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 144nm, and 2.0 × 106 and 104nm, 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.
|Number of pages||6|
|Publication status||Published - 1999 Apr|
ASJC Scopus subject areas
- Food Science
- Organic Chemistry