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Corn Phytochemicals and Their Health Benefits

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Corn Phytochemicals and Their Health Benefits

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Whole grain has a wide range of phytochemicals exhibiting health benefits of lowering risk of chronic diseases. As commonly consumed grain product, corn has unique profiles of nutrients and phytochemicals when compared with other whole grains. Corn nutrients and phytochemicals include vitamins (A, B, E, and K), minerals (Mg, P, and K), phenolic acids (ferulic acid, coumaric acid, and syringic acid), carotenoids and flavonoids (anthocyanins), and dietary fiber. More and more scientific evidences have shown that regular consumption of whole grain corn lowers the risk of developing chronic diseases such as cardiovascular disease, type 2 diabetes, and obesity and improves digestive health. Further studies on bioactive compounds of corn related to health are needed. Keywords: Corn, Maize, Whole grains, Phytochemicals, Cardiovascular disease, Resistant starch, Type II diabetes, Diet and chronic diseases
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Food
Science
and
Human
Wellness
7
(2018)
185–195
Contents
lists
available
at
ScienceDirect
Food
Science
and
Human
Wellness
jo
ur
nal
ho
mepage:
www.elsevier.com/locate/fshw
Corn
phytochemicals
and
their
health
benefits
Siyuan
Sheng,
Tong
Li,
RuiHai
Liu
Department
of
Food
Science,
Cornell
University,
Ithaca,
NY,
14850-7201,
United
States
a
r
t
i
c
l
e
i
n
f
o
Article
history:
Received
18
July
2018
Accepted
22
August
2018
Available
online
5
September
2018
Keywords:
Corn
Maize
Whole
grains
Phytochemicals
Cardiovascular
disease
Resistant
starch
Type
II
diabetes
Diet
and
chronic
diseases
a
b
s
t
r
a
c
t
Whole
grain
has
a
wide
range
of
phytochemicals
exhibiting
health
benefits
of
lowering
risk
of
chronic
dis-
eases.
As
commonly
consumed
grain
product,
corn
has
unique
profiles
of
nutrients
and
phytochemicals
when
compared
with
other
whole
grains.
Corn
nutrients
and
phytochemicals
include
vitamins
(A,
B,
E,
and
K),
minerals
(Mg,
P,
and
K),
phenolic
acids
(ferulic
acid,
coumaric
acid,
and
syringic
acid),
carotenoids
and
flavonoids
(anthocyanins),
and
dietary
fiber.
More
and
more
scientific
evidences
have
shown
that
regular
consumption
of
whole
grain
corn
lowers
the
risk
of
developing
chronic
diseases
such
as
cardio-
vascular
disease,
type
2
diabetes,
and
obesity
and
improves
digestive
health.
Further
studies
on
bioactive
compounds
of
corn
related
to
health
are
needed.
©
2018
“Society
information”.
Production
and
hosting
by
Elsevier
B.V.
on
behalf
of
KeAi
Communications
Co.,
Ltd.
This
is
an
open
access
article
under
the
CC
BY-NC-ND
license
(http://
creativecommons.org/licenses/by-nc-nd/4.0/).
1.
Introduction
Corn,
known
as
maize
(Zea
mays
L.),
is
originated
in
America.
It
was
discovered
by
an
European
explorer,
Christopher
Colum-
bus,
in
1492,
and
later,
was
introduced
to
Europe,
China,
and
all
over
the
world
within
the
following
100
years
[1,2].
Corn
is
one
of
the
major
food
sources
in
the
world.
Corn
contains
significant
amounts
of
bioactive
compounds
providing
desirable
health
ben-
efits
beyond
its
role
as
a
major
source
of
food.
Beside
corn
grain,
sweet
corn
is
considered
as
one
of
the
most
popular
vegetables
in
North
America
and
China,
and
its
popularity
has
rapidly
increased
in
the
world.
Sweet
corn
is
among
the
top
six
vegetables
consumed
in
the
United
States
[3].
Canned
and
frozen
sweet
corn
is
ranked
the
third
in
among
vegetables
consumed
in
the
United
States,
only
behind
the
canned
tomatoes
and
frozen
potatoes
[4].
Previously,
phytochemicals
of
corn
have
received
less
attention
than
these
of
fruits
and
vegetables.
The
consumption
of
corn
and
Abbreviations:
CVD,
cardiovascular
disease;
RS2,
resistant
starch;
WG,
whole
grain;
DW,
dry
weight;
RCT,
randomized
controlled
trial;
SCFA,
short
chain
fatty
acids;
TPC,
total
phenolic
content.
Corresponding
author
at:
Department
of
Food
Science,
245
Stocking
Hall,
Cornell
University,
Ithaca,
NY,
14853-7201,
United
States.
E-mail
address:
RL23@cornell.edu
(R.
Liu).
Peer
review
under
responsibility
of
KeAi
Communications
Co.,
Ltd.
other
whole
grain
products
has
been
linked
to
the
reduced
risk
of
chronic
diseases
including
cardiovascular
disease
[5–8],
type
2
diabetes
[9–12],
obesity
[13,14],
some
cancers
[15–22],
and
with
the
improvement
of
digestive
tract
health
[23–25].
Health
promoting
effects
of
phytochemicals
of
fruit
and
vegeta-
bles
including
antioxidant
activities
and
antiproliferative
activities
have
been
well
reported
[26–28].
However,
the
health
benefits
of
the
whole
grains
have
long
been
underestimated
[30].
Whole
grains
are
composed
of
intact,
ground,
cracked
or
flaked
caryopsis,
in
which
the
principle
components,
the
starchy
endosperm,
germ,
and
bran
are
presented
in
the
same
relative
proportions
as
existed
in
the
intact
caryopsis
[29].
The
health
benefitsof
corn
are
not
only
from
basic
nutrients
such
as
carbohydrates,
vitamins
and
miner-
als,
but
also
from
their
unique
phytochemicals
such
as
phenolic
acids.
The
major
components
of
corn
kernel
include
endosperm,
germ
and
bran,
and
each
of
them
contains
a
different
phytochem-
ical
profiles.
