News & Events

The Safety of Canned Foods

Author: Stephenie Wong Yoke Wei (Lecturer, UCSI University)

In the 21st century, increasing globalization and international mobilityhas created the need to make food available to every part of the world.By just staying in my home country, Malaysia, I get to indulge in various delicacies from across the globe, all thanks to food processing and preservation. One of the popular methods of food processing is canning.

To many consumers, canned foods provide quick access to tasty and nutritious food at an affordable price. Many do not realize the technological and safety aspects that have been put in place by food manufacturers in order to produce safe food. The technological advances of canned foods have a long history and this method of processing is very likely to remain popular owing to the conveniencethat it provides.

Basically, in the canning process, heat is applied to destroy microorganisms and enzymes found in food. A hermetic seal will also be put in place to prevent microorganisms and oxygen from entering the can, thereby preserving the food (Heredia et al. 2009). Canned foods that have been processed according to the correct temperature, holding time, pressure, and other recommended procedures generally have a shelf life of two years or more.

Now, under what conditions will the recommended shelf life become compromised? As outlined above, the canning process requires ‘heat + hermetic seal’ to block out microorganisms and oxygen. So, if any of the above is breached, the safety of the canned food is questionable. At the manufacturers’ level, afew of the possible factors that may cause the spoilage of canned foods are; underprocessing and post- process contamination. During the heating process, there is a risk that the canned foods are not heated to the correct temperature, thus causing the canned foods to become ‘underprocessed’. Underprocessed cans may allow microorganisms to survive, including the much feared pathogen, Clostridium botulinum. Even though this rarely happens, it is likely to be due to equipment failure or human error (Heredia et al. 2009). Another possible cause is post-process contamination, also commonly known as leaker spoilage. Post-process contamination is referring to contamination that happens after thermal processing. Abusive handling of canned foods may result in leaker spoilage. In addition, there is always a concern that water used in the cooling of heated canned food may provide an opportunity for microorganisms to enter the sterilized can through inadequately formed seams or microleaks (Podolaket al. 2010).

Today, there are many food safety and quality systems in place to ensure a wholesome food supply for the local and international market. Besides having to comply with food legislation and stringent government requirements, food manufacturers also need to be guided by other systems and practices such as the Good Manufacturing Practices (GMP), Hazard Analysis Critical Control Point (HACCP) and ISO 22000. Proper implementation, monitoring and control of such systems can help to ensure the safety of canned foods.

On the other hand, consumers, or also known as end-users, also needs to be aware of how canned foods should be handled, maintained and stored in order to preserve the integrity of the cans. A few of the questions commonly asked by consumers are discussed below:

How should unopened canned foods be stored?

It is important to note that canned food should always be stored in a cool, dry place. Storing them under an elevated temperature or in adamp place over an extended period of time is not recommended because it may affect the quality of the food and promotes corrosionof the can, which may result in perforation (Reilly, 2008). Thus, consumers need to think twice before placing their cans next to the stove or leaving them in the car boot under the hot sun!

Can we keep unopened canned foods in the freezer?

We always know that the shelf life of most food products can be extended when they are kept frozen. But can we keep unopened canned foods in the freezer? Storing canned foods in the freezer are not recommended because foods tend to expand during freezing. This may exert pressure on the seams. Damaged seams can no longer prevent microorganisms from entering the can, thus posing arisk to the safety of the canned foods.

How should we handle unused portion of canned foods after opening?

After opening canned foods, especially low-acid canned foods, it is important to consume them immediately and avoid leaving them at room temperature for an extended period of time. Low acid food is specifically referring to foods with a pH above pH 4.5 and may support the growth of Clostridium botulism. The Food and Drug Administration (FDA) recommended the ‘2-Hour Rule’ that says, ‘Discard any perishable foods left at room temperature longer than 2 hours’ (FDA, 2013). Even though bacteria grow over a wide range of temperature, most disease-causing bacteria can grow within a temperature range of 5 – 57 ºC. This range of temperature is also known as the temperature danger zone, where bacteria can multiply at a high rate (Puckett, 2012). Room temperature also falls in the temperature danger zone category. Instead of leaving them at room temperature for an extended period of time, it is advisable to refrigerate unused portions of canned food in a separate storage container as soon as possible after opening.

After looking at the possible causes of microbial spoilage, the next question that comes to mind is, how should consumers select their canned foods? As a rule of thumb, cans are considered acceptable if the cans appear intact, the seams are not damaged, the cans are not leaking and there are no visible holes. Consumers are recommended to inspect the cans for any defects before purchase.

Being a Food Microbiology lecturer at the university for the past 7 years, I am on constant look out for swollen, bulging or dented canned foods to be used as teaching material in class. Much to my dismay (though it is definitely thumbs up for the canning industry!); I have much difficulty in getting defect cans from the few hypermarkets that I commonly frequent. What I gather from my own personal experience and the literature that I have searched, spoilage of canned foods is a relatively rare event due to thesophisticated technology, stringent food legislation and safety procedures in place. From the consumers end, they also need to be aware ofhow to select, handle and store canned foods in order to preserve the safety and integrity of the canned foods. In addition, there are also non-microbiological factors that may lead to the deterioration of canned food, which are not discussed in this article.

FDA, 2013.To Your Health! Food Safety for Seniors.

Heredia, N., Wesley, I. and Garcia, S. 2009. Microbiologically Safe Foods.Wiley.

Podolak, R., Stone, W. and Black, D.G. 2010. Retort cooling water bacteriological load and possible mitigation strategies for microbial buildup in cooling water. Food Protection Trends, 30(3): 160-167.

Puckett, R. P.2012. Foodservice Manual for Health Care Institutions (4th Edition).J-B AHA Press, Wiley.

Reilly, C. 2008. Metal Contamination of Food : Its Significance for Food Quality and Human Health. Wiley.