Texture Analysis to Measure the Effects of Enzyme Addition on the Staling of Artisanal Bread: Part 2 - How can the Specifics of Staling Be Slowed or Prevented?

Improved packaging would seem the obvious choice to the home baker, keeping a loaf sealed in an air tight box to prevent moisture loss, but this is not the main solution. 

More importantly, enzymes, additives and emulsifiers can be added to counteract the mechanical property changes associated with staling. However, out of the three, the focus for artisan bread should be on enzymes.

It is not only the finished loaf that is affected by enzyme addition. The dough itself is also affected, and this can be useful for the manufacturer. Enzymes can be used to give a soft, elastic dough with low stickiness.

Addition of fat
Adding fats to dough, which are hydrophobic, slows the migration of water during starch crystallisation, keeping the bread moist. They also improve loaf volume and crumb softness.

Addition of salt
Salt is always added to dough, and not just for taste. Its ions shield gluten’s charges from one another and enable the protein molecules to approach more closely, giving a stronger and more stable dough. Governments are often anxious to reduce salt levels in the diet, but there is a limit as to how far this can be carried through with bread. In the absence of salt, dough is sticky, and the resulting bread is unpalatable.

Increase of volume
An increase in the volume of a loaf slows staling. Dough strengtheners (giving better volume) enhance shelf life.

Higher moisture content
Bread should not be overbaked. As much moisture as possible should be retained during the baking process.

Addition of monoglycerides and fatty acids
Monoglycerides and fatty acids form complexes with gelatinised starch and slow its recrystallisation. While monoglycerides slow the development of firmness, eventually a bread containing monoglycerides will become just as firm as a control bread.

Addition of enzymes
Wheatflour contains various enzymes such as alpha- and beta-amylases, proteases, lipases, phosphatases and oxidases. The enzymes are indigenous (constituents of the wheat), endogenous (produced by microorganisms naturally present in the flour or as added cultures) or exogenous (added). Enzymes are proteins that act as catalysts; substances that speed up chemical reactions but are not used up in the reaction. One enzyme molecule can catalyse hundreds of reactions. They originate from living organisms, so they catalyse reactions at temperatures compatible with foods, unlike chemical catalysts that require high activation temperatures. Enzymes are very specific in their action – generally, one type of enzyme will catalyse just one particular reaction. The use of enzymes as processing aids in bread goes back many decades, but even today we do not know the specifics of every enzyme action and why they are so effective.

Breadmaking enzymes can be divided into two groups – hydrolases (which break down large molecules) and oxidases (which add oxygen or remove hydrogen).

Hydrolases

Amylases
Amylases are the most common type of hydrolase, and there are many types of amylase. The ability of alpha-amylase to extend the shelf life of bread has been known for many years, helping to increase loaf volume and also affect crust darkness. It can come from fungal, cereal, malt or bacterial sources, bacterial being the most effective.

Maltogenic alpha-amylase makes the crumb softer and more elastic, slowing staling and extending shelf life. It works by releasing maltose units from starch as it becomes gelatinised during baking, acting to degrade it. The limited starch hydrolysis that results from this reduces the incidence of starch recrystallisation. This is not thought to slow down the process (as with monoglycerides) – instead, a reduction is seen in the size of the crystallite formed. This makes the bread softer.

Lastly, the addition of fungal amylase can lead to greater dough extensibility.
When amylases are used in bread, it never gets as firm as a control loaf would, or a loaf with added monoglycerides.

Xylanase
Xylanases are added to break down polymers of xylose, the sugar that forms the backbone of most wheatflour cell wall material, hydrolysing the non-starchy polysaccharide cell walls in the flour. They also act to strengthen gluten. These effects improve the dough’s physical properties by giving increased softness and machinability, increased ovenspring, larger volume and better dough stability.

Lipase
Lipase has gluten strengthening effects, resulting in more stable, elastic dough and improved bread quality. This also helps to increase ovenspring and improve crumb structure in the dough with no added fat or oil. Lipase’s effects on volume and crumb structure also help it improve crumb softness during storage.

Oxidases

Lipoxygenase
Lipoxygenase is thought to function by oxidising the reducing substances in the flour and bran, such as thiols and free fatty acids, which would normally weaken the dough through the breakdown of disulphide cross-links in the gluten.

Laccase
Laccase strengthens dough, most likely by coupling side chains onto the xylan polymers. This causes the xylan polymers to gel, improving dough stability.

Glucose oxidase
Glucose oxidase addition leads to a stronger dough. It can replace oxidants such as bromate (which is now a forbidden additive in the UK). It also reduces dough stickiness, a problem frequently seen in bakeries.

Enzymes can act in a synergistic manner when combined (producing a combined effect greater than the sum of their separate effects). When hydrolases and oxidases are combined in enzyme cocktails, they act in a synergistic manner, improving loaf volume, crumb softness and springiness. This results in slower staling.

The exact dose of any enzyme will be different for differing flour types and baking formulations. The addition of too much of any of the above can cause problems. For example, the addition of too much xylanase will cause dough stickiness, whereas too much lipase gives a dry and stiff dough with a reduced volume increase.

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