Along
with
the
health
promoting
compounds
such
as
https://doi.org/10.1016/j.fshw.2018.09.003
2213-4530/©
2018
“Society
information”.
Production
and
hosting
by
Elsevier
B.V.
on
behalf
of
KeAi
Communications
Co.,
Ltd.
This
is
an
open
access
article
under
the
CC
BY-NC-ND
license
(http://creativecommons.org/licenses/by-nc-nd/4.0/).
186
S.
Siyuan
et
al.
/
Food
Science
and
Human
Wellness
7
(2018)
185–195
amylase
in
corn
endosperm,
a
wide
range
of
phytochemicals
such
as
total
phenolics
and
phenolic
acids
(vannilic
acid,
syringic
acid,
cour-
maric
acid,
ferulic
acid
and
caffeic
acid)
are
found
in
corn
bran
and
germ
fractions
at
high
concentrations.
Adom
&Liu
et
el.
discovered
that
the
majority
phytochemicals
in
corn
with
beneficial
effects
on
human
health
are
presented
in
the
bran
and
germ
fractions
and
not
the
endosperm,
with
about
87%
of
total
phenolic
content
(TPC)
pre-
sented
in
the
bran
and
germ
fractions.
Thus,
corn
flour
with
ground
germ,
endosperm
and
bran
contains
higher
bioactive
compounds
than
refined
cornstarch
and
refined
corn
oil
[1,30].
All
corn
types
are
rich
in
dietary
fiber,
vitamins
(A,
B,
E,
and
K),
minerals
(magnesium,
potassium
and
phosphorus),
phenolic
acids
and
flavonoids,
plant
sterols,
and
other
phytochemicals
(lignins
and
bound
phytochemicals).
However,
different
varieties
of
corn
contain
significantly
different
phytochemical
profiles
in
terms
of
flavonoids
and
carotenoids.
Blue,
red,
and
purple
corn
possess
higher
concentration
of
anthocyanidins
(up
to
325
mg/100
g
DW
corn)
including
cyanidin
derivatives
(75%–90%),
peonidin
deriva-
tives
(15%–20%)
and
pelargonidin
derivatives
(5%–10%).
Yellow
corn
is
rich
in
carotenoids
(up
to
823
g/100
g
DW
corn)
including
lutein
(50%),
zeaxanthin
(40%),
ˇ-cryptoxanthin
(3%),
ˇ-carotene
(4%),
and
-carotene(2%).
High
amylose
corn
is
rich
in
amylose
(up
to
70%
of
all
carbohydrates)
[31–35].
Therefore,
the
consump-
tion
of
combined
different
corn
varieties
provides
wide
range
of
phytochemicals
with
optimum
nutritional
benefits
from
corn.
The
additive
and
synergistic
effects
of
bioactive
compounds
in
corn
and
other
whole
grains
along
with
many
other
nutrients
and
phyto-
chemicals
in
fruits
and
vegetables
may
be
responsible
for
their
health
benefits
in
reduced
risk
of
chronic
diseases
[36].
Starting
in
1995,
a
daily
recommendation
of
6–11
sevings
of
grain
products
was
recommended;
in
the
2005
nutrition
guidelines,
consumption
of
whole
grains
was
first
mentioned;
and
in
the
most
recently
2015
dietary
guideline
for
Americans
recommends,
it
is
recommended
to
consume
more
than
170
g
of
grains
daily,
and
half
of
them
should
be
in
whole
grain
form.
However,
the
average
intake
of
whole
grains
in
the
United
States
is
less
than
one
serving
per
day,
and
90%
of
Ameri-
cans
do
not
meet
the
recommendations
for
whole
grain
consumtion
[13,37].
The
purpose
of
this
review
will
focus
on
the
recent
research
of
the
major
nutrients
and
phytochemicals
of
corn
and
their
potential
health
benefits
related
to
the
dietary
prevention
of
chronic
diseases.
2.
Macro-
and
micro-nutrients
in
corn
Every
100
g
of
corn
provides
365
calories
and
every100
g
of
sweet
corn
provides
86
calories.
Carbohydrates
and
water
are
the
main
chemical
substances
in
corn.
Carbohydrates
content
in
corn
close
to
75%
in
and
carbohydrates
content
in
sweet
corn
takes
account
nearly
18%.
Water
content
in
corn
is
about
10%
and
water
content
in
sweet
corn
is
about
75%.
Corn
and
sweet
corn
provide
a
wide
variety
of
vitamins
(carotenoids,
thiamine,
riboflavin,
niacin,
pyridoxine,
folate,
ascorbic
acid,
vitamin
E
and
vitamin
K),
miner-
als
(calcium,
magnesium,
phosphorus,
potassium,
sodium
and
zinc)
and
resistant
starches.
The
nutrition
profiles
of
corn
and
sweet
corn
are
similar,
with
the
only
exception
being
vitamin
C,
which
is
only
found
in
sweet
corn.
Lipids
in
corn
and
sweet
corn
are
mostly
pre-
sented
in
mono-
(30%)
and
poly-
unsaturated
(50%)
forms
with
a
small
portion
of
lipids
in
the
saturated
form
(20%).
3.
Corn
phytochemicals
“Phyto”
in
the
word
of
phytochemicals
is
derived
from
the
Greek
word
“phyto”,
which
means
plant.
Phytochemicals
are
the
bioac-
tive
non-nutrient
chemical
compounds
found
in
plants
such
as
fruits,
vegetables
and
whole
grains,
which
may
function
in
reduc-
ing
the
risk
of
chronic
diseases
[36].
Although
it
is
estimated
at
least
more
than
5000
dietary
phytochemicals
have
been
discov-
ered,
it
is
believed
that
a
high
percentage
of
phytochemicals
in
foods
still
remain
unknown
[36].
Like
many
other
grain
products,
phytochemicals
in
corn
are
also
distributed
mainly
in
the
kernel
and
bran
[30,38].
Phytochemicals
composition
varies
among
dif-
ferent
type
of
corn.
Carotenoids
are
concentrated
in
yellow
and
red
corn,
anthocyanins
are
concentrated
in
red,
blue,
purple
and
black
corn,
and
phytosterols
are
concentrated
in
kernel
part
of
corn
[39].
