August 10, 2017

11/08/2017: The effect of damaged starch in flour milling on the quality of baked goods

by Dr Mahmoud Riad, Egyptian Milling Society, Secretary General

The recovery of flour ingredients from wheat during processing is not without deleterious effects

High-speed rollers and mechanical disruption of the wheat kernel bring about some damage to starch granules. While milling procedures are designed for maximum recovery of starch and the minimum inclusion of bran, they invariably result in a small but significant amount of starch damage.

Regardless of what type of milling is used five to 12 percent of the starch granules are damaged (Viot 1992). This in turn changes flour characteristics in dough mixing and bread baking. This phenomenon is also true for the production of noodles and tortilla, which are also sensitive to small changes in starch chemistry.

What is Damaged Starch?
It is a starch granule that is broken up into pieces. Not only does it increase water absorption and affect dough rheology, it increases food supply to the yeast and is more susceptible to fungal alpha amylase.

Starch represents 67-68 percent of whole grain wheat and between 78-82 percent of the flour produced from milling. The semi crystalline structure of the starch granule in the grain kernel can be damaged by mechanical operations, particularly the milling process.

Damaged starch (DS) is important in bread making: it absorbs four times its weight in water as compared to 0.4 for native starch. Damaged starch granules are also subject to preferential attack by specific enzymes (α- and β-amylases).

Some of these enzymes are incapable of attacking an intact granule because of the protective coating on the granules. The term “Damaged starch” is somewhat of a misnomer as the word “damaged” has a negative connotation implying something to be avoided. 

Figure 1: Damaged starch
The importance of damaged starch
It increases water absorption and provides extra nutrition for the yeast. A high level of damaged starch would result in sticky dough that produces a weak sidewall and a sticky crumb (if enough amylolytic enzymes are available). The level of starch damage directly affects the water absorption and the dough mixing properties of the flour and is of technological significance.

Positive and negative effects on bread quality
In fact, damaged starch should be optimised as it has both positive and negative effects on bread quality. Increasing damaged starch increases the water retention capacity of the flour; however, too much DS leads to sticky dough, strong proofing, and undesirable browning of crust.

The optimum DS value varies with the use of the flour and is greatly dependent upon the flour protein content, the alpha amylase activity, and the type of bread to be made from the flour. Most baked products around the world have specifications in terms of quality and functionality of flour used, and DS is one of these specifications. Flour with high DS cannot be used for the same purpose as the one with a low DS content.

Factors affecting the amount of damaged starch in the flourmill (figure 1):
1. The type of wheat.
2. The amount of water addition in tempering.
3. Rolls surface and speed.
4. Rolls spiral and differential.
5. Degree of grinding in rolls.
6. Rolls temperature.

Millers can manipulate damaged starch (DS) content of flours through wheat choice, grain preparation and mill setup and adjustments. The wheat choice is based on the impact of the grain hardness: the more resistant to milling, the greater the DS.

This "hardness" can be partly modified when preparing the wheat for milling. At milling, particular attention is given to the moisture conditioning and tempering time for the grain to be milled. From a proper conditioning or selection of the wheat, it is possible to increase or decrease the DS at the mill.

Furthermore, hardness is higher when the protein content is higher; thus, a direct correlation between the protein content and DS. Nevertheless, the mill set-up and adjustments are the major ways of influencing the end flour DS. This study focuses on those aspects.

Read the full article, HERE.

The Global Miller
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which is published by Perendale Publishers Limited.

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