Softness is a key parameter used to judge the freshness and, consequently, the quality of bread. Bakers are therefore interested in maintaining the softness of their bread for as long as possible. Any loss of bread crumb softness is often referred to simply as staling. Staling is defined as any change other than microbial spoilage that occurs after baking, making bread less acceptable to the consumer.
Physical or sensory changes associated with staling include: loss of crumb softness, flexibility, and strength; increase in crumb resilience; tendency to become crumbly; loss of flavor; and change in mouthfeel.
Staling Mechanisms
Starch, which makes up approximately 70 percent of flour, is regarded as the main flour component involved in staling. After baking, the gelatinized starch in bread tends to re-associate or, to use another term, retrograde.
After cooling and during the first hours after baking, the initial crumb structure is set by amylose gelatinization, creating a network in which the gelatinized starch granules are embedded. Re-crystallization of amylopectin side chains leads to the increasing rigidity of the starch granules and an overall strengthening of the crumb structure, measured as an increase in crumb firmness. Other factors, however, also have an impact on bread firming, particularly the distribution of water between protein and starch, which undoubtedly, plays an important role.
Starch retrogradation, though, is the main factor with regard to time determined changes in crumb softness. Functional ingredients that limit retrogradation are instrumental in improving crumb softness.
Starch consists of two fractions: amylose and amylopectin in a ratio of approximately 1:3. Both macromolecules comprise glucose units, although with structural differences. Amylose is a relatively small (molecular weight is approximately 250,000), linear and water-soluble macromolecule, while amylopectin is a very large (molecular weight is approximately 205,000), bulky, branched, and water-insoluble molecule.
Figure 1 on page 38 shows the changes that occur from the dough stage to fresh bread and, finally, to old or stale bread. The restoration of bread freshness by heating (toasting) is also indicated. In the dough stage, unswollen starch granules contain crystalline amylopectin, amorphous amylose, and polar lipids. The granules are embedded in gluten, which forms the continuous phase. During baking, the starch granules absorb water and swell. The amylopectin crystals are gradually disrupted at temperatures above 140 degrees Fahrenheit, and gelatinization takes place. Some of the amylopectin molecules expand into the inter-granular space and, at a somewhat higher temperature—around 176 degrees Fahrenheit, some of the
amylose that has not formed complexes with polar lipids leaks from the swollen granules. Within hours after baking, the amylose molecules develop a network, and a sliceable crumb structure is formed, giving the fresh bread its initial firmness. During aging, reformation of the amylopectin’s double helical structure and reorganization into crystalline regions takes place. While the re-association of amylose occurs within hours, the retrogradation of amylopectin takes days.
How Enzymes Work
Enzymes have been applied in bread making for decades. Bakery enzymes such as amylases help modify starch during the baking process. Slowing starch retrogradation, they ensure bread stays soft for longer than bread made without enzymes.
The varying action patterns of the most important amylases are shown in Figure 2. One effect of the enzymes is to reduce starch retrogradation by modifying the starch.
There are two main types of amylase enzymes: endo-amylases, such as classic fungal and bacterial α-amylases, that primarily hydrolyze starch at random within the amylose and amylopectin molecules; and exo-amylases that primarily hydrolyze starch from the non-reducing ends of starch molecules, cutting off two or four glucose units.
In practice, starch granules only become susceptible to enzyme attack upon gelatinization, which means the baking amylases need to be heat stable in order to be efficient. The curve in Figure 3 shows a typical temperature pattern when baking a loaf of bread. The functionality of amylases is highly influenced by the temperature profile of the baking step. A standard fungal α-amylase only has a couple of minutes in which to act on the gelatinized starch, and consequently, has no anti-staling effect. The bacterial α-amylase is active even at elevated temperatures and may cause excessive starch degradation, as it primarily weakens the inter-granular amylose network. Therefore, a narrow window of optimal dosage exists. G4-amylase and maltogenic α-amylase are optimized to modify gelatinized starch in the temperature range of 60 to 90 degrees Celsius, which is considered important for obtaining a strong anti-staling effect.
The amylopectin fraction in starch granules is more complex than that shown in Figure 2. A more comprehensive structure is shown in Figure 4 on page 39, which illustrates that the amylopectin structure consists of amorphous and crystalline regions. Endo-amylases are most likely to attack in the amorphous regions. This gives the gel structure more freedom of movement and reduces crumb rigidity. Exo-enzyme attack reduces the possibility of a re-association of amylopectin side chains.
The action pattern of specific amylases effectively combines the shortening of amylopectin side chains with balanced amylose fragmentation. Enzymes preferentially attack starch from its non-reducing ends. In this way, they shorten the amylopectin side chains and reduce the amount of amylopectin available for retrogradation, slowing the actual rate of firming. This provides substantial crumb softening and improved resilience and elasticity without excessive weakening of the amylose network. In addition to superior softness and resilience, specific amylases can generate a moister, more flexible bread crumb.
Starch is not the only component acting in the staling process. Proteins and arabinoxylans also contribute to the firming of bread crumbs. For this reason, most enzyme products are optimized with additional enzyme activities specifically designed for individual applications.
