Formulations containing both xanthan gum (F1) and TM (F2, F3, and F4) showed rela- tively close values of density, although analysis by analysis of variance and Tukey’s test showed statistically signifi cant differences. The substitution of xanthan gum by TM did not lead to intense changes in product density. This characteristic can be considered inter- esting, since the density parameter can infl uence the spreadability, and the results indi- cate little difference between the creams with TM (F1: 0.1%, F3: 0.3%, and F4: 0.5%) and the standard formulation containing xanthan gum (F1: 0.3%). The viscosity is a variable that characterizes rheologically a system and helps to determine if a product has consistency and fl uidity. The rheological evaluation is important in the study of emulsions, since it can promote information about the physical stability of a product, especially when it is subjected to temperature variations (32). The viscosity and shear rate data were adjusted to the Ostwald de Waelle model, and the consistency index (k) and fl ow behavior (n) were obtained. As can be seen in Table 3, high viscosity and consistency indices were observed both in the sample containing xanthan gum (F1: 9,624.0 mPa.s) and formulations containing TM (F2: 3,792.0 millipascal-second (mPa.s), F3: 7,752.0 mPa.s, and F4: 11,640.0 mPa.s). When using the same concentration (0.3%) of xanthan gum and TM (F1 and F3, respectively), it was demonstrated that the xan- than gum contributed to obtaining a product with a slightly higher viscosity (F1: 9,624.0 mPa.s and F3: 7,752.0 mPa.s). On the other hand, when the TM concentration was increased from 0.3% to 0.5%, there was an increase of about 21% in the value of the apparent viscosity of the product in relation to the standard formulation. In this sense, it was observed that the content of the mucilage greatly infl uences the apparent viscosity of the product. Regarding the stability test, it can be seen that the mucilage concentration also infl u- enced the rheological behavior of the samples. Whereas viscosity reduction was observed in the formulation containing xanthan gum (F1) after submission to thermal stress cycles, in contrast to formulations containing 0.1 and 0.3% (F2 and F3) of the mucilage, thermal stress led to an increase in viscosity. However, this phenomenon was not verifi ed when higher concentrations of mucilage (0.5%, F4) were used in the formulation, where Table III Properties of creams formulated with Colocasia esculenta mucilage and xanthan gum after 24 h (initial time) of preparation and after the six cycles (12 d of thermal stress) Sample Time pH Density η (mPas.s) γ (s-1) k (mPa.sn) n F1 24 h 6.92g ± 0.01 0.979e ± 0.007 9,624.0 0.24 3,193.31 0.22 12 d 6.80h ± 0.05 0.989e ± 0.003 7,152.0 0.24 2,441.17 0.24 F2 24 h 7.03a ± 0.06 0.930a ± 0.008 3,792.0 0.39 2,735.73 0.65 12 d 6.73b ± 0.11 0.972b ± 0.002 10,920.0 0.39 7,243.77 0.56 F3 24 h 6.84c ± 0.01 0.920c ± 0.006 7,752.0 0.34 3,984.25 0.38 12 d 6.68d ± 0.01 0.923c ± 0.003 8,520.0 0.34 5,089.15 0.52 F4 24 h 6.78e ± 0.01 0.915d ± 0.006 11,640.0 0.12 2,818.34 0.34 12 d 6.68f ± 0.03 0.928d ± 0.054 5,184.0 0.12 2,443.54 0.65 #F1: control formulation using 0.3% xanthan gum. *F2: 0.1% mucilage. *F3: 0.3% mucilage. *F4: 0.5% mucilage. *Equal letters in the same column do not have signifi cant differences according to the Tukey test (p 0.05). η: apparent viscosity millipascal-second (mPa.s) γ: shear rate (s-1) k: consistency index n: fl ow behavior index. JOURNAL OF COSMETIC SCIENCE 288

submission to thermal stress cycles promoted a 55.5% reduction in viscosity at the lowest shear rate studied (Table 3). Such a behavior is possibly associated with physical–chemical interactions between the constituents of the formulations, which are infl uenced by the concentrations of each component. All samples presented characteristics of a pseudoplastic fluid (Figure 5), since there was reduction of viscosity when the shear rate was increased. This phenomenon is confirmed by the values obtained for the flow behavior indices n (Table 3), where all samples presented values below 1 (n 1) (33). Pseudoplastic behavior is a desir- able rheological property in cosmetic formulations because it improves their ap- plicability and spreadability (34). The viscosity data suggest that TM could be used as a substitute thickening agent for xanthan gum in cosmetic formulations. Such a property is quite interesting considering that xanthan gum is a relatively expensive product and TM could be produced in large quantities at relatively lower costs. The use of TM in cosmetic products would add value to this mucilage and could strengthen the production chain of Colocasia esculenta in devel- oping countries where it has been cultivated. CONCLUSIONS The mucilage of rhizomes of Colocasia esculenta (L.) Schott rose variety has semicrystalline characteristics and relatively high thermal stability, considering the cosmetics and food industry standards. It has in its composition clusters of proteins and carbohydrates, which may be associated with the presence of arabinogalactan, that are responsible for the good Figure 5. Rheological behavior of the emulsion samples in the stability study for 24 h, iced (I) and defrost (D). F1: control formulation using 0.3% xanthan gum, *F2: 0.1% TM, *F3: 0.3% TM, and *F4: 0.5% TM. TARO MUCILAGE IN COSMETIC FORMULATIONS 289