Surface characterization of ginger powder examined by X-ray photoelectron spectroscopy and scanning electron microscopy

The surface composition of five types of ginger powders with the particle sizes of 300, 149, 74, 37 and 8.34 μm was investigated by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and various types of physical–chemical characteristics regarding material particle size distributions, discoloration and chemical composition. The results show that the color differences are greater for superfine ground ginger than for conventional comminuted ones; the values of crude fibre, neutral detergent fiber (NDF) and acid detergent fiber (ADF) decrease with decreasing ginger particle size. However, no relationship with the surface fat, crude protein, ash and total solids exists. With superfine grinding the XPS O/C ratios of the five ginger powders were similar since the surfaces were not oxidized. Correlations were observed between the XPS N/C ratios and the high resolution XPS N 1s spectra. SEM observations revealed that the surface of ginger powder with a particle size of 300 μm is rougher, while superfine ground powders with particle sizes of 149, 74, 37 and 8.34 μm are similar to each other. This roughness difference between these surfaces correlates with the differences in their O/C ratios and the surface morphology of five ginger powders.