Introduction

Prinsepia utilis Royle (Family: Rosaceae) is a bushy deciduous shrub having a height of about 1.5–3 m. The plant is a native of the Himalayan region, widely distributed in Nepal, Bhutan, China, India, Bangladesh, and Pakistan, up to an altitude of 1600–3000 m (Gupta et al., 2015; Kunwar and Duwadi, 2003; Watanabe et al., 2013, Zheng et al., 2022). Locally known as “Dhatelo” or “Gotyalo” in Nepal (Gupta et al., 2015), the plant is distributed at an high altitude of 1800–3000 m in central and western districts of Nepal, such as Makawanpur, Myagdi, Kalikot, Humla, Jumla, Mugu, Dadeldhura, and Jajarokot (Bagale et al., 2022; Bhattarai et al., 1992; Kewlani et al., 2022a, 2022b; Kunwar and Duwadi, 2003; Manandhar, 1986, 1995; Watanabe et al., 2013). Different parts of this plant have been used traditionally, mainly for food and medicinal purposes, by the people of Nepal, India, and China (Gupta et al., 2015; Guan et al., 2014; Manandhar, 1986). The root bark is used for stomach disorders in the far western regions of Nepal (Kunwar and Duwadi, 2003).

The indigenous population of Nepal have traditionally considered the seeds of this plant as a nutritional food material and a useful source of oil extraction (Bagale et al., 2022; Bhattarai et al., 1992; Kewlani et al., 2022b) The most relevant part of the plant is its seeds, which contain about 37.2% fat and its oil is used as a vegetable oil as well as massage oil for rheumatism, headache, acne, and boils. The seed oil is a very useful natural emollient for cracked feet and hands in the winter season. In Nepal, it has been utilized as butter for oil lamps and hair oil (Watanabe et al., 2013). The people of the Jumla district of Nepal use seed oil residue to cure eczema or ringworm as well as to wash clothes (Watanabe et al., 2013). The seed oil is considered as a suitable source of hydrogenation and soap formulation (Bagale et al., 2022; Kewlani et al., 2022b; Maikhuri et al., 1994). Warm seed oil is reported as an effective therapy to treat body ache caused by heavy physical load (Manandhar, 1995; Zheng et al., 2022).

Besides, seed oil and leaves of P. utilis are extensively used in Indian and Chinese folk medicine to treat arthritis, bone disorders, joint ailments, blood pressure, and atherosclerosis (Gupta et al., 2015; Zhang et al., 2018). Diverse bioactive compounds, such as diterpenoid glucosides, hydro-xynitrile glucosides, rutin, isorhamnetin-3-O-rutinoside, cyanidin- 3-O-rutinoside, quercetin-3-O-glucoside, triterpenoids, etc., are reportedly found in the seeds (Zhang et al., 2018). In addition, P. utilis seeds contain a rich amount of fixed oils.

In spite of the increasing demand for preparing cleansing formulations, most of the commercially available cleansing preparations have various difficulties, such as chemical instability of the base, necessity of many pharmaceutical excipients to ensure base stability, high cost of production of synthetic base, and hypersensitivity of the base to the skin. In the current scenario, numerous industries and research organizations are exploring the possible pharmacological, nutritional, and cosmeceutical applications of different fixed oils isolated from natural sources such plants, herbs, and seeds. Consequently, underused seed oil is successfully utilized for the commercial production of effective cosmetic items (Atolani et al., 2020), such as creams, soaps, shampoo, skin care products, toothpaste, beauty products, hair conditioners, deodorants, and hair care products (Tareau et al., 2017).

Although, plain or antimicrobial commercial soaps, prepared by incorporating synthetic agents, are successful to achieve desired cleansing and disease-combating effects, these products are also responsible for several adverse reactions, such as dryness of skin, damage to skin integrity, browning of hair, skin eruptions, irritation, brittle hair, etc. Different synthetic antioxidant agents used in soaps, such as butylated hydroxytoluene, butylated hydroxyanisole, and paraben derivatives, potentially induce allergic reactions and are possible carcinogens (Atolani et al., 2016; Nowak et al., 2018). Similarly, the widely used synthetic antimicrobial agents (such as triclosan) in soaps are toxic cancer-causing agents.

