Surface Activity of Natural Surfactants Extracted from Sapindus Mukorossi and Sapindus Trifoliatus Soapnuts

colloids and interfaces

Article Surface Activity of Natural Surfactants Extracted from Sapindus mukorossi and Sapindus trifoliatus Soapnuts

Patrycja Wojto ´n 1 , Magdalena Szaniawska 2, Lucyna Hołysz 2, Reinhard Miller 3 and Aleksandra Szcze´s 2,*

1 Institute of Catalysis and Surface Chemistry, Polish Academy of Sciences, ul. Niezapominajek, 30-239 Kraków, Poland; [email protected] 2 Department of Interfacial Phenomena, Institute of Chemical Sciences, Faculty of Chemistry, Maria Curie-Skłodowska University, 20-031 Lublin, Poland; [email protected] (M.S.); [email protected] (L.H.) 3 Physics Department, Technical University Darmstadt, 64289 Darmstadt, Germany; [email protected] * Correspondence: [email protected]

Abstract: Surfactants derived from renewable sources such as plants are an ecological alternative to synthetic surfactants. Aqueous solutions of natural surfactants extracted from soapnuts obtained from two plants, Sapindus mukorossi and Sapindus trifoliatus, were studied. Their properties in terms of surface tension reduction and wettability were examinated. The natural surfactants show the ability to reduce the surface tension and increase the wettability of the hydrophobic polytetraﬂuoroethylene surface. These nuts can be used repeatedly for washing also in hard water. Crude extracts from Sp. trifoliatus exhibit better surface properties than those from Sp. mukorossi. This makes these soapnuts a good potential source of biosurfactants for household use.

Keywords: biosurfactant; surface tension; wettability; Sapindacea

Citation: Wojto´n,P.; Szaniawska, M.; Hołysz, L.; Miller, R.; Szcze´s,A. Surface Activity of Natural 1. Introduction Surfactants Extracted from Sapindus Synthetic surfactants are used in large amounts in a wide range of applications in mukorossi and Sapindus trifoliatus industry and households. In 2019 the size of the global surfactants market was 41.3 billion Soapnuts. Colloids Interfaces 2021, 5, 7. USD and it is projected to reach 58.5 billion USD by 2027, reaching a Compound Annual https://doi.org/10.3390/ Growth Rate of 5.3% from 2020 to 2027 [1]. In 2006 the worldwide production of surfactants colloids5010007 was about 12.5 million tons [2]. The properties of low price and easy availability are the features of synthetic surfactants that make them extensively used as detergents in house- Received: 30 November 2020 holds. Taking into account the type of surfactants, anionic and non-ionic surfactants are Accepted: 26 January 2021 Published: 31 January 2021 most often produced [1]. Surface active compounds are emitted to waters, the atmosphere and soil, and can accumulate in living organisms [3]. It was shown that around 60% of all

Publisher’s Note: MDPI stays neutral produced surfactants end up in the aquatic environment [4]. with regard to jurisdictional claims in Synthetic surfactants are not easily biodegradable, affect the environment, may affect published maps and institutional afﬁl- the biological activity and can even be toxic or irritant to microorganisms, humans, ﬂora and iations. fauna [3,5]. The accumulation of surfactants has a negative effect on the ecosystem and this effect depends on the type of surfactant and its physicochemical properties, environmental conditions and various biotic factors [5]. In aquatic systems, the biological impact of surface active compounds is determined by both their sorption and ability to penetrate through biological membranes [6]. Moreover, anionic surfactants were found to be less toxic than Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. cationic ones [5]. This article is an open access article In nature, surface active compounds are produced by bacteria, fungi, animals and distributed under the terms and plants [4,7–13]. Surfactants produced by living matter are called biosurfactants, although conditions of the Creative Commons this name is often used to describe surfactants produced by microorganisms [10,14]. As Attribution (CC BY) license (https:// they are obtained from renewable sources, they are non-toxic or show a low toxicity and creativecommons.org/licenses/by/ they are biodegradable. Thus biosurfactants are an ecological alternative to synthetic 4.0/). surfactants [10,11,13].

