Infrared and Raman Spectroscopic Study of Casein in Cheese: Effect of Freezing and Frozen Storage

Abstract

The secondary structure of caseins in cheeses from ewe milk was studied by means of Fourier transform infrared spectroscopy and Raman spectroscopy in the 1720 to 1550 cm–1 region. For this study, lyophilized caseins were obtained from the milk, control cheeses, cheeses frozen and then thawed immediately thereafter, and cheeses frozen and stored frozen and then later thawed and ripened. In the second derivative Fourier transform infrared spectra, resolved peaks were associated with α-helix, β-sheets, β-strands, β-turns, and unordered structures. Previous freezing brought about an apparent increase in unordered structures, particularly in the batches that were frozen slowly. Results in the Raman spectra could be interpreted in the same way. The proportion of β-sheet structures apparently increased during cheese ripening, and the unordered structures greatly increased at the end of the ripening period. After 90 d of ripening, differences in the proportion of unordered structures between the frozen and control batches and between the two frozen cheese batches were lower. © 1993, American Dairy Science Association. All rights reserved.