GIDALARDA BULUNAN SERBEST VE BAĞLI DOĞAL ANTİOKSİDANLAR ARASINDAKİ ETKİLEŞİMLERİN BELİRLENMESİ
Çelik, Ecem Evrim
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This thesis study aimed at investigating the interactions between free and macromolecule- bound antioxidants naturally occurring in foods, to estimate the possible status of antioxidant environment when they are found together. Chemometric tools were used both at the experimental design and multivariate data analysis steps. Dietary fiber (DF), protein and lipid-bound antioxidants, obtained from whole wheat, soybean and olive oil products, respectively and Trolox were used for this purpose in the first and second parts of the experimental studies. In the first part, antioxidant capacity (AC) measurements were performed in aqueous ABTS radical medium by monitoring the absorbance in the presence of Trolox and macromolecule-bound antioxidants. Results revealed antagonistic interactions for Trolox with all macromolecule- bound antioxidants. The reason behind this antagonism was investigated through oxidation reactions of Trolox via mass spectrometry analysis. Consequently, a proof was obtained for inhibitory effect of bound-antioxidants on auto-regeneration reactions of Trolox. In the second part, experimental studies were carried out in an autoxidizing liposome medium by monitoring the inhibition of lipid oxidation via antioxidants. Results revealed synergistic interactions for DF and refined olive oil-bound antioxidants, and antagonistic interactions for protein and extra virgin olive oil-bound antioxidants with Trolox. A generalized version of logistic functions was successfully used for modelling the oxidation curve of liposomes. Principal component analysis revealed two separate phases of liposome autoxidation. Experiments in the third and fourth parts were performed with a structural approach to enlighten the mechanism behind the interactions of free and macromolecule- bound antioxidants. In the third part, the interactions between whole wheat (WW) DF- bound antioxidants and hydroxycinnamic acid/ hydroxybenzoic acid (HCA/ HBA) derivatives containing different amounts of –OH and -OCH₃ groups localized at different positions on their aromatic rings were investigated. Studies were performed in liposome and aqueous media by monitoring lipid oxidation and scavenging of DPPH radical respectively, in the presence of WW- bound antioxidants and HCA/ HBA derivatives. Predominantly synergistic interactions were observed in aqueous medium, while both synergistic and antagonistic interactions were seen in liposome medium. Behaviors of HCA/ HBA derivatives, linked with their substitutions were revealed. In the fourth part, the interactions of coffee and bread crust melanoidins with HCA/ HBA derivatives were investigated. Experimental studies were carried out in aqueous DPPH radical medium by monitoring the scavenging of radical via melanoidins and HCA/HBA derivatives. Synergistic interactions were revealed for both coffee and bread crust melanoidins with HCA/HBA derivatives. Phases of the radical scavenging reactions were revealed from the loadings plots. In the fifth part, the interactions between insoluble fractions of different coffee infusions and major cocoa free antioxidants, catechin and epicatechin, as well as the interactions between different coffee infusions and dark chocolate were investigated. Espresso, filtered coffee, French press, and Turkish coffee were the coffee infusions used for this purpose. Antioxidant capacity measurements were performed in DPPH radical medium, by monitoring the absorbance in the presence of antioxidant components. Results revealed synergistic interactions for the insoluble fraction of espresso, and additive/antagonistic interactions for the insoluble fractions of rest of coffee infusions with catechin and epicatechin. Interactions between coffee infusions and chocolate were synergistic for French press and Turkish coffee and additive/antagonistic for the rest of coffee infusions.