Colloids Interfaces 2021, 5, 7. https://doi.org/10.3390/colloids5010007 https://www.mdpi.com/journal/colloids Colloids Interfaces 2021, 5, x FOR PEER REVIEW 2 of 7

Colloids Interfaces 2021, 5, 7 they are obtained from renewable sources, they are non-toxic or show a low toxicity2 ofand 7 they are biodegradable. Thus biosurfactants are an ecological alternative to synthetic surfactants [10,11,13]. Saponins are one of the popular surface active compounds found in different species of plants,Saponins among are one others of the in popularspecies surfaceof the genus active compoundsSapindaceae found [4,11,12,15,16]. in different The species nuts of(called plants, soapnuts among others or reetha) in species produced of the by genus trees Sapindaceae belong to the [4,11 family,12,15 ,Sapindeae16]. The nuts growing (called in soapnuts or reetha) produced by trees belong to the family Sapindeae growing in tropical and tropical and sub-tropical regions, mainly in India and Pakistan [9,12] and contain from 6 sub-tropical regions, mainly in India and Pakistan [9,12] and contain from 6 to 10 weight% to 10 weight% of saponin [17]. The pericarp of the fruits of these trees is used for cleaning of saponin [17]. The pericarp of the fruits of these trees is used for cleaning woolen fabrics woolen fabrics and as household detergents, e.g., as shampoo. In traditional Indian med- and as household detergents, e.g., as shampoo. In traditional Indian medicine, saponins icine, saponins extracted from these pericarps are used as anti-inflammatory, antipruritic extracted from these pericarps are used as anti-inflammatory, antipruritic and antifertility and antifertility agents [16]. The research most frequently reported in literature refers to agents [16]. The research most frequently reported in literature refers to saponins of natural saponins of natural origin including saponins from Sapindus mukorossi [4,8,9,11,12,15,18]. origin including saponins from Sapindus mukorossi [4,8,9,11,12,15,18]. Saponins are amphiphilic compounds containing glycosides with non-sugar agly- Saponins are amphiphilic compounds containing glycosides with non-sugar agly- cone and belong to the glycoside derivatives of steroids or polycyclic triterpenes [12,19]. cone and belong to the glycoside derivatives of steroids or polycyclic triterpenes [12,19]. Saponins produced from soapnuts are mostly of the triterpenoid type [20]. Different crit- Saponins produced from soapnuts are mostly of the triterpenoid type [20]. Different critical ical micelle concentrations were reported in literature, depending on the extraction micelle concentrations were reported in literature, depending on the extraction method andmethod type and of the type natural of the source natural [4 ,source9,11,12 ,[4,9,11,12,15].15]. SaponinsSaponins extractedextracted fromfrom reethareetha exhibitexhibit aa surfacesurface tensiontensionreduction reductiondown downto to values values belowbelow 40 40 mN/m mN/m [[4,9,11]4,9,11] and have anan excellentexcellent emulsificationemulsification activityactivity [ 4[4,9,15],9,15] and and foaming foaming abilityability [[8,21].8,21]. Schmitt Schmitt [11] [11 ]proved proved the the ability ability of crude of crude saponin saponin extract extract to stabilize to stabilize an emul- an emulsionsion polymerization polymerization reaction reaction leading leading to tomonodisperse monodisperse latexes. latexes. The The extracts ofof SapindusSapindus mukorossimukorossi werewere also found found to to exhibit exhibit antibacterial antibacterial activity activity against against H. H.pylori pylori [18].[18 Yang]. Yang et al. et[8] al. showed [8] showed its effectiveness its effectiveness as a aspreservative a preservative against against StaphylococcusStaphylococcus aureus aureus ATCCATCC 6538. 6538. TheThe aimaim ofof thisthis studystudy waswas toto testtest thethe abilityabilityof of crude crude extracts extracts from from soapnuts soapnuts to to lower lower thethe surface surface tension tension of of water water in in respect respect to to their their possible possible use use as as detergent. detergent. Hence, Hence, aqueous aqueous solutionssolutions in in doubly doubly distilled distilled deionized deionized water water and and tap tap water water were were tested. tested. Natural Natural surfactants surfac- extractedtants extracted fromtwo from plants, two plants,Sapindus Sapindus mukorossi mukorossiand Sapindus and Sapindus trifoliatus, trifoliatus,were used. were While used. theWhile interfacial the interfacial properties properties of Sp. mukkorosiof Sp. mukkorosiare frequently are frequently studied studied in the in literature, the literature, to the to bestthe best of our of knowledgeour knowledge there there are very are very scarce scarce reports reports on Sp. on trifoliatus Sp. trifoliatus. In this. In workthis work also thealso possibilitythe possibility of using of using the same the same nuts severalnuts severa timesl times was also was investigated, also investigated, which which had not had been not donebeen sodone far. so Recent far. Recent studies studies in literature in literature include include only studies only studies with distilled with distilled water, whichwater, iswhich far from is far practical from practical in application. in application. Our goal Our was goal also was to testalso theto test properties the properties in tap waterin tap reflectingwater reflecting the conditions the conditions of practical of practical use at home. use at home.

