Phytase in Food Processing: Phytic Acid, Chemical Reaction, Mineral Bioavailability and Cereal Applications
Phytase is an enzyme that hydrolyzes phytate, the principal storage form of phosphorus in many plant seeds. Phytate is particularly relevant to cereals, legumes, oilseeds, and other plant-based foods because its phosphate groups can bind minerals and influence their bioavailability.
In food processing, phytase is important because enzymatic degradation of phytate can reduce its mineral-binding capacity. This may improve the bioavailability of minerals, particularly iron and zinc, depending on the food matrix, processing conditions, dietary composition, and extent of phytate degradation.
Phytase activity is therefore relevant to cereal processing, germination, malting, fermentation, sourdough production, and nutritional improvement of plant-based foods.
What Is Phytase?
Phytase is a group of phosphatase enzymes that catalyze the hydrolysis of phosphate ester bonds in phytate.
The principal substrate is:
myo-Inositol hexakisphosphate (IP6)
Phytases are not a single structurally uniform enzyme family. Several phytase groups exist, including histidine acid phosphatases, β-propeller phytases, purple acid phytases, and protein-tyrosine-phosphatase-related phytases. These enzyme groups differ in structure, catalytic mechanism, positional specificity, and operating characteristics.
Therefore, the older description of phytase simply as an esterase is too broad for a current scientific publication.
A more accurate description is:
Phytase is a phytate-degrading phosphatase that hydrolyzes phosphate ester bonds in myo-inositol hexakisphosphate.
What Is Phytic Acid?
Phytic acid is commonly used to describe myo-inositol hexakisphosphate (IP6).
The molecule consists of:
- A six-carbon myo-inositol ring
- Six phosphate groups
- Six phosphate ester linkages connecting the phosphate groups to the inositol hydroxyl groups
The molecular formula of the free-acid form is:
C₆H₁₈O₂₄P₆
A simplified structural description is:
Myo-inositol ring + six phosphate ester groups → myo-inositol hexakisphosphate (IP6)
The six phosphate groups give the molecule a high negative charge when ionized. This chemical property allows phytate to interact with positively charged mineral ions and other food components.
Phytic Acid vs Phytate
The terms phytic acid and phytate are closely related but are not strictly identical.
Phytic acid
Refers to the protonated form of myo-inositol hexakisphosphate.
Phytate
Generally refers to the ionized forms and salts of phytic acid.
In foods and biological systems, phytate commonly exists in ionized forms rather than as one completely protonated molecule.
At physiological pH, the phosphate groups are substantially ionized, giving phytate a strong negative charge.
For food-science writing, “phytate” is often the more appropriate term when discussing phytate present in cereal foods.
Chemical Structure of Phytic Acid
The basic molecular structure can be represented as:
myo-Inositol
→ six hydroxyl groups on a cyclohexane ring
→ phosphorylation of all six hydroxyl groups
→ myo-inositol hexakisphosphate (IP6)
Each phosphate group is attached to the inositol ring through a phosphate ester linkage.
This chemical structure explains why phytate can bind mineral cations.
How Does Phytase Work?
Phytase hydrolyzes phosphate ester bonds in IP6.
The reaction occurs through dephosphorylation.
A simplified pathway is:
IP6 → IP5 → IP4 → IP3 → IP2 → IP1 → myo-Inositol
At each step, a phosphate group is removed and released as inorganic phosphate or its corresponding ionized phosphate species.
However, this pathway should be understood as a general representation, not as an identical sequence for every phytase.
Different phytases have different positional specificities and can generate different intermediate inositol phosphate profiles.
Phytase Chemical Reaction
For one hydrolysis step, a simplified reaction is:
IP6 + H₂O → IP5 + inorganic phosphate
This represents the removal of one phosphate group from the inositol phosphate molecule.
Further reactions can occur:
IP5 + H₂O → IP4 + inorganic phosphate
IP4 + H₂O → IP3 + inorganic phosphate
and so forth.
These reactions illustrate the progressive removal of phosphate groups.
