Phytogenic and microbial phytases in human nutrition
Phytogenic and microbial phytases in human nutrition
Phytogenic and microbial phytases in human nutrition
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International Journal of Food Science <strong>and</strong> Technology 2002, 37, 823–833 823<br />
<strong>Phytogenic</strong> <strong>and</strong> <strong>microbial</strong> <strong>phytases</strong> <strong>in</strong> <strong>human</strong> <strong>nutrition</strong><br />
Ann-Sofie S<strong>and</strong>berg* & Thomas Andlid<br />
Department of Food Science, Chalmers University of Technology, PO Box 5401, SE Go¨ teborg, Sweden<br />
Summary Phytate (<strong>in</strong>ositol hexa phosphate) hydrolysis can occur dur<strong>in</strong>g food preparation <strong>and</strong><br />
production <strong>and</strong> <strong>in</strong> the <strong>in</strong>test<strong>in</strong>e, either by phytase from plants, yeasts or other microorganisms.<br />
This degradation is of <strong>nutrition</strong>al importance, because removal of phosphate<br />
groups from the <strong>in</strong>ositol r<strong>in</strong>g results <strong>in</strong> an <strong>in</strong>creased bioavailability of essential dietary<br />
m<strong>in</strong>erals. To substantially improve iron absorption the degradation has to be virtually<br />
complete. Food process<strong>in</strong>g techniques <strong>in</strong>creas<strong>in</strong>g the activity of the naturally occurr<strong>in</strong>g<br />
plant <strong>phytases</strong> are soak<strong>in</strong>g, malt<strong>in</strong>g, hydrothermal treatment <strong>and</strong> fermentation. An<br />
alternative is addition of <strong>phytases</strong> or micro-organisms produc<strong>in</strong>g phytase. Phytate<br />
degradation <strong>in</strong> the stomach <strong>and</strong> small <strong>in</strong>test<strong>in</strong>e occurs as a result of activity of dietary<br />
phytase of plant or <strong>microbial</strong> orig<strong>in</strong>. The plant phytase is less stable than fungal phytase <strong>in</strong><br />
the physiological conditions of the <strong>in</strong>test<strong>in</strong>e. Biotechnologically produced <strong>phytases</strong> may be<br />
possible for use tomorrow <strong>in</strong> food process<strong>in</strong>g as well as plant raw material <strong>and</strong> starter<br />
cultures with <strong>in</strong>serted phytase genes.<br />
Keywords Inositol hexaphosphate, food process<strong>in</strong>g, <strong>microbial</strong> phytase, m<strong>in</strong>eral absorption, phytate, plant phytase.<br />
Introduction<br />
The degradation of phytate (myo-<strong>in</strong>ositol hexakis<br />
phosphate, InsP 6) is of <strong>nutrition</strong>al importance<br />
because the m<strong>in</strong>eral b<strong>in</strong>d<strong>in</strong>g strength of phytate<br />
decreases <strong>and</strong> the solubility <strong>in</strong>creases when phosphate<br />
groups are removed from the <strong>in</strong>ositol r<strong>in</strong>g<br />
result<strong>in</strong>g <strong>in</strong> an <strong>in</strong>creased bioavailability of essential<br />
dietary m<strong>in</strong>erals (Lo¨ nnerdal et al., 1989; Brune<br />
et al., 1992; S<strong>and</strong>stro¨ m & S<strong>and</strong>berg, 1992; S<strong>and</strong>berg<br />
et al., 1999). Thus, <strong>phytases</strong> have an important<br />
role <strong>in</strong> <strong>human</strong> <strong>nutrition</strong> both for degradation<br />
of phytate dur<strong>in</strong>g food process<strong>in</strong>g <strong>and</strong> <strong>in</strong> the<br />
gastro<strong>in</strong>test<strong>in</strong>e. Major efforts have been made to<br />
reduce the amount of phytate <strong>in</strong> foods by different<br />
processes or the addition of enzymes. In contrast to<br />
the anti-<strong>nutrition</strong>al properties, dietary phytate has<br />
also been suggested to have beneficial effects, such<br />
as protection aga<strong>in</strong>st colon cancer (Graf & Eaton,<br />
1985; Shamsudd<strong>in</strong>, 1995) arteriosclerosis <strong>and</strong> coronary<br />
heart diseases (Jariwalla et al., 1990).<br />
*Correspondent: Fax: +46 31 83 37 82;<br />
e-mail: ann-sofie.s<strong>and</strong>berg@fsc.chalmers.se<br />
Ó 2002 Blackwell Science Ltd<br />
Hydrolysis of phytate dur<strong>in</strong>g biological food<br />
processes <strong>and</strong> preparation such as soak<strong>in</strong>g, malt<strong>in</strong>g<br />
<strong>and</strong> fermentation (Nay<strong>in</strong>i & Markakis, 1983;<br />
S<strong>and</strong>berg & Svanberg, 1991; Larsson & S<strong>and</strong>berg,<br />
1992; Svanberg et al., 1993) is as a result of<br />
activity of phytase enzymes, naturally synthesized<br />
by plants <strong>and</strong> many micro-organisms. Biotechnologically<br />
produced <strong>microbial</strong> phytase preparations<br />
are commercially available <strong>and</strong> used for feed<br />
preparations. In future, their use <strong>in</strong> food process<strong>in</strong>g<br />
could be feasible. Moreover, <strong>microbial</strong> genes<br />
encod<strong>in</strong>g <strong>phytases</strong> with desired properties can be<br />
cloned <strong>and</strong> <strong>in</strong>serted <strong>in</strong>to plants yield<strong>in</strong>g <strong>in</strong>creased<br />
levels of phytase <strong>and</strong> reduced phytate content.<br />
Specific isomers of <strong>in</strong>ositol phosphates have<br />
shown several important physiological functions<br />
<strong>in</strong> man <strong>and</strong> animals (Holub, 1987). Such compounds<br />
occur <strong>in</strong> biologically processed foods of<br />
plant orig<strong>in</strong>.<br />
Hydrolysis of phytate may occur <strong>in</strong> the gastro<strong>in</strong>test<strong>in</strong>al<br />
tract prior to the <strong>in</strong>test<strong>in</strong>al site of<br />
absorption. Because most of the essential m<strong>in</strong>erals<br />
<strong>and</strong> trace elements are absorbed <strong>in</strong> the duodenal<br />
or jejunal part of the small <strong>in</strong>test<strong>in</strong>e, the site <strong>and</strong>
824<br />
