Both beige and yellow shea butters prepared according to the improved Megnanou et al. ( 2007 ) method, presented the same fondant (soft) texture and rancidity-less and moderate shea characteristic odor. Such characteristics are conformed to usual consumers’ criteria about shea butter (Carette et al. 2009 ; Mégnanou and Niamké 2013b ). It is important précising about the studied samples that beige shea butter would be a natural (original) fat because of its water-exclusive extraction (Elias 2015 , Jasaw et al. 2015 ). The yellow one, despite of the natural statute of Cochlospermum tinctorium dye, could be considered as an adulterate shea butter. Indeed, Cochlospermum tinctorium is exploited as medicinal plant; its roots aqueous extract would be drink in the treatment of many diseases (Diaw 1982 ). However, both beige and yellow shea butters of the present study with conform sensorial characteristics would constitute natural (BIO) available cheap and accessible edible fats. Moreover, the present optimized shea butters also exhale a slight sweety fragrance similar to that of the sweet almond oil. Such fragrance was not noticed by Megnanou et al. ( 2007 ) about the optimized shea butter, and could be justify by the improvement of the optimized method by avoiding the step of shea oil heating (for dehydration) which could destroy the volatile compounds responsible of the fragrance.
Physicochemical characteristics of the optimized shea butters
The physicochemical characteristics presented significant difference (p < 0.05) between beige and yellow optimized shea butters, except for peroxide and refractive indexes (Table ). Acid (0.280 ± 0.001 and 0.140 ± 0.001mgKOH/g, respectively) and peroxide (0.960 ± 0.001 and 1.01 ± 0.001mEqO2/kg, respectively) indexes which are considered as fat quality characteristics were very weak. Indeed, their values were at far slighter than those (4 mgKOH/g and 15 mEqO2/kg) recommended by Codex Stan 210 (1999) about vegetable fats. These values were also weaker than those concerning Megnanou et al. (2007) optimized shea butters shea. This situation could certainly be linked to the improved optimized method which deleted the shea oil heating step. In fact according to Dieffenbacher et al. (2000), fat heating would induce glycerids hydrolysis and unsaturated fatty acids oxidation, and consequently a high amount of free fatty acids and peroxide compounds.
Table 1
ParametersBeige shea butterYellow shea butterSpecific gravity (40 °C)0.87 ± 0.01b0.92 ± 0.01aRefractive index (40 °C)1.454 ± 0.00a1.453 ± 0.00aViscosity (mPa.s) (40 °C)73.66 ± 0.20b96.00 ± 0.20aActivation energy* (kJ/mol)46.8150.43Colour (Ly)3.40 ± 0.01b3.90 ± 0.01apH (25 °C)06.50 ± 0.30b06.78 ± 0.30aAcid index (mgKOH/g)0.280 ± 0.001a0.140 ± 0.001bPeroxide index (mEqO2/kg)0.960 ± 0.001a1.010 ± 0.001aIodine index (gI2/100 g)52.64 ± 0.20b53.06 ± 0.20aOpen in a separate window
With such acid and peroxide indexes, the studied shea butter would present good aptitude for exportation/international trade though (moreover) the fat just contained 0.2 % of moisture. Additionally, values of specific gravity at 40 °C were 0.87 ± 0.00 and 0.92 ± 0.00 for the beige and the yellow shea butter, respectively. Such values added to those of the refractive index (1.454 and 1.453 for beige and yellow, respectively) and the viscosity (73.66 ± 0.20 and 96.00 ± 0.20 mPa s for beige and yellow, respectively) would confirm the quality of conventional edible vegetable oils to the shea butter samples (Codex-Alimentarius 1993; Besbes et al. 2004).
Furthermore, all studied shea butters could be classified as non-drying fats in view to their refractive index value (Rossell 1991). This property would disqualify them for varnish manufacturing in chemical industry, despite of their relatively high iodine value (52.64 ± 0.20 and 53.06 ± 0.20 gI2/100 g for beige and yellow shea butter, respectively) compared to that of marked shea butters reported by Megnanou et al. (2007). This iodine index value would suggest an interesting amount of unsaturated fatty acids and would confirm the very weak peroxide index.
