Whole wheat and atta breads are harder to make light and soft than white bread. Part of the reason is fibre. Wheat contains arabinoxylans, also called pentosans, and whole wheat flour keeps the bran where much of the fibre sits.
Arabinoxylans and water
A review in the Journal of Cereal Science describes 50 years of debate about what arabinoxylans do in bread-making, and a renewed interest driven by the growing use of xylanases, more precisely endoxylanases. Arabinoxylans come in two broad populations: water-extractable and water-unextractable. The unextractable part holds a great deal of water and gets in the way of the gluten network. Xylanase cuts it into soluble fragments, which frees water for the gluten, so the dough becomes more extensible and rises better.
Which xylanase, and when it acts
Not all xylanases do the same thing. A study in Cereal Chemistry compared two endoxylanases: one strongly selective for the water-unextractable arabinoxylan, the other for the water-extractable part. The first released its fragments mainly during mixing, and those fragments were larger. The second released its fragments mostly later.
A later study compared five xylanases and found that those able to solubilise the water-unextractable arabinoxylan during mixing raised bread volume more than those that did most of their work during fermentation. Specific volume rose by up to 28% with the best of them.
Wheat itself complicates the picture. It carries natural xylanase inhibitors, and a study of an acidophilic xylanase found that both its preference for water-unextractable arabinoxylan and its sensitivity to wheat's inhibitors governed how much it improved bread. Wheat also carries its own xylanases, most of them microbial enzymes associated with the kernel rather than the grain's own, which change the arabinoxylans during bread-making too. The same enzyme can therefore perform differently on different flours.
In whole wheat bread
A study in Bioresource Technology added a xylanase to whole wheat bread and reported:
| Measure | Change with xylanase |
|---|---|
| Water absorption | Down 11% |
| Dough rise | Up 28.5% |
| Bread moisture | 40.5% against 32.3% in the control |
| Loaf volume | Up 53% |
| Firmness | Down more than four times |
Sensory scores for flavour, taste, softness and overall acceptability were also better.
Getting it right
- Too much makes dough slack and sticky, so trials should test a range of levels rather than a single point.
- Choose by action, not only by name. Ask how selective the enzyme is for the water-unextractable fraction and how sensitive it is to wheat's inhibitors.
- Expect flour-to-flour variation. Repeat the key arm on a second flour lot before you commit.
- Measure what the customer notices: dough handling, loaf volume, crumb, and firmness at the end of shelf life.