Why foods are processed? Preserving nutrients

Nothing is as rewarding for a professor as to see a former student graduate and do well after graduation. I can distinctly remember sitting down with Rebecca Creasy during summer orientation as we selected her courses as an incoming First-Year student. That day she told me that she wanted to study at the interface between food science and nutrition. As you will see in her post, she has remained true to that quest. I have asked her to extend the discussion this month on the site about why foods are processed.

Many U.S. residents, myself included, strive to consume a nutritious, healthy eating pattern. In efforts to learn more about healthy eating, we may search internet websites or read self-help and diet books written by so-called food pundits and diet experts. A quick perusal of these popular internet websites and self-help diet books left me with the general impression that healthy eating involves consumption of “whole foods” and no processed foods. During my reading, “whole foods” were classified as being fresh foods that have undergone minimal processing. Fresh carrots, sweet potatoes, apples, and peas would all be examples of whole foods based on this definition. As a cross-trained food scientist, nutrition scientist, and educator, I felt a bit of consternation when reading that many food pundits exclude processed foods from a healthy eating pattern. One reason food scientists process foods, particularly many types of fruits, vegetables, and legumes, is to preserve nutrients in foods that will not be immediately consumed.

I do not hesitate to assert that fresh foods do contain more nutrients than processed foods. We can reap the most nutrient benefits from freshly picked foods that are prepared and consumed the same day. If the fresh foods are not eaten the same day and are not processed, then the level of nutrients, especially vitamins, can decrease as the produce sits on our kitchen counters, grocery store shelves, or bins at local produce markets. Fruits and vegetables continue to undergo changes after being harvested. Enzymes, proteins that speed up chemical reactions, break down nutrients and induce color and texture changes.

One way that food scientists preserve nutrients in fresh fruits and vegetables that will not be consumed immediately, is to freeze them. Freezing slows down the activity of the enzymes that can destroy vitamins and other nutrients. Prior to freezing, vegetables are often blanched to inactivate enzymes, which prevents further nutrient, flavor, texture, and color breakdown. Blanching involves the immersion of vegetables in boiling water or steam for a short time period, followed by immediate cooling. Exposure to heat for even a short period results in destruction of a small amount of nutrients, but this is a trade-off to preventing a greater loss in nutrients over time.

Corn

Fresh, canned, frozen or in the husk: which is safest, most stable, most nutritious and most convenient?

Much like food scientists, consumers who have a passion for home food preservation blanch and freeze vegetables to preserve nutrients in produce that will not be consumed within a few days. Growing up in southeast Georgia, I spent several weeks each summer helping my mama shuck and remove the silks from hundreds of ears of corn. After washing the corn, we blanched and froze the corn based on recommendations from the National Center for Home Food Preservation. Working outside in the Georgia heat and humidity was not always fun, but it was worth it to have a nutritious, homegrown supply of frozen corn and other vegetables available year round. Now that I am older, have a full time job, and live in a larger city, I do not have the time nor space to grow, freeze, and store a year’s worth of vegetables. Like other consumers, I rely on frozen vegetables purchased from a local grocery store and freshly harvested vegetables from my own container garden.

In addition to preserving nutrients in foods, food processing is also used by food scientists to make nutrients more bioavailable. The bioavailability of a nutrient or other food component refers to the extent to which it is absorbed and used within the body. Canning exposes foods, such as vegetables and beans to high temperatures for longer of periods of time than does blanching. This harsh heat treatment breaks down cell walls in vegetables, such as tomatoes. Entrapped phytochemicals (non-nutrient compounds found in plants that can be beneficial for health), such as lycopene, can then be released for increased absorption and use by the body.

The harsh temperatures encountered during canning can also destroy compounds, known as anti-nutrients, which decrease the digestion and absorption of proteins and minerals. Canning beans or soaking and boiling beans at home reduces the amount of the anti-nutrients, lectins and trypsin inhibitors, present. The trade-off to the increase in bioavailability afforded by canning and other high temperature, long time processes is the destruction of some water and fat soluble vitamins.

Despite what food pundits may say, I do believe that a healthy eating pattern can include processed produce and other types of processed foods. Although we can obtain the greatest amount of nutrients from fresh foods, not everyone in the U.S. has adequate time, space, and knowledge to grow and prepare fresh foods that supply all of the essential nutrients needed in the human diet. Processing of produce does decrease levels of some vitamins in the short-term, but preserves a greater quantity of vitamins and minerals and increases bioavailability of some food components in the long run. The key to ensuring that we obtain all of the essential nutrients we need to maintain health is to consume a variety of foods, both fresh and processed.

Dr. Creasy is a lecturer in Food Science and Human Nutrition at Texas A&M University. Her experience in food science and nutrition spans from the quick service restaurant industry to higher education and community outreach in low income areas. Her instructional focus at Texas A&M has been on introductory nutrition courses, study abroad programs, and undergraduate food science courses. She enjoys mentoring both graduate and undergraduate students. Her scholarly interests integrate food science and nutrition and include: 1) development and implementation of active learning techniques for food science and nutrition courses; 2) development of STEM outreach programs for youth in food science and nutrition; 3) consumer education addressing bioactive food ingredients, functional foods and effects of food processing on nutrient content. In her free time, she enjoys running, hiking, and other outdoor activities.

Next week: A review of Badditives by Linda and Bill Bonvie

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