Generally speaking, the loss of vegetables from production to sales is more than 30% due to unsalable and rotten reasons. It is difficult for a single new technology to increase the yield of vegetables by 30%, but the loss can be reduced through the processing of vegetables, thus increasing the number of vegetables relatively. Judging from the varieties of vegetable processing, China currently produces and exports mainly fresh-keeping vegetables, pickled vegetables, dehydrated vegetables, quick-frozen vegetables and canned vegetables. Among these processed varieties, fresh-keeping vegetables, pickled vegetables and dried vegetables are mainly dehydrated by traditional techniques. Dried vegetables 1. Raw materials require that most vegetables can be used for dry processing. Vegetables with thick meat, dense tissue and less crude fiber are most suitable for drying. Such as potatoes, mushrooms, carrots, green peas, green beans, eggplant, peppers, onions, bamboo shoots, kale, day lilies and so on. Some varieties of the same vegetable are more suitable for sun drying, such as onions with white bulbs and vegetables with high solid content. A few vegetables are not suitable for drying because of their unique chemical composition or organizational structure. For example, asparagus will lose its crisp quality after drying, and its tissue will become tough and inedible; Cucumber is rich in water, crisp and fragrant, so it is not suitable for drying. Dried lettuce has bad taste and flavor; Because of the high water content of tomatoes, the juice loses a lot during processing. Even the tomato powder prepared by spray drying, its strong hygroscopicity will also affect the quality of the finished product. Therefore, in order to make the quality of dried products excellent, it is necessary to choose suitable vegetable varieties and varieties. Dried vegetables have certain requirements for raw materials. The raw material requirements and suitable varieties of several common dried vegetables are introduced as follows: 1, day lily. The raw material should be orange, about 10 cm long, with fully developed buds, harvested before the flowers bloom, and the sugar content above 10%. Suitable varieties are Jingzhou flower in Henan, Camellia, Dali flower in Shanxi and Dawuzui in Jiangsu. 2. carrots. Raw materials require smooth surface, few fibrous roots, inconspicuous pith, dry matter greater than 1 1%, sugar not less than 4%, and high carotene content. Suitable varieties are Shanghai Nanjing Red and Shaanxi Persimmon Red. 3. Onions. Raw materials require large bulbs, compact structure, small neck, all-white or light yellow scales, strong spicy taste, and harvesting when the skin is fully dry. The suitable variety is Nanjing Huangpi. 4. cabbage. Raw materials require large and compact balls, small hearts, wrinkled leaves and high dry matter and sugar content. The suitable variety is yellow-green, and the flat-headed variety is good. 5. mushrooms. Raw materials require the mushroom body to be white, thick and tough, the diameter of the mushroom cover is less than 3 cm, the edge of the mushroom cover is rolled in, and the mushroom cover is harvested when there are few or no wrinkles. The suitable variety is white mushroom. 6, sword beans. The raw materials should be turquoise, fresh and tender, the meat should be thick and gluten-free, and the seeds in the pod have not yet formed or are just embryonic. Suitable varieties are white flowers and seeds, safflower and black seeds. 7. Bamboo shoots. Raw materials should be white in color, soft and plump in meat, and have no obvious bitterness. Bamboo shoots should be harvested at about 17 cm above the ground. The suitable variety is bamboo shoots. Second, the process flow 1, raw material selection. The requirements of vegetable drying for raw materials are high dry matter content, less crude fiber and waste, high edible rate, suitable maturity, freshness, good flavor, non-decay and serious damage. 2, cleaning. Manual cleaning or mechanical cleaning is adopted to remove the sediments, impurities, pesticides and microorganisms attached to the surface of raw materials, so that the raw materials can basically meet the requirements of dehydration processing and ensure the hygiene of products. 3, finishing. Remove inedible parts and unqualified parts such as peeling, roots and old leaves, and cut them properly. Peeling raw materials can improve the edible quality of products and is beneficial to dehydration and drying. Cutting adopts mechanical or manual operation to cut raw materials into certain sizes and shapes to evaporate water. It is often cut into pieces, strips, grains and silk, and its shape, size and thickness depend on different kinds and export specifications. For some vegetables, such as onion, garlic, etc., it is necessary to rinse the glue with water continuously during slicing until the glue is washed clean, which is convenient for drying and dehydration and makes the product more beautiful. 4, color protection. Dehydrated vegetables are blanched to protect their color. Some raw materials are still treated with sulfur to protect their color after blanching or drying. 