| dc.description.abstracteng | Vegetables contain health-promoting compounds, such as vitamins, phenols, and minerals. To assess the potential health benefits, this thesis investigated interactions between individual compounds and their performance in mixtures during thermal processing in model experiments. These results were applied to Urtica dioica L., Aegopodium podagraria L., both neglected wild vegetables, and Amaranthus L. leaves, which were cooked as vegetables and enriched in wheat-rolls.
In model experiments, in presence of iron the 2:1 ratio of ascorbic acid and 5 caffeoylquinic acid had strong synergistic effects on the antioxidant activity measured by TEAC, DPPH, and TPC, whereas strong antagonistic effects were observed in the 1:2 ratio. A caffeoylglucaric acid isomer, identified by NMR spectroscopy, and 5 caffeoylquinic acid had similar antioxidant activity, whereas caffeic acid, the assumed bioactive part of both, had a lower antioxidant activity. Added iron can influence the antioxidant activity of the tested substances by complexation. However, other minerals that occur naturally in plants, measured with an ICP, can form a variety of complexes. In closed microtubes, the antioxidant activity of oven-dried A. podagraria L. increased after cooking, whereas of U. dioica L. did not. In model experiments, 5 caffeoylquinic acid protected quercetin-3-rutionoside from degradation, by adding it to U. dioica L. and A. podagraria L. this effect was not detectable. For these species, fridge-storing resulted in the lowest antioxidant activity, compared to not stored and freezer stored samples. The freeze-dried Amaranthus L. genotypes did not differ in their antioxidant activity, neither in cooked nor uncooked samples. However, household cooking experiments, showed that leaching into the cooking water can be neglected and oxidation processes were the main decreasing effects. In wheat-rolls enriched with fresh leaves of Amaranthus L., total phenolic concentrations quantified by HPLC-DAD and identified by HPLC-MS were 51% to 56% lower in baked wheat-rolls than in cooked vegetables and 73% to 76% lower than in freeze dried plant powder.
Thermal processing and storage effects are complex in plant matrices and cannot be explained fully by model experiments with single substances. Interactions between phenols, minerals, proteins, and enzyme activity need to be considered. This thesis highlights advantages and disadvantages of different thermal processing and storage methods by evaluating interactions of vitamins, phenols, and minerals, including the individuality of plants. | de |