THE INFLUENCE OF AN INCREASED DEGREE OF BRANCHING ON THE PHYSICOCHEMICAL PROPERTIES OF STARCH FROM GENETICALLY-MODIFIED POTATO

Transgenic potatoes were studied which contained starch with an increa sed degree of branching of the starch as a result of the expression of the glycogen branching enzyme gene (glgB) of Anacystis nidulans or Es cherichia coil. These trans-genes were expressed in a normal amylose-c ontaining wildtype and in an amylose-free (amf) potato mutant. The deg ree of branching of these starches had increased up to 25%. This incre ase in the degree of branching could be partly explained by the presen ce of 5-15% more short chains in the amylopectin, the so-called A chai ns. The influence of the altered degree of branching on the physico-ch emical properties of the starches was investigated. No change in granu le size or morphology could be observed for the altered starches of th ese transgenic plants. Regardless of the presence or absence of amylos e, starches with an increased degree of branching showed a shift towar ds more short chains of the amylopectin, a lower peak viscosity and fo r the amylose-free starch a tendency to form weaker gels. These result s show that increasing the degree of branching of amylopectin leads to specific changes in the physico-chemical properties of the starch. (C ) 1998 Elsevier Science Ltd. All rights reserved.