—— Analysis and suggestions on citrus preservation methods.

Author: Chen Tianying, 1 class (1), tutor: Zhang Suwei.

First, the historical and economic value of oranges

1, the history of citrus

"The orange pomelo is frosted on all sides, and the pieces are as red as jade." Wenzhou has been rich in citrus since ancient times, with unique flavor and excellent quality. It is the origin of the world-famous "Wenzhou mandarin orange". Satsuma mandarin has been cultivated for more than 2400 years. In A.D. 1 178, Wenzhou well-known Han Yanzhi summed up the previous experience and wrote the world's first complete monograph on citrus, Yongjia Citrus Annals, which was 469 years earlier than the earliest one in Europe. This monograph has been circulated in new versions throughout the ages, and has been translated into English, French, Japanese and other languages for a long time, which has been widely circulated around the world. At that time, Satsuma mandarin was brought to Japan and cultivated into a forest. After several improvements, it became a treasure. Because of its origin in Wenzhou, the Japanese call it "Wenzhou mandarin orange".

2. The nutritional and medicinal value of citrus.

The orange skin is bright, sweet and juicy, which is scientifically analyzed. It is rich in vitamins C, D, fructose, citric acid, calcium, phosphorus and iron. It has a special detoxification effect on gas smoke poison. In addition to fresh food, the fruit of orange can be used to make orange cakes, fruit juice can be used to make wine, orange peel oil can be extracted from peel, flowers can extract essence, and it is also a good honey source, and fruit and orange peel are both good Chinese herbal medicines.

3. Yield and economic value of citrus.

Citrus is a specialty of Wenzhou, a citrus forest, which is fragrant when it blooms and golden when it ripens. It is really a good scenery. The city's citrus1.4000 mu, the highest season 1.983 total output of 300000 tons. There are more than 5,000 mu of citrus forests in Sanyang Street of Ouhai alone, with an annual output of more than 7,500 tons. Wenzhou has become an important citrus production and export base in China.

Citrus has high economic value. For example, the price of citrus last year was between 2-4 yuan/kg. Calculated by per mu yield 1500-2000 kg, the value is not small. Especially the stored oranges which are put on the market have higher economic benefits. When I first picked it, the skin color was green and it tasted a little sour. After storage, the flavor becomes better and is loved by people, and the market price continues to rise.

2. Fresh-keeping and storage measures of citrus and the present situation of using preservatives and other pesticides:

Fresh-picked citrus has higher fruit temperature because of its field heat and vigorous respiration. If it is put into storage immediately after picking, the storage temperature will rise rapidly, and the excessive humidity will affect the storage effect. Therefore, after citrus is harvested, it will be stored in the warehouse after being soaked in drug solutions such as sorting, grading, preservation and sterilization.

The fresh-keeping sterilization liquid of pesticides has the functions of callosity, sweating, precooling and preventing fruit from drying out. "Callus" is to heal the wound of the fruit, so as to avoid the invasion of bacteria and cause rot. "Sweating" is to evaporate part of the water in the peel cells, reduce the swelling pressure of the cells, make the fruit soft and weak, and thus reduce mechanical damage. "Pre-cooling" is to reduce the temperature of orange fruit with field heat and respiratory heat, so that the respiratory function is weakened. The result of early storage is that the peel loses water slightly and wilts, which makes it difficult to lose water during later storage, avoids "low water" and controls brown spot disease, which is especially important for citrus.

By searching for information about fruit preservation technology, there are usually the following measures to preserve citrus:

1, preservation and storage method of natural or general treatment and its practical application;

(1) cellar storage

Because most areas of Wenzhou, where citrus is produced, are often located in the plain, the altitude is too low and it is relatively humid, so this method can hardly be applied.

(2) Barrel storage method:

Because the output of orange farmers in Wenzhou is generally large, an orange farmer often has more than 5 tons of oranges. The cost of using this method is too high and the storage area is too large. No one has stored oranges in this way yet.

