Characteristics of Sesame (Sesamum Indicum l.) Seed Meal Grown in the Northern Region of Bangladesh

 

Introduction

Sesame (Sesamum indicum L.) is an economically and nutritionally important crop and it is prized for oil. The global sesame market demand is rising with increasing health awareness. Sesame is one of the oldest oilseeds and is widely cultivated in both tropical and subtropical areas. Worldwide sesame seed consumption was USD 6559.0 million in 2018 and it will reach USD 7244.9 million by 2024, with a CAGR (compound annual growth rate) of 1.7% [1] In Bangladesh, sesame is an important summer oilseed crop occupying 9.4% of the total oilseed area [2]. Sesame is labeled as the queen of oilseeds because of its high oil content (35-45%), delicious nutty aroma, and flavor [3] and a considerable amount of proteins, carbohydrates, essential minerals. Seeds contain high amount of methionine and tryptophan, fibers as well as secondary metabolites such as lignans, saponins, flavonoids, and phenolic compounds. Moreover, the seeds are a good source of calcium, phosphorus, iron, small amount of trace elements and are rich in vitamin B, E. Sesame oil has a pleasant, mild taste and is remarkably stable.
It has a high content of polyunsaturated fatty acids as oleic and linoleic acid. Sesame oil cake is good feed for poultry, fish, cattle, goat and sheep [4]. Oil cakes, the coarse residues after the removal of oil from various oilseeds is usually treated as waste products in Bangladesh. The average total production of oil cakes in Bangladesh is about 1,70,000 tons per annum [5]. Oil cakes are rich in protein and minerals, but their inherent values have never been considered actively. They are generally used as poultry and other animal feed or as fertilizer. Among the total production of oil cakes in Bangladesh, 70% of which are used as fertilizer, 10% is being exported and the remaining 15% is available for animal feeding [6].
Sesame Oil cakes or defatted sesame meal can be an ideal source as a support matrix for various biotechnological processes for the production of enzymes, antibiotics, vitamins, antioxidants [7] and various food products. So, the sustainable utilization of this seed meal is necessary for preparing cattle, poultry and fish feed and also for the preparation of protein and vitamin enriched food stuff for men and poultry, fish farming.
The present work had therefore, been undertaken with a view to finding out the major constituents of the sesame seed oil and defatted seed meal so that the proper and effective utilization of these seed meal may be ensured.

Materials and Methods

Sesame seeds were purchased from katakhali bazar, Rajshahi, Bangladesh. Then the seeds were cleaned, dried and the oil was pressed out by hydraulic press. The meal thus obtained were freed from residual oil by solvent extraction. The residual oil was extracted in a Soxhlet apparatus with n-hexane. This solvent was selected as extraction solvent because it has better effect over other polar solvents like alcohol, ketone, aldehyde etc. [8]. Physical properties such as moisture content, refractive index, density, specific gravity and viscosity of the oil were determined by the method described by Garba, et al. [9] and AOAC [10]. Acid value, saponification value, iodine value, peroxide value, unsaponifiable matter and free fatty acid were estimated according to the AOAC [11].
The defatted seed meal were air dried, and analysis of nitrogen was carried out by Micro-Kjeldhal method, and the percentage of protein was calculated [12]. The defatted meal was also used for different analysis like ash [13], fiber [14], carbohydrate [15], residual fat [16] and moisture content [17]. The minerals such as calcium, potassium, phosphorous, magnesium, sodium and iron were determined by atomic absorption spectroscopy (Model: AA-68000, Shimadzu, Japan) coupled with an auto-sampler (ASC- 6100). The fatty acid composition of the sesame oil and the chemical compound of seed meal were analyzed by SHIMADZU GC-2010 was equipped with auto-sampler (AOC- 20s), auto-injector (AOC-20i) and SH Rxi 5MS Sill capillary column with 30m×0.25mm×0.25 μm film. Detection of aflatoxin in seed meal is done following by the method Lee & Rachmawati [18] (Figure 1).

Figure 1: GCMS chromatogram of sesame oil.

