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Physicochemical and Functional Characterisation of Amaranth (Amaranthus hypochondriacus) Protein Isolates Obtained by Isoelectric Precipitation and Micellisation

Centro de InvestigaciÛn y de Estudios Avanzados del Instituto PolitÈcnico Nacional, Unidad Irapuato. Apdo. Postal 629, Irapuato, Gto. 36500 MÈxico; Instituto de Ciencias AgrÌcolas, Universidad de Guanajuato. Ex-Hda. El Copal, Km. 8.5 Carretera Irapuato-Silao, Apdo. Postal 311, Irapuato, Gto. 36500 MÈxico

J. A. Osuna-Castro

Centro de InvestigaciÛn y de Estudios Avanzados del Instituto PolitÈcnico Nacional, Unidad Irapuato. Apdo. Postal 629, Irapuato, Gto. 36500, MÈxico

A. Borodanenko

Instituto de Ciencias AgrÌcolas, Universidad de Guanajuato. Ex-Hda. El Copal, Km. 8.5 Carretera Irapuato-Silao, Apdo. Postal 311, Irapuato, Gto. 36500 MÈxico

O. Paredes-López

Centro de InvestigaciÛn y de Estudios Avanzados del Instituto PolitÈcnico Nacional, Unidad Irapuato. Apdo. Postal 629, Irapuato, Gto. 36500, MÈxicooparedes{at}ira.cinvestav.mx

Amaranth protein isolates were obtained by two distinct methods, i.e. alkaline extraction-isoelectric precipitation (IP) and micellisation (MP). IP had a greater protein yield (56.4%) and protein content (93.1%) than MP (15.9 and 80.2%, respectively). The gel filtration chromatogram of IP isolates displayed a single peak of ca. 1,380 kDa, whereas MP isolates showed two peaks at 905kDa and 190kDa. A commercial soybean isolate (CSI), analysed for comparison purposes, presented two peaks with molecular weights of 340kDa and 62kDa. Differential scanning calorimetry showed that amaranth isolates were characterised by two endothermic events, predominating in both isolates the second endotherm with a denaturation temperature of 98.7 °C for IP and 97.2 °C for MP. The better definition of MP endotherms and their higher denaturation enthalpy suggested a more homogenous and less denatured protein population, in comparison to IP and CSI. The amaranth isolates had better solubility at alkaline pHs than the CSI. Foaming and emulsification were better at acidic pH for both IP and MP. Colorimetric evaluations showed that the two amaranth isolates had a higher whiteness index than the CSI. In conclusion, extreme pH treatments in IP resulted in a partial protein denaturation and milder treatments in MP resulted in less protein denaturation and improvement of some functional properties.

Key Words: amaranth • protein isolates • isoelectric precipitation • micellisation • denaturation

Food Science and Technology International, Vol. 11, No. 4, 269-280 (2005)
DOI: 10.1177/1082013205056491


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