Comparison of Changes in the Secondary Structure of Unheated, Heated, and High-Pressure-Treated β-Lactoglobulin and Ovalbumin Proteins Using Fourier Transform Raman Spectroscopy and Self-Deconvolution

Abstract

Changes in protein secondary structure and conformation of ovalbumin and beta-lactoglobulin (15% protein w/w) were investigated by Fourier transform Raman spectroscopy and self-deconvolution. The amounts of alpha-helix, beta-sheets, random coil, and beta-turns in native beta-lactoglobulin were 15, 54, 6, and 25%, respectively, and those for ovalbumin (41, 34, 13, and 12%) compared well with published values obtained by X-ray crystallography. The proteins were heated at 90 degrees C for 30 min and high-pressure-treated at 600 MPa for 20 min. Heating increased beta-sheet structures in both proteins at the expense of alpha-helix; for beta-lactoglobulin beta-sheet structures increased from 54 to 70% and for ovalbumin, from 34 to 54%. Random coil increased from 6% in the native protein to 30% in high-pressure-treated beta-lactoglobulin. However, for ovalbumin, the contribution from beta-turns doubled in high-pressure-treated samples, with little change in random coil. Further examination of the deconvoluted amide I band in heated samples revealed several component bands. Bands at 1626 and 1682 cm(-1) for ovalbumin and at 1625 and 1680 cm(-1) for beta-lactoglobulin were observed and are associated with aggregated, intermolecular beta-sheet (beta-aggregation), indicative of heat denaturation. The band seen at 1632-1640 cm(-1) corresponded to intramolecular beta-sheet structures, whereas the band at 1625 cm(-1) is associated with exposed beta-sheets (for example, beta-strands with strong hydrogen bonding that are not part of the core of beta-sheets). In high-pressure-treated samples bands were also observed at 1628 and 1680 cm(-1) for ovalbumin and at 1626 and 1684 cm(-1) for beta-lactoglobulin, suggesting involvement of beta-sheet structures in protein aggregation. Raman bands were observed at 1665-1670 cm(-1) for ovalbumin and at 1663-1675 cm(-1) for beta-lactoglobulin due to random coil structures. The bands at 1650-1660 cm(-1) due to alpha-helices were observed in both heated and high-pressure-treated samples. In addition, in heated samples of both ovalbumin and beta-lactoglobulin, peak intensity increased for beta-sheet in the amide III region, 980-990 cm(-1), and decreased for helix structures (900-960 cm(-1)). In contrast, there was no peak at 1240 cm(-1) (amide III beta-sheet structures) in either high-pressure-treated ovalbumin or beta-lactoglobulin, suggesting that high-pressure denaturation at 600 MPa for 20 min is less extensive than heat denaturation at 90 degrees C for 30 min.

Effect of the levels of transglutaminase in frankfurters: a physical–chemical and Raman spectroscopy study

“…Cada valor representa el promedio±SD, n=4. Herman, Adams, & Howell, 2004). Thus, quantitative information about secondary structure of meat protein could be estimated from the amide I spectral profile (Alix et al, 1988).…”

Vibrational spectroscopy applied to the study of milk proteins

“…There are many other applications and trends of vibrational spectroscopy for the study of milk proteins specifically or for more general analysis of milk and milk products e.g. [2,7,10,28,34]. Fourier transform mid-infrared analyzers are now used widely and routinely in conjunction with data analysis by chemometrics to measure constituents or composition of milk and milk products, including online process testing for rapid process adjustments, such as for standardization of milk fat and protein contents prior to cheese production [2].…”

Raman and surface‐enhanced Raman spectroscopy investigation of vasopressin analogues containing 1‐aminocyclohexane‐1‐carboxylic acid residue

“…The assignments of the 1640-(-sheet), 1674-(-turn), and 1699-cm À1 (-sheet) spectral feature are obvious [31][32][33][34] ; further, they are in agreement with the allocation of these bands in the AVP Raman spectrum and with the earlier conformational investigations. [4][5][6]8,[35][36][37][38] The remaining band, at 1658 cm…”