The impact of single and dual hydrothermal modifications on the molecular structure and physicochemical properties of normal corn starch

Effect of single and dual hydrothermal modifications with annealing (ANN) and heat-moisture treatment (HMT) on molecular structure and physicochemical properties of corn starch was investigated. Normal corn starch was modified by ANN at 70% moisture at 50 degrees C for 24h and HMT at 30% moisture at 120 degrees C for 24h as well as by the combination of ANN and HMT. The apparent amylose content and swelling factor (SF) decreased on ANN and HMT, but amylose leaching (AML) increased. These changes were more pronounced on dual modification. The crystallinity (determined by X-ray diffraction), the gelatinization enthalpy (determined by differential scanning calorimetry) and ratio of 1047 cm(-1)/1022 cm(-1) (determined by Fourier transform infrared spectroscopy) slightly increased on ANN and decreased on HMT. The ANN and subsequent HMT (ANN-HMT) resulted in the lowest crystallinity, gelatinization enthalpy and ratio of 1047 cm(-1)/1022 cm(-1). The gelatinization temperature range decreased on ANN but increased on HMT. However, the gelatinization range of dually modified starches (ANN-HMT and HMT-ANN) was between ANN starch and HMT starch. Birefringence remained unchanged on ANN but slightly decreased on HMT as well as dual modification. Average chain length and amount of longer branch chains (DP> or =37) remained almost unchanged on ANN but decreased on HMT and dual modifications (ANN-HMT and HMT-ANN). HMT and dual modifications resulted in highly reduced pasting viscosity. ANN and HMT as well as dual modifications increased RDS content and decreased SDS and RS content.