Phytic acid content in milled cereal products and breads

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Food Research International 32 (1999) 217±221
www.elsevier.com/locate/foodres
Phytic acid content in milled cereal products and breads
Rosa Ma GarcõÂa-Estepa*, Eduardo Guerra-HernaÂndez, BeleÂn GarcõÂa-Villanova
Departamento de NutricioÂn y BromatologõÂa, Facultad de Farmacia, Universidad de Granada, Campus de Cartuja s/n, 18012 Granada, Spain
Received 15 February 1999; accepted 26 May 1999
Abstract
Phytic acid was determined in cereal (brans, ¯ours and milled wheat-products) and breads. The method was based on complexometric titration of residual iron (III) after phytic acid precipitation. The cereal ¯ours showed values ranged between 3±4 mg/g
for soft wheats, 9 mg/g for hard wheat and 22 mg/g for whole wheat. Corn, millet and sorghum ¯ours reported a mean of 10 mg/g
and oat, rice, rye and barley between 4 and 7 mg/g. Wheat brans had wide ranges (25±58 mg/g). The phytic acid for oat brans was
half that of wheat bran (20 mg/g) and higher value (58 mg/g) than that for rice bran. The milling products (semolinas) from hard
wheat exhibited 10 mg/g and soft wheat a mean of 23 mg/g. The breads made with single or mixture cereal ¯ours exhibited ranges
between 1.5 and 7.5 mg/g. The loss of phytic acid relative to unprocessed ¯ours was between 20% for oat bread and 50% for white
bread. # 1999 Canadian Institute of Food Science and Technology. Published by Elsevier Science Ltd. All rights reserved.
Keywords: Phytic acid; Milled cereal-products; Breads
1. Introduction
Phytic acid (myoinositol hexa-phosphoric acid, IP6) is
the major phosphorus storage compound of most seeds
and cereal grains, it may account for more than 70% of
the total phosphorus. Phytic acid has a strong ability to
chelate multivalent metal ions, specially zinc, calcium
and iron. The binding can result in very insoluble salts
with poor bioavailability of minerals (Rhou & Erdman,
1995). Besides its well-known negative properties IP6,
by complexing iron, may bring about a favorable
reduction in the formation of hydroxyl radicals in the
colon (Graf & Eaton, 1993), also positive e€ect against
carcinogenesis have been shown with in vitro cell culture systems, mice, rats and guinea pigs, but the
mechanism of action is not understood (Harland &
Morris, 1995).
Because of the numerous health bene®ts of dietary
®ber, the consumption of brans from various cereal
grains is increasing. The phytic acid is associated with
brans; some brans can contain over 5% phytic acid. As
a consequence, greater consumption of phytic acid has
resulted from increased consumption of high ®bre
* Corresponding author. Tel.: +34-958-243866; fax: +34-958243869.
E-mail address: [email protected] (R.M. GarcõÂa-Estepa)
foods. If the consumer is eating a marginal diet in
essential minerals, the phytic acid may lead to a nutritional de®ciency (Lehrfeld, 1994).
Phytic acid is hydrolyzed, enzymatically by phytases,
or chemically to lower inositol phosphates such as
inositol pentaphosphate (IP5), inositol tetraphosphate
(IP4), inositol triphosphate (IP3) and possibly the
inositol di- and monophosphate during storage, fermentation, germination, food processing and digestion
in the human gut (Burbano, Muzquiz, Osagie, Ayet &
Cuadrado, 1995). Only IP6 and IP5 have a negative
e€ect on a bioavailability of minerals, the other hydrolytic products formed have a poor capacity to bind
minerals, or the complexes formed are more soluble
(Sandberg, Carlsson & Svanberg, 1989).
Many methods of phytic acid determination have
been developed. The precipitation and ion-exchange
method's are not speci®c as they do not separate inositol hexaphosphate from lower inositol phosphates and
thus overestimate the phytate content in processed
foods (Sandberg, 1995). The HPLC method determines
the inositols in processed foods. The phytic acid in
unprocessed products mainly appear as inositol hexaphosphate (IP6); since the precipitation methods are
useful to measure the phytic acid content in unprocessed
products. Besides, they may also be appropriate to
evaluate the complexing capacity from a nutritional
0963-9969/99/$20.00 # 1999 Canadian Institute of Food Science and Technology. Published by Elsevier Science Ltd. All rights reserved.
