What is Gas Treatment in Food Preservation?

Gas treatment is a crucial tool in food preservation, utilizing different gases and their mixtures to modify or control the atmosphere surrounding food products. By doing so, the shelf life of perishable foods can be extended, preventing microbial spoilage and degradation. Here’s an overview of gas treatment as a food preservation technique:

1. Atmosphere Modification for Fruits and Vegetables: Controlling or modifying the atmosphere around fruits and vegetables is a common practice to preserve their quality and extend shelf life. These perishable products undergo respiration, where they consume oxygen and release carbon dioxide. By regulating the atmospheric composition, the respiration rate can be slowed down, reducing the degradation process. This is particularly important for climacteric fruits, which can continue to ripen after harvest due to the production of ethylene and increased respiration, and non-climacteric fruits, which have lower respiration rates and do not ripen significantly after harvest.
2. Control of Atmosphere in Storage: Apart from fruits and vegetables, other food products such as meat and cereal grains can also benefit from controlled atmospheric conditions during storage. By adjusting the atmosphere within the storage environment, factors such as oxygen levels, carbon dioxide concentrations, and humidity can be optimized to slow down deterioration processes and maintain product quality. This can include using gas treatments with specific gas ratios or modified atmosphere packaging (MAP), where the atmosphere surrounding the food is altered to inhibit microbial growth and maintain freshness.
3. Gas Treatment Options: Different gases, including nitrogen, carbon dioxide, oxygen, and their mixtures, are used in gas treatment for food preservation. Nitrogen is commonly employed to displace oxygen, reducing the oxidative reactions that lead to spoilage. Carbon dioxide inhibits microbial growth and can also act as a fungistatic agent. Oxygen is sometimes used in modified atmosphere packaging to maintain the desired level of oxygen within the package. The selection and ratio of gases depend on the specific food product, its respiration characteristics, and the desired shelf life.
4. Benefits of Gas Treatment: Gas treatment as a food preservation technique offers several benefits. It can effectively extend the shelf life of perishable food products, maintaining their quality, nutritional value, and appearance. By controlling the atmosphere, the growth of spoilage microorganisms can be inhibited, reducing the risk of foodborne illnesses. Gas treatment also provides an alternative to chemical preservatives, allowing for a more natural and eco-friendly approach to food preservation.

Gas treatment is an important component of food preservation and packaging technology. By modifying the atmosphere surrounding food products, the shelf life can be prolonged, ensuring food safety, quality, and customer satisfaction. However, it is crucial to carefully consider the specific gas treatment requirements for different food products and adhere to recommended guidelines to achieve optimal results.

Techniques to slow down respiration rate and physiological changes

To extend the shelf life of fruits and vegetables and slow down their respiration rate and physiological changes, several techniques can be employed. These techniques aim to create an optimal storage environment by manipulating factors such as temperature, oxygen levels, carbon dioxide levels, and humidity. Here are some commonly used techniques:

1. Reducing the Temperature: Lowering the temperature is one of the most effective ways to slow down the respiration rate and physiological changes in fruits and vegetables. Lower temperatures reduce the metabolic activity of the produce, slowing down respiration and delaying the onset of ripening. Cold storage or refrigeration at appropriate temperatures can significantly extend the shelf life of many perishable fruits and vegetables.
2. Reducing Oxygen Levels: Reducing the oxygen level in the storage environment can help slow down respiration and delay physiological changes in certain fruits and vegetables. Oxygen is consumed during respiration, and reducing its concentration can lower the metabolic activity. This can be achieved by using modified atmosphere packaging or controlled atmosphere storage, where the oxygen level is reduced by displacing it with an inert gas such as nitrogen. Lower oxygen levels can effectively suppress ethylene production and slow down ripening processes.
3. Increasing Carbon Dioxide Levels: Increasing the carbon dioxide level in the storage environment can also help in slowing down respiration and physiological changes. Elevated levels of carbon dioxide inhibit certain enzymes involved in the ripening process and microbial growth. This technique is commonly employed in modified atmosphere packaging or controlled atmosphere storage, where carbon dioxide is released or introduced to maintain a desired concentration.
4. Maintaining Desirable Humidity According to Fruit Types: Different fruits have specific humidity requirements to prevent excessive water loss or moisture buildup, which can lead to quality deterioration. Maintaining the proper humidity level can help slow down the respiration rate and physiological changes. This can be achieved through various means, such as using humidity-controlled storage chambers, breathable packaging, or employing moisture-retaining materials.

