Among many known drying methods, hot air drying is a commonly used one. Wash the fruits and vegetables and cut to slice or cube. Put processed slices on a plate coated with mineral oil and put them in a tunnel to dry until the moisture reaches about 4%. Then crushed into powder and quickly placed in a waterproof container to avoid moisture absorption.
Though it is simple, but it is not suitble for juice berries,like grape and strawberry。 Due to high content of sugar， drying must be carried out at a lower temperature or the substance that gives characterstic color, smell to the fruit will break down.
Freez dried fruit and vegetable concentrates or fruit and vegetable flakes. In a vacuum state, the water of the fruit and vegetable is directly sublimated, and the water inside will turn from directly from solid state to the gas state, without experiencing the liquid state. In this way, the solid part still retain their original structure without compromising its original shape.So that the aroma and color of fruits and vegetables can be well retained. The only disadvantage prevent it from wide use is the high equipment and huge engergy consupmtion. So this freeze fruit and vegateble only target the high end market that afford better experience.
The most popular drying method for dehydrating fruits and vegetables is spray drying. In spray drying, when very fine droplets are in contact with hot air, the juice is jet into droplets are dried quickly. The particles stay in the drying chamber for a few seconds, and the product is separated and collected from the air flow through suitable separation equipment.
The inlet air can reach as high as 140-160,so certain thermal ingredient like vitamin C and Anthocyanin and volatile matter is possible to get damaged. But the water solubility is remarkable due to the droplet . It is also of economic cost and convenient to transport.