Technological properties of arabinoxylans as baking additives
Arabinoxylans are soluble fibres extracted from cereal grains, such as the wheat endosperm. Due to the physicochemical and technological properties of these molecules, arabinoxylans can be used as a baking additive to improve dough consistency, increase loaf volumes, improve crumb structure and decrease bread staling. Arabinoxylans are palatable and arabinoxylan-rich foods are well accepted by consumers.
What are arabinoxylans?
Arabinoxylans are soluble fibres extractable from cereal grains. Arabinoxylans have been identified in all major cereal grains, including wheat, barley, oats, rye, rice, sorghum, maize, and millet.
In cereal grains, arabinoxylans are localized mainly in the cell walls of starchy endosperm and the aleurone layer, in the bran tissues, and in the husk of some cereals.
Arabinoxylans can be used as a dietary supplement due to their beneficial effects on gut health, glycaemic control and immune health.
Depending on the genus and species, the amount and structure of arabinoxylans in a particular tissue may vary. For instance, in wheat, there is more arabinoxylan in the walls surrounding the cells of starchy endosperm than in those of aleurone.
Not all arabinoxylans are the same. They vary on the degree of polymerization, which represents the length of the arabinoxylan chains, and on the soluble arabinoxylan content, among others.
Arabinoxylans as technologically functional food ingredients
The role of arabinoxylans in the bread-making processes and their effects on the final bread product have been widely studied. Soluble arabinoxylans, such as those found in the wheat endosperm, have positive effects on dough consistency, loaf volumes, crumb structure and bread staling.
All these characteristics contribute to their utility not only in the bread-making process, but also as neutraceuticals incorporated into functional foods. Arabinoxylans are palatable and arabinoxylan-rich foods are well accepted by consumers. Arabinoxylans have been successfully added to bread, porridge or biscuits, among others.
• Dough consistency
A clear distinction needs to be made between soluble and insoluble arabinoxylans. When added to wheat flour, soluble arabinoxylans, compete for water with other flour constituents. As a consequence, dough consistency is increased.
In opposition, insoluble arabinoxylans can form physical barriers for the gluten network during dough development. The resulting gluten has lower extensibility, which decreases dough consistency.
• Loaf volumes
Soluble arabinoxylans increase the viscosity of the dough’s aqueous phase and, thus, have a positive effect both on dough structure and stability, especially during the early baking processes.
This increased stability surrounding the gas cells is very useful in prolonging oven rise, which leads to an increased loaf volume.
Insoluble arabinoxylans, on the other hand, destabilize dough structure and have a negative effect on loaf volume. They also absorb a large amount of water, leaving less available water for proper gluten development and film formation, resulting in a lower loaf volume.
• Crumb structure
As mentioned, soluble arabinoxylans increase the viscosity of the dough’s aqueous phase, leading to greater dough stability. This increased stability surrounding the gas cells also leads to an improved crumb structure.
• Bread staling
Another functional property of arabinoxylans is associated with their role in bread staling. Bread staling is a complex phenomenon involving loss of aroma, deterioration of crust characteristics and increase in crumb firmness. Stale bread is dry and hard.
Over a 7-day storage period, arabinoxylan-fortified bread exhibits lower crumb hardness than the controls without added arabinoxylans. This is attributed to the higher moisture content in the bread fortified with arabinoxylans, as well as to the plasticizing effects of water. [1]
The bottom line
Due to the physicochemical and technological properties (e.g. water-binding capacity, gelation) of soluble arabinoxylans, such as those found in the wheat endosperm, these molecules can be used as a baking additive to improve dough consistency, increase loaf volumes, improve crumb structure and decrease bread staling. Arabinoxylans are palatable and arabinoxylan-rich foods are well accepted by consumers.
