Frozen, fresh and canned - let's talk veggies

nutrition | July 25, 2017 | Author: Naturopath

diet

Frozen, fresh and canned - let's talk veggies

While shopping at the supermarket the other day I ran into a friend and noticed that she had a bag of frozen broccoli in her trolley. In response to my question about her preference of frozen over fresh (I could clearly spot beautiful in-season broccoli at the fresh fruit and veg section), my friend explained that she read somewhere that frozen vegetables were more nutritious than fresh ones. Is that really the case? Here is what the research says:

Freezing Vegetables

Freezing is one of the oldest forms of food preservation technology in the world, allowing for a significantly extended shelf life. The process of freezing vegetables involves pre-treatments, including:

Frozen, fresh and canned - let's talk veggiesPreparation - Washing, peeling, slicing or dicing.

Blanching - All vegetables (except herbs and green peppers) need to be blanched prior to freezing. Vegetables contain enzymes that continue to activate even while being frozen, and can cause loss in quality, flavour, colour, texture, and nutrients. Blanching is the exposure of the vegetables to boiling water or steam for a brief period of time in order to inactivate these enzymes, and then rapidly cooling them in ice water to prevent them from cooking.

Canning Vegetables

Canning is another food preservation method; it involves packing blanched vegetables in an airtight sealed container, usually made of tin-coated steel, and then applying heat to the sealed container in order to destroy remaining microorganisms such as bacteria, moulds and yeast. The vegetable may be canned whole, diced, puréed, or as juice.

Here are Some Points to Consider

  • Texture. Most frozen vegetables, when thawed, will have a much softer texture when compared to fresh vegetables. Not only the process of blanching itself causes wilting or softening of vegetables, but also ice crystals that are formed during freezing expand and rupture the vegetable cell walls, resulting in a soggy texture.
  • Nutrition. Comparing the nutritional value of fresh, frozen, and canned vegetable is not an exact science. It depends on factors such as time of harvest, ripeness, climate, soil conditions and storage conditions. Very few studies followed the same product from harvest through freezing, canning or freshly stored and cooked.

Frozen, fresh and canned - let's talk veggiesGenerally, the nutritional value of vegetables begins to decline immediately after harvest, so in fact, freezing and canning may preserve nutrient value better than fresh vegetables as they lock in the nutrients soon after they are picked. Fresh vegetables, unless you pick them straight from your backyard or from the local farmers market, may travel great distances before they get to your supermarket.

Nevertheless, the blanching and heating of vegetables in the freezing and canning process may result in some nutrient depletion. Studies found content of vitamin C and of some forms of B vitamins in fresh produce to be higher than in canned and frozen produce. Additionally, many canned foods have added salt, primarily to enhance palatability. Look for no salt added, low sodium or reduced sodium labelled cans.

The Food and Agriculture Organization of the United Nations suggests that freezing is superior to canning with respect to retention of nutrients. Other research reveals that this is not always true, and that canned vegetables are similar to fresh and frozen in terms of nutritional value.

  • Bridging the seasons. Freezing and canning vegetables during peak season have the advantage of making them available all year-round. Availability of fresh vegetables varies with the season. This is not necessarily a bad thing. Eating seasonally is cheaper, tastes better, makes you eat a wider variety of vegetables, and supports local produce.
  • Convenience. Frozen and canned veggies are pre-cut, washed, and ready to go for the busy consumer.
  • Safety. Unlike canning, freezing does not actually destroy the microorganisms and will only prevent their growth. When thawed, the surviving organisms can grow again. Careful handling and preparation are required; especially if any frozen vegetables have accidentally thawed by the freezer door being left open.

Regarding consumption of canned vegetables, concerns have been raised about the use of the chemical Bisphenol A, or BPA, in the lining of cans. This chemical has been shown to leach into food and is linked to many health problems, including early puberty, infertility, breast and prostate cancer and polycystic ovary syndrome.  Food Standards Australia New Zealand (FSNAZ), along with the US Food and Drug Administration (FDA), maintain that BPA is safe at the low levels people are exposed to. Research, however, is ongoing.

Frozen, fresh and canned - let's talk veggiesStorage and shelf life. Canned foods have a long shelf life, sometimes up to two years, even at room temperature. They do not require refrigerating during transport and storage, and are easy to store even if space is limited. Both canned and frozen vegetables have a longer shelf life than fresh vegetables, thus reducing wastage and frequency of shopping. However, frozen varieties require freezer space that is not always available.

Cost. Canned varieties are more cost saving, as they are cheaper than frozen and fresh vegetables. The cost of fresh vegetables varies greatly, depending on seasonal availability.

Recycling. Steel cans are 100% recyclable, and according to Jamestrong Packaging Australia & New Zealand, Australia ranks 12th in the world for the percentage of steel cans that are recycled rather than sent to landfill. Conversly, most frozen vegetables are packed in plastic bags that cannot be recycled through your home recycling bin.

The Bottom Line

Eating plenty of fruits and vegetables is a foundation of good health. Freshly picked, unprocessed local produce is best for taste and quality. But if unavailable, inconvenient, or beyond your budget, frozen vegetables are the next best thing. Canned vegetables provide another alternative, but watch the sodium content and limit exposure to BPA.

 

References

Barbosa-Cánovas, G. V, Altunakar, B. & Mejia-Lorio, D.J., 2005. Freezing of fruits and vegetables, FOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONS Rome, 2005. Available at: ftp://ftp.fao.org/

Food Standards Australia New Zealand, 2015. Bisphenol A (BPA). FSANZ. Available at: http://www.foodstandards.gov.au/

Harvard Medical School, 2014, Fresh or frozen produce? The health benefit is all in the mix - Harvard Health. Available at: http://www.health.harvard.edu/

JAMESTRONG PACKAGING - & AUSTRALIA & NEW ZEALAND, CAN - Can and Aerosol News - Education. Available at: http://www.can-news.com.au/

Konieczna, A., Rutkowska, A. & RachoĊ„, D., 2015. Health risk of exposure to Bisphenol A (BPA). Roczniki Panstwowego Zakladu Higieny, 66(1), pp.5–11.

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), pp.430–437.

Rickman, J.C., Barrett, D.M. & Bruhn, C.M., 2007. Review 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 J Sci Food Agric, 87, pp.930–944.

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