Degradation of phytate A.-S. S<strong>and</strong>berg & T. Andlid<br />
degree of phytate degradation can affect the<br />
<strong>nutrition</strong>al value of a high phytate diet. Furthermore,<br />
enzymatic hydrolysis of phytate <strong>in</strong> the<br />
gastro<strong>in</strong>test<strong>in</strong>e leads to formation of specific<br />
isomers of <strong>in</strong>ositol phosphates. If physiologically<br />
active lower <strong>in</strong>ositol phosphates, formed dur<strong>in</strong>g<br />
food process<strong>in</strong>g, or degradation <strong>in</strong> the gastro<strong>in</strong>test<strong>in</strong>e<br />
or precursors to these are absorbed <strong>in</strong> the<br />
alimentary tract of <strong>human</strong>s it may have important<br />
health implications (Holub, 1987).<br />
Enzymatic hydrolysis of phytate<br />
Phytases (InsP 6-phosphohydrolases) are by def<strong>in</strong>ition<br />
enzymes able to hydrolyse InsP 6 to InsP 5<br />
<strong>and</strong> <strong>in</strong>organic phosphate (Pi). Typically, <strong>phytases</strong><br />
are not specific for InsP 6, lead<strong>in</strong>g to further<br />
hydrolysis to myo-<strong>in</strong>ositol via <strong>in</strong>termediate myo<strong>in</strong>ositol<br />
phosphates (penta- to monophosphates)<br />
(Cosgrove, 1966). Phytases constitutes a subgroup<br />
of the family of acid phosphatases. Those that<br />
exhibit the ability of hydrolyse InsP 6 can be<br />
considered to be <strong>phytases</strong> (Gibson & Ullah, 1990).<br />
Phytate is one of the most abundant organic<br />
phosphorous compound <strong>in</strong> nature. Hence, it<br />
follows that the ability to synthesize <strong>phytases</strong> is<br />
widely distributed among organisms, <strong>in</strong>clud<strong>in</strong>g<br />
plants, micro-organisms <strong>and</strong> animal cells. With<br />
respect to the position for <strong>in</strong>itial hydrolysis, two<br />
types of <strong>phytases</strong>, 3- <strong>and</strong> 6-<strong>phytases</strong>, have been<br />
recognized as start<strong>in</strong>g the dephosphorylation of<br />
InsP 6 at position d-3 or l-6 of the <strong>in</strong>ositol r<strong>in</strong>g.<br />
The 3-<strong>phytases</strong> (EC 3.1.3.8) have been found to<br />
dom<strong>in</strong>ate among micro-organisms while 6-phytase<br />
(EC 3.1.3.26) (4-phytase assum<strong>in</strong>g d-configuration)<br />
has been considered to be characteristic of<br />
the seeds of higher plants (Cosgrove, 1980). This<br />
is, however, not a general rule. For <strong>in</strong>stance,<br />
Escherichia coli has been shown to produce a<br />
6-phytase <strong>and</strong> soybean a 3-phytase. Depend<strong>in</strong>g on<br />
the type of food process or whether a phytase is<br />
expected to be active <strong>in</strong> the gut, different properties<br />
should be considered <strong>in</strong> the search for optimal<br />
enzyme. These may <strong>in</strong>clude stability at low pH <strong>and</strong><br />
at high temperature, level of glycosylation, resistance<br />
aga<strong>in</strong>st digestive proteolytic enzymes, high<br />
specific activity, suitable pH- <strong>and</strong> temperature<br />
optima, high level of expression, easy cultivation<br />
(of phytase produc<strong>in</strong>g organism) <strong>and</strong> purification,<br />
extracellular phytase, nonallergenic, <strong>and</strong> nontoxic.<br />
Sources of phytase<br />
Plant <strong>phytases</strong><br />
Plants may express high levels of <strong>phytases</strong> <strong>in</strong><br />
storage compartments such as seeds for the purpose<br />
of utiliz<strong>in</strong>g Pi <strong>and</strong> energy required for growth<br />
of the germ<strong>in</strong>at<strong>in</strong>g plant. Phytase enzymes have<br />
been isolated <strong>and</strong> characterized from a number of<br />
plant sources; the <strong>in</strong>itial preparation of phytase<br />
made from rice bran (Suzuki et al., 1907). It is,<br />
however, only recently that some <strong>phytases</strong> have<br />
been isolated <strong>and</strong> purified to homogenity (Gre<strong>in</strong>er<br />
et al., 1993, 1997, 1998; Konietzny et al., 1994;<br />
Gre<strong>in</strong>er & Larsson-Alm<strong>in</strong>ger, 1999).<br />
Consider<strong>in</strong>g the <strong>in</strong> vitro degradation of InsP 6 by<br />
plant <strong>phytases</strong> such as wheat phytase (Phillippy,<br />
1989; Tu¨ rk et al., 1996) <strong>and</strong> the phytase from rye<br />
(Gre<strong>in</strong>er et al., 1998), spelt (Konietzny et al., 1994)<br />
<strong>and</strong> barley (S<strong>and</strong>berg, 2002) are reported to be 6(4)<strong>phytases</strong>.<br />
The major InsP5 <strong>in</strong> raw soybean was dl-<br />
Ins(1,2,4,5,6)P 5 <strong>and</strong> thus soybean phytase seems to<br />
be a 3-phytase (Phillippy & Bl<strong>and</strong>, 1988). Another<br />
legum<strong>in</strong>ous plant, pea, was also found to have a<br />
degradation pathway of InsP 6 dissimilar to that of<br />
cereals (Skoglund et al., 1997a).<br />
The isomeric pattern dur<strong>in</strong>g degradation of<br />
InsP6 <strong>in</strong> oats, rye <strong>and</strong> barley were found to be<br />
similar to that formed by hydrolysis by wheat<br />
phytase (Skoglund et al., 1997a). The same InsP 6<br />
degradation pathway may be assumed <strong>in</strong> these<br />
cereals.<br />
Microbial <strong>phytases</strong><br />
Because InsP6 seems to be present <strong>in</strong> most liv<strong>in</strong>g<br />
cells, it follows that <strong>in</strong>tracellular InsP6 hydrolys<strong>in</strong>g<br />
enzymes must be present <strong>in</strong> most micro-organisms.<br />
However, for production of <strong>microbial</strong> <strong>phytases</strong> for<br />
food applications or fermentations with live phytase<br />
express<strong>in</strong>g micro-organisms, the extracellular<br />
<strong>phytases</strong> are the most important. These are InsP 6<br />
hydrolys<strong>in</strong>g enzymes that are secreted to the<br />
surround<strong>in</strong>gs, aimed for efficient degradation of<br />
phytate as a source of phosphorous <strong>and</strong> sometimes<br />
