ingredients solubilized in approximately 200 mL). The emulsion containing all ingredi- ents was constantly stirred until it reached room temperature, and then distilled water was added to reach the fi nal volume. The formulations developed remained standing for 24 h for stabilization before starting the characterization tests. FORMULATION STABILITY UNDER STRESS CONDITIONS Twenty-four hours after preparation , the samples were conditioned in transparent glass vials with 2/3 of their capacity, with sealed caps, to avoid the loss of gases and steam to the medium, and subjected to cycles of thermal stress: 24 h at 45°C and 24 h at 5°C for 12 d, totaling six complete cycles. The samples were analyzed after prepa ration and at the end of each thermal stress cycle. The physical–chemical analyzes performed in each sample were pH, density, viscosity, and rheological parameter evaluation. The pH was measured using a benchtop pH meter (Q400AS, Quimis), previously calibrated with buffer solutions, and the pH measurements were taken directly on the samples. The density evaluation was performed with the aid of a stainless steel pycnometer, which is recommended for semisolid products. The calculation for relative density determination was performed through equation 4: 2 1 0 – = – M M0 d M M , (4) where d = density, M0 = mass of the em pty pycnometer (g), M1 = mass of the pycnometer with distilled water (g), and M2 = mass of the pycnometer with the sample (g). The apparent viscosity of formulations was measured using a Microprocessor Rotary Viscom- eter (Q860M21, Quimis) with a spindle 3. The temperature of the samples was maintained at 20° ± 1°C with the aid of a thermostated bath. The fl ow curves were obtained by measuring the viscosity (η) in mPa.s and increasing shear rates (γ) of 0.1–1 s-1. The rheological parame- ters were adjusted to the Ostwald De Waele model (potency law), and the values of consistency index (k) and fl ow behavior index (n) were obtained by equation 5. τ = shear stress. = I k( ƣ)n–1. (5) The data of characterization parameters of t he formulations were submitted to analysis of variance and Tukey’s test [(signifi cance of 95%) (p 0.05) XLSTAT Software (version 2018 Free, Microsoft Excel, Addinsoft, Paris, France)]. RESULTS AND DISCUSSIONS CHARACTERIZATION OF TAR O MUCILAGE (TM) X-ray di ffractometry. The X-ray diffractog ram of TM (Figure 1) s hows that the mucilage of the rhizomes of Colo- casia esculenta (L.) Schott presents a semicrystalline profi le, which is a characteristic of many TARO MUCILAGE IN COSMETIC FORMULATIONS 283

natural polymers and previously reported by Mishra et al. (10) in mucilagen of fen-Greek. This crystallographic profi le is mainly due to the presence of starch in the sample. The in- tensity of diffraction with principal peaks at 15, 17, 18, and 23° (2θ) characterizes this starch as type A (20), because of the presence of amylopectin with a lower chain length (21). Scanning electron microscopy. Scanning electron m icroscopy of the mucilage of Colocasia esculenta (L.) Schott revealed an ir- regular surface area containing structures with asymmetric edges resembling broken ceramic pieces (Figure 2A and B). The presence of starch granules in circular and irregular shapes de- posited on the TM surface (Figure 2C and D) also was observed, similarly to that described by Andrade et al. (9) in the mucilage from Colocasia esculenta. The starch present in the mucilage does not interfere in its emulsifying power, but the starch may be interesting for the develop- ment of cosmetic emulsions, since it is responsible for the velvety effect and softness in creams. The EDS analysis indicated the presence of carbon and oxygen, as already expected for this type of sample, as well as magnesium, phosphorus, chlorine, and potassium (Table 2). The major minerals described in the literature for Colocasia esculenta were Mg, P, and K in different proportions, and some authors correlate these variations to the soil in which the plant was cultivated, genetics, and species variations (13,22). Thermal analysis. The sample presented three exot hermic events (Fi gure 3). The fi rst event occurred be- tween 29 and 100° C and was attributed to the loss of adsorbed material and water in the Figure 1. X-ray diffraction for the mucilage of Colocasia esculenta (L) Schott. JOURNAL OF COSMETIC SCIENCE 284