food and drink

Fruit and vegetable ripener - ethylene (C2H4)

Fruit and vegetable ripeners With the improvement of people's living standards, consumers' requirements for fruits and vegetables are both fresh and familiar, and this requirement is increasing. The ripening of fruits and vegetables is a very complicated physiological and chemical process. Usually, the composition of moisture, respiration and gas is closely related to it. Ethylene produced by its breathing and evaporation of water, even if it is only one-tenth of a centimeter, is enough to induce the ripening of fruits and vegetables. Therefore, as a method of ripening. This is achieved primarily by conditioning, supplying ethylene, or providing conditions for the production of ethylene.

    According to the relevant experts of the Municipal Academy of Agricultural Sciences, the normal mature fruit has the rich nutrition and sweet taste that the variety should have. Fruits ripened with plant growth regulators can change the color of the surface of the fruit, but the intrinsic quality of the fruit does not change and does not reach the rich nutrients that the fruit should have. Fruits using ripeners are sold in advance for a good price. To ripen immature green fruits quickly, you need to use ethephon as a ripening agent, and eating ethephon is harmful to the human body. To this end, experts remind consumers to buy less seasonal fruits, it is best to buy seasonal fruits. If you want to buy fruit, it is best to master some of the fruit's maturity and some tips for buying fruit.

Application of modified atmosphere packaging technology in the food industry

Modified atmosphere packaging is also known as MAP or CAP. Commonly used gases are N2, O2, CO2, mixed gas O2+N2 or CO2+N2+O2 (ie MAP). Modified atmosphere packaging technology can be widely used for the preservation of various foods, extending the shelf life of food and enhancing the value of food.

一、Application of CO2 in food packaging

A Swedish company introduced packaging bags, containers and storage rooms filled with 100% CO2 gas to store meat. High concentration of CO2 can inhibit the proliferation of microorganisms such as aerobic bacteria and mold, prolong the stagnation period and exponential growth period of microbial growth, and play a role in antisepsis and mildew resistance. This method enables pork to be stored for 120 days without freezing treatment, such as re-pressurization, and storage time is longer. This method has caused great concern in meat exporting countries such as the United States and Australia.

  Recently, American experts have adopted new technologies to make plastic packaging materials from CO2. That is, using a special catalyst, CO2 and ethylene oxide (or propylene oxide) are mixed in equal amounts to make a new plastic packaging material, which is characterized by glass-like transparency and non-ventilation; similar to polycarbonate and polyamide. Resin; does not completely decompose into gas at 240 ° C; biodegradability does not pollute the environment and soil.

  China has successfully used nanotechnology to efficiently catalyze the synthesis of degradable plastics from CO2. That is, the catalyst for preparing plastic by using CO2 is "pulverized" to the nanometer level to realize polymerization of catalytic molecules and CO2, so that about 0.1 g of CO2 per gram of catalyst is catalyzed, and a new packaging material containing 42% of CO2 is synthesized. As an environmentally friendly material with excellent degradability, it has broad application prospects.

二、Application of nitrogen in food packaging

Nitrogen (N2) is an ideal inert gas. It has special effects in food packaging: it does not react with food and is not absorbed by food. It can reduce the oxygen content in the package and greatly inhibit the growth and reproduction of bacteria, molds and other microorganisms. To slow down the oxidative deterioration and decay of food, so as to keep food fresh. Nitrogen-filled packaged foods can also prevent the crushing of food, the bonding or shrinking of food, and maintain the geometric shape, dryness, crispness, color and aroma of food. At present, nitrogen-filled packaging is rapidly replacing traditional vacuum packaging, and has been applied to fried potato chips and French fries, oil cooking foods, and the like. Affected by consumers, especially children and youth, nitrogen-filled packaging is expected to be applied to more food packaging.

 In the United States, N2 is used to increase the strength of the beverage can of thin aluminum material. Before the beverage is filled, the nitrogen is dissolved in the beverage; after the beverage can is sealed, the nitrogen is released from the beverage, forming a pressure on the tank wall to make the beverage can It is equivalent to an aerated tank, which increases the strength of the beverage can, and the effect is remarkable. The canned beverage will not be damaged during transportation, stacking or on the shelf, nor will it affect the quality of the beverage. This method can also be used for beverage packaging made of polyester plastic.

