The role of phytic acid in legumes: Antinutrient or beneficial function?

Abstract

This review describes the present state of knowledge about phytic acid (phytate), which is often present in legume seeds. The antinutritional effects of phytic acid primarily relate to the strong chelating associated with its six reactive phosphate groups. Its ability to complex with proteins and particularly with minerals has been a subject of investigation from chemical and nutritional viewpoints. The hydrolysis of phytate into inositol and phosphates or phosphoric acid occurs as a result of phytase or nonenzymatic cleavage. Enzymes capable of hydrolysing phytates are widely distributed in micro-organisms, plants and animals. Phytases act in a stepwise manner to catalyse the hydrolysis of phytic acid. To reduce or eliminate the chelating ability of phytate, dephosphorylation of hexa- and penta-phosphate forms is essential since a high degree of phosphorylation is necessary to bind minerals. There are several methods of decreasing the inhibitory effect of phytic acid on mineral absorption (cooking, germination, fermentation, soaking, autolysis). Nevertheless, inositol hexaphosphate is receiving increased attention owing to its role in cancer prevention and/or therapy and its hypocholesterolaemic effect.

Full text

J. Physio!. Biochem., 56 (3), 283-294, 2000
The role of phytic acid in legumes:
antinutrient or beneficial function?
G. Urbano, M. Lopez-jurado, P. Aranda, C. Vidal-Valverde, E. Tenorio and J.Porres
Departamento de Fisiologfa e Instiruto de Nutrici6n y Tecnologfa de Alimentos. Uni-
versidad de Granada.
(Received on July 27, 2000)
G.
URBANO,
M.
L6PEZ-JURADO,
P.
ARANDA,
C.
VIDAL-VALVERDE,
E.
TENORIO
and J. PORRES. The role
of
phytic acid in legumes: antinutrient or
beneficial function? (minireview). J. Physio!. Biochem., 56 (3), 283-294, 2000.
This review describes the present state of knowledge about phytic acid (phytate),
which is often present in legume seeds. The antinutritional effects of phytic acid pri-
marily relate to the strong chelating associated with its six reactive phosphate groups.
Its ability to complex with proteins and particularly with minerals has been a subject
of investigation from chemical and nutritional viewpoints.
The
hydrolysis of phytate
into inositol and phosphates or phosphoric acid occurs as a result of phytase or
nonenzymatic cleavage. Enzymes capable of hydrolysing phytates are widely dis-
tributed in micro-organisms, plants and animals. Phytases act in a stepwise manner
to catalyse the hydrolysis of phytic acid. To reduce
or
eliminate the chelating ability
of phytate, dephosphorylation of hexa- and penta-phosphate forms is essential since
a high degree of phosphorylation is necessary to bind minerals. There are several
methods of decreasing the inhibitory effect of phytic acid on mineral absorption
(cooking, germination, fermentation, soaking, autolysis). Nevertheless, inositol hexa-
phosphate is receiving increased attention owing to its role in cancer prevention
and/or
therapy and its hypocholesterolaemic effect.
Key words: Phytate, Inositol phosphates,
Legumes,
Mineralabsorption, Cancer prevention,
Hypocholesterolemic
effect.
Phytic
acid (phytate), myoinositol
1,2,3,4,S,6-hexakis
(dihydrogen
phos-
phate), is often present in legume seeds
Correspondence to G. Urbano
(Tel.:
958 24 38 79;
Fax:
95824
89 59;
e-mail:
mlopezj@ugr.es).
(10).
It
is a chelating agent for cations and
aform of cations as well as for phospho-
rus storage in many seeds (16). Phytic acid
and its salts represent the majority of the
phosphorus in plant legume seeds and
monogastric species have a limited ability

284 G.
URBANO,
~l.
L6PEZ-jURADO,
P.
ARANDA,
C.
VlDA[·VALVERDE
er at.
to
hydrolyse
phytates
and
release
phos-
phate
for
absorption.
The
anti
nutritional
effects
of
phytatc
primarily
relate to
the
strong
chelating
ability associated
with
its
six reactive
phosphate
groups.
Multivalent
cations
such
as
Ca
2+ , Mg 2+, Fe2+
and
2n
2+
are
particularly
susceptible
and
form
insoluble, indigestible complexes (19, 32,
36, 105, 128).
Phytate
rapidly
accumulates
in seeds
during
the
ripening
period
(1, 3, 4,
5, 69)
accompanied
by
other
storage
sub-
stances
such
as starch
and
lipids.
