Study On Delivery Systems For Curcumin Based On Whey Protein Isolate And The Effect Of Whey Protein Hydrolysate On Gelatinized Rice Starch Retrogradation

On the one hand,the retrogradation of gelatinized starch is primarily responsible for the decreased qualities and shelf-lives of starch-based foods.Inspired by the mixture of rice flour and infant milk powder in daily life and the inhibition on retrogradation of gelatinized starch by protein hydrolysate,one of the purposes of this study was to provide scientific insights into whey protein hydrolysate(WPH)as a potential anti-retrogradation additive for gelatinized rice starch(RS).On the other hand,the poor solubility,bad chemical stability,and low bioavailability limit the application of curcumin in food.Therefore,in this study,two curcumin delivery systems constructed by WPI were designed to solve these problems,including acid aqueous condition via WPI fibril and high internal phase emulsion(HIPE)stabilized by WPI.Besides,the formation process and mechanism of WPI fibril was also studied.Main conclusions are as follows:(1)WPH restricted the amylose leaching and swelling of RS,resulting in decreased peak viscosity and peak storage modulus;final viscosity and setback values were reduced as well,while breakdown value increased.With the increasing addition of WPH(3%-12%,RS based),the three-dimensional network density of freshly prepared starch paste gradually increased;the RDS and SDS contents in RS were significantly reduced,and the RS*contents were significantly increased(p<0.05).On retrogradation,the addition of WPH significantly reduced the hardness and molecular mobility of RS(p<0.05).The relative crystallinity of RS decreased from 13.82%to 10.44%,and the ratio of 1047 cm-1/1022 cm-1 decreased from 0.925 to 0.822.which may be attributed to the fact that WPH prevented the molecular associations and formation of hydrogen bonds among the starch polymer chains.The retrogradation kinetics was determined using the Avrami model and indicated that WPH could effectively inhibit the recrystallization of RS.These results above demonstrated WPH could be a potential anti-retrogradation additive for prolonging the shelf-life of rice-based foods.(2)WPI fibrils exhibited a delayed formation process(lag phase and growth phase)but no obvious difference in length and morphology when compared with ?-LG fibrils,which was mainly related to the influence of a-LA on the interaction between(3-LG molecules.With the reaction proceeded,the structure of WPI gradually unfolded and self-assembly;the surface hydrophobicity of protein increased significantly(p<0.05);there was no significant change in total and exposed free sulphydryl group contents.In terms of protease resistance,WPI fibrils were more sensitive to pepsin but it can last longer in trypsin.(3)The solubility of curcumin,which was almost insoluble in water,was greatly improved to 297.8 ?g/mL(400 ?g/mL added)via complexation with chitosan and WPF,and the dispersion stability at room temperature was improved as well.The hydrophobic groups of fibrils accounted for major binding sites of curcumin.Curcumin particles were attached to the surface of protein fibrils,forming a "core-shell"supramolecular structure;chitosan and fibrils combined with curcumin formed a bicontinuous polymer through electrostatic interaction and increased the repulsive force between fibrils,resulting in a delivery system with increased stability.Compared with curcumin alone,the complexes showed significantly improved antioxidant activity(DPPH radical scavenging activity and reducing power).Moreover,the delivery systems further provided opportunities for curcumin to release in the intestine.This potential vehicle may contribute further to introduce curcumin into fat-free acidic functional beverages.(4)After adding 0.1%of five kinds of anionic polysaccharides,a stable gel structure(three-dimensional network by WPI and polysaccharides)can be formed in HIPE even at a WPI concentration of 0.25%.At each WPI concentration,the addition of polysaccharides decreased the particle size of HIPE droplets and increased the gel strength and resistance to deformation,which was mainly attributed to increasing continuous phase viscosity and enhanced droplet-droplet interaction.At 1%WPI concentration,the addition of polysaccharides improved the water holding capability of HIPE;all HIPEs showed better thermal stability but poor freeze-thaw stability,however,the original structure of HIPEs with polysaccharides added could recover after homogenized again.Besides,the addition of sodium alginate significantly increased the stability and bioavailability of curcumin in HIPE samples to 66.8%and 82.0%(p<0.05),respectively.This indicates that HIPE constructed by protein and polysaccharide is a potential curcumin delivery system.