Roasting Effect on the Nutritional and Cosmetic Potential of Citrullus Lanatus Kernels Oil

The objective of this study was to evaluate the effect of roasting on the nutritional and cosmetic potential of oil extracted from kernels of C. lanatus, which is one of the most widespread Cucurbitaceae species in Sub-Saharan Africa. The dried kernels (DKO) and roasted kernels (RKO) oils were extracted by cold press and hot using hexane. The physicochemical properties of these oils were evaluated. The results showed that C. lanatus roasted kernels were important sources of lipids (40.12 %) and protein (37.50 %). Oil extracted by press was of high quality, compared to that extracted by hexane. The study of the roasting effect revealed that the physicochemical characteristics of DKO and RKO oils were significantly different, with the exception of their specific gravity (≈ 0.9) and their refractive index (≈ 1.47). The absorbance of the two oils decreased in the range of UV-A and UV-B wavelengths. Both oils had low oxalates content (≈ 0.05 %) and were free of phytates and cyanogenic glycosides. All these features suggest that the roasted kernels oil of C. lanatus could be used in food and cosmetic industries.

Contrary to palm oil and palm kernel oil, shea (Butyrospermum paradoxum) and makore (Tieghemella heckelii) butters, cucurbits oils are not produced traditionally.It has been shown that cucurbits seeds are dried, roasted and then made into a paste which is solely used in the preparation of sauces (Zoro Bi, Koffi, & Djè , 2003;Zoro Bi, Koffi, Djè , Malice, & Baudoin, 2006).In addition, high levels of polyunsaturated fatty acids confer on cucurbits oils high instability; which leads to the decrease of their nutritional and cosmetic values (Loukou, Lognay, Baudoin, Kouame, & Zoro Bi, 2012).Therefore, they require special conditions of production and storage.
Roasting is often practiced in small-scale processing of oilseeds.It is a very important operation.It changes the physicochemical compositions of the seeds (McDaniel, White, Dean, Sanders, & Davis, 2012;Agarwal, 2014) and those of their oils (Anjum, Anwar, Jamil, & Iqbal, 2006;Sultana, Saleem, & Ambrat, 2011).It develops the colour of the seeds (Moss & Otten, 1989) and their flavour (Shimoda, Nakada, Nakashima, & Osijima, 1997).It destroys undesirable microorganisms and inactivates enzymes that alter the product during storage (Torlak, Sert, & Serin, 2013).It has been shown that the roasting of oilseeds, before extraction, in general improves the oxidative stability of their oils (Harhar et al., 2011).units.In addition, the high temperature affects the oil quality (Liauw et al., 2008).Extraction by cold press is carried out at low temperature and without a solvent intake; that could contribute to the preservation of the quality of the oil and improvement of its stability.Faced with the challenge of food security, extraction by cold press is a promising alternative (Nitiè ma-Yefanova, Son, Yé , Né bié , & Bonzi-Coulibaly, 2012).
Roasting and cold pressing seem to be ways to overcome the rapid rancidity of cucurbit oil.Moreover, most biochemical data available on cucurbit oils concern those extracted from raw or dried kernels.However, in Sub-Saharan Africa, kernels of oleaginous cucurbits are usually roasted before being used in different ways (food, cosmetics, etc.).Thus, the lack of scientific data about roasted kernels properties does not allow to know the real potential of cucurbit seeds for the populations concerned.That is the reason why this study was carried out.Also, a study was conducted to evaluate the roasting effect on the nutritional and cosmetic potential of C. lanatus kernels oil, with a view to upgrading this oil in food and cosmetic.

Materials Studied
The biological material consisted of seeds of the C. lanatus variety named "bebu" (local name in Ivory Coast).It was identified on the basis of the seeds shape (flat and oval, thick and rough edge (Figure 1)).Sampling was produced in May 2015 by some farmers in the Dikodougou department (latitude 9°04'03.3"N,longitude 5°46'20.0"W)located in northern of Ivory Coast.

