Balancing Damaged Starch

Identifying damaged starch levels and controlling its impact on the flour milling process play critical roles in delivering high-quality finished products to meet the demands of the marketplace.

When discussing damaged starch, however, it’s important to point out that the term itself is a slight misnomer in that “damaged” implies a negative connotation.

Yet, damaged starch is a necessary component in flour milling, since it can have a positive impact on the final flour products’ functionality and attributes.

For example, high levels of damaged starch increase the flour’s water retention capacity significantly.

However, if damaged starch exceeds certain levels, the end result may be sticky dough, strong proofing, and undesirable browning of crust.

So, for millers everywhere, the challenge boils down to controlling and adjusting damaged starch levels to produce the desired final products that meet specific needs of the end customers.

Starch, which consists of the polysaccharides amylose and amylopectin held together by enzymes (i.e., glycosidic bonds), is formed by the simple sugar glucose (a monosaccharide) and remains a critical component in maintaining life.

First, starch represents the key form of a carbohydrate produced by most plants in order to store energy.

Second, starch is the most important source of carbohydrate in human nutrition.

Worldwide, it is the most common carbohydrate in human diets, and is contained in large amounts in staple foods like wheat, potatoes, maize (corn), rice, and cassava (manioc).

Beyond these key attributes of starch, it also is important to keep in mind that starch represents about 68% of whole grain wheat and from 78% to 82% of the flour produced from milling.

So, let’s take a closer look at the impact of damaged starch on milling.

This article is based on a presentation by Dr. M. Hikmet Boyacioglu, applications development specialist, KPM Analytics, Westborough, MA, (774-502-0908/hboyacioglu@kpmanalytics.com), given online at the 2020 International Association of Operative Millers’ (IAOM) All-District Virtual Conference and Expo, Sept. 15-17, 2020.

Dr. Boyacioglu also holds adjunct professor and graduate faculty associate positions in the Department of Grain Science and Industry at Kansas State University. Boyacioglu received his Ph.D. degree in cereal science (minor in food and nutrition) from North Dakota State University.

He is a former university professor and chairman, cereal industry R&D coordinator, and international freelance consultant. Dr. Boyacioglu is currently associate editor of Cereal Chemistry journal published by AACC International and editor-in-chief of Cereal Technology journal.

He has been a professional member of the Cereals & Grains Association (formerly American Association of Cereal Chemists), IAOM, and the Institute of Food Technologies. He also is a former delegate and Technical Committee member for the International Association of Plant Bakers.

IAOM members who registered and paid for the virtual conference still can view the presentation using their provided link, username, and password.

The article contains an excerpt of some key highlights of comments related to this presentation, which have been edited for clarity and brevity.

Damaged Starch (DS) is described as the physical rupture or breakage of starch granules into smaller semi-crystalline pieces, which typically results from the physical process of milling.

This modifies the surface properties and increases the hydrophobic bonds of the starch granules and water absorption properties by at least tenfold compared to native flour. This also will impact the dough rheology.

In addition, some damaged starch granules are more susceptible to degradation by specific fungal α-amylase and bacterial β-amylase, while other granules’ outside coatings are more resistant to this form of degradation.

Factors Affecting Damaged Starch

The presence of damaged starch also is influenced by other factors, which include:

• Genetics and the type of wheat (i.e., hard wheat, soft wheat, or durum wheat). Soft wheat, for example, crushes easily during milling and does not subject the starch to as much shear damage. It also should be noted that there is no scientific consensus on how much and whether or not damaged starch occurs before harvesting the wheat.

• Grinding forces in the mill, including the rolls’ surface, speed, the differential between rolls, spiral angle, and temperature.

• Damaged starch increases when the gap between the rolls is reduced, or vice versa.

As the table below shows, when the roll gap is decreased, damaged starch will increase.

Plus, there is a correlation between roll pressure and increased damaged starch (see table on page 18).

• There is a direct correlation between increases in damaged starch levels to higher protein content levels in hard wheat.

• The amount of water and time involved in the tempering process has an impact on softening the endosperm of the wheat kernel where the starch is located.

Damaged starch is one of many criteria used to judge product quality.

There is a direct correlation between increases in damaged starch levels to higher protein content levels in hard wheat. - Dr. M. Hikmet Boyacioglu, applications development specialist, KPM Analytics

When starch damage is kept at an optimum level, it can be beneficial in maintaining good flour consistency, desired water absorption, and optimum fermentation, to name a few. But when out of range, damaged starch can quickly become a problem for the miller to solve.

