Investigating the Effects of Moisture Content on the Composition of Soursop Seeds for Industrial Uses

— Soursop has proven to be of high economic importance and contains some essential nutrients which are needed in the human body for heathy living. The seeds contain oil of about 24.86%. The oil is of high quality and possesses good characteristics that can be used as feedstock in food industries and in many other industrial applications. This research study was focused on investigating the proximate composition, mechanical and chemical properties of soursop seeds for industrial uses and as a potential supplement for feedstock. The data obtained from this study was statistically analysed using Tukey HSD. The results for the proximate analyses of soursop seeds were found to be high for all moisture content levels (19.10%, 19.82%, 20.67%, 21.25% and 23.15%). The samples with 30% moisture contain level contained the highest level of fat. Carbohydrate content in the sample was found to be low for all moisture content level (3.21%, 3.46%, 3.79%, 4.23% and 44.76%). The relative density values were between 0.92 and 0.98 (g/cm 3 ) with specific gravity from 0.72 to 0.96 and refractive index was 1.46 at all the moisture levels employed. The results obtained from investigating the various composition of soursop seeds and also the oil expressed from the seeds indicted that, soursop seeds possess some good qualities which can be used for many industrial applications.


I. INTRODUCTION
The rapid increase in the growth of world's population and the yearning need for more vegetable oils to meet the high demand of its citizenry has prompted an urgent need for the quest of new sources of vegetable oil from edible oil crops/seeds, including the exploitation of more sources that are underutilized in order to affix for the already existing ones, since these schematic sources of vegetable oil has abruptly become inadequate to behooves with the ever progressive demands of local and international populace [14]. Soursop (Annona muricata) is widely distinguished to be a unique kind of fruit due to its high possession of economic and essential health benefits. The skin looks greenish and slightly hard with multiple spines when it is not ripped, while the ripped fruit has a tender yellowish green skin also with tender spines. The edible part of the flesh is rocky and white when unripe but it turns soft, gummy and creamy as it progresses in ripening.
Soursop is known to have good number of oval-shaped seeds with a smooth, light-textured and interspaced within the flesh [11]. According to researchers, soursop is reported to be a deciduous, flowering, evergreen tree native to Mexico, Cuba, Central America and the Caribbean and North and South America: Colombia, Brazil, Peru, and Venezuela. Soursop also grows in sub-Saharan African countries that lie within the tropics [11]. Several researches has revealed that soursop strives in areas of high humidity and relative warm winters, but in temperate regions below 5 o C can damage the leaves and small branches and temperate regions below 3 o C can be lethal to the entire plant [11]. In the rural parts of Nigeria, it is called 'shawa shawa'. The fruit in wholesome is effective and used as herbal medicine in curing cancer and diabetes, especially to indigenous people in areas where it is cultivated [11]. The pulp of soursop fruit is made up of both sweet and sour taste and can be eaten with a spoon, due to its tender and gummy nature.
Researchers have reported that agricultural fruits and other plants are dependable sources of renewable energy which are environmentally friendly, readily available and of lower cost. Thus, different species of a virgin, non-edible and waste vegetable oils have been discovered. Besides, seeds of plants are good sources of food for animals, including humans, because the seeds are embedded with nutrients essential for plant's initial growth, including many healthy fats, such as omega fats. In fact, the major sources of foods consumed by human beings are seed-based foods [10].
The monolithic disposal of bio-agricultural wastes (skin, pulp, seeds etc.) that are most frequently occurred in most fruit processing and food industries and underutilization of products has become obstructive in Holocene epoch years [9]. However, several research studies have reported the biorecovery of worthy by-products like ethanol, enzymes, pharmaceuticals and essential oils from agro-biomass wastes like mango, beniseed, sorrel, pineapple and papaya have been carried out [1], [7], [8].  Since the recent cultivation, production and output availability level of vegetable oil cannot satisfy the highincreasing demand of the citizens, it therefore becomes pertinent for the search and discovery of more oilseeds useful in the production of oil for food, paints, insecticides, detergents, cosmetics, etc especially from under-exploited oil seeds crop such as Soursop seeds [3]- [15]. Different vegetable edible-oils have been investigated and examined for use as food and raw materials for the production of snacks, cake, margarine, cosmetics, and plastics.
Oil from soursop seeds has also been discovered to possess the essential qualities of being used for the production of paints, cosmetics, insecticides, detergents, etc. [15]. From the aforementioned, it is pertinent to understudy and also evaluate some of the proximate, mechanical and chemical properties of the soursop seed oil for industrial uses.

