Damaged Starch النشا المحطم
مرسل: الاثنين مايو 07, 2018 10:29 pm
Damaged Starch
The starch in wheat occurs as partially crystalline granules. When placed in excess water, the granules will absorb about 30% of their weight. The crystallinity of the granules restricts it from absorbing additional water. During milling some of the granules are damaged. The damage results from the shear on the granule during roller milling. The shear shatters/ruptures some of the crystals. The damage may include the entire granule or just a part of it. This loss of crystals allows the granule to take up more water and swell more. Damaged starch will absorb as much as 300X its weight in water. Hard wheat flour contains a much higher level of damaged starch than does soft wheat. This apparently is because the soft wheat crushes easily during milling and does not subject the starch to as much shear.
Damaged starch is positive factor in bread flour because it increases the water absorption. High water absorption increases the yield of dough and bread from a flour, which has obvious positive effects on bakery profits. Damaged starch is a strong negative in flours for cookies and other dry finished products.
The damaged starch is highly susceptible to α- amylase attack. Much of the damaged starch is degraded to maltose and small dextrins by the combination of α- and β- amylase. This is the major reason that bread flours are malted (α- amylase added) at the mill. If the damaged starch is not removed during fermentation it interacts with the gluten and reduces bread volume.
Damaged starch is generally measured by enzymatic methods. The amount of reducing sugar produced in a certain time with excess enzyme is measured. The flour sample is subdivided into 2 subsamples, one of which is treated directly with the enzyme. The second subsample is autoclaved to gelatinize all the starch and then treated with the same enzyme system. The value obtained for the non-autoclaved sample is divided by the value for the autoclaved sample and the result is multiplied by 100. This gives the percentage of damaged starch. Most hard wheat flours will have from 6-9% damaged starch by the AACC procedure.
A second procedure used in an instrument that uses an electrode system to measure iodine. The amount of iodine bound is related to the amount of damaged starch. The procedure is accurate by requires that the electrode be properly maintained.
The starch in wheat occurs as partially crystalline granules. When placed in excess water, the granules will absorb about 30% of their weight. The crystallinity of the granules restricts it from absorbing additional water. During milling some of the granules are damaged. The damage results from the shear on the granule during roller milling. The shear shatters/ruptures some of the crystals. The damage may include the entire granule or just a part of it. This loss of crystals allows the granule to take up more water and swell more. Damaged starch will absorb as much as 300X its weight in water. Hard wheat flour contains a much higher level of damaged starch than does soft wheat. This apparently is because the soft wheat crushes easily during milling and does not subject the starch to as much shear.
Damaged starch is positive factor in bread flour because it increases the water absorption. High water absorption increases the yield of dough and bread from a flour, which has obvious positive effects on bakery profits. Damaged starch is a strong negative in flours for cookies and other dry finished products.
The damaged starch is highly susceptible to α- amylase attack. Much of the damaged starch is degraded to maltose and small dextrins by the combination of α- and β- amylase. This is the major reason that bread flours are malted (α- amylase added) at the mill. If the damaged starch is not removed during fermentation it interacts with the gluten and reduces bread volume.
Damaged starch is generally measured by enzymatic methods. The amount of reducing sugar produced in a certain time with excess enzyme is measured. The flour sample is subdivided into 2 subsamples, one of which is treated directly with the enzyme. The second subsample is autoclaved to gelatinize all the starch and then treated with the same enzyme system. The value obtained for the non-autoclaved sample is divided by the value for the autoclaved sample and the result is multiplied by 100. This gives the percentage of damaged starch. Most hard wheat flours will have from 6-9% damaged starch by the AACC procedure.
A second procedure used in an instrument that uses an electrode system to measure iodine. The amount of iodine bound is related to the amount of damaged starch. The procedure is accurate by requires that the electrode be properly maintained.