Preparation of Seeds
The C. lanatus seeds were sent to the genetics and plant breeding laboratory of the Natural Sciences Faculty (Nangui Abrogoua University, Ivory Coast).These seeds have been manually sorted and soaked in warm water for 15 min, and then shelled.The kernels were then washed with tap water and dried at 60 °C for 2 h in an oven (Model UFB 400, Memmert, Schwabach, Germany).Kernels were then divided into two batches.Batch n°1 consisted of dried kernels.Batch n°2 was composed of kernels roasted in a vessel, with continuous agitation, placed on a plate heated to 250 °C for 20 min.A quantity of each batch was ground using a micro-crusher (Laboratory crusher, Culatti AG, Zürich, Suisse) for further physicochemical analysis.

Oil Extraction
The oil was mainly extracted by cold pressing using a Komet screw press (Model CA 59 G, IBG Monforts Oekotec, Mönchengladbach, Germany) as described by Ferchau (2000).Crude oil was collected in a container and then centrifuged for 15 min using a centrifuge (Model Z 300 K, Hermle Labor-technik, Wehingen, Germany) set at 6000 rpm and 25 °C.To make a comparison of extraction methods, oil was also extracted according to AFNOR (Association Franç aise de Normalisation) protocol (AFNOR, 1986) by using n-hexane in a behrostest Soxhlet-Extractor (Model R104 T-SK, Behr Labor-Technik, Düsseldorf, Germany).All oils were stored at 4 °C, protected from light, for further analysis.

Biochemical Analysis of Kernels
The moisture content was determined gravimetrically by drying in an oven (Model UFB 400, Memmert, Schwabach, Germany) set at 105 °C to reach a constant weight.The ashes, fiber, lipids and proteins were determined on the basis of the dry matter according to standard protocols described by the Association of Official Analytical Chemists (AOAC, 1990).The protein content was calculated from the total nitrogen using a conversion factor of 6.25.The carbohydrate content was calculated by difference: Carbohydrates = 100 -(Proteins + Lipids + Fiber + Ashes) (1) The gross energy was calculated, according Atwater and Benedict (1902), by the following formula: where GE is the Gross Energy.

Physical Analysis of Oils
The specific gravity and the refractive index of oils were determined at 25 °C following protocols of International Union of Pure and Applied Chemistry (IUPAC, 1979) by using a pycnometer and a refractometer (Model AR200, Leica Microsystems, New York, USA), respectively.The viscosity of oils was determined at 25 °C by using a viscometer tube (AFNOR, 1986).The activation energy was determined according to method of Nzikou et al. (2009), based on the linearization of the Arrhenius equation.The UV-Visible spectra of the oil samples were determined by measuring the absorbance of a solution of oils in hexane (1 %: w/v) by using a UV-visible spectrophotometer (Model V-530, Jasco International, Tokyo, Japan) in the range of 200 to 600 nm (Besbes et al., 2004).

Chemical Analysis of Oils
The pH value of oil samples was determined at 25 °C following method described by Afane, Lando, Biyiti, Ossima, and Atchou (1997) by using a pH-meter (Model HI 8915, Hanna Instruments, Lingolsheim, France).Acid, peroxide, iodine and saponification values were determined according to AOAC protocols (AOAC, 1997).
The ester value was determined by difference between the saponification and acid values.Unsaponifiable matter content was determined according to IUPAC protocol (IUPAC, 1979).Carotenoid and total phenols contents were determined according to colorimetric method described by Zoué , Bé dikou, Gonnety, Faulet, and Niamké (2012) by using a UV-visible spectrophotometer (Model V-530, Jasco International, Tokyo, Japan).The oxalate and phytate contents were determined according to methods described by Inuwa, Aina, Gabi, Aimola, and Toyin (2011).The method used to determine the cyanogenic glycosides content was described by Onwuka (2005).