energy required for growth. Obviously, the<br />
advantage with extracellular <strong>phytases</strong> are easy<br />
purification <strong>and</strong> the fact that dur<strong>in</strong>g food process<strong>in</strong>g<br />
the substrate <strong>and</strong> enzyme must meet. The<br />
secretory <strong>microbial</strong> <strong>phytases</strong> are sometimes, as <strong>in</strong><br />
International Journal of Food Science <strong>and</strong> Technology 2002, 37, 823–833 Ó 2002 Blackwell Science Ltd
the case of common Baker’s yeast, fairly unspecific<br />
<strong>and</strong> may degrade other organic phosphorous<br />
sources <strong>in</strong> addition to InsP 6 (Nay<strong>in</strong>i & Markakis,<br />
1983). Regard<strong>in</strong>g the less <strong>in</strong>vestigated <strong>in</strong>tracellular<br />
InsP6 hydrolys<strong>in</strong>g enzymes it is likely to f<strong>in</strong>d<br />
enzymes with a different position specificity.<br />
Fungal <strong>phytases</strong><br />
Fungi are an important source of <strong>phytases</strong>. Among<br />
mycelia fungi, the most explored genus is Aspergillus<br />
from which the commercially produced <strong>phytases</strong><br />
orig<strong>in</strong>ate. In particular the species A. niger,<br />
A. ficuum <strong>and</strong> A. fumigatus have been <strong>in</strong>vestigated.<br />
Genes have been cloned <strong>and</strong> research has been<br />
undertaken to further improve the Aspergillus<br />
enzymes by prote<strong>in</strong> eng<strong>in</strong>eer<strong>in</strong>g (Wyss et al.,<br />
1999). For <strong>in</strong>stance, elegant work by (Lehmann<br />
et al., 2000) have resulted <strong>in</strong> improved thermal<br />
stability by am<strong>in</strong>o acid substitutions. However,<br />
these enzymes are as yet not classed as food grade.<br />
Also <strong>in</strong> yeasts, the ability to synthesize <strong>and</strong> secret<br />
<strong>phytases</strong> seems to be almost universal. All yeasts<br />
exam<strong>in</strong>ed <strong>in</strong> our laboratory showed phytase activity,<br />
as determ<strong>in</strong>ed by growth <strong>in</strong> medium conta<strong>in</strong><strong>in</strong>g<br />
InsP 6 as the sole phosphorus source followed by<br />
high-pressure liquid chromatography (HPLC)<br />
analysis of extracellular InsP 6 degradation. The<br />
yeasts tested <strong>in</strong>clude more than 10stra<strong>in</strong>s of<br />
Saccharomyces cerevisiae from various sources,<br />
different stra<strong>in</strong>s of Debaryomyces hansenii, Rhodotorula<br />
rubra, Rh. glut<strong>in</strong>is, S. boulardii, <strong>and</strong> several<br />
tropical species such as Metschmikowia lochheadii,<br />
C<strong>and</strong>ida drosophilae <strong>and</strong> C<strong>and</strong>ida tolerans. Common<br />
Baker’s yeast would be particularly attractive<br />
because of its generally regarded as safe (GRAS)<br />
status. However, data show that for high yeast<br />
phytase activity to take place, conditions must<br />
favour the expression of the <strong>phytases</strong> (Andlid,<br />
2000). Naturally, among the approximately 1000<br />
species of described yeasts, the vast majority<br />
rema<strong>in</strong>s to be exam<strong>in</strong>ed regard<strong>in</strong>g <strong>phytases</strong>.<br />
Bacterial <strong>phytases</strong><br />
Several bacteria has been shown to be able to<br />
express phytase activity. Examples are E. coli,<br />
Bacillus subtilis, Klebsiella terr<strong>in</strong>ga, Pseudomonas<br />
spp. (Gre<strong>in</strong>er et al., 1993, 1997; Richardson &<br />
Hadobas, 1997; Kerovuo et al., 1998). Some of<br />
these bacteria can degrade phytate dur<strong>in</strong>g growth<br />
<strong>and</strong> hence produce extracellular <strong>phytases</strong>. How-<br />
Degradation of phytate A.-S. S<strong>and</strong>berg & T. Andlid 825<br />
ever, <strong>in</strong> the important group of lactic acid bacteria<br />
(LAB) conclusive evidence for extracellular phytase<br />
activity are lack<strong>in</strong>g (Fredrikson et al., 2002).<br />
Studies of <strong>in</strong> vitro degradation of InsP 6 by bacterial<br />
phytase shows that <strong>phytases</strong> synthesized by<br />
K. terrigena (Gre<strong>in</strong>er et al., 1997) <strong>and</strong> S. cerevisae<br />
(Tu¨ rk et al., 2000) belong to the 3-<strong>phytases</strong><br />
whereas <strong>phytases</strong> of E. coli (Gre<strong>in</strong>er et al., 1993)<br />
belong to the 6-<strong>phytases</strong>. Naturally, most bacteria<br />
rema<strong>in</strong>s to be <strong>in</strong>vestigated for phytase activity.<br />
Enzymatic degradation of phytate<br />
dur<strong>in</strong>g food process<strong>in</strong>g<br />
Phytate hydrolysis can occur dur<strong>in</strong>g food preparation<br />
<strong>and</strong> production, either by phytase from<br />
plants, yeasts or other micro-organisms. Biological<br />
process<strong>in</strong>g techniques, which <strong>in</strong>crease the<br />
activity of native enzymes of cereals <strong>and</strong> legumes<br />
are soak<strong>in</strong>g, malt<strong>in</strong>g, hydrothermal process<strong>in</strong>g<br />
<strong>and</strong> lactic fermentation. Dur<strong>in</strong>g the germ<strong>in</strong>ation<br />
step of the malt<strong>in</strong>g process, enzymes are synthesized<br />
or activated. Lactic fermentation leads to<br />
lower<strong>in</strong>g of pH as a consequence of bacterial<br />
production of organic acids, ma<strong>in</strong>ly lactic <strong>and</strong><br />
acetic acid, which is favourable for cereal phytase<br />
activity. In addition, starter cultures may also be<br />
selected <strong>in</strong> future for high phytase activity dur<strong>in</strong>g<br />
the fermentation process. Phytase preparations<br />
can also be added <strong>in</strong> the food process. To optimize<br />
the food process for <strong>in</strong>creased m<strong>in</strong>eral bioavailability<br />
by phytate degradation, it is essential to<br />
know optimal conditions for the <strong>phytases</strong>, responsible<br />
for phytate degradation <strong>in</strong> the process.<br />
