Processing and drying technology of jujube

Jujube is a traditional health food with rich nutritional ingredients. In addition to some fresh food, most jujubes are directly eaten as wash-free dried fruit products in the consumer terminal market; in addition, the jujube producing areas are relatively concentrated, and the harvest period in autumn is concentrated, while the consumer market is oriented to the whole country. In order to facilitate storage, transportation and sales, jujubes need to be cleaned, dried, cooled back to soft and sterilized packaging processing.

jujube contains abundant dietary fiber and sugar. Different natural climate, soil and water, sunshine conditions, growth cycle and nutrient acquisition of jujube trees determine the quality of jujube. The criteria for judging the quality of jujube mainly refer to its shape, taste and color. High-quality jujube is rich in dietary fiber and sugar, full and elastic fruit shape, sweet taste, red and bright color. The core of processing jujube is drying.

The drying of jujube is the process of internal moisture evaporation and sugar transformation under the premise of preserving the original quality of jujube as much as possible. Jujube is rich in sugar, which contains polysaccharides is a non-sweetening substance, which must be converted into monosaccharides under the action of biological enzymes before sweetening, which is the reason why jujube matures and sweetens. We need to make the sugar in jujube fully converted under the action of biological enzymes, so we need to enhance the activity of biological enzymes. Experiments show that increasing temperature in a certain temperature range can improve the biological activity of the enzyme, and sugar is a highly thermal sensitive substance, which has a certain coking temperature, so the optimum drying temperature of jujube must be lower than the critical temperature of the carbonization of this sugar.

Through long-term practice, we found the optimum temperature range of sugar transformation in jujube: 64 - 67 C. In the harvesting and processing season, most jujube fruits have entered winter, and the temperature of jujube fruits is about 0 to 10 C, even below zero in some areas. In the drying process, if jujube fruits at about 0 C enter the high temperature environment suitable for sugar transformation directly, the huge difference of ground temperature causes the biological protection reaction of jujube, shrinkage of epidermal cell pore, hardening of crust, preventing the evaporation of water in jube.

Therefore, sufficient preheating is needed in the early drying stage of jujube. When the jujube fruit reaches 40 C and wrinkles are kneaded by hand, it can enter the optimum temperature environment. After entering this temperature zone, the water evaporated in large quantities, and sugar in jujube was fully transformed under the action of biological enzymes, which made the taste sweeter. In the late drying stage of jujube, the free water inside and outside the jujube has evaporated a lot, and the evaporation rate decreases;

the effect of ambient temperature on the evaporation of water inside the jujube fruit decreases, while the difference of dry humidity inside and outside the jujube body enlarges, and the internal water naturally infiltrates and evaporates outside.

At this stage, the environmental temperature should be lowered, and the effect of low temperature on water evaporation of jujube should be reduced, so as to keep the gap between internal and external dry humidity within a reasonable range, and balance the internal and external evaporation of jujube as a whole. The slow evaporation of water and the balance of internal and external evaporation of jujube are one of the important factors to keep the shape of jujube fruit.