Statistical Analysis
All essays were performed in triplicate.The data were expressed as means ± standard deviation (SD).T test of Student was used to evaluate the roasting effect on the biochemical characteristic of kernels and the physicochemical properties of their oil.The analysis of variance (ANOVA) was used to determine the effect of the extraction method on the chemical indices of oil.When a significant difference was observed between the samples for a parameter, the ANOVA was supplemented by LSD (Least Significant Difference) test to identify the averages that are different.Statistical analysis was performed using Statistica 7.1 software (StatSoft, 2005) and statistical significance was measured at P < 0.05.
The Student t test shows that the roasting influences significantly (P < 0.05) all the biochemical composition of kernels.ANOVA shows that the extraction method influences significantly (P < 0.001) all chemical indices; while roasting influences significantly (P < 0.001) the iodine value.
The Student t test shows that the physicochemical properties of both oils were significantly different (P < 0.001), with the exception of their specific gravity and their refraction index which are respectively approximately 0.9 and 1.47 (Table 3).The UV-visible spectrum consists of two superposed curves having each maximum absorbance at 220, 280 and 440 nm.The absorbance decreases rapidly between 280 and 400 nm, from 1.01 to 0.18 for dried kernels oil and from 1.06 to 0.21 for roasted kernels oil; but it varies slightly between 440 and 600 nm with a value close to 0.3 for the two oils (Figure 2).Note.UV-visible spectra were obtained by measuring absorbance, between 200 and 600 nm, of C. lanatus dried kernels and roasted kernels oils diluted to 1 % in hexane (Besbes et al., 2004).DKO, dried kernels oil; RKO, roasted kernels oil.

Roasting Effect on Antinutrients of C. Lanatus Kernels Oil
Oxalates, phytates and cyanogenic glycosides contents of two oils are shown in Table 5.The oxalates are represented by 53.57± 0.51 mg/100g in dried kernels oil and 55.74 ± 0.05 mg/100g in roasted kernels oil (about 0.05 % in the two oils).The two oils do not contain phytates and neither cyanogenic glycosides.

