What factors affect the quality of dehydrated vegetables?

At present, the main method used in the processing of dehydrated vegetables is drying control. Although the quality of the finished product has been improved, there is still room for improvement in many aspects. Dingneng has summarized this.

1. Temperature, humidity and pressure

Temperature: Evaporation of water requires a certain amount of heat. Under heating conditions, the water evaporates and vaporizes, and is taken away by the dry air, and fresh vegetables become dehydrated vegetables. Properly increasing the temperature can accelerate the evaporation of water, but attention should be paid to the damage of high temperature to the nutrition, color and texture of vegetables. Cooling can prevent dry products from burning and reduce nutritional loss.

Humidity: The relative temperature of the air is an important factor affecting the drying effect. There are two basic conditions for drying: water absorbs heat and vaporizes and water vapor is continuously removed. As the water evaporates, the ambient temperature increases, and part of the water vapor needs to be removed so that the water can evaporate continuously in order to achieve drying. Increasing the dryness of the air, heating the air, and increasing the air flow rate around the raw materials can all improve the drying efficiency.

Pressure: Reducing the ambient pressure can make the water in the raw materials evaporate at a lower temperature, which is conducive to maintaining the color, aroma, taste and nutrition of the raw materials. This drying method is called vacuum drying or reduced pressure drying. Freeze drying currently used by manufacturers belongs to reduced pressure drying. After drying by this method, the finished product is sponge-like and porous, absorbs water quickly when rehydrated, and can maintain the volume and state of the original material after recovery.

2. Browning

A common problem with dehydrated vegetables is color change, that is, browning. Heat damage during processing and poor storage conditions can cause browning. The speed of browning changes with temperature. The higher the temperature, the faster the browning. Browning is also related to heating time. Long-term heating treatment can aggravate browning.

3. Selection of drying method

The following factors should be considered when selecting a drying method: quality requirements, raw material characteristics, economic factors, etc. The drying method should be inexpensive and meet product quality and other requirements. For vegetables that are prone to browning or other adverse changes during drying, other drying methods should be considered. Freeze drying is an ideal way to dehydrate vegetables. Under vacuum conditions, water solidifies into ice and sublimates to be removed, which can minimize adverse changes caused by heating, and the rehydration time is short and the recovery condition is good. Although freeze drying increases production costs, its output value is several times higher than that of products dried with hot air.

It can be seen that there are many processes and problems involved in the production of dehydrated vegetables. The selection of production equipment and processing technology needs to be based on the characteristics of raw materials, product requirements, production conditions and processing costs to ensure the high quality of dehydrated vegetables, so as to better meet the needs of domestic and foreign customers.