Drying, dehydration, lyophilization, food preservation
Drying partially removes the free amount of water present in the food, decreasing its moisture. Fruit, meat, cod and spices are examples of food products that can use drying. In a professional environment, drying can be applied using an oven or a dehydrator. The drying time differs depending on the thickness and humidity of the food, as well as the selected temperature. When this method is used out-of-doors, environmental conditions such as air current and temperature are not controlled, requiring regular attention until the process is completed.
Dehydration eliminates all the free amount of water present in the food, reducing moisture to almost 0%. With this method, the environmental conditions are controlled by the use of dehydrators, both in professional and domestic environments. Dehydration is intended to preserve food for long periods. Examples of food that are commonly dehydrated are: fruits, mushrooms, tomatoes, herbs. To assure the quality of the product, the vacuum packaging must be carried out by using the adequate trays or boxes or by adding inert gas.
The food matrix, the presentation shape, the way the food is cut, and the temperature, will influence the drying and dehydration time and management.
Freeze-drying is a conservation method that consists of quickly freezing the product (at temperatures below -50°C) and then removing the free amount water in the product by sublimation. This method is applied in a vacuum atmosphere, allowing ice to change directly from a solid to a gaseous state without going through a liquid phase. Freeze-drying intends to reduce the loss of volatile and thermosensitive components, stabilizing the products through several steps during the process: freezing, sublimation, vacuum drying and storage. This method is mainly used in the food industry, and can be applied to fruits, vegetables, meat and coffee, among others.
Drying and dehydration aim to inhibit microbial activity and reduce enzymatic activity. These methods aim to increase the shelf life of food products, facilitate storage due to the smaller volume, and preserve the color and natural aromas. Additionally, they can be applied without adding preservatives or sugars.
Certain previously dried or dehydrated products can be hydrated once again to be consumed in their original state, such as beans and chickpeas.
The benefits of freeze drying include simplification of the aseptic environment, greater stability of dry powder such as coffee or milk, removal of water without excessive heating of the product, as well as the absence of chemical alteration of substances susceptible to deterioration by heat or loss of volatile constituents. Lyophilization also provides greater resistance to the spread of microorganisms.
The three methods increase the options for the consumer, ensuring that out-of-season products, such as dehydrated mushrooms, maintain their quality. Furthermore, they may also represent a way to reduce food waste.
Drying: fruit (plums, apples, dates and grapes), pulses (peas, broad beans and lentils), spices (rosemary and parsley), fish (cod).
Dehydration: fruit (apple, pineapple, persimmon, strawberry and mango), gelatin.
Freeze drying: fruit (passion fruit, kiwi fruit, pineapple and apple), vegetables (carrots, broccoli and tomatoes), seafood (shrimp), mushrooms, milk and coffee.
In the preparation of food through drying, dehydration and freeze-drying methods, the quality of the package and its storage are critical factors in maintaining a low level of moisture to avoid contamination of the product by microorganisms.
Temperature control is essential to determine the final product characteristics (taste, odor, texture, color), based, for example, on the loss of volatile compounds, protein denaturation, or formation of hardened layers on the surface.
- Bennamoun L, Li J. Drying Process of Food: Fundamental Aspects and Mathematical Modeling. Natural and Artificial Flavoring Agents and Food Dyes. 2018; 29–82. doi:10.1016/b978-0-12-811518-3.00002-8
- FDA [Internet]. Lyophilization of Parenteral (7/93): Guide To Inspections Of Lyophilization Of Parenterals. 2014 [citado 2021 Mar 15]. https://www.fda.gov/inspections-compliance-enforcement-and-criminal-investigations/inspection-guides/lyophilization-parenteral-793
- Chen XD, Mujumbar AS. Drying Technologies in Food Processing. Blackwell. 2008.