Principle of gas treatment for food preservation

Gas treatment is a key principle in food preservation that involves creating a specific atmosphere around the food to inhibit the growth of spoilage microorganisms, ensuring the production of safe, fresh, and high-quality food products. Here are the main principles of gas treatment for food preservation:

1. Inhibition of Microbial Growth: The use of proper concentrations of gases such as carbon dioxide, either alone or in combination with nitrogen, can effectively inhibit the growth of spoilage microorganisms. By reducing the oxygen levels in the surrounding atmosphere, the growth of aerobic microorganisms is suppressed. This helps to extend the shelf life of food products and maintain their quality.
2. Alteration of Gas Equilibria: Modifying the gas composition in the storage environment can influence the rate of microbial and enzymatic spoilage. By adjusting the concentrations of gases such as carbon dioxide, oxygen, and nitrogen, the equilibrium between these gases is altered, creating an environment that is unfavorable for the growth and activity of spoilage-causing microorganisms.
3. Ethylene Gas Evacuation: Ethylene gas is a natural plant hormone responsible for fruit ripening and aging. By evacuating or reducing the concentration of ethylene gas in the storage environment, the ripening and aging process of fruits and vegetables can be slowed down. This technique helps to extend the shelf life of produce and maintain their freshness and quality.
4. Reduction of Oxygen Concentration: Lowering the concentration of oxygen in the storage atmosphere can inhibit the growth of aerobic spoilage microorganisms, such as Pseudomonas and Achromobacter, commonly found in meat. These microorganisms require oxygen for their growth and survival. By creating an oxygen-reduced environment, their growth and spoilage activities can be suppressed.
5. Reduction of Anaerobic Counts: High concentrations of carbon dioxide or a gas mixture containing nitrogen, carbon dioxide, and a low level of oxygen can reduce the anaerobic microbial counts in food products. By creating an atmosphere with high carbon dioxide levels, the growth of anaerobic microorganisms is hindered, contributing to the preservation of food quality.

Gases commonly used in food preservation

Various gases are commonly used in food preservation to create specific atmospheres and control microbial growth. Here are the main gases used in food preservation:

1. Carbon Dioxide (CO2): Carbon dioxide is an important gas in modified atmospheric storage. It is used to control the growth of microorganisms on the surface of various food products, including meat, dairy products, fruits, and vegetables. Carbon dioxide can be applied as a surface cleaner in the form of dry ice. Its antimicrobial properties help to inhibit spoilage and extend the shelf life of food products.
2. Nitrogen (N2): Nitrogen is an inert gas commonly used in food preservation. It helps create a protective atmosphere around the food and acts as a filler gas to displace oxygen. Nitrogen is often used in modified atmospheric storage and packaging to maintain the desired gas composition. Nitrogen injection techniques can be employed to prevent spoilage microorganisms in sealed-packed food products. It is particularly effective in extending the shelf life of fresh products, meats, and dairy products.
3. Oxygen (O2): Reducing the oxygen level in the food product’s atmosphere is beneficial to minimize the growth of aerobic microorganisms. Oxygen is closely monitored and mixed with other gases in modified atmospheric (MA) and controlled atmospheric (CA) storage systems to maintain the desired atmosphere for food preservation.
4. Argon (Ar) and Helium (He): Argon and helium are inert gases commonly used in combination with other gases such as nitrogen, carbon dioxide, and oxygen in modified atmospheric storage and packaging. These gases assist in creating specific gas compositions tailored to the preservation requirements of different food products.

Different types of storage techniques for food preservation

1. Controlled atmosphere storage (CAS)

Controlled atmosphere storage (CAS) is a storage technique used in food preservation, where the composition of the storage environment is modified and controlled to extend the shelf life of food products. Here is an overview of CAS and its principles:

1. Definition and Operation: CAS involves altering the composition of the atmosphere surrounding stored food products, deviating from the atmospheric conditions found in ambient air. The proportion of gases, including carbon dioxide (CO2), oxygen (O2), and inert filler gases like nitrogen (N2), is carefully monitored and maintained at desired levels.
2. Low Temperature: Low temperature plays a crucial role in CAS. The storage facility is maintained at a low temperature to slow down biochemical reactions, enzymatic activities, and microbial growth, thereby extending the shelf life of the stored food products. The specific temperature depends on the type of food being stored.
3. Controlled and Monitored Gas Composition: CAS involves controlling and monitoring the proportion of gases in the storage atmosphere. Typically, the oxygen concentration is lowered, carbon dioxide concentration is increased, and nitrogen is used as an inert filler gas. Lowering the oxygen concentration reduces oxidative reactions and inhibits the growth of aerobic spoilage microorganisms. Increased carbon dioxide concentration helps suppress the growth of spoilage microorganisms and delays physiological changes in fruits and vegetables. Nitrogen is often used as a filler gas to displace oxygen and maintain the desired atmosphere.
4. Addition of Other Gases: In addition to the primary gases mentioned above, CAS may involve the addition of other gases at low concentrations. For example, ethylene gas may be added in certain cases to control the ripening process of fruits. Carbon monoxide and fumigants may be used in specific applications to inhibit insect infestations or microbial growth.

