Antinutrients
Phytate - antinutrient / malabsorption agent
Phytic Acid - "Malabsorption Agent"
Phytic Acid / Phytate - Phytase Enzymes Break down Phytate in Foods
PHYTASE enzymes break down phytic
acid /phytate (the salt of phytic acid)
What is Phytase and what does it do?
Phytase is any type of
phosphatase enzyme that breaks down phytic acid
(a chemical process
called
dephosphorylation ,
produces a phosphate ion and a molecule with a free hydroxyl group)
- phytase catalyzes
the hydrolysis (requires water) of phytic acid
by removing a phosphate group from its substrate
to release a usable form of inorganic
phosphorus
The break down of phytic
acid by phytases results in two specific beneficial effects - both of which increase
mineral availability and absorption (esp. bone-beneficial phosphorus)
(1) Allows the
utilization/absorption of bound/stored nutrients in phytate -phytase can hydrolyze phytic
acid, releasing phosphorus and other
nutrients bound by phytic acid (E.g. minerals,
protein and starch );
The binding is possible within a phosphate group or between two phosphate groups
on either the same or different phytic
acid molecules;
(2) Prevents phytic acid from
binding to important minerals in the digestive tract - which would otherwise make them unavailable to the body.
Humans
(and other non-ruminants)
do produce phytase en zymes
for breaking down phytic acid, but favorable gut bacteria do - interestingly, rat
intestine had 30 times the phytase activity of the human intestine (ex-vivo) and therefore the results of rodent studies examining
phytate degradation are unlikely to apply to humans.
Iqbal TH,
Lewis KO, Cooper BT. Phytase activity in the human and rat
intestine (1994) Gut, BMJ. 35(9):1233-1236
In germ and bran of whole seed/grain, germination activates phytase -
which breaks down phytic acid and releases
phosphorus and other minerals
- Some grains contain more
phytase than others
• High phytase
grains - Wheat
contains 14 times more phytase than rice; rye contains over twice as much
as wheat (the reason rye is preferred as a starter for
sourdough breads).
Egli I and others. The Influence of Soaking and Germination on the Phytase
Activity and Phytic Acid Content of Grains and Seeds Potentially Useful for
Complementary Feeding. Journal of Food Science 2002 Vol. 67, Nr. 9.
•
Oatmeal has a low phytase
content
Phytase
activity depends on pH
Phytase activity depends
on pH with the ideal pH being somewhere
in the ~4.5 - 5.5 range -adding a mild acid to soaking water of phytate foods creates that "just right" pH environment for phytase action. Note that the stomach acid pH is much
lower and not conducive to phytase activity
- "pH was the most important factor in reducing the
content of phytic acid during bread making, as phytic acid in doughs with pH
4.3-4.6 was more effectively reduced than in doughs with higher pH."
Phytase activity and degradation of
phytic acid during rye bread making by Merete Møller Nielsen •Marianne Linde
Damstrup •Agnete Dal Thomsen •Søren KjærsgËš rd Rasmussen •Ã…se Hansen Eur Food
Res Technol 2007
- Reale et al
concluded that lactic acid bacteria improved conditions for degrading phytic
acid
simply by lowering pH -they determined the ideal pH to be ~ 5.5
Reale A, Konietzny U, Coppola R, Sorrentino E, and Greiner R,
2007,
'The importance of lactic acid bacteria for phytate degradation during cereal
dough fermentation', Journal of Agriculture and Food Chemistry,
55 (8), pp 2993-2997ACSPub
- Phytase activities are pH
dependent with the highest activities being observed at a slightly acidic pH
( 5.1).
Food Reviews International
Phytic Acid
by Lori Oatway a; Thava Vasanthan b; James H. HelmField Crop Development
Centre, Lacombe, Canada b Department of Agricultural Food and Nutritional
Science, University of Alberta, Edmonton, Canada
- Bacterial
flora in the colon
Sandström, B., Cederblad, A., Stenquist, B.,
& Andersson, H. (1990). Effect of inositol hexaphosphate on retention of zinc and
calcium from the human colon. European Journal of Clinical Nutrition, 44,
705-708.
-A high phytate diet improves the ability of intestinal microbiota to
degrade phytate (Markiewicz et al) -
This is a big deal! - because it
means that gut microbes "step up to the plate" and
improve their efficiency at producing phytase enzymes to degrade phytate when
there is a dietary increase in phytates . However, studies show that
at best, still only about half of the intestinal dietary phytate is broken down.
(Schlemmer et al 2009). This may be because phytate has both negative and
positive roles to play in the body. Interestingly, of
the various microbes examined, gram-positive anaerobes and lactic acid bacteria
(i.e. the ones in sourdough) appeared to be the least
effective in the hydrolysis of phytic acid, and
E. Coli performed the best.
The message to take home here is:
(1) The importance of having a
favorable, balanced gut flora.
(2) We probably don't need to go overboard with food preparation methods to
reduce phytates unless our diet is "loaded" with them. If we moderate our
phytate intake and consume animal fats containing
natural
vitamin A and
vitamin D (mitigates effects of phytic acid), then healthy gut
flora can probably deal with them on their own.
What foods contain phytate?
L.H.
Markiewicz , J. Honke , M. Haros, D. Swiaztecka, B. Wroblewsk. Diet shapes the
ability of human intestinal microbiota to degrade phytate -in vitro studies
(2013) J. Appl. Microbiology
Schlemmer, U., Frølich, W., Prieto, R.F. and Grases, F. (2009) Phytate in foods
and significance for humans: food sources, intake, processing, bioavailability,
protective role and analysis. Mol Nutr Food Res 53, S330-S375.
Phytase
activity depends on temperature
Phytase activity is increased within an ideal
temperature
Phytase is
reduced /destroyed by:
- Steam heat -
176 °F in 10 mins. or less
- Heat-processing -such as being in a wet solution at 131-149 °F
Peers FG. Phytase of Wheat. The Biochemical Journal 1953 53(1):102-110.
• EXTRUDED bran and whole grain cereals
(E.g. All-bran ®, Bran Buds)
are a recipe for digestive disaster
and mineral deficiencies
- Slurries of
extremely high phytate grains are
forced through tiny holes at high temperatures and pressures, which destroy the
phytase enzymes that might have broken down some of the phytate - you might be
regular, but at what cost? - flaxseed
(negligible phytate content) and prunes are your better bet.
•
Freezing and long storage times -
fresh flour has more
phytase than after being stored.
With WHOLE grains and legumes, -and cooking
temperatures eventually destroy phytase
altogether. To reduce phytic acid to a
healthy level requires some preparation before cooking
Campbell J and others. Nutritional Characteristics of Organic, Freshly
stone-ground sourdough and conventional breads.
http://eap.mcgill.ca/publications/EAP35.htm .
