Nitrogen application in food

文章出处：液氮速冻,液氮速冻设备,速冻机,科威嘉尼（北京）科技有限公司责任编辑：科威嘉尼—朱向磊点击：59 发表时间：2014-02-24 10:38:04

Liquid nitrogen is a colorless, odorless , transparent, low viscosity liquid , chemically stable , not with any substance from chemosynthesis ; their specific physical properties are shown in Table 1. The liquid nitrogen as the largest air separation products, industrial oxygen byproducts , plus the unique nature of the liquid nitrogen , has been gradually people's attention and recognition. The liquid nitrogen as a refrigerant ideal for the food industry ; , especially in the frozen food has been great progress in the world , has been hailed as one of the achievements of the most outstanding foreign food industry of the 20th century . In China, the nitrogen applied in all aspects of the food industry Although the gradual rise , but there are still a lot of problems . As people increasingly high demand for food , natural , nutrition, functional and safe food to become dominant , liquid nitrogen in food technology as part of a family of low-temperature technology to replace the traditional processing methods , there are certainly areas in the food industry ideal development.

Table 1 Physical properties of liquid nitrogen
Physical Properties Number of Units
Molecular weight of 28
The proportion of air = 1 0.9674
Density kg/m3 ( at 0 ℃, l atm ) 1.2507
Boiling point ℃ -195.8
Melting point ℃ -209.9
Critical temperature ℃ -147
Critical pressure 33.5 atm
Critical density kg / kg 0.3l
Liquid Density kg / kg ( boiling point ) 0.8l
Latent heat of vaporization kJ / kg 161.19
Specific heat kJ / kg ? ℃ 1.034
Thermal conductivity J / cm ? Sec ? ℃ 2.28x10-4

