# Microbial Spoilage of Canned foods And Its Preservation Methods – Canning Steps

> Canning is a highly regarded method for packaging food, ensuring its long-term storage and preservation. Typically, food is packed into metal containers and...

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Last updated: May 24, 2024

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Canning is a highly regarded method for packaging food, ensuring its long-term storage and preservation. Typically, food is packed into metal containers and subjected to appropriate heat treatments, the specifics of which vary depending on the type of food being canned. While the incidence of food spoilage in cans is generally low, there is always a possibility that microorganisms may survive if the heat treatment is not conducted properly, thereby leading to the spoilage of the food.

Spoilage in canned foods can be attributed to both biological and chemical factors, and sometimes a combination of the two. Biological spoilage primarily occurs as a result of microbial growth within the can. Microorganisms, such as bacteria, yeasts, and molds, can find a way to survive and proliferate if the canning process does not eliminate them effectively. These spoilage microorganisms can degrade the food, causing changes in texture, appearance, flavor, and overall quality.

Chemical spoilage, on the other hand, arises from the reaction between acids present in the food and the iron in the can. This reaction produces hydrogen gas, leading to the expansion or swelling of the can. If this chemical reaction goes unchecked, it can compromise the integrity of the can and potentially result in leaks or even explosions, thereby exposing the food to further contamination and spoilage.

In addition to biological and chemical factors, certain environmental conditions can also contribute to the spoilage of canned foods. High summer temperatures and high altitudes can exacerbate the degree of swelling in cans, making them more susceptible to spoilage. Furthermore, improper handling and storage practices, such as overfilling, buckling, denting, or sealing the can while it is still cool, can also compromise the hermetic seal of the can, allowing microorganisms to enter and spoil the contents.

To mitigate the risk of microbial spoilage in canned foods, it is crucial to adhere to strict quality control measures throughout the canning process. This includes ensuring proper heat treatment to eliminate or inactivate any potential spoilage microorganisms. Additionally, using high-quality cans with protective coatings and maintaining appropriate storage conditions, such as cool temperatures, can help minimize the risk of spoilage.

In conclusion, while canned foods generally have a low incidence of spoilage, the presence of microorganisms and the potential for chemical reactions necessitate careful attention to the canning process. By employing effective heat treatments, maintaining optimal storage conditions, and adhering to proper handling practices, the risk of microbial spoilage in canned foods can be significantly reduced, ensuring the safety and quality of the preserved food products.

## Types of the food based on pH

The classification of canned food based on pH is crucial in understanding the susceptibility of food to microbial spoilage. By categorizing canned food according to its pH level, we can identify different groups with varying levels of acidity. The pH of a food product plays a significant role in determining its microbial stability and potential for spoilage. Let's explore the three main types of canned food based on pH:

- Low-acid canned food (pH > 5.2): This category comprises food products with a pH above 5.2. Examples of low-acid canned food include meat products, milk, dairy products, and seafood. Due to their higher pH levels, these foods provide an environment that is less acidic, which can promote the growth of certain spoilage microorganisms if proper precautions are not taken during the canning process.

- Acid canned food (pH 4.5-3.7): Acid canned food falls within a pH range of 4.5 to 3.7. This group includes a variety of fruits and vegetables, such as tomatoes, pears, figs, oranges, apricots, and pineapples. The natural acidity of these foods helps inhibit the growth of many spoilage microorganisms, making them less prone to spoilage. However, it is still essential to maintain proper canning techniques to ensure the long-term preservation of these acidic foods.

- High acid canned food (pH  5.2): Thermophilic flat-sour spoilage bacteria, such as Geobacillus stearothermophilus and Bacillus coagulans, can cause defects such as reducing pH, souring, off-odor, and flavor changes. Sulfide-producing anaerobic bacteria, like Clostridium nigrificans and Desulfotomaculum nigrificans, can lead to blackening, a "rotten egg" odor, and the formation of iron sulfide precipitate. Mesophilic putrefactive anaerobic bacteria, including Clostridium botulinum, can cause can swelling, putrid odor, and the production of various compounds.

- Acid canned food (pH 4.5-3.7): Mesophilic spore-forming bacteria, such as Bacillus polymyxa, Bacillus macerans, and Clostridium pasteurianum, can lead to flat or swollen cans, coagulation, gas formation, and acid production. Butyric anaerobic bacteria, like Clostridium butyricum and Clostridium tertium, can cause can swelling, fermentation, and a butyric odor. Aciduric bacteria, including G. stearothermophilus and B. coagulans, can result in changes in vacuum, pH reduction, souring, off-odors, flavors, and sometimes cloudy juice.