Besides, other synthetic additives, such as fragrances, lathering agents, preservatives, and colorants, are also considered as potential threats to human health (Gultekin et al., 2006; Nowak et al., 2018). On the other hand, the preparation of natural or organic soaps involves the incorporation of natural fixed oils and other natural additives, such as honey, essential oils, plant-derived fragrances and colorants, antimicrobial plant extracts, vitamins, and natural antioxidants (polyphenols, such as flavonoids and phenolic acids). Therefore, these soaps fascinate to have several benefits, such as moisturizing, skin smoothing, antimicrobial, anti-inflammatory, antiviral, wound-healing, and anti-aging properties (Aburjai and Natsheh, 2003; Bansal et al., 2005). Therefore, many researchers are exploring the potential of sustainable natural sources as a base (Kim et al., 2015). Thus, among different natural sources, oils from the seeds of various edible plant species could be the best alternative.

The skin is the largest exposed organ of the human body. It is highly prone to diverse harmful materials that could induce various skin-related pathological conditions. Therefore, maintaining hygiene and neatness is necessary for the protection of the skin from different possible disorders associated with microbial infections. Thus, use of soaps is an easy and effective way to remove all harmful foreign particles. Appropriate use of the soaps ensures effective cleansing, as it obliterates different microorganisms, for instance, Pseudomonas species, Klebsiella pneumoniae, Staphylococcus aureus, and Proteus vulgaris, which are main causative agents for various skin infections (Sindhu et al., 2019).

The ever-increasing demand of consumers to use cleansing agents has prompted researchers to innovate different types of soap products in terms of quality, quantity, and function (Antonić et al., 2020; Widyaningsih et al., 2018). In the present scenario, the soap industry is developing a variety of antibacterial and antifungal soaps containing active antimicrobial ingredients (Kim et al., 2015; Yu et al., 2018). In the form of topical formulations, various preparations, such as ointments, creams, gels, shampoos, soaps, and powders, are available commercially (Shirsand et al., 2012).

Ketoconazole is one of the potent broad-spectrum antifungal drug belonging to the synthetic imidazole group (Rane and Padmaja, 2012; Staub et al., 2010). The drug has a significant therapeutic effect against systemic and superficial mycosis, along with candidiasis, malassezia, and dermatophytoses (Choi et al., 2019; Shirsand et al., 2012). It inhibits the synthesis of fungal ergosterol, a key constituent of fungal cell membrane, and results in cell death. Likewise, it also interferes with the biosynthesis of fungal phospholipids, triglycerides, and oxidative enzymes, thereby increasing the cellular concentration of toxic hydrogen peroxide. In treating Candida albicans infection, it prevents the formation of invasive mycelia from blastospores (Winnicka et al., 2019). Ketoconazole soap is the most popular and convenient cosmetic product used extensively for the treatment of fungal and yeast infections of the skin. Several skin-related developments, such as seborrhoeic dermatitis (Dreno et al., 2003), pityriasis versicolor, dermatophytoses, candida infections, androgenetic alopecia, leishmaniasis, superficial dermatomycosis, and yeast-induced blepharitis (Choi et al., 2019), have been successfully treated by using ketoconazole soap.

Prinsepia utilis seed oil has a long history of ethnomedicinal and economic usage by different ethnic groups in Nepal. However, no scientific studies have been conducted on the physiochemical properties, and the possible pharmaceutical and cosmeceutical applications of PUSO. Hence, this study aimed to evaluate the physicochemical parameters (pH, specific gravity, refractive index, melting point, viscosity, acid value, iodine value, saponification value, peroxide value, and ester value) and to formulate 2% w/w ketoconazole soap by using PUSO as a soap base along with its quality control analysis.

Materials and Methods

Chemicals and solvents

Standard ketoconazole powder was obtained from Biogain Remedies, Butwal, Nepal. Similarly, iodine trichloride, sodium thiosulphate, potassium iodide, and potassium bromate iodine were obtained from Merck India. Furthermore, mercuric iodide and iodine monobromide were obtained from Thermo Fischer Scientific, India.

