Ceramides Extracted from Wool: Pilot Plant Solvent ExtractionTextile Research Journal, Jan 2008 by Ramírez, Raquel, Martí, Meritxell, Manich, Albert, Parra, Jose Luis, Coderch, LuisaE-mail Print Link

Abstract Ceramides extracted from wool fibers have proved to be beneficial in pharmaceutical and cosmetic formulations in the treatment and care of skin and human hair. This work sought to obtain internal wool lipid extract enriched in ceramides at pilot plant level without causing significant damage to the wool fiber. To this end, two extraction methodologies were performed using two solvents - acetone and methanol. Analyses of wool extracts were performed by thin layer chromatography coupled to an automated ionization detector, and chemical and mechanical evaluations of extracted wool were carried out. Larger amounts of ceramides were obtained when wool fibers were extracted with methanol than with acetone with some modifications of the fiber properties. This lipid extract could be a by-product with a high added value for the wool industry.

Wool is a natural fiber that is mainly composed of protein with an external lipid content (lanolin) and a minor internal lipid content (1.5%). Internal wool lipids (IWL), which could arouse considerable interest given their high proportion of ceramides, are also rich in cholesterol, free fatty acids and cholesteryl sulfate, and resemble those in membranes of other keratinic tissues, such as human hair or stratum corneum from skin [1,2].

This particular composition allows a highly ordered arrangement of the lipids known as lamellar lipid bilayers. The intercellular lipids of the stratum corneum play an important role in the barrier function of the skin by avoiding the penetration of external agents and by controlling the transepidermal water loss, which maintains the physiological skin water content [3].

In fact, the IWL composition, similar to that present in the stratum corneum [1], has been shown to be capable of forming liposomes with a stable bilayer structure [4-6]. Furthermore, topical application of IWL liposomes on intact and disturbed skin has been demonstrated to improve barrier skin properties [7, 8]. Accordingly, IWL could be regarded as a new natural extract, beneficial for topical application and suitable for incorporation into pharmaceutical or cosmetic formulations in the treatment and care of skin [9] and human hair [10].

In order to obtain IWL extracts with a large amount of ceramides, different extraction methodologies, such as Soxhlet with diverse organic solvent mixtures or supercritical fluid extraction with CO2 and several polarity modifiers have been optimized at laboratory levels [11-13].

The aim of this work was to obtain IWL extracts rich in ceramides at pilot plant level. Accordingly, two extraction methodologies were performed using two solvents - acetone and methanol. Lipid extracts were analyzed and ceramide content was evaluated. Furthermore, the eventual chemical and mechanical wool modifications after lipid

extraction were assessed in order to determine the feasibility of the extracted wool for textile purposes.

Materials and Methods

Wool Conditioning

Raw Spanish Merino wool samples supplied by SAIPEL (Terrassa, Spain) were used for lipid extraction and for evaluation of their chemical and mechanical characteristics. Raw wool was industrially cleaned in a process with five scouring bowls for a total degreasing. The cleaning sequence consisted of a washing at 35-40 °C (1st bowl), followed by a treatment with sodium carbonate at 45-55 °C (2nd bowl), sodium carbonate and ethoxylated nonylphenol at 50-58 0C (3rd bowl), ethoxylated nonylphenol at 50-52 °C (4th bowl), and a final rinsing with water at 45-47 °C (5th bowl). Finally, the wool was heat dried at 40 °C for 2 h.

Pilot Plant Extraction Procedures

In a first assay, A, 5 kg of wool were extracted at pilot plant level. The extraction procedure consisted of a pump-forced reflow system and was performed for 4 h with a solvent ratio of 1/40 in two organic solvents - acetone and methanol. The extraction temperature was 48 °C for acetone and 56 °C for methanol. These temperatures were lower than the boiling temperature of the solvents used in each case. A kinetic control of both extraction processes was also carried out, taking aliquots at 1,2,3 and 4 h for analysis. After distillation, lipid extracts were concentrated and stored in 1 L at -20 °C. Aliquots were dried and weighed, and lipid extraction percentages were determined.

