Effects of amino acids on gelatinization, pasting and rheological properties of modified potato starches

The effects of amino acids – cysteine (Cys), glutamic acid (Glu) and lysine (Lys) – on gelatinization, pasting and rheological properties of chemically modified starches including distarch phosphate (E 1412), acetylated distarch phosphate (E 1414) and acetylated distarch adipate (E 1422) were studied. The amino acids were added at 0.2 mol/kg of the starch dry weight. Glu contributed to an increase in gelatinization temperatures of the E 1412 and E 1422 starches, while the same effect, additionally accompanied by increase in gelatinization enthalpy, was found for Lys in the E 1414 and E 1422 systems. Addition of the amino acids decreased peak viscosity of the E 1412 and E 1422 pastes by 26.3–40.8% and 2.3–24.9%, respectively. Furthermore, the amino acids lowered final viscosity of these starches by 9.4–37.7% and 3.9–36.5%, respectively. Significant effects of Glu on pasting behaviour of E 1414 included reductions in both percentage breakdown and percentage setback in viscosity. Mechanical spectra showed that all the systems studied behaved as weak gels. The G′ and G″ values of the E 1412 and E 1422 gels with amino acids were lower than those determined for the respective control samples. The results of creep and recovery test revealed that a common effect of Lys in all the modified starch systems was an elevation of instantaneous compliance (J0) and reduction in retardation time (λret), whereas the effect of the other amino acids on rheological parameters were dependent on the type of starch.