5.4 Causes of limitations to storage for fresh cassava roots

The starch-storing root of cassava is of no importance for vegetative propagation. This means that the cassava, in contrast to the yam tuber, has no period of dormancy which naturally favours storage after the harvest.

When the cassava root has been harvested, a rapid process of deterioration sets in after 2 - 3 days at the latest. This can be differentiated in two phases.

Primary deterioration comes from the central vascular bundle in the root. This begins to take on a dark-blue to black colouring starting from broken and cut surfaces. The adjacent storage tissue is also affected and the starch stored undergoes structural changes (PLUMBLEY and RICKARD, 1991).

Experiments have shown mat no microorganisms are involved in the change of colour. This is based on an endogenous oxidative process. The colouring can be delayed by cutting off oxygen, e.g. by storing the roots in a water bath (PLUMBLEY and RICKARD, 1991).

Secondary deterioration mainly results from microbial activities but can also be due to fermentation and softening of the root tissue (PLUMBLEY and RICKARD, 1991). Secondary deterioration is caused by rot viruses which can occur in very complex compositions and vary from location to location (ibid.).

Considered economically, primary deterioration is more significant than secondary deterioration. Discolouring parallel to primary deterioration causes a distinct decline in the value of the roots and makes them impossible to sell. For this reason, it is initially essential to develop processes which allow primary deterioration to be controlled.