Structural and chemical characterization of rice and potato starch granules using microscopy and spectroscopy

Starch is a polysaccharide that plays an important role in our diet and aids in determining the blood glucose levels and is the main source of energy to humans and plants. Starch is broken down by hydrolases which are present in our digestive system. We have used α-amylase for investigating the rate of hydrolysis of rice and potato starch granules. It is found that the hydrolysis depends on the morphology and composition of the starch granules by means of the action of α-amylase. The micro-scale structure of starch granules was observed under an optical microscope and their average sizes were in the range, 1-100 μm. The surface topological structures of starches with micro holes due to the effect of α- amylase were also visualized under scanning electron microscope (SEM). The chemical and structural composition of rice and potato starches before and after hydrolysis is characterized using Fourier-transform infrared (FTIR) and X-ray diffraction (XRD) spectroscopy, respectively. The potato starch is more resistant to α-amylase than rice starch. The XRD spectra of native and hydrolyzed starch granules remain same which suggests that the degradation occurs mostly in amorphous regions but not in crystalline. Compactly bound water in starch was attributed to the sharp band at 1,458 cm^-1 in FTIR spectra. Bands at 920-980 cm^-1 associated to α-(1-4) glycosidic linkage (C-O-C) and skeletal mode vibrations in both potato and rice starches.