# Antioxidant Activity of Coffee Components Influenced by Roast Degree and Preparation Method
## 3 Results and Discussion
### Antioxidant Activity of Coffee Extracts
Furthermore, the results obtained with the CUPRAC and ABTS methods, as well as the CBA method and the method based on the autoxidation of linoleic acid, were strongly correlated with each other (\(\mathrm{r_{P}}=0.8943\) and \(\mathrm{r_{s}}=0.9510\), respectively; \(p\leq 0.001\)), which may result from the identical mechanism of the reactions used. The weak correlation between the content of phenolic compounds and the results of the CBA method (\(\mathrm{r_{s}}=0.6154\); \(p=0.033\)) and the lack of this correlation with results of the method using the autoxidation reaction may indicate that in these methods, other compounds with antioxidant activity, e.g., melanoidins, were of greater importance. In the case of the results per portion of the brew, a strong correlation was demonstrated between the content of phenolic compounds and the results of the CUPRAC, ABTS and CBA methods (\(\mathrm{r_{P}}=0.9805\), \(\mathrm{r_{s}}=0.8095\) and \(\mathrm{r_{P}}=0.8070\), respectively; \(p\leq 0.015\)). Moreover, the results obtained by the CUPRAC method were correlated with the results of the ABTS (\(\mathrm{r_{s}}=0.8810\); \(p<0.004\)) and CBA methods (\(\mathrm{r_{P}}=0.8538\); \(p=0.007\)). There were no correlations with the results obtained with the method of linoleic acid autoxidation in this case, however. This may be related to the high degree of complexity of the reaction. The differences between the correlation coefficients obtained for results expressed in different units might be explained by various proportions of the individual results after recalculations, being, among others, an effect of the nonlinear dependence of the HAT-based methods' results, as mentioned earlier. In order to better understand the importance of analyzed compounds for the antioxidant activity of the whole brew, the obtained results were presented as a percentage of the contribution of phenolic compounds and melanoidins for the antioxidant activity of coffee infusions (Figure 1). The amount of phenolic compounds was acquired by calculating Folin-Ciocalteu results with chlorogenic acid results, analyzed in every method. The values for each test sample add up to 100% so that the portion size is ignored; only quantitative proportions are shown. In the case of the method based only on the SET mechanism, the participation of phenolic compound activity is similar in all brews, and the melanoidin share was greater in infusions prepared from darker roasted beans (Figure 2a). In the ABTS method, melanoidins were of greater importance compared to phenolic compounds;however, their total participation in brew activity was less than 25% (Figure 2b). In methods based entirely or partially on the HAT mechanism (Figure 2c,d), the effect of the preparation method was evident--espresso each time showed a greater total share of the tested compounds in the entire brew activity. In the case of the autoxidation of linoleic acid, the total activity of phenolics and melanoidins tested separately was even greater than the overall activity of the coffee beans (lack of additivity in this experiment). In Figure 2c,d, the darker roast degree increased the share of melanoidin activity and slightly decreased the share of phenolic compound activity. As is well known, during the roasting process, numerous changes occur in the chemical composition of coffee beans, mainly, the degradation of thermolabile substances and the formation of new compounds, e.g., as a result of the Maillard reaction. Observed differences regarding the different proportions of the activity of phenolic compounds may result from their partial degradation in the roasting process or their different extractives during the preparation of infusions. However, the differences in the proportion of melanoidins are more pronounced and suggest that their activity depends significantly on the degree of roast. It is worth noting that the activity of melanoidins is also influenced by the phenolic compounds attached to their chain [12,31,37].