A liquid nitrogen in food applications have features
( 1 ) liquid nitrogen is colorless, tasteless , odorless and non-toxic and other basic properties ;
( 2 ) the nature of the inert liquid nitrogen with asphyxiating , bacteria and other microorganisms and inhibition of suffocation ; ensure food hygiene and quality .
( 3 ) molecular weight close to oxygen under atmospheric conditions can achieve the purpose of rapid vaporization of cryogenic oxygen row , inhibit browning in fruit and vegetable processing , the processing effect is remarkable.
( 4 ) Nitrogen is the major component of air , the air content of up to 78% ( by volume ) , a rich source .
2 nitrogen application in the food industry
2.1 quick-frozen in liquid nitrogen in food in
Among the preservation method, cryopreservation method most widely used , the effect is very significant. As frozen in liquid nitrogen cryopreservation methods have long been used by the food processing enterprises, because it can achieve cryogenic ultra quick-frozen , frozen food is also conducive to the realization of part of the glass , so to maximize recovery after thawing food to its original state and original fresh nutrients, greatly improving the quality of frozen foods , so the quick-freezing industry showed unique vitality . Compared with other methods of freezing , frozen in liquid nitrogen has the following significant advantages :
① fast freezing speed ( freezing rate of about 30-40 times faster than normal freezing method ) : quick-frozen using liquid nitrogen ,
Make food quickly through the 0 ℃ ~ 5 ℃ maximum ice crystal growth zone, food researchers have made a good attempt in this regard [ 1,2 ] .
② maintaining food quality : Because time is short frozen in liquid nitrogen , liquid nitrogen frozen foods can maximize
Maintain color, smell , taste and nutritional value before processing . Duan Zhenhua [ 3 ] and others quick-frozen with liquid nitrogen to be processed betel nut , betel results showed that after treatment of liquid nitrogen to maintain a higher chlorophyll content, good flavor .
③ dry material consumption is small : Average consumption of frozen stem the loss rate of 3 to 10 %, and frozen in liquid nitrogen can be reduced to 0.25 ~ O.5%.
④ equipment and power , low cost, easy to implement mechanized and automated assembly line and increase productivity.
2.2 Liquid nitrogen is used in beverage processing
Currently , many beverage manufacturers use nitrogen or a mixture of nitrogen and CO2 replace traditional CO2, inflating beverage packaging. High nitrogen filling carbonated drinks , beverages than the problem caused by only filling less carbon dioxide ; nitrogen -free foam for filling beverages such as wine and fruit juice is also very desirable. Filling liquid nitrogen in the non -carbonated beverages in cans advantage is the small amount of liquid nitrogen can be injected into each canned exclude oxygen in the head space , the upper space of the tank so that inert gas , thereby extending the shelf life of perishable goods .
2.3 Application of liquid nitrogen storage in the preservation of fruits and vegetables
Liquid nitrogen for storage of fresh fruits and vegetables have the advantage of atmosphere , you can adjust the contradiction between supply and demand of agricultural season and off-season areas , to reduce the loss on storage . Gas transfer function is to increase the concentration of nitrogen , while controlling gas ratio of nitrogen, oxygen and CO2 , and keep it in a stable state , reduce the respiration rate of fruits and vegetables , slow ripening process , so that the fruits and vegetables stay fresh when picked state and original nutritional value, prolong shelf life of fruits and vegetables .
2.4 Application of liquid nitrogen in the meat processing
Liquid nitrogen for raw meat stranding , chopping or mixing processes added , which can effectively improve product quality. As in沙拉米type sausage processing , meat can increase the use of liquid nitrogen retention , prevent fat oxidation, improve the quality and appearance of slices ; for remanufactured meat processed meat pastries , jerky , etc. , not only can the meat mix acceleration and enhanced retention of protein was dissolved , and the unique shape of the product is particularly effective to maintain . Also raw meat by rapid cooling in liquid nitrogen , can remain hot meat characteristics in a long time , but also ensure the health and safety of meat ; in the processing technology , no longer need to worry about the impact of rising temperatures on the meat , and the processing of raw materials can not be temperature processing time , the impact of seasonal factors, but can also make the process in a low oxygen partial pressure in a certain range to extend the shelf life of the product .
2.5 Application of liquid nitrogen cryogenic grinding of food
Cryogenic grinding, is cooled to a temperature brittle point of substance , the external force crushed into powder process . Cryogenic grinding food in recent years developed a new food processing technology, which is particularly suitable for processing multi- containing aromatic ingredients , with high fat content , sugar content and more and more food containing gelatinous substance . Cryogenic grinding with liquid nitrogen treatment, even raw bones, skin, meat , crushed shells, etc. all at once , so that the finished granule small and keep it effective nutrition. As the liquid nitrogen to freeze the Japanese seaweed , chitin , vegetables , spices , etc., into pulverizer , make up to 100μm or less finished micro- grained , and basically keep the original nutritional value. In addition, with liquid nitrogen cryogenic grinding , crushing under normal temperature can be difficult to crush the material , heat-sensitive and heat -perishable , easy to decompose substances. In addition , liquid nitrogen can be crushed as fatty meats, vegetables and more water at room temperature is difficult to crush food ingredients , and can be manufactured so far have not had a new processed foods.
2.6 Application of liquid nitrogen in food packaging
London, UK company has developed a simple and practical method of food preservation, and packaging , that is, when given food packaging, packaging bag to add a few drops of liquid nitrogen . When liquid nitrogen evaporated into gas , its volume expanded rapidly, quickly replaced most of the original gas inside the bag , reducing spoiled food caused by oxidation , thus greatly extend the shelf life of food.
2.7 Application of liquid nitrogen frozen food transport
Refrigerated transport is the food industry is an important part . Development of liquid nitrogen refrigeration technology , the development of liquid nitrogen refrigeration trains, refrigerated vehicles and refrigerated containers are common on the current international trends . Application of the developed countries for many years shows that the liquid nitrogen cold storage refrigeration system is the only commercially available technology in mechanical refrigeration system to compete with , but also the direction of the food refrigerated transport.
2.8 Other applications of liquid nitrogen in the food industry
As the liquid nitrogen refrigeration , egg , liquid seasoning , soy sauce can be processed into a free-flowing granular and can pour frozen foods , these foods can be ready to use and easy preparation. When the grinding of spices and foods absorbent additives such as lecithin and sugar substitutes , liquid nitrogen is injected into the grinding mill to protect valuable components , also increases the yield of the polishing . Expert studies have shown that the use of liquid nitrogen quenching temperature thawing Pollen synergy with good effect, broken rate, fast and pollen physiological activity remained stable , free from pollution.