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Module 4: Nutrient Composition

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Antinutrients

Evaluation of transgenic plants has also included a study of levels of inherent toxic and antinutritive substances. This has been done since genetic modification has the potential to affect expression of genes not directly involved in the nutritional (or other type) of change being made (14).

Antinutrients have been defined as substances that inhibit or block important pathways in metabolism, especially digestion (14). These substances reduce utilization of nutrients by the body, such as proteins, vitamins and minerals. The result is a decrease in the body’s ability to use the nutrients, even though they are present in the food.

Secondary, or unintentional, effects on the plant can occur when genetic material is introduced. With the transfer of one gene, multiple changes in the plant can result. Some of these effects could include increased synthesis activity of already present biochemical metabolism pathways, augmented synthesis caused by increased activation of other genes, decreased production of catabolic enzymes, or reduced degradation of substances (14).

The possibility of these effects being present in genetically engineered foods has lead to review of several products (14). The table below outlines food crops that have been tested for increased levels of antinutrients following genetic modification. The net result was a lack of significantly increased antinutrient levels in these foods, however it is important to recognize that these substances could exist and we need to be aware of them.

Rapeseed oil
Naturally occurring antinutrients

  • Glucosinolates (thyroid gland increase, thyroxin synthesis decrease, metabolism impairments, iodine absorption decreases, protein digestion decreases)
  • Phytic Acid (bioavailability of Ca, Mg, Fe, Zn, Cu, Mn decreased, protein and starch utilization decreased)

Research Findings

  • Some cases of significant differences between glucosinate content of one modified line and non-transgenic plants
  • Genetically modified lines fit within established range for glucosinate

Maize
Naturally occurring antinutrients

  • Phytic Acid (bioavailability of Ca, Mg, Fe, Zn, Cu, Mn decreased, protein and starch utilization decreased)

Research Findings

  • In plant modified to control European corn borer, gene sequence found that could encode for protease inhibitor (Inhibition of trypsin and chymotrypsin, decreased digestion of protein)
  • No protease inhibitor found in modified maize lines

Tomato
Naturally occurring antinutrients

  • Glycoalkaloids (Gastrointestinal symptoms, inflammation of kidney, binds metals, decreased iron absorption, inhibits enzymes)
  • Alpha-tomatine (Decreases during maturation so that red ripe tomatoes loose almost all tomatine when left on plant for 2-3 days)

Research Findings

  • Shorter ripening times created via genetic modification could lead to increased tomatine
  • GM tomatoes created for processing were tested
  • Glycoalkaloid levels found to be within levels of non-GM tomato pastes

Potato
Naturally occurring antinutrients

  • Solanine (Gastrointestinal symptoms, inflammation of kidney, binds metals, decreased iron absorption, inhibits enzymes)
  • Protease inhibitors (Inhibition of trypsin and chymotrypsin, decreased digestion of protein)
  • Phenols (Decrease availability of trace elements)

Research Findings

  • Overall, no increased contents of any inherent plant toxins or antinutrients examined

Soybean
Naturally occurring antinutrients

  • Protease inhibitors (Inhibition of trypsin and chymotrypsin, decreased digestion of protein)
  • Phytate (bioavailability of Ca, Mg, Fe, Zn, Cu, Mn decreased, protein and starch utilization decreased)

Research Findings

  • No significant differences between modified varieties and control soybeans

Discussion Question :

Do you think it is important to keep testing genetically modified foods for antinutrients?

 

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