Complex carbohydrates are also made up of sugars units, but in complex carbohydrates many more
sugar units are joined together, forming longer, more complex chains. This group of carbohydrates is
therefore also known as the polysaccharides.
In complex carbohydrates, many of the previously available OH groups in the sugar units have been
involved in glycosidic bonding, so the complex sugars are much less soluble than the simple sugars.
There are fewer free OH groups available (more are involved in glycosidic bonds) to bond with water
molecules, so solubility is less.
Due to their more complex structure, these carbohydrates take longer to be digested than simple
carbohydrates, and so act more as a long-term energy store. Cellulose, one of the complex
carbohydrates, has such a complex structure that it can not be digested at all, and it actually passes
through the entire digestive system unaffected.
Complex carbohydrates are synthesised by plants, and thus are found in plant sources. Complex
carbohydrates include two main groups – the fibres and the starches. The fibres are major
compartments of cell walls, and the starches are found located in small granules inside the cells. The
two groups have very different properties, despite both being complex carbohydrates, and will
therefore be considered as separate groups.
The main fibres found in cell walls are cellulose, pectin and hemicelluloses. Each has a slightly
different structure, and this affects how they behave with heating and pH.
Plant cell walls have an important role in determining vegetable and fruit texture. Understanding how
each of the cell wall components reacts in the presence of heat or pH is thus very useful in
understanding and trying to control changes in vegetable and fruit texture on cooking. Pectin acts as
the glue to hold the cell wall together, and thus tends to play the most important role in determining
fruit and vegetable texture.
Cellulose is made up of long straight chains of glucose molecules. The absence of side chains allows