الفهرس 
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Abstract
Tarek Nour Soliman. “The Use of Whey Protein Hydrogel as Potential Encapsulation Matrix for The Delivery of Bioactive Compounds”. Unpublished Ph.D. Thesis, Department of Food Science, Faculty of Agriculture, Ain Shams University, 2016
Many natural bioactive compounds bear various health-promoting benefits and can be incorporated in functional foods. The utilization or the bioavailability of the compounds in human body is usually not taken into consideration in the process of food formulation. In this Ph.D. study, the effect of pH on hydrogel formation and the problems of the poor bioavailability of polyphenols, such as curcumin, and Selenium (Se) which has been recognized as an essential nutrient limits their utilization. In addition at high concentration selenium can become toxic. The difference between the concentration in which selenium can be essential or toxic element at is very narrow. The two problems have been addressed by complexion with delivery systems micro and nanoscale.
The effects of pH and added curcumin and selenium of the textural properties and microstructure of whey protein isolate (WPI) gels were investigated. WPI gels were prepared at pH 4-9, without and with the addition of one mg curcumin or one mg selenium / g protein respectively. The texture profile (TPA), and viscoelastic properties of the prepared gels were determined, and the gels microstructures were examined by scanning electron microscopy. All TPA parameters and viscoelastic measurements were affected significantly by changing pH. Gels prepared at pH 5 were characterized by harder texture than that prepared at higher or lower pH values. Addition of curcumin (CCM) or selenium (Se) had no significant effects on TPA or viscoelastic measurements of the gels. Gels prepared at pH 4 -6 were characterized by coarser microstructure than those prepared at higher pH values. Apparent changes in the gel microstructure occurred on addition of curcumin and selenium at pH 4-6 being less coarser than WPI gels without their additions.
Micro particles from WPI-CCM and WPI-Se complexes were prepared under different conditions. Fourier Transform infrared (FT- IR) spectra showed significant interaction between WPI and CCM or Se. The micro encapsulation efficiency (EE) of curcumin and selenite with WP was found to more 98.32%. Swelling ratio (SR) reached the maximum swelling at pH 10, while SR reached the minimum swelling at pH close to the pI of whey proteins (~5.4). The release of curcumin and selenium from WP microparticles was 0.74% and 0.76%. over a period of 12 hrs under acidic conditions of pH 2.0 in the simulated gastric fluid (SGF). While under neutral pH conditions in simulated intestinal fluid the release about 56% of curcumin and 60.28% of selenium at same condition. Scanning electron microscopy (SEM) micrographs of WPI- CCM and WPI-Se microparticles showed spherical particles with wrinkled surface without cracks or disruptions at pH 7, 8 and 9, while at pH 4 the particles resembled structured protein gels with an opaque appearance.
Nanoparticles of whey proteins were prepared with the aim of developing a biocompatible carrier for the oral administration of CCM and Se as a nutraceuticals and to enhance their solubilization and bioavailability. Nanoparticle preparations and its use as a vesicle were characterized for particle size and zeta potential; encapsulation efficiency and in vitro CCM and Se release of WPI nanoparticles. Zeta potential of WPI nanoparticles went from positive value of 12.7 mV at pH 4 to negative values with WPI-CCM and WPI-Se nanoparticles of -13.1 and -17.2 mV respectively. At other pH values i.e. 5, 6, 7, 8 and 9 WPI nanoparticles had negative charges which were increased in WPI-CCM and WPI-Se nanoparticles under the same pH conditions. No significant differences were found in encapsulation efficiency of CCM and Se into WPI nanoparticles prepared at different pHs. All had similar encapsulation efficiency with different CCM and Se ratio at various pH values nearly100%.
Finally, the results indicated that the fortification with micro or nanoparticles of CCM and Se were improved organoleptic properties of resultant yoghurt.
Keywords: Whey protein isolate, Hydrogel, Microparticles, Nanoparticles, Curcumin, selenite, Functional yogurt.