A second assay, B, was performed to minimize the solvent quantity in relation to the amount of extracted wool. In this assay, four samples of 7 kg of wool were extracted at pilot plant level at different extraction times with the same organic solvents. The extraction procedure consisted of a pump-forced reflow system and was performed for 30 min, 1, 2 and 4 h with a solvent ratio of 1/25 in the same organic solvents used in the first assay. The wool samples were changed at 30 min, 1, 2 and 4 h of wool extraction time and the same solvent was maintained for the whole extraction procedure (7.5 h). The extraction temperature was lower than in the first assay, 40 °C for acetone and 45 °C for methanol in order to avoid impairing wool fibers. A kinetic control of both extraction processes was also carried out taking different aliquots during the whole process (0.08, 0.25, 0.50,1.5, 2.5, 3.5, 5.5 and 7.5 h) for analysis. Thereafter, the solvents were distilled to obtain 11 L of lipid extracts. Aliquots were dried and weighed, and lipid extraction percentages were determined.

The quantitative analysis of the IWL was performed by thin layer chromatography coupled to an automated ionization detector (TLC-FID) Iatroscan MK-5 analyzer (Iatron, Tokyo, Japan) following the analysis methodology referred to in earlier works [11-14]. Samples dissolved in chloroform/methanol (2/1, v/v) (15-20 µg) were spotted on Silica gel S-III Chromarods using a SES (Nieder-Olm, Germany) 3202/15-01 sample spotter. A

general lipid analysis (1 scan) was performed by eluting the rods consecutively four times using the following mobile phases: 1st and 2nd chloroform/methanol/water (57/12/0.6, v/v/v) twice to a distance of 2.5 cm, 3rd n-hexane/diethyl ether/formic acid (50/20/0.3, v/v/v) up to 8 cm and 4th n-hexane/benzene (35/35, v/v) up to 10 cm. A more precise analysis of polar compounds (3 scan) was performed by developing the rods initially to a distance of 10 cm with n-hexane/diethyl ether/formic acid (53:17:0.3, by vol) to separate apolar and polar lipids. After a partial scan of 85% to quantify and eliminate the apolar lipids, a second development, again to a distance of 10 cm, was performed with chloroform/n-hexane/methanol/acetone (55:5:3:7, by vol) to separate the ceramides. Following a partial scan of 85% to quantify and eliminate the ceramides, a third development, again to a distance of 10 cm was performed with chloroform/methanol/formic acid (57:12:0.3, by vol) to separate and quantify, after a total scan of 100%, the glycosilceramides and sterol sulfate. After each elution, the rods were heated for 5 min at 60 °C to dry the remaining solvent. The experimental conditions were: air flow 2000 mL/min, hydrogen flow 160-180 mL/min and scanning speed 2-3 mm/s. Data were processed with a Boreal version 2.5 software. These procedures were applied to the following standard compounds: palmitic acid and cholesterol from Fluka Chemicals (Buchs, Switzerland), type II and type V ceramides, cholesterol ester, 7 hydroxy-cholesterol, galactoceramides, cholesterol sulfate, tripalmitin and behenyl alcohol from Sigma (St. Louis, MO, USA) and type III and type VII ceramides from Iteqsa (Sabadell, Spain) to determine the corresponding calibration curves for quantification of each compound.

Wool Fiber Evaluation

Mechanical and chemical wool modifications after the extraction process were determined by the evaluation of several parameters, such as whiteness index, yellowness index, fiber diameter, fiber length, alkaline solubility, tenacity, elongation at break, pilling rate and abrasion resistance. The raw wool was carded to obtain the top wool to evaluate some of these properties.

Whiteness index (Berger 59) and yellowness index (ASTM D1925) of extracted tops were measured using a spectrophotometer Color-Eye 3000 (Macbeth, U.S.A.) with D65 illuminant and 10° observer.