Naturally, there are differences <strong>in</strong> optimal conditions<br />
for phytase activity between different plant<br />
species. Moreover, except phytate, InsP5 has been<br />
identified as <strong>in</strong>hibitor of iron <strong>and</strong> z<strong>in</strong>c absorption<br />
<strong>in</strong> <strong>human</strong> <strong>and</strong> animal studies (Lo¨ nnerdal et al.,<br />
1989; S<strong>and</strong>stro¨ m & S<strong>and</strong>berg, 1992; S<strong>and</strong>berg<br />
et al., 1999). No difference between various isomers<br />
of <strong>in</strong>ositol phosphates on iron uptake <strong>in</strong> vitro<br />
<strong>in</strong> CaCo 2 cells was shown (Skoglund et al., 1999).<br />
Recently <strong>in</strong>dications were found that InsP 4 <strong>and</strong><br />
InsP3 contribute to the negative effect on iron<br />
absorption by <strong>in</strong>teract<strong>in</strong>g with the higher phosphorylated<br />
<strong>in</strong>ositol phosphates. These f<strong>in</strong>d<strong>in</strong>gs<br />
suggest that phytate degradation of not only<br />
InsP 5 <strong>and</strong> InsP 6, but also degradation of InsP 3<br />
<strong>and</strong> InsP 4 are favourable for improvement of iron<br />
Ó 2002 Blackwell Science Ltd International Journal of Food Science <strong>and</strong> Technology 2002, 37, 823–833
826<br />
Degradation of phytate A.-S. S<strong>and</strong>berg & T. Andlid<br />
absorption from cereal <strong>and</strong> soy products (S<strong>and</strong>berg<br />
et al., 1999). This is probably also true for<br />
z<strong>in</strong>c absorption as a strong negative correlation<br />
was found between z<strong>in</strong>c absorption <strong>and</strong> the sum of<br />
native InsP3 through InsP6 from cereal <strong>and</strong> legume<br />
meals (S<strong>and</strong>berg, 1991).<br />
Soak<strong>in</strong>g, malt<strong>in</strong>g <strong>and</strong> hydrothermal process<strong>in</strong>g<br />
Soak<strong>in</strong>g of wheat bran, whole wheatflour <strong>and</strong> rye<br />
flour at optimal conditions for wheat phytase<br />
activity (pH 4.5–5, 55 °C) resulted <strong>in</strong> complete<br />
phytate hydrolysis (Mellanby, 1950; S<strong>and</strong>berg &<br />
Svanberg, 1991) <strong>and</strong> to a marked <strong>in</strong>crease <strong>in</strong><br />
<strong>in</strong> vitro iron availability. S<strong>and</strong>berg & Svanberg<br />
(1991) found that the InsP 6 <strong>and</strong> InsP 5 content<br />
must be reduced to levels beyond 0.5 lmol g )1 to<br />
give the strong <strong>in</strong>crease <strong>in</strong> iron solubility at<br />
simulated physiological conditions, when no<br />
enhancers were present.<br />
Malt<strong>in</strong>g is a process dur<strong>in</strong>g which the whole<br />
gra<strong>in</strong> is soaked <strong>and</strong> then germ<strong>in</strong>ated. The amount<br />
of phytate <strong>in</strong> malted gra<strong>in</strong>s of wheat, rye <strong>and</strong> oats<br />
<strong>in</strong>tended for the production of flour (germ<strong>in</strong>ated<br />
3 days at 15 °C sprout length 10mm) was only<br />
reduced slightly or not at all. However, when the<br />
malted cereals were ground <strong>and</strong> soaked at optimal<br />
conditions for wheat phytase there was a complete<br />
degradation of phytate (Larsson & S<strong>and</strong>berg,<br />
1992), except for oats, which under the conditions<br />
studied had a low phytase activity. By germ<strong>in</strong>ation<br />
of oats for 5 days at 11 °C followed by <strong>in</strong>cubation<br />
at 37–40 °C, phytate content of oats was reduced<br />
by 98% (to
oat <strong>and</strong> rye bran bread made with 10% sourdough<br />
(pH 4.6) or <strong>in</strong> the breads <strong>in</strong> which the pH had been<br />
adjusted <strong>in</strong> the mild scald<strong>in</strong>g with lactic acid,<br />
result<strong>in</strong>g <strong>in</strong> a pH between 4.4 <strong>and</strong> 5.1 <strong>in</strong> both dough<br />
<strong>and</strong> bread. The percentage of iron absorption from<br />
bread meals conta<strong>in</strong><strong>in</strong>g this sourdough fermented<br />
bread was similar to that of white wheat bread not<br />
conta<strong>in</strong><strong>in</strong>g <strong>in</strong>hibitory factors (Brune et al., 1992).<br />
Consequently, the amounts of iron absorbed from<br />
wholemeal bread with its high content of iron,<br />
would be greater than that from white bread,<br />
provided the fermentation is optimized.<br />
In another study of bread-mak<strong>in</strong>g, Tu¨ rk &<br />
S<strong>and</strong>berg (1992) <strong>in</strong>vestigated the effect of different<br />
additives to the dough. Bread was made us<strong>in</strong>g<br />
whole wheat flour <strong>and</strong> flour of 60% extraction<br />
rate. Addition of milk to the dough <strong>in</strong>hibited<br />
enzymatic phytate hydrolysis result<strong>in</strong>g <strong>in</strong><br />
depressed <strong>human</strong> iron absorption from the bread<br />
(Hallberg et al., 1991). Fermented milk did not<br />
significantly <strong>in</strong>hibit enzymatic hydrolysis dur<strong>in</strong>g<br />
fermentation, probably depend<strong>in</strong>g on the presence<br />
of lactic acid lower<strong>in</strong>g the pH (Tu¨ rk & S<strong>and</strong>berg,<br />
1992). Addition of acetic acid or l<strong>in</strong>gonberries to<br />
the dough <strong>in</strong>creased the phytate reduction to 96<br />
<strong>and</strong> 83%, respectively, compared with 55% <strong>in</strong><br />
control bread without additives (Tu¨ rk et al.,<br />
1996). The pH of the doughs with 96% reduction<br />
was between 4.5 <strong>and</strong> 5. This degradation was<br />
ma<strong>in</strong>ly a result of the activity of phytase <strong>in</strong> the<br />
flour whereas the contribution of phytase activity<br />
from Baker’s yeast dur<strong>in</strong>g bread fermentation was<br />
very small. It was concluded that conditions<br />
dur<strong>in</strong>g bread fermentation disfavour yeast phytase<br />
expression (Tu¨ rk et al., 2000).<br />
Addition of enzymes<br />
An alternative to activation of the <strong>in</strong>tr<strong>in</strong>sic<br />
