Evaluation … Nde Bup et al.
Evaluation of the cooking process of neem (Azadirachta indica) nuts as a pretreatment prior to oil extraction
Nde Bup Divine1,5, Siriyabe Marth2, Mohagir M. Ahmed3, Fon Abi Charles4, Zourmba Paul2, Nkeng Elambo George5, Kapseu Cesar6
1Higher Institute of the Sahel, University of Maroua, P.O. Box 46, Maroua, Cameroon
2Department of Chemistry, Higher Teachers’ Training College, University of Maroua, Cameroon
3Faculty of Science and Technologies, University of Sarh, P.O. Box 105, Chad
4Department of Chemistry, Higher Teachers’ Training College, University of Yaounde1, Cameroon
5Department of Chemistry, Faculty of Science, University of Buea, Cameroon and Ecole Nationale Supérieure des Travaux Publiques (ENSTP) B.P 510, Yaounde, Cameroon
6 Department of Process Engineering, ENSAI, University of Ngaoundere, P.O. Box 455 Ngaoundere, Cameroon
Received: 22 May 2014; Revised: 14 August 2014; Accepted: 22 August 2014
Abstract: Traditional methods are usually used locally to produce ‘bio-neem oil’ which is void of residual solvents. The major disadvantages of the method are low oil yields and high acid values. To ameliorate this process, cooking of neem nuts was evaluated by response surface methodology. Independent variables studied were cooking time and temperature while the responses were moisture content of the cooked kernels, quantity of oil extracted, acid value and the refractive index of the oil. Cooking time and temperature significantly influenced the cooking process but their interaction effect was negligible. Optimum ranges obtained for the cooking process were cooking time (5-20 min) and cooking temperature (40-50oC). At the mid-point of these ranges (12.5 min and 45 oC) the optimum responses obtained were: moisture content 46.37 % w.b., oil content 21.43 %, acid value 3.53 mg KOH/g oil and refractive index 1.460. Experiments conducted under these optimal conditions showed no significant difference with the calculated results. Results for the raw kernels were: moisture content 43.00±1.41 % w.b., quantity of extracted oil 15.88±0.26 %, Acid value 8.13±0.78 %, and refractive index 1.461±0.01, indicating that, there was a 35 % increase in quantity of oil extracted and a 57 % reduction in acid value.
Key words: Neem, cooking, traditional extraction, optimization.
INTRODUCTION
Vegetable oils have played and continue to play a very vital role in human nutrition, traditional medicines, cosmetics and other diverse uses in industry. Market demands and the development of new uses have generated interest on scientific and technical research on under exploited oilseeds and oil bearing materials1-5. Research in this area has been centered on improved extraction and characterization methods that give oil of high quality in good quantity. There exists today a plethora of oilseeds which are still under-exploited and have not been given proper research attention in order to fully derive the potential benefits that they present. One of such oilseed is Azadirachta indica commonly called the neem tree. Neem is a tree of Indian origin with almost each part of the tree having potential curative effects in traditional medicines. Tinghui et al.6 reported that, the neem tree is present in Asia (Bangladesh, Burma, Cambodia, India, Indonesia, Iran, Malaysia, Nepal, Pakistan, Sri-Lanka,Thailand and Vietnam); in Africa (Benin, Burkina Faso, Cameroon, Chad, Ethiopia, Gambia, Ghana, Guinea, Ivory Coast, Kenya, Mali, Mauritania, Mozambique, Niger, Nigeria, Senegal, Somalia, Sudan, Tanzania and Togo,) and the Americas (Antigua, Barbados, Belize, Bolivia, Brazil, Dominican Republic, Ecuador, Guatemala, Guyana, Honduras, Jamaica, Mexico, Nicaragua, Suriname, St. Lucia and Trinidad and Tobago).The tree is therefore widely distributed and given the potentials of neem oil for use in pharmaceutics, cosmetics and as a potential source of raw material in the biodiesel industry it is expected that the demand for this oil should expand in the near future7-9. Some of the applications of neem oil require the use of an extraction method that retains as much as possible the natural properties of the oil that confer curative and/or insecticidal properties. One of such methods is the cold extraction method. In Cameroon and in most African countries extraction is done mostly in a traditional manner to produce the so called ‘bio-neem oil’ (that is, neem oil extracted without the use of solvents). This method consists of depulping the fruit, and decorticating the nut to have the kernel, sun drying of the kernel, grinding and extraction. In the extraction process the ground kernels are boiled in water and the oil layer on the surface of