The diameter and length of the extracted wool fibers were evaluated following the corresponding guidelines using the Air Flow method (IWTO-6-86) and an Almeter Al -100 (IWTO-17-85), respectively. Mean diameter, in µm, was obtained with 2.5 g of fibers in triplicate by the Air Flow method at constant pressure. Fiber length and barb, in mm, were obtained by the Almeter Al-IOO with 0.5 g to 2.5 g of samples corresponding to approximately 20,000 to 120,000 fibers.

Alkaline solubility of extracted wool fibers was evaluated by triplicate following a normalized methodology (UNE-40-204.72) [15].

In fiber stress-strain tests, random fibers were taken from the samples previously conditioned for 48 h in a standard atmosphere (20 °C, 65% RH). The experiment was performed using a computer programmable dynamometer (Instron 5500R) in accordance with the ASTM Standard D 3822 (1980) with some modifications: specimen effective length was 30 mm, the deformation rate was 1%/s, and sample size was 50 fibers per sample. The calculations were corrected for any slack or pretensioning in the specimen at the start of the tensile test. The initial linear region of the curve was calculated by the intersection of the straight line passing through the points at 0.4 and 0.2 of the maximum load with the displacement axis. Fibers which break at very low strain due to weak points were discarded. The mean breaking tenacity and elongation values were obtained.

Knitwear (128 g/m^sup 2^) made up with yarn (15.6 tex X2) was used for the pilling and abrasion resistance tests. Pilling test was performed using the ICI Pilling Box method (ISO 12945-2) and abrasion resistance was evaluated using IWS TM 112 July 1996 in the Martindale Wear and Abrasion Tester (ISO 12947-2/ISO 12947-3).

Results and Discussion

Lipid Extraction and Analysis

Raw Spanish Merino wool was extracted at pilot plant level in order to obtain the lipid extract rich in ceramides. Merino wool from Spain was used because its internal lipid composition resembles that found in the stratum corneum from skin [11,12].

The extraction was performed twice with each solvent acetone and methanol - at two different temperatures employing the conditions detailed in the experimental section for assays A and B. The possibility of excluding chlorinated solvents, which are widely used at laboratory level, was the main reason for choosing these solvents as extractors. The main differences between these two assays were the following: 1) the lower temperature used in the solvent extraction in assay B; 2) change of wool at 0.5,1, 2 and 4 h of wool extraction time using the same solvent and a lower 1/25 solvent ratio in assay B; 3) a kinetic control taking aliquots at 1, 2, 3 and 4 h for analysis in the first assay A and aliquots 0.08, 0.25, 0.50, 1.5, 2.5, 3.5, 5.5 and 7.5 h in the second assay B (Figure 1).

It seems that the IWL content is in the range 1.2% o.w.w. [16] to 1.5% o.w.w. [17]. Accordingly, appropriate yields were obtained with the extraction conditions used in assay A in which lipids were extracted in about 0.8% for acetone and 1.4% for methanol. A lower amount of lipids was obtained in assay B for the same solvents, probably because of the lower temperature of the extraction procedure and the lower solvent ratio used. However, as in the previous assay, methanol percentages of lipid extracted (about 0.80%) were higher than acetone ones (about 0.40%). This has also been reported with Soxhlet extraction at laboratory level [11]. The low amount of lipids extracted using acetone could be attributed to the low swelling effect of this solvent

The kinetic control indicated that a very rapid extraction was achieved in both cases. A maximum extraction was achieved in the first aliquot analyzed from assay A at 1 h of

extraction for the two solvents studied. Also, a maximum extraction was obtained in the first aliquot at 5 min (0.08 h) for the acetone solvent and in the third one at 30 min (0.5 h) for the methanol solvent in assay B. Furthermore, the maximum extraction obtained from the first aliquot of methanol and acetone of assay A and acetone of assay B was maintained during the whole process. In the case of methanol extraction in assay B, the extraction percentage with respect to the amount of wool fell from 1.1% at 0.5 h to 0.6% at the end of the assay. The renewal of the wool using the same solvent during the process in assay B increased the lipid concentration in the acetone from 0.2 mg/mL to 0.8 mg/mL. Nevertheless, the lipid extract in relation to the amount of wool remained approximately constant (0.4% o.w.w.). However, the greater extraction capacity of methanol increased the lipid concentration in methanol from 0.4 mg/mL to a maximum of 1.3 mg/mL after 21 kg of wool extracted. This concentration fell to 1.1 mg/mL for the last 7 kg extracted. This decrease in the lipid concentration corresponded to the diminution of the lipid extract with respect to the amount of wool and was probably due to the lipid saturation in methanol.

