RAMAN-SPECTROSCOPIC STUDY OF THERMALLY-INDUCED GELATION OF WHEY PROTEINS

Alpha-lactalbumin and beta-lactoglobulin solutions [15 % (w/v) in D2O, pD 6.8, 20 mM NaCl] were heated at 50, 70, or 90-degrees-C for 30, 60 , or 90 min. Only the samples heated at 90-degrees-C formed transparen t gels. The amide I' and amide III' bands of the Raman spectra implica ted an increase of beta-sheet structure with a simultaneous decrease o f helical structure in heated alpha-lactalbumin, while an increase of beta-sheet with a simultaneous decrease of turn structure was suggeste d in heated beta-lactoglobulin. Changes in other regions of the Raman spectra could be interpreted as changes in disulfide conformation as w ell as in microenvironment around several amino acid residues, i.e., T rp, Tyr, and His. These changes were observed after heating at 70 and 90-degrees-C but were more intense in the gelled (90-degrees-C) than i n the ungelled samples and in beta-lactoglobulin than in alpha-lactalb umin. These observations are in accord with the fact that beta-lactogl obulin forms gels much more easily than alpha-lactalbumin.