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Module 4: Nutrient Composition

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Phytonutrients

Flavonoids

Flavonoids have been defined as polyphenolic compounds found in plants. These compounds are involved in plant growth and development. There has also been research that suggests flavonoids are beneficial to human health, possibly due to their antioxidant properties (5). Currently, over 400 individual flavonoids have been discovered.

The benefits include protection against chronic diseases, such as cardiovascular disease, that can be obtained by consuming foods containing these compounds. Their antioxidant properties towards free radicals have potential in anticancer activity, such as antiproliferation and promotion of differentiation and apoptosis (13).

There is some difficulty in obtaining good sources of flavonoids since many food sources have only small amounts in their edible parts. Foods may also contain flavonoids with suboptimal antioxidant characteristics, making them less than ideal sources (5).

Genetic engineering could play a role in improving these sources. Research in this area has lead to identification of enzymes needed to synthesize flavonoids, genes that encode for these enzymes, and genes that regulate the production of flavonoids. These developments puts researchers closer to being able to upregulate the flavonoid biosynthesis as well as to direct synthesis of desirable flavonoids in crop plants (5).

Isoflavonoids

Isoflavonoids are a class of flavonoids found mainly in legumes. They have been found to have oestrogenic and anticancer activity. This leads to the possibility of using isoflavones to treat or prevent hormone-related disorders.

The gene that encodes the main enzyme in isoflavonoid formation, cytochrome P450 mono-oxygenase isoflavone synthase (IFS) has been cloned. When this gene was expressed in plants, such as tobacco and maize, more isoflavonoids were found in the plant where the general flavonoid pathway was already active (5).

Experiments have also been done with non-legume plants. A transfer of the IFS gene found in soybeans to Arabidopsis (a flowering plant) resulted in conversion of narigenin to an isoflavone, genistein, a phytoestrogen of high medical interest (13). Success in studies such as this give researchers hope that they will be able to increase isoflavonoid production in crops such as tomato, maize, wheat or rice (5).

Here are some common questions about diet and cancer, including phytonutrients from the American Cancer Society.

Flavonols

Another class of flavonoids, flavonols, has been found to be good antioxidants and protective against cardiovascular disease. Tomatoes naturally contain this compound in the peel of the fruit in the form of quercetin. The peels also contain another flavonoid, chalcone narichalcone. Research data has suggested that flavonol biosynthesis in the peel is limited in part by low levels of gene expression of chalcone isomerase (CHI). Increasing synthesis of the CHI in the tomato was accomplished by using the petunia CHI gene to develop transgenic tomatoes. The result was a large increase in the amount of quercetin (70-fold) and flavonol levels within the tomato comparable to onions, which are naturally high in flavonols (5).

Here is some information about phytonutrients and cardiovascular disease from the American Heart Association.

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