Fresh-keeping scheme of fresh fruits and vegetable

2022-07-27
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Fresh fruits and vegetables fresh-keeping scheme of vacuum precooling technology 1. Fresh-keeping mechanism of fresh fruits and vegetables the primary task of fresh-keeping fresh fruits and vegetables is to maintain the appearance, hardness, taste and flavor of perishable fruits and vegetables. Most fresh fruits and vegetables lose their commodity value if they lose their appearance

the fresh fruits and vegetables after harvest are still living beings, and will continue to undergo a series of physiological changes, so that their unique flavor and taste will be further fully revealed, and they are more suitable for people's needs in terms of color, flavor and nutrients. This process is called post ripening stage; Then, the fruits and vegetables gradually lose their original color, flavor and nutrients, and even soften and disintegrate, which is the aging stage; Trying to delay the post ripening and aging process of fresh fruits and vegetables is to try to maintain the original quality process. This time process is called the fresh-keeping period

the main factors affecting the physiological changes of fresh fruits and vegetables after harvest are temperature, humidity, ambient gas, packaging, mechanical damage, etc., which will cause weight loss, loss of freshness, shrinkage, color and gloss fading, and seriously affect the storage resistance and disease resistance of products

there are two types of respiratory patterns of fruits and vegetables after harvest: climacteric and non climacteric. The former reaches the peak respiratory intensity at maturity, when the flavor quality of the fruit is the best, and then the respiratory intensity decreases, and the fruit senescence and even death follow. Ethylene can promote the climacteric fruit to reach the respiratory peak in advance, and promote early ripening and senescence

temperature, fresh fruits and vegetables after harvest have a lot of field heat and vigorous respiratory heat. Generally, within a certain temperature range, the respiratory intensity increases by 1~1.5 times or even higher for every 10 ℃ increase. The greater the respiratory intensity, the greater the material consumption and the shorter the storage life. In the range of 30 ℃ ~60 ℃, the activities and reproduction of fungi, bacteria and various microorganisms are the most vigorous. Low temperature can slow down the physiological activities of fresh fruits and vegetables and inhibit the reproduction of fungi and other microorganisms

humidity: slightly dry or wetter can inhibit respiration. Low humidity means dry, which will increase transpiration

modified atmosphere packaging. The atmosphere generally contains 20.9%o2, 78%n, 0.03%co2 and some other trace gases. Reducing the concentration of O2 in the storage environment can inhibit the respiration of fruits and vegetables and even make them in a dormant state. It can also kill some microorganisms or inhibit their activities. Properly increasing the CO2 concentration can not only inhibit the respiration of fruits and vegetables, but also inhibit the synthesis of ethylene in fruits and vegetables, and inhibit the influence of existing ethylene on the fruits and vegetables of wire pulling machine. The premature and senescence of fresh fruits and vegetables are mainly caused by ethylene gas

mechanical injury. The respiratory intensity of fruits and vegetables with mechanical injury will increase sharply, which is called injured respiration. In addition, besides increasing transpiration, mechanical injury wounds are particularly susceptible to microbial infection and cause deterioration and decay

it can be seen from the above that in order to have the longest fresh-keeping period after the harvest of fresh fruits and vegetables, it is necessary to quickly remove the field heat and inhibit the respiratory heat as soon as possible, store them in an appropriate temperature, humidity and gas environment, reduce the respiratory intensity and transpiration, inhibit or kill microorganisms, and remove harmful gases such as ethylene, ethanol (leading to fermentation corruption), acetaldehyde (leading to aging fermentation)

it can be seen from the above that the vacuum precooling combined with modified atmosphere packaging technology can not only maximize the storage period, but also maximize the shelf life. At the same time, it is light, comfortable and partially intelligent. II. Fresh-keeping scheme of fresh fruits and vegetables with vacuum precooling technology. 1. Basic principle of vacuum cooling technology: under normal atmospheric pressure (101.325kpa), water evaporates at 100 ℃. If the atmospheric pressure is 610pa, water evaporates at 0 ℃. The boiling point of water decreases with the decrease of ambient atmospheric pressure. Boiling is rapid evaporation, which absorbs heat rapidly. Fresh fruits and vegetables are placed in closed containers to quickly extract air and water vapor. With the continuous reduction of pressure, fruits and vegetables will continuously and rapidly evaporate water, so they are usually cooled at a lower conversion rate. The water loss of vacuum cooling is generally about 3%, which will not cause wilting and loss of freshness of fruits and vegetables. Due to the pressure difference inside and outside the fruit and vegetable tissues, the harmful gases and heat in the tissues are also extracted, which can delay the arrival of climacteric respiration peak in fruits and vegetables. In this way, in the case of vacuum cooling, the cooling is carried out simultaneously from the inner part of the tissue to the outer surface, that is, uniform cooling, which is unique to vacuum cooling. Any other cooling method is slow "infiltration" cooling from the outer surface to the inner part of the tissue, so the preservation time is long