The
accumulation
site
of
phytic
acid
in
dicotyledonous
seeds
(castor,
peanuts,
cotton
seeds, beans, etc.) is in
the
globoids
(which
is
one
of
the
inclusions
of
the
pro-
tein
body)
(41, 58, 116).
The
proportion
of
phytic
acid reaches up to
60-80%
of
the
dry
weight
of
globoid
in
dicotyledons
(54,
119).
The
presence
of
phytic
acid
within
the
globoids
of
dicotyledonous
seeds has
been
shown
for
peanuts,
soybeans
(10),
and
broad
beans
(66).
Major
components
of
globoids
from
peanuts
(97) arc
protein
(35.1
%),
ph
ytic
acid (28.0%),
and
metals
(Ca, Mg,
and
K) (5.0%).
The
globoidal
fraction
accounts
for
about
50%
of
the
total
magnesium
and
phytic
acid
and
13
and
80%
of
potassium
and
calcium,
respectively,
in
the
protein
bodies
of
peanuts.
Current
literature suggests
that
phytate
primarily
occurs
as
potassium
magnesium
salt in
broad
beans (53)
and
as
calcium
magnesium-potassium
salt in
soy
beans (29).
Phytates
impact
enzyme
activity
with
evidence
of
anegative effect
for
key
diges-
tive
enzymes
including
amylase,
pepsin
and
trypsin
(17, 49),
The
interaction
of
Ca
2+
and
phytate
facilitates
further
bind-
ing to
cations
in
the
diet,
thereby
reducing
solubility
and
nutrient
availability (15,
34).
The
amount
of
phytic
acid varies
from
0.40%
to
2.06%
in legumes (97).
In
many
J. Physiol. Biochem., 56 (3), 2000
cases,
the
phytic
acid
content
is
not
con-
sidered
to be
absolute
and
may
vary
depending
on
the
variety, climatic
condi-
tions, location,
irrigation
conditions,
type
of
soil,
and
year
during
which
the
plants
grow.
Phytic acid
phosphorus
constitutes
the
major
portion
of
total
phosphorus
in
some
seeds.
The
ability
of
phytic
acid to
complex
with
proteins
and
particularly
with
miner-
als has been a
subject
of investigation
for
several
reasons,
predominantly
from
chemical
and
nutritional
viewpoints.
Crystalline
preparation
of
phytate-pro-
tein
complex
at
pH
4.0 has
been
reported
(14)
from
the
Great
Northern
bean
(Phaseo/us vulgaris L.)
and
several
physic-
ochemical
properties
have
been
reported.
The
interaction
between
phytic
acid
and
proteins
is
thought
to be
of
the
ionic
type
(26).
The
interaction
between
phytatc
and
proteins
leads to decreased
solubility
of
proteins
(14, 111). It has also
been
shown
that
calcium
ions
interact
with
protein
and
phytate
to
further
decrease
the
solubility
of
proteins
(102, 126).
BARRE
et al. (8)
reported
that
the
phytatc-protein
com-
plexes
were
less subject to
proteolytic
attack
than
the
same
protein
alone.
Complexation
between
phytate
and
proteins
has
been
reported
for
several
proteins
(20,29,39,79,81-83,89,95,
101,
125)
including
those
from
Great
Northern
beans (14),
soybean
flakes (79),
soybeans
(101),
peanuts
(46) and black
gram
(95).
Conceivably,
if
proteins
are to
form
com-
plexes
with
phytic
acid,
they
have to have
some
electrical
charge
on
them
which
is
possible at
below
or
above
the
isoelectric
pH
of
the
protein.
The
nutritional
implications
of
phy-
tate-protein
complexes
are
still
under
scrutiny
(77).
The
reduced
solubility
of
proteins
as a
result
of
protein-phytate
complex
can adversely affect certain
func-

PHYTIC
ACID
ROLE
IN
LEGUMES
285
tiona
lproperties of proteins which are
dependent
on
their
hydration
and solubil-
ity,
such
as
hydrodynamic
properties (vis-
cosity, gelation, etc.), emulsifying capaci-
ty, foaming and foam performance, and
dispersibility in aqueous media. In addi-
tion, reduced bioavailability of
phospho-
rus is a distinct possibility.
