Vacuum packaging PK modified atmosphere packaging?

真空包装 PK 气调包装？

在当今商品社会中，货架寿命是个使用频繁的术语。在食品行业，这是个十分重要的指标，因为它是厂商对流通期内商品质量功效的保证与承诺，食品的货架寿命是指从感官和食用安全的角度分析，食品品质保持在消费者可接受程度下的贮藏时间。食品作为人们生存所必需的能量和营养素的基本来源，除了满足人们生理需要和营养卫生要求外，还需要具有良好的质量，消费者对食品质量的需求越来越高，少量的添加剂和环保的包装来获得感官性能好、营养价值高、健康、方便和货架寿命长的食品成为更多消费者的选择目标。但所有的食品在贮藏期间都会经历不同程度的变质。变质包括感官接受性、营养价值和食用安全性的降低等。

本质上来讲，货架寿命主要取决于四个因素即食品的组成结构、加工条件、包装和贮藏条件。这些影响因素已被纳入到食品安全和质量控制体系HACCP(危害分析关键控制点)中。食品是个复杂体系，其中生物、物理、化学的变化反应会同时进行，这些反应会导致食品的营养价值下降并产生不期望的副产物，甚至产生毒素。类似的反应在加工后的保藏过程中仍然会继续发生，此时的反应速率取决于食品的内在性质、包装类型、贮存及运输条件等。

1、冷却肉腐败变质的原因

影响冷鲜肉腐败变质的主要原因可归纳为三点：

①肉体表面微生物繁殖造成肉的腐败变质

其主要微生物在有氧的条件下主要是假单胞菌，真空条件下主要是厌氧和兼性厌氧的乳酸菌群和肠杆菌群。细菌大多数是生长在肉体表面，肉的表面细菌能够分解蛋白质和其他营养物质，从而使肉体表面发黏，产生臭味，在短时间内腐败变质。

②肉中肌红蛋白氧化变色而影响肉的外观颜色

肉的颜色变化是由肌红蛋白和残留的血红蛋白的化学状态所控制。在冷藏保藏过程中，肌肉组织吸收空气中的氧气，使肉体组织结构发生变化。在贮藏前几天，肌红蛋白形成不稳定的、使鲜肉具有鲜红色的氧合肌红蛋白，以后逐步形成稳定的、使鲜肉具有暗红色(棕色)的高铁肌红蛋白。

③因酶的作用引起肉品质量的腐败变质

温度偏高使鲜肉及微生物中的各类酶类活性增高，并使微生物所分泌到其周围的酶类活性明显增加，因而可有利各种酶促反应，使肉品腐败变质。

1）微生物对肉制品的影响

肉品微生物污染受屠宰过程、随后贮藏条件等很多方面的影响，内在和外在因素的结合与交互作用决定了肉品中微生物的生长。在正常情况下，由于冷却肉始终处于0～4℃的低温环境中，这些适冷细菌的生长受到了一定的抑制。然而，如果冷链系统不够完善，在贮藏、运输和销售过程中出现控制不当，导致控制系统的变化或失败使温度升高，微生物会迅速增殖，加速鲜肉变质，甚至会对公共健康构成潜在的威胁。

2）外界环境对肉制品的影响

温度可以引起脂肪及脂溶性成分的氧化，褐变从而导致品质下降；湿度会引起食品吸湿或脱湿，引起食品形态收缩变形；光线可以促进化学反应与食品的色、香、味的变化；在氧气存在的情况下促进化学反应而引起食品品质变化；充填惰性气体可以抑制此类化学反应，从而达到抑制食品品质下降的目的。

3）肉制品固有属性对其的影响

食品的水溶性成分较高或吸湿时会发生褐变、溶解性及复原性降低，营养成分损失等。脂溶性成分较多时则在氧、光线等条件存在时，脂肪氧化发生变色、退色、风味变化、维生素损失等。有酶存在的食品中，食品水分含量较高或吸湿时容易导致酶活化，从而引起食品色、香、味的劣化等。

