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To finish up this monster of a blog post all about The Produce Wars. Which is better, and which is worse?? (SPOILER ALERT) Well, hopefully, by now you’ve seen that each type has its pros and cons, and that not one is better than the other, because each has its own way of processing, storage, cooking method, etc. that will help it retain nutrients or lose some in these processes. With that being said, let’s finish up by discussing canned produce and its trade-offs. We’ll wrap up with some application of where and how you can use this information.
Here’s where canned produce can fall short pretty dramatically in terms of nutrient availability. For many canned products, they undergo “Thermal Processing” which simply means heating something to kill bacteria and other microorganisms. As we learned earlier, water-soluble vitamins such as C & B are very sensitive to heat, and are lost in this process.
For example, carrots and broccoli saw losses greater than 80% just from the canning process alone1. Interestingly, however, corn and beets saw very small changes when canned1, perhaps because they’re tougher on the exterior?
The B-vitamins appear to be all over the board in terms of how much of the nutrients are lost. Thiamin (B1) saw 25%-66% losses in spinach, while the same study saw no changes in the Thiamin content of tomatoes2. Honestly, the story seems pretty similar across the other B-vitamins. There was so much variability, that I’m not going to waste your time going into the details behind it all. You can read the review itself if you’re curious1. My takeaway for the B-vitmins since they’re so variable is to try to derive them from non-canned sources if you can since the losses appeared to be higher than the retention for most of the studies1. There’s a helpful chart that you can refer to that pretty much spells it out for you!
When turning to the fat-soluble vitamins, there is a different story. Vitamin A actually saw some increases in its concentration after the canning process! One study found increases ranging from 7%-50% in green beans, sweet potatoes, spinach, and collard greens3. But the picture isn’t perfect. In that same study, peaches showed a 50% drop along with a 13% decrease for vitamin A in tomatoes. Upon further reading of this review, one can see that the research about canning and vitamin A content is actually pretty fuzzy, consisting of studies on both sides4. My opinion on this would be to acquire your vitamin A from a variety of canned products if they’re your only option.
Not much research has been conducted on vitamin E and canned foods because the foods with the highest concentration of the vitamin are not typically canned or fruits/veggies; however, some studies have shown large increases after processing in tomatoes5. It appears as though heat, similar with vitamin A, activates the vitamin within the food and allows it to be extracted/consumed in a greater amount than in the raw form. This only occurs up to a certain extent. After being converted to tomato paste, some losses of vitamin E occurred5. Interestingly, the USDA reports that canned products, when compared with their fresh or frozen alternative, have higher amounts of vitamin E4.
Here is where things get kinda interesting. The amount of minerals in canned products can actually get increased during the canning process5. When canning, water is often added to preserve the food longer or create a syrup base to the food. Depending on the geographical processing location, the water may actually add minerals such as potassium and calcium5. With this, however, comes the enormous increase in sodium. That is my one caveat if you’re going to get canned, search for low sodium or salt-free options when available and financially feasible.
For fiber, the rule stays the same: physical preparation/removal is going to lower the fiber content. In foods such as tomatoes and asparagus, the researchers saw a 27% drop in fiber content; however, other foods, even after physical prep, did not see changes, largely due to the outer or thicker layers remaining intact2.
Moving on to storage of canned products, we start again with ascorbic acid (vitamin C). Pretty simple here, and, as you can imagine, not much losses are incurred after storing canned foods for a long time (18 months in these studies). Losses for vitamin C were no more than 15% for a variety of veggies1.
For the B-vitamins, there actually appears to be variety in losses depending on the food. Thiamin, riboflavin, and niacin, which are all B-vitamins, saw significant losses after 8 months in canned tomatoes6, but saw no changes in fiddlehead greens7. I had to google what fiddlehead greens are. I’m not sure we have those in the US or Arizona at least lol.
There were not a whole lot of studies that observed the effect of canned storage on vitamin A, but the few that did showed little to no change in the amount of the vitamin over time when in storage4.
One funny thing that happens with canned foods is that, depending on the material of the can, the food will experience increases or decreases in the amount of iron or copper. Steel-plated tin cans have been shown to increase the amount of iron in a food8. Other than that, other minerals are not really affected during storage8.
There wasn’t much to be said about fiber in canned foods, but the summary is that some foods like fiddlehead greens may experience a decrease as much as 25% if canned and stored for 10 months4.
Since canned products are often already cooked, there are few additional losses from cooking for vitamin C, assuming that little if any water is added and the food is cooked only to get heated1.