The Principles of CAS can be summarized as:

• Low temperature to slow down deterioration processes
• Increased carbon dioxide concentration to inhibit microbial growth and delay physiological changes
• Decreased oxygen concentration to suppress aerobic spoilage microorganisms

CAS is widely used in the storage of various fruits, vegetables, and other perishable food products. It helps maintain the quality, freshness, and nutritional value of the stored items, extending their shelf life. However, it is important to carefully monitor and control the gas composition and storage conditions to ensure optimal preservation results and prevent any negative impacts on food quality and safety.

2. Modified atmosphere storage (MAS)

Modified atmosphere storage (MAS) is a storage technique used in food preservation that involves altering the atmosphere surrounding stored food products to extend their shelf life. Here is an overview of MAS, including its characteristics, advantages, and disadvantages:

1. Definition and Operation: MAS differs from controlled atmosphere storage (CAS) in terms of the degree of active control over gas concentrations. In MAS, there is typically no active control of gas concentrations. Instead, the atmosphere is modified either actively through the addition or removal of gases or passively through the gases produced during the respiration of the stored products.
2. Active and Passive Modification: MAS can involve active modification of the storage atmosphere by adding or removing specific gases to create the desired composition. Alternatively, it can rely on the gases naturally produced by the stored products during respiration to modify the atmosphere. This passive modification occurs as the products consume oxygen and release carbon dioxide.
3. Cost and Storage Life: MAS is generally a more cost-effective technique compared to CAS, as it requires less sophisticated equipment and monitoring. However, MAS typically results in a shorter storage life for the preserved products compared to CAS.

Advantages of MAS:

• Increased shelf life of the products
• Slowing down the rate of respiration in the stored products
• Delayed ripening of fruits
• Reduction in the incidence of storage disorders such as oxidative damage and enzymatic browning

Disadvantages of MAS:

• Prevention of desirable ripening, resulting in irregular ripening of certain fruits such as bananas and tomatoes
• Increased occurrence of post-harvest disorders like sprouting in potatoes and brown heart in apples
• Potential development of off-flavors in the stored products
• Possibility of physiological disorders such as tissue injury and internal browning
• Risk of accumulation of organic acids at toxic levels in some cases

MAS is a commonly used technique in the storage of various perishable food products, providing advantages such as increased shelf life and reduced spoilage. However, it is important to consider the potential disadvantages and carefully monitor the storage conditions to ensure optimal preservation results and maintain food quality and safety.

3. Hypobaric storage

Hypobaric storage is a controlled atmosphere storage technique that involves refrigerated storage under reduced pressure, lower than atmospheric pressure. This technique combines reduced pressure with high humidity to preserve the quality and extend the shelf life of stored products. Here is an overview of hypobaric storage:

1. Reduced Pressure and High Humidity: In hypobaric storage, the storage environment is maintained at a reduced pressure below atmospheric pressure. This lower pressure is achieved to improve air throughput or facilitate the addition of different gas mixtures. Additionally, high humidity is maintained to prevent product dehydration and maintain the quality of stored products.
2. Oxygen Reduction and Humidity Control: Hypobaric storage aims to reduce the amount of oxygen available in the storage environment by decreasing the amount of air present. This reduction in oxygen helps to slow down the respiration rate and metabolic activities of the stored products, thereby extending their shelf life. However, to prevent dehydration, high humidity levels are maintained to ensure the products retain their moisture content.
3. Operating Parameters: In hypobaric storage, the products are placed in a flowing stream of air that is substantially saturated with water, maintaining a relative humidity (RH) of 80-100%. The pressure is reduced to a range of 4-400 mmHg absolute, and the storage temperature is controlled within a range of -2 to 15°C.
4. Flushing Out Gaseous By-Products: One of the advantages of hypobaric storage is that it facilitates the release and removal of vapors, as well as the flushing out of undesired gaseous by-products and other potentially noxious gases. This helps maintain a clean and controlled storage environment for the preserved products.

Hypobaric storage is commonly used for a variety of perishable food products to extend their shelf life. By combining reduced pressure with high humidity, this technique helps slow down deterioration processes, preserve product quality, and reduce the risk of spoilage. It is particularly beneficial for preserving products sensitive to dehydration and those that benefit from reduced oxygen levels.

Proper monitoring and control of pressure, humidity, and temperature are crucial to ensure the effectiveness of hypobaric storage and maintain the desired quality of stored products.

FAQ

References

1. Potter NP (1987), Food Science, CBS Pub, India
2. Rahman MS (1999), Handbook of Food Preservation, Marcel Dekker, Inc, NY
3. Desrosier EN (1963), The Technology of Food Preservation, AVI Publishing Company, New York.