In the light of these findings, it was deduced that 30 min (0.5 h) extraction was enough to reach a maximum extraction, which was 1.3% o.w.w. and 1.1% o.w.w. for methanol at 56 °C and 45 °C, respectively, and 0.8% o.w.w. and 0.4% o.w.w. for acetone at 48 °C and 40 °C, respectively. Furthermore, 28 kg of wool could be extracted with the same solvent system without reaching saturation in the case of acetone when the solvent ratio assayed was 1/6.3. However, the high extraction power of methanol allowed us to add new wool only until saturation, which was obtained with a solvent ratio of 1/8.3.

Quantitative analysis of the aliquots taken at different times for each solvent used was performed by TLC-FID following the (1 scan) methodology reported in earlier papers [11-14]. The results obtained indicated the similarity of all lipid extracts regardless of the extraction time. There was no significant variation of the content of the main compounds (free fatty acids, sterol and polar lipids) at the different stages of the extraction. This indicated a reduction of extraction time in subsequent experiments at pilot plant level. The amount of the main lipid families obtained in each extraction procedure can be visualized in Figure 2.

A comparison of the extracts using the same solvent under the two different procedures showed that in all cases a larger amount of each lipid compound was obtained in assay A at higher temperatures than in assay B at lower temperatures. Furthermore, when comparing acetone and methanol extraction, it could be seen that acetone showed a higher affinity for the most apolar compounds (sterol esters), whereas methanol showed a higher affinity for the most polar compounds (free fatty acids, sterols and the rest of polar lipids, including the ceramides).

The polar lipids were analysed by TLC-FID following the (3 scan) methodology to quantify the different ceramides, glycosilceramides and sterol sulphate (Table 1).

It can be seen that a larger amount of polar lipids was obtained using the extraction conditions of assay A where the total extraction was higher. A smaller amount of polar

lipids was obtained in assay B for the same solvents, probably because of the lower temperature of the extraction procedure and the lower solvent ratio used. Moreover, larger amounts of polar lipids were extracted when methanol instead of acetone was used in the two assays (A and B).

In order to compare the composition of lipids extracted from the two methodologies, the percentages with respect to lipid extract of apolar and polar lipids are shown in Figure 3. It can be observed that the highest content of sterol ester was achieved in the case of the acetone extracts, whereas methanol extracts were richer in free fatty acids and sterol sulfate. In assay A, smaller amounts of ceramides and larger amounts of glycosilceramides than in assay B were obtained. However, the percentages with respect to lipid extract of polar lipids were slightly higher in methanol extracts than in acetone extracts.

Wool Fiber Evaluation

Evaluation of chemical and mechanical wool characteristics before and after lipid extraction is important to determine the possible fiber modification because of the different extraction procedures applied.

The evaluation of the whiteness and yellowness indexes of the extracted tops was carried out in order to confirm the possible alteration of the fibers (Table 2). A slight decrease in the whiteness index and a small increase in the yellowness index were observed for the fibers extracted with acetone in the two assays. A marked decrease in the whiteness index and a discernible increase in the yellowness index were observed for methanol extracted fibers. These differences were much more marked in assay A at higher temperatures. These results suggested a possible alteration of the fibers caused by methanol extraction at high temperatures.

The results obtained in the evaluation of several physical characteristics are indicated in Table 3. Non-significant differences were detected in the value of the fiber diameter because of the extraction procedure. Fiber length and barb values showed a very small decrease in the two methanol extracted fibers and the acetone extracted fibers in assay B. This was consistent with the slightly higher values obtained for short fibers. However, the increase in length and barb detected in the wool extracted by acetone and subjected to a high temperature (assay A) should be noted. This could be attributed to an increase in the fracture strength of the fibers which were extracted with acetone.

