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UBC Theses and Dissertations

Total antioxidant capacity, vitamin A and E, and fatty acid content of human milk Tijerina Saenz, Alexandra


Total antioxidant capacity (TAC) of human milk was used as a measurement to evaluate milk oxidative stability. The Oxygen Radical Absorbance Capacity (ORAC) assay was used to measure oxidative stability of human milk based on the advantages of the method, the photostability of the fluorescent probe fluorescein (FL), and the specificity for antioxidant activity against peroxyl radicals. The present study consisted of two sections; firstly to standardize and validate the ORACFL assay for use in determining TAC of human milk and second to determine potential relationships between different nutritional components and TAC levels o f mature human milk. The ORACFL assay was standardized and validated by determining the linearity, precision and accuracy of the assay and by determining an optimal dilution for human milk. Good linearity (R²>0.990) and precision (2.2%) were achieved and the assay accuracy was 95.4%, which was obtained by the recovery of Trolox standard after experimental analysis. Six different milk dilutions were used to evaluate milk TAC and a dilution of 200x was chosen for routine ORACFL analyses. A convenience sample consisting of human milk samples (n=77) was obtained from Canadian women at month 1 postnatally. Contents of milk fatty acids (FA), vitamin A (alltrans-retinol), vitamin E (α-tocopherol, [formula omitted]-tocopherol, and [formula omitted]-tocopherol), and TAC were measured and the biological activity of vitamin E and a total fatty acid unsaturation index (UI) were calculated. A total o f 60 milk samples were used in the final analyses, due to the presence of 17 samples with TAC values below detectable levels. According to the results, TAC of mature human milk was positively attributed to milk α-tocopherol (r= 0.439, p<0.001). Higher contents of α-tocopherol significantly increased milk oxidative stability. On the other hand, different contents of vitamin A or fatty acids or UI had no effect on milk TAC. These results suggested that oxidative stability of mature human milk could reflect the complex sum of different antioxidants and/or mechanisms, but confirmed the importance of the presence of antioxidants, such as vitamin E , in protecting against free radical-induced lipid peroxidation reactions.

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