Methods for Preserving Fresh Fruits and Vegetables

Each type of fresh fruit and vegetable requires an appropriate concentration of O₂ and CO₂ to avoid affecting its normal physiological processes during storage. Let’s explore the methods for preserving fresh fruits and vegetables in the following article.

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1. Characteristics of fresh fruits and vegetables

Fresh fruits and vegetables have the following characteristics, spoilage causes, and factors affecting their storage life:

Characteristics and causes of spoilage during storage

• High water content (up to 95%).
• Rich nutritional composition.
• Loose, soft, and porous structure, making them susceptible to scratches, damage, crushing, and bruising.
• A series of physiological, biochemical, and hydrolysis processes continue to occur during storage.
• These conditions allow molds and microorganisms to easily enter, grow, and cause spoilage.
• In addition, fresh fruits and vegetables undergo physical changes, such as water evaporation, which causes them to wilt, lose weight, and deteriorate in quality.

Factors affecting the storage life of fresh fruits and vegetables

• Storage temperature.
• Air humidity.
• Light.
• Atmospheric gas composition in the storage environment.
• Ventilation and air circulation.

2. Methods for preserving fresh fruits and vegetables

a. Preserving fresh fruits and vegetables using vacuum packaging

Definition: This is a method in which the amount of air inside the packaging is reduced to a certain level before the package is hermetically sealed.

Advantages:

• Extends shelf life while maintaining the freshness and flavor of food.
• Prevents or slows down fat oxidation reactions.
• Prevents changes in the color of fresh fruits and vegetables.
• Reduces weight loss by preventing moisture loss.

Disadvantages:

• High investment costs.
• Potentially significant biological hazards.

Effects of vacuum packaging on the spoilage of fresh fruits and vegetables

If machinery and equipment do not operate effectively, the following problems may occur:

• Fresh fruits and vegetables may suffer structural damage or undergo anaerobic respiration if too much air is removed.
• Changes in the fresh fruits and vegetables may be accelerated if too much air remains inside the package.
• Poor equipment hygiene and excessively high or low sealing temperatures can also affect the spoilage of fresh fruits and vegetables.

b. Preserving fresh fruits and vegetables using MAP packaging

Definition: Modified Atmosphere Packaging (MAP) is a method in which all the air inside food packaging is removed and replaced with a gas mixture of CO₂, N₂, and O₂ at appropriate ratios.

However, the composition of this gas mixture can change throughout the storage period due to the respiration of the product or gases already present in the food.

Advantages:

• Nutritional content is well preserved.
• Prevents moisture evaporation and adjusts O₂ and CO₂ concentrations in a favorable direction. This helps regulate the atmosphere and reduce the respiration rate of fruits and vegetables, allowing them to remain fresh for longer than under normal conditions.
• Reduces the need for chemicals, making the method safer for consumers.
• Simple and easy to apply.

Disadvantages:

• The packaging equipment is expensive, so this method is generally used for products with large production volumes, particularly in large supermarkets.

Because the gas concentration and composition inside the package can change, MAP-packaged food is mainly susceptible to microbial spoilage when the packaging is damaged or not properly sealed.

Different types of fresh fruits and vegetables require different gas concentrations. If the ratio between the gases is not appropriate, the products may spoil.

If gas is injected without completely removing the air inside the package, the ratio of the gas mixture cannot be accurately determined, which can affect the quality of the fresh fruits and vegetables.

 

c. Preserving fresh fruits and vegetables using CAP packaging 

Definition: This method also involves removing all the air inside the package and then replacing it with a mixture of O₂, CO₂, and N₂ at appropriate ratios. With this method, the composition of the gases remains unchanged throughout the storage period.

Example: Apples can be preserved using this method for 6–9 months at 0–4°C with 10–12% O₂, 5% CO₂, and the remainder N₂. This method is mainly applied to apples, avocados, lettuce, asparagus, and bananas.

Advantages:

• Fresh fruits and vegetables packaged using this method maintain high quality.

Disadvantages:

• Expensive and complex equipment.
• Requires special attention during storage warehouse operation. Maintaining stable storage conditions can be difficult, and the requirements vary depending on the type and variety of fruit or vegetable.

Because the gas composition remains unchanged throughout the storage period, using an inappropriate gas ratio during packaging can cause various forms of spoilage:

• Excessively high oxygen levels promote ethylene biosynthesis, increasing physiological activity, respiration, and storage temperature, which can accelerate spoilage.
• Conversely, excessively low oxygen levels promote anaerobic respiration, reduce vitamin content in fresh fruits and vegetables, and encourage mold growth.
• Excessively high CO₂ concentrations can increase the acidity of fresh fruits and vegetables, cause bruised spots on fruits, lead to spoilage, and create abnormal flavors in vegetables such as cauliflower, lettuce, and beans.

3. Effects of packaging on the preservation of fresh fruits and vegetables 

Common packaging materials used for fresh fruits and vegetables include PE, PP, PVC, and other types of films.

Spoilage of fresh fruits and vegetables during storage and packaging is often affected by the following packaging properties:

• Chemical composition of the packaging.
• Mechanical strength.
• Gas barrier properties.
• Moisture resistance.
• Heat resistance.

Packaging made from recycled materials may allow substances to migrate into food and potentially cause harmful effects.

For example, VCM (vinyl chloride monomer) in PVC can affect the nervous system and has carcinogenic potential.

If packaging has poor mechanical strength and is easily deformed, torn, cracked, or opened, it can cause:

• The structure of the product inside to become deformed during loading, unloading, and transportation, reducing its visual and sensory value.
• Accelerated changes in fresh fruits and vegetables, causing them to wilt, rot, change color, and deteriorate more quickly.
• Because fresh fruits and vegetables have high water content, if the packaging does not provide adequate moisture and gas barrier properties, water inside the products will diffuse outward, causing weight loss, creating favorable conditions for mold growth, and producing abnormal odors that affect the flavor of the products.
• Since the physical, physiological, and chemical changes in fresh fruits and vegetables vary with temperature, packaging with poor heat resistance can cause changes in food temperature when the surrounding temperature changes. This can lead to moisture condensation on the packaging, creating favorable conditions for mold growth.
• In addition, if the packaging is not properly cleaned, contaminants and microorganisms may be transferred into the food.