46 Part I: Principles
intake of these phytochemicals is not always suffi-
cient, scientists are trying to enhance the nutritional
quality of plants through genetic engineering.
Isoflavonoids
Flavonoids, which include anthocyanins, condensed
tannins, and isoflavonoids, are a class of phytochem-
icals that perform a range of important functions
for plants, including pigmentation, feed deterrence,
wood protection, fungi and insect defense, and in-
duction of genes for root nodulation (Buchanan et
al. 2001). Isoflavonoids (or isoflavones) are a type of
phytoestrogen, or plant hormone, that has a chemi-
cal structure similar to human estrogen. The health
benefits believed to be provided by isoflavonoids
come from the weak estrogenic activity of these
molecules in the human body (Jung et al. 2000).
Isoflavonoids are found in soybeans, chickpeas, and
many other legumes; however, soybeans are unique
because they have the highest concentration of the
two most beneficial isoflavonoids, genistein and
daidzein (Eldridge and Kwolek 1983, Tsukamoto et
al. 1995). In the studies conducted so far, isoflav-
onoids show great potential to fight many types of
diseases. They help prevent the buildup of arterial
plaque, which reduces the risk of coronary heart dis-
ease and stroke (FDA 1999); help reduce breast can-
cer (Peterson and Barnes 1991); help prevent
prostate cancer by delaying cell growth (Messina
and Barnes 1991); fight osteoporosis by stimulating
bone formation (Civitelli 1997); and even relieve
some menopausal symptoms (Nestel et al. 1999).
The main source of isoflavonoids in human diet
comes from the consumption of soybean and its
products. Although present in high concentration in
unprocessed soybean, isoflavonoid levels can de-
crease by 50% during seed processing for traditional
soy foods (Wang and Murphy 1996). Increasing
isoflavonoid concentrations in soybean could solve
this problem. Another way to take advantage of
isoflavonoids’ health benefits is through the develop-
ment of other crops that can produce these powerful
compounds, thereby widening their consumption.
Isoflavonoids are synthesized by a branch in the
degradation pathway of the amino acid phenylala-Figure 3.8.Comparison of amino acid composition from transgenic and wild-type potatoes. (From Chakraborty et al.
2000.)