Enzymatic Modification of Potato Starch via Branching Enzyme Treatment: Physicochemical Properties and Digestibility under In Vitro Gastric Conditions

Enzymatic modification offers a sustainable, chemical-free pathway to tailor the functional and nutritional aspects of native starches. In this study, native potato starch was structurally modified using a recombinant glycogen branching enzyme (GBE) from Rhodothermus obamensis to evaluate its impact on physicochemical properties and in vitro digestibility. GBE treatment altered the starch architecture by cleaving internal α-1,4-glucosidic bonds and reattaching them as α-1,6-glucosidic branches, resulting in an increase in branching degree from 2.1% to 7.4%. X-ray diffraction analysis revealed a transition from a typical B-type crystalline pattern to an amorphous structure, accompanied by a significant reduction in relative crystallinity. Rapid Visco Analyzer profiles demonstrated that GBE modification markedly decreased peak viscosity, trough viscosity, and setback values, reflecting a reduced retrogradation tendency. In vitro gastrointestinal digestion assays indicated a substantial shift in starch fractions: rapidly digestible starch decreased from 68.4% to 31.2%, while slowly digestible starch and resistant starch increased to 42.6% and 26.2%, respectively. These results suggest that GBE-modified potato starch possesses favorable structural characteristics and slow-release glucose profiles, presenting a promising candidate for formulation into low-glycemic index functional foods.