Raman spectroscopic study of deamidated food proteins

Document Type

Journal Article

Publication Date

2009

Keywords

Deamidation, Raman spectroscopy, Soy proteins isolates, Spray-dried egg white, Whey protein isolates

DOI

10.1016/j.foodchem.2008.09.027

Abstract

Three food protein products, soy and whey protein isolates and spray-dried egg white powder, were deamidated to various levels by 0.04 N hydrochloric acid. The extents of deamidation were determined using an ammonia electrode. Raman spectra of the modified proteins were obtained and analyzed. A new C{double bond, long}O stretching vibration band was observed at 1780 cm -1, attributed to γ-carboxyl groups of aspartic and glutamic acids. Calibration curves were constructed by plotting the intensity ratio of the 1780 cm -1 band to the 1003 cm -1 phenylalanine stretching band (as an internal standard) against the extent of deamidation. Linear fits were obtained with high correlation coefficients r > 0.987. Effect of deamidation on the conformation of these proteins was also studied by monitoring changes in Raman spectral characteristics, including a transition from ordered to disordered structures, exposure of tryptophan residues from a buried, hydrophobic microenvironment, and probable conformational changes of the aliphatic residues.

Source Publication

Food Chemistry

Volume Number

113

Issue Number

2

First Page

363

Last Page

370

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