Properties of Starches Modified by Different Acids

Starches from wheat, maize, finger millet, tapioca, green gram, chick pea, and potato were acid modified using 0.5N HCl, HNO3, H2SO4, and H3PO4 at 50°C for 1.5 h. Alkali Fluidity Number (AFN) for native starches was very low (0.3–2.5) and increased upon modification. HCl and HNO3 produced the highest AFN followed by H2SO4 and H3PO4 . For each acid, cereal and millet starches showed the highest AFN, followed by root, pulse and tuber starches. The extent of hydrolysis was proportional to number average molecular weight (), of the native starch in the case of HCl and HNO3 but not in other acids. Intrinsic viscosity [η] of native starches showed positive correlation to their ,. However, the [η] of the modified starches, particularly those produced by HCl and HNO3 , showed no proportionality with their , indicating diverse structural differences in the hydrolsed products. Special behavior of finger millet starch is clear from [η] values of these four acid modified starches. The iodine binding capacity (IBC) of starches, although decreased (2 to 36%) upon modification, did not follow any particular pattern. About 0.01 to 0.94% starch got solubilized during modification—highest being in case of HCl and lowest for H3PO4 . Their and IBC were considerably lower in all cases except potato, which showed same IBC for the solubilized, as well as granular modified starch.