# The Effect of Freeze-Drying on the Properties of Polish Vegetable Soups
## 3 Results and Discussion  
Characteristic of Physical, Biochemical, and Sensory Properties of Soups before and after Freeze-Drying  
The application of the freeze-drying method for selected vegetable soups enabled the obtaining of a product with an attractive appearance (Figure 3). Also, the shrinkage of the dried soups layer was slightly noticeable. The concentration of the main compounds of soups was also changed. Based on the initial composition of soups and the measured water content in fresh soups and after drying, the concentration of sugars, fiber, and salt was calculated. The dried soup contained sugars form 13.9 (cucumber) to 44.6 (pumpkin) g/100 g (Table 3). The concentration of salt in dried cucumber soup increased to 15.41 g/100 g. According to the Polish Standard [62], the concentration of salts in fresh soup should be lower than 1.8%. The fresh soups did not exceed this limit and the concentration was lower than 1% of salts. The salt and sugar content in dried soups was very high but the final product should be served after rehydration. The fresh soups were characterized by water content in the range from 89.5 (tomato soup) to 93.7% (cuumber soup) and water activity ranged from 0.973 to 0.980 (Table 4). A similar level of moisture content (90%) was noted for fresh mushroom cream soup prepared with starch, butter, cream, button mushroom and bacon [34]. Water content after freeze-drying of the investigated soups was reduced to a level of 2-3%. A broader range of moisture content from 2.83 to 5.46% was observed by [PERSON] et al. [5] for dried-powdered vegetable soups. The difference in water content was caused by the addition of different ingredients. Also, the method of production of instant soup was different because the ingredients were dried, ground into powder, and mixed with other components [5]. The reduced water content and water activity promote the maintenance of the physical and chemical properties of dried products during storage [63]. The freeze-dried soups were stored in room conditions, and after 3 months, the freeze-dried soups' water content increased to around 4% and the water activity increased from 0.197-0.221 to 0.268-0.286 (Table 4). The highest increase of water content after storage of dried samples was observed for pumpkin and tomato soup (about 70-80%). However, the results showed that storage of dried cucumber soups led to an increase in the water content by 28%. Dried cucumber soup contained a significantly lower amount of carbohydrates than other soups (Table 3). The presence of low molecular weight sugars in dried materials may affect their physical properties such as solubility, viscosity, and hygroscopicity. Fructose is very hygroscopic whereas other sugars such as sucrose and xylitol absorb water only at the higher water activity [64]. The dried samples with a higher sugar content are more susceptible to the moisture uptake during the storage. However, the water activity and water content of stored dried soups remained at a level which ensures the microbiological stability of dried products. Figure 3: The pumpkin (A), cucumber (B), tomato (C), and beetroot (D) of fresh (**a**) and freeze-dried (**b**) soups. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Concentration of Main** & & & & \\
**Solid Compounds** & **Tomato Soup** & **Beetroot Soup** & **Pumpkin** & **C cucumber** \\
**g/100 g** & & & & **Soup** & **Soup** \\ \hline Sugars & 33.6 \(\pm\) 3.3 & 40.6 \(\pm\) 1.5 & 44.5 \(\pm\) 1.9 & 13.9 \(\pm\) 0.5 \\ Salt & 5.7 \(\pm\) 0.6 & 8.4 \(\pm\) 0.3 & 8.8 \(\pm\) 0.4 & 15.4 \(\pm\) 0.6 \\ Fiber & 8.4 \(\pm\) 0.8 & 8.5 \(\pm\) 0.3 & - & 13.9 \(\pm\) 0.5 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Concentration of the main solid compounds of different freeze-dried soups. The color of the product after drying can be an important indicator of its quality. Undesired changes or loss of color may negatively affect the evaluation of the final product by the consumer [65].