What is phytic acid and phytates?
- Found in plants, mainly grains
- Originally seen are indesirable
- However now known that they can have positive health benefits
Structure of phytic acid?
- One of the few molecules in food to have a cyclohexane structure with 6 carbon atoms in a ring which is aliphatic in character rather then aromatic
- The inositol structure then has 6 hydroxyl functional groups with one attached to each carbon atom
- Phytate then has 5 phosphate groups, each linked covalenty to one the they hydroxyl units if myo-inositol
- The links are those of a ester and these are formedduring the esterification reaction: acid + alcohol -> water + ester
Where are phytates found?
- In plant foods, particulary grains and nuts
- They are effective storage reserve for phosphorus in plants
- during germination of wheat, phytate in hydrolysed enzymatically. This provided the phosphte needed for the plant to grow
- Enzymes include phytases and phosphatases with a veriaty of substates
- Highest concentration is in the bran
Ionisation properties of phytates?
- Phytic acid readily ionises in food
- While this could be thought of as six separate
ionisation reactions, the pKa values corresponding to
each of these is within the range of 1.1 to 3.2 (Table 1).
The next three ionisations have pKa values at 5.2 to 8.0
with a further three (9.2–12.0). Therefore at the pH
levels in all foods, phytate will be present as a phytate
ion carrying six to eight full negative charges, except at
the very highest pH values.
Table 1 The pKa values of phytic acid
Phytates as chelates?
- Term chelate refers to an anion which forms a complex by binding to stringly charged cations
- The phytate6- ion is a very effective chelate of divalent and trivalent cations.
- Many ions in food such as Ca2+, Fe2+ ect bind to phytate.
- This reduced the solubility due to lower over all charge and precipitation can results except at low pH values
Phytic acid and solubility?
- Phytic acid it liquid at room temp and the term miscible is used to indiace that it can be mixed with water in any proportion. In addition, complexes do not form wuth monovalet cations so the salts, sodium and potassium phytate are also quite water soluble
- The phytate ions and di and tri valent cations in foods and in our digestive tract react to form insoluble complexes
- This will make some important mineral less available
- Can also effect protein, carb and lipid digestibility
- May have antioxidant activity
- Help reduce the risk of some cancers, heart disease, fatty liver, HIV, diabetes, tooth decay