vacuum precooling equipment is a cooling processing equipment, not a refrigeration equipment. Its purpose is to quickly cool the fruits and vegetables to the set temperature, and then take the items out of the equipment, or put them in the air, or transport them directly, or put them in the cold storage. Causal vegetables are in a dormant state, and the recovery of their vitality requires a time process, which is the fresh-keeping period

special attention: vacuum precooling can remove water from the surface of fruits and vegetables harvested in rainy days, and can "heal" small wounds on the surface of fruits and vegetables to reduce the chance of microbial invasion. At present, there are no other treatment methods, only the vacuum precooling equipment

compared with other cooling methods, the vacuum cooling method has the following characteristics:

1 The preservation time is long, so it can be transported directly without entering the cold storage, and the medium and short distance transportation can be carried without the heat preservation vehicle

2. The cooling time is very fast, generally only takes more than 20 minutes, and any packaging with air holes can be

3. The original sense organs and quality (color, aroma, taste and Nutrition) of fruits and vegetables are best maintained

4. It can inhibit or kill bacteria and microorganisms

5. It has "thin layer drying effect" - some small damages on the surface of fruits and vegetables can be "cured" and healed or will not continue to expand

6. No pollution to the environment

7. Low operation cost

8. The shelf life can be extended. Leafy vegetables pre cooled by vacuum can directly enter high-grade supermarkets without refrigeration

it can also be used for pre cooling fresh edible fungi, fresh cut flowers, raw and fresh meat, rice, steamed products, cooked food, etc. It is especially suitable for cooling articles to extend shelf life

vacuum precooling of fresh fruits and vegetables Comparison of shelf life of modified atmosphere packaging and ordinary cold storage (unit: day)

type vacuum precooling of ordinary cold storage vacuum precooling + modified atmosphere packaging

spinach 40 50

mushroom 10 16

strawberry 9 15

taro 25 32

celery 8 40 54

cabbage 8 39 50

parsley 4 40 52

cauliflower 27 35

fresh pork 71215

green pea 3038

configuration of fruit and vegetable vacuum pre Cooler:

1 The vacuum chamber is square in cross section and made of stainless steel

2. The vacuum pump is a world famous brand imported with original packaging, with air cooling

3. The refrigeration unit is an imported compressor unit with air cooling

4. The core or surface temperature of cooled articles can be set, controlled and timely displayed

5, temperature and vacuum degree are all digital display

6. The revolving door has a volume below 10m3, and the translational door has a volume above 10m3. As long as the "start" button is pressed, the machine will stop when the pre cooling temperature is set, and the door will be automatically inflated to open

2. Modified atmosphere fresh-keeping packaging technology

the so-called modified atmosphere fresh-keeping packaging is to use a certain proportion of protective mixed gas (usually CO2, N2, O2) to replace the air in the packaging, and use the different effects of various gases to inhibit the growth and reproduction of most microorganisms that cause food spoilage, so as to achieve fresh-keeping and prolong the fresh-keeping period

since the respiration of fruits and vegetables remains high after harvest, be sure to remove the package (1) when the new parts have been damaged (such as the pump sealing gasket); Only when the oxygen content in the container drops below 5% to keep it in a dormant state, and then CO2 is used to inhibit the growth of bacteria, can the product maintain its original fresh state

modified atmosphere fresh-keeping packaging has the following characteristics:

1 Not only the storage period is long, but also the shelf life is long

2. Maintain the original quality (color, shape, aroma, taste, taste and nutrients) most effectively

3. Change the packaging style and improve the product packaging level

the modified atmosphere fresh-keeping packaging has the following configuration:

the machine adopts the internationally leading Panasonic programmable controller (PLC) and man-machine interface. The operating procedures such as gas mixing, gas replacement, heat sealing cutting, heat sealing film collection and release, and material mold conversion are automatically controlled by the microcomputer. Each link can be adjusted and set on the touch screen according to the needs of the packaging process

it is widely used in supermarket distribution of raw and cooked meat products, fish, poultry, fruits, vegetables, bread and other foods

the vacuum cooling modified atmosphere fresh-keeping packaging technology can not only prolong the fresh-keeping period of fruits and vegetables, but also maintain their original flavor and bright color. The modified atmosphere packaging of fruits and vegetables not only improves the packaging grade, but also extends the shelf life and increases the added value of the product. Therefore, more and more fruit and vegetable processing and distribution enterprises are paying attention to the vacuum rapid cooling modified atmosphere fresh-keeping packaging technology. For example, Shanghai Xinya group, Shanghai Chuangxin Food Co., Ltd., Wuhan COFCO Meat Food Co., Ltd. and other enterprises cooperate to develop modified atmosphere fresh-keeping packaging for fresh cut vegetables, cold fresh meat and other products

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