- High acid canned food (pH < 3.7): Yeasts such as Saccharomyces and Zygosaccharomyces can cause can swelling, leakage, fermentation, CO2 production, and yeasty odor. Molds, including B. fulva, Aspergillus, Penicillium, and Citromyces, can also result in can swelling, leakage, fermentation, CO2 production, and yeasty odor. Lactic acid bacteria such as L. brevis, L. mesentericus, L. dextranicum, and L. mobilis can cause can swelling, acid odor, ropiness, and the formation of acid and CO2.

## Preservation of canned food from microbial spoilage

Canned food undergoes thermal processing to achieve "commercial sterility" and ensure long-term storage. However, it's important to note that canning alone does not guarantee freedom from microbial spoilage. Recontamination of canned food can occur due to various factors. To prevent microbial spoilage and extend the shelf life of canned food while maintaining its nutritive quality, additional preservation methods can be applied in combination with canning. Let's explore some of these methods:

- Radiation: Radiation sterilization, also known as radappertization, involves exposing food in sealed containers to ionizing radiation. This process effectively kills all spoilage-causing organisms. Radiation is particularly useful for eliminating microorganisms on the surfaces of canned jars and their lids, further reducing the risk of spoilage.

- Preservative agents: Preservatives are substances that inhibit or retard the growth of microorganisms and are considered "Generally Regarded As Safe (GRAS)." They can be used in conjunction with canning to enhance the preservation of canned food. Some examples of preservatives include simple organic acids, sulfite, ethylene oxide, sodium nitrite, ethyl formate, lactic acid bacteria (LAB), and bacteriocins. These agents help to inhibit the growth of spoilage microorganisms and extend the shelf life of canned food.

- Chilling storage: Canned foods can be stored at temperatures between 0–5 °C. Chilling storage is employed to reduce the rate of microbial growth and enzymatic activities. Lower temperatures inhibit the proliferation of microorganisms, helping to extend the shelf life of canned food. Chilling storage also slows down enzymatic reactions, preserving the quality and freshness of the product.

Implementing a combination of these preservation methods with canning can effectively safeguard canned food from microbial spoilage. Each method has its own advantages and considerations, and the selection of preservation techniques may depend on factors such as the specific food product, desired shelf life, and regulatory requirements.

It is crucial for manufacturers to adhere to good manufacturing practices, maintain strict quality control measures, and conduct regular inspections and testing to ensure the efficacy of preservation methods and prevent recontamination. By employing a multi-faceted approach to preservation, producers can maintain the safety, quality, and longevity of canned food, meeting consumer expectations and reducing the risk of spoilage.

## What is Canning?

- Canning is a highly effective method of food preservation that involves processing and sealing food contents in a hermetically sealed container, such as metal cans, glass jars, plastic cans, thermostable plastic, or multilayered flexible pouches.

- This preservation technique, also known as Appertization after its inventor Nicolas Appert, is widely used to extend the shelf life of food for an extended period. The primary objective of canning is twofold: to eliminate pathogenic and spoilage microorganisms through heat application and to prevent contamination by new microorganisms through the hermetic sealing of the container.

- The process begins with the preparation of the food, which may involve cleaning, cutting, cooking, or other treatments depending on the specific product. The prepared food is then packed into the selected containers, and the containers are sealed to create a tight, impermeable seal.

- The next crucial step is the application of heat. The sealed containers are subjected to heat treatment, often using methods such as steam, boiling water, or pressure canning. The specific heat treatment parameters, including temperature and duration, are carefully determined based on the type of food being processed. The goal is to raise the temperature sufficiently to destroy any existing microorganisms, including harmful pathogens, while also inactivating enzymes that can cause spoilage.

- Once the heat treatment is complete, the containers are rapidly cooled to prevent any potential recontamination. This cooling process helps maintain the integrity of the food and ensures its quality and safety.

- The hermetically sealed containers play a crucial role in preserving the food. They create a barrier that prevents the entry of air, moisture, and microorganisms from the surrounding environment. This sealing process helps safeguard the food, maintaining its freshness, flavor, and nutritional value over an extended period.

- Canning is widely employed in the food industry to preserve a wide range of products, including fruits, vegetables, meats, seafood, soups, sauces, and more. It allows for safe, convenient, and long-term storage of food, reducing waste and ensuring food availability even when fresh produce is not in season.

- By employing the canning process, food manufacturers can provide consumers with high-quality, shelf-stable products that can be stored for extended periods without compromising safety or taste. Canning continues to be a popular and reliable method of food preservation, contributing to food security and reducing food waste worldwide.

