Different for Food autoclave and Medical autoclave

Using the correct type of autoclave to ensure the appearance and flavor of packaged food

1. Retort Autoclaves Help Maintain the Appearance of Packaged Food

If conventional autoclaves are used for sterilization, the product's appearance often suffers after testing various products. In a sterilization batch, a large proportion of bags may become inflated, wrinkled, or have heat-sealed seams that burst. Similarly, food packaged in plastic or metal cans often becomes dented or deformed.

Food Sterilization Retort Autoclave

Retort autoclaves are manufactured with various features, but the basic principle consists of three main stages:

AIR REMOVAL > HEATING > STERILIZATION > COOLING

1. Air Removal: This stage eliminates all cold air inside the autoclave, as air is a poor heat conductor and can cause uneven temperatures inside the autoclave.

In medical autoclaves, air is typically removed using a vacuum (Prevacuum). Retort autoclaves cannot use a vacuum method for air removal, as sudden pressure changes can deform the product. Instead, they use gravity methods. Saturated steam is pumped into the chamber while air vents are opened to push out cold air, ensuring that the pressure inside and outside the product does not increase abruptly but balances out.

Medical autoclaves usually supply steam through a single inlet. The steam diffuses evenly thanks to the pressure difference inside the autoclave. Retort autoclaves for packaged food typically have multiple steam inlets to ensure even contact with the product.

2. Heating: Some large retort autoclaves are equipped with blowers to enhance steam diffusion. This helps the product reach sterilization temperature faster, reducing the thermal denaturation of the food.

3. Cooling:

In medical autoclaves, this stage is also known as drying. The autoclave cools simply by venting air to reduce the temperature and pressure inside or by using a vacuum to dry.

For retort autoclaves, this stage is crucial. In addition to venting air, the autoclave sprays cold water or air to cool the product while balancing the pressure inside. When the product's temperature is cooled to a certain level (usually below 90°C), the machine automatically stops the cooling water or air, and only then do the air vents reduce the internal pressure to atmospheric pressure.

Thus, the structure and features of retort autoclaves solve the packaging appearance issues encountered with other types of autoclaves.

2. Retort Autoclaves Help Minimize Changes in Color, Texture, Aroma, and Nutritional Values of Food

Have you encountered situations where, after sterilization, the food's color no longer retains its freshness and vibrant appearance? Particularly, the flavor changes. To address this issue, retort autoclaves not only control temperature, time, and pressure during the sterilization process but also use a crucial parameter: the F0 value, which is suitable for each type of food.

Do you know what the F0 value is and how it is used?

Basically, bacteria are completely destroyed at a temperature of 121°C, considered the standard temperature. If we want to sterilize at different temperatures, how long is needed to achieve the same sterilization effect as at 121°C? The F0 value represents this time.

Temperature and sterilization time are interrelated. To preserve the food's flavor while ensuring sterilization, retort autoclaves allow us to adjust the sterilization temperature and calculate the appropriate F0 value for each type of food. This way, we can increase or decrease the temperature to shorten the sterilization process while ensuring product quality.

3. Determining the End Point of the Sterilization Process

The sterilization value F must be determined for each type of microbial spoilage. This value is calculated based on z = 10°C and the conventional temperature of 121.1°C, denoted as F0. Years of practical experience in canning have concluded that for moist heat sterilization, the F10121.1 (Clostridium botulinum) process, i.e., F0 = 3 minutes at the center of the canned product, ensures safety from a health perspective. Spores of heat-resistant microorganisms may survive processes designed to kill Clostridium botulinum spores and can spoil the product but do not produce toxins during food storage.

Therefore, establishing a minimum heat process aims to destroy the spores of Clostridium botulinum strains based on the z value (the temperature change needed for a tenfold reduction in microbial population) and the temperature used for microbial destruction.

The end point of the sterilization process is usually determined by the “Probability of a Non-Sterile Unit” (PNSU).