Corn
has
the
highest
total
antioxidant
activity
(181.4
±
0.86
mol
of
vitamin
C
equiv/g
of
grain)
among
all
common
grains
such
as
rice,
wheat
and
oats
[30].
Phytochemicals
are
the
major
contributors
to
the
total
antioxidant
activity
in
corn.
Flavonoids
and
ferulic
acids
contribute
to
the
total
phenolics
in
corn
and
are
directly
related
to
the
total
antioxidant
activity,
87%
of
them
were
in
bound
form
[30].
Thermal
processing
increases
the
antioxidant
activity
of
sweet
corn
by
releasing
bound
form
phytochemicals
[40].
Dewanto
et
al.
firstly
reported
that
thermal
processed
sweet
corn
had
higher
antioxidant
activity
than
the
unprocessed
sweet
corn
[40].
3.1.
Phenolics
Phenolics
are
defined
as
chemical
substances
possessing
one
or
more
aromatic
rings
with
one
or
more
hydroxyl
groups
in
their
structures
[41].
They
are
commonly
categorized
as
phenolic
acids,
flavonoids,
stilbenes,
coumarins,
and
tannins
[41].
Among
these
phenolics,
flavonoids
and
phenolic
acids
are
the
major
compounds
found
in
corn.
Total
phenolic
content
varies
among
different
corn
varieties,
and
the
range
is
from
243.8
±
4.6
to
320.1
±
7.6
mg
of
gal-
lic
acid
equiv/100
g
of
dry
weight
(DW)
of
corn.
High
carotenoid
corn
(320.1
±
7.6
mg
of
gallic
acid
equiv/100
g
of
DW
of
grain)
has
the
highest
total
phenolic
content
followed
by
yellow
corn
(285.8
±
14.0
mg
of
gallic
acid
equiv/100
g
of
DW
of
corn),
blue
corn
(266.2
±
0.7
mg
of
gallic
acid
equiv/100
g
of
DW
of
grain),
white
corn
(260.7
±
6.1
mg
of
gallic
acid
equiv/100
g
of
DW
of
grain),
and
red
corn
(243.8
±
4.6
mg
of
gallic
acid
equiv/100
g
of
DW
of
grain)
[33].
Adom
and
Liu
reported
that
corn
had
the
highest
total
phenolic
content
(15.55
±
0.60
mol/g
of
grain)
among
all
com-
monly
consumed
grains
such
as
rice
(7.99
±
0.39
mol/g
of
grain),
oats
(6.53
±
0.19
mol/g
of
grain)
and
wheat
(5.56
±
0.17
mol/g
of
grain)
[30]
(Fig.
1).
3.1.1.
Phenolics
acids
Phenolic
acids
are
one
of
the
major
phytochemical
components
of
corn.
Phenolic
acids
can
be
subdivided
into
hydroxybenzoic
acid
and
hydroxycinnamic
acid
derivatives
(Fig.
2)
[36].
In
corn,
phe-
nolic
acids
contribute
to
the
sour,
bitter,
and
astringent
taste,
at
taste
level
threshold
of
40–90
ppm
[42].
Natural
phenolic
acids
such
as
trans-cinnamic
acid
and
ferulic
acid
are
considered
as
effec-
tive
fungitoxicants
for
A.
flavus
and
A.
parasiticus
in
corn
[43].
For
hydroxybenzoic
acids,
vannilic
acid
and
syringic
acid
are
detected
in
corn,
and
for
hyrocinnamic
acid,
p-courmaric,
ferulic
and
caffeic
acids
are
detected
in
corn.
[44].
The
structures
of
benzoic
acids
and
cinnamic
acids
are
displayed
in
Fig.
2
(Table
1).
Sosulski
et
al.
reported
that
total
phenolic
acid
content
in
yellow
dent
corn
flour
was
309
ppm,
and
cis
and
trans-ferulic,
p-courmaric
and
syringic
acids
were
the
predominant
phenolic
acids
in
corn
flour.
The
distribution
of
free
and
soluble
and
bound
form
of
dif-
ferent
phenolic
acids
in
corn
flour
is
shown
in
Table
2
[45].
The
phenolic
acid
found
in
the
highest
quantities
in
corn
is
ferulic
acid
and
is
mainly
presented
in
the
bound
form
linked
to
cell
wall
structural
components
such
as
celluloses,
lignins
and
pro-
teins
by
ester
bonds
[15].
Different
from
the
results
reported
by
Sosulski
et
al.,
Adom
&
Liu
reported
that
more
ferulic
acids
pre-
sented
predominately
in
bound
form
while
the
former
research
S.
Siyuan
et
al.
/
Food
Science
and
Human
Wellness
7
(2018)
185–195
187
Fig.
1.
Structures
of
common
phenolic
compounds.
(Table
2)
indicated
lower
contrast
ratio
of
different
form
of
fer-
ulic
acids.
total
ferulic
acid
content
in
corn
is
906.13
±
9.09
mol
/100
g
of
grain,
98.9%
of
that
is
in
bound
form,
1%
is
in
soluble
con-
jugate
form
and
only
0.1%
is
in
free
from
[30].
From
the
data
above,
the
bound,
soluble
conjugate
and
free
form
ratio
for
ferulic
acid
is
100:1:0.1.
Thus
processing
techniques
such
as
thermal
process-
ing,
pasteurization,
fermentation,
and
freezing
play
critical
roles
in
releasing
bound
phenolic
acids
and
increasing
their
total
antioxi-
dant
activity
by
44%
to
reach
the
optimum
nutrition
value
of
corn
[30,40].
3.1.2.
Flavonoids
Flavonoids
are
the
largest
group
of
phenolic
compounds
in
corn.
It
has
been
reported
by
epidemiological
studies
that
high
consumption
of
flavonoids
reduce
the
risk
of
chronic
diseases
including
CVD,
diabetics,
and
cancers
[36].
The
generic
structure
of
flavonoids
consists
of
2
aromatic
rings
(A
and
B
rings)
linked
by
an
oxygenated
heterocycle
ring,
known
as
C
ring.
Different
structures
in
the
C
ring
of
flavonoids
classify
them
into
flavonols,
flavones,
flavanols,
flavanones,
anthocyanins,
and
isoflavonoids
[41].