PII: S0963-9969(99)00092-7
218
R.M. GarcõÂa-Estepa et al. / Food Research International 32 (1999) 217±221
standpoint (Phillippy, Johnston, Tao & Fox, 1988).
Thus, the goal of this work was to assess total phytate
content of cereal samples by a complexometric measure
of residual iron after phytic acid precipitation and know
the complexing capacity in processed foods (breads). So,
according to our results to estimate the phytic acid
intake from some products in Spain.
2. Materials and methods
2.1. Flours
Barley (Hordeum vulgare); corn (Zea mays); millet
(Panicum miliaceum); oat (Avena sativa); rice (Oryza
sativa); rye (Secale cereale); sorghum (Sorghum vulgare);
wheat (Triticum aestivum) and whole wheat samples
were analyzed.
2.2. Brans
Nine wheat, ®ve oat and one rice commercial samples
were investigated.
2.3. Wheat milling products
Soft wheat (Triticum aestivum) cv. Astral, cv. IngleÂs
and cv. Yecora and Hard wheat (Triticum durum) were
ground by the milling industry. The bran, semolina, and
¯our products from these varieties were analyzed. Brans
and ¯ours of three varieties (unknown cultivars), were
also studied.
2.4. Breads
White, whole, bran, mixed-grains, oat, and soy breads
were obtained from a bakery in Granada, Spain. The
¯ours used to manufacture the breads were also supplied by the industry. The di€erent types of breads were
made with baking ¯our mixed with other cereal ¯ours.
The composition and proportion of cereal are reported
in Table 3.
The brans were purchased from the di€erent local
markets in Granada, Spain. The cereal ¯ours and milling products were obtained from Spanish companies.
The samples were ground in a Moulinex 320 grinder
to pass a 0.60-mm sieve. The breads were dried at room
temperature. All the samples were stored at ÿ40 C prior
to analysis.
2.5. Determination of phytic acid
The original method (GarcõÂa-Villanova, GarcõÂa-Villanova & Ruiz de Lope, 1982) was developed to analyze cereal samples. The same methodology was used in this study
with modi®cations (GarcõÂa-Estepa, GarcõÂa-Villanova &
Guerra-HarnaÂndez, 1998). The ground samples (0.5±5.0
g) were extracted under magnetic agitation with 40.0 ml
of extraction solution (10 g/100 g Na2SO4 in 0.4 mol/l
HCl) for 3 h at room temperature. The suspension was
centrifuged at 5000 rpm for 30 min and the supernatant
was ®ltered.
Ten millilitres of supernatant (containing between 3.3
and 9.0 mg of phytic acid) were pipetted into a 100 ml
centrifuge tube together with 10.0 ml of 0.4 mol/l HCl,
10.0 ml of 0.02 mol/l FeCl3 and 10.0 ml of 20 g/100 g
sulphosalicylic acid, shaked gently and the tube used
was sealed with a rubber cork through which passes a
narrow 30-cm long glass tube, to prevent evaporation.
The tube was placed in a boiling water bath for 15 min,
then allowed to cool. The sample was centrifuged at
5000 rpm for 10 min, decanted, ®ltered and the residue
was washed several times with small volumes of distilled
water. The supernatant and washed fractions were diluted (100.0 ml). One aliquot (20.0 ml) adjusted to pH
2.5‹0.5 by addition of glycine was diluted to 200 ml.
The solution was heated at 70±80 C and, whilst still
warm, titrated with 50 mmol/l EDTA solution. The 4:6
Fe/P atomic ratio was used to calculate phytic acid
content.
The moisture was determined by air oven method
(AOAC, 1990).
3. Results and discussion
3.1. Precision
The precision, expressed as coecient of variation,
obtained in 11 samples of wheat bran (A) was 1.62%.