The
nutritionally
important
minerals,
such
as calcium, magnesium, copper,
iron
(Fe2+ and Fe3+) and
others
form
com-
plexes
with
phytic
acid, resulting in
reduced solubility of
the
metals. Synergis-
tic effects of divalent metal ions in the for-
mation
of metal-phytate complexes have
also been reported. Decreased iron avail-
ability due to iron-phytate complexes is
also of concern (67). Magnesium availabil-
ity also decreases
through
complexation
with
phytate.
Nutritional
implications
Digestion
of
phytate
and
its bioavail-
ability.- In mature legumes, the major
portion
of the total
phosphorus
is present
in
the
form of phytate.
The
hydrolysis of
phytate
into inositol and phosphates
or
phosphoric
acid occurs
due
to phytase
(12,21,31,33,51,52,56-60,74,87,90,92,
93, 124) or to nonenzymatic cleavage (37,
74, 113). Enzymes capable of hydrolysing
phytates
are widely distributed in micro-
organisms, plants and animals (129). Phy-
tases act in a stepwise
manner
to catalyse
the
hydrolysis of phytic acid to myo-inos-
ito
Iintermediates (IPs, IP4, IP3, IP2,IP)
and
myoinositol,
ZYTA
(130) studied the
phytate
degrading capacity of Aspergillus
niger
and
concluded
that
phytase specifi-
cally splits
phytate
while an acid
phos-
phatase attacks hydrolysis intermediates
and accelerates the reaction.
If
phospho-
rus availability is the
major
objective,
J. Physiol. Biochem., 56 (3), 2000
complete
hydrolysis
is desirable. To
reduce
or
eliminate the chelating ability of
phytate, dephosphorylation of hexa- and
penta-phosphate forms is
most
important
since a high degree of
phosphorylation
is
necessary to
bind
minerals (104) and affect
enzyme
activity (49). Responses to
phy-
tase have included an improvement in
growth
rate and feed conversion efficien-
cy in
both
pigs and chickens.
Phosphorus
retention
has
been
substantially improved
and as a consequence the
amount
in faeces
reduced. Phytase addition
to
piglet diet
improved
the
apparent
absorption
of
Mg2+
and
Zn2+and the
absorption
of Fe2+
and
Ca
2+tended to
improve;
Mn2+reten-
tion
was not affected by phytase adition
(86). Anew phytase
enzyme
has been
studied
by
STAHL
et al. (112)
which
improves the bioavailability of
phytate
phosphorus
to weaning pigs.
The
availability of
phosphorus,
when
present in the
form
of
phytate, depends on
the species, the age of
the
experimental
animal, and the level of phytase activity in
the intestinal tracts of the specific species.
Phytate
is regarded generally as being less
biologically available than
most
inorganic
phosphorus.
FERNANDEZ
et al. (28) and
NESTARES
et al. (72) have
reported
that
inositol
hexaphosphate
from
raw
and
processed faba bean and chick peas is
transformed
during
digestion and more
phytic
acid
phosphorus
is available.
Many
factors, including
the
nature of
the diet, can affect the level of
phytate
uti-
lization.
High
levels of
Ca
2+reduce while
high levels of vitamin D3 increase,
phytate
phosphorus
retention. Aspecific role for
the active metabolite of vitamin D3is
demonstrated by the finding
that
adding
1,25-
(OH)z
-cholecalciferol
to
diets low
in
phosphorus
but
adequate in vitamin D3
increased
phytate
retention.
In
the
absence of dietary fractions capable of

286 G.
URBANO,
M.
LOPEZ-JURADO,
P.
ARANDA,
C.
VIDAL·VALVERDE
er al.
binding phytate, it may be possible
that
phytate is almost entirely digested.
Oral
administration of IP6in solution
to
rats
resulted in rapid dephosphorylation in the
upper
portion
of the gastrointestinal tract,
followed by absorption and transfer of
myo-inositol to the liver, muscles and skin
(103).
Effects
of
phytate on minerai bioavaii-
abiiity.- Phytic acid in plant foods com-
plexes with dietary essential minerals such
as calcium, zinc, iron, and magnesium and
makes them biologically unavailable for
absorption(77). The mechanism by which
phytate affects mineral nutrition is
not
clearly understood. Most research (6, 11,
37,55,63,70,71,75,78,113,121)
suggests
that formation of insoluble phytate-metal
complexes in the intestinal tract prevents
metal absorption.