Flavonoids
content
various
among
corn
varieties,
as
a
most
consumed
corn
variety,
total
flavonoid
content
in
yellow
corn
is
about
1.68
±
0.17
mol
catechin
equiv/g.
Most
of
them
are
in
bound
form
(1.52
±
0.03
mol
catechin
equiv/g),
with
a
small
amount
in
the
free
form
(0.16
±
0.004
mol
catechin
equiv/g)
[30].
Anthocyanins
are
one
of
major
groups
of
water
soluble
flavonoids
in
corn,
imparting
the
color
of
purple
to
pinkish
depend-
ing
on
the
pH
levels
and
concentrations.
Pericarp
in
corn
contains
the
highest
level
of
anthocyanins
(up
to
50%),
and
aleurone
con-
tains
a
small
portion
of
anthocyanin
[46].
The
color
of
the
corn
kernel
indicates
the
content
of
anthocyanins.
Purplish-red
corn
kernel
contains
the
highest
amount
of
anthocyanins
(141.7
mg
anthocyanins/100
g
flour),
and
blue
corn
kernel
contains
less
antho-
cyanins
(62.7
mg/100
g
flour)
[35].
Six
major
and
17
minor
antho-
cyanins
have
been
identified
from
purple
corn.
The
structures
of
major
anthocyanins
found
in
purple
corn
are
shown
in
Fig.
3
includ-
ing
perlargonidin-3-glucoside,
cyanidin-3-glucoside,
delphinidin-
3-glucoside,
peonidin-3-glucoside,
petunidin-3-glucoside,
and
malvidin-3-rutinoside
[47,48].
Anthocyanins
in
colored
corn
may
have
a
positive
effect
on
digestive
health.
A
twelve-week
animal
study
conducted
by
Wu
et
al.
suggested
that
anthocyanins
reduced
the
risk
of
colon
cancer
by
increasing
fecal
butyric
acid
content
as
well
as
lowering
the
body
weight
by
16.6%
at
200
mg
kg
treatment
[49].
Some
other
research
supported
the
same
results
[50,51]
and
the
proposed
mechanism
is
that
corn
anthocyanins
inhibit
the
synthesis
of
fatty
acids
and
triacylglycerol
by
suppressing
the
mRNAs
level
of
enzymes
thus
decreasing
the
accumulation
of
triacylglycerol
in
liver
and
white
adipose
tissue.
Among
the
anthocyanins
in
purple
corn,
cyanidin
3-O-ˇ-D-glucoside
possess
substantial
health
benefits
such
as
anti-
inflammatory
beyond
its
antioxidant
effect
[52].
Fig.
2.
Structures
of
common
phenolic
acids
found
in
corn:
(A)
benzoic
acid
deriva-
tives
and
(B)
cinnamic
acid
derivatives
(Adopted
from
Liu,
2007).
3.2.
Carotenoids
Carotenoids
are
natural
pigments
with
yellow,
orange,
and
red
colors.
More
than
600
carotenoids
have
been
identified
in
nature.
Their
physiological
functions
in
promoting
health
are
as
pro-vitamin
A
and
as
antioxidants
quenching
singlet
oxygen
radi-
cals.
Carotenoids
generally
have
a
40-carbon
skeleton
of
isoprene
unites
cyclized
at
one
or
both
ends
[15].
The
majority
of
carotenoids
that
occur
in
nature
are
in
trans
form.
Because
of
the
long
series
of
conjugated
double
bonds
in
the
central
part
of
its
chemical
structure,
carotenoids
exhibit
light
absorbing
and
unique
singlet
oxygen
quenching
capability
[53].
Carotenoids
are
lipid-soluble
compounds,
thus
the
absorption
of
carotenoids
requires
3–5
grams
of
fat/oils
presented
in
a
meal.
Processing
such
as
mechanical
homogenization
and
thermal
processing
may
increase
carotenoid
bioavailability.
On
the
other
hand,
un-absorbable
fat-soluble
com-
188
S.
Siyuan
et
al.
/
Food
Science
and
Human
Wellness
7
(2018)
185–195
Table
1
Nutrient
profiles
of
corn
and
sweet
corn
(data
reported
on
wet
basis)a.
Units
White
corn yellow
corn white
sweet
corn
yellow
sweet
corn
Water
g/100
g
10.37
10.37
75.96
76.05
Energy
kcal/100
g
365
365
86
86
Protein
g/100
g
9.42
9.42
3.22
3.27
Total
lipid
(fat)
g/100
g
4.74
4.74
1.18
1.35
Carbohydrate,
by
difference
g/100
g
74.26
74.26
19.02
18.7
Fiber,
total
dietary
g/100
g
N.D.
7.3
2.7
2
Sugars,
total g/100
g N.D.
0.64
3.22
6.26
Minerals
Calcium,
Ca
mg/100
g
7
7
2
2
Iron,
Fe
mg/100
g
2.71
2.71
0.52
0.52
Magnesium,
Mg
mg/100
g
127
127
37
37
Phosphorus,
P
mg/100
g
210
210
89
89
Potassium,
K mg/100
g 287
287
270
270
Sodium,
Na mg/100
g35
35
15
15
Zinc,
Zn
mg/100
g
2.21
2.21
0.45
0.46
Vitamins
Vitamin
C,
total
ascorbic
acid
mg/100
g
0
0
6.8
6.8
Thiamin
mg/100
g
0.385
0.385
0.2
0.155
Riboflavin
mg/100
g
0.201
0.201
0.06
0.055
Niacin
mg/100
g
3.627
3.627
1.7
1.77
Vitamin
B-6
mg/100
g
0.622
0.622
0.055
0.093
Folate,
DFE
g/100
g
N.D.
19
46
42
Vitamin
A,
RAE g/100
g0
11
0
9
Pro
-Vitamin
A,
IU
IU/100
g
0
214
1
187
Vitamin
E
(alpha-tocopherol)
mg/100
g
N.D.
0.49
0.07
0.07
Vitamin
K
(phylloquinone)
g/100
g
N.D.