(3) ventilated storage

As Wenzhou is located in the subtropical zone, it will face the possibility of warming up in March, and it is impossible to naturally maintain the low temperature below 12 degrees. The rot probability is too high and the relative cost is low, but the good fruit rate is difficult to guarantee. Except for low-yield orange farmers, this method is generally not used by orange farmers, otherwise the risk is too great.

(4) The temperature of the cold storage is 3-4℃, and the cold storage should be ventilated to eliminate excessive harmful gases such as carbon dioxide. Ventilation is usually carried out in the morning when the temperature is low. In order to quickly reduce the temperature in the warehouse to the required low temperature, the fruits in storage were precooled and cooled.

In real life, this method is rare in citrus except for the storage of Chashan Myrica rubra in cold storage. One is that it is too expensive for individuals to build a cold storage, and the other is that citrus is stored for a long time, and there is not much room for appreciation after storage, which is often not worth the candle.

(5) Single fruit or big bag in film bag is packed with polyethylene plastic film and stored in ventilated warehouse, which can play an obvious fresh-keeping effect. Citrus can be 0.0 1-0.04 mm thick, and each bag of fruit is 2.5- 12.5 kg. When packaging with film, fruits should be pre-stored, and then individual fruits should be twisted, sealed and packaged.

This is a good method, but after investigation, this method is basically unnecessary. According to experienced people, after the experiment, the short-term effect is good, for example, one to two months, after a long time, the temperature rises, and the problem comes. The oranges in the bag are sweating, and the moisture is too heavy, which affects the preservation.

(6)γ -ray preservation method.

Soak the fruit10min with 2% calcium chloride solution, air-dry it and put it in a wooden box, or soak the fruit10min with 1% thiophanate, air-dry it and put it in a wooden box, and irradiate it with cobalt 60γ rays respectively. Then, the treated fruit box is stored on the wooden mat in the normal temperature warehouse.

This method is advanced and focuses on theoretical research. In today's rural areas, it is not at all, and orange farmers have not yet learned this method.

2. Chemical anticorrosion and its application

The key of citrus preservation is to prevent rot, and the root of rotten fruit is disease, and Penicillium and Penicillium are the two most serious diseases in preservation, accounting for about 70% ~ 90% of the total rotten fruit rate. In particular, the occurrence of wide-skinned oranges such as mandarin oranges is more common.

Penicillium and Penicillium belong to fungal diseases. It will soften the fruit, produce all kinds of downy mildew and make the fruit rot. At the beginning of the disease, the symptoms of the two diseases are the same, that is, light brown, round and watery lesions, and the affected area becomes soft and easy to shrink. After that, they quickly expanded and grew white hyphae, and then conidia quickly grew in the central part, showing the difference between the two diseases. The conidia mass is cyan, and the outer white hyphae circle is very narrow, only1~ 3 mm. The outer edge of green mold is green, and the mycelium ring is wide and white, and the rotten fruit is easy to attach to the adjacent fruit.

Commonly used methods are:

(1) special comprehensive preservative.

For example: fruit preservatives S-M, s-p-m.

The components are tablets made of bactericide, inhibitor, adhesive and a small amount of additives through chemical treatment.

S-M is white or light yellow powder. The content of effective components is above 86%, water-insoluble matter is above 0. 1%, and Fe (calculated by FeO) is not more than 0.0 1%. Soluble in water, insoluble in alcohol, the aqueous solution is acidic. If left in the air for a long time, it will be oxidized and decomposed above 150℃. S-P-M is white crystalline powder. S-M and S-P-M are light yellow tablets with smooth surface and neat edges. Purity: S-M content >; 84%; The content of sulfur-phosphorus-magnesium is more than 86%.

This product can be widely used for the preservation of grapes, watermelons, apricots, plums, oranges and other fruits. The ingredients used meet the national standard of People's Republic of China (PRC) and the standard GB-2760-8 1 for food additives.

After investigation, citrus comprehensive preservative is available in pesticide stores, but there are few buyers, and orange farmers basically don't need it. The possible reason is that citrus farmers think that this preservative is expensive and the reliability of comprehensive preservative is not high, so they often use their familiar pesticides to keep fresh.

