First, the choice of raw materials
The quality of fruit or vegetable products is better, although it is limited by processing equipment and technical conditions, but it is more closely related to the quality and maturity of raw materials. Therefore, it is necessary to select raw materials according to different processed products. The same raw material, due to different varieties (or germs), the processing effect is different, that is, the same type of the same variety, due to different origins, or the quality of processing and production, the quality of the processed products are also different, such as processing pears, It is necessary to use a variety of pear systems with less water and less stone cells. The same variety, different regions of origin, different quality mountains, such as jujube, the South is better than the north, and the candied dates are crisper than the north. Different processed products, the maturity of the selected raw materials is also different, such as processing fruit, candied fruit requires fruit maturity of 75-85% (that is, fruit ripening period), to be rich in meat, tight tissue, less tannins When the color is bright, it is good. Fruit and vegetable cans are generally required to be ripe. At this time, the fruit is fully developed, with proper flavor and color. The meat is tight and not soft, and it is invariable after sterilization. However, leafy vegetables are different from most fruits, and are generally required to grow in the growing season. Harvested, at this time, the crude fiber is less and the quality is good.
The raw materials used in processing must be fresh and complete. Otherwise, once the fruits and vegetables are fermented, there will be many microbial infestation, resulting in the decay of fruits and vegetables. The more fresh and complete the processed raw materials, the better the preservation of nutrients and the better the quality of the products.
Second, fruit and vegetable processing pretreatment
1. Classification of raw materials: The classification of fruits and vegetables can be classified according to the requirements of different processed products, using different classification methods, including size classification, maturity classification and color classification. In China, maturity grading is commonly used for visual estimation, while size grading is the main content of grading. Almost all processed fruits and vegetables need to be sized. The grading methods include manual grading and mechanical grading.
2, the cleaning of raw materials: the purpose of fruit and vegetable raw materials cleaning is to wash away the dust, sand and a large number of microorganisms and some chemical pesticides attached to the fruit, to ensure the cleanliness of the products, thus ensuring product quality. For fruits and vegetables with pesticide residues, chemical detergents are often added to the water during washing. Commonly used are salicylic acid, acetic acid, and sometimes strong alkali such as sodium hydroxide and strong oxidizing agents such as potassium hydroxide and potassium permanganate. The method of cleaning fruits and vegetables shall be determined according to the shape, texture, surface state, degree of pollution, amount of soil entrained and processing methods. There are mainly manual cleaning and mechanical cleaning. The latter needs to be equipped with drum type, spray type, gas pressure type, paddle type and other equipment.
3, peeling of fruits and vegetables: all fruits and vegetables raw materials rough, hard, with bad flavor should be peeled, in order to improve quality, only in the processing of certain fruit, candied fruit, fruit juice and fruit wine, because of beating and pressing, There is no need to peel, the method of peeling the skin is as follows:
(1) Manual process: artificial peeling with special knives, planing tools, etc., peeling clean, less loss, but labor inefficiency. Commonly used in citrus, apple, pear, persimmon, alfalfa, asparagus, bamboo shoots, melons and so on.
(2) Mechanical peeling: mainly used for comparatively strong raw materials for fruits and vegetables, such as rotary skin machine, mainly used for apple, pear, persimmon, pineapple, etc.; peeling machine, mainly used for potatoes, sweet potatoes, carrots, etc.; Leather machinery: green beans, soybeans, etc.
(3) Peeling of lye: The corrosiveness of the lye is used to dissolve the gel layer on the surface of the vegetable, thereby separating the peel. Alkaline peeling is commonly used sodium hydroxide, which is highly corrosive and inexpensive. Surfactants such as sodium 2-ethylhexylsulfonate are often added to the lye to make the lye evenly distributed to help peel. The concentration of lye, the time of treatment and the temperature of lye when lye is peeled should be determined according to the type, maturity and size of different fruits and vegetables. Increasing the concentration of lye, long treatment time and high temperature will increase the degree of loosening and corrosion of the cortex. Fruits and vegetables treated with lye must be immediately soaked in cold water, washed, and repeatedly changed to water until the surface is not greasy, and the taste is not alkaline. Rinsing must be sufficient, otherwise it may cause ph to rise, insufficient sterilization, and product deterioration.
