Nutrition Guarantee During Quarantine: Frozen and Canned Veggies and Fruits

 

You don’t have to compromise your nutrient intake when eating frozen/canned foods. 

 

The pandemic has been keeping us indoors more often than ever. I’m facing this problem that you may be experiencing as well: less access to fresh vegetables and fruits.

Just to name some of the problems I have been facing so far during the pandemic:

  • The long lineup at the grocery stores doesn’t help me get fresh produce as frequently as before.
  • I can’t stock up too much because they can go bad or lose their nutritional values (for example, when stored in fridge, 77% of vitamin C in fresh green peas was lost in 7 days, and 23% was lost in spinach in 5 days [1]).
  • Fresh produce is getting more expensive due to the pandemic-related supply shortage.

Is this limited access a sign from the Universe that I can forego my needs of vitamins and fibres, and survive on only popcorn and chips? Of course not. Thanks to advanced food technology, we can still get vegetables and fruits that are nutrient-dense, last longer, and taste good.

How does fresh produce turn into frozen packages and cans?

Well, the names are pretty straightforward, but we won’t get the same quality by just stuffing fresh produce into our freezer.

In the industrial process, veggies and fruits are picked at the peak of freshness and immediately processed for preservation, to avoid the nutrient loss during transportation and storage. The produce is washed and screened to remove dirt and stones, and peeled/pitted/sliced/diced if needed. After that, it goes on different routes for freezing and canning [2].

Steps Freezing Canning

1

Blanched (i.e. quickly heated up by boiling or steaming) to deactivate enzymes that can cause changes to the color, flavor or texture May be blanched (depending on the produce), then fill the cans (with liquid) and seal the lids

2

Rapidly frozen in an ultra-cold environment (-30 to -40°C, much lower than our freezer which is -18 to -20°C) Steamed under pressure at an ultra-high temperature (116-121°C)

3

Packaged under a nitrogen atmosphere Quickly cooled

The treatment with extreme temperatures is the key to limit microbe growth (freezing) or destroy them (heating), and to maintain the quality of frozen and canned produce. For example, canned foods are often heated for at least 3 minutes at 121°C to kill the spores of Clostridium botulinum, a microbe that is heat-resistant and can produce paralyzing toxins [3]. Regarding freezing, the time needed to freeze something is shorter in the industrial ultra-cold environment than in a home freezer. The shorter freezing time reduces the formation of large ice crystals, which can break into the strawberry’s flesh, leading to poor shape and texture after thawing [4].

Does the freezing and canning process reduce nutrient content in the produce?

Freezing does quite a good job of preserving nutrients. As an experiment, a group of scientists split a batch of freshly harvested produce (corn, carrots, broccoli, spinach, peas, green beans, strawberries, and blueberries) into two portions – one for refrigeration at 2°C and the other one for freezing at -27.5°C [5][6]. And guess what? Most vitamins, minerals, fibres, and total phenolic compounds (antioxidants!) were retained in all these eight commodities after 90 days of frozen storage. Heck, frozen blueberries carry even more vitamins B2, C and E than fresh ones [5]! However, this isn’t true for all foods — frozen peas lose 21% of the vitamin B2 than fresh; they also lose 68% of beta-carotene, a carotenoid that can be converted to vitamin A by our body (good for ya eyes 😉) [5]. Nevertheless, frozen peas still possess almost all the vitamin C and E before freezing, so not a completely sad story 😅.

Similar to freezing, the ability of canning to preserve micronutrients depending on specific nutrient types, and also commodities. Water‐soluble, heat- or oxygen‐sensitive nutrients (e.g. vitamin C and the B group, and phenolic compounds) may be reduced by the blanching and steam pressure treatments, but they remain quite stable during canned storage because of the lack of oxygen [7]. Other nutrients that are less “fragile” are found to be at a level comparable to those in fresh produce, sometimes even higher [8]. For example, carotenoids (remember beta-carotene?) were found HIGHER in canned collard greens and peaches than in fresh ones. It is partially due to the heat treatment breaking down the produce, allowing the carotenoids to release from the food matrix more easily [8].

