Raman spectroscopic determination of extent of O-esterification in acetylated soy protein isolates

Soy protein isolates were chemically modified with varying amounts of acetic anhydride, and the extent of O-esterification was determined by a standard wet chemistry method. Raman spectra of the modified soy proteins were obtained. A characteristic 1737 cm−1 CO vibrational band was observed and its intensity was dependent on the degree of O-esterification. The ratio of intensity of the 1737 cm−1 band to a 1003 cm−1 phenylalanine stretch band (used as an internal standard) was plotted against the extent of O-esterification determined chemically. A linear fit was obtained with a correlation coefficient (R2) of 0.9986. Hence, Raman spectroscopy represents a rapid non-destructive method to determine the degree of O-esterification in food proteins.