Impact of Damaged Starch on Products

For millers and bakers, one common objective is to increase the water absorption without causing problems with dough rheology and baking performance.

However, if you have a very high or very low amount of damaged starch, it can cause a very pale crust color or very dark crust color.

Consequently, as a result of the starch degradation, the damaged starch also will affect the bread’s shelf life.

Excessive amounts of damaged starch can cause dough stiffness, decreased diameter, and reduced spread in products like cookies and biscuits.

Cookies: Moreover, a high damaged starch level increases the susceptibility to enzymatic reactions that result in smaller cookies.

High damaged starch levels can cause broken cookies when the packaging is opened and nonuniform coloration and size.

Consequently, analyzing damaged starch content is a very important aspect in implementing a quality control program.

Noodles: In Chinese noodle production, excessive damaged starch reduces the noodle’s cooking and eating quality due largely to more water being absorbed beyond what the gluten can actually hold.

Tortillas: Similar problems can occur in wheat flour tortillas, which is why maintaining optimum damaged starch levels is necessary to produce tortillas with acceptable roll ability without becoming too firm or less stretchable.

When damaged starch occurs at low levels, or at optimum/moderate levels for the desired product, this condition is considered to be beneficial to flour performance based on better water absorption capability and enzyme (maltase) penetration (i.e., the condition provides fermentable maltose for the yeast).

However, if damaged starch levels are too high, amylases preferentially attack damaged starch, not the native starch.

Under this condition, yeast activity will likely intensify and create too much carbon dioxide (CO2) and thereby reduce gas-retention capacity.

The coloration also may be impacted or increased, as well as have an influence on the Maillard reaction and caramelization.

(Editor’s note: The Maillard reaction is a chemical reaction between amino acids and reducing sugars that gives browned food its distinctive flavor. Seared steaks, fried dumplings, cookies and other kinds of biscuits, breads, toasted marshmallows, and many other foods undergo this reaction. It is named after French chemist Louis Camille Maillard, who first described it in 1912 while attempting to reproduce biological protein synthesis.)

Damaged starch content in wheat flour from the same cultivar also exhibits a strong correlation with acrylamide formation in bread due to increased levels of sugar content.

Mitigating acrylamide formation in bread can be achieved by reducing damaged starch in flour and by fermentation of the dough.

The level of damaged starch also influences bread staling due to the retrogradation of the amylopectin and crumb firmness. This adversely affects the quality of the resulting products and their shelf life.

(Editor’s note: Bread staling is predominantly a process of chemical and physical change in the baked bread which reduces it palatability by impacting its taste and also makes it dry and leathery in texture. The term does not include the changes caused by spoilage organisms.)

If the level of damaged starch becomes too high, the dough rheology and baking performance are affected negatively. Some of those drawbacks include stickiness, fermentation, changes in texture and color, and cracks.

However, damaged starch levels don’t increase indefinitely for at least two basic reasons.

1. As water absorption increases with an increase in damaged starch, the air-dough interface in gas cells becomes proportionally less stable during baking, leading to a loss of volume and a coarse texture.

2. With a high level of starch granule fragmentation, the available gluten can be insufficient to coat the surface of the starch, resulting in a loss of gas retention capacity, a lower loaf volume, and a breakdown of cell structure.

Measuring Damaged Starch

In order to control the damaged starch levels in flour, testing and analyzing the damaged starch content in each processing stream represents the best strategy.

Even if each stream has some amount of damaged starch, it doesn’t necessarily mean that all the finished products will contain unacceptable levels of that damaged starch.

On the contrary, being able to determine the amount of damaged starch in each stream offers the opportunity to target or isolate the problem area.

Therefore, damaged starch levels are a key parameter to review and evaluate when studying the floor diagrams or flow sheets.

Even if each stream has some amount of damaged starch, it doesn’t necessarily mean that all the finished products will contain unacceptable levels of that damaged starch.

While there may not be an optimum or moderate level of damaged starch that fits the needs of every product, it still remains important to quantify whether or not the damaged starch levels are well within acceptable limits for the customer.

Measuring damaged starch levels also will greatly help determine possible production problems or unacceptable products, as well as to determine that everything is okay.

