Effects of Active Grids Gap’s Adjustment on Technical Performances of a Power-Driven Dehuller Devised for African Locust Beans Parkia Biglobosa

 

Roger Houêchéné Ahouansou^{1, 2*}, Gontrand Comlan Bagan^{1, 3}, Pélagie Bidossessi Agbobatinkpo⁴, Emile Adjibadé Sanya¹, Antoine Cokou Vianou¹, Djidjoho Joseph Hounhouigan⁴

¹Laboratory of Applied Energetic and Mechanic (LEMA), Polytechnic School of Abomey-Calavi (EPAC), University of Abomey-Calavi (UAC). 01 POB: 2009 Cotonou, Republic of Benin.

²Program of Agricultural and Food Technology (PTAA), National Institute for Agricultural Research of Benin (INRAB). POB: 128, Porto-Novo, Republic of Benin.

³School of Agricultural Mechanization and Mechanical Construction (EMACOM); National University of Agriculture of Porto-Novo, Republic of Benin.

 

ABSTRACT:

African locust bean (ALB) seeds are processing into afitin through a succession of operations, of which dehulling of pre-cooked seeds. Dehulling is laborious for processors. To remove this constraint, a motorized dehuller has been developed. This study aims to evaluate the effects of the setting gap between the fixed and mobile grids of dehuller on these performances. Boiled ALB seed were subjected to mechanical dehulling with inter grid gap varying from 2 to 25 mm. The obtained results showed that, when the gap varies from 2 to 25 mm, the dehulling rate decreases from 100 to 0%, the breaking rate from 50.83% to 0%. The machine performs well when ALB seed cooked during 4 h and grids’ gaps in the range of 5 to 15 mm. The values of these cited parameters that give the best performance are obtained when gap’s adjustment is fixed at 9 mm.

 

 

1.      INTRODUCTION:

The aroma and flavor of traditional dishes in Africa are determined primarily by taste enhancers produced locally. In West Africa, afitin (iru, sounbala or dawadawa) product based on African locust bean (ALB) (Parkia biglobosa) determine the flavor of vegetable sauce: gumbo or tomato. Unlike synthetic or industrially manufactured flavor enhancers, in addition to nutritional and aromatic qualities, afitin also has therapeutic value. African locust bean is very popular in Africa [1] and well consumed in Benin and West Africa [2]. As a Non-Wood Forest Product (NWFP) it provides relief for rural communities in terms of subsistence as well as revenue generation [3-4].

 

African locust bean’s clove is composed of pod (or chaff, used as animal feed), small beans and sweet edible pulp (a source of chocolate substitute). Its pod’s extract can significantly increase compressive strength of laterite blocks by 78.57% and the higher the concentration of locust bean pod’s extract, the greater the compressive strength of Laterite blocks. [5] Its pulp is a potentially good source of food which can compete favorably with most cereals and legumes. Chemical composition indicates that its pulp is a good source of macro and micro-nutrients. The bright yellow color and high sugar content impart sensory appeal to its pulp[6].“Iru” or dawadawa is a typical example of fermented food obtained from the small beans [1]. According to UNU, [7] iru is one of traditional fermented condiments used to flavor soups and stews in Nigeria due to Locust bean seedsrichest in proteins: 30-40% [8-9]. They also provided significant amounts of carbohydrates (10-15%), fats (15-20%), minerals (4%) and vitamins mainly from B7 and B8 groups [10-11]. Afitin, irou or sonrou are generally sold in plant-type packages having certain physicochemical and physic mechanics [12,13,14] properties. The product provided significant incomes to their processors [3, 15].

 

ALB tree felling/burning, low technology application and storage were the major production constraints. Many authors recommended, development of appropriate ALBS processing technology (such as a de-pulping machine) [16]. Traditional processing of locust bean into afitin includes many unit operations’ witch are: seeds rinsing and sorting, seeds precooking in water, dehulling by feet-pressing, hulls and cotyledons separation, cotyledons rinsing, sorting, boiling and alkaline fermentation. Some constraints have been identified in production of this condiment, such as: low production due to rudimentary equipment, high wood consumption in cooking, and poor production practices [17]. Among these operations, feet-pressing used for dehulling of seeds was known as the most tedious and least hygienic method. Dehuller machine; hulls separator, steaming unit, packaging, fermentation basket, were the main needed equipments in the manufacture of African locust bean into” iru” in Nigeria[18].Moreover, different studies were conducted here and there to determine the effects of the cooking duration on some engineering properties of the African locust bean seeds.  Obtained results showed that, when these seeds were water-cooked respectively for 1 hour, 2 hours, 3, 4, 5 and 6 hours, their dimensions varied: between 10.38 to 12.52 mm in length, 8.61 to 10.04 mm in breadth, and 4.79 to 5.83 mm in thickness [19-20].

