Effect of Enzymatic Hydrolysis on Structural, Chemical and Elemental Properties of Sweet Potato Flour

In the present study, the structural, chemical and elemental changes of sweet potato flour after hydrolysis by α-amylase (liquefaction) and a mixture of α-amylase and glucoamylase (saccharification) were investigated. Thin layer chromatography (TLC), high performance liquid chromatography (HPLC), scanning electron microscopy (SEM), fourier-transforms infrared spectroscopy (FTIR) and energy dispersive X-ray fluorescence spectrometry (EDXRF) were used to study the properties of the hydrolyzed sweet potato starch. Efficient hydrolysis was evidenced from both TLC and HPLC that the thermostable α-amylase was able to yield the simple forms of sugar such as glucose, fructose, maltose and maltotriose whereas, only glucose is depolymerized after the combined effect of α-amylase and glucoamylase. SEM analysis of raw, liquefied and saccharified sweet potato root flour (SPRF) showed the various porous starch granules with a high degree of structural changes in saccharified samples in comparison to others, which indicates the active involvement of tested the enzymes. The saccharified SPRF were fermented by Saccharomyces cerevisiae and Zymomonas mobilis separately and the results confirmed that Z. mobilis was able to produce more stretching vibration of –OH than S. cerevisiae , suggesting better production of bioethanol. In addition, the elemental analysis was carried out to evaluate the impact of S. cerevisiae and Z. mobilis with respect to elemental constituents. The results of the elemental analysis showed increase in the concentrations of S, Cl, Ca, Mn, Fe and Zn and decrease in the concentrations of P and K in the fermented residue of S. cerevisiae and Z. mobilis , however more variation was observed in Z. mobilis . Graphic Abstract