## 3 Results and Discussion
### Comparative Analysis of the AOA of Aqueous Extracts of Treated and Untreated Coffee Beans  
The data of the potentiometric evaluation of the AOA of aqueous extracts of untreated and treated coffee beans are presented in Figure 3. The AOA of untreated coffee bean extracts (846.9 \(\pm\) 12.5, 491.5 \(\pm\) 8.8 and 410.7 \(\pm\) 9.3 \(\mu\)mol Fe\({}^{2+}\)-E/g DW for green, medium roasted and dark roasted coffee, respectively) were taken as control values. As can be seen from Figure 3, green coffee turned out to be sensitive to all treatments, whereas roasted coffee was most sensitive to thermal treatments. After SF treatment, there was an increase in the AOA of the extracts to 910.3 \(\pm\) 24.6 (green coffee), 521.2 \(\pm\) 17.7 (medium roasted coffee) and 481.5 \(\pm\) 20.9 (dark roasted coffee) umol Fe\({}^{2+}\)-E/g DW (0.01 \(<\)\(p\) < 0.05), which in percentage terms gave a rise in the mean AOA value by 7.5%, 6.0% and 17.2%, respectively. After FF treatment, green, medium roasted and dark roasted coffee showed an increase in the AOA of extracts to 882.4 \(\pm\) 21.1, 511.5 \(\pm\)14.8 and 479.1 \(\pm\) 15.3 \(\mu\)mol Fe\({}^{2+}\)-E/g DW (0.01 \(<\)\(p\) < 0.05), which in percentage terms gave a rise in the mean AOA value by 4.2%, 4.1% and 16.6%, respectively. These results are explained by the destruction of the cell matrix due to the presence of ice crystals and a yield of antioxidant extractives. [PERSON] et al. reported that pre-treatment of corn by freezing caused an increase in the yield of extractive antioxidant compounds (lutetin and zeaxanthin) and also led to an increase in the AOA of the extract [46]. In the SF treatment process, larger ice crystals are formed, which causes the most severe cell damage [44, 45]. For this reason, the samples treated with SF showed the greatest positive deviations of AOA compared to  
Figure 2: The AOA of aqueous extracts of untreated coffee beans measured by spectrophotometric (**a**) and potentiometric (**b**) methods (\(n=3\)). Percentage indicates the change in mean AOA after roasting relative to green coffee. Bars indicate the upper boundaries of the SD. Statistically significant differences are indicated by two (\(p\) < 0.01) and three (\(p\) < 0.001) asterisks. the samples treated with FF. Apparently, the microstructural changes caused by roasting were amplified by the damage caused by freezing. Due to this fact, dark roasted coffee seemed to be most sensitive to freezing and showed the highest growth in the AOA of aqueous extracts. [PERSON] et al. [55] reviewed the effect of freezing on the AOA of plant food extracts; however, their work did not discuss coffee. Apparently, the present study is one of the first to report on the effect of freezing on the AOA of coffee bean extracts. [PERSON] et al. [55] concluded that the effect of freezing on the AOA of plant food extracts depends on the initial state of the treated sample, i.e., its variety, origin, integrity, etc. As a result of the breakage of the cellular structure caused by ice crystals in whole fruits, bioactive substances are released. At the same time, the AOA of the extract can: (a) increase if antioxidants stay in the product; (b) decrease if antioxidants are leached during thawing; (c) remain unchanged. After MWR treatment, green coffee presented an increase in the AOA of the extract to 895.3 \(\pm\) 31.7 \(\upmu\)mol Fe\({}^{2+}\)-E/g DW (\(p\) < 0.05), or an approximately 5.7% rise in the mean AOA value. The changes in the AOA of roasted coffee extracts were insignificant. Green coffee has the highest MC and, as a consequence, the best dielectric capacity [51; 52]; therefore, it was most sensitive to MWR treatment. MWR treatment can be accompanied not only by cell breakage and release of extractive antioxidant compounds but also by the transformation of some antioxidant substances into others [14; 49; 50]. After the roasting process, the MC in  
Figure 3: The AOA of aqueous extracts of untreated (control) and treated coffee beans (\(n\) = 3).