Raman Spectroscopic Analysis of L-Phenylalanine and Hydrolyzed Eggwhite Protein Penetration into Keratin Fibers

The study investigated the penetration of L-phenylalanine (Phe) and hydrolyzed eggwhite protein (HEWP) into keratin fibers of human hair using Raman spectroscopy. It was found that hydrophobic amino acids, like Phe, penetrated deeply into virgin white human hair, while hydrophilic amino acids did not. The Phe content increased at various depths after treatment at 50°C for 16 hours. Similarly, HEWP treatment increased disulfide and random coil contents at various depths in bleached human hair, indicating deep penetration.