Influence of pH on structure and function of amaranth(Amaranhtus Hypochondriacus) proteins isolates”

ABUGOCH, L; MARTINEZ, E.N; AÑON, M.C

CEREAL CHEMISTRY

AMER ASSOC CEREAL CHEMISTS

Año: 2010 vol. 87 p. 448 - 453

0009-0352

ABSTRACT Structural and functional properties of two amaranth protein isolates as a function of pH were studied. The isolates, A9 and A11, were obtained by alkaline extraction at pH 9 and 11, respectively. Gel filtration chromatograms of A9 and A11 showed similar profiles. The A11 isolate contained mainly albumins and globulins, and a small proportion of globulin-P aggregates, suggesting the presence of species with a higher degree of denaturation compared to A9. Differential scanning calorimetry (DSC) showed that A9 was characterized by two thermal transitions (65.8 and 98 ºC); A11 exhibited only a small endotherm (66.6 ºC) and a second, less defined one. DSC analysis of A9 at pH 2 to 4 did not show endotherms, but at pH 5 some protein structures were observed. A11 showed a greater degree of denaturation. FPLC results showed that the proteins in A9 are more folded and their conformation is closer to the native state compared to those in A11, which are more unfolded due to pH-mediated denaturation, mainly in acid media. The surface hydrophobicity of the isolates in acid media was lower than in alkaline media. The fluorescence emission spectra of the isolates showed differences in acidic pH conditions. As expected, the highest solubility was found at alkaline pH. The water holding capacity was similar for both isolates. The water imbibing capacity and speed of foaming was higher for A11 than for A9. In summary, 18 intense pH treatment of amaranth isolates generated partial or total protein denaturation 19 and differences in the functional properties. Keywords: amaranth protein isolate; pH, structure; functional properties