Study of Structural Changes in Whey Protein Isolate-Dextran Conjugate Using Fourier Transform Infrared Spectroscopy
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Abstract:
Measurement of A294, the degree of browning, and the content of free amino groups showed that a grafting reaction based on the Maillard-type reaction had occurred between the whey protein isolate (WPI) and dextran under dry-heating treatment. The effect of this grafting reaction on the structure of WPI was investigated by using Fourier transform infrared spectroscopy (FT-IR). Compared to the original WPI, the conjugate showed a broad peak in the range of 3700~3200 cm-1 and an increase in absorption between 1260 and 1000 cm-1. The peak shapes of amide I and amide II bands showed remarkable changes, the peak intensity increased, and the red shift phenomenon occurred in the corresponding absorption peaks. Using deconvolution and second derivative methods, the curve of amide I band was fitted for quantitative analysis of the secondary structural changes in WPI before and after the grafting reaction. The results showed that the secondary structure of WPI had been destroyed owing to the introduction of macromolecule dextran. The number of β-turns and random coils increased, whereas the number of α-helix and β-sheet decreased after the graft reaction, indicating that the structure of WPI had become relatively unordered.
