Optimization of the isoelectric precipitation method to obtain protein isolates from amaranth (Amaranthus cruentus) seeds

This research was conducted to evaluate the effect of extraction pH (7.8-9.2) and precipitation pH (4.3-5.7) on four selected quality attributes of protein isolates from amaranth seeds (Amaranthus cruentus) such as protein content (PC), whiteness index (WI), enthalpy of transition (EN), and denaturation temperature (DT). Ten different treatments involving extraction and precipitation pH combinations were analyzed by a central composite design; the experimental data were fitted by a second-order model using a least-squares method for each one of the four dependent variables. Response surface methodology was used for the optimization process; in addition, a common optimum value for the four dependent variables was obtained utilizing the desirability method. A confirmatory test showed that the generated regression equations could adequately predict performance of this isoelectric precipitation method. The results indicate that extraction pH and precipitation pH showed an important effect on PC, WI, and EN. However, the different combinations did not significantly affect the DT. Values of 9.2 and 8.0 for extraction pH and 5.7 for precipitation pH produced the best overall result for all responses. Finally, the results have shown that it is possible to obtain protein isolates from A. cruentus seeds at optimized values of extraction pH and precipitation pH, which presented a high protein content and good physicochemical properties.