Complete Hydrolysis of Phytic Acid
As a formal free-acid equation, complete hydrolysis can be represented as:
C₆H₁₈O₂₄P₆ + 6H₂O → C₆H₁₂O₆ + 6H₃PO₄
Products:
- C₆H₁₂O₆ = myo-inositol
- H₃PO₄ = phosphoric acid
This equation represents complete hydrolysis of the six phosphate ester groups.
However, this equation should not be interpreted as the dominant chemical form of phosphate in a food or physiological system. At relevant pH values, phosphate exists in several ionized forms, including H₂PO₄⁻ and HPO₄²⁻.
For food-processing applications, the more useful reaction is therefore:
Phytate + H₂O → Lower inositol phosphate + inorganic phosphate
What Are IP6, IP5, IP4 and IP3?
The notation describes the number of phosphate groups attached to the inositol molecule.
| Compound | Number of phosphate groups |
|---|---|
| IP6 | 6 |
| IP5 | 5 |
| IP4 | 4 |
| IP3 | 3 |
| IP2 | 2 |
| IP1 | 1 |
| Myo-inositol | 0 |
Thus:
IP6 = myo-inositol hexakisphosphate
IP5 = myo-inositol pentakisphosphate
IP4 = myo-inositol tetrakisphosphate
IP3 = myo-inositol trisphosphate
and so on.
The intermediate products are chemically important because their mineral-binding properties differ from those of intact IP6.
Why Is Phytate Important in Cereal Foods?
Phytate has an important biological role in plants.
It functions as a major storage form of phosphorus in seeds.
However, in human nutrition, phytate can reduce the bioavailability of certain minerals because its highly phosphorylated structure allows it to interact with mineral ions.
Minerals of nutritional interest include:
- Iron
- Zinc
- Calcium
- Magnesium
The strongest nutritional concern in human diets is generally associated with iron and zinc bioavailability.
The effect depends on:
- Phytate concentration
- Mineral concentration
- Food matrix
- Dietary composition
- pH
- Processing
- Mineral status of the individual
Therefore, phytate should not simply be described as a universally harmful compound.
Phytate and Mineral Binding
The negatively charged phosphate groups of phytate can interact with positively charged mineral ions.
For example:
Phytate + Zn²⁺ ⇌ Phytate–Zn complex
Similar interactions can occur with other mineral cations.
These complexes can reduce the fraction of some minerals that is available for absorption.
The strength of mineral binding depends on the chemical environment.
Factors include:
- pH
- Mineral concentration
- Phytate concentration
- Mineral-to-phytate ratio
- Food composition
- Presence of proteins and other ligands
Therefore, the simple reaction above represents mineral association, not a single fixed chemical compound that forms under every food condition.
How Phytase Can Improve Mineral Bioavailability
Phytase progressively removes phosphate groups from IP6.
The simplified relationship is:
IP6 → IP5 → IP4 → IP3 → Lower inositol phosphates
As phytate is degraded, the resulting lower inositol phosphates generally have a lower capacity to bind minerals than intact IP6.
This can increase the fraction of minerals available for absorption.
A useful process concept is:
Phytate → Phytase → Phytate degradation → Reduced mineral-binding capacity → Potentially improved mineral bioavailability
Human intervention research supports the potential for phytase treatment or food dephytinization to improve iron and zinc bioavailability, although the magnitude of the effect varies between food matrices and study conditions.
Phytase in Cereals
Cereal grains contain phytate and may contain endogenous phytase activity.
The concentration of phytate and endogenous phytase activity varies among cereal species and cultivars.
Therefore, two cereal samples can have substantially different phytate-degradation behavior.
Important variables include:
- Cereal species
- Cultivar
- Initial phytate concentration
- Endogenous phytase activity
- pH
- Temperature
- Moisture
- Germination
- Fermentation
- Processing time
The presence of endogenous phytase does not mean that extensive phytate degradation will automatically occur.
Phytase During Germination
Germination activates metabolic processes that mobilize stored nutrients in the seed.
Phytate is one of the important phosphorus-storage compounds.
During germination, endogenous phytase and other phosphatase activities can contribute to phytate degradation.
A simplified pathway is:
Seed phytate → Phytase activity → Lower inositol phosphates + inorganic phosphate
This can alter the distribution of phosphorus and reduce the amount of intact phytate.