A. Sample Collection and Preparation
Soursop (Annona muricata) was purchased from Urua-Akpokpo market in Etinan Local Government Area of Akwa Ibom State. The fruits were cut into different smaller sizes and the seeds were carefully removed from the pulps. The seeds were washed to remove dirt, stones and unwanted particles from the pulp and then dried at room temperature. Cracking of the seeds were done manually in order to obtain the whole kernels. One hundred (100) kernels were randomly selected from the whole samples for the determination of initial moisture content.
The kernels were then oven-dried in an air-tight oven at a temperature of 105 0 C for 6 hours, after which they were allowed to cool and weighed using the electronic weighing balance. The continuous weighing was carried out at an interval of 30 minutes until a constant weight was achieved [13]. The moisture content was then calculated in a wet basis using (1).
where ! = moisture content (%), = wet weight of sample or the initial weight of sample (g) and = dry weight of sample or the final weight of sample (g) The oven-drying method was employed in determining the desired moisture content levels of the conditioned samples.
The conditioned samples were then heated at different temperatures and time intervals. The oil yield was calculated using (2) as adopted by Ossom et. al. [14].

B. Proximate Composition Determination
Procedure: Determination of the chemical composition of the samples was carried out using the standard methods of analysis of Association of Official Chemists [5]. Analyzes were carried out on the samples for crude protein, crude fibre, carbohydrate, moisture content, fat content and ash contents. The methods are described below. The same procedures were repeated for all the samples.

1) Determination of crude protein
Procedure: Five grams (5 g) of the ground samples was weighed and inserted in a Kjeldahl flask. Ten grams (10 g) of sodium sulphate (Na2SO4), 1.5 g of Copper Sulphate (CuSO4) and 10 ml of concentrated sulphuric acid (H2SO4) was introduced to the sample in the flask. The flask was then placed to an angle tilted towards the digester, boiled and allowed to stand until the solution turns bluish. The solution was allowed to cool while gradually, addition of 90 ml of distilled water was further introduced to the digested sample and the volume was made-up to 100 ml using 100 ml volumetric flask. 20 ml of the digested solution and 20 ml of 40% sodium hydroxide solution was added into the 250 ml flat bottom flask.
The flask was immediately connected to the distillation unit and the distillate was collected under 10 ml saturated boric acid in a 250 ml conical flask. At the completion of the distillation process, the distillate was titrated 0.1 M hydrochloric acid (HCL) using drops of mixed indicator until the solution changes colour, from blue to reddish brown. This procedure was repeated for all the samples in triplets in order to obtain precision in the experiment. Thus, at the end of the experiment, crude protein content was then calculated using (3). where, A= weight of the crucible with dry residue (g) B = weight of crucible with ash (g) C = weight of sample C. Determination of Total Ash Procedure: Determination of Total ash content was carried out by igniting previously dried sample (2.00g) in a muffle furnace at 500 0 C for 4 hours. The same procedure was done repeatedly for samples in triplicate in order to precision in the experiment. The ash content was further calculated using (4).

