Chemical Analysis of Noni (Morinda citrofolia) Seeds and the Characterization of the Seeds Oil

Seeds of Noni (Morinda citrofolia) were analyzed for proximate composition, minerals, antinutritional factors and amino acid profile, while the oil extract was investigated for physicochemical properties and fatty acids contents. Values for moisture, ash, crude protein, crude fat and crude fiber are 5.46 ± 0.01, 1.83 ± 0.01, 1.72 ± 0.02, 5.40 ± 0.07 and 4.67 ± 0.0 6% respectively. The calorific value of the seed was found to be 1585.90 KJ. The seed was found to be a potential source of minerals such as sodium, potassium, magnesium, calcium, phosphorous, iron and zinc. The anti-nutritional factors such as alkaloid, cyanide, flavonoid, oxalate and saponin were determined. The essential amino acids: glutamic acid, leucine and aspartic acid are present in higher concentrations as 6.33, 6.31 and 5.11 mg/100g crude protein, respectively. The physical and chemical properties of the seed oil were determined, thus the saponification value of the oil was found to be 32.26 mg KOH/g.


Introduction
Protein-energy malnutrition which has adverse health and economic consequences is a wide spread problem throughout the world. It is the most common deficiency disease especially in developing countries [1]. In the food processing industry, edible portion of fruits are processed in to products such as puree, canned-slices, juice and pickles whereas the seeds are often discarded as wastes since they are not utilized for commercial purposes. However, seeds are promising sources of useful compounds, because of their favourable nutritional properties [2].
Although, certain seeds contain moderately high amounts of protein, calories, certain minerals and vitamins, their use as food and feeds formulations is still limited by their low amounts of sulphur-containing amino acids, low protein digestibility and the presence of several anti-nutritional components [3 -4]. Also, despite the fact that these seeds are of high nutritional values, their intake is unfortunately lower than what is desirable. It is in this vein that the presence of anti-nutrients in plant protein sources has constituted a major constraint in their full utilization as livestock feeds. For full utilization as either foods or animal feeds, it has been asserted that seeds should be free of anti-physiological substances, have high nutrients bioavailability and be easily processed into edible products [5]. In order to achieve these goals, appropriate and effective processing techniques are employed by either the consumer or the feeds processing companies.
Some physical and chemical processes normally used to reduce or remove anti-nutritional factors in foods include; soaking, cooking, fermentation, irradiation, enzymatic treatment and selective extraction. Industrial processes used to achieve this include canning, fractionation, toasting and isolation of protein concentrates. However, processing can also introduce undesirable compounds like volatile aldehydes, ketones and peroxides as a direct result of lipid oxidation or reduce level of desirable compounds like protein and essential minerals [6 -7].
Noni (Morinda citrofolia) is a well-known plant of the family Rubiaceae and found mostly in the South -East Asia and Australasia part of the world. The species has now been introduced into the tropics where it is fast naturalizing [8 -9]. Morinda citrofolia is called by various names for instance the Hawaiians call it noni or mulberry, Malays refer to it as mengkudu while the Philippines call it apatots. Also in Barbados it is known as dog dumping [10 -11]. These seeds are contained in the fruits which are sometimes known as starvation fruits. The noni seeds which have very tough and relatively thick coats are covered with cellophane-like parchment layers and are edible when roasted [12]. In general, only soft, ripened noni fruits which usually contain over 100 seeds are chosen for seed selection. The seeds are separated from the fibrous, clinging fruit flesh as depicted in figures 1 and 2 [2].  The phyto-chemical profile of Morinda citrofolia was studied by Senthilkumar et al. [13] and it was reported that this plant increases the levels of antioxidant activity in the body. It also inhibits or prevents the growth of tumors and helps the immune system [14]. Morinda citrofolia is also used to treat hypertension, aches, inflammation and infections by Bacillius subtilis, Staphylococcus aureus, Proteus morgali, Pseudomonas aeruginosa, Salmonella and Shigella spp [15 -17].
The Noni plant is also used in lowering the blood sugar thus making it good for diabetics just as it is used in treating mycobacterium tuberculosis [18]. It also prevents arteriosclerosis as it inhibits low-density-lipoprotein oxidation, heart disease, gastric ulcer, mental depression and drug addiction [11,19]. The ripe noni fruit is used as poultice for facial blemishes or as a remedy for skin sores, boils or infections. The fruits are also used in treating gastric ulcer, menstrual cramps, heart disease and cancer. The leaves and bark are made into a liquid tonic for urinary problems and muscle or joint pain [20 -21]. Studies have also shown that noni juice lowers the number of DNA adducts in rats induced with a carcinogen [22 -23]. The juice of this plant also affects the physical endurance of mice [24] and athletes [25] in addition to its anti-inflammatory effect [26]. This wonderful fruit has also been demonstrated to have positive effect on preventing arteriosclerosis [19].
This research, therefore, is geared towards the effective utilization of this inexpensive plant material through the knowledge of its proximate, mineral, fatty acid, amino acid, oil characterization and anti-nutritional properties. This is because its utilization in food and industrial product development has not been accorded the attention it deserves.

