Freeze dried foods

Freeze Drying Vs Dehydration of Food

Freeze drying and dehydration are two very popular processes of preservation implored in the food industry today. Since microorganisms require water to multiply and cause spoilage to foods, these processes preserve food by removing free water inside the food, resulting in more dry matter. However, they do so imploring different techniques which also give varying results, especially as far as the quality of the final product is concerned. Apart from extending a food’s shelf life (durability), drying of foods also has other advantages like reducing packaging, storage, and transportation expenses (1).

  1. Freeze drying

Freeze drying is a process of removing water from food through quick freezing at very low temperature and pressure, and subsequent sublimation. All available moisture in the food is frozen quickly which reduces the deteriorating effect of low temperature on foods, as the ice crystals that are formed are smaller. This prevents compression which allows the food to retain its solid structure and enables the food to maintain its soft texture. Thus, the overall quality of the food is maintained. Furthermore, sublimation occurs which is a process in which a solid is converted directly to gas without passing through the liquid phase. The resulting product contains many little pores which account for its great rehydration properties (2).

  1. Dehydration

Dehydration is a process of removing water from food by evaporation using hot air at high temperatures. Sun drying is the oldest method of dehydration known to man where food is exposed to the sun for the heat of the sun to evaporate the water thereof. Today, modern methods of dehydration include conventional oven drying, air drying, microwave oven drying, solar drying and electric dehydrator drying. The heat supplied to dry food using these different techniques vary and can range from 95oF for herbs to as high as 135oF for meats (3, 4).

Differences between freeze drying and dehydration

  1. Freeze drying implores the use of low temperature and sublimation to remove water from foods while dehydration uses hot air at high temperature (2, 3).

  2. Freeze drying moves up to 99% of water from foods while dehydration removes up to 95% of water from foods. Thus, freeze dried foods have a longer shelf life than dehydrated foods (5).

  3. Freeze dried products maintain their taste, color and structure while dehydrated products do not. This is because high temperature induces oxidation reactions which results in browning that is typically of dehydrated products. Hence freeze-dried foods (especially fruits and vegetables) are more appealing to consumers, increasing their acceptability (6).

  4. Freeze drying maintains up to 90% of the nutritional value of the original products than dehydration. This is because the high temperature applied to dehydrate foods destroys many nutrients that are heat sensitive like vitamin C, vitamin A, folate, and many B vitamins like pantothenic acid (vitamin B5) (7).

  5. Freeze drying results in products which have numerous little pores, that makes them absorb water very quickly. This great rehydration property of freeze-dried foods makes them a great addition to many products like breakfast cereals in the case of freeze-dried fruits (8).

  6. Freeze drying is a more expensive process (high energy cost and lengthy processing time) than dehydration and its equipment is expensive. Consequently, freeze dried products tend to be more costly than dehydrated products. Typically, freeze-drying foods costs 2 – 5 times more than dehydrating food (6).

Freeze drying and dehydration are both great food preservation techniques. The method of preservation chosen should depend on the food in question. For fruits and vegetables especially, freeze drying is best suited as they are prone to nutrient loses and oxidation at high temperatures. On the other hand, foods like potatoes, yams, meats, and fish do well with dehydration.

 

REFERENCES

  1. Oyinloye, T. M., & Yoon, W. B. (2020). Effect of freeze-drying on quality and grinding process of food produce: A review. Processes (Basel, Switzerland), 8(3), 354. doi:10.3390/pr8030354

  2. Nowak, D., & Jakubczyk, E. (2020). The freeze-drying of foods-the characteristic of the process course and the effect of its parameters on the physical properties of food materials. Foods (Basel, Switzerland), 9(10), 1488. doi:10.3390/foods9101488

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

  4. Introduction to food dehydration. Retrieved August 1, 2022, from Missouri.edu website: https://extension.missouri.edu/media/wysiwyg/Extensiondata/Pub/pdf/hesguide/foodnut/gh1562.pdf

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

  6. 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.

  7. Pantothenic acid. (n.d.). Retrieved August 1, 2022, from Nih.gov website: https://ods.od.nih.gov/factsheets/PantothenicAcid-HealthProfessional/

  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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