Canned tomatoes are a popular pantry staple, providing a convenient way to access the flavor and nutrition of tomatoes year-round. These products are preserved by sealing tomatoes in an airtight container, usually a metal can, and then sterilizing them using high heat. While this process ensures a long shelf life, it has also generated health concerns among consumers. Scrutiny often focuses on the changes that occur during processing, including how the heat alters the nutritional profile and the potential for chemical transfer from the lining of the can. The question of whether canned tomatoes are inherently toxic can be answered with a general “no,” but a deeper look at the chemistry and additives involved reveals specific points for consumers to consider.
Nutritional Shifts During Processing
The intense heat used during the canning process significantly changes the nutritional composition of tomatoes. One notable change is the reduction of Vitamin C, a nutrient known to be sensitive to heat. The sterilization process can cause a measurable decrease in the total Vitamin C content compared to fresh, raw tomatoes.
Conversely, the heat treatment dramatically improves the bioavailability of lycopene, the powerful antioxidant found in tomatoes. Lycopene is tightly bound within the tomato’s cell walls, and high-temperature processing helps break these walls down. This thermal treatment also converts the all-trans form of lycopene into cis-isomers, which are more easily absorbed by the human body. Canned and processed tomato products are often considered a more efficient source of absorbable lycopene than their fresh counterparts.
Chemical Migration from Can Linings
The primary health concern related to canned tomatoes is the potential for chemicals to leach into the food from the can’s protective lining. Most metal cans are coated on the inside with an epoxy resin to prevent corrosion. Historically, many of these resins were made using Bisphenol A (BPA), a synthetic compound classified as an endocrine disruptor.
Tomatoes present a particular risk because their high acidity accelerates the breakdown of the resin and increases the rate at which BPA can migrate into the food product. Consumer concern has driven a major shift in manufacturing, despite regulatory bodies maintaining that the minute levels of BPA found in foods are safe. Many manufacturers have transitioned to “BPA-free” linings, often using alternative bisphenols like Bisphenol S (BPS). However, some replacement chemicals have also raised questions regarding their long-term safety and potential for endocrine disruption.
Managing Sodium and Other Additives
Beyond the can lining, the use of various additives warrants attention from a health perspective. Sodium is the most significant concern, as it is frequently added in large amounts for preservation and flavor enhancement. A single serving of certain canned tomato varieties can contribute a substantial percentage of a person’s recommended daily sodium intake. High sodium consumption is strongly associated with increased blood pressure and cardiovascular health issues.
To maintain food safety, manufacturers often add citric acid to standardize the product’s pH level and prevent the growth of harmful bacteria. Another common additive, particularly in diced varieties, is calcium chloride. This compound acts as a firming agent, helping the tomato pieces retain their shape and texture throughout the intensive heat sterilization process. Consumers looking to minimize additive intake can find options labeled “No Salt Added” or varieties containing only tomatoes and tomato juice.
Choosing and Storing Canned Tomatoes Safely
Consumers can take several practical steps to reduce potential risks associated with canned tomatoes. When purchasing, look specifically for cans labeled “BPA-free” to mitigate exposure to the traditional resin lining. An even better option is to choose tomatoes packaged in glass jars or aseptic cardboard cartons, which avoids the metal can entirely.
It is prudent to select products labeled “low sodium” or “no salt added” and check the ingredient list for unnecessary additives. Additionally, avoid purchasing any cans that appear damaged, such as those with deep dents, bulges, or leaks, as these signs can indicate a compromised seal or potential spoilage.
Once a can of tomatoes is opened, any unused portion should be immediately transferred from the metal can to a clean, non-reactive container, such as glass or plastic, before being stored in the refrigerator. This practice prevents the acidic contents from reacting with the exposed metal surface of the opened can, which could affect both flavor and safety.