This article was written by one of our contributors; medical student with a BSc in human nutrition + MSc in clinical and public health nutrition – Rebecca Fox.
When you think of fruits and vegetables what’s the first image that comes to mind? Is it a bountiful basket of carrots, kale, broccoli and peas fresh from the farmer’s market? Or is it a freezer or pantry filled with frozen peas and canned tomatoes?
We each have our own perception of what form fruits and vegetables should come in. These perceptions are based on a variety of personal, environmental and social factors that all play important roles in how we choose the food we eat.
However, in a recent study, it was shown that 60% of UK consumers believe frozen vegetables are less nutritious than fresh (1,2).
But are there any major differences between fresh, frozen and canned produce? And what’s the best way to get your 5-a-day?
A Few Definitions
Let’s breakdown what goes into producing fresh, frozen and canned fruits and vegetables:
Fresh: Fresh fruits and vegetables are those that are picked from the field, washed and sold in their raw form without any cooking or other processing. Depending on where in the world they’re harvested, they may be transported and stored before being consumed.
Frozen: There are a number of different freezing techniques used in vegetable preservation, with the technique depending on a couple of things including 1) the type of vegetable being frozen 2) cost and 3) size of retail packaging. Most frozen vegetables undergo a two-step freezing process in which they are blanched (i.e. briefly exposed to boiling water/steam, then rapidly cooled in ice water) (3), then frozen. The blanching process de-activates enzymes that affect taste and nutritional content. The method of freezing fruit on the other hand largely depends on the type of fruit, but in general, most fruits are simply washed, cut, then frozen without blanching and will often have some preservatives such as ascorbic acid (vitamin C) added to prevent oxidation (4)
Canned: The canning process includes washing and cutting the vegetables, packing them into cans, then sealing and heating. This heating step ensures that bacteria and spores are killed, and creates a vacuum inside the can when cooled, ensuring that no further bacteria or fungi can enter the can. This process allows canned vegetables/fruit to last for many months at room temperature. Many types of canned fruit such as peaches follow a similar method, however, addition of a sweetened liquid often accompanies the canned fruit.
In the debate between fresh, frozen and canned fruits and vegetables, storage time and processing conditions are two of the most important factors that affect nutrient content.
In terms of storage time, after vegetables and fruits are harvested, they still continue to respire until the point of cooking. This means the vegetable or fruit’s cellular metabolic processes continue to work and use up the vitamins and minerals already present in the fruit or vegetable while it’s in storage. However, cold temperatures slow down the metabolism of fruits and vegetables, so they retain greater nutrient contents during storage. Since frozen fruits and vegetables are typically frozen very shortly after harvesting, there isn’t much time for this continued respiration and nutrient loss compared to fresh produce.
Thus, the nutrient content of frozen vegetables at the time you eat it pretty much matches the levels that were present when it was picked.
This was found in a study comparing produce storage times where nutrient changes in frozen veg were less over 12 months compared to fresh produce stored at 4℃ for 7 days (5). Further, in a recent study, frozen vegetables were not only largely equivalent, but in fact retained more nutrients than their fresh counterparts in some instances (5).
In terms of processing, vitamins and minerals are affected by things like heat and water in different ways. For example, since Vitamin C is water soluble, it tends to leach out of fruits and vegetables when they’re boiled or blanched. On the other hand, heat may increase the bioavailability (i.e. how much of it our body can utilize) of some fat-soluble vitamins and antioxidants such as Beta-carotene and lycopene due to their chemical structure. Thus, when comparing the nutritional content of fruits and vegetables that are processed differently, it’s important to look at the overall nutritional composition rather than individual nutrients.
For example, the blanching process used in frozen and canned veg has a dual effect. On one hand, blanching reduces heat sensitive and water soluble vitamins by up to 50%, while on the other hand it may increase fat soluble carotene content. Similar findings go for canned produce specifically, which tend to have higher carotenoid levels, while vitamin C levels are generally lower due to the high heat treatment required (6). Overall, canned vegetables tend to have greater antioxidant losses compared to fresh or frozen veg though (7).
Canned foods are a convenient and affordable way to incorporate more fruits and vegetables into your diet. Although, one thing to mention about canned fruits and vegetables though is that oftentimes they’re packed in water with extra salt and/or sugar added or in syrup. Therefore it’s important to check the label before you buy and try to choose fruit that is canned in water or it’s own juice, and canned veg that has no added salt.
Cost Difference and Environmental Impact
It is estimated that nearly 1/3rd of all food products purchased are wasted. This includes fresh fruits and vegetables that have gone off (I see you, mushy bag of lettuce at the back of the fridge!). Due to so much food waste, frozen and canned fruits and veg likely have a lower carbon footprint than fresh since they can be stored for so much longer (See our article here on the environmental impact of produce). In addition, frozen and canned fruits and vegetables are, on average, between 20-50% less expensive than fresh produce, making these products more available to more people (8).
Overall, there are a number of reasons why people choose fresh, frozen or canned fruits and vegetables. Nutritionally speaking, there are some slight differences in vitamin content between preservation techniques, which mostly has to do with different storage times and heating procedures. However, these nutritional differences are minimal in the grand scheme of things. Lastly, canned and frozen fruits and vegetables are often much less expensive than their fresh counterparts which can make them a lot more accessible for many people. Regardless of whether your fruit and veg is frozen, canned or fresh – they all count as one of your 5-a-day.
→ There are some slight differences in nutrient content depending on storage method and processing techniques
→ Watch out for added sodium and sugar in some canned vegetables and fruit
→ Frozen and canned fruits and vegetables are often less expensive than fresh versions and still provide similar nutritional value
→ Take home message: eating more fruits and vegetables in any form is better than none at all!
- Connell PM, Finkelstein SR, Scott ML, Vallen B. Negative associations of frozen compared with fresh vegetables. Appetite. 2018 Aug 1;127:296-302.
- Mintel, 2010 U.K. Mintel Chilled and frozen ready meals. (May 2010) Available online at http://store.mintel.com/chilled-and-frozen-ready-meals-uk-may-2010 (2010)
- Mazzeo T, Paciulli M, Chiavaro E, Visconti A, Fogliano V, Ganino T, Pellegrini N. Impact of the industrial freezing process on selected vegetables -Part II. Colour and bioactive compounds. Food Res Int. 2015 Sep;75:89-97. doi: 10.1016/j.foodres.2015.05.036. Epub 2015 May 16. PMID: 28454976.
- Woodroof J, editor. Commercial fruit processing. Springer Science & Business Media; 2012 Dec 6.
- Li L, Pegg RB, Eitenmiller RR, Chun JY, Kerrihard AL. Selected nutrient analyses of fresh, fresh-stored, and frozen fruits and vegetables. Journal of Food Composition and Analysis. 2017 Jun 1;59:8-17.
- Rickman JC, Bruhn CM, Barrett DM. 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. 2007 May;87(7):1185-96.
- Murcia MA, Jiménez AM, Martínez-Tomé M. Vegetables antioxidant losses during industrial processing and refrigerated storage. Food Research International. 2009 Oct 1;42(8):1046-52
- Miller SR, Knudson WA. Nutrition and cost comparisons of select canned, frozen, and fresh fruits and vegetables. American Journal of Lifestyle Medicine. 2014 Nov;8(6_: 430-7.