FactCheck: Are canned and frozen fruits and vegetables not as healthy as fresh ones?


by Cena Gillana and Joco Macatangcay


Pub by: Bea Jacinto, Cena Gillana, and Arlan Jondonero

Canning has made it possible to enjoy food items made at another time in a cheaper, safer, easier, and more readily available form. However, there are claims that canned foods have much less nutrients than fresh produce. So can it still be a healthy alternative to fresh fruits and vegetables?

MISCONCEPTION:

Canned and frozen fruits and vegetables are not as healthy as fresh.

WHAT SCIENCE SAYS:

No.

How canning works?

Canning is a method that aims to preserve food by placing them in containers and applying heat at a specified temperature in time, destroying the microorganisms and inactivating the enzymes therein. Another method used is the removal of oxygen, for the purpose of preventing the proliferation of aerobic microorganisms.[1] 

A typical commercial canning follows a general process from washing, sorting, preparation, container filling and sealing, heat sterilization, cooling, labeling, and storage However, it must be noted that there is a great diversity among plants and fruits. Hence, this process may be modified accordingly in terms of sequence or the addition of other operations.[1]

Canned vegetables are prepared and processed at their peak nutrition. It requires a full sterilization process to reach a low-acid pH range, depending on the recommended parameters, unless they are acidified. Salt or brine (sodium chloride) is usually added to preserve the flavor and quality of the vegetables.[2]

Canned fruits are processed similarly, in that they utilize a pasteurization process, but at a temperature less than 100°C, preserving its texture. However, some fruits higher in pH are often acidified and processed at a lower temperature. Preliminary treatment steps are usually done such as peeling, coring, halving, pitting, and finally, blanching.[3]

A significant difference in the canning procedures of fruits and vegetables is the blanching step, as well as other steps prior to heating. The majority of fruits are not blanched before canning, while many vegetables undergo this step. This can be traced to the inherent low acidity and the abundance of heat-resistant soil organisms in vegetables, hence its need to undergo a sterilization process. Subsequently, vegetables may require a longer heating process as compared to fruits.[1]

What happens to nutrients when fruits and vegetables are canned?

A study by Miller & Knudson compared the nutrient scores and price per edible cup of 8 common vegetables, namely: white corn, yellow corn, carrots (whole), spinach, turnip greens, green beans, peas, and asparagus in different packaging which were canned, frozen, and fresh. They found that the nutrient scores in these 8 common vegetables were remarkably similar among the three packaging options. They even found that in green beans and carrots, the canned packaging provided a better nutritional option compared to the frozen and fresh ones. However, when it came to costs per edible cup, canned vegetables had lower costs compared to frozen and fresh vegetables. For fruits, it was found that fresh fruits have a greater nutritional score. 

Adding to that, a two-part paper by Rickman, Barrett & Bruhn (2007) reviewed the loss of nutrients from fresh products. They reported the following:

Vitamin C: The canning process causes significant initial loss of ascorbic acid; however, losses due to storage and cooking are minimal. 

Vitamin B: Studies show that B vitamins are sensitive to thermal processing albeit the inconsistencies in methodology and data reporting. Differences in the vitamin content in fresh, frozen, and canned products are not yet well studied thus the call for more research. 

Thiamin: losses range from 25% dry weight (DW) to 66% DW.

Riboflavin: retention is higher than thiamin and ranges from 68% to 95% DW in different vegetables and fruits.  

Vitamin B6: retention ranges from 54% to 80% in different vegetables and fruits 

Niacin: stable to processing with retention rates of 93% or higher

Vitamin A: effects of processing on carotenoids are hard to interpret given the inconsistent reporting of studies available on the topic. It was found, however, that despite oxidation and isomerization, provitamin A carotenoids, and lycopene are more stable to processing, storage, and cooking relative to water-soluble vitamins 

Fiber: Data on the effects of processing on dietary fiber are very limited. With the existing set of studies, however, it was seen that changes due to processing, storage, and cooking in fiber in intact vegetables and fruits appear to be minimal.  

Given these facts, why are vegetables and fruits canned?

When vegetables are not readily available, one convenient and effective way to preserve them for consumption is through canning, and when vegetables are canned, they are full of essential nutrients and also render some nutrients more readily digestible compared to fresh vegetables in some cases.[2] Canned vegetables provide comparable nutritional content with lower consumer costs and lower energy costs for consumer storage.[4]

Moreover, it may be a challenge for some households to obtain fresh fruits not only because of seasonality but also because of the costs of vegetables and fruits during the off-season. Compared to their fresh counterparts, canned fruits have a longer shelf life.[4] For these families, such as those who are struggling financially, and those who live in places where it may be hard to buy fresh produce, buying canned vegetables and fruits may be more practical for their budget for food. 

Lastly, it was observed in the United States of America that diets with high nutrient-dense (fruits, vegetables, dairy, and protein foods) canned food consumption, in addition to fresh foods, provide more dietary options that improve nutrient intakes and overall diet quality.[7]

So while it is true that some amounts of nutrients are lost when vegetables and fruits are canned, we cannot just label them completely as “unhealthy.” We saw from above that canned vegetables can provide comparable nutritional content with lower consumer costs and lower energy costs for consumer storage. Moreover, we must also consider the other aspects. For example, the economic aspect of canned fruits and the practicality it can offer to consumers who struggle with different factors such as geography (including seasonality of fruits) and financial constraints.

References:

[1] US EPA. (n.d.). Canned fruits and vegetables. https://www3.epa.gov/ttnchie1/ap42/ch09/final/c9s08-1.pdf

[2] Featherstone, S. (2016). Canning of vegetables. A Complete Course in Canning and Related Processes, 3–84. doi:10.1016/b978-0-85709-679-1.00001-5

[3] Featherstone, S. (2016). A Complete Course in Canning and Related Processes, 85–134. https://doi.org/10.1016/b978-0-85709-679-1.00002-7

[4] Miller, S. R.; Knudson, W. A. (2014). Nutrition and Cost Comparisons of Select Canned, Frozen, and Fresh Fruits and Vegetables. American Journal of Lifestyle Medicine, 8(6), 430–437. doi:10.1177/1559827614522942 

[5] Rickman, J. C., Barrett, D. M., & Bruhn, C. M.  (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. doi:10.1002/jsfa.2825 

[6] Rickman, J. C., Barrett, D. M., & Bruhn, C. M. (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. doi:10.1002/jsfa.2824 
[7] Comerford K. B. (2015). Frequent Canned Food Use is Positively Associated with Nutrient-Dense Food Group Consumption and Higher Nutrient Intakes in US Children and Adults. Nutrients, 7(7), 5586–5600. https://doi.org/10.3390/nu7075240

The contents of this article are for educational purposes and are not intended as a substitute for professional or personal medical advice, diagnosis, or treatment. Seek advice from your physician or other qualified health providers about any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read on this page/website.

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