RACKIS
and
ANDERSON
(89) reported
that
reduced availability of
essential minerals by either phytate or
phytate-protein complexes in legumes and
other protein foods depends on several
factors, such as:
1. Ability of endogenous carriers in the
intestinal mucosa to absorb essential min-
erals bound to phytate and other dietary
substances.
2.
Concentration
of
phytic
acid in
foodstuff.
3. Concentration of minerals in food-
stuff.
4. Digestion or hydrolysis of phytate
by phytase enzyme in the intestine.
5. Phytate inhibition.
6. Processing of products or methods
of processing.
Other
food
constituents,
such
as
dietary fiber, polysaccharides, oxalates,
and polyphenolic compounds, may also
playa
major role in mineral bioavailabili-
ty. Dietary fiber in whole wheat bread
J. Physiol. Biochem., 56 (3), 2000
accounts for most of the
poor
availability
of minerals (42, 76, 98, 99).
DAVIES
et ai.
(22) have suggested that phytate rather
than fiber largely determines the availabil-
ity of zinc for absorption.
DAVIES
and co-
workers (22-25) have published several
reports dealing
with
the bioavailability of
different minerals from high-phytate
and
high-fiber cereals and legumes.
Effects of processing
on
phytates
Cooking.-
The
correlation of phytate
with the cooking quality of legume seeds
has been reported (61, 100).
CREAN
and
HAISMAN
(20) studied
the
interaction
between
phytic
acid and
the
divalent
cations, calcium and magnesium, during
the cooking of dried peas. They found
that phytic acid in dried peas exists whol-
ly as a water-soluble salt (probably potas-
sium phytate),
but
on cooking, some of it
combines with the calcium and magne-
sium in the pea to form insoluble calcium
and magnesium phytate.
Cooking processes decrease
both
water
and acid-extractable phytate phosphorus
in legumes (50).
Poor
extractability of
phytate Pwith water and.
HCI,
noticed
by
KUMAR
et ai. (50) in cooked legumes,
could be due to formation of insoluble
complexes between phytate P and
other
components in legumes during cooking,
which subsequently could
not
be extract-
ed with water or
HCI.
REDDY
et al. (96)
did
not
find any breakdown of phytate P
during cooking of black gram seeds and
cotyledons. Whatever the losses in total P
and phytate P
they
observed during
short-
time cooking,
they
were due to leaching of
those components into the cook water.
Cooking for 45 min at
115°C
caused
small losses in total P and phytate con-
tents into the cooking water which may

PHYTIC
ACID
ROLE
IN
LEGUMES
287
have been due to reabsorption of phytate
by beans from cooking water.
Germination.- The phytate is utilized
as a source of inorganic phosphate during
seed germination and the inorganic form
becomes available for purposes of plant
growth
and development.
The
liberation
of phosphate from
phytate
occurs by
enzyme hydrolysis. Phytase is the cur-
rently accepted enzyme, which is respon-
sible for the complete hydrolysis of
phy-
tate (inositol hexaphosphate) into inositol
and
phosphate.
Germination
reduces
and/or
eliminates considerable amounts
of phytate from the seeds or grains (114).
Disappearance of phytate during germina-
tion
depends on the phytase activity. A
rapid rise in phytate activity was observed
commencing after 48h germination of
bush beans (124). Germination reduced
the phytic acid content of chickpea and
pigeonpea seeds by over 60% and soy-
bean by about 40% (18).
Fermentation.- Fermentation of cereals
and legumes appreciably reduces the
phy-
tate content owing to endogenous phytase
of cereals and that of added yeast and
other
useful microorganisms (40).
SUDAR-
MAD]I
and
MARKAKISL
(114) studied the
changes in phytic acid
during
tempeh
preparation by fermenting boiled soy-
beans with Rhizopus oligosporus. Boiling
of soybeans resulted in a
reduction
(14.0%) of phytic acid. Phytic acid was
reduced by about one third in soybeans as
aresult of fermentation
with
mold (R.
oligosporus). The decrease in phytic acid
was accompanied by an increase in inor-
ganic phosphorus. They concluded that
the reduction in phytic acid obtained was
due to the action of the enzyme, phytase,
which was mixed with salt solution
pro-
duced by mold during fermentation.
J. Physio!. Biochem., 56 (3), 2000
Soaking, autolysis and other processes.-
There have been many reports of the pres-
ence of a phytase in legumes. The effects
of time, temperature,
pH,
soaking, and
heating on the autolysis of phytate in Cal-
ifornia small white beans were evaluated
by
CHANG
et al. (21). At
50°C,
the hy-
drolysis of phytate from the beans was
31.0% and it reached a maximum of 49%
at
60°C.
