178 HAIR TREATMENT Virgin Hair Control Kelihemp Kelipro Sesame
110 100 90 80 70 60 50 40 30 20 10 0
*
x500 passes
Figure 2: Hair strength evaluation. Data are normalised to hair diameter and expressed as % F/d (mN/μm) change respect to virgin – hair (100%). One-way ANOVA test resulted statistically significant (p < 0.05). * Statistically significant vs virgin – hair (p < 0.03).
Objective
The aim of the present study was to evaluate the thermal protection efficacy of hair pre-treatments based on two selected protein hydrolysates. Virgin Caucasian hair samples were pre-treated with protein hydrolysates aqueous solutions and subjected to repetitive thermal stress cycles using a straightening iron. Since mechanical properties of hair fibres are a direct consequence of their internal arrangement and thermal damage seems to particularly affect the typical hair keratin conformation, both physically and chemically, any decline in hair strength can be considered indicative of the disruption of this structure. In this study single-fibre tensile evaluation was adopted to assess hair damage; dry- state hair break stress and hair diameter were the parameters taken into account.
Materials and methods Protein hydrolysates and test solutions Two of Kelisema’s protein hydrolysates derived from sesame (Sesamum indicum L.) seed proteins (INCI: Hydrolyzed Sesame Protein) and hemp (Cannabis sativa L.) seed proteins (INCI: Hydrolyzed Cannabis Sativa Seed Extract) were used in the test. The typical average molecular weight of sesame and hemp hydrolysates is about 1500 Da, presenting different peptides molecular weight fractions with prevalence of the lower molecular weight fractions in their composition. Pre-treatment aqueous solutions used in the test were prepared diluting protein hydrolysates with demineralised water up to a protein matter concentration of 0.5%;
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control hair tresses were treated only with demineralised water.
Hair samples
Caucasian, dark-blonde, straight, chemically untreated hair samples were purchased from a local commercial source in Italy. Hair diameter mean value was 45.41 µm; each hair tress was 20 cm long, 5 cm wide and 5 g in weight. Before treatment, hair tresses were washed with 10% sodium lauryl ether sulfate (SLES) solution and dried in air circulating oven at 50°C-60°C.
Thermal treatment of hair samples Test hair tresses were subjected to a series of standardised thermal stress cycles in order to achieve a number of hot ironing passes of 500; each stress cycle comprised the following phases:
1. Application of a fixed amount of protein or control aqueous solution on the dried hair tresses; a spray dispenser was used in order to cover all the hair surface exposed to the flat iron used in the test; 2. Hair tresses drying in hair circulating oven at 50°C-60°C for 30 minutes; 3. 20 ironing passes using a non- professional, ceramic-type, flat iron with 6.5 x 2 cm of hot surface and maximum temperature of 200°C, according to the manufacturer’s specifications; hair tresses were hot ironed from top to bottom and each pass lasted on average 3/4 seconds; 4. Hair tresses washing using a shampoo containing 8% of SLES and 4.5% of cocamidopropyl betaine, pH 5-6; each wash was performed using a standardised procedure;
5. Hair tresses drying in hair circulating oven at 50°C-60°C for 30 minutes.
Hair strength evaluation After the thermal stress was completed, the dried hair tresses were subjected to break stress testing evaluations using Shimadzu Autograph AGS-D500 tensile instrument; each hair fibre was anchored to two grips, placed at a fixed distance, and stretched to break. The mean diameter of each tested hair fibre was evaluated using a digital microscope connected to a specific software for image analysis and the obtained force values were normalised to the diameter of the hair. At least 10 hair fibres for each test sample were analysed and for each of them, 3 diameter measurements were carried out. All analyses were performed at 25°C ± 2°C and at 70% R.H.
Results of the statistical analysis on the
acquired data were obtained using one-way Anova analysis and Mann-Whitney test.
Results and discussion Test hair samples seem to have benefited from the application of the protein hydrolysates before hot ironing. The obtained results showed a significant decrease of contro –hair diameter respect to virgin–hair; in contrast, in the case of the hair tresses pre–treated with sesame and hemp hydrolysates, a significant increase of the hair diameter was found respect to virgin–hair (Fig 1). Hair tensile testing results showed a
positive trend for the hair tresses pre- treated with protein hydrolysates: control –
April 2018
% F/d
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