Sterilization in food processing is crucial to eliminate harmful bacteria, toxins, and spoilage microorganisms that may contaminate the food. However, it is important to preserve the beneficial microorganisms or spores present in the tank without compromising the food quality. This process is often referred to as "commercial aseptic" to emphasize its dual purpose. During sterilization, it is also necessary to deactivate the enzymes present in the food while maintaining its nutritional value and overall quality.
Canned food is typically sterilized through heating. High-pressure sterilization involves subjecting the food to temperatures above 100 ℃, whereas normal-pressure sterilization or pasteurization involves temperatures below 100 ℃. The sterilization process is primarily controlled by temperature, time, and back pressure to achieve the required sterilization intensity (F0) for different products.
Canned foods are categorized based on their pH value: low acidity (pH>4.5), medium acidity (pH 3.7~4.5), and high acidity (pH<3.7). These categories are affected by different spoilage microorganisms, requiring different bactericidal strength (F0) values. Low-acid canned food requires high sterilization intensity and is subjected to high-pressure sterilization. On the other hand, medium-acid and high-acid canned food can be sterilized at relatively low intensities using normal-pressure sterilization.
Traditionally, the specific sterilization process conditions for each canned food were determined empirically. However, nowadays, more scientific methods are employed. This involves determining the heat resistance (D) value of the spoilage bacteria present in the product, which represents the time required to kill 90% of the bacteria at a particular temperature. Additionally, various parameters relating to heat transfer characteristics during the sterilization process are measured. These measurements are then used to calculate the minimum sterilization intensity required using specific formulas.
Sterilization operations generally involve the use of direct steam or heated water in vertical or horizontal sterilizers. Another method known as aseptic canning or aseptic packaging involves sterilizing the food before canning and then placing it in an aseptic container in a sterile environment before sealing it. Flame sterilization (directly heating metal cans using flames) and hot air sterilization methods are also utilized. Different equipment types, such as rotary, vibration, basketless, water sealing, and hydrostatic pressure methods, are employed accordingly.
In summary, sterilization is a crucial step in ensuring the safety and longevity of canned food. By carefully controlling the sterilization process and considering factors such as pH value and heat resistance, food processors can effectively eliminate harmful microorganisms while preserving the quality and nutritional value of the food.