# The Effect of Freeze-Drying on the Properties of Polish Vegetable Soups
## 3 Results and Discussion
The lightness L* for all investigated soups increased after drying, which can be related to the degradation of pigments in vegetables used to prepare the soups. The highest difference of lightness between fresh and dried samples was observed for betroot soup; the L* increased from 23.05 to 55.07. The dried samples became slightly brighter after storage except for betroot soup, of which L* value did not change significantly in comparison to the dried sample (Table 5). The intensity of color depends on the values of a* and b*. The a* value (redness) decreased from +39.64 to +21.91 after drying of the betroot soup. The decrease of redness of the soup can be linked with the degradation of betali \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Kind of Soup** & **Product** & **Water Content (\%)** & **Water Activity** \\ \hline Tomato soup & fresh & 89.5 \(\pm\) 0.4 ** & 0.976 \(\pm\) 0.001  \\  & dried & 2.0 \(\pm\) 0.2  & 0.206 \(\pm\) 0.006  \\  & stored & 3.6 \(\pm\) 0.2  & 0.268 \(\pm\) 0.051  \\ \hline Beetroot soup & fresh & 89.7 \(\pm\) 0.2  & 0.980 \(\pm\) 0.002  \\  & dried & 4.1\(\pm\) 0.4  & 0.286 \(\pm\) 0.011  \\ \hline Pumpkin soup & fresh & 93.2 \(\pm\) 0.1  & 0.980 \(\pm\) 0.001  \\  & dried & 2.3\(\pm\) 0.1  & 0.197 \(\pm\) 0.001  \\  & stored & 3.9 \(\pm\) 0.3  & 0.279 \(\pm\) 0.009  \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Water content and water activity of different fresh freeze-dried and stored soups. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Product** & **L* & **+a* & **+b* & **Chroma** & **Hue** & **Total** \\  & & & **C* & **h** & **Color Change** \\  & & & & **\(\Delta\)E*\({}_{\text{ab}}\)** & \\ \hline \multicolumn{6}{c}{**Tomato soup**} \\ \hline fresh & 44.67 \(\pm\) 0.08 **  & 59.84 \(\pm\) 0.24  & 68.81 \(\pm\) 0.40  & 60.41 \(\pm\) 0.20  & - \\ dried & 52.09 \(\pm\) 0.05  & 32.46 \(\pm\) 0.20  & 54.40 \(\pm\) 0.12  & 63.35 \(\pm\) 0.20  & 59.17 \(\pm\) 0.10  & 9.32 \(\pm\) 0.08  \\  & stored & 60.05 \(\pm\) 0.95  & 28.74 \(\pm\) 0.91  & 45.64 \(\pm\) 0.93  & 53.93 \(\pm\) 1.27  & 57.90 \(\pm\) 0.32  & 21.64 \(\pm\) 0.35  & 21.64 \(\pm\) 0.35  & \multicolumn{2}{c}{**Betroot soup**} \\ \hline fresh & 23.05 \(\pm\) 0.04  & 39.64 \(\pm\) 0.60  & 10.72 \(\pm\) 0.40  & 41.06 \(\pm\) 0.63  & 15.25 \(\pm\) 0.35 [FOOTNOTEnoted a positive and strong correlation between the betanins content (the betacyanins mainly present in beetroot) and the color parameter a* of freeze-dried red beet extract. The degradation of betanins led to the discoloration of the product and reduction of the a* parameter. The storage did not affect the a* of beetroot soup, but for pumpkin and tomato soups, the redness decreased. The yellowness b* decreased after drying and storage of tomato, pumpkin, and cucumber soup. The increase of water content in dried samples after storage may affect the changes of color attributes. It can be assumed that the shrinkage and porosity of samples were changed due to the increase of water content after storage of products. Structure and opacity of fresh, dried, and stored material may significantly affect the optical refection capacity. Table 5 shows that chroma values decreased after freeze-drying of tomato, beetroot, and pumpkin soups. A significant difference between the chroma values was obtained for fresh (41.06) and dried (25.98) beetroot soup. [PERSON] and [PERSON] [67] noted for the freeze-dried beetroot puree the high chroma value (33.39-35.97), indicating the most saturated color. The hue angle describes the relative amount of redness (h\({}^{\circ}\) = 0\({}^{\circ}\)) and yellowness (h\({}^{\circ}\) = 90\({}^{\circ}\)). The lowest value of hue h\({}^{\circ}\) was observed for the fresh beetroot soup, which indicated a redder product. The beetroot contains the natural red-violet food colorant (betanin) with biological activity [68]. Betanins are unstable in the presentence of light and oxygen and can be degraded when subjected to heating [66]. The drying process resulted in the increase of hue value of beetroot soup. [PERSON] et al.