The extent of degradation depends on:
- Germination time
- Temperature
- Moisture
- Cereal species
- Endogenous enzyme activity
- pH
Therefore, no universal phytate-reduction value should be assigned to germination.
Phytase in Cereal Fermentation
Fermentation can reduce phytate through a combination of:
- Endogenous cereal phytase activity
- Microbial phytase activity
- Acidification
- Increased substrate accessibility
- Extended processing time
A simplified pathway is:
Cereal phytate → Endogenous/microbial phytase → Lower inositol phosphates + inorganic phosphate
The degree of degradation varies with the fermentation system.
Important variables include:
- Microbial species
- Fermentation time
- Dough or slurry pH
- Temperature
- Flour extraction rate
- Whole-grain content
- Initial phytate concentration
- Endogenous phytase activity
Therefore, claims such as “fermentation removes all phytate” should not be used without product-specific experimental evidence.
Phytase in Sourdough
Sourdough is a useful food-processing system for studying phytate degradation.
During fermentation, lactic acid bacteria and other microorganisms produce organic acids, lowering dough pH. This change can affect endogenous cereal phytases and microbial enzyme activity.
The simplified process is:
Flour + Water → Fermentation → Acidification → Phytase activity → Phytate degradation
The actual amount of phytate degraded depends on the flour, microorganisms, fermentation conditions, and process duration.
For a commercial product, the final phytate concentration should be measured if phytate reduction is an important product specification or nutritional objective.
Phytase in Bread Production
Phytase activity can be relevant to whole-grain and cereal-based bread production.
A simplified process is:
Whole-grain flour → Hydration → Fermentation → Phytate degradation → Baking
Baking can substantially affect enzyme activity because phytase proteins are sensitive to processing temperature.
Consequently, phytase activity during dough fermentation and the phytate concentration remaining after baking are two different questions.
A food manufacturer should not assume that an enzyme remains active throughout baking.
For process validation, the appropriate measurement is often residual phytate in the finished product rather than enzyme activity alone.
Phytase and Mineral Bioavailability
The nutritional effect of phytase is not simply “more phytase equals more nutrition.”
The outcome depends on how much phytate is degraded and the mineral composition of the food.
Human intervention evidence indicates that phytase supplementation or food dephytinization can improve the bioavailability of certain trace elements, especially iron and zinc, in appropriate conditions. However, results are not identical across all studies.
Therefore, the scientifically appropriate wording is:
“Phytase-mediated phytate degradation can improve the bioavailability of certain minerals, particularly iron and zinc, depending on the food matrix and dietary conditions.”
Is Phytic Acid Harmful?
Phytic acid should not be described simply as a harmful substance.
In plants, phytate has an important biological role as a phosphorus-storage compound.
In food and nutrition, phytate can be considered an antinutritional factor because high concentrations can reduce the bioavailability of certain minerals.
Its nutritional significance depends on:
- Total dietary phytate intake
- Mineral intake
- Food processing
- Dietary pattern
- Mineral status
- Phytase activity
Thus, the goal of food processing is not necessarily complete phytate elimination.
The appropriate target depends on the nutritional and technological objective.
Is Myo-Inositol a Vitamin?
The statement that inositol is a vitamin should not be retained in a current scientific article.
Myo-inositol is a naturally occurring cyclitol involved in cellular signaling and metabolism.
It has historically been referred to as “vitamin B8,” but this terminology is not appropriate for modern scientific writing.
Therefore, phytase should not be described as converting a harmful compound into a vitamin.
A scientifically accurate statement is:
“Extensive phytate hydrolysis can ultimately produce myo-inositol and inorganic phosphate.”
Phytase Classification
Phytases comprise several enzyme families.
Important groups include:
- Histidine acid phosphatases
- β-Propeller phytases
- Purple acid phytases
- Protein-tyrosine-phosphatase-related phytases
These groups differ in their:
- Protein structure
- Catalytic mechanism
- pH activity profile
- Temperature stability
- Positional specificity
- Substrate specificity
Therefore, “phytase” describes a functional group of enzymes rather than one single protein structure.