the water is ladled off and further heated to remove the residual water. This is called the water extraction method. In the second traditional extraction method, the ground kernels are mixed in a mortar with a pestle with very little quantities of warm water added at intervals to decrease oil viscosity and aid oil flow. This is referred to as water assisted traditional extraction method. The major disadvantages of these methods are low yields and high acid values of the oil. Meanwhile it has been demonstrated that cooking oilseeds prior to processing improved oil yields and reduced FFA values of shea butter10-11. Cooking of neem nuts prior to oil extraction may also offer these advantages. The precise cooking conditions vary as a function of type and size of oilseed, temperature, cooking time etc. It is necessary to define these optimum conditions for each type of oilseed as such data is very valuable in engineering calculations for process scale-up. The Doehlert experimental design has been reported as a useful surface response method to optimize various processes12. The various advantages of this design over others are well elaborated by Mathieu and Phan-Tan-Luu13 and Imandi et al.12 and are summarized in Bup Nde et al.10. Studies evaluating the influence of cooking of neem nuts on oil yields and quality to the best of our knowledge are scarce in the literature. It is worth noting that the traditional processing and sale of neem oil is done mostly by local women and this represents substantial income earning opportunities for them. Studies that can improve yields and quality of neem oil will therefore be beneficial to them as they may sell at higher prices and earn more money. The aim of this work was therefore to evaluate the effect of cooking on the traditional oil extracted yields and some quality parameters of neem oil.
Table 1: Experimental matrix and values of the responses obtained
Coded Values / Real values / ResponsesExp't N0 / x1 / x2 / X1 / X2 / Y1 / Y2 / Y3 / Y4
1 / 0 / 0 / 62.5 / 70 / 51.02 / 14.60 / 7.39 / 1.463
1 / 0 / 0 / 62.5 / 70 / 46.94 / 18.67 / 7.70 / 1.461
1 / 0 / 0 / 62.5 / 70 / 45.10 / 18.51 / 7.08 / 1.463
2 / 1 / 0 / 120 / 70 / 53.06 / 16.61 / 8.71 / 1.465
2 / 1 / 0 / 120 / 70 / 48.98 / 16.42 / 8.09 / 1.463
2 / 1 / 0 / 120 / 70 / 52.20 / 16.45 / 8.80 / 1.463
3 / 0.5 / 0.866 / 91.25 / 100 / 58.00 / 16.97 / 6.41 / 1.463
3 / 0.5 / 0.866 / 91.25 / 100 / 56.00 / 18.09 / 5.29 / 1.461
3 / 0.5 / 0.866 / 91.25 / 100 / 59.31 / 18.20 / 5.85 / 1.463
4 / -1 / 0 / 5 / 70 / 48.08 / 20.71 / 5.05 / 1.463
4 / -1 / 0 / 5 / 70 / 49.02 / 18.57 / 6.35 / 1.461
4 / -1 / 0 / 5 / 70 / 48.65 / 18.91 / 5.66 / 1.461
5 / -0.5 / -0.866 / 33.75 / 40 / 48.98 / 19.59 / 4.95 / 1.461
5 / -0.5 / -0.866 / 33.75 / 40 / 44.90 / 19.33 / 5.04 / 1.461
5 / -0.5 / -0.866 / 33.75 / 40 / 47.08 / 19.31 / 3.92 / 1.461
6 / 0.5 / -0.866 / 91.25 / 40 / 50.00 / 15.46 / 7.40 / 1.461
6 / 0.5 / -0.866 / 91.25 / 40 / 46.00 / 16.81 / 8.46 / 1.461
6 / 0.5 / -0.866 / 91.25 / 40 / 48.34 / 15.55 / 7.72 / 1.461
7 / -0.5 / 0.866 / 33.75 / 100 / 59.18 / 13.53 / 7.79 / 1.463
7 / -0.5 / 0.866 / 33.75 / 100 / 60.78 / 14.66 / 7.40 / 1.463
7 / -0.5 / 0.866 / 33.75 / 100 / 58.90 / 14.50 / 8.01 / 1.461
x1, and x2 are the coded values while X1, and X2 are real values of cooking time and cooking temperature respectively. Y1, Y2, Y3 and Y4 are moisture content, amount of oil extracted, acid value and refractive index respectively
MATERIALS AND METHODS
Mature neem fruits used in this work were collected from the town of Maroua, Cameroon in April 2013. They were stored in a freezer at -18oC to limit oil hydrolysis. Before the cooking experiments, the fruits were withdrawn from the freezer and stored on a laboratory bench overnight to thaw at ambient temperature. The samples were then depulped manually and washed in a large quantity of distilled water to remove the residual pulp. The nuts were cooked following the Doehlert experimental design chosen in this work (Table 1).In the cooking process, the experimental variables were cooking time (5-120mins) and cooking temperature 40-100oC. 350mL of distilled water were placed in a 600 mL beaker and heated to the desired experimental temperature. 300g of neem nuts were then placed in the beaker and the beaker covered with Aluminium foil and cooked for the required length of time (Table1). After cooking the water was drained and the nuts were manually cracked to give the kernels. A portion of the kernels was withdrawn for the determination of moisture content while the other portion was dried at 50oC in an electric oven for 24 h to a constant mass. This latter portion was used for oil extraction and subsequent oil analysis.