2.2. MaterialsMaterials andand MethodsMethods 2.1.2.1. SampleSample PreparationPreparation WeWe used used well well dried dried commercially commercially available available fruit fruit pericarp pericarp of ofSapindus Sapindus mukorossi mukorossiand and ´ SapindusSapindus trifoliatus trifoliatus(Bio (Bio Company Company Pulst Pulst J.M, J.M, Siemianowice SiemianowiceSl., Śl., Poland) Poland) (Figure (Figure1). 1).

FigureFigure 1. 1.Sapindus Sapindus mucorossimucorossi and and Sapindus Sapindus trifoliatus trifoliatus fruit fruit pericarps. pericarps.

The ratio of fruit pericarp to water was selected according to the manufacturer’s recommendation. To prepare a water extract 4 g of fruit pericarp (without grinding) was Colloids Interfaces 2021, 5, 7 3 of 7

placed in 500 mL of Milli-Q water and incubated in a shaker (100 rpm) for 15 min at 25 ◦C. The fruit pericarp was placed in sterile gauze which facilitated their easy removal from the solution. The aqueous solutions obtained in this way were prepared just before measurements and diluted for further experiments. The aqueous solutions were also prepared by extending the contact time of the fruit pericarp in water to 30, 45, 60, 75 and 120 min. To check the properties under the conditions of practical use, aqueous solutions were also prepared in tap water (with a conductivity of 115.6 µS/cm) under the same conditions as for Milli-Q water. As the surfactant content in the investigated soapnuts is unknown, the concentration was later expressed as the mass of fruit pericarp per water volume. The initial nut concentration for the extraction process was 8 g/L, then the extract was diluted. In order to investigate the possibility of using the same fruit pericarp multiple times, after extraction, they were dried at room temperature and used again to prepare an aqueous solution. These operations were repeated ﬁve times using the same batch of nuts extracted for 15 min at 25 ◦C. For the determination of effect of extraction temperature on the surface tension, the extraction was conducted over 15 min in water at temperatures of 25 ◦C, 40 ◦C, 50 ◦C and 60 ◦C, respectively. Surface tension measurements were done at 20 ◦C. The surface tension and conductivity of solutions prepared in the given way were measured using the automatic KSV Sigma 700 (KSV, Espoo, Finland) ring tensiometer and a multiparametric system ELMETRON CX-731, respectively at 20 ± 2 ◦C. Before the measurements, each solution was thermostated at 20 ◦C. Each sample was measured several times and the presented results are averaged values.

2.2. Contact Angles Measurements The advancing contact angles of aqueous solution of both fruits pericarp extracts were measured on polytetraﬂuoroethylene (PTFE) (Nitrogen Industrial Plant in Tarnow, Poland) using the sessile drop method using the contact angle meter equipped with a video-camera system (GBX, Bourg-de-Peage, France) at 20 ± 2 ◦C. The single drop volume for the contact angle measurements was 4 µL.

