# The Impact of Freeze Drying on Bioactivity and Physical Properties of Food Products
## 6 Conversion of Waste and By-Products  
Waste is a global problem that every person must consider in terms of several reasons, including the cause of the environmental pollution, especially, and governmentally the cost of degrading it [157; 158]. Waste and by-product conversion has been a significant topic in recent years for several industries and researchers [159; 160; 161]. Waste product transformation into valuable material is conducted according to the zero waste policy [162]. Communities are solving the problem of waste, which is produced in various ways [163]. The waste products, including peels, pomaces, and seeds, that are obtained from foods have a high potential to improve the bioactivity of other industrial production [164; 165; 166]. Instead of using new sources, the bioactive contents in the waste products, which are dried and protected via FD, can be used by manufacturers based on a zero waste policy, which is important in all fields [168; 169; 170; 171]. Valorization of waste products is enhanced by using the FD techniques in various industrial areas [30; 172; 173; 174]. The utilization of bioactive content derived from bread waste as a product for various industries is possible [175]. In this study, bioactive peptides were obtained, microencapsulated, and protected from environmental conditions such as oxygen and temperature. Maltodextrin was used in the microencapsulation method to protect the bioactive peptides in the sample, and it was also found to facilitate freeze-drying processes. The bioaccessibility of bioactive compounds increased in the waste and by-products was enhanced using the FD process. In a study conducted by [PERSON] et al., waste tomato peels, which contain a high number of total carotenoids, were encapsulated via applying the FD to preserve the total carotenoids for reuse in industrial applications [176]. Another study investigated the conversion of the waste cocoa bean shells valorized by FD [177]. In this study, the ingredients of the shells supported the nutritional value of cookies to show the importance of waste product conversion. As a result of the study, the shells were dried using FD and spray drying techniques to preserve the ingredients of the shells, especially the protein, antioxidant activity, and polyphenol contents. Also, while the powder produced by applying FD had the highest protein content, the powder obtained via spray drying had the highest antioxidant activity and total phenolic content in the cookies. In another study on carotenoids, FD was used to obtain these pigments, which are the bioactive components of most foods [178]. These were obtained from waste carrot products with the application of the encapsulation which provides better preservation of the sample ingredients. In the study by [PERSON] et al., carotenoids were obtained via spray drying and FD from carrots by applying various wall materials, including whey protein, maltodextrin, and inulin. Also, this study demonstrated which drying technique was most effective for the preservation of the carotenoids. Spray drying was successful due to the lowest water activity, moisture content, and particle size of the samples that were achieved via encapsulation, while encapsulation using FD produced the freeze-dried sample which had the highest hygroscopicity, oxidative stability, and original color properties. These results may be due to the application of high temperatures that significantly impact the bioactive properties and morphology of the samples, during the spray drying processes. In addition to these, a study examined the conversion of berry pomace and oregano processing wastes via FD [179]. Freeze-dried waste materials were used as the bioactive ingredient of various products instead of new sources. These studies explained why and how FD was chosen to transform waste products into nutritionally rich products via improving bioactive properties; also, its potential was highlighted in sustainable food processing (Table 2) [15, 180, 181, 182, 183, 184, 185, 186, 187].