INFRARED AND RAMAN-SPECTROSCOPIC STUDY OF CASEIN IN CHEESE - EFFECT OF FREEZING AND FROZEN STORAGE

The secondary structure of caseins in cheeses from ewe milk was studie d by means of Fourier transform infrared spectroscopy and Raman spectr oscopy in the 1720 to 1550 cm(-1) region. For this study, lyophilized caseins were obtained from the milk, control cheeses, cheeses frozen a nd then thawed immediately thereafter, and cheeses frozen and stored f rozen and then later thawed and ripened. In the second derivative Four ier transform infrared spectra, resolved peaks were associated with al pha-helix, beta-sheets, beta-strands, beta-turns, and unordered struct ures. Previous freezing brought about an apparent increase in unordere d structures, particularly in the batches that were frozen slowly. Res ults in the Raman spectra could be interpreted in the same way. The pr oportion of beta-sheet structures apparently increased during cheese r ipening, and the unordered structures greatly increased at the end of the ripening period. After 90 d of ripening, differences in the propor tion of unordered structures between the frozen and control batches an d between the two frozen cheese batches were lower.