Wheat flour is the most important product of wheat milling. It is used on an industrial scale in baked goods, pasta, food concentrates, and confectionaries.
Ash is one of the major indicators of wheat flour’s quality. The ash obtained from flours consists of mineral compounds of phosphorous, potassium, calcium, magnesium, iron, zinc, and copper.
Phosphorus (approximately 45%), potassium (approximately 38%), magnesium, and calcium (approximately 13% and 3%, respectively) are the main elements present in ash, while the other elements amount to only 1%.
The whole wheat grain contains 1.17–2.96% of the mineral constituents. This variation is caused by the genotype, wheat class and cultivar as well as the growing location and year.
Minerals in the kernel are distributed unevenly. The aleurone layer and pericarp contain approximately 68%, the starch endosperm 20%, and the embryo 12% of the total minerals.
Flour characterized by a higher ash level is usually less purified and contains more particles of fine bran and endosperm adjacent to the bran. Therefore, ash is a widely used index of flour purity and its extraction rate during milling.
However, it should be noted that some wheat types, e.g., durum wheat, naturally have a higher level of endosperm ash due to genetic factors and soil conditions. From a nutritional point of view, an increase in the ash content in flour combined with an increase in the content of dietary fiber, vitamins, and non-gluten proteins is desirable. However, the technical quality of high-ash flour is lower because it is characterized by a darker color and greater activity of proteolytic and amylolytic enzymes.
Dietary fiber and non-gluten proteins disintegrate and weaken the protein matrix during dough formation.
Therefore, the ash content in flour is an important parameter in the assessment of flour quality. Measurement of the ash content is routinely performed using a standard ash analysis method in which the sample is burned at 550 ◦C for soft wheat flours and 575–590 C for hard wheat flours. Incinerating is carried out until light gray ash is obtained or until a constant weight is reached. The time of this determination is long and varies from 5 to 7 h.
In an industrial practice, this method is not frequently used because the time needed is too long and does not allow the wheat flour’s quality to be verified effectively. Numerous instrumental techniques have been proposed for ash and moisture analysis in different types of flour samples. Undoubtedly the most important and often applied in an industrial practice, is near-infrared spectroscopy (NIR).
The instrument that has become a global standard since 1987 is Infratec, which is based on NIR transmittance, fast and reliable for quantifying ash, moisture, protein, starch, wet gluten, fiber, oil and many more in grinding fractions of wheat.