Results and Discussion

Moisture, Density, specific gravity and refractive index of sesame oil were determined and depicted in Table 1. All values were within the WHO/FAO permissible limits. The results showed in Table 1 that the free fatty acid, acid value, peroxide value, iodine value and unsaponifiable matters of oil were 0.40%, 0.81%, 3.96 meq O2/kg, 118g I2/100g and 2.1 respectively. These results were similar to those reported in other studies [19-21]. The proximate analysis of defatted sesame seed meal were determined, and the results were given in Table 2. It was found that the protein content of meal was 22.5% and the carbohydrate content was the highest, 56.7%. The content of crude fiber was 4.6% whereas moisture, ash and residual fat content were 5.5%, 6.8% and 3.9% respectively. All values were in an appreciable level. Table 3 showed the mineral contents of defatted sesame meal. Sesame meals contain good percentages of minerals which may added better nutritive value for foods or in pharmacological preparations.

Table 1: Physicochemical characteristics of sesame oil.

Table 2: Proximate composition of defatted sesame meal flour.

Table 3: Aflatoxin and some mineral contents in defatted sesame seed meal.

Scientists are looking for an alternate source of cheaper oil cake with low level of aflatoxin. The literature on the incidence of aflatoxin in sesame oil cake is scanty. Mirocha, et al. [22] reported the presence of Fusarium toxins in sesame seeds. While Laxma Reddy and Reddy [23] observed the incidence of trichothecene producing fungi was low as compared with that of Aspergillus and Penicillium species in sesame oil cake. The allowable limit of aflatoxin for human consumption is 4 ppb [24]. Aflatoxin of seed meal was determined shown in Table 3 is 0.113 ppb that is much lower than allowable limit for human consumption. The fatty acid composition is an essential indicator of the nutritional value of the oil. Sesame seed oil belongs to the oleic–linoleic (mono unsaturation-poly unsaturation) acid group. It has 25% poly unsaturated fatty acid, 9,12-Octadecadienoic acid methyl ester and 31% mono unsaturated fatty acid, 9-Octadecenoic acid methyl ester. Oil also consists of palmitic acid 22%, stearic acids 19% and Heneicosanoic acid, methyl ester 2.4% (Table 4).The chemical compounds of sesame seeds were analyzed by GC-MS and summarized in Table 5 and their GC-MS chromatograph in Figure 2.

Table 4: Fatty acid composition of sesame oil.

Table 5: Identification of the chemical compounds present in sesame seed meal.

Figure 2: GCMS chromatogram of sesame seed meal.

GC-MS analysis of sesame seed meal identified 30 chemical compounds representing the highest yield, 32.77% of glycerin and 11.4% gamma-tocopherol (vitamin E), 10.85% hexadecanoic acid methyl ester and 8.19% 13- docosenamide depending on relative area. Glycerin has antimicrobial and antiviral properties. Gammatocopherol is the main component and represented about 90.5% of total tocopherols, shows a higher antioxidant capacity as compared to alpha-tocopherol. Sesame oil rich in tocopherols and in lignans (notably sesamin and sesamolin) provide exceptional oxidative stability compared with other edible oils [25]. Hexadecenoic acid, methyl ester possesses antioxidant and anti-fungal property [26] and the presence of 13-Docosonamide impart antioxidant activity [27]. It was also found that there were some compounds in lower concentration including Phenol, 2-methoxy-3-(2-propenyl)-, 3-Allyl- 6-methoxyphenol, 2-Propyl-1-pentanol, pentafluoropropionate that have antimicrobial activity [28].
Compound found in meal Phenol, 3,5-bis(1,1-dimethylethyl)- is a naturally synthesized compound within both plant and bacterial cell that impart antioxidant [29], antibacterial [30] and antifungal activity [31]. Seed meal also contain 11-Octadecanoic acid methyl ester, Fumaric acid, 2-dimethylaminoethyl nonyl ester, Octadecanoic acid, methyl ester, Sesamin as well as many other bioactive compounds with relatively low concentration presented in Table 5. Rahman, et al. [32] reported that 11-octadecenoic acid methyl ester is responsible for antioxidant and antimicrobial activity. Fumaric acid, 2-dimethylaminoethyl nonyl ester has antimicrobial properties and Octadecanoic acid, methyl ester has anti-inflammatory properties. Sesamin, a major lignin isolated from sesame seeds and sesame oil, is known to possess antioxidant and anti-inflammatory properties, play a major role in a variety of cardiovascular diseases and biochemical actions [33].

Conclusion

Sesame is a valuable seed oil have numerous beneficial properties for applications in food industry. The present investigation indicates that it is a rich source of many essential nutrients that have beneficial and very positive effect on human health. The presence of good percentages of minerals, protein, carbohydrate and various essential bioactive compounds as well as other desirable fatty acids make the sesame seed suitable ingredient in the food and poultry industries.

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