About the viscosity, those of liquids as vegetable oil are commonly perceived as thickness, or resistance to pouring (Ndangui et al. 2010). Beige shea butter was less viscous than the yellow one, probably due to the presence of mucilage contained in Chochlospermum tinctorium dye (Jensen 2005). In addition, yellow shea butter viscosity was higher than the mean value (75 mPa.s) of most vegetable oils (Besbes et al. 2004). This physical property linked to the solid state of the studied shea butters could be used in food and cosmetic industry to confer an adequate texture to final fat products (Dubois et al. 2007).
The profile of the temperature effect on viscosity and specific gravity are depicted on Figs. and , respectively. Each sample observed a typical variation of viscosity (y = 0.0627×2 − 8.6818x + 318.74 and y = 0.106×2 − 13.99x + 485.19, for beige and yellow, respectively) and specific gravity (y = 0.0002×2 − 0.0205x + 1.4299 and y = −0.0037x + 1.0684, for beige and yellow, respectively) which were materialized by the mathematical equations on the figures. These equations (relations) could be exploited by any factory, in order to obtain precisely the viscosity/specific gravity in conformity with any utilization. In summary, the value of viscosity decreases (90.41–20.01 and 125.37–23.55 mPa.s, for beige and yellow shea butters, respectively) continuously when the temperature increases from 35 to 65 °C and would confirm the Arrhenius law (Nzikou et al. 2007). The low indicates that the viscosity of fats decreases exponentially with increasing of temperature. It was also observed a relative similitude in the evolution of the viscosity for both samples; this could suggest similarity in fatty acids composition. However, such rheological property (viscosity/temperature and specific gravity/temperature) linked to the relatively important energy of activation (46.81 and 50.43 kJ/mol for beige and yellow, respectively) of the studied shea butters could be exploited in cosmetic industry for emulsions making (Lefur and Arnaud 2004). Above all, the pH of the studied shea butters would be indicated for such industry, mainly for body care because of its values (06.50 ± 0.30 and 06.78 ± 0.30 for beige and yellow, respectively) which around the human body proteases pH (Forestier 1992).
The spectra (Near infrared and UV–visible) of both shea butters presented, at the whole, the same profile (Figs. , ); which was in general similar to those of marked and original traditional shea butter reported by Mégnanou and Niamké (2014). This similitude would suggest for both beige and yellow optimized shea butters the content in molecular bearing ethylenic bonds with conjugation and carbonyl compounds (Yadav et al. 2004). The shea butters of these authors would also contain UV-filter compounds (molecular) materialized by the rapid decrease of the absorbance (0.15–0.05 and 0.2–0.075, for yellow and beige shea butters, respectively) from 300 to 400 nm (Besbes et al. 2004). Moreover, another interesting peaks were observed at 400 nm (about the beige shea butter), and at 500 nm (for both butters); they correspond to chlorophyll (A and B) and carorenoïds wavelengths, respectively. The melting of such interesting molecular would justify the great interest of cosmetic and pharmaceutical industry for fats like shea butters, and would then constitute an advantage for using the studied shea butters in cosmetic formulations as UV protectors against carcinogenic UV A and B.
The information delivered by the optimized shea butters near infrared spectra was identical to that reported by Mégnanou and Niamké (2014) about marked shea butters. Such similitude would recall and confirm the proposition of these authors to adopting the spectra (UV–visible and near infrared) as shea butter essential distinctive characteristics. Hence, any adulteration of shea butter with other fats and/or alteration would be clearly detected through the profile. As precision, the difference noticed about the intensity of peaks at 450–500 nm wavelengths, between the yellow (1.5224) and the beige (1.1734) shea butters, could be correlated to the Lovibond color value in red light (3.9 against 3.4 for the beige one). That dissimilitude would suggest the implication of carotenoids (carotene and other carotenoids) in shea butter color.
In summary, both beige and yellow optimized shea butters would contain the same compounds like hydrocarbon, unsaturated molecular, fatty acids and moleculars protecting against sun rays damages (allergy and cancer), in probably different amounts.