D. Total Carbohydrate Content
Procedure: Determination of available carbohydrate content in the samples was carried out following the method reported by Alfrtis, et al [6]. This was calculated as the difference obtained after subtracting the fat, ash and fiber values from the total dry matter, thus, (5) was used.
where a = percentage of crude protein b = percentage of fat c = percentage of ash content d = percentage of crude fibre

E. Determination of Mechanical and Chemical Properties 1) Determination of refractive index
Refractive Index is defined as the quotient sine of the lightincident angle present in the air and the sine of the lightrefraction angle present in the substance. Thus, the refractive index was determined using the Abbe's 60/70 refractometer (Bellingham Stanley Ltd).
2) Determination of smoke, flash and fire point These points were determined by pouring 10 ml volume of the oil into an evaporation dish. When the oil sample gives off a blue smoke continuously, this indication was noted as the smoke point (Ts). Also the temperature at which the oil started flashing was noted as its flash point (Ts). Recording of Fire point was done at a level with which the temperature of the oil starts combusting. This point is known as fire point (Tc).

3) Free Fatty Acid (FFA) content determination of soursop seed oils
The Free Fatty Acids (FFA) was obtained using the standard recommended by the Association of Official Analytical chemist [5]. The FFA was calculated as oleic acid (1ml 0.1M sodium hydroxide = 0.0282 oleic acid), in which case the acid value.

4) Determination of iodine value
The iodine value measures the degree of unsaturation in vegetable oils. The iodine value is calculated in line with the AOAC (1992) standards.

A. Proximate Analysis of Soursop Seeds
The results of the determined proximate composition of soursop seeds at moisture content of 10%, 15%, 20% and 25% and 30% respectively is presented in Table I. The proximate composition of the soursop at these moisture levels were found to be on the same value range with very little variations. The average summary of the result from the soursop seeds with its physical, mechanical and chemical characteristics at 5 different levels of moisture content using Tukey HSD (Tukey Honest Significant Difference), is presented in Table I and II. Table I shows the result of the proximate properties (Fat, Protein, Carbohydrate, Crude fibre, Ash content, of the sour seeds oil at 5 levels of moisture content. Table II shows results for the mechanical and chemical (Relative density, Specific gravity, Refractive index, Fire point, Acid value, Free fatty acid, and Peroxide value) of the soursop seeds at 5 different levels of moisture content.
The ash content in 30% moisture content was discovered to be slightly higher when compared (2.69%) to all others (2.50% at 25% MC, 2.1% at 20% MC and 2.23% at 15% MC and 2.16 at 10%MC). In general comparison, these values are relatively low as to that of Ash content in Bush mango (5.00%), bitter leaf (15.86%) and moringa oleifera (15.09%) [4]. Fiber content in the sample was found to be high for all moisture content levels (42.16%, 42.48%, 42.80%, 43.14%, and 43.77%).  However, the sample with 30% moisture level contained the most fiber. Crude Protein content in the sample was found to be high for all moisture levels (27.62%, 27.08%, 26.48%, 26.31% and 26.02%), however, the sample with 30% moisture level contained the most of crude protein. Fat content in the sample was found to be high for all moisture levels (19.10%, 19.82%, 20.67%, 21.25% and 23.15%). However, the sample with 30% moisture level contained the most of fat. Carbohydrate content in the sample was found to be low for all moisture levels (3.21%,3.46%, 3.79%, 4.23%, and 4.76%). The values for the carbohydrate content showed that soursop seed is good in energy giving regardless of the amount of moisture in it.