3. Results and Discussion Saponins are considered as weakly acidic due to the hydrolysis of glycosides [22]. The pH values of Sp. mukorossi and Sp. trifoliatu solutions at an amount of 8 g/L were respectively 4.6 and 4.8 in distilled water and 7.1 in tap water. Figure2 shows the surface tension changes as a function of crude reetha concentration in distilled and tap water. The surface tension (γ) reduction with increasing extract concentration is slightly higher in distilled water. The minimum surface tension values in distilled water were ca. 52 mN/m and 47 mN/m for Sp. mukorossi and Sp. trifoliatus, respectively. In tap water this value tends to 48 mN/m for both tested solutions. Similar minimal value of γ of 51 mN/m for Sp. mukorossi was obtained in [12] after 3h extraction. An extraction lasting overnight led to a surface tension lowering to 38 mN/m [9] and 35.3 mN/m [4], whereas in [11] a value of 36 mN/m after extraction with 5 min microwave irradiation was reported. The critical micelle concentration (cmc) obtained from the surface tension isotherms in deionized water are 0.32 g/L and 0.24 g/L for Sp. mukorossi and Sp. trifoliatus, respectively. This refers to 0.032 wt% and 0.024 wt% of crude extract. These values are similar to 0.045 wt% obtained for Sp. mukorossi in [15] and 0.03 wt% Sp. trifoliatus reported in [23]. Muntaha and Khan [12] found the cmc of Sp. mukorossi to be 0.13 wt% and Ghagi et al. [9] as 1.7%. However, they used solutions extracted from soapnuts over 3 h and overnight. Schmitt et al. [11] determined the cmc of crude Sp. mukorossi extract to be 0.005% mass fraction in distilled water. Colloids Interfaces 2021, 5, x FOR PEER REVIEW 4 of 7

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Figure 2. Changes of the surface tension of aqueous solutions of investigated fruit pericarps prepared using Milli-Q and tap water, respectively.

The critical micelle concentration (cmc) obtained from the surface tension isotherms in deionized water are 0.32 g/L and 0.24 g/L for Sp. mukorossi and Sp. trifoliatus, respectively. This refers to 0.032 wt% and 0.024 wt% of crude extract. These values are similar to 0.045 wt% obtained for Sp. mukorossi in [15] and 0.03 wt% Sp. trifoliatus reported in [23]. Muntaha and Khan [12] found the cmc of Sp. mukorossi to be 0.13 wt% and Ghagi et al. [9] as 1.7%. However, they used solutions extracted from soapnuts over 3 h and overnight. FigureSchmittFigure 2. Changes 2. etChanges al. [11] of ofthe determined the surface surface tension tension the ofcmc of aqueous aqueous of crude solutions solutions Sp. mukorossi of of investigated investigated extract fruit fruit to pericarps pericarpsbe 0.005% pre- prepared mass paredfractionusing using Milli-Q in Milli-Q distilled and and tap water. water,tap water, respectively. respectively. In tap water, the cmc value was 2.4 g/L for both soapnuts. It was found that the cmc In tap water, the cmc value was 2.4 g/L for both soapnuts. It was found that the cmc of crudeThe critical soapnut micelle extracts concentration increase with (cmc) the obtainedpH and water from hardnessthe surface [15]. tension Schmitt isotherms et al. [11] of crude soapnut extracts increase with the pH and water hardness [15]. Schmitt et al. [11] in founddeionized that thewater cmc are of 0.32Sp. mukorossi g/L and 0.24at pH g/L 7.9 for and Sp. in mukorossi 0.12 M NaCl and amounts Sp. trifoliatus to 0.07%, respec- which found that the cmc of Sp. mukorossi at pH 7.9 and in 0.12 M NaCl amounts to 0.07% which tively.is about This 10 refers times to higher 0.032 wt% than and in distilled 0.024 wt% water. of crude extract. These values are similar to is about 10 times higher than in distilled water. 0.045 wt%In the obtained next step, for theSp. impactmukorossi of inthe [15] extraction and 0.03 time wt% on Sp. the trifoliatus surface tensionreported changes in [23]. of In the next step, the impact of the extraction time on the surface tension changes of Muntahasolutions and prepared Khan [12] with found 8 g/L the reetha cmc ofin Sp.deioni mukorossized water to be were 0.13 checked.wt% and As Ghagi can etbe al. seen [9] in solutions prepared with 8 g/L reetha in deionized water were checked. As can be seen as Figure1.7%. However,3 the surface they tension used solutions values decreased extracted wifromth increasing soapnuts overextraction 3 h and time overnight. up to 1 h. in Figure3 the surface tension values decreased with increasing extraction time up to 1 h. SchmittFurther et prolongational. [11] determined of the extractionthe cmc of time crude did Sp. not mukorossi significantly extract change to be the 0.005% γ value. mass The Further prolongation of the extraction time did not signiﬁcantly change the γ value. The fractionobtained in distilled surface tensionwater. changes correlate with changes in the conductivity. obtained surface tension changes correlate with changes in the conductivity. In tap water, the cmc value was 2.4 g/L for both soapnuts. It was found that the cmc of crude soapnut extracts increase with the pH and water hardness [15]. Schmitt et al. [11] found that the cmc of Sp. mukorossi at pH 7.9 and in 0.12 M NaCl amounts to 0.07% which is about 10 times higher than in distilled water. In the next step, the impact of the extraction time on the surface tension changes of solutions prepared with 8 g/L reetha in deionized water were checked. As can be seen in Figure 3 the surface tension values decreased with increasing extraction time up to 1 h. Further prolongation of the extraction time did not significantly change the γ value. The obtained surface tension changes correlate with changes in the conductivity.