The determinations were carried out in di€erent days to
consider possible day-to-day variations.
3.2. Phytic acid in cereals
3.2.1. Flours
The phytic acid content in commercial ¯ours of different cereals is presented in Table 1. The values for
wheat were 4 mg/g in white and 22.2 mg/g for whole
wheat ¯ours. The phytic acid content reported in other
studies shows a wide variability depending on ¯our
yield, extraction method and ¯our types. The values
reported for white wheat ¯our were between 1.54 and
3.2 mg/g (Graf & Dintzis, 1982; Harland, 1993; Oberleas & Harland, 1981). Higher values (9.6 and 17.5 mg/g)
were reported for whole wheat ¯ours (Harland, 1993;
March, Villacampa & Grases, 1995). The phytic acid
content in other cereal ¯ours (Table 1) ranged between 4.5
and 7.5 mg/g for rye, rice, barley and oat. Corn, millet and
sorghum ¯ours contained approximately 10 mg/g of
phytic acid. These values are slightly lower than those
reported for whole grain samples (Blatny, Kvasnicka &
R.M. GarcõÂa-Estepa et al. / Food Research International 32 (1999) 217±221
Kenndler, 1995; Harland, 1993; Marfo, Simpson, Idowu
& Oke, 1990; Ockenden, Falk & Lott, 1997).
3.2.2. Brans
The phytic acid content in brans are summarized in
Table 1; this compound is found in outer layers of the
kernel (De Boland, Garner & O'Dell, 1975; Ravindran,
Ravindran & Sivalogan, 1994) and therefore, present in
higher amounts in bran products.
Wheat bran samples from nine commercial brands
consumed in Spain, were analyzed. The wheat bran is
very commonly consumed in Spain. Wide di€erences of
phytic acid were found. The values were between 25 and
59 mg/g. Howewer, the 80% of samples showed values
between 34 and 47 mg/g. It was observed that the brans
with greater size particle (visual observation) exhibited
higher phytic acid content (48.2 mg/g). The brans with
medium size particle showed an average value of 39.8
mg/g and those with smaller size exhibited a content of
29.5 mg/g. It could be due to the fact that the commercial brans with smaller size particle contained higher
proportion of endosperm than the brans with bigger
particle size. On the other hand, this wide range could
also easily be due to the wheat varieties analyzed which
are unknown for these samples. Di€erences between the
phytic acid contents of wheat brans was also reported
by the following researchers. A collaborative study
(Harland & Oberleas, 1986) reported values between 34
and 47 mg/g by AOAC method. The values found for
hard and soft wheat bran by the colorimetric method
were 42±54 mg/g and 46±67 mg/g by HPLC method
(Camire & Clydesdale, 1982; Knuckles, Kuzmicky &
Betschart, 1982). Other researchers applied the Latta and
Eskin's method (1980), reported values of 36±48 mg/g
Table 1
Phytic acid contenta (mg/g) of commercial ¯ours and brans of cereals
Flours
Barley
Corn
Millet
Oat
Rice
6.32‹0.22
10.78‹0.13
10.64‹0.22
7.44‹0.14
5.52‹0.42
Rye
Sorghum
Wheat
Whole wheat
4.52‹0.22
10.12‹0.29
4.04‹0.41
22.20‹0.90
Brans
Wheat
A
B
C
D
E
47.08‹0.76
40.39‹1.76
46.97‹0.75
33.68‹1.07
40.49‹1.45
F
G
H
I
25.32‹0.77
38.57‹1.51
58.39‹1.97
40.75‹1.73
Oat
J
K
L
21.51‹0.11
22.11‹0.83
24.06‹0.45
M
N
18.97‹0.43
20.16‹0.57
Rice
57.71‹0.80
a
Mean and standard deviation of four determinations, expressed
on a dry weight basis.
219
(Lee & Abendroth, 1983; Bos, Uerbeck, van Eeden,
Slump & Wolters, 1991; Blaney, Zee, Mangenau &
Marin, 1996). Recently, Kasim and Edwards (1998) by
the HPLC method reported values of 39.5 mg/g of IP6.
