| Whey is a valuable by-product of cheese manufacturing process and casein production.Whey protein is one of high quality protein supplements because of high nutritional value,easy to be digested and absorbed,and its high bioavailability.With the development of dairy processing technology,whey protein is widely used as an ingredient in many traditional and novel food products primarily because of its high nutritional value and some desirable functional properties.However,there are still some limitations in the application of whey protein in food formulation.Excellent properties of whey proteins need to be developedfurther.High-intensity ultrasound has gained particular attention for utilisation in food industry.In addition to microbiological destruction effect,high intensity ultrasound technology has been used to enhance food protein quality in recent years.In order to further expand the application of whey protein,the presentstudy focuses on modification of whey protein,whey protein soluble aggregates and acid-induced gelation behavior of whey proteins by high intensity ultrasound.Whey protein-based systerm was studied for astaxanthin delivery.This dissertation includes the following aspects:(1)Modification mechanism of whey protein by high intensity ultrasound;(2)Modification mechanism of whey protein soluble aggregates by high intensity ultrasound;(3)Modification mechanism of acid-induced gelation behavior of whey proteins by high intensity ultrasound;(4)Physicochemical stability and cellular uptake properties of astaxanthin-loaded emulsions stabilized by whey proteins prepared by ultrasound;(5)Bioaccessibility,Uptake,and Transport of whey protein-astaxanthin nanodispersions.(1)Use of high-intensity ultrasound to modify certain functional properties of whey proteins is an alternative to traditional method in food industry.Whey protein isolate(WPI)solutions were treated with an ultrasound probe(20 kHz)at different intensities(20 or 30% amplitude)and durations(10 or 20 min).Results showed that ultrasound treatment changed physical and several functional properties of whey proteins including decreased particle size(from 190.4 nm to 138.0 nm),increased surface hydrophobicity(from 5.13×105 to 5.77×105),free sulfhydryl groups(from 52.64 ?mol SH/g to 53.64-58.77 ?mol SH/g),solubility(from 74.95% to 89.70%),emulsionactivity index(from 3.18 m2/g to 3.59-5.32m2/g)and emulsionstability index(from 62.26 min to 71.44-104.83 min),and changed viscosity(from 5.51 mPa.s to 4.81-5.64 mPa.s).Results indicated that high intensity ultrasound could be potentially applied to whey protein to improve its specific functions during food processing.(2)The aim of this study was to determine the effect of high intensity ultrasound on physicochemical and emulsifying properties of thermally aggregated of whey proteins.Whey protein isolate(WPI)solutions were sonicated for 20 min using an ultrasonic probe(frequency: 20 kHz;amplitude: 20%)pre-and post-thermal treatment(85oC for 30 min).Changes in particle size,zeta-potential,surface hydrophobicity,free sulphydryl group content,turbidity,thermal denaturation properties,rheological properties,and emulsifying properties were studied.Soluble aggregates prepared with ultrasound treated post-thermal aggregation resulted in significantly smaller particle size and broader size distribution compared with those prepared by untreated or ultrasound treated pre-thermal aggregation(P<0.05).It was suggested that surface hydrophobicity of the soluble aggregates was significantly increased by ultrasound applied post-thermal aggregation(P<0.05).There was a significant reduction in turbidity of whey protein solutions by ultrasound applied post-thermal aggregation(P<0.05).The apparent viscosity of whey protein soluble aggregate model systems has been decreased significantly by ultrasound pre-and post-thermal aggregation(P<0.05).Emulsionactivity index and emulsionstability index of soluble aggregates wereincreased significantly by ultrasound applied post-thermal aggregation(P<0.05).There were no significant changes in zeta-potential,total free sulphydryl group by ultrasound either pre-or post-thermal aggregation(P>0.05).We conclude that ultrasound treatment on post thermal aggregation has improving effect on physiochemical and emulsifying properties of whey protein soluble aggregates for potential industrial application.(3)Whey protein isolate solutions(10% w/v)were heated at 85 oC for 30 min and subjected to high intensity ultrasound treatments at different durations(20 kHz,40% amplitude,5-40 min).Then,the glucono-?-lactone was added into the solution to induce gel formation.Results showed that high intensity ultrasound disrupted the non covalent interaction of whey protein soluble aggregates.Ultrasound treatment reduced the particle size,increased surface free sulfhydryl groups of whey protein soluble aggregates,resulting in a more dense and uniform structure.Some reactive groups were encased in the compact structure,the non covalent interaction between proteins was reduced,and the water holding capacity and gel strength were increased by high intensity ultrasound.Frequency scanning showed that ultrasound treatment significantly increased the frequency dependence of WPI gel(P<0.05).Pearson correlation test showed that the particle size of whey protein soluble aggregates(WPISA)solutions was negatively correlated with water holding capacity,gel strength and gel firmness.Therefore,we conclude that high intensity ultrasound can be potentially applied to whey proteins to improve gelling properties including waterholding capacity(WHC),gel strength and gel firmness.(4)Use of astaxanthin in foods is currently limited because of its poor water-solubility,chemical instability,high melting point,and low bioavailability.Emulsions could be good carrier to improve the bioavailability of astaxanthin.Six different emulsifiers were used to prepare astaxanthin-loaded emulsions : WPI,PWP,WPI/Lecithin,PWP/Lecithin,Lecithin and Tween20.The results showed that the droplet size of the emulsion was from 194 to 287 nm and the particle size distribution was narrow(PDI<0.3).The entrapment efficiency was about 90%.Low temperature storage was more conducive to improve the chemical stability of astaxanthinin in the emulsions.High salt concentration(>200 mM)increased the droplet size of emulsions and had no impact on retention rate of astaxanthin.The emulsifier type had a strong impact on the degradation rate of astaxanthin.The emulsions showed no cytotoxicity and had good biocompatibility.Cellular uptake of astaxanthin in all samples increased with increasing incubation time,indicating a time dependent cellular uptake behavior.After 4 h of incubation,an emulsion stabilized with WPI showed the highest intracellular accumulation of astaxanthin(0.5 ?g),followed by that stabilized with PWP(0.42 ?g),WPI-Lecithin(0.30 ?g),PWP-Lecithin(0.25 ?g),Lecithin(0.17 ?g),Tween 20(0.11 ?g).The results suggested that emulsion significantly improved the cellular uptake of astaxanthin and potentially improved bioavailability.(5)Astaxanthin nanodispersions were produced using WPI and PWP through a solvent-evaporation technique.We then characterized the resulting astaxanthin nanodispersions in terms of their particle size,particle size distribution,zeta potential,encapsulation efficiency,flow behavior,apparent viscosity,and thermal properties.Transepithelial transport of astaxanthin was assessed by Caco-2 cell model.Astaxanthin nanodispersions were prepared with WPI and PWP at the concentration of 2.5%(w/w),with the particle size 121.3 nm and 80.4 nm,zeta potential-19.32 mV and-35.01 mV,encapsulation efficiency 92.08% and 93.46%,respectively.The DSC curves indicate that astaxanthin crystal had a endothermic peak around 222 oC,which should be the melting point of astaxanthin.WPI-astaxanthin nanoparticles and PWP-astaxanthin nanoparticles had no endothermic peak around 222 oC,which indicated that amorphous astaxanthin existed in the nanodispersions.The nanodispersions showed no cytotoxicity and good biocompatibility.The results indicated that delivery by a nanodispersion significantly improved the transepithelial transport cellular of astaxanthin and might potentially improve its bioavailability. |
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