Infrared modification of sorghum to produce a low digestible grain fraction.

The present study was aimed to modify sorghum grain by infrared thermal treatment (IRTT) under various
moisture regimes and to obtain a modified corneous endosperm (CE) fraction. The CE fraction was studied for
starch digestibility, functional, thermal and structural characteristics. The study revealed that the IRTT increased
the resistant starch and slowly digestible starch contents in the CE. An increase in storage elasticity modulus
(51000–118000 Pa) and peak gelatinization temperature (73.36–76.89 ◦C) in the modified CE was also observed.
The characteristics of starch isolated from modified CE differed from the CE fraction with respect to rheology, oil
absorption capacity and starch digestibility. Scanning Electron Microscopy and birefringence micrographs
revealed high degree of structural modifications in starch at 30% moisture content. Fourier Transform Infrared
spectroscopy revealed that IRTT increased crystallinity at low moisture and it promoted starch retrogradation at
high moisture content. Further, the –OH stretching suggested that the starch-protein interaction depended on the
moisture content. The IRTT caused structural modifications and hence low starch digestibility. The study indicated
that the IRTT could be efficiently used to modify grain starch fraction having low glycemic index with
potential in developing functional food formulations.