Fruit and vegetable storage and preservation knowledge

I. Common types and effects of preservatives for fruits and vegetables

Fruit and vegetable preservatives can be divided into the following eight categories according to their functions and methods of use:

(1) Ethylene removal agent: It can inhibit respiration and prevent ripening after aging. Including physical adsorbents, oxidative decomposition agents, catalyst-type removal agent.

(2) Anti-corrosion and anti-staling agents: The use of chemical or natural anti-bacterial agents to prevent the proliferation of mold and other contaminating bacteria, prevent disease and preservation.

(3) Fresh-keeping agent: It can inhibit respiration, reduce water dispersion, and prevent microbial invasion. Including wax coating agent, shellac coating agent, oily film coating agent, and other coating agents.

(4) Gas generating agent: It can be ripened, colored, deastringent, and preserved. Including sulfur dioxide generator, halogen gas generator, ethylene generator, ethanol vapor generator.

(5) Gas regulators: Can produce a modified atmosphere effect. Including carbon dioxide generators, oxygen absorbers, carbon dioxide removal agent.

(6) Physiological activity regulator: It can regulate the physiological activity of fruits and vegetables. Including stimulating bud Dan, benzyl adenine, 2,4-D.

(7) Humidity modifier: adjust humidity. Including steam inhibitors and dehydrating agents.

(8) other types of preservatives: such as burning alum and so on.

Second, the use of ethylene remover fresh fruits and vegetables

In the storage environment of fruits and vegetables, even if one-thousandth of the concentration of ethylene is enough to induce the ripening of fruits and vegetables, so the use of ethylene removal agent within one to five days after the harvest of fruits and vegetables can inhibit the respiration of fruit and prevent ripening and aging. The following examples illustrate their deployment and use.

(1) Physical adsorption type ethylene removal agent

Activated carbon is packed in breathable cloth, paper, and other sachets, and it is stored in plastic bags or other containers along with the fruits and vegetables to be stored. If the storage of fruits and vegetables is large, the activated carbon is dispersedly placed on the middle and upper layers of fruits and vegetables. Generally 0.3% -3% of the weight of fruits and vegetables. If the activated carbon is damp, the adsorption performance will be reduced and it should be replaced.

(2) Oxidative adsorption type ethylene removal agent

The oxidizing type preservative is generally not used alone, but is coated on the surface of a porous adsorbent having a large surface area to constitute an oxidative adsorption type ethylene scavenger. For example, 5 grams of potassium permanganate, 5 grams of phosphoric acid, 5 grams of sodium dihydrogen phosphate, 20 grams of zeolite 65 grams of bentonite, put together and mixed (or mixed in proportion), add a small amount of water, stir evenly, fully infiltrate, after drying After smashing into small particles with a particle size of 2-3 mm or made into columns of about 3 mm. The preservative is put into a breathable pouch and put into a container together with the fruits and vegetables to be stored, and the sealed pack is stored in the shade. It is suitable for all kinds of fruits and vegetables, especially suitable for melon, grape, peach fresh storage, the use of the weight ratio of 0.6% -2%.

(3) Catalytic ethylene remover

Catalytic ethylene remover is used to catalyze the oxidative decomposition of ethylene with specific selective metals, metal oxides or inorganic acids, suitable for the removal of low concentrations of endogenous ethylene. For example, 100 grams of lanthanum hypochlorite, 100 grams of chromium oxide, and 200 grams of zeolite are mixed together (or mixed according to this ratio) and a small amount of water is added and stirred to make pellets or columnar bodies with a particle size of about 3 mm. Artificial drying at 10 °C, after cooling is the required preservative, this preservative is suitable for all kinds of fruits and vegetables, the use of 0.2% -1.5%.

Third, use of preservatives to preserve fresh fruits and vegetables

Bio-dip is often an important cause of spoilage of fruits and vegetables, and bactericidal preservatives are the most effective way to eliminate micro-organisms. However, the bactericidal preservatives used for different microorganisms are different, and the microorganisms infringing on certain fruits and vegetables are not limited to one pathogenic bacteria. Therefore, the proper use of bactericidal preservatives can improve the antiseptic effect.

If 4.5 g of sorbic acid and 1.8 g of benzoic acid are dissolved in hot water, then 1 g of citric acid, 2.7 g of malic acid are added, shaken or stirred to dissolve, and the volume is adjusted to 2000 ml to adjust the pH to 3.5-4.0. The desired preservative is made. Large amount can be prepared according to the above ratio. This preservative is suitable for the storage and preservation of apples and pears. When used, it can be impregnated or sprayed to make the surface of the fruit evenly coated with a layer of medicament. After air drying, it can be bagged, packed and stored.