enzymes of foods is the addition of phytase dur<strong>in</strong>g<br />
food process<strong>in</strong>g. Microbial phytase enzyme preparations<br />
are now available commercially mak<strong>in</strong>g<br />
their use <strong>in</strong> food process<strong>in</strong>g technically feasible.<br />
Moreover, the phytase encod<strong>in</strong>g gene A. niger<br />
(phyA) has been cloned <strong>and</strong> over-expressed<br />
result<strong>in</strong>g <strong>in</strong> a more than tenfold <strong>in</strong>crease <strong>in</strong><br />
phytase activity per biomass unit compared with<br />
the wild-type stra<strong>in</strong> (Hart<strong>in</strong>gsveldt et al., 1993).<br />
Phytase from A. niger 1500 PU g )1 flour (one<br />
phytase unit, PU, is the amount of enzyme<br />
Degradation of phytate A.-S. S<strong>and</strong>berg & T. Andlid 827<br />
which liberates under st<strong>and</strong>ard conditions, pH<br />
5.0, 37 °C, 1 nmol of Pi from sodium phytate<br />
dur<strong>in</strong>g 1 m<strong>in</strong>) was added to the doughs prepared<br />
us<strong>in</strong>g whole wheatflour <strong>and</strong> flour of 60%<br />
extraction rate. The phytate hydrolysis <strong>in</strong> the<br />
dough was, however, not complete (maximum<br />
88% hydrolysis), unless the pH was lowered to<br />
3.5 which is close to the lower pH optimum<br />
(Tu¨ rk et al., 1996). A. niger phytase, therefore,<br />
may be useful <strong>in</strong> the production of lactic acid<br />
fermented cereals <strong>and</strong> legumes (which normally<br />
have a low pH value) aimed at high m<strong>in</strong>eral<br />
availability. A very effective phytate degradation<br />
was achieved by add<strong>in</strong>g A. niger phytase to an<br />
oat-based nutrient solution fermented by Lactobacillus<br />
plantarum, but the added enzyme had a<br />
negative <strong>in</strong>fluence on the viable counts of<br />
Lactobacilli as well as the aroma (Markl<strong>in</strong>der<br />
et al., 1995). However, further studies us<strong>in</strong>g<br />
highly purified enzyme preparations are likely<br />
to reduce such negative effects.<br />
The effect of reduc<strong>in</strong>g the phytate <strong>in</strong> soy-prote<strong>in</strong><br />
isolates on iron absorption was <strong>in</strong>vestigated <strong>in</strong><br />
<strong>human</strong>s (Hurrell et al., 1992). Addition of A. niger<br />
phytase <strong>in</strong> amounts which almost completely<br />
removed phytate <strong>in</strong> soy isolates <strong>in</strong>creased iron<br />
absorption 4–5-fold.<br />
Hydrolysis of phytate <strong>in</strong> the gut<br />
A number of factors have to be considered when<br />
discuss<strong>in</strong>g phytate degradation <strong>in</strong> the gut, e.g. if<br />
there is an effect of dietary phytase, <strong>in</strong>test<strong>in</strong>al<br />
mucosa phytase or phytase produced by the<br />
<strong>in</strong>test<strong>in</strong>al microflora. It has also been suggested<br />
that an adaptation to <strong>in</strong>creased phytate degradation<br />
may occur (Widdowson & Thrussell, 1951).<br />
Potentially, this might happen as a result of either<br />
changed enzyme secretion or altered <strong>in</strong>test<strong>in</strong>al<br />
flora. Balance studies <strong>in</strong> <strong>human</strong>s <strong>in</strong>dicate that an<br />
<strong>in</strong>creas<strong>in</strong>g dietary calcium level reduces the degree<br />
of phytate degradation <strong>in</strong> <strong>human</strong>s (Cruickshank<br />
et al., 1945; Walker et al., 1948; Ellis et al., 1986).<br />
Degradation of phytate <strong>in</strong> the stomach<br />
<strong>and</strong> small <strong>in</strong>test<strong>in</strong>e<br />
Few studies have been performed to determ<strong>in</strong>e<br />
hydrolysis of phytate <strong>in</strong> the stomach. It is likely that<br />
consumption of raw plant foods may lead to some<br />
Ó 2002 Blackwell Science Ltd International Journal of Food Science <strong>and</strong> Technology 2002, 37, 823–833
828<br />
Degradation of phytate A.-S. S<strong>and</strong>berg & T. Andlid<br />
hydrolysis <strong>in</strong> the stomach, as the enzyme phytase is<br />
present <strong>and</strong> <strong>in</strong> particular cereal phytase activity<br />
<strong>in</strong>creases when the pH is lowered. Investigat<strong>in</strong>g<br />
hydrolysis of <strong>in</strong>ositol phosphates <strong>in</strong> the stomach of<br />
slaughtered pigs showed that approximately 50%<br />
of the feed InsP 6 was hydrolysed (Skoglund et al.,<br />
1997b). This hydrolysis was probably a result of<br />
activity of the native feed phytase as raw barley was<br />
<strong>in</strong>cluded <strong>in</strong> the feed. Lantzsch et al. (1988) found<br />
little hydrolysis <strong>in</strong> the stomach of pigs <strong>in</strong> the<br />
absence of feed phytase. Remov<strong>in</strong>g some of the<br />
phosphate groups <strong>in</strong> the stomach, the <strong>in</strong>ositol<br />
phosphates with lower degree of phosphorylation<br />
formed probably are more easily hydrolysed further<br />
by phosphatases located <strong>in</strong> the <strong>in</strong>test<strong>in</strong>e, which<br />
are not able to hydrolyse InsP 6.<br />
Soluble sodium phytate is hydrolysed by homogenized<br />
mucosal tissue from a wide range of<br />
species. Crush<strong>in</strong>g the cell of the mucosa may,<br />
however, cause the release of <strong>in</strong>tracellular phytase,<br />
which normally would have no contact with the<br />
<strong>in</strong>test<strong>in</strong>al contents. The situation <strong>in</strong> the <strong>in</strong>tact<br />
<strong>in</strong>test<strong>in</strong>e may therefore differ. Us<strong>in</strong>g this type of<br />
methodology, Bitar & Re<strong>in</strong>hold (1972) claimed<br />
that <strong>human</strong>s also had a mucosal phytase, an<br />
observation which was further supported by Iqbal<br />
et al. (1994). Davies & Flett (1978) found mucosal<br />
phytase <strong>in</strong> the rat <strong>and</strong> showed that it was<br />
