Carrots are rich in nutrients, including a large amount of carotene, vitamin B, vitamin C, and various inorganic salts. They have the effects of penetrating the lungs, strengthening the spleen, resolving stagnation, detoxifying, and penetrating rashes. Especially, their anticancer effect doubles their value. Carrot is one of the important autumn vegetables due to its wide source of raw materials, low cost, and high net vegetable yield. However, the peel of carrot fleshy roots has a poor water retention ability and is prone to water loss, which affects their freshness. Therefore, their storage and processing products are very popular. After raw material pretreatment, carrots are quickly frozen in a quick-freezing device at - 30 ℃ and stored at a low temperature of - 18 ℃. This can maintain their original bioactive ingredients for a long time, maintain their flavor and quality, extend their marketing time, regulate market supply, and is conducive to long-distance transportation and export sales, improving economic benefits.
1、 The principle of quick freezing and preservation. Using a low temperature below - 25 ℃, carrots can be quickly frozen in a very short time, resulting in the formation of numerous small and uniform ice crystals within the cells and in the intercellular spaces. Therefore, the organizational structure of the cells will not be mechanically damaged, and can be more completely restored to its original state after thawing. At the same time, the low temperature after freezing inhibits the metabolic activity of microorganisms such as bacteria and molds, leaving them in a dormant state, which can slow down the deterioration of the vegetable body due to the action of microorganisms and extend the shelf life. Moreover, the freezing low temperature inhibits the enzyme activity that catalyzes various biochemical reactions in fruits and vegetables, reducing the speed of various enzymatic reactions in quick-frozen vegetables, thereby delaying the consumption of color, flavor, quality, and nutrition of vegetables.
2、 Process flow. Raw material acceptance → cleaning → finishing → peeling → slicing → selection → blanching → cooling → draining → quick freezing → packaging → refrigeration → thawing
3、 Key points of operation
3.1. Acceptance of raw materials: Carrots are required to be selected as raw materials with red flesh color, smooth surface, no groove marks, straight shape, soft meat, small pulp, uniform size, no disease or insect pests, no damage, no decay or deterioration, no stains, normal root shape, and fully mature.
3.2. Cleaning: Remove the soil, sand particles, a large amount of microorganisms, and residual pesticides attached to the surface of carrots. At the same time, replace the cleaning water to maintain its cleanliness in a timely manner.
3.3. Finishing: Cut off the head and surface fibrous roots of carrots.
3.4. Peeling: Use manual or mechanical peeling to remove the surface and inedible parts.
3.5. Cutting: Generally, according to international market sales habits or customer requirements, it can be cut into different shapes. The slice specification is: the thickness is generally about 0.3 cm, and the diameter is about 3 cm (circular); The cutting specification is: 0.8-1 cm small square or orange petal block; Cutting specifications: 0.2 cm thick, 3-4 cm long filaments.
3.6. Selection: Screening method can be used. The raw materials cut into diced, sliced, and shredded are graded, and the raw materials of the same specification and size are screened together. According to actual needs, they are divided into different levels to facilitate rapid freezing of different levels of raw materials in batches.
3.7. Blanching: Place the sliced carrots in a basket and blanch them in boiling water at pH 6.5-7 for 1.5-2 minutes to inactivate enzyme activity in the tissue, kill some microorganisms, and remove some gas and water from the tissue. To prevent excessive and insufficient blanching, it is necessary to continuously stir during blanching, and add 1% sodium chloride or calcium chloride as needed to prevent oxidation and discoloration of the product.
3.8. Cooling: Immediately after blanching, cool in stages to reduce the damage of residual heat effects on the quality and nutrition of raw materials. First, use tap water for the first cooling in a flowing water tank, and then use cold water of 0-5 ℃ for the second cooling in the cooling tank to finally achieve a material temperature of 1-5 ℃.
3.9. Drain: Use a medium speed centrifuge or vibration machine to drain excess water from the surface. The centrifuge has a rotational speed of 2000 r/min and a drain time of 10-15 minutes.
3.10. Quick freezing: Put bulk raw materials into a freezing tray or directly lay them on a conveyor belt, and use liquid nitrogen for rapid freezing. The freezing temperature is from - 25 ℃ to - 35 ℃. The thickness of the frozen raw materials is 5-7.5 cm, and the freezing time is 10-30 minutes.
3.11. Packaging: To prevent dehydration, drying, wilting, and oxidation discoloration of frozen products during refrigeration, frozen raw materials should be immediately packaged. Generally, 0.06-0.08mm polyethylene film bags are used, and the packaging capacity of each bag is 500 grams. To prevent a shortage of portions during thawing and refrigerated drying, each bag should be appropriately weighted by 2-3%. The temperature in the packaging room is 0-5 ℃.
3.12. Refrigeration: Quick-frozen packaged products are immediately stored in a cold storage with a relative humidity of 95-100% and a temperature fluctuation of ± 1 ℃ between - 18 ℃ and - 21 ℃ to avoid recrystallization and moisture evaporation. Generally, the safe storage period is 12-15 months, and they can be sold fresh at any time.
3.13. Thawing: There are many methods for thawing, which can be thawed in a refrigerator, room temperature, cold water, warm water, or hot water. The shorter the thawing process, the better. Thawing in a microwave oven is better. The thawed raw materials should not be excessively heated during cooking, and the cooking time should be short.