*** Note: The data mentioned above are based on dry weight, meaning that the measurement of nutrients was done after the foods are dehydrated to reduce the interference of water content, which can fluctuate a lot based on the environment and our usage (e.g. how much do we drain that can of tomato chunks before using it). Nevertheless, the nutrition facts labels on the products usually present data based on wet weight (except when indicated otherwise), because we consume those foods without dehydration. So, don’t forget to refer to the nutrition facts when purchasing frozen or canned foods!

Aren’t canned foods loaded with preservatives?

Nope. The heat treatment during the canning process is very harsh. The sealed cans do not let in oxygen or microbe contamination. Sugar or salt may be added to 1) replenish the flavor lost during heating, and 2) reduce water activity to further limit microbe growth, but they aren’t the main reason why the canned foods are safe for long-term room temperature storage.

How to choose frozen/canned veggies and fruits?

It is simple for frozen ones – choose whatever you like, as long as veggies or fruits are the only ingredients. Avoid the lumpy ones, they likely have been thawed and refrozen, not the best for tasting (yucky mushy texture), nutrient contents (some nutrients can be lost during this process [9]), or safety (microbe growth during the thawing).

For canned produce, choose low salt/sodium and low sugar/no syrup as much as possible. Plan ahead how you are going to use the whole can of contents before purchasing it, because once the can is open, the content won’t stay good for too long due to lack of preservatives.

How to use frozen/canned veggies and fruits?

I know — the sogginess is such a big challenge when using frozen and canned produce. However, there are a few tips to improve the taste, and safety.

For frozen produce:

  1. DON’T DEFROST. Just don’t, use directly from the bag (a big lesson from my past mistake – why didn’t I look at the cooking instructions on the package anyway?!). Defrosting destroys the texture and allows microbes to grow again.
  2. Frozen veggies should always be cooked before consumption. Sautéing or roasting with some oil is the best bet if you still want a crispy texture.
  3. Frozen fruits are supposed to be safe to consume raw, but if possible, microwave it to boiling before usage. FDA reported 3 hepatitis A outbreaks and 1 norovirus outbreak associated with frozen berries between 1997 to 2016 – not a high number but worth taking the caution [10].

For canned produce:

  1. Watch out for the sugar/salt content of canned produce, and adjust the use of sugar/salt in your cooking
  2. Mix the canned veggies with fresh veggies when cooking, but add the canned veggies later.
  3. Canned veggies are best for making stews or casseroles where texture is not required as much.
  4. Drained, blended canned veggies are great for making stuffing or mixing with meat for burgers (a recipe will be coming up)!

 

The bottom line: we should NOT replace fresh veggies and fruits completely with frozen and canned products. Instead, consider frozen/canned produce as a convenient and cheap alternative to help us maintain a healthy diet when fresh produce is not as available.

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[1] https://getd.libs.uga.edu/pdfs/li_linshan_201312_ms.pdf

[2] https://www.safefoodfactory.com/en/knowledge/21-vegetable-processing/

[3] https://www.fsai.ie/faq/botulism.html#:~:text=To%20kill%20the%20spores%20of%20Cl.,greater%20than%2080%C2%B0C%20.

[4] http://www.mpagro.org/tenders/INDIVIDUAL-QUICK-FREEZING.pdf

[5] https://pubs.acs.org/doi/10.1021/jf5058793

[6] http://www.fruitandvegetable.ucdavis.edu/files/217153.pdf

[7] https://onlinelibrary.wiley.com/doi/abs/10.1002/jsfa.2825

[8] https://onlinelibrary.wiley.com/doi/abs/10.1002/jsfa.2824

[9] https://www.sciencedirect.com/science/article/abs/pii/S0963996912001330

[10] https://www.washingtonpost.com/news/voraciously/wp/2019/07/31/frozen-fruits-and-vegetables-can-carry-foodborne-illnesses-heres-how-to-avoid-them/

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