concentrated <strong>in</strong> the brush border. Factors <strong>in</strong>fluenc<strong>in</strong>g<br />
the hydrolysis of InsP 3–InsP 6 by mucosal<br />
homogenates from the pig were recently reported<br />
by Hu et al. (1996). Phytase activities towards<br />
substrates <strong>in</strong>creased with decreas<strong>in</strong>g number of<br />
phosphate groups. This suggests that hydrolysis <strong>in</strong><br />
the <strong>in</strong>test<strong>in</strong>e may be enhanced by earlier phytase<br />
activity that had led to production of some lower<br />
<strong>in</strong>ositol phosphates <strong>in</strong> the stomach. Phytate disappearance<br />
from digesta has been demonstrated<br />
when soluble phytate was <strong>in</strong>cubated <strong>in</strong> loops of rat<br />
duodenum, jejunum <strong>and</strong> ileum (Davies & Flett,<br />
1978). In all natural diets, however, calcium <strong>and</strong><br />
magnesium are present <strong>and</strong> reaction with phytate<br />
is to be expected, <strong>and</strong> the strength of this depends<br />
on the number of phosphate groups on the <strong>in</strong>ositol<br />
molecule (Xu et al., 1992). The ma<strong>in</strong> part of the<br />
phytate <strong>in</strong> the diet <strong>and</strong> ileal digesta therefore is<br />
present as an <strong>in</strong>soluble complex.<br />
For determ<strong>in</strong>ation of degradation of feed or<br />
food components <strong>in</strong> the stomach <strong>and</strong> small <strong>in</strong>test<strong>in</strong>e,<br />
studies <strong>in</strong> ileostomized pigs (S<strong>and</strong>berg et al.,<br />
1993; Skoglund et al., 1997b) <strong>and</strong> <strong>human</strong>s have<br />
been performed (S<strong>and</strong>berg et al., 1981, 1983). The<br />
ileostomy model was used for <strong>in</strong>vestigation of the<br />
extent of phytate hydrolysis (S<strong>and</strong>berg et al.,<br />
1987; S<strong>and</strong>berg & Andersson, 1988) <strong>and</strong> factors<br />
affect<strong>in</strong>g this hydrolysis. Specific analyses of InsP 6<br />
<strong>and</strong> its hydrolysis products (InsP 3–InsP 5) were<br />
performed us<strong>in</strong>g HPLC ion pair chromatography<br />
(S<strong>and</strong>berg & Ahder<strong>in</strong>ne, 1986; S<strong>and</strong>berg et al.,<br />
1989). The effect of dietary phytase <strong>and</strong> <strong>in</strong>test<strong>in</strong>al<br />
phytase on InsP 6 hydrolysis was <strong>in</strong>vestigated<br />
(S<strong>and</strong>berg et al., 1987). Hydrolysis of InsP 6 from<br />
raw wheat bran <strong>and</strong> extruded bran was compared.<br />
Seven ileostomy subjects were studied dur<strong>in</strong>g two<br />
4-day periods with a constant low-fibre diet <strong>and</strong><br />
the addition of 54 g of raw mixture of bran, gluten<br />
<strong>and</strong> starch dur<strong>in</strong>g one period <strong>and</strong> 54 g of the<br />
correspond<strong>in</strong>g extruded product dur<strong>in</strong>g the other<br />
period. S<strong>and</strong>berg et al. (1987) found that 60% of<br />
the InsP 6 from raw bran were hydrolysed dur<strong>in</strong>g<br />
the passage through the stomach <strong>and</strong> small<br />
<strong>in</strong>test<strong>in</strong>e result<strong>in</strong>g <strong>in</strong> an improved Ôapparent<br />
absorptionÕ of z<strong>in</strong>c <strong>and</strong> phosphorus (Kivisto¨ et al.,<br />
1986) <strong>and</strong> that hydrolysis products were formed,<br />
but this did not occur when the subjects were fed<br />
extruded bran. Dur<strong>in</strong>g extrusion cook<strong>in</strong>g the<br />
<strong>in</strong>tr<strong>in</strong>sic bran phytase was deactivated. S<strong>and</strong>berg<br />
& Andersson (1988) extended the study us<strong>in</strong>g<br />
phytase-deactivated wheat bran <strong>and</strong> found no<br />
hydrolysis of InsP 6 <strong>and</strong> no formation of hydrolysis<br />
products. Further, S<strong>and</strong>berg et al. (1987), S<strong>and</strong>berg<br />
& Andersson (1988) concluded that dietary<br />
phytase is of significance for phytate hydrolysis <strong>in</strong><br />
the stomach <strong>and</strong> small <strong>in</strong>test<strong>in</strong>e, while <strong>in</strong>test<strong>in</strong>al<br />
phytase if present <strong>in</strong> <strong>human</strong>s does not play a<br />
significant role. It was recently demonstrated that<br />
very low phytase activity occurs <strong>in</strong> the <strong>human</strong><br />
small <strong>in</strong>test<strong>in</strong>e, thus confirm<strong>in</strong>g that the <strong>human</strong><br />
small <strong>in</strong>test<strong>in</strong>e has very limited ability to digest<br />
InsP 6 (Iqbal et al., 1994). These conclusions were<br />
further supported by analysis of the specific<br />
isomers formed <strong>in</strong> the ileal content dur<strong>in</strong>g<br />
hydrolysis. Wheat phytase starts the hydrolysis<br />
at the l-6 position form<strong>in</strong>g specific isomer<br />
dl-Ins(1,2,3,4,5)P5, which was found <strong>in</strong> the <strong>in</strong>test<strong>in</strong>al<br />
content follow<strong>in</strong>g consumption of raw wheat<br />
bran (Skoglund et al., 1997c), but not after consumption<br />
of phytase deactivated wheat bran.<br />
Indirect evidence for phytate hydrolysis <strong>in</strong> the<br />
<strong>human</strong> stomach <strong>and</strong> small <strong>in</strong>test<strong>in</strong>e by A. niger<br />
International Journal of Food Science <strong>and</strong> Technology 2002, 37, 823–833 Ó 2002 Blackwell Science Ltd
phytase was reported <strong>in</strong> an iron absorption study<br />
by S<strong>and</strong>berg (1996). Add<strong>in</strong>g A. niger phytase to<br />
the phytate-conta<strong>in</strong><strong>in</strong>g meal markedly <strong>in</strong>creased<br />
iron absorption. Thus, both <strong>phytases</strong> from wheat<br />
<strong>and</strong> A. niger are active <strong>in</strong> the <strong>human</strong> gut. The<br />
phytase activity of wheat bran was, however,<br />
not sufficient to <strong>in</strong>crease iron absorption. For<br />
improved iron absorption the phytate degradation<br />