(2) Mix homemade preservatives (commonly used)

For many years, carbendazim and thiophanate-methyl have been widely used to control citrus green mold and penicillium. The concentrations of carbendazim and thiophanate-methyl were 250 ~ 1000 ppm, 500 ~ 1000 ppm and 100 ~ 200 ppm respectively. Due to long-term use, it is found that tobuzine has been used in recent years. In recent years, Bifuron, a bactericide developed in Japan, has a good control effect on Penicillium. And Penicillium species. Tobuzin of carbendazim. The results showed that the effect of soaking seeds with 70% thiophanate 1000 times of 200ppm2-d and storing 100 days was only 7.8% ~ 53.6%. However, soaking the fruit in 25% Befulang water solution for 2000 ~ 3000 times, the disease prevention effect reached 82.5% ~ 88.7%, the good fruit rate reached over 90% after storage 100 days, and the fruit brightness was obviously higher than that of conventional chemicals.

In practical use, citrus farmers will also mix preservatives (triethylaluminum phosphate) with pesticides (dicofol and omethoate).

1) triethylaluminum phosphate is systemic fungicide, which has both protective and therapeutic effects. The pure product is white crystal, and the original drug is white powder, which is easily soluble in water and does not volatilize. The original drug and preparation are stable under natural conditions and easy to decompose in strong acid and alkali medium. Non-toxic to people and animals, low toxic to fish and bees, and relatively safe.

2) Dicofol is a single acaricide with strong selectivity. It mainly inhibits the activity of transferase in mites and has little effect on natural enemies. Control nymphs, adults and eggs of various harmful mites. The effect is obvious, the speed of knocking down mites is fast, the effective period can reach more than 20 days, and it is not easy to produce drug resistance to mites, especially to phytophagous mites.

3) omethoate is an organophosphorus pesticide synthesized by the factory according to the principle that omethoate is a more toxic and toxic compound than omethoate formed by oxidation and metabolism in organisms. Its original medicine is an oily liquid with a strong smell of onion and garlic. Soluble in water, but the stability of aqueous solution is worse than dimethoate, and it is easy to decompose and fail. Omethoate is stable in neutral and acidic solutions, but it will quickly decompose and fail under alkaline conditions.

Omethoate has a strong contact killing effect on pests and mites, especially on some aphids that have developed resistance to omethoate. Omethoate is a highly toxic pesticide, but it is not easy to penetrate into human body from skin, and there is little difference in contact toxicity with omethoate.

Third, food safety (food safety problems caused by preservatives)

Changes in taste and appearance.

In actual planting, citrus treated with pesticides or chemical preservatives is more resistant to storage. At the same time, the operation process is simple and the time spent in the middle is not much, so according to the principle of economy, most orange farmers adopt the method of drug preservation and antisepsis. (Only a few oranges eaten in time have not been chemically treated) This one is far more beautiful in appearance than those untreated oranges. However, if the storage time is too long, more than half a year, it may still be the same outside, but the taste has changed, and even the phenomenon of "golden jade is outside, but it is defeated" appears.

2, the harm of pesticides after use

As the saying goes, "three drugs are toxic." The chemically treated surface of citrus is more or less attached with drugs. They decompose after a certain period of time, but there are always pesticide residues, which constitutes a problem invisibly. At the same time, orange farmers often don't necessarily prepare according to the relevant proportion when preparing fresh-keeping or drugs. According to the survey, although there has never been an incident of poisoning caused by eating citrus, we should pay enough attention to the safety and hygiene of citrus under the situation that the whole country attaches importance to food safety.

Step 3: Countermeasures

(1) mostly adopts physical methods.

1) Refrigeration mode: Relevant citrus farmers can be organized to build a cold storage to refrigerate some oranges. Deal with those parts with good fruit quality, and you can sell them after a long time. Low cost, safety and sanitation.