0.3
0.3
0.3
Lipids
Fatty
acids,
total
saturated
g/100
g
0.667
0.667
0.182
0.182
Fatty
acids,
total
monounsaturated g/100
g 1.251
1.251
0.347
0.432
Fatty
acids,
total
polyunsaturated
g/100
g
2.163
2.163
0.559
0.487
DAE
stands
for
dietary
folate
equivalent;
RAE
stands
for
retinol
activity
equivalent
and
IU
stands
for
international
unit.
N.D.
stands
for
not
determined.
aData
is
from
USDA.
National
Nutrient
Database
for
Standard
Reference
Release
28.
Fig.
3.
Structure
of
common
anthocyanins
found
in
purple
corn
[48].
pounds
may
reduce
carotenoid
bioavailability
by
one
order
of
magnitude
[54–56].
3.2.1.
Carotenes
ˇ-carotene,
˛-carotene
and
ˇ-cryptoxanthin
are
pro-vitamin
A
carotenoids,
which
means
they
can
be
converted
to
retinol
(Vita-
min
A)
in
the
human
body,
whereas
xanthophylls
do
not
possess
this
function.
Theoretically,
one
molecule
of
ˇ-carotene
can
be
con-
verted
into
two
molecules
of
retinol
through
enzymatic
reactions
mainly
in
the
intestinal
mucosa.
Realistically,
the
conversion
rate
of
pro-vitamin
A
to
retinol
is
lower,
vitamin
A
conversion
rates
of
ˇ-
and
˛-
carotenoids
are
expressed
in
retinol
equivalents
(RE)
based
S.
Siyuan
et
al.
/
Food
Science
and
Human
Wellness
7
(2018)
185–195
189
Table
2
Free,
soluble
and
bound
forms
of
different
phenolic
acids
in
yellow
dent
corn
flour
(data
reported
on
dry
weight
basis)
[45].
phenolic
acids free
(ppm)
soluble
form
(ppm)
Bound
(ppm)
p-hydroxybenzoic
acid
0.3
1
trace
(p-hydroxyphenyl)
acetic
acid
1.1
trace
N.D.
Vannilic
acid
1
2.7
N.D.
Protocatechuic
acid
1.1
1.9
trace
Syringic
acid
1.1
10.4
trace
quinic
acid
N.D.
N.D.
N.D.
cis-p-coumaric
acid N.D.
trace
N.D.
trans-p-coumaric
acid
6.2
12.7
trace
cis-ferulic
acid
0.6
5.1
0.8
trans-ferulic
acid
5.1
44.9
208.6
Caffeic
acid
trace
trace
4.5
cis-ferulic
acid
trace
N.D.
N.D.
trans-sinapic
acid N.D.
trace
trace
Chlorogenic
acid
N.D.
N.D.
N.D.
total
16.5
78.7
213.9
N.D.
stands
for
not
determined.
on
in
vivo
tests
where
1
RE
=
1
g
of
retinol
=
6
g
of
ˇ-carotene
or
12
g
of
˛-carotene
[57].
The
conversion
of
pro-vitamin
A
to
retinol
is
up
to
the
individual
status
of
vitamin
A,
and
regulation
mecha-
nisms
inhibit
the
conversion
to
vitamin
A
if
retinol
content
in
the
human
body
is
over
the
demand
of
body
[58,59].
3.2.2.
Xanthophylls
Unlike
other
carotenoids,
xanthophylls
(lutein
and
zeaxanthin)
cannot
be
converted
into
vitamin
A.
Lutein
and
zeaxanthin
are
selectively
taken
up
into
the
macula
region
(yellow
spot)
in
eye,
where
they
absord
90%
of
blue
light
(450–470
nm)
thus
reducing
the
shortwave
length
light
from
reaching
the
critical
part
of
eye
and
causing
oxidative
damage
and
stress
[15,60].
The
average
xan-
thophyll
concentration
in
corn
(the
sum
of
lutein,
zeaxanthin
and
ˇ-cryptoxanthin)
is
21.97
ug/g
corn.
Lutein
is
15.54
g/g
corn,
zeax-
anthin
is
5.84
g/g
corn,
and
ˇ-cryptoxanthin
is
0.54
g/g
corn
[61].
De
la
Parra
et
al.
measured
carotenoid
content
of
white,
yellow,
red,
blue
and
high
carotenoid
corn,
and
data
is
shown
in
Table
3
[33].
The
chemical
structures
of
major
carotenoids
identified
in
corn
are
shown
in
Fig.
4.
3.3.
Vitamin
E
Vitamin
E
is
a
family
of
eight
isomers
(vitamers)
with
two
types
of
structures,
the
tocopherols
(˛-tocopherol,
ˇ-tocopherol,
-tocopherol,
ı-tocopherol)
and
the
tocotrienols
(˛-tocotrienol,
ˇ-tocotrienol,
-tocotrienol,
and
ı-tocopherol)
[15].
The
generic
structures
of
the
2
classes
of
Vitamin
E
are
composed
of
a
6-
hydroxychroman
group
and
a
phytol
side
chain
made
of
isoprenoid
unites
(Fig.
5),
with
tocopherols
and
tocotrienols
sharing
a
similar
chemical
structure
with
minor
differences
on
the
phytol
side
chain.
Tocopherols
have
saturated
phytol
side
chains
while
tocotrienols
have
carbon-carbon
double
bonds
in
the
phytol
side
chain
[15].
The
main
functions
of
vitamin
E
in
human
body
are
maintaining
mem-
brane
integrity
and
as
lipid
soluble
antioxidant.
When
compared
with
tocopherols,
tocotrienols
have
stronger
function
in
prevent-
ing
cancer
and
cardiovascular
diseases
[62–65].
Vitamin
E
also
improves
immune
system
function
and
repairs
DNA
damage
[66].
All
vitamin
E
vitamers
are
found
in
corn,
with
the
only
exception
of
ˇ-tocotrienol.