5. dry. The best drying methods are freeze drying, vacuum drying and microwave drying. However, considering the cost, economic benefits and other factors, airflow drying equipment is the most widely used equipment in vegetable drying at present. Of course, natural drying can also be used. 6. Post-processing. After drying, some vegetables can be directly packaged after cooling, and some need to be softened, selected and pressed. Softening is also called soaking. Because of the uneven distribution of hot air or uneven cutting and laying of raw materials during drying, the water content of products is often slightly different. Therefore, after the product is slightly cold, it should be put into a closed tinplate barrel with a cover or a box covered with plastic bags at a certain distance, which is convenient for the moisture balance of the product, soft in texture and convenient for packaging, storage and transportation. Selection is to remove the broken particles and impurities from the softened or pre-softened products, and then pour them into the sorting table to remove the unqualified products. The selection operation should be rapid to prevent the product from absorbing moisture and rising moisture. The selected finished products need to be tested for quality and moisture, and those that fail to pass the test need to be baked again. Squeezing is mainly aimed at dehydrated vegetables. Dehydrated leafy vegetables are fluffy and bulky, which is not conducive to packaging and transportation, so some need to be compressed. Generally speaking, vegetables are dried and pressed while they are hot. In terms of packaging and storage, corrugated boxes are generally used for packaging, and the boxes are lined with moisture-proof aluminum foil bags and plastic bags for sealing. For products that are prone to oxidative browning, they need to be packaged in composite plastic bags and aluminum foil bags, retail packaging100g and 250g, and then packaged in cartons, each with a net weight of 20kg or 25kg. After packaging, it is best to store the product in the cold storage at about 65438 00℃. The warehouse must be dry, cool, free of peculiar smell and pests. During storage, the water content and pests of finished products should be checked regularly. Canned vegetables. Raw material requirements Although most vegetable raw materials can be processed, the processing adaptability varies greatly, and improper selection of raw materials will affect the product quality. When selecting raw materials for canned vegetables, we should consider the yield, supply period, storage period, proportion of edible parts, physical properties, chemical composition, sensory quality and so on. Canned vegetables require varieties and varieties with rich meat quality, delicate texture, less crude fiber, more edible parts and good color. The quality requirements of several canned vegetables are introduced below. 1, concanavalin. The raw materials are fresh, tender and full, green or light green, and the pods are round and rod-shaped, not bent, moderately mature (milk-ripe period), free from pests and diseases and mechanical damage. Flat, deformed, rusty, moldy, thick-ribbed pods, safflower and protruding pods are not allowed. 2. Green peas. The pods are fresh, tender and full, turquoise, moderately mature (that is, full of green pods), free from pests and mechanical damage. Pods are green and tender, with more sugar and less starch. Use white flowers instead of red flowers. Each pod contains more than 5 beans, and the raw materials must not exceed 24 hours from harvest to production. 3. mushrooms. The seedling body is fresh, the mushroom color is white, there is no mechanical damage and insect pest, the umbrella is allowed to be slightly speckled, slightly deformed, slightly thin, with no opening, no peculiar smell, smooth cut on the handle, no space center, no mud roots, and the length is not more than1.5cm.. 4. tomatoes Bright red tomato, full fruit, no pests and mechanical damage, no serious deformity, mildew and deterioration, thick flesh, few seeds, solid tissue, soluble solids above 4%. The transverse diameter of tomato fruit is 30-50 mm, and the transverse diameter of tomato sauce fruit is more than 35 mm. Bamboo shoots. Winter bamboo shoots are tender and crisp, with milky white or light yellow meat and no pests and diseases. Slight damage to the thick and old parts of tender stems is allowed, but bamboo shoots are not allowed to be harmed; Bamboo shoots are fresh and tender, white or yellow-white, with slight jointing allowed, and bamboo shoots have no obvious cavities, deformities and shrinkages. 6.asparagus. The required length is 12- 16 cm, and the average length of the stem is lo-36 mm The first-class products should be fresh, complete, well-shaped, sharp and white, and compact. A small number of bamboo shoots are allowed to have a light blue or purple color not exceeding 5 mm, and there is no damage such as sediment, cavities, cracks, deformities, pests and diseases, rust spots, etc. If the light blue or purple part of the head is more than 5 mm but less than 40 mm; Or the whole head, the length is less than 12 cm, but more than 5 cm; Or there are slight bends, cracks and small holes; Or the tip below 40 mm has slight mechanical damage, all of which are second-class. 