Phytase

Phytase is an enzyme that can break down the undigestible phytic acid (phytate) that is found in the outer sheath of grains and thus release digestible iron, phosphorus and calcium.

Phytase plays a significant role in human nutrition, especially of iron, because it releases minerals in bread and grains, allowing assimilation in the human digestive system. It is also an important supplement for domestic pigs.

Soaking whole grains

Soaking whole grains such as brown rice, wheat or barley overnight for 8 to 12 hours in dechlorinated water allows the phytase enzyme already present in the environment (or the grain itself) to remove the phytic acid from the grain coverings, making them more digestible.

The standard practice is to start grains soaking at bedtime for cooking the next day. Start the soak with two cups of dechlorinated warm (but not too hot to touch) water per one cup of whole grain. An easy way to achieve the desired warmth is to bring less than half the soak water close to a boil, then add it to the rest of the water which is at room temperature. The combined water should feel warm, but not too hot to touch. Then add the grain to be soaked. Wheat, rye, barley, hato mugi and brown rice can benefit from soaking in this manner. Do not refrigerate, but cover while leaving a crack for air to get in and out. By the next morning, tiny dots in the water will indicate that the enzyme has done its job of leaching out the phytates from the grain coverings. To see these dots, examine the water with light reflecting onto its surface.

People disagree on whether grains soaked in this manner should then be cooked in their soak water, which may contain other nutrients from the grains, or whether the water should be changed before cooking. Phytate molecules are too large to pass across the stomach lining and into the bloodstream. The molecules are also unaffected by digestive juices and colonic bacteria, so are lost in the excreta. However, some people believe that phytate actually combines with minerals in the gut, acting as an anti-nutrient or having a leaching effect. Thus, it is possibly better to discard the soak water and cook soaked grains in fresh water after soaking.

To enhance and speed up the enzymatic conversion of phytic acid, cooks may save a small portion of used soak water (already rich with phytase) to add to the warm water used to soak the next batch of whole grains.

Breadmaking

A loaf of bread made using a home bread machine does not allow time for the phytase enzyme to break the phytic acid bonding with mineral constituents in the grain; hence, bread machines usually require the addition of yeast. Traditional sourdough bread making produces a mix that spends 8-12 hours or more in the form of a dough, before baking. This time is required for the phytase enzymes to release the mineral constituents in the flour.

Animal feed supplement

Phytase is used as an animal feed supplement to enhance the nutritive value of plant material by liberation of inorganic phosphate from phytic acid (myo-inositol hexakisphosphate) and, thereby, to reduce environmental phosphorus pollution.

Production

Phytase can be purified from transgenic microbes. Phytase has been produced recently in transgenic canola, alfalfa and rice plants. Phytase can also be massively produced through cellulosic biomass fermentation using genetically modified (GM) yeast.