Broccoli (Brassica oleracea L.Var.votrytis), also known as tender stems cauliflower, broccoli, is a crucifera Brassica Brassica Varieties, native to Italy. Broccoli is rich in protein, IQF vegetable frozen broccoli sugar, fat, vitamins and minerals, nutrient composition is complete, has a high market value, is China's exports of one of the main vegetable species. The edible part of the young pedicels and buds, after harvest at room temperature green yellow flowers, water softening, which seriously affect their commodity value. IQF vegetable frozen broccoli Therefore, the broccoli for vacuum freeze-drying process research, improve product quality, expand exports, improve agricultural production efficiency, to meet market demand has practical significance.
Raw materials selection: should choose the color of green vegetables bright green, flower surface without flowers, buds close strong, feel more heavy, no pests and diseases, IQF vegetable frozen broccoli maturity, size is basically the same and not the old man is appropriate; cleaning: qualified raw materials Cleaning and cleaning the surface of the sediment and dirt to ensure the quality of the product; cutting: the clean and drained after the broccoli cut into buds 3 ~ 4cm, stem radius of 0.5 ~ 1cm of the ball; blanching and cooling: drift Hot can passivate enzymes in vegetables, kill eggs and microbes, reduce oxidation and bad flavor, so that broccoli color bright green. Therefore, after cutting the broccoli placed in the temperature 95 ~ 100 ℃ in the hot for 2 min, IQF vegetable frozen broccoli immediately into the 0 ~ 5 ℃ cold water cooling cooling, the cooling time as short as possible; drain and plate: after cooling Broccoli small ball surface will stay some water droplets, which is detrimental to the freeze, easy to freeze after the broccoli balls knot together, is not conducive to the next vacuum drying. In the vibration of the drain machine on the vibration of the drain, remove the surface of the water after the broccoli evenly spread on the stainless steel tray, the volume of 10 ~ 12Kg / ㎡, the thickness of 3 ~ 4 cm.
Freeze the process should grasp the freezing temperature and freezing rate . In order to determine the vacuum freeze-drying process of broccoli, the eutectic temperature should first be known. Broccoli due to variety, origin, water content of different eutectic temperature is also slightly different, eutectic point temperature according to the principle of Aloni Ross liquid conductivity by ion, IQF vegetable frozen broccoli broccoli when the resistance is infinite, with resistance method for the determination of broccoli Crystal point temperature. As the temperature decreases, the current is decreasing, and when the temperature of the broccoli is reduced to -10 to -15 ° C, the current approaches 0, indicating that the broccoli has been frozen at this time. IQF vegetable frozen broccoli It is thus confirmed that the eutectic temperature of broccoli is -10 to -15 ° C. In actual production, the freezing temperature is generally 15 ℃ lower than the eutectic temperature, broccoli freezing temperature between -25 ~ -30 ℃. The broccoli's freezing process is an exothermic process that takes some time. In the library temperature to maintain -35 ℃, frozen about 3h is more appropriate, IQF vegetable frozen broccoli the freezing rate is generally 0.1 ~ 1.5 ℃ / min.
After the sublimation drying is completed, the adsorption energy of these water is high in order to further remove the frozen water that is not frozen in the broccoli cells, IQF vegetable frozen broccoli and if they do not give enough heat, they can not be resolved, so the material temperature at this stage should be high enough The maximum temperature of the orchid is 50 ℃, in order to have enough water vapor to promote the escape, should be in the broccoli inside and outside the formation of a larger pressure, therefore, this stage should have a higher vacuum 50 ~ 70Pa. This process takes about 2h, water content can reach about 3%, in line with the quality requirements of processed products.