 

Someequipment have been developed intending to reduce the workload donkeywork of ALB seeds processing. A machine for de-pulping locust bean has been designed, fabricated and tested for preliminary performances in Nigeria. The highest value of de-pulping efficiency of 98% was achieved at working speed of 350 rpm and at hot-water soaking time of 45 minutes [1].

 

Some obtained maximum values for dehulling efficiency and throughput on a developed locust bean dehuller in Nigeria were of respectively 70.3% and 0.51 kg/min [21]. This equipment was not adopted for feebleness of its throughput (30 kg/h). In Republic of Benin, a dehuller centered on the requirements of afitin processors had been devised [20, 22] developed in Benin a dehuller centered on the processors requirements. The authors analyzed the effects of different applied pre-treatments to ALB seeds on the technical efficiency of this developed machine. Achieved results clearly showed that the realized apparatus had provided its best performances when the cooked seeds for 4 to 6 hours were used. But the setting gap between the fixed and the mobile grids to get the best performance of dehuller was not known. The current research is carried out to assess the effects of setting gap on efficiency characteristics of the mechanical dehuller in order to identify the most suitable value to be insured it for collecting the best dehuller performance

 

2. MATERIAL AND METHODS:

2.1Material

The experiments were conducted in laboratory of Agricultural and Food Technology Program (PTAA) of the National Institute of Agricultural Research of Benin and in the Laboratory of Applied Mechanics and Energy (LEMA) of the Polytechnic School of Abomey-Calavi (EPAC) / University of Abomey-Calavi (UAC).

 

Plant materials:

ALB (Parkia biglobosa) seeds used were acquired from International market of Dantokpa - Cotonou (Benin). Such the seeds, as shown on Figure 1, belonged to those of all coming quality, originated from N’Dali region, in Northern Benin. Approximately 100 kg of seeds were cleaned, sorted and stored in polystyrene bags and kept in laboratories at controlled room temperature of 25±2 °C. The raw seeds of this used variety have been sizes characterized enlightening average dimensions values for entire seeds of respectively: length 10.12±1.26 mm, width 8.30±1.20 mm and thickness 4.94±0.72 mm. [23]

 

Experimental equipment:

The illustrated apparatus on Figure 2 was the new designed and manufactured dehuller photography. It’s the fruit of the built synergy between researchers from both the University of Abomey-Calavi (UAC) and the National Institute for Agricultural Research of Benin (INRAB).  Different parts of this machine are shown in Table 1 and Figure 1. It consisted of a welded frame (1), a 5-hp thermal internal combustion motor (23) coupled to a shelling cage (2) by gear transmission mechanism and a feed hopper (6). The shelling system, main body of this produced machine, contained two active plates: a fixed one (4) and a mobile (12). On each plate, was fixed a metallic grid made of perforated high strength stainless steel sheet. In running, the motor drove the moving plate through gear transmission and the seeds, poured in hopper, fed into annular space between the two abrasive grids where they were shelled by shear3

 

Photo 1 : African locust bean seed	Photo 2 : Aftin (iru, sumbala, netetou)

 

 

 

                               

                                                                                                                                                          

 

	Figure 1:  Overview of the dehuller

 

Photo 3 : African Locust bean dehuller

 

 

 

 

 

 

 

Figure 1:  Overview of the dehuller

 

 

 

 

 

 