has to be virtually complete (Fig. 1). As the<br />
contents of the stomach acidify dur<strong>in</strong>g the digestive<br />
process, the pH would appear to favour<br />
A. niger phytase considerably over wheat phytase.<br />
In addition, it was recently reported that wheat<br />
phytase is more susceptible to <strong>in</strong>activation by<br />
gastro<strong>in</strong>test<strong>in</strong>al enzymes (Phillippy, 1999).<br />
A possible adaptation to <strong>in</strong>creased phytate<br />
degradation <strong>in</strong> small <strong>in</strong>test<strong>in</strong>e after a longer<br />
period of high phytate <strong>in</strong>takes was <strong>in</strong>vestigated<br />
Relative absorption (%)<br />
100<br />
90<br />
80<br />
70<br />
60<br />
50<br />
40<br />
30<br />
20<br />
10<br />
0<br />
White + 1 g deactivated + 1 g raw + 1 g deactivated bran<br />
wheat roll bran bran + <strong>microbial</strong> phytase<br />
Figure 1 Effect of dietary phytase on iron absorption <strong>in</strong><br />
<strong>human</strong>s from bread meals measured by radionucleide<br />
technique. The meals consisted of white wheat rolls<br />
supplemented with wheat bran with or without phytase<br />
activity (experiment 1) or phytase deactivated wheat bran<br />
with or without addition of <strong>microbial</strong> phytase from A. niger<br />
(experiment 2). Addition of A. niger phytase to the meal<br />
<strong>in</strong>creased iron absorption from 14.3 ± 2.6 to 26.8 ± 3.8%<br />
(P < 0.0001, n ¼ 10subjects).<br />
Degradation of phytate A.-S. S<strong>and</strong>berg & T. Andlid 829<br />
(A.-S. S<strong>and</strong>berg, P. Tidehag, G. Hallmans,<br />
P. A ˚ man, J.-X. Zhang & E. Lund<strong>in</strong>, unpublished<br />
results). N<strong>in</strong>e ileostomy subjects consumed oat<br />
bran added to a low-fibre diet dur<strong>in</strong>g the 3 week<br />
period. Ileostomy contents from days 3 <strong>and</strong> 17<br />
were analysed (A.-S. S<strong>and</strong>berg et al. unpublished<br />
results). A complete recovery of <strong>in</strong>ositol InsP 6 was<br />
found <strong>in</strong> ileostomy subjects both dur<strong>in</strong>g day 3 <strong>and</strong><br />
17. No <strong>in</strong>creased phytate degradation was found<br />
after 17 days of consumption, show<strong>in</strong>g that no<br />
adaptation occurred dur<strong>in</strong>g this period. Furthermore,<br />
a complete recovery of dietary <strong>in</strong>ositol<br />
penta-, tetra- <strong>and</strong> triphosphates was obta<strong>in</strong>ed.<br />
In these ileostomy studies, the dietary level of<br />
calcium was relatively high (around 30mmol<br />
day )1 ). However, <strong>in</strong> another ileostomy study<br />
(S<strong>and</strong>stro¨ m et al., 1986a), where degradation of<br />
phytate from soyflour, soy concentrates <strong>and</strong> soy<br />
isolate was <strong>in</strong>vestigated, different dietary calcium<br />
levels were used. The calcium:phytate molar ratios<br />
<strong>in</strong> this study were 20; 22; 28 <strong>and</strong> 4.5. Independently<br />
of these molar ratios an almost complete<br />
<strong>in</strong>ositol InsP 6 recovery was obta<strong>in</strong>ed suggest<strong>in</strong>g<br />
that these differences <strong>in</strong> the dietary calcium level<br />
did not affect the degradation of <strong>in</strong>ositol InsP 6 <strong>in</strong><br />
the stomach <strong>and</strong> small <strong>in</strong>test<strong>in</strong>e (S<strong>and</strong>berg, 1996).<br />
Similar results were obta<strong>in</strong>ed <strong>in</strong> pigs, <strong>in</strong>dicat<strong>in</strong>g no<br />
effect of dietary calcium level on phytate degradation<br />
<strong>in</strong> the stomach <strong>and</strong> small <strong>in</strong>test<strong>in</strong>e (S<strong>and</strong>berg<br />
et al., 1993; Skoglund et al., 1997b).<br />
Degradation of phytate <strong>in</strong> the colon<br />
Consider<strong>in</strong>g the large number of micro-organisms<br />
present <strong>in</strong> the colon degradation of phytate by<br />
<strong>microbial</strong> phytase could be expected to occur <strong>in</strong><br />
the colon. The germ-free animal would be a useful<br />
model to <strong>in</strong>vestigate the extent of phytate degradation<br />
by <strong>microbial</strong> phytase <strong>in</strong> vivo. In a study by<br />
Wise & Gilburt (1982) the hydrolysis of phytate<br />
was compared <strong>in</strong> germ-free <strong>and</strong> conventional rats.<br />
In conventional rats fed with high- <strong>and</strong> lowcalcium<br />
diet 22 <strong>and</strong> 55% of phytate was hydrolysed,<br />
respectively, while negligible hydrolysis was<br />
observed <strong>in</strong> the germ-free rats. It was concluded<br />
that the microflora had been responsible for the<br />
observed hydrolysis. Indirect support for bacterial<br />
hydrolysis was reported by Wise et al. (1983).<br />
Hydrolysis products were found <strong>in</strong> the caecum,<br />
with <strong>in</strong>creas<strong>in</strong>g amounts <strong>in</strong> the colon <strong>and</strong> faeces<br />
Ó 2002 Blackwell Science Ltd International Journal of Food Science <strong>and</strong> Technology 2002, 37, 823–833
830<br />
Degradation of phytate A.-S. S<strong>and</strong>berg & T. Andlid<br />
followed by phosphorous nuclear magnetic resonance.<br />
Lantzsch et al. (1988) also found evidence of<br />
phytate hydrolysis <strong>in</strong> the colon of pigs.<br />
A balance study <strong>in</strong> <strong>human</strong>s dur<strong>in</strong>g three consecutive<br />
24-day periods on white, brown <strong>and</strong><br />
whole meal breads was performed to <strong>in</strong>vestigate<br />
the effect of dietary fibre on m<strong>in</strong>eral absorption<br />
(Andersson et al., 1983). The phytate content was<br />
held constant dur<strong>in</strong>g the three periods by addition<br />
of sodium phytate to the diet <strong>in</strong> periods with<br />
brown <strong>and</strong> white bread to the same level as <strong>in</strong><br />
whole meal bread. Inositol phosphates <strong>in</strong> the<br />
