Modifying Macronutrient Compositions

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Enhancing Vitamins/Minerals ___ Reducing Undesirable Components ___ Modifying Macronutrient Compositions

Macronutrients are substances that provide the body with energy - carbohydrates, proteins, and fats - which are vital components of the human diet. Genetic modification has been used to alter the levels of macronutrients produced by several crops to enhance their nutritional value.

Carbohydrates
Proteins
Fats/Oils


Carbohydrates:

- High Fructan Beets

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Fructans are oligosaccharide polymers of fructose molecules. They have gained public interest, because they could potentially serve as a no-calorie replacement for sugar sweeteners; even though humans can taste fructans as being sweet like sucrose (normal sugar), we lack the enzymes to digest them. In addition to this dietary benefit, fructans have also demonstrated health benefits to the gastrointestinal (GI) system. While humans cannot digest fructans, the bacteria in their GI tract can, and the by stimulating bacterial growth, the fructans increase digestive health.

Fructans are made within the vacuoles of plant cells by first converting sucrose into fructose, and then assembling fructose molecules into a longer fructan chain. Previously, fructans have been produced commercially with bioreactors or have been extracted from the few plants that possess the enzyme machinery to naturally produce and store fructans - wheat, onions, chicory, and Jerusalem artichoke. However, producing fructans via these methods has been inefficient, as they are expensive, yields are typically low, and the fructan polymer products are all different sizes, while homogeneity is preferred.

Researchers have been able to identify, isolate, and clone the 2 genes that encode the enzymes that facilitate fructan synthesis:
1-sucrose fructosyl transferase (1-SST) converts sucrose into short fructose polymers and
1-fructan fructosyl transferase (1-FFT) produces the longer fructan chains.
With biotechnology, researchers have been able to insert these genes into plants which would not naturally produce fructan, enabling them to produce homogenous quantities of fructan molecules.

Although staple crops - tobacco, corn, and potato - were all successfully transformed with the fructan genes, transgenic sugar beets appear to be the most effective at producing high yields of useful fructan. The reason for this likely lies in that the sugar beet naturally produces large amounts of sucrose, the precursor of fructan, and stores it in its cell vacuoles, the site of fructan synthesis. "Fructan beets" (as they are called instead of "sugar beats") may make fructans more widely available as a low-calorie and health benefiting sugar substitute. (Granger, 2000)

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