Discussion Board

Hello.

I like to shop for vegetables once a week. Over the period of a week, some produce necessarily sits longer than others before cooking or use. I've wondered how much of the food value of the produce is lost as it ages. Also, should some produce be used more quickly than others?

I'm new. If this has been answered before, please direct me to the post.

Hatshepsut

Hi, Hatshepsut.

Interesting question. Here's a page that talks about deterioration of fruits and veggies in storage and due to processing. It might provide some information.

http://www.fao.org/docrep/V5030E/V5030E08.htm

It will also be interesting to hear what Jeff has to say about it.

Hi,

I do not think there is any one simple answer as it will depend on so many variables including which nutrient, and which food we are talking about.

Below is a summary review from a recent study that looked at this issue.

My simple rule at home is "simple," as look as the fresh produce is still "fresh" and firm, and not wilting, or turning color, then I will use it.


In Health
Jeff Novick, MS, RD

A Nutritional Comparison of Canned, Fresh and Frozen Fruits and Vegetables

J Sci Food Agric 87:930 – 944 (2007)

The 2005 Dietary Guidelines urge Americans to increase their fruit and vegetable intake regardless of type (fresh, frozen, canned and dried), yet Americans are far from meeting fruit and vegetable goals. Exclusively recommending one form of fruits or vegetables over another ignores the benefits that each form provides and limits consumer choice.
Specific Key Study Findings Include:

* A diet should include a variety of fruits and vegetables. Fresh, frozen and canned each contain important nutrients and contribute to a healthy diet.

* For some nutrients canned products were higher than fresh.

* By the time food is consumed, fresh, frozen and canned fruits and vegetables may be nutritionally similar.

Canned

* The canning process locks in nutrients at their peak of freshness and due to the lack of oxygen during the storage period, canned fruits and vegetables remain relatively stable up until the time they are consumed and have a longer shelf-life.

Fresh

* Eat fresh fruits and vegetables as soon as possible. Some fresh vegetable, such as spinach and green beans, lose up to 75% of their vitamin C within 7 days of harvest, even when held at the recommended refrigerator temperature.

Frozen

* Frozen products are also packed at their peak of freshness. Frozen fruits and vegetables may be more nutritious in some cases if stored for short periods of time under well-controlled temperatures.

Executive Summary

Nutritional comparison of fresh, frozen, and canned fruits and
vegetables

Joy C. Rickman, Diane M. Barrett, PhD, Christine M. Bruhn, PhD, Department of Food Science and Technology, University of California- Davis, Davis, CA. 95616


Recent and classical literature was reviewed to obtain current information on the nutrient value of fresh, canned and frozen foods with an emphasis on fruits and vegetables.

Research that has undergone the scrutiny of peer review and the USDA nutrient database served as the source of information. The literature indicates that by the time they are consumed, fresh, frozen and canned fruits and vegetables may be nutritionally similar, depending on the post harvest handling and processing treatments.

Loss of nutrients in fresh products may be more substantial than commonly perceived. Storage and cooking can lead to overall losses of up to half of the original nutrient content prior to consumption. Depending on the commodity, freezing and canning processes may preserve nutrient value. While the initial thermal treatment of canned products can result in loss, nutrients are relatively stable during subsequent storage due to
the lack of oxygen. Frozen products lose fewer nutrients initially because of the short heating time in blanching, but they lose more nutrients during storage due to oxidation.

Vitamin C, a water-soluble nutrient, is sensitive to heat, light, and oxygen. If fresh products are held at the appropriate temperature and consumed in a short period of time, they have more vitamin C than commercially canned products. However vitamin C degrades rapidly after harvest, and depending on commodity, as much as 77% of the nutrient (in green beans) may be lost in 7 days storage at 4°C (39°F). Vitamin C is lost when frozen vegetables are blanched, but some fruits have ascorbic acid added to prevent browning, so the nutrient level may be higher in the frozen than the fresh fruit. Between 10 to 90% of vitamin C is lost during canning, however the nutrient changes little during storage of canned products and little is lost during reheating because the heating time is short.

Among B vitamins, thiamin, B6 and riboflavin are sensitive to heat and light, resulting in loss in canned products. Since these nutrients are also water soluble, from 20-60% is lost in the blanching step prior to freezing. Water soluble polyphenolic compounds, found primarily in the skins of peaches, pears and apples, are lower in products canned without the skin compared to fresh, however if juice is included, such as in canned cherries, levels are higher in the canned than fresh products. Mineral and fiber content are similar in fresh, canned and frozen fruits and vegetables.

Fat soluble nutrients, including vitamin A, E, and carotenoids including lycopene are sensitive to heat, light, and oxygen. Since these nutrients are fat soluble, little is lost in blanching. Nutrient loss varies by commodity. For example, cooked fresh green beans contained higher levels of beta- carotene than cooked frozen and cooked canned green beans, however cooked frozen green peas contained higher levels of beta-carotene than
cooked fresh and cooked canned. Compared to fresh tomatoes, canned tomato products have been reported to have high levels of beta-carotene, a precursor of vitamin A. Processed tomatoes are also reported to have higher lycopene content than fresh, likely due to the heat-induced release of this nutrient from its cellular matrix.

Protein and carbohydrates as well as fatty acid composition is not significantly affected by canning for freezing. For example, the level of Omega 3 fatty acids in fish is not adversely affected by canning or freezing.

The literature review is complicated by variations in experimental procedure and method of reporting. Some studies measure the same cultivar, grown under controlled conditions, and evaluated as fresh, canned, or frozen. This approach provides data on the effect of
processing treatment. Others obtain samples from the supermarket, measuring what the consumer has available, but increasing nutrient variability due to cultivar, growing conditions, and handling practices. Further, changes in moisture content during storage, cooking, and processing can misrepresent changes in nutrient content expressed as
percent of product weight. Nutritional comparison would be facilitated if future research would express nutrient data on a dry weight basis to account for changes in moisture.

The nutritional comparison of fresh, canned and frozen products indicates that each can contribute to a health diet. Exclusive recommendations of fresh produce ignore the nutrient benefits of canned and frozen products and limits consumer choice.

Very interesting findings. This makes me feel better about my diet. I'm not a big fan of salads and fresh greens, just cannot eat a salad a day, but I do enjoy using frozen spinach and/or sauteeing greens in with my meals and eat greens as well as a variety of veggies very day. Thanks for the info

I was thinking about asking this question and a search turned it up right away. What a resource this mine of information this forum is!

My concern was convenience vs nutrition, particularly for salads. All that chopping - it's a lot easier to make a huge salad and save the leftovers in the fridge, but I was wondering if after the first serving I was just eating fiber with all the nutrients gone.

It's a very complex question. At least for the next few months I'll get my greens right from the garden so as fresh as possible. Now I just have to worry about the condition of my soil.

So, Jeff, when we see nutritional information on a nutritional label, or in Cron0Meter, or in your videos, in what state of the food is that information valid? When I see the nutrient profile of a tomato, or Romaine lettuce, in CronOMeter, does that mean "Fresh picked, eaten off the wagon," or "After transport to the grocery store and a day on the shelf"?

Or... is this even something to concern oneself about?

Great Question!!

I would say it is fairly valid but (as you are eluding to) you have to know the way the numbers are achieved and the variables that may be impacting them. The USDA describes these in full in the section on the SR Database



It depends, I think analysis can give us insight and we can learn but in the end, its the bigger picture, dietary patterns and the following of the recommended guidelines and principles that will matter most.

In Health
Jeff