Introduction to Gas Treatment as a Food Preservation Technique
The shelf life of different perishable food products can be prolonged through the application of gas treatments.
In food preservation, gas treatment involves the use of gases such as nitrogen, carbon dioxide, oxygen, or their mixtures in different ratios to extend the shelf life of food products.
Gas treatment plays a significant role in food preservation and packaging technology by ensuring food quality and safety.
Modifying or controlling the atmosphere surrounding food products helps extend their shelf life and prevents degradative changes that may cause microbial spoilage or other forms of deterioration.
This technique is especially useful for preserving fruits and vegetables by controlling or modifying the atmosphere to slow down their respiration rate.
Besides fruits and vegetables, other food products such as meat and cereal grains are also preserved by controlling the atmosphere during storage.
Respiration during storage is a major concern, as fruits and vegetables consume oxygen and release carbon dioxide, which can affect their shelf life and quality.
Based on their respiration behavior, fruits are categorized into two types:
Climacteric fruits – These fruits can ripen even after harvest due to the production of ethylene, which is accompanied by an increased rate of respiration.
Non-climacteric fruits – These fruits cannot ripen after harvest, do not undergo proper respiration, and produce only a low level of ethylene.
Techniques to slow down respiration rate and physiological changes
Respiration rate and physiological changes in stored fruits and other perishable foods can be slowed down by applying specific techniques.
Reducing the temperature helps decrease the metabolic activity of fruits and vegetables, thereby lowering respiration and delaying spoilage.
Reducing the oxygen level in the storage atmosphere slows down oxidative processes and respiration, which helps extend shelf life.
Increasing the concentration of carbon dioxide around stored products suppresses respiration and delays microbial growth, further enhancing preservation.
Maintaining desirable humidity according to fruit types is essential, as too low humidity causes dehydration and shriveling, while too high humidity may promote microbial spoilage.
Principle of gas treatment for food preservation
The main principle of gas treatment in food preservation is to create a surrounding atmosphere that prevents the growth of spoilage microorganisms while maintaining food safety, freshness, and quality.
Proper concentrations of carbon dioxide gas, either alone or mixed with nitrogen gas, can inhibit the growth of spoilage microorganisms by reducing the oxygen level around the food.
Altering the gas equilibria in the storage environment can affect and slow down both microbial activity and enzymatic spoilage.
The evacuation or removal of ethylene gas from storage reduces the ripening and aging processes in fruits and vegetables.
Lowering oxygen concentration can suppress aerobic spoilage microorganisms, particularly in meat, including bacteria such as Pseudomonas and Achromobacter.
Anaerobic counts can also be reduced by using high levels of carbon dioxide or by employing specific gas mixtures, such as 70% Nitrogen, 25% Carbon dioxide, and 5% Oxygen.
The selection of gases and their concentrations is not universal but instead depends on the type of food product being preserved.
Gases commonly used in food preservation
Carbon dioxide (CO₂):
One of the most important gases used in modified atmospheric (MA) storage.
Controls the growth of microorganisms on the surface of foods such as meat, dairy products, fruits, and vegetables.
Can also be applied directly to the surface of food products in the form of dry ice, where it acts as a surface cleaner.
Nitrogen (N₂):
An inert gas that helps create a protective atmosphere around food and functions as a space filler gas to displace oxygen.
Commonly used in modified atmospheric storage.
Nitrogen injection techniques can be applied to prevent spoilage microorganisms in sealed-packaged food products.
Plays an important role in extending the shelf life of fresh products, meats, and dairy products.
Oxygen (O₂):
Reducing the oxygen level in the atmosphere of food storage slows down the growth of aerobic microorganisms.
In modified atmosphere (MA) and controlled atmosphere (CA) storage systems, oxygen is carefully monitored and mixed with other gases for preservation.
Argon (Ar) and Helium (He):
These inert gases are sometimes combined with nitrogen, carbon dioxide, or oxygen in MA storage and packaging systems.
Different types of storage techniques for food preservation
1. Controlled atmosphere storage (CAS)
A storage technique in which the atmosphere’s composition is deliberately altered from that of normal air.
The proportions of gases such as CO₂, O₂, and inert filler gas N₂ are carefully monitored and maintained in a controlled state.
Food products are stored at low temperature to extend shelf life.
Typically, oxygen concentration is lowered, carbon dioxide concentration is increased, and nitrogen is used as an inert filler.
Other gases such as ethylene, carbon monoxide, or fumigants may also be added at low concentrations.
Principle of CAS:
Low temperature storage.
Increased carbon dioxide concentration.
Decreased oxygen concentration.
2. Modified atmosphere storage (MAS)
Differs from CAS in terms of the degree of control over gas concentrations.
In MAS, there is no active control of gas concentrations once the atmosphere is modified.
Atmosphere modification can be:
Active (through the addition or removal of gases).
Passive (due to gases naturally produced during respiration).
MAS is cheaper than CAS but results in a shorter storage life.
Advantages of CAS or MAS:
Increase in the shelf life of food products.
Reduction in respiration rate of stored products.
Delay in fruit ripening.
Lower incidence of storage disorders such as oxidative damage and enzymatic browning.
Disadvantages of CAS or MAS:
Prevention of desirable ripening and occurrence of irregular ripening in fruits such as bananas and tomatoes.
Increased post-harvest disorders such as sprouting in potatoes and brown heart in apples.
Development of off-flavors in stored products.
Possible physiological disorders such as tissue injury and internal browning.
Accumulation of organic acids at toxic levels.
3. Hypobaric storage
A specialized form of controlled atmosphere storage.
Food products are stored under reduced pressure (lower than atmospheric pressure) combined with refrigeration and high humidity.
Oxygen concentration is reduced by lowering the amount of air, while high humidity is maintained to prevent dehydration of products.
Products are placed in a flowing stream of air saturated with water vapor (relative humidity = 80–100%), at reduced pressure (4–400 mmHg absolute), and a controlled temperature (-2 to 15°C).
Reducing pressure improves air through-put and facilitates the addition of different gas mixtures.
This system flushes out released vapors, undesirable gaseous by-products, and other noxious gases during storage.
References
Potter, N.P. (1987). Food Science. CBS Publishers, India.
Rahman, M.S. (1999). Handbook of Food Preservation. Marcel Dekker, Inc., New York.
Desrosier, E.N. (1963). The Technology of Food Preservation. AVI Publishing Company, New York.
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