B. Mechanical and Chemical Analysis of Soursop Seeds
The values obtained for the various oil properties for Soursop seed oil are as presented in Table II. The relative density values were between 0.92 and 0.98(g/cm 3 ) with specific gravity from 0.72 to 0.96, and the refractive index was 1.46 at all the moisture levels considered. The fire point was observed to increase with increased moisture content from a value of 60 to 80 0 C, while fire point decreased with moisture content from a value of 208 to 182 0 C. Both the acid value and FFA increased with increasing moisture content from 1.22 to 1.93 (mg/g) and 3.20 to 4.7 (g/g) respectively. The peroxide value also generally increased from 0.10 to 0.31 with increase in moisture content of the seed.
The statistical analysis revealed that all the oil properties were significantly different (p> 0.05) at different moisture levels except the refractive index which was unaffected by moisture change. The quantity of oil recovered from the conditioned seeds was higher at low moisture levels than high levels suggesting that there could be an optimum level to which moisture may be present in the seeds for maximum yield; increasing moisture beyond which could mitigate the oil recovery. In terms of quality, fire point was observed to have been influenced by moisture content as increase in moisture content led to increased flash point and vice-versa. This is in agreement with the report of Okoro and Osunde [11].
Both the acid value and FFA increased with increasing moisture content from 1.22 to 1.93 mg/g and 3.20 to 4.87 g/g respectively. The peroxide value also generally increased from 0.10 to 0.31 with increase in moisture content of the seed which in line with Adepoju et al. [2]. This observation is a true representation of most common edible oils.
Finally, soursops unlike every other fruit have seeds having oil rich in properties expected from any other oil seed. Harnessing the potentials through effective design of processing equipment is crucial. Results from this experiment after studying the proximate, chemical and mechanical properties of the seeds revealed that all the attributes assessed falls within the range of other oil seeds and if processed on large scale could apart from income generation lead to conversion of waste-to-wealth for human and livestock consumption [14].
The results from the experiments conducted and analyzed revealed that soursop seeds possess an excellent source of ash content, protein, fat, carbohydrate and crude fiber, which people that cannot afford animal protein can fall back to. Ossom et al. [14] reported that soursop seeds are an important source of food supplement that can be exploited especially in the developing countries where there is shortage of animal protein and under nutrition.
For the range of moisture content employed in the analysis of the proximate, mechanical and chemical properties of soursop seeds, it was discovered that, moisture content variation had significant effect on the proximate, mechanical and chemical parameters at 5% probability using Tukey HSD (Tukey Honest Significant Difference). According to Oladije et.al. [12], it is reported that, the presence of Free Fatty Acid (FFA) can trigger the oxidative determination of oils caused by enzymatic chemical formation which in turn results in an off-flavour component. The presence of low FFA shows an indication that, the oil contains some good qualities that is capable of resisting hydrolysis [2].
The Acid value present in the oil is an indication that, the oil is edible and falls within the recommended standards for edible oils. The presence of small quantity of Acid value in the oil is an indication that, the oil is not only edible but also has a durable shelf life in terms of preservation [2]. The specific gravity in soursop seed oil was found to be less than one (<1), indicating that, the oil less is less dense than water when compared [12].
Several reports have it that, Peroxide value measures the level of hydro-peroxides present in the oil and its presence indicates that the oil can be stored for a longer period of time without being deteriorated. Thus this also demonstrates that the oil possesses some desirable qualities which can be used as an edible oil and for other industrial purposes [2].
To this end, it therefore means that soursop seeds and oil can be used for food purposes and as a feed stock in many industrial applications.

IV. CONCLUSION
Based on the findings of this research study, it was therefore concluded that; i. Soursop seeds are an excellent source of food nutrients.
ii. Proximate analysis shows that there was statistically significant effect of moisture variation in fat, crude fibre, carbohydrate, ash content and protein compositions. iii. There was statistically significant effect of moisture variation on mechanical composition of soursop seeds. iv. The chemical composition revealed that soursop seeds oil has appreciable qualities which could be employed in many applications. v. Moisture content has no effect on the refractive index of soursop seed oil at different moisture content of harvest to storage. vi. Both the acid value and FFA increased with increasing moisture content from 1.22 to 1.93(mg/g) and 3.20 to 4.87 (g/g) respectively. vii. The seed oil advocated that it contains a reasonable and recommendable source of edibility and can serve as an industrial oil for many applications as it is proven in this study. It is also a good source of fat and oil for animal feedstock as the oil properties were within the standards and recommended levels of edible oils.