Thesis (Ph. D.)--University of Hong Kong, 2002. / Includes bibliographical references (leaves 167-219).

abstract / Biological Sciences / Doctoral / Doctor of Philosophy

This thesis is an investigation of binding of casein micelles to polyphenols such as epigallocatechin gallate (EGCG), resveratrol, and curcumin. The incorporation of the bioactive molecules in casein micelles seems to be beneficial. The results from this study clearly demonstrated that casein micelles can incorporate polyphenols. There is a difference in the binding behaviour between curcumin and resveratrol. Curcumin is able to penetrate the core of the micelles, but resveratrol has less affinity for the hydrophobic sites, instead, it can be bind in the core of the micelles through the water channels. The processing of milk (heating, cooling, static high pressure and microfluidization) alters the surface or the internal structure of the casein micelles resulting in increased incorporation. The release of β-casein caused alteration to the core of the casein micelles, without any effect on the colloidal calcium phosphate composition and any changes in the surface properties of the micelles. These internal rearrangements lead to an increase in the affinity of the hydrophobic sites for curcumin and resveratrol in the inner core of the micelles. This work clearly confirmed that β -casein plays a role in stabilizing internal structures in the casein micelle and its release causes an increase in the micellar size by increasing the hydration and repulsion occurring within the water pockets present in the inhomogeneous inner structure of the casein micelles. Inner core of casein micelles undergoes rearrangements during application of static high pressure and microfluidization. In the case of static high pressure, the results indicated that the persistent rearrangement of the amino acid residues induced by high-pressure treatment result in an increase in the amount of curcumin association with milk proteins. It was shown that in both untreated and microfluidized milk, the presence of polyphenol molecules significantly affects rennet induced gelation, by delaying the gelation. However, the behavior of casein micelles incorporated with resveratrol is different comparing to curcumin, as resveratrol strongly affected the surface interactions during rennet-induced gelation. Further research is needed to explain the practical aspect ( functionalities such as acid gelation, emulsification and foaming) of application of casein micelles as natural nanocarrier of bioactive compounds. / The National Sciences and Engineering Research Council (NSERC),The Ontario Dairy Council.

No description available.

Thesis PlanA (M.S.)--University of Wisconsin--Stout, 2008. / Includes bibliographical references.

Thesis (M.S.)--Oregon State University, 2011. / Printout. Includes bibliographical references (leaves 75-80). Also available on the World Wide Web.

No description available.

No description available.

Mushroom polyphenol oxidase (EC 1.14.18.1) was investigated to determine its potential for application as a biocatalyst in the synthesis of o-quinones, in organic medium. In order to determine the kinetic properties of the biocatalyst, a system was devised which comprised an immobilised polyphenol oxidase extract, functioning in chloroform. The system was hydrated by the addition of buffer. A simple method for the consistent measurement of reaction rates in this heterogenous system was designed and used to obtain detailed enzyme kinetic data relating to optimisation of reaction conditions and substrate specificity. The aqueous content of the system was optimised using p-cresol as a substrate. A crude, immobilised extract of Agaricus bisporus was used to hydroxylate and oxidise a range of selected p-substituted phenolic substrates, yielding, as the sale products, o-quinones. These products were efficiently reduced to catechols by extracting the reaction mixtures with aqueous ascorbic acid solution. The biocatalytic system was also successfully utilised to produce L-DOPA, the drug used to treat Parkinson's disease, from L-acetyl tyrosine ethyl ester (ATEE). Michaelis-Menten kinetics were used to obtain apparent Km and V values with respect to the selected phenolic substrates, and the kinetic parameters obtained were found to correlate well with the steric requirements of the substrates and with their hydrophobicity. In the course of the investigation, a novel ¹H NMR method was used to facilitate measurement of the UV molar absorption coefficients of the o-quinones in reaction mixtures, thus avoiding the necessity to isolate these unstable, water-sensitive products. The biocatalytic system was extended to a continuous process, in which the immobilised enzyme was shown to function successfully in the chloroform medium for several hours, with high conversion rates. Modifications, involving partial purification and the addition of a surfactant, were investigated to determine their effect on the kinetic parameters. The results obtained using partially purified enzyme indicated that the removal of extraneous protein and/or melanoid material lead to a reduced capacity for conversion of sterically demanding substrates. The addition of the anionic detergent, sodium dodecyl sulphate (SOS), enhanced the ability of the biocatalyst to bind and oxidise sterically demanding substrates. These effects are attributed to changes in the polar state of groups within the protein binding pocket, which result in altered flexibility and hydrophobicity. Computer modelling of several biomimetic dinuclear copper complexes also indicated the importance of flexibility for effective biocatalysis. Novel binuclear copper (II complexes, containing a flexible biphenyl spacer and imidazole or benzimidazole donors, were prepared and analysed using NMR, UV, AA and cyclic voltammetric techniques. The complexes were also shown, in a detailed kinetic study, to mimic the catecholase activity of polyphenol oxidase by oxidising 3,5-di-tertbutylcatechol, and to catalyse the coupling of the phenolic substrate 2,4-di-tert-butylphenol. However, the complexes were apparently too flexible to react with smaller substrates. These biomimetic complexes provided valuable insights into the nature of the dinuclear copper binding site.

The distribution of anthocyanin pigments and polyphenolics of sweet (Prunus avium) and sour cherries (Prunus cerasus) were determined by Ultraviolet- Visible (UV-Visible) spectrophotometry and High Performance Liquid Chromatography with photodiode array detector (HPLC-DAD). Their antioxidant properties were determined by Oxygen Radical Absorbance Capacity (ORAC) and Ferric Reducing Antioxidant Power (FRAP). The effect of frozen storage, canning, and brining on those properties was measured. Experiments were conducted on three sweet cherry cultivars; Bing, Rainier, Royal Ann and one sour cherry cultivar; Montmorency. Cherries were separated into skins, flesh, pits, and pitted cherries for subsequent analyses. Bing had the highest anthocyanin pigments (60.6 mg/lOOg fw) while Montmorency had both the highest total phenolic content (5.6 mg GAE/g fw) and the highest antioxidant activities (ORAC 51.02 μmoles Trolox equivalent (TE) /g fw, FRAP 47.96 μmoles TE/g fw). Hydroxycinnamates predominated in sweet cherries (70-80%) while flavanols were the major class of polyphenolics in sour cherries (70%). The major anthocyanins in sweet and sour cherries were cyanidin-3-rutinoside and cyanidin-3- glucosylrutinoside, respectively. Skins contained the highest amount of anthocyanins, polyphenolics, and antioxidant activities. Anthocyanins and flavonol glycosides predominated in cherry skins. Bing cherries were different from the others in that it had substantial anthocyanins in flesh and pits. The proportion of flavanols increased from skins to pits. Pitted Bing cherries were frozen and stored at -23 and -70°C for 3 and 6 months. Pitted Bing cherries were also canned in light syrup and stored at 2 and 22°C for 5 months. Both Bing and Royal Ann cherries were brined in bisulfite for one year. In all processing experiments, polyphenolics were more stable than anthocyanins. Degradation of hydroxycinnamates occurred during frozen storage and canning while flavonol glycosides were relatively stable. With both canning and brining, anthocyanins and polyphenolics leached into syrup and brine. With brining, hydroxycinnamates and flavonol glycosides disappeared, and unidentified compounds with UV-Visible spectra similar to flavanols were formed. Unidentified compounds possessed antioxidant activity. Cherry skins are high in anthocyanins, polyphenolics and antioxidant properties. Cherry pits and spent brine solution may be a potential source for natural colorants, nutraceuticals, and natural antioxidants. / Graduation date: 2004