413 THE EFFECT OF VEGETABLE OIL COMPOSITION Table II SAXS and WAXS Average Value for d-Spacings Measured for Oleogels in Olive, Apricot, Camelina, or Rapeseed Oils with Various Ratios of Behenyl Alcohol:Behenic Acid (BO:BA): (a) 10:0, (b) 8:2, (c) 7:3, (d) 5:5, (e) 3:7, (f) 2:8, (g) 0:10. The Nature of Crystals Deduced from SAXS/WAXS Results is Indicated: Pure BO, Pure BA, or Mixed Crystals BO/BA. R = 10:0 Oleogel SAXS d-spacing (Å) WAXS d-spacing (Å) Type of crystals Sunflower 57.1, 48.3 4.3, 4.1, 4.1, 3.9, 3.7, 3.6 Olive 57.1, 52.4 4.3, 4.2, 4.1, 3.9, 3.7, 3.6 Apricot 57.1, 48.3 4.3, 4.2, 4.1, 3.9, 3.7, 3.6 Pure BO Camelina 57.1, 48.3 4.3, 4.2, 4.1, 3.9, 3.7, 3.6 Rapeseed 57.1, 49.1 4.3, 4.2, 4.1, 3.9, 3.7, 3.6 R = 8:2 Oleogel SAXS d-spacing (Å) WAXS d-spacing (Å) Type of crystals Sunflower 57.1 4.6, 4.5, 4.0, 3.8, 3.6, 3.5 Olive 57.1 4.6, 4.5, 4.0, 3.8, 3.6, 3.5 Apricot 57.1 4.6, 4.5, 4.0, 3.8, 3.6, 3.5 Mixed BO/BA Camelina 57.1 4.6, 4.5, 4.0, 3.8, 3.6, 3.5 Rapeseed 57.1 4.6, 4.5, 4.0, 3.8, 3.6, 3.5 R = 7:3 Oleogel SAXS d-spacing (Å) WAXS d-spacing (Å) Type of crystals Sunflower 57.1 4.6, 4.5, 4.0, 3.8, 3.6, 3.5 Olive 57.1 4.6, 4.5, 4.0, 3.8, 3.6, 3.5 Apricot 57.1 4.6, 4.5, 4.0, 3.8, 3.6, 3.5 Mixed BO/BA Camelina 57.1 4.6, 4.5, 4.0, 3.8, 3.6, 3.5 Rapeseed 57.1 4.6, 4.5, 4.0, 3.8, 3.6, 3.5 R = 5:5 Oleogel SAXS d-spacing (Å) WAXS d-spacing (Å) Type of crystals Sunflower 57.1 4.6, 4.5, 4.0, 3.8, 3.6, 3.5 Olive 57.1 4.6, 4.5, 4.0, 3.8, 3.6, 3.5 Apricot 57.1 4.6, 4.5, 4.0, 3.8, 3.6, 3.5 Mixed BO/BA Camelina 57.1 4.6, 4.5, 4.0, 3.8, 3.6, 3.5 Rapeseed 57.1 4.6, 4.5, 4.0, 3.8, 3.6, 3.5 R = 3:7 Oleogel SAXS d-spacing (Å) WAXS d-spacing (Å) Type of crystals Sunflower 57.1, 48.3 4.6, 4.5, 4.3, 4.1, 4.0, 3.8, 3.7, 3.6 Olive 57.1, 48.3 4.6, 4.5, 4.3, 4.1, 4.0, 3.8, 3.7, 3.6 Apricot 57.1, 48.3 4.6, 4.5, 4.3, 4.1, 4.0, 3.8, 3.7, 3.6 Mixed BO/BA Camelina 57.1, 48.3 4.6, 4.5, 4.3, 4.1, 4.0, 3.8, 3.7, 3.6 + pure BA Rapeseed 57.1, 48.3 4.6, 4.5, 4.3, 4.1, 4.0, 3.8, 3.7, 3.6 R = 2:8 Oleogel SAXS d-spacing (Å) WAXS d-spacing (Å) Type of crystals Sunflower 57.1, 48.3 4.6, 4.5, 4.3, 4.1, 4.0, 3.8, 3.7, 3.6 Olive 57.1, 48.3 4.6, 4.5, 4.3, 4.1, 4.0, 3.8, 3.7, 3.6 Apricot 57.1, 48.3 4.6, 4.5, 4.3, 4.1, 4.0, 3.8, 3.7, 3.6 Mixed BO/BA Camelina 57.1, 48.3 4.6, 4.5, 4.3, 4.1, 4.0, 3.8, 3.7, 3.6 + pure BA Rapeseed 57.1, 48.3 4.6, 4.5, 4.3, 4.1, 4.0, 3.8, 3.7, 3.6 R = 0:10 Oleogel SAXS d-spacing (Å) WAXS d-spacing (Å) Type of crystals Sunflower 48.3 4.4, 4.3, 4.1, 4.0, 3.7 Olive 52.4, 48.3 4.4, 4.3, 4.1, 4.0, 3.7 Apricot 48.3 4.4, 4.3, 4.1, 4.0, 3.7 Camelina 69.8, 48.3 4.4, 4.3, 4.1, 4.0, 3.7 Pure BA Rapeseed 52.4 , 48.3 4.4, 4.3, 4.1, 4.0, 3.7