2、延长货架期方法

1）真空包装真空包装

①真空包装简介

真空包装是指将产品装入气密性包装容器，抽去容器内部的空气，使密封后的容器内达到预定真空度的一种包装方法。真空包装通过保持包装袋内缺氧环境，抑制许多腐败性微生物的生长，减缓肉中脂肪的氧化，同时还可减少肉的失水，保持外观整洁，从而延长肉制品的保质期。

②真空包装的优点

真空包装的主要优势在于防护性好，密封性可靠，真空度高，残留空气少，能有效抑制细菌等微生物繁殖，避免内装物氧化霉变和腐败。

对于生鲜肉类来说，真空包装还有以下优点：

(1)防止变干

包装材料给水蒸气屏蔽，防止干燥，使鲜肉表面保持柔软。

(2)防止氧化

抽真空时，氧气和空气一起排除，包装材料和大气屏蔽，使得没有氧气进入包装袋中，氧化被彻底防止。

(3)防止肉香味的损失。

包装材料能有效的阻隔易挥发性的芳香物质的溢出，同时也防止不同产品之间的传味。

(4)避免冷冻损失。

包装材料使产品与外界隔绝，因此冷冻时冰的形成和风干可将损失减少到较小的程度。

③真空包装的缺陷

真空包装的原理比较简单：除去包装中的氧气，防止内容物性能发生改变(如食品变质)，一般而言，氧气浓度小于1％，微生物的生长和繁殖速度会急速下降，真空包装的低温肉制品货架期一般达一个月以上。然而，如果污染微生物，特别是活力强的致腐菌株会不断生长繁殖，致使产品在货架期内常发生腐败，影响产品质量。

真空包装不能抑制厌氧菌的繁殖和酶的反应引起的食品变质和变色，乳酸菌是真空包装低温肉制品中的主要腐败菌。当低温肉制品进行真空包装后，贮藏初期，这些腐败菌用培养的方法常常不能检出(<10cfu/g)，然而随后产品却快速腐败，这样的致腐特性增加了产品的腐败率，给质量管理造成很大困难，产品安全亦受到严重威胁。所以有时需要结合其他辅助性方法，如冷藏、高温杀菌、腌制等。

2）气调保鲜

Vacuum packaging PK modified atmosphere packaging?

In today's commodity society, shelf life is a frequently used term. In the food industry, this is a very important indicator, because it is the manufacturer's guarantee and commitment to the quality and efficacy of the product during the circulation period. The shelf life of food refers to the analysis from the perspective of sensory and edible safety, and the quality of food remains acceptable to consumers. storage time at the level. As the basic source of energy and nutrients necessary for people's survival, food needs to have good quality in addition to meeting people's physiological needs and nutritional hygiene requirements. Consumers have higher and higher demand for food quality, a small amount of additives and environmentally friendly Packaging to obtain food with good sensory properties, high nutritional value, health, convenience and long shelf life has become the choice target of more consumers. But all foods undergo varying degrees of deterioration during storage. Deterioration includes the reduction of sensory acceptability, nutritional value and food safety.

Essentially, shelf life is mainly determined by four factors, namely the composition of the food, processing conditions, packaging and storage conditions. These influencing factors have been incorporated into the food safety and quality control system HACCP (Hazard Analysis Critical Control Point). Food is a complex system in which biological, physical, and chemical changes occur simultaneously, which can lead to a decrease in the nutritional value of the food and the production of undesired by-products and even toxins. Similar reactions will continue to occur during storage after processing, and the reaction rate at this time depends on the intrinsic properties of the food, the type of packaging, storage and transportation conditions, etc.

1. Reasons for the deterioration of chilled meat

The main reasons for the deterioration of chilled meat can be summarized into three points:

①The reproduction of microorganisms on the surface of the flesh causes the spoilage of the meat

Its main microorganisms are mainly Pseudomonas under aerobic conditions, and mainly anaerobic and facultative anaerobic lactic acid bacteria and Enterobacteriaceae under vacuum conditions. Most of the bacteria grow on the surface of the meat. The bacteria on the surface of the meat can decompose proteins and other nutrients, so that the surface of the meat is sticky, odorous, and spoiled in a short time.