These results suggest an initia-
tion of enzyme activity at about
60°C
and
inactivation of the enzyme at 70 "C. They
also reported that after 10 h of incubation
of beans at
60°C,
only
anegligible
amount
of phytic acid was found in the
beans, approximately 75% of the total
phytic acid being hydrolysed and 25%
being diffused into the water in which the
beans were incubated. The autolysis of
phytate in beans was slow at
both
35° and
55°C.
TABEKHIA
and
LUHL
(115) demonstrat-
ed a phytate decrease of 7.7,8.1, 13.2, and
19.1%, respectively, for black-eyed beans,
red kidney beans, mung beans, and pink
beans
on
soaking these beans for 12 h at 24
°C in tap water.
!YER
et al. (43) found that
when pinto, Great
Northern,
and red kid-
ney beans were soaked in distilled water
for 18 h at room temperature, the phytate
content of beans was appreciably reduced
(52.7, 69.6,
and
51.7%, respectively).
However, they noticed somewhat less
phytate hydrolysis when the beans were
soaked in a mixed salt solution (2.5%
sodium chloride plus 1.5% sodium bicar-
bonate plus 0.5% sodium carbonate plus
1.0% sodium tripolyphosphate) at
pH
7.0
and a
room
temperature of
22°C.
Removal
of
phytates.- Several process-
ing methods (germination, soaking, auto-
claving, autolysis, fermentation, special
treatments, etc.) discussed in the previous
section are shown to reduce or remove

288 G.
URBANO,
M.
L6PEZ.JURADO,
P.
ARANDA,
C.
VIDAL·
VALVERDE er al.
considerable amounts of
phytate
in
legumes (18). Differential solubility meth-
ods to selectively precipitate and remove
phytate from soybeans have been investi-
gated. Such methods usually involve
extraction
with
water or alkali, followed
by careful
pH
adjustment so that the
phy-
tate (insoluble and precipitated) can be
removed by centrifugation or filtration.
McKINNEY
et al. (64) reported about 80%
removal of
phytate
from the alkaline
soy-
bean extract by precipitation with calcium
and barium ions and subsequent centrifu-
gation. In their studies, they were able to
recover about 80% of the soybean meal
nitrogen in
the
process of protein concen-
tration described above (while removing
the phytate simultaneously).
Ultrafiltration
seems
promising
for
selective removal of low molecular weight
components such as phytic acid. Ultrafil-
tration offers the advantages of mild
pro-
cessing conditions and selectivity (ability
to discriminate different molecules of dif-
fering shape and size).
OKUBO
et al. (82)
employed
ultrafiltration for specific
removal of phytic acid from soybeans by
first dissociating protein-bound phytate.
Phytate dissociation was affected by
phy-
tase (at
pH
5.2) addition of 0.5M
CaCh
at
pH
3.0.
Beneficial effects of
phytic
acid
Anticancerfunction.- The reputation of
inositol hexaphosphate (IP6) has had a
roller coaster ride ever since its discovery;
it has undergone alternate eminence and
infamy. Its popularity early on stemmed
mostly from the fact that it is the chief
storage form of phosphorus for germinat-
ing seeds. Biochemists and cell biologists
have been interested in the phosphoryla-
tion and dephosphorylation of IP6and
how
this might affect cellular functions.
J. Physio!. Biochem., 56 (3), 2000
Lower inositol phosphates (IPI-4) are rec-
ognized as intracellular messengers.
The
second messenger role of inositol 1,4,5-
trisphosphate [(1,4,5) IP3] in bringing
about ahost of cellular functions includ-
ing mitosis via mobilizing intracellular
Ca2+is well
recognized;
1,3,4,5-tetrak-
isphosphate (IP4) has also been shown to
induce Ca2+sequestration. Higher forms
of IP, inositol1,3,4,5,6-pentakisphosphate
(IPs) and inositolhexakisphosphate, are
also abundant and represent the bulk of IP
content of mammalian cells.
Why
should
there be an intracellular abundance of
these compounds, which are presumed
toxic by nutritionists or inert at best by
biochemists (65), although we
know
very
little of their purpose? Recent studies
provide an increased understanding of the
functional roles of IP
s,6.
