Physicochemical properties of waxy corn starch and corn amylopectin illuminated with linearly polarised visible light

Abstract

Aqueous suspensions (30%) of either waxy corn starch or corn amylopectin were illuminated with visible linearly polarised light ( λ>500 nm) for 5–50 h. Pasting profiles, thermal properties, iodine binding capacity and intrinsic viscosity (in DMSO/water, 90:10) were taken for them after illumination. The illumination for 5, 15, and 25 h was not reflected in overall paste viscosities. Prolonged illumination (50 h) led to significant decrease in the peak and final viscosities. Illumination for 5 h (6.76 J/g), 15 h (7.74 J/g), 25 h. (7.95 J/g), and 50 h (2.85 J/g) decreased the melting enthalpies which for original waxy corn starch was 9.67 J/g. Decrease in intrinsic viscosity, [ η], as compared to that of native waxy corn starch (7.9 dl/g) was observed for the sample illuminated for 15 h (5.9 dl/g). Further illumination led to increase in [ η] values after 25 h (6.6 dl/g) and 50 h (8.0 dl/g). Blue value (BV) measured for the sample illuminated for 5 h (0.106) was higher than for waxy corn starch (0.076). Gradual decrease in BV was observed for samples illuminated for 15 (0.086), 25 (0.071) and 50 h (0.030). No changes in intrinsic viscosity and BV were found in the case of corn amylopectin irrespective of the illumination time. Findings indicate that polarised light induced depolymerisation of starch polysaccharide only if molecules were organised in crystal structures in same manner as in starch granule.