Determination of moisture content of cooked kernels: Moisture content was determined by drying a known quantity of the cooked kernels in a ventilated electric oven at 105oC for 24 hours. The dried kernels were cooled in a dessicator and reweighed14. Moisture content (Y1 % w.b.) was calculated from the relation
Y1=M0-M1M0×100 [1]
M0 is wet mass of sample and M1 is the dry weight of the sample. All experiments were carried out in triplicates.
Oil extraction process: The dried kernels were ground using a kitchen type manual grinder. The adjusting knob of the grinder was set to maximum for each run, to ensure that grinding for the different runs was done under uniform conditions. In the extraction process, the traditional water assisted extraction method which is normally used in the production of organic neem oil was used. This consisted of mixing and pressing the ground paste in a laboratory porcelain mortar using a pestle with occasional addition of 15-20ml of warm water (40oC) at 3 different intervals. The oil was then drained from the mortar and filtered through a Whartman No. 42 filter paper. The oil was placed in an oven at 60oC to remove residual water for 2 hours. A control experiment was carried in a similar manner but for the fact that the samples were not cooked prior to drying and oil extraction. The average extraction time for each run was 15-20 minutes. All extraction experiments were carried out in triplicates. The quantity of oil extracted was calculated from the equation
Y2=Mass of oilSample mass×100 [2]
Determination of Acid value: Acid value was determined by back titration. 2 g of the oil sample was weighed into a conical flask and 0.2N ethanolic KOH solution was added to the flask and shaken vigorously for about 1 minute. Excess KOH remaining in the flask was then titrated against 0.1N HCl, using phenolphthalein as indicator. A blank titration was carried out in a similar manner without the oil sample. This was done in triplicates. Acid value was calculated from the equation.
Y2 =NV1-V2×56.01Sample mass [3]
N is the normality of KOH, V1 is the titre volume for the blank and V2 the titre volume for the test sample.
Modeling of the cooking process: A second order model with interaction was proposed to describe the cooking process of neem kernels. This model was represented as follows:
Y=b0+b1x1+b2x2+b11x12+b22x22+b12x1x2 [4]
The coefficients of the model b0, b1, b2, b11, b22 andb12 were determined through multiple linear regressions on SigmaPlot 11.0 (SystatInc, USA).
Validation of Models: The criteria for validating models were the regression coefficient (R2) and/or absolute error (AE) observed between the experimental and theoretical results. R2 was obtained from regression analysis while AE was determined from the equation,
100nn=1nYexp-YcalYexp [5]
Where Yexp and Ycal are the measured and calculated responses respectively. n is the number of points at which measurements were carried out. A model was considered valid if at least one of the two criteria was satisfied. That is R2>0.7 and/or EA<10%
Optimization of the cooking process: To optimize the cooking process, the optimum point for each response (minimum or maximum point) of Eq. 1 was defined as the point where the first partial derivative of the function equals zero10:
∂Y∂x1=b1+2b11x1+b12x2 [6] ∂Y∂x2=b2+b12x1+2b22x2
The system of equations for each response was solved to give the values of x1 and x2 in coded values which were then transformed to real values. Experiments were then conducted at these points to verify the mathematically determined optimal conditions.
RESULTS AND DISCUSION
Modeling of the cooking process : Values of the responses studied Y1 (Moisture content % w.b), Y2 (Quantity of oil extracted %) and Y3 (acid value mg KOH/g oil) are presented in Table 1 while the model constants, P values, value of model constants (VMC), R2 and AE values for the second order models are presented in table 2. A model was considered valid if R2 > 0.700 and/or AE < 10. Table 2 shows that all of the responses satisfied either one or all of the conditions. These models were therefore judged satisfactory to describe the influence of the variables (cooking temperature and cooking time separately or in combination) on the measured responses.