# The Impact of Freeze Drying on Bioactivity and Physical Properties of Food Products
## 4 Impact on Bioactive Properties  
The nutritional value of samples and their shelf life can be preserved and increased using the FD technique [82; 83]. It generally yields a high-quality product that retains several bioactive properties crucial for human health [84; 85; 86]. FD is an effective technique that uses low temperatures and especially low pressure, which varies among drying processes [38]. Compared with other techniques, lyophilization generally minimizes the degradation of bioactive components in the sample [87; 88; 89]. Milk and dairy products are in the most widely consumed animal-based food category and are rich in nutrients [90; 91; 92]. The various functions are antimicrobial, antioxidant, neuroprotective, and other effects of products based on their bioactive components, including lactoferrin, growth factors, lactoperoksidase, and liposomes, etc. [93; 94; 95]. Additionally, the bioactive components can protect against various diseases [96; 97; 98]. This category appeals to all age groups, from childhood to old age, as well as athletes with special needs [99; 100; 101]. Products including milk, cheese, yogurt, and colostrum are used as different foods or supplements processed via FD [102; 103; 104]. The effects of different techniques on milk and colostrum drying regarding content and digestibility are noteworthy issues [102]. Colostrum is a functional food known as the first milk produced by the mother after birth. This milk is produced between 0 and 7 days after birth [105]. Since the components in its content change every day, it is both remarkable and needs to be preserved very well [106]. At this point, drying techniques such as spray drying and FD are considered ideal techniques for colostrum samples. In a recent study conducted by [PERSON] et al., these two techniques were compared in terms of preserving the content of colostrum [107]. When the results were evaluated, it was determined that FD preserved the protein content, IgG, and IgA content of colostrum better than spray drying. In addition, new products are being created via combining milk and dairy products with various freeze-dried materials to create a wide range of products [108]. In particular, the combination of dried fruits and vegetables with widely consumed products was used to obtain health-supporting or health-enhancing properties in the production of functional foods [30; 109]. Fruits being consumed outside of their seasons is an increasingly widespread manner. People use different production and preservation techniques to ensure this [110; 111]. Forthis purpose, the preservation of the content, taste, and rheological properties of products is maintained through drying techniques applied according to samples [112; 113]. At this stage, FD was applied to various species of fruits, and the results explained the efficiency of FD compared with several drying techniques [114]. For example, FD and spray drying were applied to Correlian cherry in a study to compare these drying techniques in terms of product quality [115]. Consequently, a greater preservation ability than that of spray drying regarding the total phenolic contents, antioxidant capacity, and anthocyanins of the sample was provided via FD. In another study on fruits, white mulberries were dried using FD and oven drying to preserve the fruits' quality after drying in terms of their bioactive ingredients and physical properties [7]. When compared with fresh samples, air drying produced better redness, and FD resulted in better lightness and yellowish as physical properties. Also, the L-ascorbic acid of the sample degraded minimally, and the highest total phenolics and antioxidant capacity as other bioactive properties were obtained from the application of FD. Similarly, maoberry fruits (_Antidesma bunius_ L.) were used to determine the effects of FD and convective hot air drying in order to choose the best technique for the maximum quality of the final product when this was looked from divergent perspectives [8].