* * * There are many kinds and varieties of citrus, which are generally resistant to storage, but there are also great differences between different kinds and varieties. Generally speaking, lemons are the most storable; Followed by sweet oranges, such as Sichuan Jin orange, true sweet orange, Hunan red sweet orange, Fujian snow orange and so on. Can be kept for about half a year; Third, oranges, such as banana oranges and satsuma oranges; Wide-peel orange has the worst storage tolerance, especially Sichuan red orange. Of course, in every orange population, there are naturally points of tolerance to storage and intolerance to storage. For example, in the wide-peel citrus with poor storability, mandarin oranges and mandarin oranges are storable.
Citrus fruit trees grow in warm and rainy subtropical and tropical areas, so the storage temperature of their fruits should not be too low, which is easy to cause chilling injury. However, respiration increases with the increase of temperature. In order to inhibit respiration and prolong storage life, it is necessary to store at low temperature. According to the test results, the storage temperature of different citrus varieties is obviously different. The suitable storage period of sweet orange is about 2℃ (quoted from Zhang Baichao), generally 3-5℃, 4-6℃ for satsuma, 0/0-/0/2℃ for red orange and 7-9℃ for banana orange, and/0/0-65438 for kloc. Due to the use of preservatives, the storage temperature will also change. The experimental results in some provinces show that citrus fruits can be stored for about half a year under the conditions of high humidity and high concentration of carbon dioxide at storage temperature 10- 15℃. Such a storage temperature can be achieved in many ventilation warehouses, which is conducive to expanding storage.
* * * Strawberries are bright red in color, watery, soft and juicy, sweet and sour, and contain rich nutrients such as calcium, phosphorus, iron and vitamin C. Strawberries have high water content and delicate tissues, and are prone to decay and deterioration due to mechanical damage and microbial infection. At room temperature, the fruit began to change color and taste after storage for 1~3 days, which made it difficult to keep fresh.
3. Storage method ① Modified atmosphere storage. Cover the sealed strawberry special fruit bowl with a polyethylene film bag with a thickness of 0.04mm and store it at 0 ~ 0.5℃ and relative humidity of 85% ~ 95%. The gas in the bag is 3% oxygen and 6% carbon dioxide. Under these conditions, strawberries can be stored for more than 2 months.
* * * Myrica rubra can be stored at room temperature for a short time without any treatment. As the saying goes, "One day, two days, three days." Therefore, it is extremely important to control the appropriate storage conditions. The experiment of Shanghai Fruit Company showed that soaking Myrica rubra fruit in 1000ppm salicylic acid for 2 minutes the next day after harvest could maintain the good quality and flavor of the fruit and reduce the rot rate. According to the experiment, bayberry fruit can be stored for 1-2 weeks at 0-0.5℃ and relative humidity of 85%-90% without deterioration. In addition, frozen storage can keep fresh for about half a year, but generally 1-2 months is appropriate. As far as possible, use small bamboo baskets and baskets as fruit containers, lined with banana leaves and lotus leaves, which can not only play a buffering role, but also keep bayberry moist and fresh.
* * * * Plum storage and fresh-keeping method
3. Modified atmosphere storage: ① Modified atmosphere storage. Plums are sealed in a polyethylene film bag with a thickness of 0.025mm, and can be stored for 70 days under the conditions of air temperature of 0-65438 0℃, carbon dioxide content of 7-8% and oxygen content of 65438 0-3%. ② Modified atmosphere refrigeration in small packages. Prunes harvested at the right time are removed from stems, pests and damaged fruits, packed in polyethylene film bags, each bag is 1- 1.5 kg, sealed and stored at-1℃ for 2-3 months.
* * * * Apple is one of the fruits that can be stored well. However, different varieties have different storage tolerance, among which late-maturing varieties have stronger storage tolerance than early-middle-maturing varieties, and middle-maturing varieties have stronger storage tolerance than early-maturing varieties. Red Fuji, Guoguang and other late-maturing varieties have little change in hardness and quality during storage, and have strong disease resistance and are suitable for long-term storage. Mid-mature varieties such as Red Star, Marshal, Ruby, Jonakin and Beidou are easy to mature after storage, and their quality changes greatly. These varieties have strict storage conditions and generally have a short storage time, but they can also be stored in modified atmosphere until February to March of the following year.
References:
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Food, like the human body, is metabolized every day and has a "aging" process. Fruits and vegetables will be dehydrated, meat will rot and processed products will be moldy. In order to slow down the "aging" process of food and extend the shelf life, various storage technologies such as refrigeration, vacuum and heat treatment are widely used. Plastic wrap is one of the simplest and most commonly used preservation methods.