Total
vitamin
E
content
is
66.9
mg/kg
DW
of
yellow
corn,
including
3.7
mg/kg
DW
corn
of
˛-tocopherol,
5.3
mg/kg
DW
corn
of
˛-tocotrienol,
0.2
mg/kg
DW
corn
of
ˇ-tocopherol,
45
mg/kg
DW
corn
of
-tocopherol
(the
major
isomer
in
corn),
11.3
mg/kg
DW
corn
of
-tocotrienol,
1.0
mg/g
DW
corn
of
ı-tocopherol,
and
0.4
mg/kg
DW
corn
of
ı-tocotrienol
[67].
About
95%
of
vitamin
E
isomers
are
found
in
the
germ
faction
of
corn
[68]
(Fig.
6).
Table
3
Major
phenolic
acids
content
in
yellow,
Mexican
blue,
American
blue
and
white
corn
[45,108].
Type
of
corn p-coumaric
acid
mg/kg,
DW
ferulic
acid
mg
/kg,
DW
Yellow
dent
18.9
265
American
blue
N.D.
927
Mexican
blue
1.3
202
white
6.6
2484
N.D.
stands
for
not
determined.
3.4.
Phytosterols
Phytosterols
are
a
collective
term
for
plant
sterols
and
stanols
with
a
similar
structure
as
cholesterol,
differing
only
in
the
side
chains
[15].
They
are
the
essential
components
of
plant
cell
walls
and
membranes.
As
minor
constituents
in
corn
oil,
phytos-
terols
are
classified
into
sub-groups:
4-demethylsterols,
simply
sterols,
4,4-dimethylsterols,
4-monomethylsterols,
and
sitosterols.
The
classification
is
based
on
the
number
of
methyl
group
at
the
C-4
position
[69,70].
Corn
oil
is
rich
in
phytosterols,
56
to
60%
of
phytosterols
in
corn
oil
occur
as
steryl
esters,
while
esterified
sterol
content
is
much
lower
in
other
vegetable
oils
[71].
The
majority
of
veg-
etable
oils
contain
1–5
g/kg
of
plant
sterols,
while
corn
oil
contains
5.13
to
9.79
g/kg
of
plant
sterols
[72].
Crude
corn
oil
contains
a
higher
plant
sterol
content
(8.09–15.57
g/kg)
than
the
refined
oil
(7.15–9.52
g/kg)
[72,73].
In
the
corn
kernel,
the
germ
fraction
con-
tained
the
highest
amount
of
oil
(24.2%–30.7%),
while
endosperm
and
pericarp
factions
only
contained
0.4%–1.2%
oil.
Sitosterol
is
the
predominant
phytosterols
found
in
corn,
which
accounts
for
approximately
77%–87%
of
all
phytosterols
extracted
from
corn,
followed
by
campestanol,
which
accounts
for
13%–23%.
Stigmas-
terol
and
delta5-avenasterolare
were
found
in
trace
amount
in
corn.
The
endosperm
fraction
contained
the
highest
level
of
phy-
tostanols.
[74].
High
intakes
of
plant
sterols
(1.6
g
per
day)
can
lower
serum
LDL
and
total
cholesterol
concentrations
without
affecting
HDL
cholesterol
concentration
in
humans
[75].
The
proposed
mech-
anism
is
that
phytosterols
and
cholesterol
compete
for
the
micelle
formation
in
the
intestine,
thus
inhibiting
the
absorption
of
choles-
terol
[76].
3.5.
Other
bioactive
compounds
Besides
the
major
bioactive
compounds
listed
above,
there
are
some
other
bioactive
compounds
found
in
corn
[77].
Four
types
of
resistant
starches
have
been
identified
based
on
their
struc-
tures,
natures
and
sources
[78,79].
Type
2
resistant
starch
(RS2),
a
starch
difficult
to
digest
due
to
its
native
granules
structure,
is
the
major
resistant
starch
found
in
corn
and
presented
at
a
high
level
in
high
amylose
corn.
High
amylose
corn
(70%
amylose)
has
the
highest
amylose
content
among
all
whole
grains
[80].
Due
to
the
nature
of
starch
granules,
RS2
is
resistant
to
digestion
in
intes-
tine
exhibiting
beneficial
effect
on
blood
sugar
and
colon
health
[81].
Lignins
(lariciresinol,
matairesinol,
pinoresinol,
and
secoiso-
lariciresinol)
is
a
common
bioactive
compounds
found
in
all
whole
grains,
with
health
benefits
such
as
anticancer
and
antioxidant
effect
[82].
Secoisolariciresinol
is
present
in
corn
at
12
g/100
g
DW
and
lariciresinol
is
present
at
11
g/100
g
DW,
while
matairesinol
and
pinoresinol
are
not
presented
in
corn
[83].
4.
Health
benefits
Whole
grain
corn
is
rich
in
nutrients
and
bioactive
compounds
including
fiber,
vitamins,
minerals,
and
phytochemicals.
More
and
more
scientific
evidence
suggests
the
regular
consumption
of
190
S.
Siyuan
et
al.
/
Food
Science
and
Human
Wellness
7
(2018)
185–195
Fig.
4.
Structures
of
carotenoids
found
in
corn:
ˇ-carotene
(A),
˛-carotene
(B),
ˇ-cryptoxanthin
(C),
Lutein
(D),
and
Zeaxanthin
(E)
(Adopted
from
Liu,
2007).
whole
grains
reduce
the
risk
of
developing
chronic
diseases,
includ-
ing
CVD,
type-II
diabetics,
overweight
and
obesity,
and
digestive
disorders
(Tables
4
and
5).
4.1.
Cardiovascular
disease
(CVD)
It
has
been
reported
by
the
World
Health
Organization
that
17.7
million
people
died
from
CVDs
in
2015,
and
by
2030,
23
million
people
will
die
of
CVD
annually
around
the
world
[84].
Many
recent
epidemiological
studies
and
clinic
interventional
trials
suggest
a
strong
association
of
the
increased
consumption
of
whole
grains
and
whole
grain-derived
products
with
the
reduced
risk
of
CVD
[5–7,85,86].
Tighe
et
al.
reported
that
whole
grain
consumption
and
CVD
on
middle
aged
people
and
suggested
that
3
portions
of
daily
consumption
of
whole
grain
foods
lowered
the
risk
of
CVD
by
low-
ering
blood
pressure
in
a
randomized
controlled
trial
(RCT).
