Issue: 65 Page: 46-49
The Potential Health Benefits of Purple Corn
by Kenneth Jones
HerbalGram. 2005; 65:46-49 American Botanical Council
Purple corn is fast approaching classification as a
functional food—an integral component of the diet that provides energy and
essential nutrients. Researchers in the fields of food and nutrition are
intensely searching for functional foods in almost every corner of the world
and from a diversity of plants. Examples include purple corn (Zea mays L., Poaceae), green tea (Camellia sinensis [L.] Kuntze, Theaceae), soy isoflavones (Glycine
max [L.] Merr., Fabaceae), various nuts,
plus various other natural substances in the human diet containing antioxidant
and other substances with alleged or proven potential disease-preventive
Purple corn (frequently referred to as blue corn) is
botanically the same species as regular table corn. Yet by a twist of nature,
this corn produces kernels with one of the deepest shades of purple found
anywhere in the plant “kingdom.” Research has shown that purple corn contains
cell-protecting antioxidants with the ability to inhibit carcinogen-induced
tumors in rats. Many plant-derived substances are believed to show these
properties, but few have also demonstrated anti-inflammatory capabilities and
the potential to help prevent obesity.
The kernels of purple corn (maiz morado in Spanish) have long been
used by the people of the Peruvian Andes to color foods and beverages, a practice
just beginning to become popularized in the industrialized world. They also make
a fermented/alcoholic drink from the kernels which they call chicha morada.1
Researchers at the
Horticultural Sciences Department of Texas A&M University in College
Station, Texas, recently determined that the mean anthocyanin content of whole,
fresh purple corn from Peru was 16.4 mg/g, which was much higher than fresh
blueberries (1.3-3.8 mg/g). On a dry weight basis, the mean content of purple
corn was comparable to blueberries (17.7 and 9.2-24.0 mg/g, respectively). The
kernel pericarp held by far the greatest concentration of anthocyanins,
contributing 45% of the total content. More intriguing, the in vitro
antiradical capacity of purple corn extract against the DPPH
(2,2-diphenyl-1-picrylhydrazyl) radical was greater than that of blueberries (Vaccinium
corymbosum L., Ericaceae), which
have shown higher antioxidant values than many other commercial food plants.5
deeper, the most abundant anthocyanin found in purple corn, called “C3G” (3-O-? -D-glucoside6,7), also known as cyanidin-3-O-?-glucopyranoside,8
has been keeping researchers very busy lately. In a number of tests designed to
assess the potential health benefits of this anthocyanin, one study after another
has proven its antioxidant strength. Like other anthocyanins, C3G is found in
a wide variety of food plants and is actually the most common anthocyanin found
in nature. C3G is the most abundant anthocyanin in some foods, such as the juice
of ruby oranges (Citrus sinensis [L.] Osbeck “Blood orange,” Rutaceae)8
and blackberry (Rubus allegheniensis [L.] Bailey, Rosaceae) extract.9
Red wine also contains appreciable amounts,10,11 but other anthocyanins
C3G displays significant in vitro antioxidant activity. In
one study C3G came out on top when compared to 13 other anthocyanins in the ORAC
(oxygen radical absorbance capacity) assay, which tests for antioxidant
activity. The strength of C3G was 3.5 times that of Trolox® (a
synthetic and potent antioxidant analogue of vitamin E).13 To date,
the radical scavenging/antioxidant capacity of C3G has been demonstrated in at
least a dozen different assays.8,14-20 In one in vitro study, C3G
was tested for the potential to prevent damage caused by ultraviolet (UV)
light. Its ability to inhibit the oxidation of fat cells induced by UVB
(280-315 nm) light was at least 40 times that of vitamin E; however, vitamin E
is a weak inhibitor of UVB-induced lipid oxidation because it rapidly breaks
down under UV light.19 Oxidative stress and immune suppression
caused by UV light are well-known for their role in the induction of skin
Oxidative stress is described as a state in which there is
an excess of oxygen-based free radicals. To avoid the damage they can cause to
cells, the body produces antioxidants to inactivate these free radicals. If
they prove insufficient, however, the body suffers from oxidation of lipids,
proteins, and nucleotide bases. In models of oxidative stress using oxidative
injury to the liver, male rats fed a diet containing 0.2% C3G (2 g/kg of feed)
for 2 weeks beforehand showed significantly less liver injury compared to the
control group.21 A similar study in rats fed C3G in liquid form (0.9
mmol/kg) also found significant hepatoprotective effects.22
In a study on the anti-inflammatory potential of C3G, male
rats administered the anthocyanin orally in liquid form (0.9 mmol/kg) prior to
chemically-induced acute inflammation showed significantly less inflammation
and significantly attenuated levels of pro-inflammatory cytokines
(interleukin-6, interleukin-? , and
tumor necrosis factor-? , and inducible
nitric oxide [iNOS] expression) and nitric oxide (a free radical).23 Based
on these results, it is possible that this plant pigment may also suppress the
inflammatory response in diseases marked with inflammation.