Figure 3. Dependence of surface tension (ﬁlled symbols) and conductivity (opened symbols) of Figure 3. Dependence of surface tension (filled symbols) and conductivity (opened symbols) of aqueous solutions of the investigated fruit pericarp extracts as a function of the extraction time. The aqueous solutions of the investigated fruit pericarp extracts as a function of the extraction time. Theamount amount of fruit of fruit pericarps pericarps was was 8g/L 8g/L in Milli-Q in Milli-Q puriﬁed purified water. water. Figure4 shows the change in surface tension of the solutions obtained by 15 min extraction of soapnuts at an amount of 8 g/L as a function of the extraction temperature.

The increase in temperature affects the efﬁciency of extraction to a greater extent in the case of Sp. mukorossi soapnuts. The deterioration of the surface activity with increasing temperatures is not large and shows that the soapnut extraction works more effectively at

room temperature. This is consistent with results reported by Góral and Wojciechowski [13] Figureshowing 3. Dependence a lowering of surface of the surfacetension activity(filled symbols) of the saponinand conductivity plant extracts (opened in symbols) hot water. of aqueous solutions of the investigated fruit pericarp extracts as a function of the extraction time. The amount of fruit pericarps was 8g/L in Milli-Q purified water.

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FigureFigure 4 4shows shows the the change change in in surface surface tens tensionion of of the the solutions solutions obtained obtained by by 15 15 min min extractionextraction of of soapnuts soapnuts at at an an amount amount of of 8 8g/L g/L as as a afunction function of of the the extraction extraction temperature. temperature. TheThe increase increase in in temperature temperature affects affects the the efficien efficiencycy of of extraction extraction to to a agreater greater extent extent in in the the casecase of of Sp. Sp. mukorossi mukorossi soapnuts. soapnuts. The The deterioration deterioration of of the the surface surface activity activity with with increasing increasing temperaturestemperatures is is not not large large and and shows shows that that the the soapnut soapnut extraction extraction works works more more effectively effectively at at Colloids Interfaces 2021, 5, 7 5 of 7 roomroom temperature. temperature. This This is is consistent consistent with with results results reported reported by by Góral Góral and and Wojciechowski Wojciechowski [13][13] showing showing a alowering lowering of of the the surface surface activity activity of of the the saponin saponin plant plant extracts extracts in in hot hot water. water.