② Myoglobin in the meat is oxidatively discolored and affects the appearance color of the meat

The color change of meat is controlled by the chemical state of myoglobin and residual hemoglobin. During cold storage, muscle tissue absorbs oxygen in the air, which changes the structure of the body tissue. During the first few days of storage, myoglobin forms unstable oxymyoglobin, which gives fresh meat a bright red color, and then gradually forms stable methemoglobin, which gives fresh meat a dark red (brown) color.

③ Corruption and deterioration of meat quality due to the action of enzymes

High temperature increases the activity of various enzymes in fresh meat and microorganisms, and significantly increases the activity of enzymes secreted by microorganisms to its surroundings, which can facilitate various enzymatic reactions and make meat spoiled.

1) The influence of microorganisms on meat products

The microbial contamination of meat is affected by many aspects such as slaughtering process and subsequent storage conditions. The combination and interaction of internal and external factors determine the growth of microorganisms in meat. Under normal circumstances, the growth of these cold-adaptive bacteria is inhibited to a certain extent because the cooled meat is always in a low temperature environment of 0 to 4 &deg;C. However, if the cold chain system is not perfect, improper control occurs during storage, transportation and sales, resulting in changes or failures of the control system to increase the temperature, microorganisms will multiply rapidly, accelerate the deterioration of fresh meat, and even pose a potential risk to public health. threat.

2) The influence of the external environment on meat products

Temperature can cause oxidation and browning of fat and fat-soluble components, resulting in quality degradation; humidity can cause food to absorb or dehumidify, causing food shrinkage and deformation; light can promote chemical reactions and changes in food color, aroma and taste; In the presence of oxygen, it promotes chemical reactions and causes changes in food quality; filling inert gas can inhibit such chemical reactions, thereby achieving the purpose of inhibiting the decline of food quality.

3) Influence of the inherent properties of meat products on it

Foods with high water-soluble components or moisture absorption will cause browning, reduced solubility and recovery, and loss of nutrients. When there are many fat-soluble components, in the presence of oxygen, light and other conditions, fat oxidation will cause discoloration, fading, flavor changes, and vitamin loss. In foods with enzymes, high moisture content or moisture absorption of foods can easily lead to enzyme activation, resulting in deterioration of food color, aroma and taste.

2. How to extend the shelf life

1) Vacuum packing Vacuum packing

①Introduction to vacuum packaging

Vacuum packaging refers to a packaging method in which the product is put into an airtight packaging container, the air inside the container is removed, and the sealed container reaches a predetermined degree of vacuum. By maintaining an oxygen-deficient environment in the packaging bag, vacuum packaging inhibits the growth of many spoilage microorganisms, slows down the oxidation of fat in the meat, and at the same time reduces the water loss of the meat, keeps the appearance clean and tidy, thereby prolonging the shelf life of meat products.

②Advantages of vacuum packaging

The main advantages of vacuum packaging are good protection, reliable sealing, high vacuum degree, and less residual air, which can effectively inhibit the reproduction of microorganisms such as bacteria, and avoid oxidative mildew and corruption of the contents.

For fresh meat, vacuum packaging has the following advantages:

(1) Prevent drying out

The packaging material provides a barrier to water vapour, preventing drying and keeping the surface of the fresh meat soft.

(2) Prevent oxidation

When vacuuming, oxygen and air are removed together, and the packaging material is shielded from the atmosphere, so that no oxygen enters the packaging bag, and oxidation is completely prevented.

(3) Prevent the loss of meat flavor.

The packaging material can effectively block the overflow of volatile aromatic substances, and also prevent the transfer of taste between different products.

(4) Avoid freezing loss.

The packaging material insulates the product from the outside world, so ice formation and air-drying during freezing minimize losses.

③Defects of vacuum packaging

The principle of vacuum packaging is relatively simple: remove oxygen in the packaging to prevent changes in the properties of the contents (such as food spoilage). Generally speaking, when the oxygen concentration is less than 1%, the growth and reproduction speed of microorganisms will drop rapidly. Vacuum-packed low-temperature meat The shelf life of products is generally more than one month. However, if the contaminating microorganisms, especially the vigorous rot-causing strains, will continue to grow and multiply, the products will often spoil during the shelf life and affect the quality of the products.

