Humidity Control By Conservation
Water availability is one of the most important factors for the maintenance of life on our planet, as well as the presence of macronutrients like carbohydrates, proteins, lipids; micronutrients such as vitamins and minerals and air quality. All these factors, in appropriate quantity and quality, is responsible for maintaining the physiological balance of life.
Like us, the microorganisms require water for maintenance. She as a universal solvent used, for example, to transport nutrients throughout the intracellular space and nutrients to solubilize in its original form may not be used by the microorganisms.
Conservation by humidity control is the food water withdrawal, i.e., the dehydration. Azeredo (2004), states that the main goal of reducing food water activity is the reduction of microbiological changes rates.
There are also other additional objectives, such as reducing chemical change, reducing packaging costs, transport, and distribution, plus the convenience.
The dewatering of food can be made in the following ways:
Warm air drying
The conventional hot air drying is performed in driers which system is based on the circulation of heated air combining, thus, the heat transfer (heat production) and mass (moisture removal) (Azevedo, 2004).
This method, however, cause undesirable changes to the food especially the hardening of the outside of the same, which is perceived by the consumer and causing contempt of the product.
To achieve the same objective with lower degrees of nutritional and sensory changes can use lyophilization, atomization, and osmotic dehydration.
The freeze-drying process comprises two steps, quick freezing and sublimation of the water present in the frozen vacuum. The sublimation of water is the process of passing the same solid state (ice) to a gas without passing through the liquid state. This is done due to the appropriate combination of pressure and temperature.
The process is quick and causes the little change of sensory and nutritional products to order due also to the low-temperature requirements. The main limitation of this process is economic since this is the most expensive drying process among processes.
Spray drying involves spraying a feed liquid, forming droplets that are released in a closed chamber. The droplets come in contact with a stream of heated air (in concurrent flow or counter), which supplies the heat required for evaporation, thus, there was formation of dry particles (Azeredo, 2004).
The differential of this process is the product residence time in the dryer, 5-100 seconds, which is good for sensitive products.
Osmotic dehydration is widely used as a pre-dehydration process since water is removed in the order of 40% to 70%. The remaining water may be removed, for example, by atomization, which considerably reduces energy costs.
The process consists of immersing the food (usually fruits and vegetables for example: artichoke, rhubarb) in a supersaturated solution solute. What happens is the “capture” of food by the solute water. The solutes are poorly absorbed by the product since the permeability of cell membranes of this type of compound is small.