Physiological
functions of IPs include regulation of
the
affinity of avian haemoglobin for oxygen,
and along
with
IP6it may be involved in
neuronal excitation (65). Recent demon-
strations that IP
s,6
are precursors of sever-
al derivatives
that
turnover rapidly sug-
gest that these forms of IP are not inert
and that they play a more dynamic role
than has previously been appreciated (65).
One
aspect of IP6receiving increased
attention is its role in cancer prevention
and
lor
therapy (85, 110, 123).
Because IP6undergoes dephosphoryla-
tion to IP 1-Sand IP3 is central in cellular
signal transduction and intracellular func-
tion, IP6could exert its anticancer func-
tion through lower inositol phosphates by
entering into the intracellular IP pool (47,
107-109).
Different species (rats and mice) and
different colon carcinogens were used to
examine the effectiveness of IP6 across
species and agents. The effect of IP6 was
studied in cancer chemoprevention.
When
the treatment of
Na-IP
6was begun 1-2

PHYTIC ACID ROLE (N LEGUMES 289
weeks before
the
beginning of carcinogen
administration,
six
months
after
the
beginning
of
the
experiment,
animals
receiving IP6had fewer neoplasms
than
did
those
without
IP6,and the
tumours
were approximately
two-thirds
smaller.
It
was also observed that the rate of cell divi-
sion in the
nontumourous
colonic epithe-
lium of IP
6-treated
animals was similar to
that
of the normal
control
animals (109).
The
mitotic rate of
the
animals receiving
IP6 treatment
but
not
the
carcinogen was
normal
(106, 107, 109, 120).
In
order
to
study
whether
IP6might be
effective in cancer therapy even after the
beginning of cancer induction, IP6was
administered as late as 5
months
after car-
cinogen. Animals
showed
significantly
lower
tumour
size
when
given
IP
65
months
after initiation, atime when
most
of
the
animals are expected to have can-
cers (106).
The
fact that colorectal cancer
inhibition was observed
when
IP6treat-
ment
was begun as late as 5 months after
initiation
suggested
that
the
beneficial
action of IP6is
not
restricted to the
pre-
vention of
tumour
development
but
may
perhaps
apply in the treatment of existing
cancers as well.
The
antiturnour action of IP6may be
mediated via
lower
phosphorylated
forms
of Ins (lP), which are
important
in cell
division.
Mechanisms
of
antineoplastic activity.-
The
exact mechanisms
through
which
IP6 exerts its
antitumour
effects are
not
known.
It
has been
showed
(27, 68) that
IP6could be absorbed and might act intra-
cellularly.
SAKAMOTO
et al. (103)
demostrated that 3H_ IP6,
when
intragas-
trically administered to rats, is very quick-
ly absorbed from
the
stomach and
upper
small intestine and distributed to various
organs as early as 1
hour
after administra-
J. Physiol. Biochem.• 56 (3), 2000
tion,
The
radioactivity isolated
from
the
gastric epithelium at this time is associated
with Ins and
IP
I-6,and
that
in the plasma
and
urine
with Ins and
IPt,
indicating a
very rapid metabolism of
the
compound.
The
presence of InsP6 in
the
gastric
epithelium suggests that
the
intact mole-
cule is perhaps transported inside
the
cell
wherein it is rapidly dephosphorylated.
IP6induced
growth
inhibition and differ-
entiation of
HT
-29 cancer cells (73, 127).
Pilot studies of
the
absorption of IP6 by
malignant cells in vitro also demonstrate
that
the
cells almost instantaneously begin
to accumulate IP6intracellularly (122).
It
is reasonable to conclude that a cen-
tral pathway of
IP
6action is via
control
of
cell division; and that IP6reduces
the
rate
of cellular proliferation
both
in vivo and
in vitro.
On
the
basis of the above data,
the
fol-
lowing pathways may be operational for
the action of IP6:
Chelation
of
Fe3+and suppression
of
.OH
formation.-
The
1,2,3 (equatorial-
axial-equatorial) phosphate grouping in
IP6has a conformation
that
uniquely
pro-
vides a specific interaction
with
iron
to
inhibit completely its ability to catalyse
hydroxyl
radical formation. IP6has the
unique ability to remove
02
without
gen-
erating oxy-radicals.
Thus
it inhibits
.OH
production
by chelating
iron
in the pres-
ence of
02,
O2
-' or any reducing agent.
IP6
could
reduce active oxygen species-
mediated carcinogenesis
and
cell injury
via its antioxidative function. Protection
against cancer and a multitude of
other
applications are based on this antioxidant
function.