Methods of Measuring Damaged Starch

Because of its importance in the flour and baking industries, many methods have been developed to quantify damaged starch presence. Those include the colorimetric, polarimetric, spectrophotometric, enzymatic, and amperometric methods.

Apart from these conventional means, the damaged starch also could be characterized by a series of other specific techniques like scanning electron-microscopy, transmission electron microscopy, near infrared reflectance (NIR), and light refraction, which are largely based on the changes in shape, surface, and particle size.

However, some of these methods aren’t practical for industrial use.

So, against this backdrop, there are currently three American Association of Cereal Chemists (AACC)-approved methods to determine damaged starch levels.

1. Reducing sugar level is often estimated by titrimetric method or colorimetric method. In this AACC-approved testing method, determining the damaged starch level is achieved through the titrimetric method and by measuring the reduction in sugar content.

In this method, the proportion of damaged starch is reflected by the calculated and reduced sugar content in the sample.

2. In the spectrophotometric method, or also known as the enzymatic method, testing is based on the principle that damaged starch has high susceptibility to α-amylase, allowing it to be hydrolyzed readily in the reduced sugars, which can then be measured colorimetrically.

3. In the iodine-absorption testing method, the amount of the absorbed iodine by starch granules is correlated with the damaged starch levels.

The SDmatic

This AACC-approved method, also known as the amperometric method, is the basis for Chopin Technologies’ SDmatic testing unit.

The SDmatic is the result of several years of research and development. The SDmatic provides a simple, rapid, and precise measurement of damaged starch in flour.

The SDmatic is recognized by many international standards for its proof of accuracy and quality of measurements. Making a test is quick and simple, with results available in fewer than 10 minutes.

The device measures the speed and capacity of flour dissolved in an acid solution to absorb iodine. Iodine has the characteristic to very rapidly bind to damaged starch granules.

Before the flour is introduced, the SDmatic’s electrode generates iodine in the reaction bowl. During operation, the device measures continuously an electrical current that is proportional to the quantity of free iodine in the solution.

Once the flour is added, the iodine binds to the damaged starch granules. Any reduction in the electrical current intensity correlates to an increased proportion of starch damage. The result is then displayed as a percentage of the iodine absorbed or in other selected international standard units that may be required.

Conclusion

Damaged starch shouldn’t carry a negative connotation, but knowing the exact levels in the processing stream is critical in managing it effectively to produce the final products which meet the specific needs of the customers.

Improving flour quality hinges on achieving optimum damaged starch levels for various products. One size does not fit all when it comes to damaged starch levels. In many ways, the miller is faced with a balancing act in trying to achieve optimum levels of damaged starch.

But with accurate and rapid testing methods, the miller has the means to blend flours with different damaged starch amounts to achieve desired outcomes, as well as increase production flows, optimize the roll’s lifespan, avoid lower yields, and still maximize the value of the final product.

Damaged starch shouldn’t carry a negative connotation, but knowing the exact levels in the processing stream is critical in managing it effectively to produce the final products which meet the specific needs of the customers.

Damaged starch levels represent a key factor in determining the behavior of the dough during mixing.

Damaged starch also directly influences the behavior of dough during fermentation, and thus affects the volume of the finished product, as well as its color.

A lack of control over the level of starch damage can lead to a number of problems during the processing of flour into baked goods.

For example, those problems may include sticky dough that is hard to handle either by operators or machines; lack of fermentation that may reduce volume, reduced shelf life of finished products; and quality defects such as off colors and cracking in the baked product.

While there may not always be perfect levels of damaged starch to achieve for all baked goods, a way to identify and maintain at least optimum levels during flour production will always be needed to meet the needs of the customer.

Karl Ohm, contributing editor

Editor’s note: For further reading, see:

• Measuring Starch Damage as a Mill Optimization Technique, a PowerPoint presentation available as a .pdf, by Shawn Thiele, milling operations manager, IGP Institute, Department of Grain Science and Industry, Kansas State University (KSU), Manhattan. Available at: iaom.org/wp-content/uploads/07ksula16.pdf

• Damaged Starch in the Flour Mill: How to Reduce the Electricity Bill, by Charles Loubersac D’Hotel, a master thesis completed in 2012 at KSU’s Department of Agricultural Economics. The master thesis, which is available as a .pdf download, can be accessed at: krex.k-state.edu/dspace/handle/2097/13684

From 4th Quarter Milling Journal