7. lettuce. Requirements of fresh, tender, no rot, black heart, hollow, hard heart, mildew, peeling tendons. After salt soaking, the meat is crisp and tender, without obvious green or bitter smell, and it is light yellow or light green. Second, the processing technology 1, raw material selection. The types of vegetables used in canning are extremely important. Different products have their own varieties that are particularly suitable for canning, such as mushrooms, tomatoes, green beans and peas. Each raw material requires a certain degree of maturity, and different varieties require different degrees of maturity, such as green beans, peas and sweet corn. Tomatoes need to be fully ripe. The fresher the raw materials, the better the quality of the processed products. Therefore, the time from harvest to processing of vegetables should generally not exceed 24 hours, and some vegetables such as peas and sweet corn should be processed within 6 hours. 2. Select and grade. Reject unqualified raw materials such as rot, pests and diseases, deformity, insufficient maturity or overripe. In order to ensure the quality of canned products, facilitate processing operation, improve labor efficiency and reduce raw material consumption, it is necessary to classify raw materials according to their size, maturity and color, so that the quality of each batch of raw materials is basically the same. If you classify by shape and size, you can use mechanical classification. There are vibrating and drum classifiers. If raw materials are graded according to quality, they are generally graded manually on the workbench or on the conveyor belt. 3. cleaning. The purpose is to remove dust, silt, dirt, residual pesticides and some microorganisms attached to the surface of raw materials, and clean them manually or mechanically. Different washing methods should be adopted for different kinds or properties of raw materials. Generally, it is soaked in flowing clean water first, so that impurities such as sediment on the surface can be easily separated and removed, and then washed under the condition of blowing water or washed with high-pressure water.
Vegetable raw materials with pesticide residues or contaminated microorganisms can be soaked in 0.5%- 1.0% hydrochloric acid solution, 0. 1%-0.2% potassium permanganate solution or 0.06% bleaching powder solution for 3-5 minutes, and then washed with running water. 4, finishing. Remove the inedible part of the skin, keep the appearance of peeled fruit bright and clean, prevent peeling from being too thick and increase the consumption of raw materials. General peeling methods include manual method, mechanical method, thermal method and alkali method. Different varieties of fruits and vegetables have different peeling methods, such as peeling potatoes with lye. Raw materials treated with lye must be washed with running water immediately after peeling to prevent discoloration. 5, color protection. Some vegetables will turn yellow quickly after being peeled and exposed to the air. Immediately after peeling, it must be put into 0. 1% citric acid solution or 1%-2% salt solution for color protection. 6. Segmentation. Slice, dice or cut raw materials according to different types of raw materials and product requirements. 7. Pre-cook. Most vegetable raw materials must be pre-cooked before canning; Its main purpose is to soften the tissue, facilitate canning and eliminate the air in the raw material tissue; Destroy enzyme activity, stabilize color, improve flavor and texture, remove part of water, and maintain the stability of open cans and solid shapes; Kill some microorganisms attached to raw materials. 8. Classified canning. According to the quality requirements, vegetables of different colors and sizes were canned separately. The amount of vegetables in each can is adjusted according to the product requirements, such as the solid content, raw material variety, tenderness, pre-cooking, dehydration rate after sterilization, etc. When canning, the soup must be filled up to prevent the gap at the top of the can from being too large, causing the vegetables exposed to the liquid surface to oxidize into rings or change color. 9. Exhaust seal. Canned soup must be quickly heated, emptied or sealed. Those who heat the exhaust should pay attention to the exhaust time and temperature so that the exhaust center can reach above 80℃; For varieties with slow heat conduction, the hotter it is before canning, the hotter it is after canning, and add boiling water before exhausting; Seal immediately after exhausting; During exhaust, steam condensate should be prevented from dripping into the tank, and exhaust seal should be adopted after exhaust seal or pre-seal. When vacuum sealing, the vacuum degree should meet the requirements. 10, sterilization and cooling. After the canned food is sealed, it immediately enters the sterilizer for sterilization, and the specific sterilization conditions vary with varieties. Canned vegetables are mostly foods with low acidity or close to neutrality. Because raw materials are more likely to be contaminated by thermophilic Bacillus in soil, most of them are sterilized at high temperature. The canned food after sterilization must be cooled quickly to prevent the contents, shape and taste from being affected by continuous heating, and to prevent the development and growth of thermophilic spores. Generally, the back pressure is used to cool down for about 5 minutes, and it is appropriate to cool down to the central temperature of 37℃ in the tank. 1 1, test. According to the quality standards, inspection methods, inspection rules and packaging requirements of canned fruits and vegetables.