The labeling information requests two or three tablespoon for a serving. It may suppose a variable intake of
phytic acid ranged between 200 and 300 mg per serving.
Oat bran samples from ®ve commercial brands were
analysed. The phytic acid content was lower than wheat
brans. The values ranged between 19.0 and 24.0 mg/g.
According to the labeling information (2±3 tablespoons), the intake of phytic acid from oat bran is
similar to wheat bran so the weight of each serving of
oat is often double that of wheat bran.
Rice bran is not commonly available in our country and
only one commercial sample was studied. The phytic acid
content was 57.7 mg/g. The values obtained by colorimetric and HPLC's methods were 54, 73 and 78 mg/g
respectively (Knuckles et al., 1982). Values lower (36.5
mg/g) were found by the colorimetric method (Ravindran
et al., 1994). Kasim and Edwards (1998) reported values
of 60 mg/g of IP6, determined by the HPLC method.
3.2.3. Milled wheat products
Table 2 summarized the phytic acid contents in different milled wheat fractions (bran, semolina and ¯our)
and their mixtures. Hard wheat and three soft wheat
varieties (Astral, IngleÂs and Yecora) are common in
Spain. The mixture of varieties is often carried out to
improve the quality of ¯ours. The brans are commercialized by a milling company primarily to animal feed
industries and to a lesser extent as for human food. The
values range between 24.6 and 45.4 mg/g. The hard
wheat and fraction (B)-mixture 2 showed the lowest and
the fraction (A)-mixture 3 brans have the highest values.
The fraction (A) of mixtures 2 and 3 corresponds to the
Table 2
Phytic acid contenta (mg/g) of milling wheat products
Brans
Semolinas
Flours
Soft wheat
cv. Astral
cv. Ingles
cv. Yecora
Hard wheat
34.50‹1.22
30.34‹0.91
36.42‹1.43
24.96‹0.90
25.49‹0.21
26.73‹0.41
20.18‹0.40
9.87‹0.46
2.97‹0.33
2.94‹0.30
4.04‹0.50
9.41‹0.24
Wheat mixtures
mix. 1
mix. 2
fraction Ab
fraction Bc
mix. 3
fraction Ab
fraction Bc
34.82‹1.41
±
40.45‹1.35
24.63‹0.91
±
45.44‹0.95
35.24‹1.07
±
±
±
±
±
±
±
3.04‹0.12
3.34‹0.22
±
±
5.49‹0.59
±
±
a
Mean and standard deviation of four deteminations, expressed on
a dry weight basis.
b
Bran obtained in ®rst steps milling.
c
Bran obtained in later steps milling.
220
R.M. GarcõÂa-Estepa et al. / Food Research International 32 (1999) 217±221
Table 3
Phytic acid and moisture content of breadsa and the ¯ours utilized to
breadmaking
Phytic acid
(mg/g)b
White bread
Baking ¯our (a)
(wheat ¯our)
Bread
Oat bread
Oat ¯our (b)
(oat ®ber; wheat
and oat ¯akes;
wheat ¯our)
Mix. ¯ours (a:b, 1:1)
Bread
Bran bread
Bran ¯our (c)
(wheat bran;
wheat, soy and
malt ¯ours;
germ wheat; whey)
Mix. ¯ours (a:c, 1:1)
Bread
Soy bread
Soy ¯our (d)
(soy granulated;
whole wheat
and rye ¯ours)
Mix. ¯ours (a:d,1:1)
Bread
Mixed-grains bread
Mix. ¯our (e)
(wheat, corn, sesame,
¯ax, oat, barley, millet,
whole soy and whole
rye ¯ours)
Mix. ¯ours (a:e, 1:1)
Bread
Whole bread
Whole white ¯our (f)
(wheat and whole
wheat ¯ours)
Mix. ¯ours (a:f,1:2)
Bread
Reduction
(%)
2.98‹0.20
1.48‹0.09
15.0
50
0.36‹0.23
6.43‹0.20
5.16‹0.29
20
33
27
13.0
27.4
13.1
29
11.55‹0.35
7.49‹0.10
4.74‹0.19
12.7
31.1
10.8
9.81‹0.24
5.35‹0.23
3.81‹0.08
12.2
24.5
10.2
11.71‹0.35
7.54‹0.24
5.51‹0.23
28.6
10.7
20.00‹0.79
11.30‹0.22
7.53‹0.19
Moisture
(%)
13.2
23.2
14.6
37
13.0
30.2
Fermentation: time (25±30 min), Ta (30±35 C) baking time (30
min), Ta (200±225 C).
