Benefits of Freeze Drying Over Dehydrating Food

Benefits of Freeze Drying Over Dehydrating Food

Every food contains water in varying amounts, and the shelf life of a food is directly affected by the amount of water it contains. This is because microorganisms need water to grow and multiply, thus the more water available to them, the more they will multiply quickly, spoiling the food (1).

Dehydration is a food preservation method which involves the removal of water from food to reduce its moisture content. Popular dehydration methods include sun drying, oven drying, air drying, electric drying and microwave drying. All these processes remove moisture from food by supplying heat or hot air to the food to evaporate the water and leave a dry solid (1, 2).

Freeze drying (also called lyophilization) on the other hand is a preservation process in which water is removed from food by sublimation which occurs at very low temperature and pressure. In sublimation, water moves from the solid phase (ice) directly to gas phase without passing through the liquid phase. So, in freeze drying, the food is first rapidly frozen after which sublimation occurs which allows the ice to transform directly to gas (is vaporized) leaving a dry solid (3).

Benefits of freeze drying over dehydration

In the food industry, freeze drying and dehydration are popularly used to preserve food. However, freeze drying has been demonstrated to have more advantages and benefits for many reasons such as are discussed below.

  1. Preservation of nutrients. Freeze drying has been demonstrated to retain the most nutrients in a food. Research studies have reported that more than 90% of a food’s nutrient are retained when freeze dried. This is because unlike dehydration that implores that use of heat to remove water from foods, freeze drying uses far lower temperatures. Hence it can preserve many more nutrients that are typically heat sensitive and consequently destroyed during dehydration. Vitamin C, B vitamins and folate for example, are highly sensitive to heat and tend to be destroyed when exposed to high temperatures for a long time. Vitamin C is vital for the growth, development, and repair of all the tissues of the body. It is needed for the production of white blood cells (thus boosting the immune system), absorption of iron, and formation of collagen which is crucial for good skin, bones, and cartilage (4, 5).

Fruits are also a rich source of polyphenolic compounds, many of which show both antioxidant and anti-inflammatory activities that help prevent oxidative stress and consequently the onset of diseases in our bodies. These polyphenols are also heat sensitive and research studies have demonstrated that fruits that have been freeze dried tend to have higher concentrations of total polyphenols than those that are dehydrated by other methods like hot air drying (6).

  1. Longer shelf life. Dehydration can remove up to 95% water from foods whereas freeze drying can remove up to 99% of water from foods. Thus, freeze dried foods have far less moisture content than their dehydrated counterparts, and consequently will last longer as there is far less water available for microorganisms to grow and spoil the food (7).

  2. Retains physical properties of the food. Freeze drying tends to allow a food to retain their natural color and taste, which increases the acceptability of the consumer. The food’s texture is also retained as freeze drying prevents compression and cell destruction due to sublimation (3).

  3. Excellent re-hydration properties. Freeze dried foods tend to be airy which makes them absorb water faster than dehydrated foods. As such they are easier to re-hydrate (8).

Freeze drying is a better method of food preservation than dehydration as it can retain more nutrients, which is the main reason we eat food. For foods that are particularly sensitive to heat degradation and oxidation like fruits and vegetables, freeze drying is the way to go.

 

REFERENCES

  1. Jayas, D. S. (2016). Food Dehydration. In Reference Module in Food Science. Elsevier.

  2. Introduction to Food Dehydration. Retrieved July 25, 2022, from Missouri.edu website: https://extension.missouri.edu/publications/gh1562

  3. Waghmare, R. B., Perumal, A. B., Moses, J. A., & Anandharamakrishnan, C. (2021). Recent developments in freeze drying of foods. In Innovative Food Processing Technologies (pp. 82–99). Elsevier.

  4. Vitamin C. (2012, September 18). Retrieved July 26, 2022, from The Nutrition Source website: https://www.hsph.harvard.edu/nutritionsource/vitamin-c/

  5. Vitamin C. (2020, November 17). Retrieved July 26, 2022, from Mayo Clinic website: https://www.mayoclinic.org/drugs-supplements-vitamin-c/art-20363932

  6. Tylewicz, U., Nowacka, M., Rybak, K., Drozdzal, K., Dalla Rosa, M., & Mozzon, M. (2020). Design of healthy snack based on kiwifruit. Molecules (Basel, Switzerland), 25(14), 3309. doi:10.3390/molecules25143309

  7. Berk, Z. (2013). Freeze drying (lyophilization) and freeze concentration. In Food Process Engineering and Technology (pp. 567–581). Elsevier.

  8. Kowalska, H., Marzec, A., Kowalska, J., Ciurzyńska, A., Samborska, K., Bialik, M., & Lenart, A. (2018). Rehydration properties of hybrid method dried fruit enriched by natural components. International Agrophysics, 32(2), 175–182. doi:10.1515/intag-2016-0100

 

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