Fourth, the use of coated fresh-keeping agent for fresh fruits and vegetables

The coated fresh-keeping agent is usually made of wax (beeswax, paraffin wax, insect wax, etc.), natural resin (the best quality of Yuxi native Yuxi of China), lipids (such as cottonseed oil, etc.), gelatin, starch and other film-forming substances. Made of a suitable concentration of aqueous solution or emulsion. It is applied on the surface of fruits and vegetables by dipping, painting, spraying, etc., and a thin transparent film is formed after air drying to achieve the purpose of inhibiting the respiration of fruits and vegetables.

(1) Wax film coating agent: If 100 g of beeswax and 10 g of sucrose fatty acid ester are dissolved in ethanol first, 20 g of casein sodium is dissolved in water, and the volume of the two liquids is mixed to 1000 ml. Proportional preparation), rapid stirring, emulsification and dispersion are the required preservatives. Dip coating method applied to the surface of tomatoes, eggplants, apples, pears, etc., dried to form a layer of plastic wrap.

(2) Natural resin film coating agent: If 50 g of shellac is added to a mixed solution of 80 ml of ethanol and 80 ml of ethylene glycol, it is soaked and dissolved. Add 1500 ml of aqueous sodium hydroxide solution (formulated from 20 g of NaOH), heat and stir to saponify the dissolved shellac (the amount is adjusted to the above ratio). Apples, citrus fruits, pears and other fruits are soaked in this solution. After being taken out, they are air-dried to form a thin transparent plastic wrap.

(3) Grease film coating agent: First dip the agar in 1000 ml of warm water and heat it until it is swelled. Then, 2 g of casein sodium, 2.5 g of fat and fatty monoglyceride, 400 g of soybean oil were added, and the mixture was stirred at a high speed to obtain an emulsion (the amount was adjusted to the above ratio). The fresh food to be immersed in the emulsion, taken out and stored after air drying, significantly longer preservation period. For example, the broad bean pods were treated with the above emulsion and stored at room temperature for half a month and remained green. Untreated broad bean pods, the surface becomes dark after 3 days, this preservative is suitable for storage and transportation of fruits and fruit and vegetables.

(4) Other film coating agents: First mix 100 g starch with a little cold water and pour into 10 kg boiling water to prepare a thin paste. After cooling, add 50 g of sodium bicarbonate and stir well. The oranges are immersed in the slurry, removed and dried to form a protective film, packaged according to conventional methods, and stored in a cool place.

V. Using gas generating agents to preserve fresh fruits and vegetables

Gas generating agents are volatile substances or gases produced by chemical reactions. These gases can sterilize or eliminate gases such as ethylene to achieve a longer shelf life.

(1) Sulfur dioxide generating agent: This method is suitable for storage of grapes, asparagus, hard flower bulb cauliflower and other fruits and vegetables susceptible to gray mold disease. For example, 50 grams of sodium bisulfite and 100 grams of oxidized silica gel are mixed (or in this ratio) and packed in small bags made of cotton paper. The selected Kyoho grapes are arranged in the box with two layers of stems facing upwards. Energy used to remove ethylene film. Stored at a temperature of 0-2°C in the storage room and 90% in relative humidity can be stored for more than 4 months, and the amount used is generally 0.5%-1%.

(2) Halogen gas generating agent: 10 g of potassium iodide, 10 g of activated clay, and 80 g of lactose are thoroughly mixed together and packaged with breathable fibrous materials such as paper and cloth. It can also be packaged in a granular package for use in the package. The amount of use varies greatly depending on the type of packaging stored and the permeability of the packaging material. In general, 10-1000 mg of inorganic halide is used per kilogram of fruit.

(3) Ethanol vapor generating agent: 30 g of anhydrous silica gel was impregnated in 40 ml of anhydrous ethanol to make it fully adsorbed. After the absorption is finished, the remaining liquid is removed, put into a moisture-proof and air-permeable container, and put into a polyethylene film bag together with 10 kg of green bananas, sealed and placed in an environment with a temperature of about 20° C., and stored for 3 to 6 days. Can be mature. This ripening method is most suitable for long-distance transportation from the south to the north, and can be sold after reaching the destination.

Six, the use of gas conditioners to preserve fresh fruits and vegetables

Gas conditioning agent refers to the regulation of the gas composition in a controlled atmosphere storage, wherein it is mainly a preparation for regulating oxygen and carbon dioxide gas. (1) Deoxidizers: In the storage and preservation of fruits and vegetables, the use of deoxidizer must be matched with the corresponding breathable and moisture-permeable packaging materials such as low-density polyethylene film bags, polypropylene film bags, KOP (polyethylene, vinylidene chloride, polypropylene) Laminate) film bags, etc. used in conjunction, in order to achieve better results. 60 grams of iron powder, 10 grams of ferrous sulfate (FeSO4.7H2O) 7 grams of sodium chloride, 23 grams of soy flour mixed evenly (larger in proportion to this ratio), into a breathable pouch, together with the fruits and vegetables to be preserved It can be sealed in a container such as plastic. Generally 1g of preservative can remove 1000ml of oxygen in a confined space.