Experimental F10121.1 values for:

1. Public Health

   • Clostridium botulinum spores
     • N0 = 10^3
     • D121.1 = 0.2 minutes
     • PNSU = 10^-9
     • F0 = 3 minutes

2. Preventing Spoilage

   • Average heat-resistant spores

     • N0 = 10^4

     • D121.1 = 0.5 minutes

     • PNSU = 10^-6

     • F0 = 5 minutes

     • D121.1 = 0.7 minutes

     • F0 = 7 minutes

   • Heat-resistant spores

     • Distributed at temperatures < 30°C

       • N0 = 10^2
       • D121.1 = 1.5 minutes
       • PNSU = 10^-2
       • F0 = 6 minutes

     • Distributed at temperatures > 30°C

       • N0 = 10^2

       • D121.1 = 1.5 minutes

       • PNSU = 10^-6

       • F0 = 12 minutes

       • D121.1 = 2.5 minutes

       • F0 = 20 minutes

4. Choosing the Sterilization Regimen

We must select a reasonable sterilization regimen, ensuring the elimination of harmful microorganisms in the canned food while minimizing nutrient loss and maintaining the best product quality.

A. Selecting Sterilization Temperature

All types of food brought for canning are living environments for microorganisms. Although many factors affect microbial activity, acidity significantly influences it, making acidity crucial for choosing the sterilization temperature.

Canned products are classified into two groups based on their active acidity for determining the sterilization temperature:

• Non-acidic and low-acid canned products with pH > 4.6
• Acidic canned products with pH < 4.6

For non-acidic or low-acid canned products with pH > 4.5 (e.g., canned meat, fish, certain canned vegetables), microorganisms thrive in this environment, mainly heat-resistant microorganisms. The most harmful, affecting consumer health, are protein-degrading Clostridium botulinum spores, the most dangerous heat-resistant microorganisms considered the primary target for elimination. Killing its spores is considered the minimum sterilization standard, although it is not the most heat-tolerant representative of putrefactive microorganisms. In canned meat and fish, we may also encounter anaerobic spoilage bacteria like Clostridium sporogenes, more heat-resistant than Clostridium botulinum.

Moreover, low-acid canned products often contain heat-resistant bacteria like Clostridium thermosaccharolyticum, anaerobic thermophiles that degrade glucids, and aerobic thermophiles like Bacillus stearothermophillus, which spoil canned food.

Therefore, non-acidic canned products with pH > 4.6 require high sterilization temperatures to destroy heat-resistant spoilage microorganisms. The temperature ranges from 105°C to 121°C, known as the sterilization process.

For acidic canned products with pH < 4.6 (e.g., canned fruits, tomatoes, pickled vegetables), heat-resistant bacteria do not develop well and are less heat-resistant, making them easier to destroy at higher temperatures. Yeasts and molds thrive in acidic environments but are generally less heat-resistant. Thus, high-acid canned products can be sterilized at lower temperatures than low-acid canned products, typically at 100°C or lower, around 80°C.

When determining the sterilization temperature, it must be the temperature of the entire product mass to be sterilized, especially the temperature at the can's center (for solid products, the center is in the middle; for liquid products, it's 2/3 from the top). Practically, the temperature at this point is nearly equal to the sterilization device's temperature for liquid canned products or 0.5-1.5°C lower for solid canned products.

B. Selecting Sterilization Time

At a certain sterilization temperature, microorganisms in the canned product are not instantly killed but require a certain time called the sterilization time or heat treatment time, denoted as t (minutes).

During sterilization, the product in the can is not immediately heated to the desired sterilization temperature. Heat must gradually transfer from the heating medium through the packaging to the outer layer and then to the can's center. This process takes time, called the heat transfer time (denoted as t1). Once the can's center reaches the sterilization temperature, it is held at that temperature for a certain period, called the lethal time (denoted as t2).

Thus, the overall sterilization time for the canned product (or the time it undergoes heat treatment) includes the heat transfer time (t1) and the lethal time (t2):

t = t1 + t2 (minutes)

However, in practice, we need to cool the sterilized product to stop heat treatment at the end of the sterilization process, requiring a certain time for cooling. This cooling time does not affect the sterilization process, as it is included in the lethal time. Therefore, the actual overall sterilization time in practice includes the heat transfer time (t1), lethal time (t2), and cooling time (t3):

t' = t1 + t2 + t3

In the sterilization process, the cooling time should be limited, as an overly long cooling time may alter the product's nutritional content. Thus, the sterilization time is often controlled within 30 minutes.

To achieve the desired product quality, we need to calculate the appropriate sterilization time and temperature. This requires a detailed understanding of the product characteristics and the target microorganisms for elimination. The retort autoclave's precise control over temperature and pressure helps achieve the best sterilization results while maintaining product quality.