Judging the ‘Freshness’ of Bread

Figure 3 (click for larger image, image credit: Dupont)

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.

Figure 4 (click for larger image, image credit: Dupont)

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.