All
233
participants
were
separated
into
three
groups
treated
with
refined,
wheat,
and
oat
plus
wheat
diets.
After
16
weeks,
significant
decreases
of
both
systolic
and
diastolic
blood
pressure
in
the
oat
plus
wheat
group
was
observed.
The
researchers
suggested
that
the
blood
pressure
lowering
effect
was
contributed
by
the
high
amount
of
viscous
soluble
fiber
(ˇ-glucans)
in
whole
grains
[7].
Holloender
et
al.
conducted
a
meta-analysis
of
randomized
controlled
trials
(RCT)
and
concluded
whole
grains,
including
corn,
rye,
and
brown
rice,
lowered
risk
of
CVD
(20%–25%
reduction)
when
compared
with
the
refined
grains.
The
mechanism
is
due
to
lowering
LDL
choles-
terol
and
total
cholesterol
without
effects
on
HDL
cholesterol
or
triglycerides
[85].
Mellen
et
al.
reported
a
meta-analysis
on
seven
prospective
cohort
studies
with
quantitative
measures
of
dietary
whole
grains
and
clinic
CVD
outcomes.
They
found
that
consumption
of
whole
grains
(corn
meal
and
popcorn,
barley,
buckwheat,
millet,
oatmeal,
quinoa,
brown
rice,
rye,
and
sorghum)
(2.5
servings/day
vs
0.5
serv-
ings/day)
was
associated
with
a
21%
lower
risk
of
CVD
(0.79,
with
95%
CL:
0.73-0.85).
On
contrary,
the
consumption
of
refined
grains,
in
which
only
the
carbohydrate
rich
endosperm
was
retained,
was
not
associated
with
the
reduced
risk
of
CVD,
suggesting
the
bran
and
germ
fractions
carry
more
health
benefits
than
the
endosperm
fraction
[8].
Campbell
and
Fleenor
reported
a
case
control
study
on
22
obese
young
men
and
found
that
whole
grains
exhibited
a
significant
effect
on
reducing
obesity-associated
aortic
stiffness,
which
could
lead
to
CVD.
This
study
suggested
that
the
synergistic
effects
of
phy-
tonutrients,
micronutrients,
and
macronutrient
in
whole
grains
are
contributed
to
the
reduced
risk
of
CVD.
However,
the
fiber
content
did
not
contribute
to
the
beneficial
effects
in
this
study
[87].
Based
on
the
data
collected
from
two
prospective
cohort
studies,
74,341
women
in
the
Nurses’
Health
Study
(1984–2010)
and
43,744
men
in
the
Health
Professionals
Follow-Up
Study
(1986–2010),
Wu
et
al.
reported
that
with
each
serving
of
whole
grain
increment,
the
pooled
hazard
ratios
(HR)
for
CVD
was
0.91
with
95%
confi-
dence,
with
each
serving
bran
only
intake,
HR
for
CVD
was
0.80,
while
with
serving
germ
only
intake,
no
effect
was
observed.
The
S.
Siyuan
et
al.
/
Food
Science
and
Human
Wellness
7
(2018)
185–195
191
Fig.
5.
Structures
of
tocopherols
and
tocotrienols
found
in
corn.
Fig.
6.
Structures
of
common
plant
sterols
found
in
corn.
whole
grain
products
in
this
study
included
corn
products
such
as
whole
cornmeal,
whole
corn
flours,
and
popcorn.
It
was
con-
cluded
that
the
intake
of
WGs,
including
whole
corn
products,
is
negatively
associated
with
the
increased
mortality
of
CVD
[88].
Recent
cohort
study
and
meta-analysis
also
suggested
the
nega-
tive
association
between
whole
grain
intake
and
the
risk
of
CVD
[89–91].
4.2.
Type
II
diabetics
It
is
estimated
by
World
Health
Organization
that
people
who
live
with
diabetes
increased
from
108
million
in
1980
to
422
million
in
2014,
and
1.5
million
deaths
was
related
to
diabetes
in
2014
[92].Most
the
people
who
have
diabetes
have
type
2
diabetes
and
they
are
unable
to
use
insulin
produced
by
their
body
properly.
192
S.
Siyuan
et
al.
/
Food
Science
and
Human
Wellness
7
(2018)
185–195
Table
4
Carotenoid
content
of
white,
yellow,
red,
blue,
and
high-carotenoid
corn
[32,33].
Carotenoid
content
(g/100
g
of
dry
weight
of
corn)
type
of
corn
lutein
zeaxanthin
ˇ-cryptoxanthin
ˇ-carotene
˛-carotene
white
5.73
±
0.18
6.01
±
0.06
1.27
±
0.06
4.92
±
0.18
0.04
±
0.1
yellow
406.2
±
4.9
353.2
±
23.1
19.1
±
1.2
33.6
±
1.2
11.7
±
1.8
red
121.7
±
12.1
111.9
±
9.2
13.1
±
1.8
20.2
±
1.9
N.D.
blue
5.17
±
0.49 14.3
±
1.0 3.41
±
0.39
23.1
±
2.1
N.D.
high
carotenoid
245.6
±
9.4
322.3
±
10.7
23.1
±
1.0
45.8
±
3.9
N.D.
N.D.
stands
for
not
determined.
Table
5
Vitamin
E
content
in
yellow
corn
[67].
mg/kg
of
dry
weight
corn
˛-tocopherol
3.7
˛-tocotrienol
5.3
ˇ-tocopherol
0.2
-tocopherol
45.0
-tocotrienol 11.0
ı-tocopherol
1.0
ı-tocotrienol
0.4
Total
66.9
A
number
of
recent
reviews
[10,11,93,94]
and
epidemiology
studies
[9,12]
have
suggested
that
the
consumption
of
whole
grains
and
whole
grain
derived
products
are
associated
with
reduced
risk
of
type
2
diabetes.
Dietary
magnesium,
fiber
and
vitamin
E,
which
engage
in
the
insulin
metabolism,
are
found
in
whole
grains.
Reg-
ular
consumption
of
these
substances
from
whole
grains
may
help
regulate
the
insulin
levels.
