DSC study on the thermal properties of soybean protein isolates/corn starch mixture

The use of soybean protein isolates (SPI) and corn starch (CS) for the manufacturing of textured protein by thermo-mechanical means requires a characterization of their thermal properties. SPI and CS mixtures were examined at starch mass fractions from 0 (pure SPI) to 100 (pure CS). The blends were determined by means of differential scanning calorimetry, with water content of 30, 50, and 70 % and heating rate of 5 and 10 °C min−1 over 20 to 130 °C. The results obtained showed that protein in the blend increased the onset (To) and peak (Tp) temperatures of the starch gelatinization, while starch in the blend decreased the ΔH and ΔT1/2 of the protein. To, Tp, and ΔT1/2 of SPI and CS decreased significantly with the increase of water content. Tp and ΔT1/2 of SPI and CS had a marked increase with an increase of heating rate from 5 to 10 °C min−1. These results suggested that there was no chemical reaction between SPI and CS when they were heated from 20 to 130 °C. SPI in the blend restricted the CS gelatinization, while the presence of CS protected the SPI from denaturation. The increasing water content did promote thermal transition of the mixture. Higher heating rate leads to higher transition temperature.