Microwave vacuum drying combines microwave energy and vacuum conditions. Microwaves are electromagnetic waves with a wavelength range of 1mm-1m and have penetration characteristics. When the microwave frequency is 2450MHZ, polar molecules in the material, such as water molecules, will change their original molecular structure after absorbing microwave energy, and do electric field general motion at the same speed, resulting in frequent collisions with each other and generating a large amount of frictional heat, so that each part of the material obtains heat energy and heats up at the same time. Under vacuum conditions, the boiling point of water is reduced, which enables low-temperature evaporation of moisture, thus achieving the purpose of drying figs.
Advantages
- Short drying time: Compared with traditional vacuum drying, microwave vacuum drying can greatly shorten the drying time. For example, traditional vacuum drying of figs may take 36 hours, while microwave vacuum drying can complete the drying within 120 minutes.
- Nutrient retention: Microwave vacuum drying can retain more total phenolic compounds and total flavonoids in figs. The content of total phenolic compounds in figs dried by microwave vacuum drying can reach 245.11mg/100g dm, which is higher than that dried by other methods, helping to maintain the nutritional value of figs.
- Appearance and texture maintenance: Different from hot air drying, heat pump drying, and far-infrared radiation drying, which will cause the surface of figs to wrinkle irregularly and the internal structure to collapse, microwave vacuum drying is the same as freeze-drying. The water in the material is directly sublimated from the ice crystal state. The dried figs have a good - maintained structure, obvious pores, and a loose structure, which can better maintain the original appearance of figs.
- Flavor retention: The controlled heat of the microwave prevents excessive moisture loss and preserves the delicious taste of figs, avoiding the "burnt" or "stale" taste caused by high - heat drying.
- Energy saving: Microwave vacuum drying uses microwave energy to directly heat the material, without the need to heat a large amount of air like traditional drying methods, so it has higher energy efficiency and can save energy.