414 JOURNAL OF COSMETIC SCIENCE and rapeseed oils, they all had a percentage of fatty acid with 18 carbons (C18) equal or higher than 90%. For the second group formed by the olive and camelina oil, they both had a percentage of fatty acid with C18 lower than 90%: 86.5% for olive oil and 72.5% for camelina oil. The key parameter leading to two different optimal R in terms of oleo- gel properties seems to be directly linked to the percentage of fatty acid chain with a length of 18 carbons. Our findings are in agreement with previous results showing that the fatty acid chain length in the oil can modify the rheological behavior of oleogels (39). It is important to emphasize that in our study we used commercial cosmetic grade oils without further purification steps, since our goal was to study cosmetic industrial oleogel systems, which can be used directly to produce oil foams from hair and skin treatments (40). However, based on the recent literature on the role of minor polar compounds in different oleogel systems, it appears that to confirm our results on the effect of fatty acid chain length on the oleogel properties it would be necessary in a future study to remove these polar compounds for each oil (34). By removing these polar compounds, it would be possible to understand their effect on the BO/BA oleogelator system. For example, in the oleogelator system based on γ-oryzanol and β-sitosterol, Scharfe et al. demonstrated a strong impact of polar minor compounds on the self-assembled structures and on the resulting oleogel properties (34). In the same way, polyphenols, which are minor polar compounds of extra virgin olive oil, decreased the oleogel hardness for ethylcellulose oleogels (38). Moreover, to better understand the links between the nature of the oils and the effect of R, it would be necessary to study a wider range of oils in terms of polarity, viscosity, density, fatty acid chain length, and so on. CONCLUSIONS In this study, we showed that R influenced the oleogel properties (i.e., hardness and oil-binding capacity) for all the vegetable oils tested. The optimum R was different depending on the type of oil: R =7:3 or R = 8:2. However, these two R were around the specific 3:1 molar ratio, for which a minimum area per molecule could occur leading to a decrease of the interfacial energy and into a decrease in the average crystal size. Therefore, at the optimum R, small crystals were formed as a co-crystal form of BO and BA. The small crystals might contribute to the enhancement of the oleogel hardness and oil-bind- ing capacity. We classified the oils into two groups. The first one composed of sunflower, apricot, and rapeseed oils, which exhibited an optimal weight ratio at R = 7:3. The second one composed of olive and camelina oils, which exhibited an optimal weight ratio at 8:2. We highlighted that the key parameter leading to two different optimal R in terms of oleogel Table III Surface Tension, Viscosity, and Density of the Vegetable Oils at 25°C. The Values Are the Average of Three Measurements. The Small Letters a to d Indicate Groups of Statistical Differences According to Tukey’s test (p 0.1) Sunflower Olive Apricot Camelina Rapeseed Surface tension (mN·m−1) 32.5 ± 0.7a 33.7 ± 0.3a 33.5 ± 0.5a 33.1 ± 0.6a 35.4 ± 0.2b Viscosity at 25°C (mPa.s) 70.2 ± 0.2a 62.5 ± 0.7b 60.8 ± 0.8b 52.7 ± 0.5c 56.1 ± 0.3d Density 25°C (g.cm3) 0.92 ± 0.01a 0.91 ± 0.01a 0.91± 0.01a 0.92± 0.01a 0.90 ± 0.01a