Chelation
of
divalent cation.- Mg2+
and
Zn
2+are essential for cell proliferation
including that in tumours, so deprivation

290 G.
URBANO,
M.
L6PEZ-JURADO,
P.
ARANDA,
C.
VIDAL-VALVERDE
er al.
of these cations may cause a decrease in
tumour
growth.
JARIWALLA
et al. (44) and
THOMPSON
and
ZHANG
(117) consider
that
InsP
6brings
about
its anticancer
effect by removing these cations.
But
the
observed rapid dephosphorylation
of
IP6
by
both
normal rats in vivo and malignant
cells in vitro to lower IPs, particularly
IPl-3, make the above
two
hypotheses less
credible; they are both based on the abili-
ty of six phosphate groups to chelate diva-
lent cations.
Participation in intracellular inositol
phosphate pool.- The administration of
IP6results in alterations in the cellular
inositol phosphate pool.
What
specifically
brings
about
the
observed biological
effects is yet to be elucidated. Apilot
study
demonstrated that 3hours after
0.05% IP6treatment, intracellular
Ca
2+
increases
by
57% (P<0.02) (108).
Although
the
current dogma is
that
an
increased intracellular Ca2+concentration
secondary to an increase in IP4,
may
be
responsible for mitosis, the data reported
by
SHAMDUDDIN
et al. (108) correspond
to a decrease in cell division.
The
fact
that
kinases and phosphate isomers may gen-
erate a large
number
of inositol phosphate
isomers, means that the highly
phospho-
rylated inositol may produce more mes-
senger molecules than currently has been
appreciated (65). Because Ins can be
con-
verted to IPl-3 and perhaps IP
4-6,
it is
quite plausible that the observed anti-
cancer effect
of
Ins given alone is perhaps
aresult of its conversion to metabolically
active InsP. IP 6has an enhancing effect on
NK
cells (9)
that
could be an additional
mode of its antineoplastic action. Because
NK-cells
play
an important role in
host
defence against neoplasia, it is quite likely
that
the contribution of IP6via boosting
NK-cell cytotoxicity may be important.
J. Physiol. Biochem., 56 (3), 2000
Hypocholesterolaemic effect.- A large
body
of literature indicates that
protein
from soybeans reduces blood cholesterol
concentrations in experimental animals as
well as in humans (2, 85).
The
mechanism
and
component
of soy responsible has
not
been fully established.
One
hypothesis
suggests amino acid composition
or
pro-
portionality of
soy
causes changes in
cho-
lesterol
metabolism
(possibly via
the
endocrine system).
Others
have proposed
that
nonprotein
components
(such as
saponins, fiber, phytic acid, minerals and
the isoflavones) associated with soy
pro-
tein affect
the
cholesterol metabolism
either directly
or
indirectly.
Phytic acid has received a great deal of
attention because of its mineral-binding
capabilities in
the
gut. Phytic acid chelates
both
divalent and trivalent metals includ-
ing Fe, Ca,
Zn
and Mg, decreasing their
absorption. By modulation of the
Zn:Cu
ratio in the blood, it is plausible that
phyt-
ic acid plays a role in cholesterol lowering
associated
with
high plasma cholesterol
concentrations. Diets containing soy are
rich in
both
phytic
acid and
Cu.
In the
gut, however, Zn and Cu shame the same
carrier;thus, if Zn is chelated by phytic
acid, more
Cu
can be absorbed and the
Zn:Cu
ratio in blood is decreased, which
some argue mediates lower plasma choles-
terol concentrations (48).
Little is
known
regarding the effect of
dietary phytic acid on blood lipid profiles
in humans. In rats, however,JARlwALLA et
al. (45)
reported
that
the addition
of
9g/Kg phytic acid to
dry
pellet diets
with
or
without
cholesterol lowered
serum
total cholesterol and triglyceride concen-
trations
in rats.
Zn:Cu
ratios
were
decreased
only
in rats consuming food
supplemented
with
cholesterol and phytic
acid. Thus, it appears that phytate
may

PHYTIC
ACID
ROLE IN LEGUMES 291
have a role,
but
it may
not
be mediated by
perturbation of the Zn:
Cu
ratio.
In
addition to the posible lipidaemic
influences of phytic acid, chelation of Fe
in
the
gut, decreasing its absorption, may
suppress oxidative damage to lipids and
proteins in blood, thereby decreasing ini-
tiation of atherosclerotic lesion formation.