Discussion
The biochemical composition analysis showed a significant difference between dried kernels and roasted kernels of C. lanatus.This significant difference is due to the heat treatment (250 °C for 20 min) to which the kernels were subjected during roasting.On this point, Agarwal (2014) showed that the heat treatment of soybeans causes changes in their biochemical composition.Similar results were obtained by Jimoh, Fagbenro, and Adeparusi (2011) who studied the changes in the chemical composition during processing (raw, cooked and grilled) of sesame (Sesamum indicum) seeds meal.As for Yaacoub (2009), he showed that among the steps of the oilseeds and nuts processing method, the step of roasting is particularly critical in the formation of newly formed compounds.Given these results, it appears necessary to control the couple temperature/time during roasting to limit these biochemical changes and preserve the nutritional and cosmetic values of kernels.
Furthermore, we observed that both kernels (dried and roasted) are rich in lipid and protein.The abundance of lipids and proteins of dried kernels has already been demonstrated by Loukou et al. (2007) and Gbogouri et al. (2011) who also worked on the seeds of C. lanatus cultivated in Ivory Coast.Regarding the roasted kernels, these results could confirm that the roasting parameters (temperature: 250 °C; time: 20 min) used in this study are appropriate to preserve the wealth of C. lanatus kernels in these two compounds.The protein content of the roasted kernels is higher than that of dried kernels.Similar results were obtained by Mariod et al. (2012) that determined the effects of roasting and boiling on the chemical composition of safflower seeds.This indicates that the roasted kernels are considerable sources of protein.The lipid content of the roasted kernels is lower than that of dried kernels obtained by Taiwo et al. (2008) and by Olaofe et al. (2012).However, the lipid content is higher than that of conventional oilseeds such as cotton (15.0 to 24.0 %), soy (17.0 to 21.0 %) and olive (20.0 -25.0 %) (Pritchard, 1991).This means that the C. lanatus roasted kernels are also significant sources of lipids.
Proteins and lipids play many roles in the human and animal organism, and are important in human nutrition.Therefore, their presence in large quantities in the C. lanatus roasted kernels mean that these kernels are a good nutritional potential for food and feed.
The acid value is a chemical indicator that allows both the classification of the oils, and obtains information on their state of alteration by hydrolysis.As for the peroxide value, it allows to evaluate the early stages of oxidation of the oils.These two parameters are therefore important to assess the quality of oil.
From the results obtained, C. lanatus kernels oils extracted by press have low acid and peroxide values relative to those extracted by solvent.These results agree with those obtained by Haloui, Zekhnini, and Hatimi (2015) for argan oils.Oils extracted by press have thus better chemical quality compared with those extracted by solvent.Oils extracted by press are to be classified in the category "virgin oils and cold pressed oils" as their acid and peroxide values are respectively below 4.0 mgKOH/g and 15 meq.O 2 /kg (Codex Alimentarius, 1999).The oils extracted by solvent have acceptable acid and peroxide values; however, after extraction, it should be refined to improve their quality.The high acid and peroxide values of oils extracted by solvent are probably due on the one hand, to the heating of the oil during the extraction (60 to 80 °C for 4 -6 h) and the evaporation of the solvent (100 °C for 24 h), and on the other hand, in that the cucurbits oils are rich in polyunsaturated fatty acids which hydrolyze and oxidize rapidly under the effect of heat (Loukou et al., 2012).
According to the results, roasting and solvent extraction have decreased iodine values of oils.This can be explained by the fact that heat treatments, employees at these two methods, have led to changes in the biochemical composition (Agarwal, 2014).However, all studied oils are classified in the category "di-unsaturated oils" as their iodine values are between 100 and 150 gI 2 /100g.Previous work by Olaofe et al. (2012) and Gbogouri et al. (2013) revealed that C. lanatus kernels oil contains linoleic acid over 60 % (di-unsaturated fatty acid).That would justify the results obtained in this study.Thus, despite the variation of the observed iodine values, the structure of the oil seems not to have changed significantly.
The specific gravities of C. lanatus kernels oils are similar to that reported for most conventional oilseeds (Codex Alimentarius, 1999) which are 0.9.Additionally, their viscosities are in the range (50 to 100 mPas) of most vegetable oils (Besbes et al., 2004).These results confirm their liquid state at room temperature and this physical characteristic is suitable for the preparation of skin care products (Dhellot et al., 2006).Low peroxide values obtained in this study indicate that C. lanatus kernels oils are less susceptible to oxidative rancidity at room temperature (DeMan, 1992).Therefore, these oils are suitable, in combination with antioxidants, for cosmetic formulations (Judde, 2004).Their high saponification values make it recommendable for manufacturing soap, creams and shaving foam (Wolf, 1968).Furthermore, their unsaponifiable contents are higher than those reported for other cosmetic oils such as cottonseed (0. 52%), peanut (0.33 %) and palm kernels (0.22 %) oils (Kapseu & Parmentier, 1997).This lipid fraction is a good source of stabilizers and provides essential moisture to the skin (Helme, 1990).The decrease in their absorbance, in the range of 290 to 400 nm, would be advantageous for use in the formulation of cosmetic products that offer protection against UV rays (Besbes et al., 2004).
The refractive indices of the C. lanatus kernels oils are in the range of those reported for edible oils (Rossell, 1991).These oils have low free fatty acids contents; then they would be advisable for seasoning salads (Matos et al., 2009) and could be kept for a longer period (Anwar, Chata, & Hussain, 2007).Their iodine values are higher than oils rich in saturated fatty acids such as coconut (6.3 to 10.6 gI 2 /100g), palm (50 to 55 gI 2 /100g), palm kernels (14.1 to 21 gI 2 /100g) oils; but they are similar to those oils rich in polyunsaturated fatty acids such as cottonseed (100 to 123 gI 2 /100g), sesame (104 to 120 gI 2 /100g) and sunflower (118 to 141 gI 2 /100g) oils (Codex Alimentarius, 1999).Given their iodine values, the C. lanatus kernels oils are semi-drying and rich in di-unsaturated fatty acids (linoleic acid).Therefore, they would be nutritionally beneficial for patients with lipid disorders (Njoku, Muma, Ononogbu, & Eleanya, 2001).
The oxalates contents of C. lanatus kernels oils are significantly lower than those of groundnut (0.42 %) and palm (0.49 %) oils (Inuwa et al., 2011).In addition, these oils do not contain phytates and neither cyanogenic glycoside.These results confer on them better suitability for food use.