 At the N2 application, attention must be paid to the purity and quality of N2. The purity of the nitrogen separated from the compressed air by membrane separation or pressure swing adsorption can reach 99.9% or more. The purity of N2 used in food packaging must be pure nitrogen (ie safety grade).

三、Application of compound gas in packaged food

The composite modified atmosphere packaging is collectively referred to as MAP packaging in the world. The modified atmosphere is generally composed of CO2, N2, O2 and a small amount of special gases. CO2 can inhibit the growth and reproduction of most aerobic spoilage bacteria and molds; O2 inhibits the growth and reproduction of most anaerobic spoilage bacteria; maintains the color of fresh meat, maintains the oxygen-rich breath and freshness of fresh fruits and vegetables; and fills the gas with N2. The composition ratio of the composite gas is appropriately selected according to the type of food, the preservation requirements and the packaging materials, so as to achieve the effect of high preservation quality of the packaged food, good maintenance of the nutrients, real ability to achieve the original traits, and delaying the shelf life of the fresh-keeping.

Composite modified atmosphere packaging has been widely used at home and abroad.

  ▲Modified atmosphere of fresh fish and shrimp Fresh fish and marine fish are mainly metamorphosed by bacteria. The decomposition of trimethylamine in fish meat releases trimethylamine, which is succulent, fish fat oxidative rancidity, fish body enzymes degrade fish soft, fish surface Bacteria (aerobic Escherichia coli, anaerobic Clostridium) produce poisoning toxins that endanger human health.

The gas used for modified atmosphere packaging of fish is composed of CO2, O2 and N2. The concentration of CO2 gas is higher than 50%, which inhibits the growth of aerobic bacteria and mold without causing the fish to seep out; the concentration of O2 is 10%-15%. Oxygen bacteria reproduction. The fish's cockroaches and internal organs contain a large amount of bacteria, which must be removed, cleaned and disinfected before packaging. Because CO2 easily oozes out plastic film, the packaging material for fish modified atmosphere packaging needs to use a composite plastic film with high gas barrier property, which can be maintained for 15-30 days at 0 °C - 4 °C. British tuna uses 35% - 45% CO2 / 55% - 65% N2 gas fresh-keeping packaging shelf life of 6 days.

   The deterioration of shrimp is mainly caused by microorganisms. Its intrinsic enzyme action causes the shrimp to darken. The grass shrimp can be kept fresh in a modified atmosphere package. The shrimp was first immersed in a preservative solution of 100 mg/L lysozyme and 1.25% sodium hydrogen sulfite, and then inflated with 40% CO2 and 60% N2 mixed gas, and the shelf life was longer than that of the control sample. The extension was 22 days, which was 6.5 times the shelf life of the control sample.

  ▲Livestock fresh meat modified atmosphere packaging

The modified atmosphere packaging of fresh pork, sheep and cattle meat should keep the fresh red meat and preserve the fresh and fresh food. The gas of the modified atmosphere packaging is composed of O2 and CO2. The gas composition varies according to the type of meat. The gas composition of pork modified atmosphere packaging is 60%-70%O2 and 30%-40% CO2, and the shelf life is generally 7-10 days at 0 °C - 4 °C (including cooling at 0 °C - 4 °C after slaughter). 24h, the ATP active substance is lost, the texture becomes soft and fragrant, and the palatability is good. The poultry meat modified atmosphere packaging is mainly antiseptic and fresh, the fresh-keeping gas is composed of CO2 and N2, and the poultry meat is packaged at 50 ° - 70% CO2 / 50% - 30% O2 in the shelf life of 0 ° C - 4 ° C for 14 days.

 In meat-conditioned fresh-keeping packaging, the use of high-concentration O2 can keep fresh meat brighter and brighter. In anoxic environment, the meat is lavender. If CO2, N2 and other fresh-keeping gases are used, the color of the meat is lavender and fresh. The period can be up to 30 days. Fresh meat packaging materials also require the use of composite plastic packaging materials that have high barrier properties to gases.

▲Modified fresh-keeping packaging for baked goods and cooked foods

Baked goods include cakes, cakes, biscuits, bread, etc. The main ingredient is starch. Deterioration caused by bacterial mold, etc., rancidity caused by fat oxidation, aging and hardening of starch molecular structure, etc., cause food deterioration. The gas used in this type of food modified atmosphere packaging consists of CO2 and N2. The cake without cream is kept fresh for 20-30 days at room temperature, and the high-barrier composite film of moon cake and pudding cake can be stored for 60-90 days at room temperature.

