Does freeze-dried product still have nutritional value?

In the process of food processing, dehydration treatment can greatly extend the shelf life of products and reduce transportation and storage costs. However, different dehydration treatments have great differences in nutrient retention and physical properties of food/products. For example, dehydration and heat drying are widely used, because the drying process is accompanied by heating, it is easy to cause a large loss of some heat sensitive nutrients. For example, when milk is spray-dried into milk powder, the B vitamins in it almost disappear. Fruit dried in the sun will also be accompanied by a large amount of Vitamin loss. So what are the advantages of lyophilization over traditional thermal drying?

Freeze-drying technology was first applied to astronaut space food. Astronauts stationed in the space station for a long time do not have enough fresh, nutritious and healthy food, which is a serious challenge to their health. How to get space to nutritious and fresh food was a headache for scientists until the advent of freeze-drying technology. The freeze-dried food can be well restored to its original state after adding water, and can retain its original nutrients, which is a good solution to the problem of "eating" in space for astronauts.

Freeze-dried food was dubbed the "aristocrat" of space food when it first appeared, and was not available to ordinary people. However, with the progress of technology, the application of lyophilization technology is more and more widely, especially in the field of medicine which requires high material activity. Many drugs and vaccines are made by lyophilization technology. So how does lyophilization do this?

Freeze-drying technology is called vacuum freeze-drying technology, or FD for short. Its scientific principle is not complicated, simply speaking, first of all, the material needs to be processed in the cryogenic freeze dryer freezing and freezing, and then the dryer is pumped into a vacuum, slowly heating up (the temperature is still very low) so that the water in the material directly from solid sublimation into gas, so as to get dry products. Freeze-drying process is carried out in low temperature and low pressure environment, so it will not be like the high temperature generated in the drying process of protein and other easily denaturated active substances lose their vitality. It also does not combine with oxygen in the air as in the air drying process, thus avoiding oxidation reactions.

To sum up, compared with other drying methods, lyophilization technology generally has the following three advantages:

1.Water restores easily. Freeze-dried solids exhibit a porous structure due to the sublimation of tiny ice crystals and retain their original frozen volume, so they are easily dissolved and restored by adding water. Compared with other drying methods, freeze-drying technology has incomparable advantages in maintaining the original physical properties and flavor of products.

2. Protect the activity of heat-sensitive substances. Many substances must remain active in order to do their job. Once inactivated, they have little nutritional value. For example, when collagen is used, its structure and pore size have an important impact on the growth of new tissues. If it is damaged, the original active function may be lost, so the processing technology has relatively high requirements. Freeze-drying drying is carried out at low temperature as a whole, and still maintains low temperature during the sublimation process, so it can greatly protect the activity of substances, especially suitable for drying such as collagen, vitamins, enzymes, hormones, nucleic acids, blood, immune products, probiotics, etc.

3. Prevent oxidation. The freeze-drying process is carried out under vacuum conditions, so it has a strong protective effect on those substances that are afraid of being oxidized, such as vitamin C, anthocyanin, lycopene, etc.

A study on the comparison of nutrient retention in drying methods showed [3] that the loss of anthocyanin nutrients in lyophilized purple mulberry fruit was less than 1%, with the highest retention rate. However, the retention rate of anthocyanin in the products of freezing puffed drying, hot air puffed drying and hot air drying decreased successively, among which, the loss of anthocyanin in the fruit of hot air drying was the largest, the anthocyanin content was less than 5%, and the loss was more than 20% compared with that of fresh purple mulberry fruit.

Another study compared the retention of vitamin C in five common fruit freeze-dried -- star fruit, mango, papaya, melon and watermelon -- and showed little loss of VITAMIN C

It can be seen that freeze-dried foods and products, especially freeze-dried fruits and vegetables, can retain their original nutrients to a large extent.

[1] Yang, R.-L., Li, Q., & Hu, Q.-P. (2020). Physicochemical properties, microstructures, nutritional components, and free amino acids of Pleurotus eryngii as affected by different drying methods. Scientific Reports, 10(1)

[2] Chen Q , Li Z , Bi J , et al. Effect of hybrid drying methods on physicochemical, nutritional and antioxidant properties of dried black mulberry[J]. LWT - Food Science and Technology, 2017, 80:178-184.

[3] Effect of Freeze-Drying on the Antioxidant Compounds and Antioxidant Activity of Selected Tropical Fruits[J]. International Journal of Molecular Sciences, 2011, 12(12):4678-4692.

Shaanxi Huike Botanical Development Co., Ltd. a integrated enterprise which is focus on natural products, plant extract related products and services.We mainly focus on pharmaceutical, functional food, Freeze-dried powder,Natural Pigment,Homology of medicine and food,beverages and other business services.

Shaanxi NHK Technology Co., Ltd.

2021-11-24