X-ray photoelectron spectroscopic analysis of rice kernels and flours: Measurement of surface chemical composition

• XPS was evaluated to differentiate rice macromolecules and surface composition.
• Surface composition was significantly differing from bulk composition.
• Over-expression of lipids and proteins and under expression of starch was found.
• Polysaccharides (mainly starch), proteins and lipids can be differentiated.
• Results have significance on the chemical stability and functionality of the grain.

The objectives of this study were to evaluate the ability of X-ray photoelectron spectroscopy (XPS) to differentiate rice macromolecules and to calculate the surface composition of rice kernels and flours. The uncooked kernels and flours surface composition of the two selected rice varieties, Thadokkham-11 (TDK11) and Doongara (DG) demonstrated an over-expression of lipids and proteins and an under-expression of starch compared to the bulk composition. The results of the study showed that XPS was able to differentiate rice polysaccharides (mainly starch), proteins and lipids in uncooked rice kernels and flours. Nevertheless, it was unable to distinguish components in cooked rice samples possibly due to complex interactions between gelatinized starch, denatured proteins and lipids. High resolution imaging methods (Scanning Electron Microscopy and Confocal Laser Scanning Microscopy) were employed to obtain complementary information about the properties and location of starch, proteins and lipids in rice kernels and flours.