Instruments

The following instruments were used in the study: Brookfield viscometer (Brookfield AMETEK, DV plus model, Boulevard Middleboro, USA), digital balance (ATX224, SHIMADZU Corporation, Manila, Philippines), hot air oven (S.M. Scientific Instruments, New Delhi, India), rotary evaporator (R-210/215, BUCHI Labor Technok AG, Flawil, Switzerland), UV spectrophotometer (UV-1800 model; Shimdazu Corporation, Shanghai, China), sonicator (INDOSATI Scientific Lab Equipments, Haryana, India), Abbe refractometer RFT-A1 (Toledo, OH, USA), and PC9500 benchtop digital pH meter, (Columbus, Ohio, USA).

Extraction of seed oil

Ripened fruit of P. utilis were collected from Khalanga-1, Jumla district, Nepal (a temperate region, 2518 m above sea level) in November 2020. The collected plant material was identified and authenticated by National Herbarium and Plant Laboratory Godawari, Nepal (Letter No. 078/079). The pulp of collected fruit was separated from hard seeds. Seed kernels were removed from hard shells and dried on clean filter papers in a well-ventilated laboratory room at 25^oC for 2 weeks.

Dried seed kernels were comminuted using a grinder and a sticky coarse powder was obtained for the presence of oil content. The coarse powder was then subjected to extraction by applying cold maceration method, in which 100-g dried powder was soaked in 500 mL of hexane in conical flasks with occasional shaking for 2 days. The menstrum was strained, and the marcs were pressed and filtered. The process was repeated for three times. The filtrate was collected and dried with the help of a rotatory vacuum evaporator at 40^oC to obtain orange color liquid hexane extract in the form of PUSO. The extract was again dried in a vacuum desicator for a few days and stored at 4^oC for further use. The photographs of collected fruits, dried seeds, seed kernels, and hexane extract (oil) of P. utilis are shown in Figure 1.

Figure 1. Photographs of P. utilis (A) ripen fruits, (B) dried seeds, (C) dried seed kernels, and (D) hexane extract (PUSO).

Physiochemical evaluation of PUSO

The physicochemical analysis was carried out in accordance with the Indian Pharmacopeia (Vol 1; Government of India, 2018) and relevant literature (Pandey et al., 2021). All the experiments were conducted in triplicate.

Acid value

Approximately 20 g of PUSO was dissolved in 100 mL of neutralized mixture of ether and 95% ethanol (1:1 v/v). The titration was fulfilled between the sample solution and the standardized potassium hydroxide (KOH) to determine acid value by using Equation 1 (Pandey et al., 2020):

where n is the volume of 0.1-M KOH reacted and w is the weight of the sample used for evaluation.

Iodine value

The iodine value was calculated by adopting the Hanus method (Pandey et al., 2020). At the beginning, 290 g of sample was mixed with 15 mL of chloroform in a 300-mL dry iodine flask. Then, 25 mL of iodine monobromide solution was poured gently from the burette. The sample mixture was incubated for 30 min at a dark place with occasional shaking. Then, 100 mL of distilled water and 10 mL of 30% w/v of potassium iodide solution were added. After incubation, the sample mixture was titrated with a standardized solution of 0.1-M sodium thiosulphate, in which starch solution was used as an indicator at the end of titration. The volume of 0.1-M thiosul-phate (mL) reacted was determined as “x” value. The same titration process was repeated without using the sample and volume consumed (mL) was observed as “y” value. Finally, the iodine value was determined by using Equation 2:

where w is the weight of the sample (g) used for evaluation.

Saponification value

Tentatively 2 g of PUSO was placed in a 250-mL round bottom flask connected to a reflux condenser. Then, a small amount of pumice powder and 25 mL of ethanolic 0.5-M KOH were added and boiled in a water bath for 30 min. After cooling of the sample for a few minutes, it was titrated against 0.5-M HCl by adding phenolphthalein. Blank titration was also carried out without adding the sample. The saponification value was determined using Equation 3 (Pandey et al., 2020):

where w is the weight of the sample (g) used for evaluation; x and y are the volume of HCl (mL) consumed by the sample solution and the blank solution, respectively.

