# The Impact of Freeze Drying on Bioactivity and Physical Properties of Food Products
## 4 Impact on Bioactive Properties
The research showed morphological and bioactive compound differences among the techniques. FD preserved the antioxidant activity of the sample better and resulted in better color and fullness compared with other drying techniques. Additionally, in another study on the FD of the mushrooms, some bioactive properties were detected in the dried samples but not in the fresh ones [136]. Hot air drying and FD were used to process shiitake mushrooms and preserve their bioactivity. Both bioactive and physicochemical properties were assessed. Interestingly, cysteine was found in the dried samples but not in the fresh ones. These results may be attributed to the temperatures used in the drying techniques. In addition to these studies, several studies on the effect of FD on the bioactive properties, physical properties, and flavor of various materials, including potatoes, cabbage, garlic, eggplant, and tomatoes as vegetables; berry species, apples, hawthorn fruit, strawberries, and pears as fruits; other plants, honey, milk, seafood, and mushrooms, were examined (Table 1) [15; 84; 137; 138; 139]. \begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
**Samples** & **Drying Conditions** & **Percentage of Removed Water** & **Outcomes** & **References** \\ \hline \multirow{6}{*}{_Gastrolia elata_} & & & -The retention of active ingredients and original color. & \\  & & & -The retention of the internal structure and main components. & \\  & & & -The preservation of pungent odors as physical and sensory properties. & \\ \hline \multirow{6}{*}{Basil leaves (_Oclum husilicum_)} & & & -The no net change in pH. & \\  & & & -The decrease in the chlorophyll content and vitamin C. & \\  & & & -The increase in total polyphenols, flavonoids, antioxidant activity, and total carotenoids. & \\  & & & -The darkening as color changes. & \\ \hline \multirow{6}{*}{_Pleurotus eryngi_} & & & -The preservation of the color and texture features. & \\  & & & -The decrease in the hardness. & \\  & & & -The high retention capacity of total phenolic contents. & \\  & & & -The decrease in the amount of polysaccharide content, ascorbic acid content, and antioxidant capacity for ABTS was high but low for DPPH total volatile constituents, eight-carbon volatiles, essential amino acids, and free amino acids. & \\ \hline \multirow{6}{*}{Potato tubers} & & & -The high lightness and yellowness color. & \\  & & & -The high retention of the amount of L-ascorbic acid, total phenolics, and antioxidant activity as bioactive properties. & \\ \cline{1-1}  & & & -The high retention of the amounts of potassium, sodium, iron, zinc, and vitamin B6. & \\ \cline{1-1}  & & & -The moisture value changed with exposure time by freeze-drying. For example, absorbed moisture was & \\ \cline{1-1}  & & & -The increase in the total content of alcohol-soluble flavonoids in terms of quercetin, phenolic compounds, and low molecular weight antioxidants according to mg/g dry matter compared with a fresh sample. & \\ \cline{1-1}  & & & -The retention of the bioactive proteins and immunoglobulins. & \\ \cline{1-1}  & & & -The no net change on the secondary structure of proteins. & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Effects of freeze drying on nutritional and physical properties of various products.