Resumen de Investigation of the antioxidant properties of five aromatic plants in model food systems
Nurul Aini Binti Mohd Azman
In this PhD it has been analyzed the antioxidant activity of five plants: Camelia sinensis, Gentian lutea, Betula pendula, Convolvulus arvensis and Arctostaphylos uva-ursi. An Electronic Paramagnetic Resonance has been tuned up to determine the antiradical activity of white tea against the methoxy radical using ferulic acid as a standard. It has been proven that the components with more antiradical activity, against the methoxy radical, are the ones with the gallate group, EGCG and ECG. Active ingredients of the Gentian root have been obtained with hydroalcoholic extraction and their antioxidant activity has been demonstrated in both in vitro methods and food models. The antiradical activity of such extracts was determined by FRAP, DPPH, TEAC and ORAC assays. The lyophilized extract, added to the ecological beef meat in a proportion of 2% (by mass), inhibited the meat oxidation (measured by TBARS assay) in high oxygen content atmospheres (80% in volume) as well as in low oxygen content ones (20% in volume). The simultaneous addition of ascorbic acid (0.5% by mass) resulted in significant improvements in color and stability. The lyophilized extract (0.5% by mass) also inhibited oxidation in model systems, oil-in-water emulsions, stored in forced oxidation conditions and constant agitation. The protein BSA addition (0.1% by mass) showed synergic effect and increased the emulsion stability against oxidation. HPLC quantitative analysis found that gentian contained secoiridoid-glycosides (gentiopiocroside and sweroside) and the post-column addition of ABTS cationic radical demonstrated the scavenging activity of each of its compounds. For Convolvulus and Betula, the effect of the solvent polarity in the total polyphenol extraction (by the Folin Ciocalteau assay) was determined. The 50% ethanol extract was the best performer. The scavenging activity of the Convolvulus extract was analyzed by TEAC, FRAP and ORAC assays and against methoxy radical (by EPR). Furthermore, lyophilized extract was added to minced meat hamburgers in different proportions (0.1 and 0.3% by mass). They were stored in a modified atmosphere (80% of O2 and 20% of CO2). Lastly, an edible gelatin film, with Convolvulus extract, was designed. All the assays showed capacity to protect the hamburgers against oxidation. The antiradical activity of the Betula extract was also determined by TEAC, ORAC and FRAP assays and against methoxy radical (by EPR). Some of its phenolic acids were identified by HPLC. Hamburgers, with a proportion of 0.1% and 0.3% by mass of the lyophilized extract, were made and stored under refrigeration (4ºC) and in a modified atmosphere (80% of O2 and 20% of CO2). Colour and percentage of metmyoglobin changes were analyzed as well as the oxidation degree (by TBARS assay). Both percentages provided significant improvements in all the studied parameters. The last part of this thesis was focused in the study of Arctostaphylos uva-ursi. The scavenging activity against ABTS+ and methoxy radical was determined (by EPR). A percentage of 0.1% by mass of the lyophilized extract was added to oil-in-water emulsions. Oxidation was measured by VP and TBARS. There was a significant delay in oxidation. Extract was incorporated to edible gelatin films with 0.1% by mass. If such a film protects the hamburger, its life is increased. In conclusion, all five plants presented in this study have antioxidant activity (in the used proportions) that made them suitable to formulate new foods, more stable over time against oxidation without using the controversial synthetic antioxidants. Moreover, they will be able to provide additional advantages (incorporating natural antioxidants), which would provide functional foods.