Plastic wrap has moderate permeability and impermeability. Wrapping food with plastic wrap of different materials can adjust the ratio of oxygen and carbon dioxide around the fresh-keeping products. Secondly, it can keep the moisture content in the bag and prevent the water loss in food; Third, it can block the dust in the air and reduce the infection of germs, thus prolonging the shelf life of food.
Generally speaking, the food with plastic wrap can be kept fresh for about a week at room temperature. However, the fresh-keeping effect of plastic wrap is relative, and the fresh-keeping effect of plastic wrap with different quality and composition is very different. If the air permeability of the membrane is poor, the carbon dioxide produced by food breathing cannot be discharged, and water will also accumulate in the bag, thus causing food to undergo chemical reaction and deteriorate.
In addition, if the raw materials used to make plastic wrap do not meet the production requirements of healthy products, harmful ingredients in inferior raw materials may also penetrate into food or react with ingredients in food, which will not only make food fresh, but will turn healthy food into harmful food. PVC, which is often mentioned recently, is one of the raw materials for making plastic wrap-PVC.
At present, the plastic wrap circulating in the market is mainly made of three kinds of raw materials: the first is polyethylene, referred to as PE, and most household plastic wrap sold in supermarkets is made of polyethylene; The second type is polyvinyl chloride (PVC), which is often used in supermarkets to package cooked food, vegetables, fruits, bread, cakes, semi-finished products and so on. The third type is polyvinylidene chloride (PVDC), which is mainly used for the packaging of cooked food and ham.
Among the three raw materials, PE is recognized as the safest because it can be produced without adding any plasticizer. However, PVC and PVDC are considered to be health hazards because of chlorine. Among them, PVDC is relatively expensive, and it is difficult to make membrane technology, and there are few preservative films made with it in the market. Relatively speaking, PVC is widely used in homes and supermarkets. Polyvinyl chloride (PVC) is a film formed by polymerization of a large number of vinyl chloride monomers and processing AIDS under high pressure. Because PVC is a hard plastic, a large amount of plasticizer must be added to make a transparent and soft plastic wrap.
At present, most PVC cling films used in the domestic market use DEHA as plasticizer. DEHA is a substance that can increase the flexibility and elasticity of products when added to synthetic resin materials, and its content in PVC plastic wrap is about 40%-50%. In addition, there is another way to use dioctyl phthalate (DOP) as plasticizer, but the price of DOP is much higher than DEHA, so it is not commonly used.
PVC itself is an ultra-stable compound, which is non-toxic and harmless. The food packaging produced by PVC contains free vinyl chloride monomer that does not participate in polymerization. A large number of animal experiments and human epidemiological data show that vinyl chloride can induce liver cancer, lung cancer, gastric cancer and lymphoma, and can cause chromosome abnormalities in animals and humans. Therefore, the International Center for Research on Cancer (IARC) lists it as a carcinogen.
In addition, the plasticizer DEHA used in the production of PVC cling film can be released from the cling film at room temperature and infiltrated into food, especially foods with high fat content, such as meat products.
When food is heated, the release of DEHA in plastic wrap will also accelerate. The International Center for Research on Cancer classifies DEHA into three carcinogens. DEHA will not only cause cancer to human body, but also cause endocrine dysfunction, reduce male reproductive function and even cause mental illness.
In addition to the processing AIDS mentioned above, antistatic agents, smoothing agents and anti-blocking agents, hardening agents, heat stabilizers, antioxidants, blocking agents, etc. It can also be added in the processing of food packaging film according to different needs to ensure the transparency, flexibility and oxidation resistance of the film. However, these processing AIDS are all composed of chemicals with different structures, which will gradually accumulate in the human body after long-term use, resulting in different toxic and side effects or related diseases.
■ Master several methods to distinguish materials.
Because of its reasonable price and high safety, polyethylene plastic wrap can be used as the first choice for family shopping. Some consumers equate the household plastic wrap sold in supermarkets with the PVC plastic wrap described in the article, which is wrong.
1.PE material has poor transparency, pale color and blurred food; PVC material has good gloss and looks clear and thorough, just like through glass.
2. flexibility. PE is soft, but its toughness is poor, and it will break after stretching. PVC material has strong toughness, can be greatly widened and stretched without breaking, and is easy to stick to hands.
3. Combustible materials. After the PE cling film is ignited by fire, the flame is yellow and will not go out when leaving the fire source, with oil droplets and no pungent smell; The PVC cling film is chlorine-containing, and the flame is yellow-green after being ignited by fire, and there is no oil dripping phenomenon. It will go out after leaving the fire source and has a strong pungent smell.
Although some plastic wrap films meet the international safety standards when they are made, they seem to be safe and non-toxic, but some harmful substances, such as DEHA, have the characteristics of accelerated release when heated and subjected to oil.
■ Proper use is very important.
1. Avoid contact. Cover the utensils with plastic wrap, do not fill them, and avoid touching food, especially foods with high fat content such as meat.
