Structural properties of high-protein, low glycaemic index (GI) rice flour

Abstract

Low glycaemic index (GI) rice flour was prepared by the enzymatic hydrolysis method. The protein content of treated (high-protein, low GI) rice flour was about 3.5 times higher than untreated rice flour, suggesting its use in infant formula or other protein-fortified food products. The GI of untreated and treated rice flour was found to be 88.0 ± 0.2 and 46.1 ± 0.2, respectively. High-protein, low-GI rice flour was studied for thermal and structural properties, which showed significant (p < 0.05) differences from untreated rice flour. The results of thermal properties showed a decrease in transition temperatures and enthalpy of gelatinization. The ratio of peaks at 1045 cm⁻¹ and 1015 cm⁻¹ of treated rice flour was significantly (p<0.05) lower than that of untreated rice flour. This could be ascribed to the loss of crystallinity due to enzymatic degradation. These results further support the decrease in transition temperatures and enthalpy of gelatinization. The results of the rheological studies of high-protein, low-GI rice flour revealed that both untreated and treated rice flour samples exhibited non-Newtonian shear-thinning flow behaviour (n < 1), which is characterized by a decrease in viscosity with an increase in shear rate.

KEYWORDS:

• Glycaemic index
• Shear-thinning
• Differential Scanning Calorimetry
• Fourier-transform Infrared Spectroscopy