Dried B. elegana Choisy (alhydwan) seeds were supplied by a single farm in Wad Hadramout, South Yemen. The seeds were transported by air, in sealed polyethylene bags, to Jiangnan University’s Food Processing and Ingredients Laboratory (Wuxi, China). Arachis hypogaea L. (peanut) seeds, in dry form, were purchased from a local supermarket in the same city in China. All chemicals were of analytical grade and were obtained from trusted suppliers.

Seeds (200 g) of B. elegana Choisy or A. hypogaea L. were milled, mixed with 1 L of n-hexane, and shaken for 4 h at 440 rpm using a shaker (IKA^® RW 20 digital overhead stirrer, UK-plug; Staufen, Germany). The suspension was then centrifuged at 10,000 ×g at 4 °C for 20 min. The supernatant was then filtered. The extraction process was repeated once with the same debris to ensure that all of the oil was completely extracted. Recovery of the oil from the n-hexane was done by evaporating the solvent using a rotary evaporator (Model N-1; Eyela, Tokyo Rikakikal, Japan). The solvent remaining in the oil was evaporated at 37 °C for 30 min using a laboratory fume hood. The extracted oil was drained under a stream of nitrogen. The oils of B. elegana Choisy and A. hypogaea L. were then blended in proportions of 10:90, 20:80, 30:70, 40:60 and 50:50 (v/v). The blended oils were then sealed in glass tubes and stored at 4 °C in a refrigerator until analysis.

A Hunter Lab digital colorimeter (TC-PIIG system, Beijing Optical Instrument Co. Ltd., Beijing, China) was used to measure the oil blends’ color and color scales such as L* a* b* values were recorded. A cylindrical plastic dish (58 mm in diameter and 15 mm in depth) containing the same amount of sample was placed at the light port (50 mm in diameter).

Various methods stipulated by the American Oil Chemist’s Society AOCS (1997) for various chemical parameters of oils were used. These included methods Ca 5a-4, Cd 8-53, Cd 3-25, and Ca 6a-40 for the determination of free fatty acids, peroxide value, saponification value, and unsaponifiable matter, respectively. Specific gravity was determined using a 10-mL pycnometer at 25 °C. An Abbe refractometer was used at 25 °C to determine the refractive index of the oil blends. The iodine value was calculated according to the method of (Kyriakidis and Katsiloulis, 2000).

The composition of fatty acids was determined following the method of (He and Xia, 2007) with some modifications. First, the methylation of the crude oils was conducted to prepare fatty acid methyl esters (FAME). Then, 1 μL of the FAME sample was analyzed in a gas chromatograph (Series PEG30 M) connected to a flame ionization detector. The column used was a model PEG30M column with dimensions of 30 m × 0.32 mm × 0.50 μm. Nitrogen was used as the carrier gas at a flow rate of 0.8 mL/min. The oven temperature was held at 190 °C for 1 min, then increased at a rate of 3 °C/min to 230 °C, and held for 10 min. The injection port and detector were set at 240 and 250 °C, respectively. Standards were run to facilitate the identification of the peaks generated from the samples. Percentage (%) values were used to express fatty acid contents.

The oxidative stability of the oil blends was determined with a 743 Rancimat apparatus (Metrohm Co., Basel, Switzerland). An oil blend sample of 3.6 g was weighed, placed in the reaction vessel, and heated at 120 °C with an air flow of 20 L/h. As degradation of the oil progressed, volatile compounds were collected in a receiving flask containing 60 mL of distilled water. The conductivity of the resultant product was then measured.

The tocol composition was determined according to the NY/T 1598-2008 method. First, a solution containing the blended oil sample (250 mg), ethanol (25 mL), 10% ascorbic acid (5 mL), and 50% KOH (10 mL) was prepared. This solution was subjected to saponification in a capped flask heated at 90 °C for 1 h in a water bath. Then, the solution was cooled and 100 mL of distilled water were added. After mixing thoroughly, 50 mL of diethyl ether were added to extract the solution. The upper layer was scooped off and washed to a neutral pH with distilled water. After separation, the organic layer was dried over Na₂SO₄. The dry matter was then dissolved in 2 mL of ethanol and centrifuged at 5000 rpm for 5 min. The upper layer of the supernatant (10 μL) was analyzed with a high performance liquid chromatography (HPLC) system (Waters Corp., Milford, MA, USA) with a Spherisorb silica column (250 mm×4.6 mm, 5 μm) operating at 30 °C with methanol/water (98:2, v/v) as the mobile phase flowing at a rate of 1.0 mL/min. The detector used was a model 2996 PAD (Waters Corp.) with the wavelength set at 290 nm. Tocol was calculated as mg/kg oil.

The acceptability of the B. elegana Choisy and A. hypogaea L. oil blends was assessed by a trained panel of 10 members, using the conventional 9-point hedonic scale (ranging from 1 [extremely bad] to 9 [excellent]). The measurement attributes included crust color, crumb color, crumb texture, flavor, taste, and overall acceptability.

All the data were expressed as the mean ± standard deviation. A statistical analysis was performed using one-way analysis of variance. Comparisons between pairs of means were made using Duncan’s multiple range test, with statistical significance at p ≤ 0.05 (Snedecor and Cochran, 1980). The statistical analysis was conducted with the SAS program (SAS,2002).