2) Adopt new functional plastic wrap. Such as an ethylene adsorption membrane. In order to remove harmful ethylene gas, LDPE ethylene adsorption membrane is mixed with gas adsorption porous substances, such as tuffaceous stone and zeolite, quartz stone and silica, clay minerals, stone powder and other micro-powders, most of which can adsorb ethylene or block far infrared radiation. At present, tuffaceous stone film is widely used abroad, mainly adding silica anhydride ceramics, and the effect is good.

3) Fresh corrugated boxes

Corrugated paper box with heat insulation function. At low temperature, not only the respiration of vegetables and fruits is weakened, but also the activity of bacteria is greatly reduced. Therefore, low-temperature storage is the most effective means and development direction to maintain food freshness. This kind of corrugated box is lined with composite resin and aluminum evaporation film in the inner and outer packaging of traditional carton, or foamed resin is added in the paper core. This corrugated box has excellent heat insulation performance, which can prevent the temperature of vegetables and fruits from rising during circulation. Prevent the water evaporation of vegetables and fruits, achieve the effect of controlling gas content, and thus maintain the freshness of vegetables and fruits.

4) New fresh-keeping tray.

The fresh-keeping tray is formed by heating and vacuum forming and stamping the continuously extruded original plate (thermoplastic resin sheet). The use of tray can not only prevent fresh food from being destroyed, but also has certain heat insulation. The so-called new pallet is a molded product formed by adding functional film or long fiber non-woven fabric to the original plate. On the basis of the original function, the tray also has the functions of adjusting humidity, controlling gas content and preventing mold propagation, so the freshness of vegetables and fruits can be maintained. In addition, the tray can reduce the change of packaging size caused by moisture absorption.

5) Radioactive sterilization.

In order to reduce the influence of pathogenic microorganisms on the freshness of fruits and vegetables during storage and transportation, the fruits and vegetables can be sterilized by radiation after picking and then packaged and transported. At present, the United States, South Africa and other countries all adopt irradiation treatment of certain varieties of vegetables and fruits under certain radiation intensity.

(2) Develop safer and more effective preservatives.

[1] Biological preservative:

A, using bio-related raw materials, extracting effective components through scientific methods to make natural fruit preservative, which is safe, hygienic and environmentally friendly.

Example: garlic extract

Garlic contains garlic volatile oil, the main component of which is allicin, which has inhibitory and killing effects on fungi. Preparation of garlic extract: soak fresh garlic slices in cold water for 12 hours, and then boil until boiling. Make 10% garlic lixivium, or take 1 garlic, mash it, add 10 hot water at 80℃ ~ 90℃, and cool it to normal temperature for later use. Soak the picked citrus fruits in the extract for 10 ~ 15 minutes, then take them out, ventilate and dry them, put them in wooden boxes with hard paper mats, and store them in ventilated warehouses or ordinary houses. After 20 days, the good fruit rate was over 92.4%.

B, coated fruit preservative.

Preservation technology of covering fruit surface with water-soluble plant fiber. After implementation, the effect is good, colorless, odorless and nontoxic. (under development)

[2] Use nontoxic or low toxic preservatives to replace the existing mixed preservatives (pesticides)

On the one hand, newspapers, radio and television programs and other propaganda tools are used to publicize the use of non-toxic comprehensive preservation system for the majority of orange farmers; On the other hand, relevant departments should speed up the development of new non-toxic or low-toxic fresh-keeping or antiseptic chemical pesticides to replace the current high-toxic pesticides, such as replacing high-toxic omethoate, and reduce the use opportunities of toxic pesticides.

[3] Develop more effective citrus varieties.

Through transgenic and other high-tech means, new citrus varieties with better storage resistance have been cultivated. Through the preservation and anti-corrosion function of citrus itself, it can keep a certain freshness under natural storage conditions without changing its taste and quality, so as to achieve economic benefits and safety and hygiene.

Food safety is a major issue related to the national economy and people's livelihood. Citrus is a kind of fruit and a favorite food of Wenzhou people. Its safety and health problems should be paid enough attention by relevant departments, and safety work should be done well to make our oranges sweeter and more worry-free.