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Conformation changes in human hair keratin observed using confocal Raman spectroscopy after active ingredient application

Abstract : OBJECTIVE: In hair care cosmetic products' evaluation, one commonly used method is to evaluate the hair appearance as a gold standard in order to determine the effect of an active ingredient on the final state of the hair via visual appreciation. Although other techniques have been proposed for a direct analysis of the hair fibres, they give only surface or structural information, without any accurate molecular information. A different approach based on confocal Raman spectroscopy has been proposed for tracking in situ the molecular change in the keratin directly in the human hair fibres. It presents a high molecular specificity to detect chemical interactions between molecules and can provide molecular information at various depths at the cortex and cuticle levels. METHODS: To evaluate the potential of confocal Raman spectroscopy in testing the efficiency of cosmetic ingredients on keratin structure, we undertook a pilot study on the effectiveness of a smoothing shampoo on natural human hair, by analysing α-helix and β-sheet spectral markers in the Amide I band and spectral markers specific to the cystin sulfur content. RESULTS: We confirmed that an active proved to be effective on a gold standard decreases α-helix keratin conformation and promotes β-sheet keratin conformation in the hair fibres. We also showed that treatment with the effective active decreases the intensity of covalent disulfide (S-S at 510 cm-1 ) cross-linking bands of cysteine. These data confirm that the effective active also acts on the tertiary structure of keratin. CONCLUSION: From these experiments, we concluded that the effective active has a smoothing effect on the human hair fibres by acting on α-helix and β-sheet keratin conformation and on the tertiary structure of keratin. Based on these results, confocal Raman spectroscopy can be considered a powerful technique for investigating the influence of hair cosmetic ingredients on keratin structure in human hair fibres. Moreover, this analytical technique has the advantage of being non-destructive and label free; in addition, it does not require sample extraction or purification and it can be applied routinely in cosmetic laboratories.
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https://hal.univ-reims.fr/hal-02309312
Contributor : Brigitte Perron Connect in order to contact the contributor
Submitted on : Wednesday, October 9, 2019 - 10:51:31 AM
Last modification on : Tuesday, March 1, 2022 - 7:26:17 AM

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M. Essendoubi, M. Meunier, A. Scandolera, C. Gobinet, M. Manfait, et al.. Conformation changes in human hair keratin observed using confocal Raman spectroscopy after active ingredient application. International Journal of Cosmetic Science, Wiley, 2019, 41 (3), pp.203-212. ⟨10.1111/ics.12528⟩. ⟨hal-02309312⟩

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