Asignificant negative association between
serum
ferritin
concentrations
and
myocardial infarction was noted.
Howev-
er, numerous studies have shown
that
consumption of diets predominantly con-
taining soy products
with
high contents of
phytic
acid can lead to mineral deficien-
cies, including iron deficiency anaemia
(118). Thus, although phytic acid may be
protective with respect to some risk fac-
tors
associated with cardiovascular dis-
ease, caution should be used in prescribing
diets high in phytic acid to individuals at
risk for mineral deficiency (88).
Other
biological effects
and
applications
of
IP6
Acomprehensive review of the antiox-
idant functions and the industrial applica-
tions of 1P6has been carried
out
by
GRAF
and
EATON
(35). There is evidence that it
plays important roles in various
other
conditions and holds promise for use
therein.
HENNEMAN
et al. (38) successfully used
pure
Na-IP
6to treat idiopathic hypercal-
ciuria, which is associated
with
a high fre-
quency of kidney stones. A diet contain-
ing high IP6has also been used to treat
Hypercalciuria and kidney stones (80).
IP6has a hyocholesterolaemic effect and
may find potential use in the clinical man-
agement of hyperlipidaemia and diabetes
(45). A strong in vitro anticoagulant activ-
ity
of
Na-IP
6has been demonstrated in
the blood of various animals (13). Addi-
J. Physiol. Biochem., 56 (3), 2000
tionally, ADP-induced platelet aggrega-
tion was inhibited in rats treated
with
IP6•
Also administration of IP6effciently
pro-
tects
the
myocardium
from
ischaemic
damage and reperfusion injury (94).
Finally,
OTAKE
et al. (84) demonstrated
that
IP6inhibited the cytopathic effect of
human
inmunodeficiency virus (HIV) and
HIV
-specific antigen expression in MT-4
cells; inositol hexasulphate
showing
a
even stronger inhibition.
Coupled
with
the facts that IP6 enhances NK-cell activi-
ty and polymorphonuclear cell priming
function, it is possible
that
IP6may have
use in the management of
HIV
infection
and associated immunodeficiency-related
problems.
IP6can play an important modulatory
role in the regulation of insulin exocytosis
and
the
specific role may then be to
recruit secretory granules to the site of
exocytosis (7). IP6may be able to regulate
the (1251)
IGF
II receptor binding sites
either
directly
or
indirectly, possibly
through
clathrin-associated
AP-2
sites
(46).
Do
all these
potentially
beneficial
effects sound
too
good to be true? Per-
haps not; there is at least one
other
sub-
stance which claims the same distinction
of being useful in a variety of diseases
including cancer and cardiovascular dis-
ease and that is aspirin.
G.
URBANO,
M.
L6PEZ-JURADO,
P.
ARANDA,
C.
VIDAL-VALVERDE,
E.
TE-
NORIO
y
J.
PORRES. Papel del dcido
[itico
en las legumbres (minirrevision), J. Physiol.
Biochem., 56 (3), 283-294, 2000.
Esta revision describe
eI
estado actual de
conocimientos sobre eI acido fftico, presente
de forma natural en muchos alimentos deriva-
dos de plantas, y, sobre todo, en las legumbres.
Sus efectos antinutritivos se relacionan con su
fuerte capacidad para formar complejos con
proteinas y minerales. La hidrolisis del fitato

292 G.
URBANO,
M.
L6PEZ-JURADO,
P.
ARANDA,
C.
VIDAL-VALVERDE
et al.
en inositol yfosfatos se
produce
por
accion de
fitasas, ampliamente distribuidas en
microor-
ganismos, plantas y animales, y tam bien
por
procesos no enzimaticos, Las fitasas acnian de
forma escalonada siendo necesario conseguir la
defosiorilacion del inositol hexa y penta fosfa-
to, ya que estas
son
las formas con
mayor
capa-
cidad quelante.
Hay
varios
metodos
para
dis-
minuir
el efecto antinutricional del acido fftico,
tales como e! remojo, cocinamiento, la germi-
nacion, fermentacion yadicion de enzimas. Sin
embargo, e! inositol hexafosfato esta siendo
objeto de nuevo interes
por
su pape! en la pre-
venci6n de! cancer
y/o
en su terapia, y
por
su
efecto anticolesterolernico.
Palabras
clave: Fitato, Inositol fosfatos, Legum-
bres, Absorcion mineral, Prevencion del cancer,
Efecto hipocolesterolernico
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