Selected functional properties of waxy corn and potato starches after illumination with linearly polarised visible light

Aqueous suspensions (30%) of waxy corn and potato starches were illuminated for 5-50 h with linearly polarised visible light ((lambda) (greater than) 500 nm). Molecular weights (Mw) and radii of gyration (Rg) of the amylopectin and amylose fractions of illuminated waxy corn starch, and the amylopectin, intermediate, and amylose fractions of illuminated potato starch were measured by high-performance size exclusion chromatography coupled with multiangle laser light scattering and refractive index detection. The weight-average molecular weight (Mw) and radius of gyration (Rg) of the amylopectin fraction of native waxy corn starch were 14.45 × 107 and 161.1 nm respectively. After 15 h of illumination a decrease in Mw (5.80 × 107) and Rg (117.6 nm) was observed. Illumination for 25 h, led to an increase in Mw (7.60 × 107) and Rg (134.0 nm). Further illumination, up to 50 h resulted in a slight decrease in Mw (6.74 × 107). The molecular weight and radius of gyration of the amylopectin fraction of native potato starch were 21.30 × 107 and 207 nm respectively. Illumination for 15 h led to a decrease in Mw (14.87 × 107) and Rg (141.5 nm), followed by an increase in both values after 25 h (18.97 × 107, 146.6 nm) and 50 h (19.69 × 107, 207.1 nm) of illumination. Illumination influenced the swelling power, solubility, susceptibility to -amylolysis and X-ray diffractogram of the starches. A varying increase in the solubility passed through a minimum after 25 h of illumination. The X-ray diffraction pattern and susceptibility to enzymatic hydrolysis of waxy corn starch did not change, but in potato starch a gradual, illumination time-dependent increase in the amylolysis rate took place. This effect could result from the reduction in crystallinity of the starch as indicated by the X-ray diffraction pattern.