Peroxide value

About 5 g of the test sample was added in a 250-mL conical flask, having a glass stopper. A mixture of glacial acetic acid and chloroform (3:2 ratio) was poured slowly with continuous shaking, followed by the addition of 0.5 mL of saturated potassium iodide. The homogenous sample mixture was then kept for 1 min, with frequent shaking. Then, 20 mL of distilled water was mixed and the titration of the obtained sample mixture was performed against a standardized solution of 0.01-M sodium thiosulphate until the disappearance of yellow color. In addition, 0.5 mL of 5% w/v starch solution was put dropwise and titration was continued with vigorous shaking until the disappearance of blue color (“x” in mL). In the same manner, blank titration was performed without sample (“y” in mL). Finally, the peroxide value was determined by using Equation 4 (Pandey et al., 2020):

where w is the weight of the sample (g) used for evaluation.

Ester value

Ester value of the sample was determined by using Equation 5 (Pandey et al., 2020):

Determination of specific gravity

At first, a clean and dried pycnometer, having a 50-mL capacity, was weighed along with its cap, noted as “a.” Then, the pycnometer was filled with samples until it was overflowed, closed with a stopper, and weighed again with contents and noted as “b.” After cleaning and drying, the same pycnometer was filled with water and weighed, recorded as “c.” Finally, the specific gravity was calculated using Equation 6 (Muhammad et al., 2013):

Measurement of pH and refractive index

For measuring pH, 100 mL of oil was poured in a clean and dry beaker. The pH was measured thrice by using a digital pH meter. The refractive index was determined at room temperature with the help of Abbey refractometer (Muhammad et al., 2013; Pandey et al., 2020).

Measurement of viscosity

For measuring the viscosity of PUSO, a DV-III ULTRA Brookfield viscometer was used. For this, approximately 20 g of oil was poured in a dry 250-mL beaker. Viscosity was determined by using spindle No. 64. The test sample was subjected to rotation for 1 min at 10 rpm with 16.1 dyne-cm torque. The operation was carried out at a temperature of 25^oC. The experiment was conducted thrice and the data was presented in centipoises (cps) (IP, Vol 1, Government of India, 2018; Mekkawy et al., 2013; Pandey et al., 2021).

Formulation of 2% w/w ketoconazole soap

Soap was developed using basic saponification reaction; in which natural PUSO was reacted with KOH to produce soap. For this, 100 g of PUSO was taken in a beaker and heated in a water bath at 55^oC. In another beaker, 19.413-g KOH required to saponify 100-g oil was dissolved in an optimum volume of deionized water and allowed to cool to 35–40^oC. Then, both solutions were mixed with continuous stirring for about 30 min, until the oil is completely converted into a homogenous solution. The solution was cooled followed by filtration using Buchner funnel and Whatman filter paper No. 1. After that, 300 mL of saturated sodium chloride solution was poured into the filtrate to precipitate the soap. The precipitate was removed and kept in a clean beaker. To prepare 25-g medicated soap, 24.5-g soap and 0.5-g ketoconazole were mixed with mild heating and continuous stirring for 20 min. Finally, the product was poured in a suitable mold and allowed to solidify for a few hours to get the desired medicated soap (Ruckmani et al., 2014; Touré et al., 2010).

Evaluation of 2 % w/w ketoconazole soap

pH measurement

Aqueous solution, 100 mL and 10% w/v, was used to measure pH by using digital pH meter (Pandey et al., 2021; Sindhu et al., 2019).

Foam-forming ability

Exactly 1-g soap was dissolved in about 50-mL water in a 100-mL graduated measuring cylinder, shaken for about 2–3 min and allowed to stand for 10 min. Then, the height of the foam formed was measured by using a measuring scale (Sindhu et al., 2019).

