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Zhang, Huiying

University of British Columbia

Curcuminoids are the major group of bioactive polyphenolic compounds isolated from turmeric (rhizome of Curcuma longa) that has been attributed to several bioactivities and health benefits. Within this group, curcumin (CUR) is the principal component that accounts for 77%; other major components are demethoxycurcumin (DMC) and bisdemethoxycurcumin (BDMC) that account for 17% and 3%, respectively. Some factors limiting the pharmaceutical and nutraceutical applications of curcuminoids include relatively poor water solubility, bioavailability and chemical stability. This thesis aims to compare the chemical- and cell-based antioxidant capacity of a random selection of commercial curcuminoid-based nutraceutical products with pure CUR, DMC, and BDMC standards (Chapter 2); emphasis was given to investigate the photochemical stability of CUR upon pulsed light (PL) treatment, an emerging light-based food processing technology, and to determine if the antioxidant capacity of curcumin would be affected (Chapter 3). Chemical-based antioxidant capacity was assessed by 2,2’-azino-bis-3-ethylbenzothiazoline-6-sulfonic acid radical cation (ABTS•+) and oxygen radical absorbance capacity (ORAC) assay, and cell-based antioxidant capacity was assessed by 2’,7’-dichloro-dihydro-fluorescein diacetate (DCFH-DA) and glutathione assays using a differentiated Caco-2 cell model. In Chapter 2, it was found that the chemical-based antioxidant capacity of curcuminoid supplements was positively correlated with total curcuminoid content and each of the individual curcuminoid content, and CUR showed the strongest correlation among the three major curcuminoids. The cellular antioxidant capacity in differentiated Caco-2 cells was more dependent on the formulation techniques used to manufacture the supplements. In Chapter 3, a positive correlation was found between losses of CUR content with the fluence of PL treatment within the tested range (0.14 – 12.75 J/cm²). However, fluence level and losses of CUR did not directly relate to losses in antioxidant capacity. When compared to the untreated control, PL-treated CUR at relatively high fluence levels showed a decreased chemical-based antioxidant capacity but an increased capacity to alleviate oxidative stress in differentiated Caco-2 cells. Tentative curcumin dimers were identified as potential photochemical transformation products of CUR by PL treatment. In conclusion, the application of PL on CUR can induce photochemical transformation of the compound, such as dimerization, and this may potentially enhance the biological antioxidant capacity.

Text

2024-01-31

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/83378

Food Science

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/