b
Mean and standard deviation of four determinations, expressed
on a dry weight basis.
a
®rst steps of the milling process for which the outer
layers predominate and the particle size is greater. The
fraction (A) is traditionally commercialized for animal
feed but recently it has been used in whole ¯ours and
dietetic products. The fraction (B) obtained from the
subsequent steps contents more proportion of internal
layers and endosperm and, consequently smaller size
particle. Blatny et al. (1995), analyzed the di€erent
fractions obtained in wheat milling; the phytic acid
decreased about 45% for the 2nd fraction. We found
less di€erences, 22 and 39% for mixture 3 and 2
respectively. The semolina contained a mean of 24.4
mg/g except for hard wheat which had 9.9 mg/g. The
soft ¯ours had 3.0±5.5 mg/g phytic acid which are
approximately 1/10 times than the lowest of the respective brans. Similar results were reported by Blatny et al.
(1995). However, the phytic acid in hard wheat ¯our
(9.4 mg/g) is only 1/4 times that of the bran.
3.2.4. Breads
The wheat bread is the main cereal product consumed
in Spain. Because of the numerous health bene®ts of
dietary ®ber, the consumption of whole wheat breads
and breads added to other cereals has been increased.
During bread-making, the content of phytic acid
decreases due to the action of phytases as well as the
high temperature (Plaami, 1997). Table 3 shows the
phytic acid content of ¯ours used for breadmaking, as
well as the values found in the bread. The bread-making
¯our revealed the lowest value of phytic acid (2.98 mg/
g) and the whole ¯ours of di€erent cereals showed the
highest contents (10.0±20 mg/g).
The ¯ours used in bread-making had 5.4±11.3 mg/g of
phytic acid. The values of phytic acid in breads ranged
between 1.48 mg/g (white wheat-bread) and 7.53 mg/g
(bran bread). Lower values were reported for white
bread (Harland, 1993; Harland & Harland, 1980; Phillippy et al., 1988). However, similar values were reported for whole wheat breads (Harland, 1993; Harland &
Harland, 1980; Phillippy & Johnston, 1985).
The breads analyzed had similar form, size and processed conditions. The reduction of chelating capacity
(expressed as phytic acid content) in these breads is found
between 20% for oat bread and 50% for white bread.
Nayini and Markakis (1983a,b) compare the inositols
contents in breads made with di€erent extraction grade
(70±100%) ¯ours and also found a minor reduction of
phytate for whole breads.
3.2.5. Intake of phytic acid
The intake of cereals in Spain is estimated as 224 g/
day of which, 151 g/day correspond to bread (SauraCalixto & GonÄi, 1993).
According to our results, the phytic acid supplied
from white bread would be 159 mg/day. Considering
other types of breads, the intake from mix-cereal bread
would be 442 mg/day, whole bread 500 mg/day, oat
bread 589 mg/day, soy bread 604 mg/day and bran
bread 784 mg/g. The intake would be increased 3±5
times with respect to white bread. The recomendation of
bran intake according to labeling information request
20 and 10 g/day for oat and wheat brans respectively.
The phytic acid supplied by brans would be close to 375
mg/day (wheat brans 367 mg/day and oat brans 389 mg/
day). The intake of whole bread instead of white bread
or brans would cause a daily increase of phytic acid of
approximately 350 mg.
R.M. GarcõÂa-Estepa et al. / Food Research International 32 (1999) 217±221
Acknowledgements
The authors thank Abbott Laboratories, milling
industry ``La Merced'' and ``Alcampo'' market for their
contribution.
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