Conclusion
This study showed that roasting influences the physicochemical characteristics of C. lanatus kernels and their oil, and oil extracted by cold pressing is better chemical quality.It found that C. lanatus roasted kernels are also sources of lipid and protein for human being and animal food, and roasted kernels oil are rich in di-unsaturated fatty acids; which would give him nutritional and cosmetic properties.Moreover, the saponification value and the physical properties of this oil make it suitable for cosmetic industry of skin care products.Its low acid and peroxide values, the virtual absence of anti-nutrients make it safe for human use.Given all these potentialities, C. lanatus roasted kernels oil could be used in food and cosmetic industries.This study could be improved by optimization of the roasting process of C. lanatus kernels, and the study of the effects of roasting on the minor compounds and oxidative stability of oils.

Figure 1 .
Figure 1.Seeds and kernels of C. lanatus grown in Ivory Coast

Figure 2 .
Figure 2. UV-visible spectra of C. lanatus dried kernels and roasted kernels oils

Table 1 .
Biochemical composition of C. lanatus dried kernels and roasted kernelsNote.All determinations were carried out in triplicate and mean value ± standard deviation (SD) is reported.For each component, values with different superscript letters are significantly different (P < 0.05).KD, Kernels dried; KR, Kernels roasted.4.2Effect of Extraction Method on Chemical Indicators of C. Lanatus Kernels OilThis part of the work concernes oils extracted by press and those extracted by solvent.The results showed that the acid values are 1.50 ± 0.39 and 2.22 ± 0.19 mgKOH/g in oils extracted by press against 4.06 ± 0.53 and 4.18 ± 0.25 mgKOH/g in oils extracted by solvent; and the peroxide values were 0.76 ± 0.01 and 1.99 ± 0.01 meq.O 2 /kg in oils extracted by press against 6.70 ± 0.99 and 5.06 ± 0.66 meq.O 2 /kg in oils extracted by solvent.Iodine values are 125.25 ± 3.31 and 116.75 ± 1.77 gI 2 /100g in dried kernels oils against 114.88 ± 2.49 and 103.23 ± 1.32 gI 2 /100g in roasted kernels oils (Table2).

Table 2 .
Chemical indices of C. lanatus dried kernels and roasted kernels oils extracted by mechanical and chemical methods Note.All determinations were carried out in triplicate and mean value ± standard deviation (SD) is reported.For each chemical index, values followed with same superscript letters do not differ significantly (P < 0.05).DKOP, dried kernels oil extracted by press; DKOS, dried kernels oil extracted by solvent; RKOP, roasted kernels oil extracted by press; RKOS roasted kernels oil extracted by solvent.

Table 3 .
Physical properties of C. lanatus dried kernels and roasted kernels oils

Table 4 .
Chemical properties of C. lanatus dried kernels and roasted kernels oils Note.All determinations were carried out in triplicate and mean value ± standard deviation (SD) is reported.For each property, values with different superscript letters differ significantly (P < 0.05).DKO, dried kernels oil; RKO, roasted kernels oil.

Table 5 .
Antinutritional factors of C. lanatus dried kernels and roasted kernels oils Note.Values are means ± standard deviation (SD) of triplicate determinations.For each antinutrient, values with different superscript letters are significantly different (P < 0.05).DKO, dried kernels oil; RKO, roasted kernels oil.