HAIR TREATMENT 179
hair tresses strength resulted significantly reduced respect to virgin–hair; in contrast, this decrement in hair strength did not occur for the hair tresses pre–treated with sesame and hemp hydrolysates (Fig 2). It has been known for a long time that
protein hydrolysates exhibit a certain affinity for hair keratin, in fact low molecular weight peptides and free amino acids can be adsorbed on hair surface; this property, termed hair substantivity, is given by the many binding sites and reactive groups present in their molecules and can be affected by many variables like molecular weight, amino acid composition, concentration, application time and last, but not least, by hair damage degree.5
To
supplement the information provided so far, we report the hair substantivity values (Fig 3) obtained from another study6
of the two
tested sesame and hemp protein hydrolysates and of another Kelisema hydrolysate derived from Merino wool (Keliwool, INCI: Hydrolyzed Keratin) which presents a higher molecular weight of about 3000 Da. Briefly, virgin hair tresses of the same type used for the heat protection test described above, were immersed in protein hydrolysate aqueous solutions containing 1% of protein substance from tested hydrolysates at pH 5.0-6.0, for 2 hours at 25°C (control – hair tresses were treated the same way using demineralised water); after the adsorption step, hair tresses were rinsed with tap water and excess of water was removed using a soft paper towelette. The adsorbed protein substance was extracted by immersing hair tresses in NaCl 0.5M aqueous solution for 20 hours at 30°C (the amount of water remained in hair tresses after the adsorption step was taken into account); nitrogen quantitative evaluation was carried out by Kjeldahl method and the amount of the extracted protein substance present in the saline solutions was determined. Protein sorption on an identical substrate results in differences between the tested hydrolysates; this is most likely due to the hydrolysis degree and amino acid compositions, in fact sesame and hemp hydrolysates have a lower molecular weight than merino wool hydrolysate and a pretty different amino acid composition (data not reported). Lower molecular weight hydrolysates derived from sesame and hemp proteins seem to have a greater penetration power into the hair shaft with respect to the higher molecular weight keratin hydrolysate which, in contrast, presents higher film-former properties. However, results obtained from another study (data not reported) suggest that also the application of the keratin hydrolysate before hot ironing could help prevent hair protein degradation, at least at cortex level;
April 2018 Kelipro Sesame Kelihemp Keliwool
4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0
Figure 3: Hair substantivity on virgin hair. Data reported on the graph are expressed after subtraction of control values
an aqueous solution containing 0.5% of protein matter from keratin hydrolysate was applied on hair before hot ironing following the same procedure of the test described above and the results obtained from this data set showed a significant hair diameter reduction with respect to virgin–hair only for control–hair and a more positive hair strength trend for keratin–treated hair respect to the control.
Conclusion The presented study shows through the use of hair analysis and hair tensile testing that the application of the selected Kelisema’s protein hydrolysates before hot ironing can help to protect virgin hair from thermal damage. Thermal protection against degradation of keratin in the cortex as well as hair cuticle can be associated to a decrease in hair strength and of hair diameter respectively. Low molecular weight hydrolysates Kelipro Sesame (INCI: Hydrolyzed Sesame Protein) and Kelihemp (INCI: Hydrolyzed Cannabis sativa Seed Extract) have a high substantivity on hair and provide thermal protection, resulting in an increase of hair diameter and preserving hair strength after repeated hot-ironing. In contrast, untreated hair shows thermal damage both at cuticle and cortex level, resulting in a decrease of hair diameter and in hair strength respectively, after repeated hot-ironing. The capacity of hydrolysed proteins on protecting hair from protein degradation was further validated by another study conducted in parallel where the application a higher molecular weight hydrolysate (Keliwool, INCI: Hydrolyzed Keratin) protected hair from protein degradation by maintaining hair diameter
after repeated hot-ironing. In summary, the above described study suggests the use of the tested protein hydrolysates can provide significant protection from heat damage over repeated hot flat ironing and can contribute to the realisation of specifically designed hair heat protectant cosmetic products.
Acknowledgments The authors to thank Technological Development Laboratory of Cosmetic Products, director Prof. Paola Perugini, Department of Pharmaceutical Sciences, University of Pavia for providing hair analysis and tensile testing of the hair samples used in this work.
References 1 Harper D, Qi JC, Kaplan P. Thermal styling: Efficacy, convenience, damage tradeoffs. J. Cosmet. Sci. 2011; 62(2):139-147.
2 Gomez-Garcia M. Void and pore formation inside the hair cortex by a denaturation and super-contraction process occurring during hair setting with hot irons. J. Cosmet. Sci. 2011; 62(2):109-120.
3 Zhou Y, Rigoletto R, Koelmel D, et al. The effect of various cosmetic pretreatments on protecting hair from thermal damage by hot flat ironing. J. Cosmet. Sci. 2011; 62(2):265-282.
4 Evans T. Beating the damaging effects of heat on hair. Cosm & Toil. 2015; 130(5): 28-33.
5 Teglia A, Secchi G. Proteins in cosmetics. In: Goddard ED, Gruber JD. (eds.). Principles of polymer science and technology in cosmetics and personal care, cosmetic science and technology series, vol 22. New York, USA: Marcel Dekker Inc.; 1999. p. 391-464.
6 KELISEMA technical documentation. Keliwool Dossier 2017.
PERSONAL CARE EUROPE
PC
mg protein / g hair
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