Study of Acetylated Food Proteins by Raman Spectroscopy

Abstract

Three food proteins, soy protein isolates, spray-dried egg white, and whey protein isolates, were acetylated to varying levels, and the extent of modification was determined by wet chemistry methods. Raman spectra of the modified proteins were obtained. A new C=O stretching vibration was observed at 1737cm -1 and was attributed to ester carbonyl groups appended to the proteins during acetylation. Calibration curves were obtained by plotting the intensity ratio of this Raman band to the 1003cm -1 phenylalanine stretching band against the extent of substituted hydroxyl groups. Linear fits were obtained with correlation coefficient r > 0.9979. The Raman spectral data were also analyzed to study the effect of acetylation on the conformation of the 3 proteins. Marked conformational changes were observed in the modified proteins.

Flow Properties of Acetylated Chickpea Protein Dispersions

“…Marked conformation changes were also observed in several modified proteins. The effect of acetylation on the conformation of egg white powder, soy and whey protein isolates were analyzed using Raman spectra by Zhao and others (2004). In this study, a chickpea protein conformational change did occur between the acetylation degree of 45% and 49%.…”

“…Among several chemical modifications, acetylation has been widely used to improve functional properties, such as emulsion and foaming properties of some food proteins by introducing acetyl groups to the protein molecules. Acetylation not only improves functionality, taste and appearance of some proteins for wider usage in the food industries (Franzen and Kinsella 1976; Rhama and Narasinga‐Rao 1983), but also allows us to better understand their functional properties and conformation relationship (Rhee 1989; Krause and others 2001; Zhao and others 2004).…”

Advances in Chemical Engineering

“…A disadvantage of this method is that TNBS also reacts with free sulfhydryl groups, albeit at a slower rate than with amino groups and to form a labile product (Kotaki et al, 1964). The TNBS assay has been used for various types of protein modification including fatty acid incorporation (Andersson et al, 1971;Ibrahim et al, 1991Ibrahim et al, , 1993, glycosylation of proteins as a result of the Maillard reaction (Sun et al, 2004), succinylation (El-Adawy, 2000Schwenke et al, 1998;Zhao et al, 2004aZhao et al, , 2004b, and acetylation of faba bean legumin (Krause et al, 1996).…”

“…This can be achieved for example by incorporating an isotopically labeled reagent or inclusion of a chromophore or fluorophore which can then be quantified by read-out of fluorescence intensity using a fluorimeter or simple absorbance measurements using a standard spectrophotometer. Raman spectroscopy was shown to provide direct insight into degrees of succinylation and acetylation of a range of proteins originating from soy, egg white or whey by distinct contributions of the conjugated groups at 1737 cm -1 and 1420 cm -1 (Zhao et al, 2004a(Zhao et al, , 2004b. The peak intensities at these wavelengths could be directly converted to obtain information on the degree of modification.…”

Application Potential of Food Protein Modification

“…A disadvantage of this method is that TNBS also reacts with free sulfhydryl groups, albeit at a slower rate than with amino groups and to form a labile product (Kotaki et al, 1964). The TNBS assay has been used for various types of protein modification including fatty acid incorporation (Andersson et al, 1971;Ibrahim et al, 1991Ibrahim et al, , 1993, glycosylation of proteins as a result of the Maillard reaction (Sun et al, 2004), succinylation (El-Adawy, 2000;Schwenke et al, 1998;Zhao et al, 2004aZhao et al, , 2004b, and acetylation of faba bean legumin (Krause et al, 1996).…”