Also,
whole
grains
may
help
regulate
insulin
levels
by
the
beneficial
effects
of
releasing
satiety
feeling
and
lowering
body
weight
index
(BWI)
[16].
High
amylose
content
is
positively
associated
with
the
high
type
2
resistant
starch
content.
Human
studies
with
arepas,
made
of
cornstarch,
suggested
that
high
amylose
corn
consumption
is
asso-
ciated
with
a
lower
metabolic
response
[95].
In
this
study,
blood
and
serum
insulin
responses
of
people
who
consumed
ordinary
corn
arepas
were
significantly
higher
than
those
who
consumed
high
amylose
corn
arepas,
suggesting
that
the
high
amylose
content
in
corn
is
responsible
for
the
slower
metabolic
response.
[95].
Behall
et
al.
reported
that
after
5
weeks
of
consumption
of
high
amylose
starch
diet
compared
to
the
amylopectin
starch
diet,
glucose
and
insulin
responses
were
significantly
lower
[96].
In
a
long-term
study,
Behall
et
al.
investigated
24
men,
10
of
them
were
healthy
and
acted
as
the
control
group
and
14
of
them
were
hyper-
insulinemic
(HI)
and
acted
as
the
treatment
group.
HI
is
not
type
2
diabetes
but
often
seen
in
the
early
stage
of
the
disease.
Sub-
jects
consumed
products
made
with
either
high
amylopectin
(70%
amylopectin,
30%
amlyose)
or
high-amylose
starch
(70%
amylose,
30%
amylopectin).
After
14
weeks,
glucose
response
in
both
groups
were
similar,
but
the
insulin
response
curves
of
the
high
amylose
consumption
group
were
much
lower
than
the
high
amylopectin
group.
Fasting
triglyceride
concentration
was
also
much
lower
in
the
high
amylose
consumption
group
than
of
the
high
amylopectin
consumption
group.
The
results
suggest
that
long
term
consump-
tion
of
high
amylose
corn
starch
may
have
beneficial
effects
on
people
with
HI
and
diabetes
by
normalizing
insulin
response
[97].
A
latter
research
study
conducted
by
Behall
et
al.
on
25
healthy
subjects,
13
men
and
12
women
with
different
concentration
of
amylose
(30%–70%),
found
similar
results
to
the
study
above
that
consumption
of
a
meal
in
high
amylose
corn
starch
lower
peak
com-
pare
to
that
in
low
amylose
corn
starch.
This
study
also
found
that
intake
of
high
amylose
corn
starch
also
lowered
peak
glucose
levels.
In
addition,
the
results
suggested
that
amylose
content
needed
to
be
greater
than
50%
to
have
a
significant
effect
on
lowering
glucose
and
insulin
levels
[98].
Resistant
starch
from
corn
has
exhibited
beneficial
effects
on
lowering
type
2
diabetes.
Yamada
et
al.
reported
that
daily
con-
sumption
of
6
to
12
g
of
RS2,
which
is
retrograded
amylose,
has
beneficial
effects
on
postprandial
glucose
and
insulin
levels
(Yamada
et
al.,
2005).
High
amylose
starch
is
a
type
of
RS
with
amy-
lose
content
usually
ranging
from
30
to
70%
of
the
total
weight.
A
study
conducted
by
Maki
et
al.
on
beneficial
effects
of
resistant
starch
from
high
amylose
corn
on
overweight
and
obese
adults
(11
men
and
22
women,
33
total)
suggested
that
RS2
from
corn
increased
insulin
sensitivity
only
on
men
and
women
are
less
sen-
sitive
to
change
of
circulating
free
fatty
acids
[99].
4.3.
Obesity
In
2016,
the
estimated
worldwide
overweight
and
obesity
pop-
ulation
were
1.9
billion
and
650
million,
respectively
[100].The
number
of
obesity
nearly
tripled
since
1975.
Results
from
short-
term
[14]
and
long-term
[13]
epidemiology
studies
support
that
the
intake
of
whole
grains
and
whole
grain
derived
foods
are
inversely
associated
with
the
increased
risk
of
obesity.
In
a
prospective
cohort
study,
Liu
et
al.
conducted
research
on
the
association
between
whole
grains
and
dietary
fiber
intake
and
development
of
obesity
on
74,091
US
female
nurses.
Over
the
12-
year
period,
women
who
consumed
more
dietary
fiber
weighed
1.52
kg
less
than
those
who
had
only
a
slight
increase
intake
of
dietary
fiber.
Women
who
consistently
consumed
more
whole
grains
weighted
less
than
those
who
consumed
less
whole
grains.
The
research
also
indicated
that
obesity
was
positively
related
to
the
intake
of
refined
grains
[13].
Higgins
et
al.
conducted
research
on
replacing
total
carbohydrates
with
0%–10.7%
RS
(retrograded
amylose),
which
is
abundant
in
high
amylose
corn
starch.
The
results
indicated
that
replacement
of
5.4%
or
more
of
total
dietary
carbohydrates
with
corn
RS
significantly
increased
post-prandial
lipid
oxidation,
suggesting
the
consumption
of
corn
RS
decreases
fat
accumulation
[24].
Corn
bran
may
have
a
benefit
on
lowering
weight
gain
and
obe-
sity
by
providing
satiety
feelings.
A
study
of
satiety
response
of
high
fiber
muffins
(8.0–9.6
g
fiber)
versus
low
fiber
food
(1.6
g
fiber)
con-
ducted
by
Willis
et
al.
on
20
healthy
men
and
women
suggesting
that
muffin
with
resistant
starch
and
corn
bran
had
the
most
impact
on
satiety
[101].
Oat
and
barley
bran
seems
do
not
exhibit
the
simi-
lar
effect
as
corn
bran
of
providing
better
satiety
response
than
the
control
low
fiber
diet
[102].
4.4.
Digestive
health
A
daily
consumption
of
20
g
resistant
starch
had
a
beneficial
effect
on
promoting
digestive
heath
[103].Corn
and
corn
derived
products
are
rich
in
resistant
starch,
a
form
of
insoluble
dietary
fiber.
According
to
the
USDA
national
nutrient
data
base,
7.3
g
of
dietary
fiber
presented
in
every
100
g
of