Drug content

Initially, grinding of 10 pieces of soap (length, 4.7 cm, width, 2.12 cm, height, 0.78 cm, and weight, 25 g) was done in a pestle and mortar to prepare infinitesimal pieces. Then, 2.5 g of sample and 50 mg of ketoconazole were mixed in a 100-mL dry volumetric flask and dissolved with methanol. The sample solution was sonicated for 30 min to ensure complete solubilization of ketoconazole. After filtration, the sample was diluted to have the final solution of 25 parts per million (ppm). Similarly, the standard solution was also prepared by taking 50 mg of ketoconazole standard in a 100-mL volumetric flask dissolved with methanol. With proper dilution, a standard ketoconazole solution of 25 ppm concentration was prepared. Thus, both sample and ketoconazole solution were analyzed at 240 nm using a UV-visible spectrophotometer (Naveed and Jaweed, 2014). Content of the drug was determined by using pharmacopeial method with the help of Equation 7 (Dhakal et al., 2022; Koirala et al., 2021; Naveed and Jaweed, 2014; Pandey et al., 2020):

where sp is the sample, std denotes the standard solution, Wsp is weight of the sample ointment taken (2.5 g), Wstd is weight of the standard drug taken (50 mg), and LOD is loss on drying of the standard.

Determination of moisture content

At first, a dried clean crucible was weighed, “a,” and tarred. Then, about 6 g of soap was weighed, “b.” The crucible content was then heated for 2 h at a temperature of 101^oC. After that, the crucible was kept inside a desicator and cooled. Finally, the weight of crucible containing sample was noted, which is “c.” The moisture content was calculated by using Equation 8 (Sindhu et al., 2019):

Determination of total fatty matter (TFM)

About 10-g soap (W) was dissolved in 150-mL distilled water. The solution was mixed with 20% sulfuric acid and heated until a clear solution is obtained. After few minutes, a thick film of fatty acid appeared on the surface of the solution. Then, about 7 g of wax (X) was added to the solution and heated. A cake was formed (Figure 2C) on cooling, which was removed and weighed (A). Finally, TFM was calculated by using Equation 9 (Sindhu et al., 2019):

Results and Discussion

Yield of P. utilis seed extract

The yield of P. utilis seed hexanolic extract was found as 26.43%. Previous studies have reported extractive yield for some of the commercial oils, such as olive oil (14%; Abenoza et al., 2013), coconut oil (61.3%; Famurewa et al., 2021), and palm oil (59.32%; Teixeira et al., 2013). This demonstrates the moderate yield of PUSO.

Physicochemical analysis of PUSO

Different physicochemical properties of PUSO were analyzed for the characterization of its quality and condition. Table 1 shows the comparison of physicochemical parameters of PUSO with olive oil (Muhammad et al., 2013) and Diploknema butyracea (Roxburgh) seed fat (chyuri fat; Krist, 2020; Pandey et al., 2021). The oil was orange yellow in color (Figure 1D). The acid value of PUSO was higher than that of olive oil, which indicated the presence of higher proportion of free fatty acids in the sample. However, it had a lower acid value, compared to chyuri fat.

The acid value signifies the susceptibility of oil toward triglyceride degradation because of temperature, light, cold, and lipase enzyme activity (Inekwe et al., 2012; Oladiji et al., 2010; Pandey et al., 2021). Besides this, acid value demonstrates the suitability of oil for edible purposes. Any oil or fat having an acid value higher than 4 mg/g is considered unhealthy for edible purposes (Amoo et al., 2004). Thus, the acid value of date oil suggests that its consumption could be harmful for human consumption.

The higher iodine value signifies that the proportion of unsaturated fatty acids is high. Determination of iodine value is helpful to identify the proportion of double bonds, which are prone to oxidative degradation, in oil sample (Bello et al., 2011). The higher value of iodine in PUSO (98.89 g I₂/100 g) indicated that it contained a higher proportion of unsaturated fatty acids. Main fatty acids found in PUSO are ester polyunsaturated oleic acid (28.9%), monounsaturated linoleic acid (16.4%), vaccenic acid (11%), saturated stearic acid (11.4%), and saturated palmitic acid (22.1%). Overall, the amount of unsaturated fatty acids found in PUSO was 65.2% (Kewlani et al., 2022b; Maikhuri et al., 1994; Yang et al., 2012).

