The effects of iodine on kidney bean starch: films and pasting properties.

In the present study the effect of iodine on the structural characteristics (by infrared spectroscopy and X-ray) of films made from kidney bean starch was evaluated. The pasting properties as affected by iodine and glycerol were also evaluated. Kidney bean starch showed C-type (mixture of A- and B-type) crystalline structure, the conversion of starch into films resulted into reduction in intensity of diffractograms. The starch powder FTIR spectra had peaks centered at 1020 and 995 cm(-1) with a higher intensity at 1020 cm(-1), which is consistent with a partially crystalline material since fully crystalline material show similar intensity peaks centered around 1020 and 1006 cm(-1). Films without iodine showed one main peak centered around 1000 cm(-1) consistent with a disordered state similar to that in gelatinized starch. Iodine addition gradually increased the intensity of the bands around 1020 cm(-1) consistent with the formation of more ordered conformation similar to that in the crystalline material. Iodine encourages the formation of helical structures, however, the formation of crystalline material cannot be inferred. The increasing amounts of iodine up to 0.33% level progressively increased the peak-, through- and breakdown-viscosity. Iodine beyond 0.33% level gradually decreased peak-, trough-, breakdown- and setback-viscosity. Pasting temperature gradually increased with the increase in iodine.