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, HNO(3), H(2)SO(4) , and H(3)PO(4) at 50 degrees 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 HNO(3) produced the highest AFN followed by H(2)SO(4) and H(3)PO(4) . 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 ((M) over bar (n)), of the native starch in the case of HCl and HNO(3) but not in other acids. Intrinsic viscosity [eta] of native starches showed positive correlation to their (M) over bar (n),. However, the [eta] of the modified starches, particularly those produced by HCl and HNO(3) , showed no proportionality with their (M) over bar (n), indicating diverse structural differences in the hydrolsed products. Special behavior of finger millet starch is clear from [eta] 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 modificationhighest being in case of HCl and lowest for H(3)PO(4) . Their (M) over bar (n) and IBC were considerably lower in all cases except potato, which showed same IBC for the solubilized, as well as granular modified starch.