Many of the studies that considered B-vitamin retention consistently showed that, while frozen and canned products may contain the same amounts of B-vitamins (even though they were low), both forms still have lower amounts than fresh counterparts1.
Vitamin A studies showed that cooked fresh carrots and other veggies had higher amounts than frozen and canned options, but all forms were still good sources of vitamin A1.
Unfortunately, there was not much to report about vitamin E except data from the USDA which showed that canned products compared to fresh and frozen had significantly lower amounts of the vitamin1.
The effects on mineral losses in canned goods was focused primarily on sodium losses. A 1975 study showed that if you rinse the canned food in water before cooking, you can reduce a significant amount of the sodium content by 23-45%9.
There were no mentions of fiber losses from canned products, but I imagine that it would be similar to cooking fresh or frozen foods since the main thing that affects fiber content is physical processing.
This is going to be a bit longer than my normal takeaway, as I’m going to wrap up this entire series, but I hope you have learned something from this small series of posts. The primary idea I wanted to communicate to you was that fruits, veggies, and other produce goods come in different shapes, sizes, and forms. Each form has its own pros and cons, and each contains more or less of certain nutrients than the other. Mainly, this set of posts was to relieve stress that some people feel when getting hung up about buying the fresh or frozen option. Either one is fine. The fact that you’re eating veggies is great, and be happy about that. With that, a quick summary of each option’s yays and nays:
Fresh produce often showed higher amounts of the nutrients, but would degrade significantly faster. Unless you’re going through your produce drawer every three days, I’d advise mixing it up a bit. Fresh produce can also cost more than the frozen or canned, which can be a barrier for many people. No one shouldn’t feel bad about buying cost-appropriate options, as they can contain similar or even more of certain nutrients.
Frozen and canned goods possess a lot of benefits just like fresh foods do. Obviously, they last longer and retain their nutrients for a longer period of time. Also, many food companies are now making strides in nutrient-dense frozen meals that taste freaking awesome! If you’re busy and on-the-go, frozen meals can be an awesome option for you.
Canned goods are great in that they are often enhanced with delicious flavors that would be a pain in the ass to make your own. Or, they are already cooked, and all you have to do is heat them up and you have food! My advice with canned foods is drain the sodium before cooking by rinsing it for a few seconds.
I also think it’s important to note that there were some limitations in the review and research I used, so these data are not going to 100% accurate and correct all the time 24/7. The studies varied greatly on how they measured losses and retention-mostly on a dry weight vs. wet weight basis-and the years that they were published. As time goes on, research methods improve and may even invalidate some older studies, so these papers are not without their faults, but they still provide some valuable information about how you can make smarter decisions about what you eat!
In conclusion, fresh, frozen, and canned foods are all great and can be part of a healthy diet. Learn to experiment with all the options an variety you’re given, and you’ll come across some pretty cool stuff! Let me know some canned or frozen recipes or foods you found that changed your life! Thanks for reading!
1Rickman, J., Barrett, D., & Bruhn, C. (2007). Nutritional comparison of fresh, frozen and canned fruits and vegetables. Part 1. Vitamins C and B and phenolic compounds. Journal of the Science of Food and Agriculture, 87(6), 930-944.
2Proximate composition, minerals and vitamins in selected canned vegetables. Eur Food Res Technol 212: 182–187(2001).and ,
3Quantification of cis–trans isomers of provitamin A carotenoids in fresh and processed fruits and vegetables. J Agric Food Chem 45: 3728–3732 (1997)., and ,
4Rickman, J., Bruhn, C., & Barrett, D. (2007). Nutritional comparison of fresh, frozen, and canned fruits and vegetables II. Vitamin A and carotenoids, vitamin E, minerals and fiber. Journal of the Science of Food and Agriculture, 87(7), 1185-1196.
5Change in carotenoids and antioxidant vitamins in tomato as a function of varietal and technological factors. J Agric Food Chem48: 2075–2081 (2000)., and ,
6Effects of production technology and storage conditions on the content of water-soluble vitamins in tomato purees. Ind Conserve 76: 107–118 (2001)., , , , and ,
7Effect of processing method and storage time on the nutrient composition of fiddlehead greens. J Food Sci 50: 1491–1492, 1516 (1985)., , , , and ,
8Nutrient content of raw and canned green beans, peaches, and sweet potatoes. Food Technol 33: 66–70 (1979).,
9Sodium in four canned vegetables. J Am Diet Assoc66: 155–157 (1975).and ,