3-Phytase and 6-Phytase
Phytases can also be classified according to the position where hydrolysis begins.
3-Phytase
A 3-phytase initiates dephosphorylation at the 3-position of the inositol phosphate substrate.
6-Phytase
A 6-phytase initiates dephosphorylation at the 6-position.
This classification describes positional specificity.
It does not mean that the enzyme performs only one reaction.
The subsequent hydrolysis pathway can produce multiple lower inositol phosphates.
Measuring Phytase Activity
Phytase activity can be measured using a defined phytate substrate and monitoring the release of inorganic phosphate.
A simplified analytical principle is:
Phytate + H₂O → Lower inositol phosphate + inorganic phosphate
The released phosphate can be quantified using an appropriate analytical method.
Other approaches measure:
- Residual phytate
- Formation of IP5
- Formation of IP4
- Formation of IP3
- Other lower inositol phosphates
These measurements provide different information.
Phytase Activity vs Phytate Reduction
These two measurements should not be confused.
Phytase activity
Measures enzyme performance under defined laboratory assay conditions.
Residual phytate
Measures how much phytate remains in the actual food.
Lower inositol phosphates
Provide information about the extent and pathway of phytate degradation.
For process validation, residual phytate concentration may be more directly relevant than an isolated phytase activity value.
An enzyme can show high activity in a laboratory assay but perform differently in a complex food matrix.
Factors Affecting Phytase Activity
pH
Phytases have enzyme-specific pH activity profiles.
There is no universal optimum pH for all phytases.
Temperature
Temperature affects catalytic activity and enzyme stability.
Excessive heat can inactivate phytase, depending on the enzyme source and formulation.
Moisture
Water is required for hydrolytic reactions and influences enzyme-substrate interactions.
Processing time
Longer reaction times can increase phytate degradation when the enzyme remains active and substrate remains accessible.
Substrate accessibility
The physical structure of the cereal matrix can affect access to phytate.
Fermentation
Microbial growth, acidification, and microbial phytase production can all influence phytate degradation.
Phytase in Food Processing
Phytase can be relevant to:
- Whole-grain processing
- Cereal fermentation
- Sourdough production
- Germination
- Malting
- Cereal-based nutritional products
- Plant-based food processing
The enzyme may originate from:
- Endogenous cereal enzymes
- Fermentation microorganisms
- Commercial phytase preparations
The contribution of each source depends on the process.
Phytase in Malting
Malting involves controlled germination of cereal grains.
During germination, endogenous enzyme systems become active and mobilize stored nutrients.
Phytate degradation can contribute to changes in phosphorus distribution and mineral-binding characteristics.
As with other cereal processes, the extent of phytate degradation depends on grain characteristics and malting conditions.
Food Safety and Regulatory Considerations
When a commercial phytase preparation is used as a food enzyme, its regulatory status must be evaluated according to the requirements of the relevant jurisdiction.
Important considerations include:
- Enzyme identity
- Production organism
- Production strain
- Manufacturing process
- Purity
- Intended food
- Technological purpose
- Conditions of use
- Regulatory authorization
In Canada, Health Canada’s List of Permitted Food Enzymes identifies authorized food enzymes, their permitted sources, specified food applications, and conditions of use.
Regulatory status should be checked for the specific phytase preparation and intended application. Authorization of one enzyme preparation does not automatically establish authorization for every phytase source or food use.
Common Scientific Errors About Phytase
“Phytase is simply an esterase.”
Correction: Phytase is more accurately described as a phytate-degrading phosphatase.
“Phytic acid is inositol hemophosphoric acid.”
Correction: The modern chemical name is myo-inositol hexakisphosphate (IP6).
“Phytase converts phytic acid directly into inositol and phosphoric acid.”
Correction: Phytase generally catalyzes stepwise dephosphorylation, producing lower inositol phosphates and inorganic phosphate. Complete hydrolysis can ultimately produce myo-inositol.
“Inositol is vitamin B8.”
Correction: Do not use this terminology in a modern scientific publication.
“Phytate prevents all mineral absorption.”
Correction: Phytate can reduce the bioavailability of certain minerals, particularly iron and zinc, but the effect depends on the food and dietary conditions.