FigureFigureFigure 4. 4. 4.Surface SurfaceSurface tension tension tension of of aqueous of aqueous aqueous solution solution solution of of invest ofinvest investigatedigatedigated fruit fruit fruitpericarp pericarp pericarp extracts extracts extracts prepared prepared prepared at at at differentdifferentdifferent temperatures. temperatures. temperatures. The The The amount amount amount of of of fruit fruit fruit pericarps pericarps was was 8g/L. 8g/L.

AccordingAccordingAccording to to to the the the producers, producers, producers, soapnuts soapnuts can can be be used used several several times. times. Figure Figure 5 5 5shows showsshows the thethe dynamicdynamicdynamic surface surface tensions tensions of ofof aqueous aqueousaqueous solutions solutionssolutions of of soapnuts soapnuts extracted extracted upup up toto to ﬁvefive five timestimes times using us- us- ingingthe the the same same same nuts. nuts. nuts. It It canIt can can be be be seen seen seen that that that forfor for bothboth both types types of of nuts nuts nuts the the the largestlargest largest and andand fastest fastestfastest reduction reduction ininin surface surface surface tension tension tension was was was obtained obtained obtained after after after the the thefirst first ﬁrst extraction. extraction. extraction. Each Each Each subsequent subsequent subsequent extraction extraction extraction of of the the of samesamethe samebatch batch batchof of nuts nuts of leads nutsleads leadsto to less less to and and less slower slower and slower decreasing decreasing decreasing γ γ values. values.γ values. With With extraction extraction With extraction times times longerlongertimes than longerthan 15 15 thanmin, min, 15the the min, effectiveness effectiveness the effectiveness of of the the repeated repeated of the repeated use use of of the the use same same of the nuts nuts same decreases. decreases. nuts decreases. How- How- ever,ever,However, the the obtained obtained the obtained values values values of of surface surface of surface tension tension tension indi indi indicatecatecate that that that it it is itis still isstill still reasonable reasonable reasonable to to touse use use the the the samesamesame nuts nuts nuts a a afew few few more more more times, times, times, especially especially during during shorter shorter contact contact times times with with the the solution. solution.

Figure 5. Surface tension of aqueous solutions of: (A) Sp. Mukorossi and (B) Sp. trifoliatus after repetitive 15 min extraction FigureFigure 5. 5. Surface Surface tension tension of of aqueous aqueous solutions solutions of: of: (A (A) Sp.) Sp. Mukorossi Mukorossi and and (B) (B) Sp. Sp. trifoliatus trifoliatus after after repetitive repetitive 15 15 min min extraction extraction ◦ ofof the the same same pericarps pericarps at at 25 25 °C. °C.C. Wetting of solids by liquids plays a crucial role, among others, during washing. It WettingWetting of of solids solids by by liquids liquids plays plays a acrucial crucial role, role, among among others, others, during during washing. washing. It It is is is known that the addition of surfactants to water improves the wetting of hydrophobic knownknown that that the the addition addition of of surfactants surfactants to to water water improves improves the the wetting wetting of of hydrophobic hydrophobic sur- sur- surfaces such as PTFE [24]. In Figure6 the advancing contact angle of aqueous extract facesfaces such such as as PTFE PTFE [24]. [24]. In In Figure Figure 6 6the the advancing advancing contact contact angle angle of of aqueous aqueous extract extract solu- solu- solutions of the investigated soapnuts on PTFE surfaces is depicted. The contact angle tionstions of of the the investigated investigated soapnuts soapnuts on on PTFE PTFE surfaces surfaces is is depicted. depicted. The The contact contact angle angle de- de- decreases with increasing surfactant concentration. Sp. trifoliatus shows much lower contact creasescreases with with increasing increasing su surfactantrfactant concentration. concentration. Sp. Sp. trifoliatus trifoliatus shows shows much much lower lower contact contact angles as compared to Sp. mukorossi indicating its better wetting ability. The contact angle anglesangles as as compared compared to to Sp. Sp. mukorossi mukorossi indicating indicating its its better better wetting wetting ability. ability. The The contact contact angle angle values at a soapnut amount of 8 g/L for Sp. mukorossi and Sp. triﬁliatus are 102.6◦ and 73◦, respectively. Paria et al. [25] found for Sp. mukorossi 109.88◦ as the minimum contact angle. In [26] the minimum contact angle of aqueous solution of saponins extracted from Saponaria ofﬁcinalis on a PTFE surface was 82◦. For comparison with synthetic non-ionic surfactants, the contact angles values on PTFE were 68◦ for TX-100 and 78◦ for TX-165 [24]. This shows that the surfactant solutions obtained from Sp. trifoliatus have only a moderate wettability. Colloids Interfaces 2021, 5, x FOR PEER REVIEW 6 of 7

