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SMART PRODUCTION

การเลือกวิธีการเก็บรักษาอาหารแบบใช้การท�าแห้งแบบแช่เยือกแข็งในอาหาร ควรค�านึงถึง
ความเหมาะสม เช่นอาหารที่เหมาะจะเลือกใช้การท�าแห้งแบบแช่เยือกแข็งควรเป็นอาหารที่ไวต่อการสูญเสีย
คุณภาพและคุณค่าทางโภชนาการได้ง่ายด้วยความร้อน เช่น สมุนไพร อาหารทะเล ผัก ผลไม้ อาหาร
ที่ต้องการเก็บรักษายาวนาน และต้องการจะคืนสภาพของอาหารเมื่อต้องการ

รูปที่ 3 แสดงชนิดของการท�าแห้ง
Fig 3 The Type of Drying

Freeze Drying

Process

Presently, there are many procedures to keep and reserve Sublimation of ice layer begins at the surface of the product,
food for long period, while also maintain the nutritional value which is exposed to air. The sublimation makes the surface
area the dry layer, and then the sublimation of the ice layer
of the food. Each procedure has different methods, expenses, inside the sublimation product passes through the dry layer to
and prices. The freeze dry method is one of the most popular the surface of the product, respectively. The sublimation period
methods in current, and tend to be more popular as this depends on the size, shape and structure of each product.
3. Secondary Drying - When primary drying is completed,
method can retain the shape, taste, and nutrition, while can the ice will be sublimated. However, there may be residual
keep the product for years. humidity, which must be dried by increasing the temperature in
order to remove the residual moisture to a safe level for storage.
Freeze dehydration or lyophilization or freeze dry refers to dehydration by
freezing method by changing the phase of water in the cell from liquid into ice Advantages of Freeze Drying
crystals (Solid) or small ice. After that, the pressure will be reduced to vacuum Freeze drying is an effective process of processing and storing
so that the ice can be sublimate into vapor as shown in Figure 1 (with products. Foods that have been passed this process will less
temperature equal or below 0˚C, ice will be sublimated at 4.7 mmHg or below). nutritional value as it is a low temperature drying process. Thus,
it does not lose the nutrition from the heat. The structure and
Freeze Dry Processes tissue of the cell are less damaged so the food is dried and
The preliminary steps for the production of food by freeze drying method are have high quality, while can effectively rehydration, as well as
similar to those of conventional production processes, which are included can keep color, flavor, taste and texture of the food better than
selection, washing, peeling, trimming and so on. There are three main any other drying methods, such as spay drying or hot air drying,
processes as follows: which will change the food, cause some damage and loss
1. Freezing is the process of lowering the temperature of a product to nutritional value as shown in Figure 3.
freezing point rapidly to make the water in the cell become ice crystal. The The selection of frozen food by freeze dry method should
most popular freezing method is air blast freezing and cryogenic freezing. consider base on the appropriateness. For instance, the ideal
2. Primary Drying is the reduction of water content or dehydration by food to use freeze drying should be food that is sensitive to loss
sublimation of ice crystals in the cell into vapor by lowering the surrounding of quality and nutritional value through heat, such as herbs,
atmospheric pressure to a vacuum level of less than 132 Pa and 132 mPa, seafood, fruits and vegetables, and food that need to be reserved
respectively. As a result, ice crystals sublimation will be completely formed. for long period, while need to be reformation when needed.

42 FOOD FOCUS THAILAND OCT 2018