Carbohydrate modification

Two main approaches have been successfully attempted in herbaceous plants:

1. qualitative or quantitative change of an existing compound (usually sucrose or starch)
2. introduction of a novel high value product or products (usually non-calorific carbohydrates such as fructans, bacterial cyclodestrins).

Increasing starch content in plants is possible by modifying the enzymes responsible for its synthesis such as the ADP glucose pyrophosphorylase (ADPGPP), the starch synthase, and branching enzymes. An increase of 20–30% in starch content was obtained in transgenic potato through regulation of the ADPGPP bacterial enzyme. The resulting fried potatoes had better flavour, reduced calories, improved texture and a less greasy taste (Stark et al. 1996). Fructan-encoding gene of onion has been transferred to chicory (Vijn et al. 1997) and bacterial cyclodestrins to potato (Oakes et al. 1991). The same strategy increased the solids in tomato.