Specific amylases, such as maltotetrahydrolases, are mainly responsible for the anti-staling effects; although phospholipase enzymes and bacterial xylanases can provide some additional softness. The amylases help products retain original production freshness by primarily modifying the amylopectin portion of the wheat starch, which greatly reduces recrystallization over time, resulting in softer product. The enzymes used for improving volume are usually selected from hexose oxidase, glucose oxidase, xylanase, and phospholipase, often in combination. There are several mechanisms involved in increasing volume. Phospholipases modify naturally occurring lipids in the wheat flour, producing emulsifiers that strengthen the protein structure. Xylanases specifically modify the arabinoxylan polysaccharides naturally present in flour. This releases water that can be absorbed by gluten to produce stronger networks and greater volume. Hexose oxidase and glucose oxidase oxidize small amounts of sugars in the product, resulting in production of very small amounts of hydrogen peroxide, which helps to cross-link gluten proteins also generating stronger networks and increased volume.
Enzymes used in baking help breads and bagels retain their original freshness for longer, thereby reducing food waste, energy consumption, and their carbon footprint. Enzymes used in cakes and muffins enhance softness, moisture, and reduce crumbling, helping improve taste perception and convenience in the on-the-go market. Other baked goods that benefit in similar ways to bread would include buns and rolls, bagels, pretzels, English muffins, tortillas, etc.
Enzymes are of course present in flour, yeast, bacteria, and several other common raw materials used in bakery products, and therefore were used unknowingly for thousands of years before their discovery and the introduction of commercial enzymes. Commercial industrial enzymes were introduced as a way to better control the amount and type of enzyme activity in baked goods and to give bakers better control. Enzymes can play an important role in the vast majority of baked goods with only a few exceptions.
The products that tend to benefit the most are those that require fresh keeping, and in particular, those that also have a specific volume requirement. Most traditional pan breads are expected to be soft and light in texture and are now also expected to have shelf lives of up to three weeks. Anti-staling enzymes can help baked goods retain their original freshness for extended periods and can be used to improve volume and dough handling properties.
How to Evaluate Freshness
Expert sensory evaluation of bread is usually done three and 10 days after production, comparing the market standard to the new recipe. Parameters such as foldability, softness, moistness, crumbliness, and freshness are measured.
Some common tests to evaluate freshness over the course of several days are measuring firmness (units in HPa), also called crumb softness; and crumb resilience (units in %).
In Summary
By applying custom enzyme, emulsifier, and softener solutions, you can obtain optimal performance baked goods with enhanced consumer appeal, fewer returns, and improved consumer loyalty. Your potential product benefits include longer-lasting softness, fine homogeneous crumb structure, fresh mouthfeel, and improved resilience.
Aside from their specificity, enzymes often offer other benefits that stretch beyond the product itself. Enzymes can often replace substances or processes that may present safety or environmental issues, help reduce salt and sugar content of foods, and enhance nutritional value. Enzymes are very specific and will work under mild reaction conditions, allowing selective reactions in the presence of sensitive substances. Today enzymes are already used in a variety of foods from beer, dairy, oils and fats, meats, and of course, bakery products. However, innovative new applications and solutions are continuously being found together with food producers to help meet the needs of the growing population.
Saral is the global business director food enzymes for DuPont Industrial Sciences, Netherlands. Reach her at [email protected].
What Are Enzymes?
Enzymes used in food processes have the same properties as those found in nature. They are specialized proteins—but not living organisms. Enzymes are biodegradable proteins that act as catalysts helping the food manufacturing industry to reduce
food production costs, increase yields, enhance quality, and provide tastier, healthier, and safer food.They are enabling various industries to help guarantee quality and stability of products with increased production efficiency.
Enzymes are processing aids, not ingredients. Current labeling legislation does not require enzymes to be listed on product labels when used as processing aids because they have already performed the action they were intended to perform. Enzymes often perform different tasks from emulsifiers, and in most cases actively work with additives to provide a given effect in the finished product. The confusion arises when enzymes are presented as being equal to, or in some cases alternatives to, additives—this leads to the misconception that enzymes are additives.
All enzymes are proteins. They are made up of small amino acids strung together in a linear polymer. Enzymes can be found in nature and extracted from plants, bacteria, fungi, and animal glands. Commercial industrial enzymes are more commonly produced by microorganisms under optimized and contained conditions, or to a minor extent extracted from plant material. Commercial industrial enzymes share the same properties as naturally existing enzymes, and only small quantities are needed to perform the function (for instance, bread would contain less than 0.002 percent enzyme protein).
In some industrial enzymes, a small number of amino acids are changed to improve enzyme performance, for example, at different temperatures, or enhanced pH stability or increased specificity of the catalyzed reaction. This technology is referred to as protein engineering. Fermentation, recovery, purification, and formulation processing steps are controlled from start to finish and the enzyme is separated from its production microorganism after fermentation. The microorganism is then destroyed before being disposed of in a controlled way. Enzymes are finally formulated in either solid or liquid form and sold commercially to food manufacturers.
Enzyme products are only introduced onto the market when their safety has been fully established according to internationally accepted assessments and regulatory procedures. This safety assessment evaluates all aspects and steps in the production chain—from the safety of the development of production organisms, through the production process, and to the final enzyme products in their intended uses.–D.S.
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