Effect of salts on the gelatinization process of Chinese yam (Dioscorea opposita) starch with digital image analysis method

A comparative study was undertaken to examine the effect of different salts on the gelatinization of C-type Chinese yam starch. The digital image analysis, integral optical density (IOD) method and the model of response difference of crystallite change (MRDCC) were employed to dynamically detect the gelatinization process in our research. Different concentrations and various salts had different degree of improvement and inhibition effect on the gelatinization process when heated in water. With the increase of NaCl concentration from 0 to 4 mol/L (M) the gelatinization degree (DG) of B-type allomorph increased at lower concentration to a maximum value and then decreased with increasing concentration, however all of the concentrations (1–4 M) had inhibition effect on A-type polymorph. The inhibition effect of low NaCl concentration contributed to the dominated water structure-making effect of Na+, while in high concentration the electrostatic interaction between starch –OH groups and Na+ ions was significant. The influence of various neutral anions was in accordance with the Hofmeister series while the situation of cations was far more complicated. Anions with higher charge density had water structure making effect to reduce water activity, and repeled starch –OH groups to stabilize starch granules at the same time; however, the higher charge density of cations increased the water structure on the one hand, while attracted starch –OH groups and destabilize starch granules with generated heat on the other hand.