2. Master the temperature. Pay attention to the temperature that plastic wrap can withstand when heating, and heat it in strict accordance with the temperature marked on the brand or choose plastic wrap with good heat resistance.
3. Container substitution. In daily life, we can have many substitutes, which can replace plastic wrap, such as ceramic or glass containers. These substitutes are safe, non-toxic and oil-resistant, which is beneficial to protect human health.
Ten methods of fruit storage and preservation
Fruit is fresh food, and it will rot easily after harvest. In order to prolong the shelf life, researchers from all over the world have invented a variety of new preservation technologies, and now they have introduced 10.
1. Fresh-keeping carton: This is a new carton developed by Japan Food Circulation System Association in recent years. The researchers used a kind of "rectorite" (a silicate rock) as an additive for paper pulp. Because this kind of stone powder has a unique good adsorption effect on various gases, and its price is cheap, it does not need low-temperature and high-cost equipment, especially it has a long-term preservation effect, and the weight of fresh fruit will not be reduced, so merchants love to use it, which is more suitable for long-distance storage and transportation.
2. Microwave preservation: This is a method for a Dutch company to keep fruits fresh by low-temperature disinfection. After being heated to 72℃ by microwave for a short time (120s) and then put into the market at 0~4℃, the processed food can be preserved for 42~45 days without deterioration. It is very suitable for supplying "seasonal fruits" in the off-season and is favored by people.
3. Edible fruit preservative: This is an edible fruit preservative developed by the British Food Association. It is a "translucent emulsion" made of sucrose, starch, fatty acid and polyester. It can be sprayed, brushed, dipped and covered on the surface of watermelon, tomato, sweet pepper, eggplant, cucumber, apple and banana, and its preservation period can be as long as more than 200 days. This is because this preservative forms a "sealing film" on the surface of fruits and vegetables, which completely prevents oxygen from entering the interior of fruits and vegetables, thus achieving the purpose of prolonging the ripening process of fruits and enhancing the preservation effect.
4. New film preservation: This is a disposable moisture-absorbing and fresh-keeping plastic packaging film developed in Japan. It consists of two translucent nylon membranes with strong water permeability, and natural paste and syrup with high osmotic pressure are installed between the membranes, which can slowly absorb the water oozing from the surface of fruits and meat to achieve the effect of preservation.
5. Pressurized preservation: The method of making food by pressure was successfully developed by the Institute of Food Science, Kyoto University, Japan. After pressure sterilization, the fresh-keeping time of fruits can be prolonged and the fresh taste can be improved. But acid can't work under pressure, so it is ideal to keep the fruit in the best condition.
6. Ceramic fresh-keeping bag: This is a fruit fresh-keeping bag with far infrared effect developed by a Japanese company. It is mainly to coat a very thin layer of ceramic material on the inside of the bag, so that the infrared rays released by the ceramic can have a strong "* * * vibration" movement with the moisture contained in the fruit, thus promoting the preservation of the fruit.
7. Microbial preservation method: ethylene can promote the aging and ripening of fruits, so in order to achieve the purpose of fruit preservation, ethylene needs to be removed. Scientists isolated a kind of "NH- 10 strain" through screening and research. The strain can be made into "ethylene remover NH-T" to remove ethylene, which can prevent grapes from browning, loosening and falling off during storage, prevent tomatoes and peppers from losing water, changing color and softening, and has obvious fresh-keeping effect.
8. decompression preservation method: it is a new method of fruit storage with good preservation effect, convenient management, simple operation and low cost. At present, some countries such as Britain, America, Germany and France have developed low-pressure containers with standard specifications, which are widely used in long-distance transportation of fruits.
9. Hydrocarbon mixture preservation method: This is a "natural edible preservative" developed by a British biotechnology company, which can extend the shelf life of pears, grapes and other fruits by 1 times. It uses a complex hydrocarbon mixture, which is dissolved in water to form a solution, and then the fruit to be preserved is soaked in the solution, so that the surface of the fruit is evenly coated with a layer of liquid agent. This greatly reduces the absorption of oxygen, and almost all the CO2 produced by fruits is discharged. Therefore, the role of preservatives is similar to that of "anesthetics" acting on fruits to make them dormant.
10, electronic technology preservation method: it uses negative oxygen ions and ozone generated by high-voltage negative electrostatic field to achieve the goal. Negative oxygen ions can inactivate enzymes that metabolize fruits, thus reducing the respiratory intensity of fruits and weakening the survival of ethylene, a fruit ripening agent. Ozone is a strong oxidant and a good disinfectant, which can not only kill and eliminate microorganisms and toxins secreted by fruits, but also inhibit and delay the hydrolysis of organic substances in fruits, thus prolonging the storage period of fruits.
References:
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