Quality Evaluation of Oil from Seeds of Wild Plant Tylosema fassoglensis in Kenya

Tylosemafassoglensis isaplantspeciesthatisnativetoSub-SaharanAfrica.Theaimofthisstudywastoevaluatethephysicochemical properties of oil from T. fassoglensis in Kenya. Seeds of T. fassoglensis were collected from Mombasa, Taita Taveta, Homa Bay, and Siaya regions. Counts of T. fassoglensis in each region were recorded during the entire survey period. The highest distribution was recorded in Homa Bay followed by Siaya region. Distribution was the least in Taita Taveta and Mombasa regions. The analysis of the physicochemical characteristics of the oil was performed according to the official methods of analysis and the recommended practices of the American Oil Chemists Society. Oil content of 36.4% was obtained. The oil had refractive index 1.47 at 40 ∘ C, peroxide value 6.34 meq O 2 /kg, iodine value 94.06 g of I 2 /100g, saponification value 145.93 mg KOH/g of oil, acid value 2.49 ± 0.56 mgKOH/g of oil, and unsaponifiable matter 5.87 g/kg. The oil had Lovibond color index of 2.0Y+28.0R. Oil content of T. fassoglensis is comparable with those of most oil crop under commercial production. The physicochemical properties of oil from T. fassoglensis are within the range recommended by FAO/WHO and hence suitable for human consumption.


Introduction
Oils from plant sources are widely used for food and industrial applications. The predominant world sources of edible oil are palm, rapeseed, soy bean, and sunflower [1,2]. With new applications of edible oils such as in the production of biodiesel, demand for edible oils in the international market has significantly increased.
Production of oil crops is a major economic activity in Kenya. Currently, Kenya produces approximately 380,000 tons of edible oils. This figure accounts for just about onethird of its annual demand [3]. The deficit is imported at a cost of $140 million. The country is currently exploring various alternatives to help bridge the deficit in vegetable oil sector with local manufacturers engaging in the production of selected oil crops. Much effort has been directed to growing oil crops with emphasis on palm oil [3].
Several species of edible wild plants in Kenya have not been exploited despite their potential as new sources of edible oils. Members of the genus Tylosema are herbaceous plants that have numerous traditional uses. The plant is reported to be native to Africa and has been traditionally used in ethnomedicine and as source of food in South Africa, Zambia, Zaire, and Congo [4]. In Kenya, many traditional rural communities use its seeds as food [5]. Recent studies have confirmed antimicrobial properties of extract from this plant species [6]. The species has also been used in the formulations of herbal remedy with the ability to halt the replication of HIV virus in human blood [7,8]. Previous study reported oil content of 24-35% on a dry weight basis [4]. Climatic conditions, among other factors, have been reported to influence the amount and properties of oil in plant seeds. This study was therefore undertaken to evaluate the physicochemical properties of oil from seeds of T. fassoglensis that are native to Kenya.

Seed Collection and Preparation.
Mature seeds were collected and cleaned to remove stones, dirt, and any other foreign materials. Deformed seeds were also sorted out. The cleaned seeds were decoated and dried in an electric oven to a moisture content of 8.3%. Single dried seeds were then weighed and then milled into fine powder using laboratory blender (Dynamic Corporation, USA). The fine powder was passed through 80-mesh sieve.

Solvent Extraction.
The ground seed material was fed into a Soxhlet extractor fitted with a 0.5 L round-bottom flask and a condenser. The extraction was carried out for 6 h with 0.3 L n-hexane on a water bath. After extraction, hexane was distilled off under vacuum using a rotary evaporator (Eyela, N-N Series, Rikakikai Co. Ltd., Tokyo, Japan) at 45 ∘ C.

Refining of Oil.
Aliquots of the crude oil (25 mL) were degummed at 65 ∘ C with 0.1 NaOH. Then, 12.5 mL portions of degummed oil were bleached using 0.7 g of fuller's earth at 105 ∘ C for 1 h. The refined oil was then stored at 4 ∘ C for further analysis.  Figure 1 illustrates

Oil Content.
Seeds of T. fassoglensis exhibited oil content of 36.4% (w/w) on dry weight basis. This is slightly more than the 24-35% oil content reported by Dubois et al. (1995). The variation could be due to various factors including differences in plant varieties, climatic conditions, season and time of harvest, type of pretreatment of the seed prior to oil extraction, and the type of solvent used for the extraction [12]. The recovered amount of oil is comparable to oil content of many conventional oil-bearing seeds which already have commercial value [13,14] as illustrated in Figure 2. Table 1 illustrates properties of oil from T. fassoglensis seeds compared with selected crop oils under commercial production.