Could the anthocyanin pigment also help prevent some types
of cancer? That question was put to the test in rats first treated with a
carcinogen (1,2-dimethylhydrazine) and then fed a diet containing a known
environmental carcinogen (PhIP or 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine) that also targets the mammary gland,
prostate, and large intestine in rats and causes colorectal cancer.
Incidentally, the carcinogen used in the study, known as a heterocyclic amine,
is the most abundant of around 20 other types found in cooked meats and fish.
Both the early signs of colorectal cancers and the numbers of malignant and
benign tumors that formed in the colons of rats that had the purple pigment in
their diet (5% of feed for 32 weeks; a nontoxic dose based on previous
carcinogenicity studies of PCC) were significantly reduced, and there were no
adverse effects. The authors of the study note that extract or juices of plants
that contain high amounts of anthocyanins have previously been reported to
inhibit mutagenesis induced by heterocyclic amines.24
The oxidation of fats or lipids in blood serum contributes
to the condition known as atherosclerosis. When male rats were fed a diet
containing a high amount of C3G (0.2% of feed for 2 weeks) in place of sucrose
content in the control diet, their blood serum showed a significantly lower
level of oxidation along with a significant decrease in the susceptibility of
their serum lipids to undergo oxidation, yet their body’s natural antioxidants
(serum levels of vitamins C and E, glutathione, and uric acid) remained
unaffected. Another intriguing discovery in this study was that the rats with
C3G in their feed also showed significant decreases in levels of total
cholesterol—about 16% less.25
What would happen if rats
were fed C3G as part of a high-fat diet? To find out, researchers in Japan
compared the body weights of male mice fed a high-fat (HF) diet with another
group fed the same HF diet but with the addition of purple corn color (PCC)
which provided C3G (0.2% or 2 g/kg of feed). Results were also compared to 2
control groups: one fed a normal diet and one fed a normal diet with C3G. After
12 weeks, the results were obvious: mice in the PCC-HF group showed significantly
less signs of developing obesity, yet exhibited no significant difference in
food consumption compared to the control groups with or without the PCC in
their feed. When related to the primary control group (no HF diet or PCC), the
adipose tissue weights of the PCC-HF group were not significantly different. In
addition, fatty tissue in HF-diet group was found to be growing in size but
showed no increase in the PCC-HF group. The HF-diet group also developed a
state of hyperglycemia along with an over-production of insulin. Interestingly,
this was not observed in the PCC-HF group in which both pathologies were
completely normalized. In conclusion, the researchers stated that their tests
of PCC provide a nutritional and biochemical basis for the use of the pigment
or anthocyanins as a “functional food factor”—one that may be beneficial for
helping to prevent diabetes and obesity.26 It now remains for future
studies to determine the possible contributing effects of other substances from
purple corn which are extracted along with PCC.
More recent efforts to determine the potential anti-obesity
mechanisms of purple corn pigment have focused on the effect of C3G on fat cell
dysfunction, fat cell-specific gene expression, and the regulation of chemical
messengers (adipocytokines) secreted by fat cells, such as the fat-derived
hormone adiponectin. After feeding male mice a diet containing PCC to provide
C3G (2 g/kg of feed for 12 weeks), gene expression levels of adiponectin in
white fatty tissue was upregulated 1.7-fold compared to the control group not
fed the food colorant.27 Plasma and gene expression levels of
adiponectin are decreased in obese humans and mice and in insulin resistant
states.27,28 When adiponectin was administered intravenously to mice
fed high-fat/sucrose diets, weight gain was significantly inhibited.
Adiponectin (i.v.) also lowered plasma glucose levels in lean mice fed a
Rich in C3G (approximately 70 mg/g), about 50,000 kg of PCC is used in Japan
as a food color for confections and soft drinks annually.26 So far,
PCC remains to be officially approved for use as a food colorant by the U.S. Food
and Drug Administration. However, approval seems likely because “grape skin color”
and “grape skin extract” (“enocianini” or “enocyanin”)2 made from Concord
grapes29 (Vitis vinifera L., Vitaceae) are also rich in anthocyanins2
and both are FDA-approved for use in beverages and non-beverage foods.29
Kenneth Jones is a medical writer specializing in the field of medicinal plants.
He is the co-author of Botanical Medicines: The Desk References for Major Herbal
Supplements by McKenna, Jones, and Hughes (Haworth Herbal Press, 2002). He
has no affiliation with any commercial producers of purple corn or any of the
other products mentioned in this article.
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29. FDA, Dept. of Health and Human Services. Code of Federal Regulations.
Part 73. Listing of Color Additives Exempt from Certification. Sec. 73.169. Sec.
73.170. April 1, 2003. Available at: http://www.access.gpo.gov/cgi-bin/cfrassemble.cgi?title=200321.