Sample Collection and Preparation
The fruits of Morinda citrofolia used in the course of this project were obtained from Bosso Local Government Area of Niger State, Nigeria and a fine powdered sample was made from them. The fresh noni (Morinda citrofolia) fruits were washed and opened up to remove the seeds. The seed samples were then sun dried and ground using porcelain mortar and pestle to obtain fine powder. The sample was stored at 4°C in a well labeled air-tight container prior to analysis.

Proximate Analysis
The ash, moisture, crude fat, crude protein (N x 6.25), crude fibre and carbohydrate (by difference) weredetermined in accordance with the methods of AOAC [27]. All proximate analyses of the sample flour/powder werecarried out in triplicate and reported in percentage. All chemicals were of Analar grade.

Mineral Analysis
The minerals were analysed from solutions obtained by first dry-ashing the flour sample at 550 o C and dissolving the ash in distilled deionized water in flasks [28]. All the metals (except Na and K) were determined by using atomic absorptionspectrophotometer (Buck model 210 VGP). Sodium and potassium were determined using a flamephotometer (Corning, UK Model 405), while NaCl and KCl were used to prepare the standards [27]. Phosporus was determined by vanadomolybdate colourimetric method [29].

Anti-Nutritional Factors Determination
The contents of saponin, tannin, alkaloid, chemotrypsin, phytate, oxalate and cyanide were determined on flour sample by methods described by some researchers [30 -31].

Amino Acid Analysis
The amino acid analysis was by Ion Exchange Chromatography (IEC) [32] using the Technico Sequential Multi sample (TSM) Amino Acid Analyzer (Technicon Instruments Corporation, New York). The period of analysis was 76 min for each sample. The gas flow rate was 0.50 mLmin-1 at 60°C with reproducibility consistent within ±3%. The net height of each peak produced by the chart recorder of the TSM (each representing an amino acid) was measured and calculated. Amino acid values reported were the averages of two determinations. Nor-leucine was the internal standard.

Extraction of Oils
The powdered sample was oven dried and extracted with Soxhlet apparatus using n-hexane of Analar grade (British Drug Houses, London) for the recovery of undiluted oil. The crude oil extract was made free of water by filtering through the anhydrous sodium sulphate salt. The hexane was removed from the oil/hexane mixture by using a rotary evaporator.

Determination of Physicochemical Parameters of Seed Oils
The determinations of physicochemical parameters of sample oil for refractive index, acid value, iodine value, saponification value, unsaponifiable matter, peroxide value, free fatty acid and specific gravity are always carried out according to the methods of AOAC [33]. The proximate compositions of Noni seed are shown in Table 1. The seed is an excellent source of carbohydrate (82.08 ± 1.68%) since its amount is high but of low crude fibre (4.67%). Also, the protein content is extremely low (1.72%) just as the fat is low (5.40%). The proximate composition of the Morinda citrofolia seed was compared to that reported by Magdai [34]. The protein content of the seed was extremely lower than 18.4 ± 0.5 reported for baobab seed from North-eastern Nigeria by Lockett [35].
The amino acid compositions of the Morinda citrofolia seed are shown in Table 3. The seed contained high amounts of glutamic acid, leucine and aspartic acid but low amounts of the sulphur-containing amino acids. In contrast to the baobab seed, Noni seed protein contains low amountof lysine.
The physicochemical characteristics of Noni seed oil are shown in Table 4. The saponification and acid values were high (32.26 and 30.86 mgKOH/gOil). Pearson [36] reported that oils with higher saponification values contain higher proportion of lower fatty acid. Since the acid value is high, it shows that the oil from Noni seed should not be consumed since the acid value is an indicator for edibility of oil and suitability for use in the industry. However the peroxide value (7.52 mg/g oil) is lower than expected compared to the rancid oil which range from 20.0 -40.0 mg/g oil [37].

Conclusion
The long chain fatty acids found in the oil have a low saponification value because they have a relatively fewer number of carboxylic functional groups per unit mass of the oil as compared to short chain fatty acids. The triglycerides with highvalue of saponification value as is the case with the Noni seeds oil are considered to make better quality soaps than those withlow saponification value.
Theacid value whichis an indirectmeasure of the amount of free acids is present in fats and oils. Since the Noni oil is high in the amount of acid value, the higher the deterioration or rancidity of the oils are undergonedeterioration or rancid. As the rancidity increases, the oil achieves a foul smell along witha sour taste. Therefore the oil from Noni seed should not be consumed since the acid value is an indicator for edibility of oil and suitability for use in the industry.