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- Materials and methods
In a country like Portugal, where coffee consumption is so deeply rooted in the cultural habits of the population, the total import of coffee is increasing within time and it reached almost 55 thousand tons in 2009 1. Spent coffee grounds (SCG), which are the residue obtained from the treatment of coffee with hot water or steam for extracting flavor substances therefrom, can be used for industrial applications such as to produce high quality biodiesel 2, 3. Due to their high content in carbohydrates, lipids, and proteins 4, the cosmetic products might be a suitable application for these types of residues.
Brazil is the largest coffee producer in the world 5. On average, a fifth of the Brazilian coffee production consists of defective beans which after roasting process decrease the final beverage quality 6. Several studies have been developed in order to find an alternative use for these defective coffee beans. One of the alternatives being considered is the cosmetic application of the oil extracted from the defective beans.
The human stratum corneum (SC) consists of several layers of keratinized corneocytes embedded in a lipid matrix of ordered lamellar structure. SC intercellular lipids particular composition allows a highly ordered arrangement of lipids playing an essential role in keeping an optimal skin barrier and in regulating the skin hydration. Deficiency of ceramides, cholesterol, essential fatty acids, and triglycerides leads to enhanced transepidermal water transport in addition to dryness of the skin, i.e., xerosis 7. The etiology of dry skin is variable but is often related to skin disorders and changes in lipid composition, particularly ceramides, as they are the major lipid constituent of lamellar sheets, followed by cholesterol, fatty acids, and triglycerides. A correct lipid ratio in SC is necessary to maintain the lipidic lamellae 8, 9. Ceramides play an important role and with cholesterol, free fatty acids, and cholesterol sulfate, which are ionized at physiological pH, they form ordered structures.
Traditionally, dry skin treatments were based on rehydration of the epidermis, through the use of emollients and/or an occlusive emulsion. Emollients or moisturizers are often used in the treatment of xerosis with the aim of improving skin hydration and sebum levels 8, 10, 11.
The purpose of this work was to assess the feasibility of using the lipid fraction of SCG in the development of cosmetic formulations (oil-in-water (O/W) creams) with improved skin hydration and sebum capacity. Their physicochemical characterization, stability, biological effects, and sensory acceptability were evaluated and compared with formulations containing green coffee oil and no coffee oil.
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- Materials and methods
The vehicle used to deliver the topical lipids was carefully selected, not only because it played an important role in the product efficacy and stability, but also because topical cream formulations must provide easy application on the skin surface without leaving any oil residue. The rationale behind this study was the physicochemical characterization of creams containing different lipids and simultaneously assessing their biological effects. In addition to the traditional emollients and occlusive constituents we intended to provide spent coffee oil, which is the residue obtained from the treatment of coffee.
The lipid fraction of SCG was extracted with supercritical carbon dioxide, an environmentally friendly solvent that allows the extraction and recovery of the oil at such conditions that no degradation of the lipid composition of the oil may occur.
All the formulations developed within this work were suitable to skin application: acidic pH and pseudoplastic or shear thinning behavior. This behavior occurs because entities in the fluid referred to as “flocs” tend to disassemble or assemble when stress is applied.
Apparent viscosity values provide a comparison of the resistance to structural breakdown between the emulsions and the loop areas compare the amount of structure that fractures in the standardized cycle. The inclusion of spent and green coffee oil seems to slightly increase the resistance to structural breakdown when compared with placebo (NoCofOil cream).
The emulsion maintained the mean particle size after oil coffee inclusion indicating that the oil did not destabilize the emulsion structure. Moreover, with the inclusion of the oil the population becomes thinner, i.e., with a more homogeneous population. However the inclusion of green coffee oil seems to slightly destabilize the original emulsion structure since we obtained a bi modal population with higher particle size. As known the emulsion stability is related to its particle size and distribution. Smaller the particle size, higher the stability. The results obtained show that the SpentCofOil cream present lower values when compared to the other formulations, especially with the GreenCofOil cream suggesting a better stability.
In general, there is a correlation between SC hydration and TEWL values, as lower TEWL (intact epidermal barrier function) corresponds to normal hydration state of the horny skin layer 19.
Estimation of the dynamics in SC hydration is used in efficacy claim studies on topically applied potentially hydrating (moisturizing) agents 20, 21. The increase in SC hydration is correlated with the improvement of the skin barrier function (lowering TEWL) 22. In this study it was observed that the SpentCofOil and GreenCofOil creams increased the epidermal capacitance and lowered the TEWL suggesting skin hydration.
Being a major component of this superficial layer, sebum lipids take part in the non-specific protective mechanisms of the skin barrier. Sebum is produced by the sebaceous glands (with higher density on the forehead, chest, and back) and consists predominantly of triglycerides, wax esters, and squalene 23. The role of sebum for the epidermal barrier was demonstrated in asebia mice (with profound sebaceous gland hypoplasia) 24. Despite the unaffected permeability barrier, asebia mice displayed epidermal hyperplasia, inflammation, and decreased (>50%) SC hydration, associated with a reduction in sebaceous gland lipids. The barrier abnormalities were attributed to the insufficient glycerol levels, derived from the triglyceride hydrolysis.
Elias and coworkers 25 showed that application of exogenous selected lipid mixtures optimized barrier repair in murine skin. In our study we used creams containing sebum-like lipids (SpentCofOil and GreenCofOil creams). When applied in human volunteers they had a restored effect as well as an increase in the sebum levels when compared with the cream with no coffee oil (NoCofOil cream) and with the control area as shown on Fig. 6.
Therefore, both creams (SpentCofOil and GreenCofOil creams) significantly increased skin hydration and sebum levels suggesting that the barrier properties of the skin were increased, probably by supplementation of skin lipids.
It is clearly shown that greasiness and skin feel on application were the attributes with the most significant difference whereas hydration and tackiness were the ones with the least difference among them. These observations are in accordance with the results obtained so far in epidermal capacitance, TEWL, and sebometry.