The Tunable Preparation And Emulsification Stabilization Mechanism Of Casein Hydrogel Particles

The soft gel particles have the advantages of both excellent emulsifying capacity and emulsifying stability,which could offer broad prospects in emulsion-based systems.However,the emulsifying mechanism of soft gel particles is still unclear,which limited their application in many aspects.Besides,no commercial food-grade soft gel particle products are available.In this research,we created food-grade soft gel particles with tunable properties with caseins.The influence of the ?-potentials,size and hardness on the emulsifying properties of casein gel particles and the related mechanism of action were investigated.The main results were as follows:The hardness of casein gel particles were adjusted by tailoring the crosslinking degree of casein molecules in the particles.On this basis,the emulsifying stability of casein gel particles with different hardness was investigated.The casein gel particles with hardness of 263.9±20.5?2036.2±189.4 pN/nm were achieved by adjusting the mass ratio of casein to genipin(50:1-5:1).The Turbiscan instability index of casein gel particle-stabilized emulsions with hardness lower than 315.8±17.2 pN/nm were higher than 8.75±1.25.In the range of 522.7±74.0?2036.2±189.4 pN/nm,the Turbiscan instability index of casein gel particle stabilized emulsions increase from 1.66±0.40 to 3.04±0.32 as the increase of the hardness.Particles with hardness lower than 315.8±17.2 pN/nm could be overly deformed at the oil-water interfaces,the oil-water surface coverage was lower than 60%,leading to the easier occurrence of coalescence and aggregation of the oil droplets than particles with higher hardness values Among the range of 522.7±74.0?2036.2±189.4 pN/nm,the interfacial tension increased from 14.3 mN/m to 19.6 mN/m as the increase of the hardness,indicating the adsorption capacity of casein gel particles was adversely proportional to the hardness values.This lead to the surface coverage decrease from 91.4±2.1%to 76.7±3.0%.The diameters of casein gel particles was tailored by modifying the self-assembly condition of caseins.On this basis,the emulsifying stability of casein gel particles weith different diameters were investigted.The casin gel particels with diameter of 53.7±8.4?87.1±10.4 nm were obtained by treating the casein micelles under high pressure.By adjusting the condition of caseins in different concentration of alcohol-water mixtures,casin gel particles with diameter of 160.4±7.6?393.8±22.4 nm were prepared.In the range of 53.7±8.4?393.8±22.4 nm,the Turbiscan backscattering intensity of casein gel particle-stabilized emulsions was positivelyg related to particle diameters.Among the range of 53.7±8.4?393.8±22.4 nm,the interfacial tension increase from 12.4 mN/m to 21.8 mN/m.Besides,the viscous modulus formed by the casein gel particles decreased form 19.56±2.27 mN/m to 9.15±1.41 mN/m.This lead to the easier coalescence and aggregation oil droplets as the increase of diameter.By adjusting the pH values,the casein gel particles with ?-potential of-1.7±0.5?-53.2±2.70 mV were obtained.When the ?-potential of casein gel particles were between-1.7±0.5?-10.8±6.0 mV,the casein gel particle stabilized oil droplets were easy to coalescence and aggregation.In the range of-17.3±5.2?-53.2±2±2.7 mV,the Turbiscan backscattering of casein gel particle stabilized emulsions increase with ?-potentials,indicating casein gel particles with higher ?-potential exhibited lower emulsifying stability.Casein gel particles with ?-potentials of-1.7±0.5?-10.8±6.0 mV will flocculation or precipitation,lead to the surface coverage lower than 19%.In the range of-17.3±5.2?-53.2±2.7 mV,the repulsive force was enhanced as the increase of ?-potentials(absolute value),the surface coverage decreased from 97.9±5.5%to 73.5±5.6%,resulting in the decrease of mechanical strength,and easier coalescence and aggregation of oil droplets.The emulsifying properties of casein gel particles were compared with two commercial emulsifying agents,including lecithin and sodium caseinate.The result confirmed the casein gel particles prepared in the research exhibit highest stability against coalescence and aggregation.All the results were explained in terms of the mechanical strength,adsorption ability and packing density at the water-oil interfaces.This research achieved the tunable preparation of food-grade soft gel particles.On the basis of this,the influence of the softness,size and ?-potentials of the particles on the emulsion stability and the mechanism of action were clarified.This research provided the theoretical basis for preparation of and application of food-grade soft gel particles.