Effect of Temperature on the Recrystallization Characteristics of Branched Amylopectin

Abstract:

In this paper，the pullulanase was applied to hydrolyze and debranch the amylopectin samples that fully gelatinized for 12 hours，then，the resulting samples underwent heat-moisture treatment（101 kPa，121 ℃） for 2 hours. After these procedures the products were kept static for recrystallization for 2 days at 4，25(room temperature），30，40 ℃，respectively. For each sample，two parts of the supernatant and the precipitate were obtained by centrifugation，and then characterized and comprehensively analysed for the effect of the temperatures on the self-assembly processes of debranched amylopectin in aqueous solution. The effects of the temperatures on the morphologies，molecular weight distributions，crystalline structures，thermal properties of supernatant and precipitation samples with different temperature treatments were studied using Scanning electron microscopy（SEM），dynamic light scattering（DLS），high performance liquid chromatography（HPLC），X-ray diffraction，Fourier transform infrared spectroscopy（FTIR） and thermogravimetric analyzer（TGA），respectively. Results showed that the yield of recrystallization precipitation decreased as the temperature increased. SEM indicated that the starch molecules in the supernatant were larger than that in the precipitates. The morphology of the particle in the low temperature supernatant was flaky and a part of them were in a state of round bars. X-ray diffraction results demostrated that all the crystals of the precipitate had similar and strong diffraction peak. After debranching and recrystallization treatments，the B-type crystal was transformed into the B-V-type one at 40 ℃. TGA analysis suggested that the fastest temperature of weightlessness from precipitation and supernatant were lower than that from the native starch，and the thermal stability decreased accordingly. As displayed in distribution curves，the molecular weight of the starch molecules in both the supernatant and the precipitate increased after recrystallization，and the content of different components increased with the increase of temperature.