   Microwave dishes, soy products, and cooked meat products of livestock and poultry can be effectively inhibited from coliforms by filling CO2 and N2. Store at room temperature 20 ° C -25 ° C for 5-12 days, after 85 ° C -90 ° C conditioning sterilization, fresh at room temperature for about 30 days, at 0 ° C - 4 ° C refrigeration temperature preservation for 60-90 days.

  ▲Fresh fruits and vegetables, fresh-keeping and fresh-keeping packaging, fruits and vegetables can still maintain the metabolism of CO2 and CO2 after harvesting, while consuming nutrients.

Preservation of fruits and vegetables is to reduce the respiratory progress by reducing the O2 content in the environment and low temperature storage, and to eliminate the CO2 produced by breathing to delay the ripening and aging of fruits and vegetables to achieve the preservation effect. The modified atmosphere packaging material of fruits and vegetables is composed of O2, CO2 and N2. The fruits and vegetables are packaged with a gas permeable film, filled with low O2 and high CO2 and mixed gas, and sealed, so that the O2 content in the package is lower than air and the CO2 is higher than air. Gas exchange through the membrane to achieve a balance between the fresh-keeping environment of fruits and vegetables and the maintenance of weak aerobic respiration.

 Most fruits and vegetables are packaged in a mixture ratio of 5% O2, 5% CO2, and 90% N2, and have a long shelf life at a low temperature of 6 ° C - 8 ° C. The modified atmosphere packaging is used for lychee preservation and preservation. The lychee fruit is treated with 10% CO2+90%N2 and 20%CO2+80%N2 for 24hr, which can not only achieve the purpose of fresh-keeping, but also improve the fruit's good fruit rate and maintain the red skin without affecting the nutrients. The combination of ozone treatment (4.3mg/M3 concentration) with high CO2 and low oxygen conditions and the use of an edible thin film can extend the shelf life of strawberries by 8-10 days.

 American scientists used a modified atmosphere packaging test on mangoes. The mangoes were peeled and diced, packaged in oxygen, mixed with gas (N2 86%, CO 210%, O2 4%) and vacuum packed. The result was a mango shelf packed with mixed gas. The longest period, during storage, the color and texture of mango have good appearance and the damage caused by microorganisms is minimal.

 Modified atmosphere packaging is also suitable for clean dishes. Clean vegetables, also known as cutting fruits and vegetables, semi-processed fruits and vegetables, are designed to cater to the office workers' new food processing products. They are safe, fresh, nutritious and convenient, but they are easy to brown after cutting. The use of modified atmosphere packaging to reduce oxygen content maximizes shelf life. For example, shredded lettuce in the United States prevents browning with 1% to 3% O2, 5% to 6% CO2, and 90% N2. The modified atmosphere packaging is also suitable for peeling and slicing apples, potatoes, leafy vegetables and other fruits and vegetables. It is the key to broaden the way of fresh-keeping of fruits and vegetables by developing packaging film suitable for the fresh-keeping effect of fruit and vegetable modified atmosphere packaging.

What gases are currently used for food preservation or food processing?

High-purity nitrogen: High-purity nitrogen is used for food preservation. The principle is high-purity nitrogen-packed food, which prevents food from being isolated from oxygen in the air and prevents food from deteriorating by contact with oxygen. In addition, the packaging of the food filled with high-purity nitrogen also prevents the food from being squeezed and destroys the shape of the food.

Carbon dioxide: Food grade carbon dioxide is used in the production of carbonated beverages and beer. The food carbonate is pressure-dissolved in cola and beer to obtain the taste of the existing carbonated beverage. In addition, food carbon dioxide is also used to produce high quality purified water, vinegar drinks and the like.

High-purity ethylene: High-purity ethylene is widely used in the ripening of navel oranges, mangoes, bananas, and tangerines. The gas ripened by high-purity ethylene conforms to the law of biological growth, which is conducive to the preservation and transportation of the fruit, and is harmless to the body itself, but the taste will be worse.

High-purity carbon monoxide: High-purity carbon monoxide is used for the preservation of tuna and tilapia. Since these fish meat contains more hemoglobin and myoglobin, the reducibility is very strong, and the contact with oxygen in the air easily makes the color of the meat brown and makes people feel unfresh. The use of carbon monoxide is reductive, and the tuna meat treated with carbon monoxide is bright red, which also achieves the preservation effect.