(2) Carbon dioxide generator: Sodium bicarbonate, 73 grams, 88 grams of malic acid, and 5 grams of activated carbon were mixed together (the amount of which was more than this ratio), and a fruit and vegetable preservative capable of releasing carbon dioxide gas was obtained. In order to facilitate the use and give full play to the effect of preservation, preservatives should be packaged into small bags of about 5 to 10 grams. When used, it can be sealed together with fresh fruits and vegetables in containers such as polyethylene bags and corrugated paper boxes.

(3) Deoxidation (carbon dioxide generation) agent: This type of preservative is characterized by the production of carbon dioxide gas while deoxygenating, resulting in a low oxygen and high carbon dioxide storage environment. 200 grams of iron powder, 120 grams of ferrous chloride, 200 grams of sodium bicarbonate, 80 grams of phthalic acid, and 200 grams of bentonite are mixed together (a large amount is formulated according to this ratio) and filled with air permeability. Can be put into use in the pouch. This preservative is characterized by the ability to remove oxygen and produce carbon dioxide gas. Put fruits and vegetables into low-density polyethylene film bags with a thickness of 0.02-0.04 mm. At the same time, put fresh-keeping agents at a dose of 3-8 g/L. After being sealed and kept at room temperature, low oxygen and high carbon dioxide gas can be produced. Atmosphere storage environment.

(4) Carbon dioxide removal agent: Moderate carbon dioxide gas can inhibit the respiratory intensity of fruits and vegetables, but must adjust the gas composition accordingly according to the adaptability of different fruits and vegetables to carbon dioxide. Carbon dioxide removal agents are more effective when it is possible to cause high carbon dioxide concentrations. Dissolve 500 g of sodium hydroxide in 500 ml of water to prepare a saturated solution. Put the peat into an aqueous solution of sodium hydroxide. Stir it so that it is fully absorbed, filtered, and dried. Use this preservative when used. The purpose of breathability.

Seventh, using humidity regulators to preserve fresh fruits and vegetables

During the storage of fruits and vegetables, in order to maintain a certain degree of humidity, it is usually adopted in the plastic film packaging application of evaporation inhibitor and anti-condensation agent to adjust, in order to extend the storage period. The sodium polyacrylate sodium is packaged in an air-permeable pouch and enclosed in a plastic film together with the fruits and vegetables. When the humidity in the pouch decreases, it can release the trapped moisture to adjust the humidity. The use amount is generally 0.06% of the weight of the fruits and vegetables. 2%. This preservative is suitable for vegetables such as grapes, peaches, plums, apples, pears, oranges and other fruits and mushrooms, cauliflower, spinach, garlic sprouts, green peppers, and tomatoes.

Use of Physiological Activity Modifiers Preservation of Fruit and Vegetable Physiological Activity Modifiers are substances (plant hormones) that are physiologically active for plant growth and chemical agents that can modulate or stimulate plant growth. Dissolve 0.1 g of benzyl adenine in 5000 ml of water, and prepare 0.002% of Chau Chau. Treating leafy vegetables with impregnation method can inhibit respiration and metabolism and effectively maintain quality. This preservative is suitable for celery, lettuce, cabbage, broccoli, cabbage and other leafy vegetables and beans, green peppers, cucumbers and so on. The use concentration is usually 0.0005% - 0.002%.

Nine, commonly used fresh-keeping packaging materials

The fresh-keeping packaging material is a packaging material that adds fresh-keeping agent or special processing on the basis of ordinary packaging materials to give fresh-keeping function. Freshly-packed packaging materials that have been developed include fresh-keeping packaging paper, fresh-keeping containers, and catalyst-type ethylene removal agents that are filled into papermaking raw materials or dip-coated onto manufactured papers to provide fresh-keeping performance. The preservation box is the same as the plastic wrap, and all or part of the box can be kept fresh, or the freshness paper can be attached to the inside of the box. The fresh-keeping bags include silicone rubber window air-conditioning bags, anti-condensation film bags, micro-porous film bags, and plastic film bags made of antibacterial agents, ethylene removing agents, deoxidizers, and deodorants. Because of its many advantages, the fresh-keeping packaging material is a promising packaging material that is popular among users. In recent years, it has been widely used for storage and preservation of fruits and vegetables.

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