In order to evaluate a possible reinforcement of the wool fibers due to acetone extraction, the alkaline solubility was determined (Table 4). Although there were no differences between non-treated fibers, methanol extracted fibers in both assays and acetone extracted fibers in assay B, a marked decrease in the alkaline solubility in acetone extracted fibers in assay A should be noted. This decrease together with the greater fiber length and barb in these acetone extracted fibers suggested possible reticulation of the fibers when acetone was used as extractor solvent at high temperatures.

Moreover, individual values of tenacity and elongation at break were examined (Table 5) using the Analysis of Variance technique [18]. Non-significant differences were observed in the tenacity of the non-extracted and extracted wool fibers, even though a slight decrease was detected in the tenacity values of assay B perhaps because of the high tenacity value of the non-extracted fiber. This finding agreed with the results obtained in an earlier work [19], where nonsignificant differences were also observed in fiber tenacity when measured in bundle form.

According to Table 5, it seems that the different extraction procedures decreased elongation at break. This decrease was more marked in the case of acetone extracted fibers, although the differences observed between nonextracted and extracted fibers were non-significant. An ear lier work [20] based on modeling the stress-strain curves suggested that the IWL extraction could be related to a decrease in the elongation at break of the fibers.

The pilling rate and the abrasion resistance of the fibers were determined only with the mixture of fibers obtained from assay B extracted at different times (Table 6) because a considerable amount of wool was necessary to spin and knit the corresponding wool fabrics.

Few differences were observed between the pilling results obtained for the untreated wool fibers and the two extracted wool fibers. However, the abrasion resistance increased because of the lipid extraction. The wool fiber extracted with methanol was significantly more resistant than the others. In fact, the extraction of cell membrane lipids of wool with various polar solvents has been shown to significantly improve the abrasion resistance of wool fabrics [17, 21-23]. In our case, the methanol extraction obtained almost twice as many lipids as the acetone process with the result that a better abrasion resistance was obtained for wool extracted by methanol. The mechanism by which this improvement was obtained has not yet been established [17,23].

Conclusions

A larger amount of ceramides was obtained when wool fibers were extracted with methanol than with acetone; 0.16-0.29% o.w.w. by methanol extraction and 0.10-0.16% o.w.w. by acetone extraction, depending on the experimental conditions used. A reduction in the extraction time (about 30 min) could occur in the two assays performed at pilot plant level using acetone or methanol when the amount of lipids is the main objective of the process. Furthermore, the solvent ratio of 1/40 used in assay A for the two solvents was reduced in assay B to 1/6.3 for acetone extraction and only to 1/8.3 for methanol extraction because of its greater extraction power.

Moreover, the wool fiber modifications due to the different extraction procedures applied were evaluated to determine their possibilities in textile further processing. In general, the different extraction procedures slightly modified some properties of the fibers, such as the fiber diameter, pilling rate, tenacity and elongation at break, but these differences were non-significant. However, other modifications in chemical and mechanical

characteristics of the fibers extracted should be noted. Acetone extracted fibers under severe conditions had lower alkaline solubility and greater fiber length and barb than non-extracted fibers because of possible reticulation of the fibers extracted in these conditions. Although lower whiteness and higher yellowness indexes were obtained in methanol extracted fibers, abrasion resistance increased with respect to nonextracted fibers because of the greater lipid extraction. In the light of our findings, it may be concluded that the wool did not deteriorate, which would have affected further processing.

Thus, this work presents an extraction method at pilot plant level for obtaining IWL with a large amount of ceramides, without significantly impairing the wool fiber. This lipid extract could be a by-product with a high added value for the wool industry.

Acknowledgements

We wish to thank SAIPEL for supplying the wool and for the physical test parameters evaluations. We are also indebted to Keratec Limited for the pilling rate and abrasion resistance assay and to George von Knorring for improving the final version of the manuscript.

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