It has been reported that oil or fat samples having iodine value lower than 100 g I₂/100 g are considered stable chemically for industrial purposes (Chinedu et al., 2017), such as cosmeceutical industry, margarine production, bakery production, and drug industry (Samuel et al., 2017). The low iodine value of any oil or fat indicates its chemical stability against rancidity and oxidation of products manufactured (Chinedu et al., 2017; Samuel et al., 2017). The iodine value of PUSO was almost similar to that of edible sesame oil (Yermanos et al., 1972).

The stability of oil or fat against possible rancidity could be correlated with its peroxide value, which indicates possible auto-oxidation (Chinedu et al., 2017). Oil or fat having a peroxide value higher than 10 meq/kg is susceptible to auto-oxidation because of peroxidase and lipoxygenase enzymes if moisture content or other trace elements are present (Bello et al., 2011; Chinedu et al., 2017). The higher peroxide value of PUSO indicated its susceptibility toward peroxidation (Aremu and Akinwumi, 2014). Generally, unrefined oil has a comparatively higher peroxide value than refined oil. This could be a possible reason for higher peroxide value of PUSO (Aremu and Akinwumi, 2014). Therefore, comparative study of different extraction techniques for PUSO could be a significant scientific investigation to improve its peroxidation value.

The saponification value of oil or fat indicates the type of fatty acid present in terms of molecular weight. If any oil/fat sample has a low saponification value, then the sample contains a higher amount of fatty acids having high molecular weight. The higher saponification and ester values of PUSO indicated that it contained a greater amount of lower molecular weight short-chain and easily saponifiable triglycerides. These types of oils are suitable candidates for pharmaceutical, cosmeceutical and related industrial purposes (Bello et al., 2011; Inekwe et al., 2012). PUSO had higher saponification value (194.13), compared to commercially utilized oils, such as palm oil (192.64; Udensi and Iroegbu, 2007), olive oil (186.33; Muhammad et al., 2013), and sunflower oil (182.23; Alibe and Inuwa, 2012).

Specific gravity of any oil/fat sample represents its one of the most significant quality control parameters. Adulteration of an expensive oil sample by cheaper oil alters the specific gravity of the sample oil. Thus, specific gravity is a useful indicative parameter to check the quality of any oil sample (Yadav, 2018). In the present study, the specific gravity of PUSO was 0.89 g/mL, which was almost similar to that of olive oil (0.91 g/mL; Nierat et al., 2014).

The refractive index of oil correlates with its possible rancidity. It has been proved that oil with a higher refractive index has a greater chance of rancidity (Arya et al., 1969). In this study, refractive index of PUSO (1.464) was found similar to that of pumpkin oil (1.465; Alfawaz et al., 2004) but higher than that of olive oil (1.46; Muhammad et al., 2013). In addition, oil samples having a refractive index in the range of 1.475–1.485 are classified as drying oil (Aremu et al., 2006). In other terms, oil sample having an iodine value lower than 115 g I₂/100 g is classified as non-drying oil. Thus, it can be concluded that PUSO was a non-drying type of oil. These oil types do not form layer when having contact with air, and their chemical stability is always higher than that of drying oil (Islam et al., 2014).

In addition, PUSO had higher viscosity, compared to other common oil samples, such as pumpkin oil (48.09 cp; Alfawaz et al., 2004) and olive oil (84 cp; Nierat et al., 2014). Oil samples with higher viscosity are suitable for lubrication purposes (Nierat et al., 2014).

Evaluation of 2% w/w ketoconazole soap

After ensuring chemical suitability of PUSO as a soap base, 25 g of 2% w/w ketoconazole soap (Figure 2A) was formulated by basic saponification method. As shown in Table 2, various quality control parameters, namely pH, foam-forming ability, moisture content, TFM, and drug content, were determined. All the measured parameters were found within the limits as specified by the pharmacopeia and literature.

Figure 2. Photographs of ketoconazole soap (2% w/w) formulated by using (A) PUSO oil as a base, (B) foam-forming ability shown by newly formulated PUSO-based soap, and (C) total fatty matter present in the soap.

pH of soap

The pH of ketoconazole soap was optimal for the human skin. It is reported that pH of 5.5–7.5 is normal for the human skin (Sindhu et al., 2019).