“More phytase always means better nutrition.”
Correction: The nutritional outcome depends on the extent of phytate degradation and the food matrix.
“Phytase activity equals phytate reduction.”
Correction: Enzyme activity measured under assay conditions does not necessarily predict the extent of phytate degradation in the finished food.
“Fermentation removes all phytate.”
Correction: Fermentation can reduce phytate, but the degree of reduction is process-dependent.
Frequently Asked Questions
What is phytase?
Phytase is a group of phosphatase enzymes that hydrolyze phytate, principally myo-inositol hexakisphosphate (IP6), by removing phosphate groups.
What does phytase do to phytic acid?
Phytase progressively removes phosphate groups from IP6, producing lower inositol phosphates and inorganic phosphate. With sufficiently extensive hydrolysis, myo-inositol can ultimately be produced.
What is the chemical formula of phytic acid?
The molecular formula of the free-acid form of myo-inositol hexakisphosphate is C₆H₁₈O₂₄P₆.
What is IP6?
IP6 means inositol hexakisphosphate. It contains six phosphate groups attached to the inositol ring.
What happens when phytase removes one phosphate group?
A simplified reaction is:
IP6 + H₂O → IP5 + inorganic phosphate
The exact ionic form of the released phosphate depends on the pH of the system.
Does phytase produce inositol?
Extensive hydrolysis can ultimately produce myo-inositol, but phytase action normally proceeds through lower inositol phosphate intermediates.
Is myo-inositol a vitamin?
No. It should not be described as an essential vitamin or “vitamin B8” in a modern scientific publication.
Can phytase improve iron and zinc bioavailability?
Yes. Human intervention evidence indicates that phytate reduction or phytase treatment can improve iron and zinc bioavailability under appropriate conditions, although the magnitude varies between food systems and studies.
Does fermentation reduce phytate?
Yes. Fermentation can reduce phytate through endogenous cereal phytase and microbial phytase activity. The amount of reduction depends on the cereal, microorganisms, pH, temperature, moisture, and fermentation time.
Does baking destroy phytase?
Phytase enzymes can be inactivated by heat, but the exact thermal behavior depends on the enzyme source and processing conditions. Therefore, phytase activity during fermentation should not be assumed to continue after baking.
Is phytate always harmful?
No. Phytate is an important phosphorus-storage compound in plants. In human nutrition, it can act as an antinutritional factor by reducing the bioavailability of certain minerals under some dietary conditions.
Practical Guidance for Food Manufacturers
When evaluating phytase in a cereal-processing system:
- Measure the initial phytate concentration.
- Characterize endogenous phytase activity where relevant.
- Define the required phytate-reduction target.
- Select an enzyme appropriate for the process conditions.
- Evaluate pH and temperature compatibility.
- Control moisture and reaction time.
- Evaluate performance in the actual food matrix.
- Measure residual phytate in the processed product.
- Measure mineral bioavailability when a nutritional objective requires it.
- Verify the regulatory status of the exact commercial phytase preparation.
Conclusion
Phytase is a phytate-degrading phosphatase that hydrolyzes myo-inositol hexakisphosphate (IP6).
Phytic acid contains a myo-inositol ring with six phosphate groups. Its molecular formula, as the free-acid form, is C₆H₁₈O₂₄P₆.
Phytase removes phosphate groups through enzymatic hydrolysis. The reaction generally proceeds through lower inositol phosphates such as IP5, IP4 and IP3, with inorganic phosphate released during dephosphorylation. Extensive hydrolysis can ultimately produce myo-inositol.
The nutritional importance of phytase comes primarily from reducing intact phytate and its mineral-binding capacity. This can increase the bioavailability of certain minerals, with the strongest human evidence concerning iron and zinc.
For cereal processors, phytase performance depends on cereal type, phytate concentration, endogenous enzyme activity, pH, temperature, moisture, fermentation, processing time, substrate accessibility, and the specific enzyme preparation.
The appropriate processing objective is therefore not simply to eliminate all phytate. It is to achieve a controlled and measurable reduction in phytate appropriate to the nutritional and technological requirements of the food product.
