Raman Spectroscopic Study of Casein Structure

Open Access
Publisher Website
Google Scholar
Abstract
The secondary structure of caseins was investigated with resolution-enhanced laser Raman spectroscopy. Raman spectra in the 1580 to 1720 cm -1 region were obtained from the following lyophilized proteins: 1) asl-casein , 2) /3-casein, 3) a natural mixture of bovine whole casein, and 4) micelles of the natural mixture in the presence of Ca 2+ ions. In addition, /3-casein was also investigated in D20 solution. The spectra obtained were Fourier deconvolved and curve fitted with Gaussian components. The results suggest that both as1 and /3-casein have around 10% helical structure, around 20% /3-structure, and from 20 to 35% turns. The turns are clearly distinguishable from the moiety usually called undefined, random, or structureless. Freeze-dried micelles in the presence of Ca 2+ ions and submicelles in the presence of K + ions appear to contain an increased amount of turns and of /3-structure as compared with the as1- and 3-caseins. The increase in turns is at the expense of the amount of undefined structure. All conformational designations here are based on spectroscopic assignments de- rived from crystallized proteins with well characterized structures. These designa- tions thus have a more qualitative, descriptive meaning for caseins than for other milk proteins, such as a-lactalbumin or 3-1actoglobulin.