## Steps of canning

Canning involves a series of carefully executed steps to ensure the preservation and safety of food. Let's explore the various stages involved in the canning process:

- Preparations: The containers that will hold the food are preheated to sterilize them. This step helps ensure the cleanliness and safety of the containers. The food preparation varies depending on the type of food being canned. It may involve washing, trimming, sorting, grading, peeling, cutting, dicing, slicing, segmenting, pitting, or blanching, among other processes specific to the food item.

- Filling in the containers: The prepared food is then filled into the sterilized containers. Depending on the specific product, the canned goods may be filled with hot solutions such as sugar syrup or fruit juices, brine with spices for vegetables, or gravy for meats. This step adds flavor, preservative agents, and helps with further sterilization while minimizing the presence of air space within the container.

- Exhausting: Exhausting is the process of removing air from the can before sealing. This step is crucial to prevent excessive pressure and strain during sterilization. By eliminating excess air, exhausting reduces the likelihood of can bulging and minimizes chemical reactions between the container and the food contents.

- Sealing: Once exhausting is complete, the can is immediately sealed. The sealing method varies depending on the type of product. Glass jars and bottles may be sealed using screw-type or crown capping machines, while plastic pouches are sealed using dielectric or conduction heating. It is essential to maintain the temperature of the canned food during sealing, ensuring it remains above 74°C.

- Processing of the can: The sealed cans undergo heat treatment immediately after sealing. The primary purpose of can processing is to eliminate microorganisms and their spores while preserving the nutritional quality of the food. Heat is applied at temperatures typically above 100°C. Vegetative bacteria are killed at 80°C for 30 minutes, spore-forming microorganisms are killed at 110°C for 30 minutes, and spores are destroyed at 121°C for 3 minutes.

- Container cooling: Following processing, the cans are rapidly cooled to room temperature. This cooling process can be achieved by immersing the hot cans in cold water or by spraying them with jets of cold water. Rapid cooling helps maintain the quality and safety of the canned food.

- Labeling and storage: After cooling, the outer surface of the cans is dried for labeling. The labels provide important information such as product identification, brand name, net content by weight or volume, code number, name and address of the processor, list of ingredients, nutritional information, and manufacturing and expiry dates. Once labeled, the cans are stored in cool and dry places before being dispatched.

Following these steps ensures that canned food is properly processed, sealed, and labeled, maintaining its quality, safety, and shelf life. Canning is a reliable method of preserving food, allowing for long-term storage and availability of various food items throughout the year.

## FAQ

### What is microbial spoilage of canned foods?

Microbial spoilage refers to the growth and activity of microorganisms in canned foods, leading to changes in taste, texture, odor, and appearance, making the product unfit for consumption.

### How does microbial spoilage occur in canned foods?

Microbial spoilage can occur when microorganisms survive the canning process, recontamination happens after processing, or if the can's integrity is compromised, allowing entry of spoilage microorganisms.

### What are the common signs of microbial spoilage in canned foods?

Signs of spoilage can include off-odors, off-flavors, gas production leading to can swelling, discoloration, texture changes, presence of molds or yeasts, and other visible abnormalities in the product.

### How can microbial spoilage be prevented during canning?

Microbial spoilage can be prevented by applying proper heat treatment during processing to destroy microorganisms, ensuring a hermetic seal to prevent recontamination, and maintaining good hygiene practices throughout the canning process.

### What preservation methods are used in conjunction with canning to prevent microbial spoilage?

Preservation methods such as radiation sterilization, use of preservatives (GRAS substances), chilling storage, and controlling factors like pH, temperature, and atmosphere can be employed to further inhibit microbial growth and extend shelf life.

### How does radiation sterilization help prevent microbial spoilage in canned foods?

Radiation sterilization exposes canned food to ionizing radiation, effectively killing spoilage-causing microorganisms on the surfaces of jars and lids, reducing the risk of spoilage.

### Which microorganisms are responsible for microbial spoilage of canned foods?

Various microorganisms can cause spoilage, including bacteria, yeasts, and molds. Examples include thermophilic bacteria, mesophilic bacteria, spore-forming bacteria, fermentative yeasts, and spoilage molds.

### Can preservatives be used to prevent microbial spoilage in canned foods?

Yes, preservatives can be added to inhibit or retard the growth of microorganisms. Preservative agents like organic acids, sulfites, ethylene oxide, and bacteriocins are commonly used in canned food preservation.

### Why is chilling storage important in preventing microbial spoilage of canned foods?

Chilling storage involves storing canned foods at low temperatures (0–5 °C) to reduce microbial growth rates, enzymatic activity, and chemical reactions, helping to extend the shelf life of the products.

### Is canning an effective method to prevent microbial spoilage in canned foods?

Yes, canning is a highly effective method of preserving food by eliminating or inactivating spoilage-causing microorganisms, maintaining the quality and safety of the product over an extended period.

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