The physiochemical profiles of the oil blends are presented in Table 1. The results show that all of the blended samples were in the liquid state at room temperature and that no differences in appearance could be observed among them. However, significant differences (p < 0.05) were observed across all blend ratios in all of the remaining physicochemical parameters. The addition of alhydwan seed oil to peanut oil decreased the peroxide value (meq O₂ /kg oil) of the blended oil significantly from 6.97 at a blend ratio of 10:90 to 6.02 at a blend ratio of 50:50. Similar trends between the same two blend proportions were observed for the refractive index at 25 °C (1.462 to 1.446), free fatty acids (2.29 to 1.71%), and saponification value (186.44 to 183.77 mg KOH/g). Nevertheless, the addition of alhydwan seed oil to peanut oil increased the iodine value and relative density at 25 °C from 98.10 to 102.89 and from 0.89 to 0.91 for the same two blend proportions, respectively.

There is a positive relationship between the saponification value of oil and the solubility of a soap product made from that oil (Alyas et al., 2006). The reduction in saponification value with increases in the proportion of alhydwan oil in the blends may indicate that the resultant soap would have lower solubility. That is, these oils would be better used for products other than soap. The peroxide value is defined as the weight of active oxygen in 1 g of oil (Pandurangan et al., 2014). It indicates that the oil has started to degrade, a situation that is common in unsaturated oils (Al-Farga et al., 2015). The reduction in peroxide value observed for the oil blends signifies that the addition of alhydwan oil to peanut oil makes the latter slightly more resistant to degradation. According to the method developed by (Kyriakidis and Katsiloulis, 2000) the iodine values of the blended oils ranged from 98.10 to 102.89. These high values may be attributed to the observed high unsaturated fatty acid contents. This result indicates that the seed oil has good edibility and drying qualities (Eromosele et al., 1997). Based on the chemical compositions of the blended oils, there were no negative effects caused by the addition of alhydwan seed oil.

The fatty acid compositions of the alhydwan seed, peanut, and blended oils are recorded in Table 2. In total, 10 fatty acids were identified, of which 5 were unsaturated. Oleic acid and linoleic acid were more abundant in all the blended oil samples. The 50:50 and 10:90 (alhydwan–peanut) oil blends had the highest oleic acid and linoleic acid contents, respectively. Table 2 also shows that the blended oils were significantly enriched with unsaturated fatty acids.

The results of the fatty acid determination showed high contents of oleic acid in the pure alhydwan seed oil. This indicates that alhydwan seed oil has potential health benefits for patients with arteriosclerosis and hypertension (Oomah et al., 2000). The results further demonstrate that incorporating alhydwan oil into peanut oil may increase the monounsaturated fatty acid (MUFA) content of the latter, which would contribute to reductions in low-density lipoprotein cholesterol in the human body (Wahida, 2005). The addition of alhydwan seed oil to peanut oil has positive effects on the content of fatty acids and potential health benefits.

The results from the Rancimat test are presented in Table 3. Stability is expressed as the oxidation induction time (h). The oxidative stability index values for pure alhydwan seed oil and pure peanut oil were 16.82 and 2.78 h, respectively. Compared to the value for pure peanut oil, the blending of the two oils increased the oxidative stability as the proportion of alhydwan oil was increased.

The oxidative stability of alhydwan seed oil was found to be similar to the stability obtained by (Mariod and Matthäus, 2007) in Cucumis melo var. agrestis oil. The higher stability values shown by the blended samples in this study may be attributable to the high content of MUFAs which contain single double bonds in their chain and have a slower rate of oxidation associated with their corresponding esters than polyunsaturated esters (da Silva Araujo et al.,2014). On the other hand, this value may be justified by the fact that the oil was crude. A linear regression based on the ratio of linoleic acid and the contents of tocopherols and phenols in virgin olive oil and a good correlation with oxidative stability measured by the Rancimat test have been reported (Aparicio et al.,1999).

Table 4 presents the tocopherol contents (γ, δ, and α) of the oil samples. β-Tocopherol was not detected. γ-Tocopherol had the highest proportions in all of the blends (54.25, 64.64, 66.59, 67.07, and 66.59% in the 10:90, 20:80, 30:70, 40:60, and 50:50 alhydwan–peanut blends, respectively) followed by δ-tocopherol (29.10, 32.85, 31.22, 30.87, and 31.43%, respectively), the incorporation of alhydwan seed oil into peanut oil improved the quality characteristics of the high-quality blended oils, because alhydwan oil is a rich source of tocopherols (AL-Farga et al.,2015). The total tocopherol content in all of the blended oils (580–719 mg/kg) was close to the content obtained by (Azhari and Wenshui, 2015) in a blend of 5% Cucumis melo var. tibish oil and 95% peanut oil, but lower than those of 50:50 coconut oil–rice bran oil, 50:50 coconut oil–palm oil, and 20:80 coconut oil–sunflower oil blends (Bhatnagar et al., 2009). It has been reported that α-tocopherol is good for human nutrition due to its higher biological activity than other tocopherols (Fatnassi et al., 2009). Thus, the addition of alhydwan seed oil to peanut oil can be considered a good method to improve the quality characteristics and oxidative stability of the oils.

The sensory characteristics (color, flavor, turbidity, taste, and overall acceptability) of the oil blends were recorded and are shown in Table 5. The results in Table 6 show that all of the blended oils are generally acceptable for consumption, with no significant differences among them. Thus, additional studies pertaining to the utilization of alhydwan seed oil and peanut oil blends in other food products should be carried out.