Study of succinylated food proteins by Raman spectroscopy.
Three food protein products, soy protein isolates, spray-dried egg white, and whey protein isolates, were chemically modified to varying levels with succinic anhydride, and the extent of modification of these proteins were determined by standard wet chemistry methods. Raman spectra (500-2000 cm(-1)) of the modified proteins were obtained. New C=O stretching vibrations were observed at 1420 and 1737 cm(-1) and were attributed to the carboxylate (COO-) and ester carbonyl (RCOO-) groups, respectively, which were appended to the proteins during succinylation. Two series of calibration curves were obtained by plotting the intensity ratio of the 1420 and 1737 cm(-1) to 1003 cm(-1) phenylalanine stretching band (used as an internal standard) against the extent of substituted epsilon-amino (and alpha-amino) groups and aliphatic hydroxyl groups, respectively. Linear fits were obtained with correlation coefficient r > 0.988. The Raman spectral data were also analyzed to study the effect of succinylation on the conformation of the three proteins. Some conformational changes were observed, including a transition from ordered to disordered structures, an exposure of tryptophan residues from a buried, hydrophobic microenvironment, and probably conformational shift of cystine residues.
Zhao
Yu
Y
Department of Botany, The University of Hong Kong, Pokfulam Road, Hong Kong.
Ma
Ching-Yung
CY
Yuen
Sze-Nga
SN
Phillips
David Lee
DL
D004044:Dietary Proteins / Q000032:analysis*; D004527:Egg Proteins / Q000032:analysis / Q000737:chemistry; D008894:Milk Proteins / Q000032:analysis / Q000737:chemistry; D011487:Protein Conformation; D011506:Proteins / Q000737:chemistry*; D030262:Soybean Proteins / Q000032:analysis / Q000737:chemistry; D013059:Spectrum Analysis, Raman / Q000379:methods*; D013329:Structure-Activity Relationship; D013387:Succinic Anhydrides / Q000737:chemistry*; D000067816:Whey Proteins
D004044:Dietary Proteins; D004527:Egg Proteins; D008894:Milk Proteins; D011506:Proteins; D030262:Soybean Proteins; D013387:Succinic Anhydrides; D000067816:Whey Proteins; C031801:succinic anhydride