Molecular Distribution and Pasting Properties of UV-Irradiated Corn Starches

Abstract

Suspension (30 %, w/w) of corn starch (25 % amylose) in water was irradiated by UV‐light with wavelength greater than 250 nm at 25°C, under a stream of nitrogen or air, for time intervals ranging from 5 to 25 h. Effects of the irradiation on the transition enthalpy and temperature for melting, and the pasting viscosity profile of the irradiated starch were examined. Weight‐average molecular weight (Mw) and radius of gyration (Rg) of the irradiated starch molecules were measured by high performance size exclusion chromatography coupled with multiangle laser light scattering and differential refractive index detectors (HPSEC‐MALLS‐RI). In the case of starch irradiated under nitrogen, the transition enthalpy (ΔH) decreased with increasing irradiation time whereas the melting temperature was not changed. Similarly, the peak paste viscosity (Pv) decreased from 97 to 56 RVU by 25 h irradiation. Average Mw and Rg of amylopectin and amylose fractions, which were 93 × 106 and 144 nm, and 2.0 × 106 and 104 nm, respectively, were decreased by irradiation to 32.2 × 106 and 93.7 nm, and 0.7 × 106 and 83.6 nm by the irradiation for 15 h under nitrogen, respectively. When the starch was irradiated with aeration, sharp drops of all measured parameters were observed in 5 h of irradiation (ΔH 11.4 J/g, Pv 53.2 RVU, amylopectin Mw 50 × 106). After 15 h under air, however, all measured values increased (ΔH 16.8 J/g, Pv 65.5 RVU, amylopectin Mw 63.1 × 106). Molecular size distribution profiles confirmed oxidative the photodegradation in the early stage (up to 5 h), and cross‐linking reactions in the late stage (5—15 h) of irradiation under aeration.

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

“…The UV irradiation of corn starch slurries under nitrogen depolymerised the starch, whereas such irradiation under oxygen induced photodegradation followed by recombination of generated polysaccharide radicals. 4 An increase in the water binding capacity and solubility of starch exposed to UV light was noted 8 together with a decrease in the hot paste viscosity. 1,4 The crystalline structure 2 and gelatinisation enthalpy 4,9 of starches did not change, although the intrinsic viscosity decreased.…”

“…4 An increase in the water binding capacity and solubility of starch exposed to UV light was noted 8 together with a decrease in the hot paste viscosity. 1,4 The crystalline structure 2 and gelatinisation enthalpy 4,9 of starches did not change, although the intrinsic viscosity decreased. 9,10 Induction of depolymerisation-repolymerisation reactions of polysaccharide molecules in normal corn, potato and waxy corn starches illuminated with linearly polarised visible light was reported in our previous papers.…”

Rheological Properties of Acidified and UV-Irradiated Starches

“…However, UV irradiation did not change the rheological properties of corn starch. These results are not concordant with those of a previous study [12] which found a decrease in viscosity from 90 to 65 RVU after UV irradiation of a corn starch suspension.…”

Investigation of the photo-oxidation of cassava starch granules

“…The treatment of starch with UV radiation induces changes in its functional properties, such as increases in water binding capacity and solubility, and decreases in hot paste viscosity [16]. The usage of a combined method, like the one realised by this study (UV radiation ?…”