# The Effect of Freeze-Drying on the Properties of Polish Vegetable Soups
## 3 Results and Discussion
[66] observed that the betanin content in the microcapsules with red beet extracts obtained by freeze-drying were negatively correlated with the hue angle. Also, degradation the color of samples occurred from opaque red to clearer yellow after freeze-drying and spray-drying. Samples of dried beetroot soup after storage showed the lower values of hue h\({}^{\circ}\) than dried product. The L*, a*, C* vales of dried beetroot soup remained constant after storage but the b* parameter as well as hue h\({}^{\circ}\) decreased that may be attributed to browning reactions such as non-enzymatic browning. It may also lead to a reinforcement of the sample color [69]. Tomato soups dried and stored also showed the reduction of the hue angle values which can be also related to browning processes. The pumpkin soups showed after drying and storage an increase of hue and a slight decrease of chroma value. The drying process resulted in the brighter sample with lower color saturation which can linked with lycopene and \(\beta\)-carotene degradation. Also, Guine and Barroca [70] observed that the freeze-during process made the samples more dully than fresh pumpkin. However, the storage of dried pumpkin soups caused a further decrease of color saturation (degradation of pigments). The similar trend was observed for cucumber soup after drying and storage. The total color difference between fresh and dried beetroot soups was several-fold higher than that observed for other soups (Table 5). However, the \(\Delta\text{E}^{*}_{\text{ab}}\) obtained for other soups also showed high values. The total color change was also compared between fresh soup and dried samples after storage. The highest total color change after storage of samples were obtained for the beetroot soup. The results of \(\Delta\text{E}^{*}_{\text{ab}}\) showed that freeze-drying of beetroot soup caused the significant changes of color but the storage of the dried sample did not affect this parameter. The total changes of color due to drying process of other soups were smaller. The value of \(\Delta\text{E}^{*}_{\text{ab}}\) considerably increased for tomato and pumpkin dried soup after storage. During storage, the degradation of pigments and bioactive compound probably occurred. The pH of fresh soups ranged from 3.89 to 5.59 for cucumber and pumpkin soups, respectively (Table 6). After freeze-drying and storage of dried samples, the pH of soups was similar to that obtained for most fresh soups. [PERSON] et al. [71] observed that after drying, pH of goldenberry was maintained. However, the pH of banana leaves after drying increased slightly after drying due to the degradation of acid compounds in that material [72]. Dried cucumber soup also showed a higher pH value than fresh soup but after storage the pH of dried soup did not differ. The scavenging activity against DPPH\(\bullet\) radical was described by the EC50 coefficient. The lower values of EC50 relate to a higher antioxidant activity [56]. The freeze-drying of soups caused a slight increase of EC50 for the tomato, pumpkin, and cucumber soups (Table 6). The drying process did not statistically alter the scavenging activity in the case of the beetroot soup. The content of polyphenic compounds (TPC) also did not change after drying and storage of the beetroot soup. Red beetroots contain several phenolic acids (both hydroxycinnamic and hydroxybenzoic acids) and flavonoids [73], which affect their bioactivity. The beetroot soups before and after drying had a lower value of the EC50 than cucumber and tomato soups, which means that beetroot soups represented higher antioxidant activity than cucumber soup, which might contain less bioactive compounds. [PERSON] al. [74] observed the increase in the total phenol produced by the heat-treated beetroot puree and the heat caused an increase in the amount antioxidants. However, color of samples was significantly reduced by heat. The hydrolysis of C-glycos in the flavonoid composition caused the formation of monomers that increase the antioxidant capacity.