Development and demand of fruit and vegetable drying:
Fruit and vegetable products have high water content and are easy to rot. At present, the loss rate of fresh fruits and vegetables in China reaches 30% for fruits and 40% - 50% for vegetables, while the loss rate in developed countries is less than 7%. Fruit and vegetable products have strong seasonal and regional characteristics, and the harvest and marketing periods are short and concentrated, forming obvious peak season and off-season; In addition, if a large number of juicy and nutritious fruit and vegetable products are not sold, stored and processed in time, they will be overstocked, dried, shrunk or even deteriorated, causing economic losses, and fruit and vegetable products are difficult to meet the market demand. At present, the application range of fruit and vegetable raw materials has been broadened by drying fruit and vegetable products, processing fruit and vegetable dried, fruit and vegetable powder, especially edible skin and core, and become a good nutritional deep processing product. The traditional methods of fruit and vegetable drying are coal burning drying, electric heating drying and other methods, which cause large pollution and energy consumption. As a high-efficiency energy-saving product, heat pump drying has significant energy-saving effect compared with traditional drying, and the drying quality of drying materials is maintained better, especially for drying sensitive and volatile products, which improves the quality of materials. At the same time, the whole heat pump drying process adopts intelligent control technology, with built-in drying process curves, which greatly saves labor costs, time and labor.
Pretreatment of fruits/vegetables before drying:
1. Selection and washing of raw materials - remove the raw materials with serious mildew, disease and insect pests. Use clean water at normal temperature for washing. It can also be soaked in water and turned manually. Ensure that the sorting and cleaning process does not damage or damage the raw materials.
2. Peeling, nucleating and splitting of raw materials.
3. Scalding treatment of raw materials (blanching) - put fruit and vegetable raw materials in hot water or steam for short time heating treatment, and then immediately cool. Scalding can destroy the oxidase system of fruits and vegetables, prevent browning caused by enzyme oxidation and further oxidation of vitamins. Scalding can also make the protoplasm in the cell coagulate and separate from the cell wall after losing water, which increases the permeability of the cell membrane, is conducive to the water evaporation of the tissue, and accelerates the drying speed.
4. Hot water or steam is generally used for scalding, and the time is generally short. It shall be controlled within 2-18 minutes.
Important problems in the drying process of fruits and vegetables
1. Loss of vitamin A and vitamin C - vitamin A (carotene) is easily oxidized. Vitamin C is easily oxidized when heated.
2. Color change - color is one of the important signs of quality acceptance of drying materials. It is very important to keep the natural color of materials during drying. If not handled properly, it is easy to have bad color changes such as yellow, brown, or black. If necessary, it is necessary to add the cyaniding process before drying.
3. Loss of aromatic substances - volatile loss of aromatic substances. The loss of aromatic substances is related to temperature, humidity and oxidation. Generally speaking, low temperature drying is easy to retain aromatic substances. The retention of aromatic substances largely determines the flavor of materials.
4. Tissue change - hot air convection drying causes great tissue damage to materials. Especially under the drying process of high temperature drying and rapid dehydration, the material dehydration is uneven and the tissue damage is large.