# Phytochemicals and Antioxidant Properties of Edible Flowers
## 3 Antioxidant Activity of Edible Flowers
Finally, phenolic compounds have the ability to bind with potentially pro-oxidative metal ions operating as secondary antioxidants [104]. Antioxidant activity has been correlated with the maintenance of good health in humans, and therefore is very important to develop analytical protocols to evaluate it to several food products, including edible plants. The first important step to evaluate the antioxidant activity, in plant-based materials, is the extraction of the antioxidant compounds. There are several extraction methods available and each one has its benefits and negatives, and therefore its selection is very crucial for the final estimation of antioxidant activity [105]. Furthermore, for the quantification of antioxidant activity of edible flowers' extracts, there are several methods available that may be categorized based on the chemistry of the reactions involved. The methods that pertain to the mechanisms of hydrogen-atom transfer include oxygen radical absorbance capacity (ORAC) assay, while those that pertain to the mechanisms of single-electron transfer include Ferric-reducing antioxidant power (FRAP) assay and Cupric-reducing antioxidant capacity (CUPRAC) assay. However, there are also methods that pertain to both mechanisms, such as Trolox equivalent antioxidant capacity (TEAC) assay, 2,2-azinobis (3-ethyl-benzothazoline-6-sulfonic acid) (ABTS) assay or DPPH\(\bullet\) (2,2-diphenyl-1-picrylhydrazyl radical cation) assay [102]. In the case of edible flowers, all of these methods have been applied for the estimation of antioxidant activity (Tables 12-14). There are numerous studies in food products that have found a correlation between the TPC and antioxidant activity; however, there are also some studies available that were not able to confirm such correlation. As already highlighted, the mechanisms of antioxidant activity are very complicated and they are affected by a wide range of variables [102]. In addition, since different assays for evaluation of antioxidant activity are available and based on different mechanisms, it is common to detect a correlation between, for example, TPC and DPPH assay, and not for FRAP assay. In the studies where a correlation was observed, this was attributed to the antioxidant capacity of phenolic compounds; while in the studies where the correlation was absent, this was attributed to other compounds, not quantified by TPC analysis, which had antioxidant activity. In a study with 65 edible flowers from China, the correlations between TPC and antioxidant capacities were 0.6344 for DPPH, 0.7587 for ABTS and 0.8588 for FRAP. The correlations between TFC and antioxidant capacities were 0.3265, 0.2435 and 0.2205, respectively [20]. In a similar study with 51 edible flowers, positive linear correlations between total antioxidant capacities and TPC (R\({}^{2}\) = 0.911 and 0.954 for FRAP and TEAC values, respectively) were reported. Similar results were reported for water-soluble and fat-soluble fractions [13]. Lower correlations were reported in a study with 23 edible flowers [18]. More specifically, in the case of TPC, the correlations were 0.9589 for ABTS, 0.6333 for DPPH and 0.5991 for FRAP; and in the case of TFC they were 0.2598, 0.0794 and 0.6188, respectively. All these studies confirm that there is not a specific pattern for the correlation of TPC and TFC with the antioxidant capacity and especially by using different antioxidant assays. In general, there is a positive correlation between TPC and antioxidant activity, something that it is not the case for TFC.