Vacuum packaging cannot inhibit the reproduction of anaerobic bacteria and the food deterioration and discoloration caused by the reaction of enzymes. Lactic acid bacteria are the main spoilage bacteria in vacuum-packed low-temperature meat products. When low-temperature meat products are vacuum-packed, in the early stage of storage, these spoilage bacteria are often not detected (<10cfu/g) by culturing, but then the product is rapidly spoiled. Such spoilage characteristics increase the spoilage rate of the product, giving Quality management has caused great difficulties and product safety has also been seriously threatened. Therefore, it is sometimes necessary to combine other auxiliary methods, such as refrigeration, high temperature sterilization, pickling, etc.

2) Modified atmosphere preservation

Modified Atmosphere Packaging

①The principle of modified atmosphere preservation

The preservation mechanism of modified atmosphere packaging is to protect food with packaging materials with good barrier properties, which means filling the packaging with a certain ideal gas component, improving the environmental components in the packaging under certain temperature conditions, inhibiting the growth of microorganisms and preventing enzymes. Corruption caused by the deterioration, to achieve the purpose of preservation and preservation, thereby extending the shelf life of the product. The gases used are usually carbon dioxide, oxygen and nitrogen or their various combinations, and each gas has a different effect on fresh meat preservation. Generally, the shelf life of fresh meat packaged by air can reach 10 to 14 days.

(1) Carbon dioxide acts as a bacterial inhibitor

Carbon dioxide is a stable compound, colorless, odorless, and has a strong inhibitory effect on the reproduction of most aerobic bacteria and molds. At the same time, it can also prolong the lag period of bacterial growth and reduce the speed of its logarithmic growth period. The bacteriostatic effect of carbon dioxide is that in the packaging bag with high concentration of carbon dioxide, carbon dioxide replaces oxygen, and the high carbon dioxide environment makes a large number of aerobic microorganisms ( Such as Pseudomonas) growth is inhibited; the second is due to carbon dioxide, soluble in water to form carbonic acid, reducing the pH value in the environment, so that some acid-intolerant microorganisms lose the necessary conditions for survival; the third is through the osmotic effect on cells , at the same temperature and pressure, the solubility of carbon dioxide in water is 6 times that of oxygen, and the rate of infiltration into cells is 30 times that of oxygen. Due to the large infiltration of carbon dioxide, it will affect the structure of the cell membrane, increase the permeability of the membrane to ions, and change the membrane The balance of internal and external metabolism, and interfere with the normal metabolism of cells, so that bacterial production is inhibited. The infiltration of carbon dioxide also stimulates the activity of mitochondrial ATPase, accelerates oxidative phosphorylation, reduces ATP, and reduces the energy required for metabolic growth of the body.

(2) The role of oxygen

The use of oxygen in modified atmosphere packaging is mainly due to the bright red color of myoglobin in the muscle after combining with oxygen molecules to become oxymyoglobin. Therefore, in order to maintain the bright red color of the meat, there must be oxygen in the packaging bag. Oxygen content in natural air is about 20.9%, so the surface of freshly cut meat is light red when exposed to the air. % oxygen), the formation of methemoglobin is more, and the oxygen must be above 5% to reduce the formation of methemoglobin. However, according to Bartkowski (1982), oxygen must be above 10% to maintain bright red, and more than 40% oxygen can maintain good color for 9d. The formation of bright red oxymyoglobin is also related to whether the surface of the meat is wet or not. If the surface is wet, the amount of dissolved oxygen is large, and it is easy to form bright red.

(3) The role of nitrogen.

Nitrogen is an inert gas, which generally does not work on the packaged material, nor is it absorbed by the food. The air permeability of nitrogen to plastic packaging materials is very low, so it can be used as a mixed gas to buffer or balance the gas in the packaging, and can prevent the collapse caused by filling carbon dioxide.