values at a soapnut amount of 8 g/L for Sp. mukorossi and Sp. trifiliatus are 102.6° and 73°, respectively. Paria et al. [25] found for Sp. mukorossi 109.88° as the minimum contact angle. In [26] the minimum contact angle of aqueous solution of saponins extracted from Sapo- naria officinalis on a PTFE surface was 82°. For comparison with synthetic non-ionic surfactants, the contact angles values on PTFE were 68° for TX-100 and 78° for TX-165 [24].

Colloids Interfaces 2021, 5, 7 This shows that the surfactant solutions obtained from Sp. trifoliatus have only a moderate6 of 7 wettability.

Figure 6. Contact angle vs. logarithm of the amount of fruit pericarp. Figure 6. Contact angle vs. logarithm of the amount of fruit pericarp. The obtained results show that the tested extracts of nuts exhibit surface activity and moderateThe obtained wetting properties. results show According that the totested the manufacturer, extracts of nuts they exhibit can be surface used several activity times and andmoderate do not wetting lose their properties. activity in According tap water. Thisto th makese manufacturer, them promising they can green be biosurfactants used several fortimes household and do not use. lose their activity in tap water. This makes them promising green biosurfactants for household use. 4. Conclusions 4. ConclusionsIn this study we investigated the surface activity and wettability of surface active componentsIn this study extracted we investigated from the soapnuts the surfaceSp.mukorossi activity andand wettabilitySp. trifoliatus of .surface The extracts active werecomponents used as extracted obtained from via the a mild soapnuts extraction Sp. mukorossi in water and without Sp. trifoliatus subsequent. The extracts separation were andused purification as obtained ofvia particular a mild extraction components. in water The without extracts subsequent of both tested separation soapnuts and showpuri- afication decrease of particular in surface components. tension value The and extracts an increase of both intested wettability soapnuts of show the hydrophobica decrease in polytetrafluoroethylenesurface tension value and surface. an increase Crude in soapnuts wettability do notof the lose hydrophobic their properties polytetrafluoro- in tap water and their surface activity depends to a small extent on the extraction temperature. Better ethylene surface. Crude soapnuts do not lose their properties in tap water and their properties have been shown for Sp. trifoliatus. These green surfactants derived from natural surface activity depends to a small extent on the extraction temperature. Better properties sources can be used instead of synthetic and non-biodegradable synthetic surfactants. have been shown for Sp. trifoliatus. These green surfactants derived from natural sources can be used instead of synthetic and non-biodegradable synthetic surfactants. Author Contributions: Conceptualization, A.S. and R.M.; methodology, A.S. and L.H.; validation, A.S., R.M. and L.H.; formal analysis, P.W. and M.S.; investigation, P.W. and M.S.; writing—original Author Contributions: Conceptualization, A.S. and R.M.; methodology, A.S. and L.H.; validation, draft preparation, A.S.; writing—review and editing, R.M. and A.S. All authors have read and agreed A.S., R.M. and L.H.; formal analysis, P.W. and M.S.; investigation, P.W. and M.S.; writing—original to the published version of the manuscript. draft preparation, A.S.; writing—review and editing, R.M. and A.S. All authors have read and Funding:agreed to Thisthe published research receivedversion of no the external manuscript. funding. DataFunding: Availability This research Statement: receivedNot no applicable. external funding ConflictsData Availability of Interest: Statement:The authors Not declareapplicable. no conflict of interest.

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