Foam-forming ability

The foaming index of the formulation was 14.5±0.5 cm, while the foam retention time was 15 min. Compared with other soaps, we concluded that the foam-producing ability of the soap was satisfactory and stable (Akuaden et al., 2019; Jagdale et al., 2011). Figure 2B shows the foam-forming ability of newly formulated 2% w/w ketoconazole soap.

Moisture content

Total moisture content predicts the shelf life of any soap. If the moisture content of soap is in excess, even in normal storage conditions, water present in it could react with unsaponified oil or fat to liberate glycerol and free fatty acids because of hydrolysis. According to the Encyclopedia of Industrial Chemical Analysis, normal range of moisture content for any soap is 10–15% (Akuaden et al., 2019). Thus, the newly formulated ketoconazole soap demonstrated satisfactory results in terms of moisture content (10.35%).

Total fatty matter

Determination of TFM (Figure 2C) is one of the significant parameters to ensure the quality of any soap. TFM demonstrates the extent of moisturizing effect produced by soap when applied to the skin. If the TFM of soap is lower, it may increase the dryness of the skin (Ahmed et al., 2021; Akuaden et al., 2019; Jagdale et al., 2011). Based on the TFM value, soaps are classified into different grades. Soaps having TFM above 76% are categorized as Grade 1 soap whereas the TFM limit for Grade 2 soap is 60–70% (Ahmed et al., 2021). The TFM of PUSO-based soap was 69.31%, thus insuring it a Grade 2 category, and was compared to some commercially available soaps such as Lifebuoy (63.4%; Mwanza and Zombe, 2020; Sindhu et al., 2019), Lux Beauty (60.7%; Sharma et al., 2020), Dettol (65.4%; Mwanza and Zombe, 2020), and Liril Lime and Tea Tree Oil soap (70.4%; Sharma et al., 2020).

Drug content in the soap

The pharmacopeial assay was performed to quantify the amount of active ketoconazole present in the soap, and it was found within the limits (95–105%), as specified by the US Pharmacopeia 2020 (USP 2A; pp. 2506–2507). Therefore, commercial manufacturing of a medicated soap by using PUSO as a base could be a useful alternative. However, extensive studies regarding various parameters, such as real-time stability, accelerated stability, skin irritation test, drug release profile of the soap, and microbial studies, are important to ensure commercial acceptability of the soap.

Conclusions

This study examined various physicochemical parameters (iodine, acid, peroxide, saponification, and ester values, viscosity, pH, and refractive index) of PUSO and concluded that that it was suitable for pharmaceutical, cosmeceutical, and related industrial purposes. However, its high acid value signified that it is not suitable for human consumption as a food material. In addition, the peroxide value of PUSO could be minimized by its lead purification.

The antifungal soap prepared by using PUSO only demonstrated acceptable results, related to its chemical and physical stability. Different quality control parameters, namely pH, foam height, foam retention time, TFM, and drug content, were within the acceptable limits and comparable to several Grade 2 marketed soaps. The antifungal soap prepared by using natural oil only may show several beneficial effects, such as moisturizing, antioxidant, antiseptic, and skin soothing effects, rejuvenation of hair and skin, and no risk of carcinogenicity as observed in synthetic soaps. Therefore, further investigation is required so that PUSO could be commercialized as a suitable alternative for other synthetic oil or fat samples. Moreover, commercialization of PUSO could benefit economically the local communities involved in the cultivation and collection of P. utilis.

Data Availability

All the data used to support the results of this research are available in this manuscript.

Author Contributions

Jitendra Pandey conceived and designed the experiment. Srijana Acharya, Rakshya Bagale, Jitendra Pandey, Pooja Chaudhary, Akriti Gupta, and Bikash Rokaya performed the experiment. Jitendra Pandey analyzed the data and wrote the manuscript. Jitendra Pandey, Hari Prasad Devkota, Pramod Aryal, and Manju K.C. revised the final manuscript.