2.5. Differential Scanning Calorimetry (DSC)

Thermal properties of the modified starches were analyzed using a Differential Scanning Calorimeter Phoenix 204 F1 (Netsch, Selb, Germany) that was calibrated using iridium. An empty pan was used as a reference.

Starch (3.5 mg) was loaded into an aluminum pan (Netzsch, Germany) and distilled water was added using a micropipette to create a suspension with a 75% moisture content. Samples were hermetically sealed and equilibrated for 24 h at room temperature before being heated in the DSC. The measurements were conducted at a heating rate of 10 °C/min from 20–100 °C. The enthalpy of the phase transitions (ΔH₁ J per g d.w.b. of starch) was measured from the endotherm of DSC thermograms using the Netzsch Proteus–Thermal Analysis software (Netzsch, Germany) based on the mass of the dry solids. The onset temperature (T_o1), peak temperature (T_p1), and conclusion temperature (T_c1) were calculated. The gelatinization temperature range (ΔT₁) was calculated as T_c1-T_o1. The peak height index (PHI₁) was computed from the ΔH₁/(T_p1-T_o1) ratio as described by Kaur [3]. The reported values are the means of four measurements.

After being heated for gelatinization analysis, the samples (in the original sealed pan) were cooled to 4 °C and were stored at this temperature. After a week, the stored samples were heated from 20–100 °C at 10 °C/min (the second run). The enthalpy (ΔH₂), onset temperature (To₂), peak temperature (Tp₂), and conclusion temperature (Tc₂) were determined. The transition temperature range of the melting of recrystallized amylopectin (ΔT₂), the peak height index (PHI₂), and the retrogradation ratio ΔH₂/ΔH₁ were calculated. The reported values are the means of four measurements.