②The advantages of modified atmosphere preservation

Modified atmosphere packaging is one of the most common and effective ways to extend the shelf life of various foods, including chilled meats. Reasonable modified atmosphere packaging can not only ensure the hygienic quality of meat products, prolong the shelf life, but also have a good impact on the sensory quality of cooled meat. The most commonly used gas components in modified atmosphere packaging are mainly carbon dioxide + oxygen + nitrogen.

The use of this gas mixture is mainly from the point of view of controlling microbial growth and organoleptic quality (such as color). The fresh-keeping effect of this form of modified atmosphere packaging on fresh meat mainly depends on the initial bacterial count of the raw meat, the concentration of carbon dioxide, the presence or absence of oxygen in the packaging bag, the permeability of the packaging material, the storage temperature and the gas composition. It acts as an inhibitor of microorganisms by causing changes in bacterial synthase and enzymatic reaction rates, as well as affecting carboxylation and deamination reactions. The mixed gas is equipped with a certain proportion of oxygen to maintain the color of fresh meat and inhibit the growth of pathogenic bacteria.

The modified atmosphere packaging system is a closed system, in which two processes exist at the same time: one is the physiological serialization process of the product, that is, the metabolic respiration process; The exchange process, these two processes make the air-conditioning system a dynamic system.

The principle of modified atmosphere packaging can be summarized into two points: ① Destruction of the environment in which microorganisms grow and reproduce; ② It can maintain a certain activity of the cells inside the food and maintain a certain degree of freshness. There are two main factors affecting food storage, namely the need for Oxygen bacteria and oxidation reactions, both require oxygen. Therefore, to prolong the shelf life, it is necessary to reduce the oxygen content of the environment. Modified atmosphere packaging technology can make up for the deficiencies of vacuum packaging to a certain extent and further inhibit the spoilage of microorganisms.

③ Precautions for modified atmosphere packaging

(1) Processing of fresh meat before packaging

If the pig is cooled at 0℃-4℃ for 24h after slaughtering, the acid excretion process will occur after the ATP stops moving. The cooled meat treated in this way has far better nutrition and taste than quick-frozen meat and hot fresh meat. In addition, in order to ensure the preservation effect of modified atmosphere packaging, it is also necessary to control the hygienic indicators of fresh meat before packaging to prevent microbial contamination.

(2) Selection of packaging materials

Modified atmosphere packaging should use packaging materials with good barrier properties to prevent the leakage of gas in the packaging and at the same time prevent the infiltration of oxygen in the atmosphere. Generally, composite packaging films such as PET, PP, PA, and PVDC are used as the base material. To measure the gas barrier properties of plastic films, it is generally expressed by the air permeability coefficient: the smaller the air permeability coefficient, the better the barrier properties. In addition, most packaging materials must have sufficient mechanical strength to withstand pressure changes during vacuum. At the same time, the material is also required to have a certain stiffness so that the packaging bag can be automatically opened and inflated.

(3) Control of product storage temperature

The influence of temperature on the preservation effect comes from two aspects: one is that the level of temperature directly affects the activities of various microorganisms on the surface of the body; the other is that the barrier properties of packaging materials are closely related to temperature. The higher the temperature, the better the barrier properties of packaging materials. Low. Therefore, it is necessary to realize the temperature control of the whole process from product, storage, transportation to sales.

3. Summary

At present, vacuum packaging technology can inhibit the growth of microorganisms, prevent secondary pollution, slow down the rate of fat oxidation, make the meat neat and prolong the shelf life of meat products. If the cold meat is vacuum packed, it will have a certain effect on preservation, but its color will be purple. This technology is not perfect. Only modified atmosphere packaging is an ideal method to extend the shelf life of meat products. Modified atmosphere packaging technology to inhibit the growth of microorganisms, thereby extending the shelf life of meat products. Modified atmosphere packaging can not only make the meat bright red, but also inhibit the growth and reproduction of spoilage microorganisms, ensure the hygienic quality of meat products, and maintain the good sensory quality of fresh meat products, significantly extending the shelf life.