Acid Value.
Acid value (AV) indicates the level of oxidative deterioration in oils by enzymatic and/or chemical oxidation. The acceptable limit for edible oils is ≤10 mg KOH/g [15]. The extracted oil had AV of 2.49 ± 0.56 mg KOH/g. This is lower than AV of cottonseed oil (11.50 ± 0.33 mg KOH/g) and groundnut oil (4.40 ± 0.10 mg KOH/g) but higher than soy bean oil (2.72 ± 0.17 mg KOH/g), sunflower oil (1.02 ± 76 mg KOH/g), and canola oil (0.071 ± 0.49 mg KOH/g) as shown in Table 1. This implies that Tylosema seed oil is likely to stay longer without forming offflavors.  [9].

Iodine Value.
Iodine value (IV) is the degree of unsaturation in oil. The extracted oil had IV of 94.06 ± 0.14 gm I/100 gm. This value is comparable to the IV of cottonseed oil (94.7 ± 0.12 gm I/100 gm) and groundnut oil (95.30±0.43 gm I/100 gm). However, it is lower than IV of soy bean oil (119.21 ± 0.40 gm I/100 gm), sunflower oil (119.92 ± 0.00 gm I/100 gm), and canola oil (116.10 ± 0.50 gm I/100 gm) ( Table 1). The indicated IV implies that oil from the seeds of T. fassoglensis has longer shelf-life and storability [16,17]. It also indicates that Tylosema seed oil is nondrying oil [18].

Peroxide Value.
The extent to which the oil has undergone rancidity can be determined by the peroxide value (PV). The PV of Tylosema seed oil was 6.34 ± 0.58 meq/kg. This is comparable with PV of sunflower oil (6.32 ± 12 meq/kg) and canola oil (7.36 ± 0.140 meq/kg) as indicated in Table 1. However, it is lower than those of cotton oil (9.25 ± 0.47 meq/kg) and soy bean oil (21.38 ± 1.61 meq/kg) but higher than groundnut oil (1.97±0.10 meq/kg). The reported PV is within the permitted peroxide level of not more than 10 meq/kg of oil [9]. Oils having high percentages of peroxide are unstable and grow rancid easily [19]. Tylosema seed oil therefore has a lower degree of rancidity.

Refractive Index.
Refractive index (RI) is a good measure of oil purity following refining. Values of RI for different oils generally vary between 1.447 and 1.482 [20]. The RI of extracted oil was 1.47 ± 0.85 which is close to the values reported for other seed oils like groundnut, soy bean, and sunflower (Table 1). Oils with RI between 1.48 and 1.49 are more viscous [21]. This implies that the Tylosema seed oil is less viscous.

Saponification Value. Saponification value (SV) was
145.93 ± 0.69 mg KOH/g of oil. This is lower than SV reported for some common oils such as palm oil (196-205 mg KOH/g), corn oil (187-196 mg KOH/g), groundnut oil (188-96 mg KOH/g) [16], coconut oil (253 mg KOH/g), and palm kernel oil (247 mg KOH/g) ( Table 1). However this value is within the SV range reported for many edible oils [22,23]. The reported SV indicates high percentage of fatty acids in Tylosema seed oil, hence potential for application in soap industry.
3.3.6. Unsaponifiable Matter. Unsaponifiable matter (UM) in oils is important raw materials in cosmetic and soap industries [24,25]. The content of UM in Tylosema seed oil was 5.87 g/kg. This is higher than those of most plant oils (Table 1). It means, therefore, that Tylosema seed oil is good in cosmetic and soap production.

Oil Colour.
The oil had a Lovibond color index of 2.0Y+28.0R. The red and yellow indices are comparable with those of most commercial edible oils [26]. The low oil color intensity indicates that the oil is well refined [27]. This implies, therefore, that bleaching during refining of Tylosema seed oil may not be necessary thereby lowering the overall processing costs.

Conclusion
Tylosema fassoglensis is not widely distributed across Kenya. The highest distribution is on the western part of the country. Seeds of T. fassoglensis are rich in oil. The oil content is comparable with most oil crops currently under commercial production. Similarly, quality attributes of oil from seeds of T. fassoglensis are identical to those of most commercial edible oils. The T. fassoglensis therefore has prospects as a good source of edible oil with commercial potential in Kenya.