Fibrils And Their Properties

Formation of β-lactoglobulin or WPI fibrils at unconventional conditions (low pH and ionic strength) had already been studied, mainly focusing on the formed mechanism and the polymerization conditions. Research were wanting in interfere of complex protein components on fibrils formation. Casein,as a main based component of milk protein, is crucial to effects and the formation of whey protein fibrils. Therefore, the aim of project was to research the formation of aggregates by adding casein to WPC at different periods of the heat-induced formation of WPC fibrils, In addition, we studied the effect of casein on formation of WPC fibrils(microstructure and ThT), polymerization capacity, the differences of main force (surface hydrophobicity and free sulfydryl group) between whey-casein fibrous polymers and non-fibrous polymers,and the differences of functional properties (foaming, emulsifying and gelation properties). We hope that the whey-casein polymers could improve or expand the applications of milk protein. Our main results were as follows:Interference of casein on the formation of WPC fibers Structure of polymers were determined by time of adding casein during periods of the heat-induced formation of WPC fibrils. When casein was added to WPC during nucleation period,structure of WPC fibrils were severely damaged; It has some impacts on structure of WPC fiber when casein was added in growth; the effect is little and structure of WPC fiber were well when casein was added in ending. A sort time of adding casein(1.5wt%～3.5wt%) was identified0h,0.83h,1.5h, B sort time was identified2h, C sort time was identified3-9h. Whey-casein fibrous polymers could form when casein were added to WPC heating for3h. A sort time of adding casein(6.0wt%) was identified Oh,0.83h,1.5h, B sort time was identified3h and4h, C sort time was identified5-9h. Whey-casein fibrous polymers could form when casein were added to WPC heating for5h Adding casein is easlier, inhibition on the formation of the WPC fibers is more obvious. Simultaneously, if adding high concentration of casein, time of adding casein, affecting formation of whey-casein fibrous polymers, would be postponed.Major force The differences of structure between whey-casein fibrous polymers and non-fibrous polymers are related to major force of aggregation. The results indicated that major force of the whey-casein (the ratio is1.7:1)aggregations is hydrophobic interaction in pH2.0. If disulfide bonds formed are too much, the fibrous structures of hybrid polymers will be destroyed.The major force of the whey-casein fibrous polymers (C sort) is hydrophobic interaction, variable rate of surface hydrophobicity of the polymers was1.67times compared with at Oh adding casein, and also44.47%compared with2.0wt%WPC fibrils. Variable rate of surface hydrophobicity of the non-fibrous polymers was38.64%compared with2.0wt%WPC fibers, while variable of disulfide bonds of the former was1.64times compared with the latter.Kinetic parameters for whey protein with casein micelles Characteristic of whey-casein fibrous polymers:mixed caseins were the later (after5h mixing), the polymerization rate constant k was smaller. Most whey proteins had initially formed fibrils in the early stage, caseins only assemble with small amounts of whey protein, aggregation mainly occurs on surface of fibrils structure. Conversely, mixed caseins early, the polymerization rate constant k was greater. The amount of polymerization of the whey proteins with caseins was increasing, which damages framework of fibrils and weakens interaction the between whey protein and whey protein. Finally, the hybrid fibrils can not be formed.Functional properties Compared with the conventional whey-casein(the ratio is1.7:1) aggregations(pH6.5), the whey-casein aggregations(pH2.0) have higher functional property, the foaming capacity and the foam stability increasing approximately15%,296%, respectively, while their emulsifying activity increasing about31.0%. At pH2.0, the involvement of casein made he interfacial properties mostly increased:1) intervention of caseins had a slight boost in foaming ability compared with WPC fibrils, emulsifying activity increasing about32.6%, emulsifying stability improveing about19.3%;2) Compared with aggregations by adding other concentration of caseins to WPC, aggregations by adding low concentration of casein had boost in foaming and emulsion property, the foaming capacity of aggregations by adding1.5wt%casein (the ratio whey:casein is4:1)increasing slightly than6.0wt%casein(1:1), foaming stability improving17%, the emulsifying activity improving about50.4%, emulsion stability improving86.5%;3) Interfacial properties of whey-casein fibrous polymers precede to non-fibrous polymers,the foaming capacity of aggregations by adding casein to WPC heating for9h increased slightly than Oh, the foam stability enhancing23.6%. While for emulsification, when the ratio whey proteins to caseins is (1.7-4):1, the emulsifying activity of fibrous polymers by adding casein at9h increasing approximately10.8%than Oh, the foam stability enhancing36.2%. When the ratio whey proteins to caseins is1:1, the emulsifying activity of aggregations by adding casein at2h increasing approximately8.0%than0h. Furthermore, adding casein to WPC (the ratio is1:1)heating for2h and continuing to heat for1h, heat-induced gels were formed at only4.0wt%protein concentration.