(4) Thermal peeling: After the short-term high temperature treatment, the skin quickly heats up, the peel expands and ruptures, separates from the internal pulp tissue, and then rapidly cools and peels, which is suitable for peaches, plums and apricots with high maturity. The heat source for hot peeling is mainly steam and hot water. This method has less loss of raw materials, good color and good flavor.
(5) Enzymatic peeling: Under the action of pectinase, the pectin in the citrus capsule is hydrolyzed and the capsule is removed. The key is to grasp the concentration of the enzyme and the optimal conditions of the enzyme such as temperature, time, Ph value and so on.
(6) Freezing and peeling: The fruits and vegetables are frozen in a freezer until they are slightly frozen, then thawed, and the skin is peeled and peeled. This method is suitable for peach, apricot, tomato, etc., and the quality is good but the cost is high.
(7) Vacuum peeling: the mature fruits and vegetables are heated first, so that the skin and the flesh are easily separated, and then enter the vacuum chamber with a certain degree of vacuum, and properly treated, so that the liquid under the peel quickly "boils", skin and meat. Separate, then break the vacuum, rinse or agitate the peel. Suitable for mature peaches and tomatoes.
Separation, enucleation (heart), dressing and crushing of raw materials: Large-volume raw materials for fruits and vegetables should be cut and denucleated (heart) when they are preserved in cans, dried, processed preserves, preserves and vegetables. Sometimes, in order to maintain a good appearance after processing the raw materials, it is necessary to carry out trimming. These require some special small tools, such as nuclear (Hawthorn, jujube), puncture (Kumquat, plum) and special machinery, such as the peach machine, multi-function slicer, special slicer. The crushing of fruits and vegetables is usually done by a broken beater.
Blanching of fruits and vegetables: Put the cut or other pretreated fresh ingredients into boiling water or steam for a short period of time. It can heat inactivate enzymes, improve tissue and color; soften or improve tissue structure; stabilize or improve color; remove some spicy and other bad odors of fruits and vegetables; reduce the amount of pollutants and microorganisms in fruits and vegetables. The commonly used methods for blanching fruits and vegetables are steam and hot water. In order to protect the color of green fruits and vegetables, alkaline substances such as sodium hydrogencarbonate and calcium hydroxide are often added to the blanched water. However, the loss of vc is large, and the degree of blanching of fruits and vegetables should be determined according to the type of fruit and vegetable, block shape, size, and process requirements. The fruits and vegetables after blanching should be soaked in cold ice in time to prevent excessive heat and soften the tissues.
Vacuum treatment of raw materials: Due to the loose internal structure of some fruits and vegetables, such as tomatoes, it contains a lot of air, which is unfavorable for processing, especially for canning. Vacuum treatment is required, that is, the raw materials are placed under vacuum in a certain medium to release internal gas. Come out and replace it with sugar water and salt water. The methods of vacuuming are dry pumping and wet pumping. The conditions and parameters controlled by it are: vacuum degree, temperature, pumping time and vegetable extraction area.
Fruit and vegetable color protection
During the processing of the fruit, peeling, cutting, crushing, air contact and high temperature treatment of the raw materials may promote chemical changes and produce colored powder. These include enzyme browning and non-enzymatic browning.
Method to prevent enzyme browning: 1 Select processing materials containing less tannins and less tyrosine acid, such as citrus and berry; 2 control the supply of o2 to create an oxygen-deficient environment. Such as vacuuming, pumping nitrogen, using stone oxygen, etc.; 3 inactivation of enzymes: blanching, soaking in salt solution, immersion in sulfite solution (2%, -3%), soaking in sulfur solution.
Ways to prevent non-enzymatic browning: 1 use processing materials with low amino acid and reducing sugar content; 2 use so2 treatment, can prevent non-enzymes and enzymes; 3 apply hot water blanching; 4 maintain enzyme conditions to decompose sugar Slow, inhibit the form of colored substances; 5 keep the product low moisture content, storage environment, keep dry at low temperature.