Influence of pH on structure and function of amaranth (Amaranthus hypochondriacus) protein isolates

ABUGOCH, L; MARTINEZ, E.N; AÑON, M.C

CEREAL CHEMISTRY

AMER ASSOC CEREAL CHEMISTS

Lugar: St. Paul; Año: 2010 vol. 87 p. 448 - 453

0009-0352

Structural/functional properties of amaranth protein isolates and their influence by the pH were studied. Two isolates were obtained by alkaline extraction (A9 and A11). Results showed that their polypeptide composition was: globulins, glutenins and albumins. By gel filtration chromatogram of A11 isolate showed mainly albumins and globulins, and a small proportion of globulin-P aggregates, species with a higher degree of denaturation or a higher degree of molecular dissociation as compared to A9. Differential scanning calorimetry showed that A9 were characterised by two thermal transitions: (Td) of 65.8 ± 0.6 ºC and 98 ± 3 ºC; A11 isolate exhibited a small endotherm at Td 66.6 ± 0.2 ºC and a second less defined endotherm between 95 and 110 °C. The results of the DSC of the A9 at acid pHs between 2-4 did not exhibit endotherms, but at pH 5 some protein structures were observed. The DSC results for A11 were similar to those for A9, except that proteins contained a lower structure. Proteins present in A9 are more folded and their conformation is closer to the native state, while those of A11 are more unfolded. The surface hydrophobicity of the isolates in acid media was lower than in alkaline media. The fluorescence emission spectra of the isolates showed differences at acid pHs The highest solubility for the protein isolates was found at pH alkaline. The WHC in water was similar for both isolates, and at pH 3 an increase of this parameter was observed. The WIC was higher for the A11. The A11 form foams faster than the A9. The amaranth isolates had better solubility at alkaline pHs than at acid pHs. In summary, intense pH treatments in amaranth isolates generate a partial or total protein denaturation and enhancement of a few functional properties.