Abstract
It was indicated in the previous papers that the gelatinization temperature (GT) of starch in food and isolated starch could be determined successfully by differential thermal analysis (DTA). In the present investigation, the effect of salts and sugars on the GT of starch was studied by DTA in aqueous medium. NaF increased the GT, while NaCl, NaBr or NaI decreased it in a order of the periodic table. Na-carbonate and -bicarbonate had no influence on the GT, and nitrate and perchlorate decreased it, while sulfate, phosphate and thiosulf ate increased it strongly. The influences of salts of organic acids on the GT were relatively small, while sugars had great increasing effects on the GT. Difference between these substances in the influence on the GT could be demonstrated quantitatively by the critical concentration index defined by authors as the index of minimum concentration required to make a change of the GT. This index was in linear relation with the lyo tropic value and the hydration number of ions, and furthermore correlated very closely with the B-coefficient of salts. This suggests that the ability of salts to influence the water structure takes part in the gelatinization phenomenon of starch. Thermal Behavior of High Molecular Substances in Foods Part 3