faeces material were analysed (A.-S. S<strong>and</strong>berg,<br />
H. Andersson, J. H. Cumm<strong>in</strong>gs, unpublished<br />
results; S<strong>and</strong>berg, 1996). A mean of 25–35%<br />
hydrolysis of InsP 6 was found, although <strong>in</strong>dividual<br />
variation occurred. There were no significant<br />
differences between the dietary periods, neither<br />
was there an <strong>in</strong>creased degradation after the third<br />
period compared with the first. As the diet did not<br />
conta<strong>in</strong> phytase activity, the results suggest that a<br />
degradation of phytate occurs <strong>in</strong> the colon of<br />
<strong>human</strong>s. The calcium level of this study was rather<br />
high (30–40 mmol day )1 ). It has been demonstrated<br />
previously that <strong>in</strong> healthy <strong>human</strong>s phytate was<br />
hydrolysed to a great extent but was <strong>in</strong>versely<br />
related to the calcium <strong>in</strong>take (McCance &<br />
Widdowson, 1935; Cruickshank et al., 1945;<br />
Walker et al., 1948). In a study with ileostomized<br />
pigs, S<strong>and</strong>berg et al. (1993) found that the dietary<br />
calcium level markedly affected the phytate degradation<br />
<strong>in</strong> the colon. Total gastro<strong>in</strong>test<strong>in</strong>al degradation<br />
of <strong>in</strong>ositol InsP 6 <strong>in</strong> pigs fed with a<br />
rapeseed diet (not conta<strong>in</strong><strong>in</strong>g phytase activity) was<br />
97, 77 <strong>and</strong> 42% (P < 0.001) when calcium <strong>in</strong>takes<br />
were 4.5, 9.9 <strong>and</strong> 15 g day )1 , while no differences<br />
<strong>in</strong> phytate hydrolysis of ileal digesta were found<br />
between periods. Similar to these results, Skoglund<br />
et al. (1997b) found an impaired <strong>in</strong>ositol InsP 6<br />
degradation <strong>in</strong> the colon when the pig feed was<br />
supplemented with calcium.<br />
Hydrolysis of phytate <strong>in</strong> the colon may release<br />
calcium, which can be absorbed by the colon<br />
(James, 1980) <strong>and</strong> may therefore be of <strong>nutrition</strong>al<br />
significance. S<strong>and</strong>stro¨ m et al. (1986b) demonstrated<br />
that 14% of calcium labelled with 47 Ca was<br />
absorbed when <strong>in</strong>stalled dur<strong>in</strong>g colonoscopy. The<br />
authors concluded that colonic absorption of<br />
calcium could account for a substantial part of<br />
the total calcium uptake.<br />
Conclusions<br />
Phytate can be degraded us<strong>in</strong>g biological food<br />
process<strong>in</strong>g techniques <strong>in</strong>creas<strong>in</strong>g the activity of the<br />
naturally occurr<strong>in</strong>g enzyme phytase by soak<strong>in</strong>g,<br />
malt<strong>in</strong>g hydrothermal treatment, fermentation or<br />
by addition of <strong>phytases</strong>. Degradation of phytate<br />
improves the bioavailability of iron, z<strong>in</strong>c <strong>and</strong><br />
phosphorus <strong>in</strong> man. However, to substantially<br />
<strong>in</strong>crease iron absorption, degradation of phytate<br />
must be virtually complete.<br />
Phytate degradation <strong>in</strong> the stomach <strong>and</strong> small<br />
<strong>in</strong>test<strong>in</strong>e of <strong>human</strong>s occurs as a result of activity of<br />
dietary phytase of plant or <strong>microbial</strong> orig<strong>in</strong>. The<br />
plant phytase is less stable than fungal phytase at<br />
the physiological conditions of the gastro<strong>in</strong>test<strong>in</strong>e.<br />
The activity of <strong>in</strong>test<strong>in</strong>al mucosa phytase is low <strong>in</strong><br />
<strong>human</strong>s <strong>and</strong> does not lead to any significant<br />
phytate degradation <strong>in</strong> the <strong>in</strong>test<strong>in</strong>e when consum<strong>in</strong>g<br />
a normal diet. No adaptation to <strong>in</strong>creased<br />
phytate degradation <strong>in</strong> the stomach <strong>and</strong> small<br />
<strong>in</strong>test<strong>in</strong>e occurs after a period of consumption of a<br />
high phytate diet. The phytate degradation <strong>in</strong> the<br />
colon could be considered as an effect of <strong>microbial</strong><br />
phytase produced by the microflora present. This<br />
degradation is reduced by <strong>in</strong>creas<strong>in</strong>g the calcium<br />
<strong>in</strong>take, probably because of the formation of<br />
<strong>in</strong>soluble calcium phytate complexes. It is not<br />
known, however, which <strong>and</strong> to what extent<br />
<strong>in</strong>ositol phosphates, formed by degradation of<br />
phytate, may be absorbed by the <strong>in</strong>test<strong>in</strong>al epithelia<br />
<strong>and</strong> potentially exert a physiological response.<br />
Further work is needed on the positive <strong>and</strong>/or<br />
negative health effects of different <strong>in</strong>ositol phosphates<br />
<strong>and</strong> their stereoisomers. Biotechnologically<br />
produced phytase, used today <strong>in</strong> animal feed<strong>in</strong>g,<br />
may be possible to use tomorrow <strong>in</strong> food process<strong>in</strong>g<br />
as well as plant raw material <strong>and</strong> starter<br />
cultures with <strong>in</strong>serted phytase genes. Some of the<br />
degradation products of InsP 6 have been identified<br />
as m<strong>in</strong>eral absorption <strong>in</strong>hibitors <strong>and</strong> some may<br />
have health benefits. A controlled degradation of<br />
InsP 6 form<strong>in</strong>g desired specific isomers of <strong>in</strong>ositol<br />
phosphates with health benefits is a challenge for<br />
the future.<br />
References<br />
Andersson, H., Nävert, B., B<strong>in</strong>gham, S.R., Englyst, H.N. &<br />
Cumm<strong>in</strong>gs, J.H. (1983). The effects of breads conta<strong>in</strong><strong>in</strong>g<br />
International Journal of Food Science <strong>and</strong> Technology 2002, 37, 823–833 Ó 2002 Blackwell Science Ltd
similar amounts of phytate but different amounts of<br />
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