	Table 1: Different parts of the dehuller
	Réf. Quantity Item 24 1 Drive belt 23 1 Engine 22 1 Rotor belt 21 1 Pulley 1 reducer 20 1 Pulley 2 reducer 19 1 Reducer 18 1 Blower pallets 17 1 Blower shaft 16 1 Belt of blower shaft 15 1 Pulley of blower shaft 14 2 Bearing of blower shaft 13 1 Rotor pulley 12 1 Rotor grid 11 2 Rotor locking  system 10 1 Rotor 9 1 Bearing 6306 8 1 Setting shaft 7 1 Adjustment spindle 6 1 Hopper 5 1 Stator grid 4 1 Stator plate 3 1 Bean exit channel 2 1 Dehulling cage 1 1 Frame
Figure 2: Sectional view of the dehuller

 

 

 

2.2. METHODS:

Seeds precooking:

The method of [20] was used to cook the locust bean seeds. The locust bean seeds, taken from the packaged clean stock, were poured in unionized water at temperature of 30±2°C and at ration of 2.5 liters of water per kilogram andheated in aluminum pots on wood fire. The mixture (water - seeds) had been carried to boiling point after about 15 min and maintained during 4 hours experimental cooking time.

 

Effect of the grids gap on theoretical values of dehulling and breaking rates:

Determination of theoretical values of dehulling rate and breaking rate using the cooked seeds for 4 hours is based on the obtained data from measurements of thicknesses of respectively the entire seeds and their cotyledons. [23-24] Indeed, theoretical value of  dehulling rate is based on the assumption that, when the gap between the grids is set to a value '' a '', all the seeds (x) possessing half-thickness ''µ'' less than ''a'' will be husked. On the other hand, the seeds (y) possessing half-thickness greater than  "a" will not be dehulled, since they will not be able to enter space between the two active grids: ”inter grids’ gap”. Similarly, theoretical value of the breaking rate is based on the hypothesis that, all cotyledons (w) owning their half-thickness ''μ1'' greater than ''a1'' will be broken. On the other side, cotyledons (v), having their half-thickness less than ''a1'', will not be broken. From then, a cotyledon is not brokewhen it stays whole or normally splits into its two (2) half-cotyledons. Dimensions of 100-seeds and 100-cotyledons cooked were measured.

 

Theoretical values of the hulling rate (Tdt) and breakage rate (Tbr) are calculated using the following frequency formulas:

 

T_dt= 100 [x_n / (x_n+y_n)] (%)                                                                                                                                                                                      (1)

T_bt = 100 [v_n / (w_n+v_n)] (%)                                                                                                                                                                                      (2)

 

Where these used variables respectively signified:

-       X_n : number of seeds having half-thickness less than the adjusted gap value;

-       Y_n : number of seeds having half-thickness greater than the adjusted gap value;

-       V_n: : number of cotyledons having half-thickness less than the adjusted gap value;

W_n: number of cotyledons having half-thickness greater than the adjusted gap value.

 

Effect of the grids gap on experimental values of dehuller’s performance indicators:

Experimental determination of performance indicators, such as Dehulling Rate, Breakage Rate, Dehulling Index and Yield Rate, was performed on this devised equipment (Figure 3) using the cooked ALB seeds for four (4) h. Adjustment of the gap between the two grids (fixed and movable) was varied from 2 to 25 mm at 0.5 mm intervals. The adopted values for hopper’s diameter (116 mm) and equipment’s rotational speed (666 rpm) are those obtained from previous studies [22, 24].

 

Performance parameters evaluation:

For each experimental test series, a seeds’ sample weight of Ms = 500 g was taken. Those collected seeds samples were then manually shelled with the aid of a pair of pliers and separated into four (04) fractions, respectively weighed for determining the values of following parameters: mass of whole cotyledons and those cracked in two (M_C), mass of un-hulled or partially hulled seeds (M_U), mass of broken cotyledons (M_B) and mass of resulting hulls (M_H). One considered that, an individual seed was hulled, when about 90% of its hull/shell was removed[25].

 

The efficiency of a dehuller was evaluated on the basis of performance parameters, such as dehulling index (I_D), dehulling rate (T_D), broken cotyledons ratio (T_B) and dehulling yield (R_D), calculated using the respective following formulas.^[23-26-27]

 

-        Dehulling Index   (I_D):                                                         (3)

-        Dehulling Rate (T_D): (%)                                                                                       (4)

-        Brokencotyledons Ratio (T_B): (%)                                                                   (5)

-        Dehulling Yield (R): (%)                                                                                (6)

 

The Dehulling Index (I_D) was known to allow appreciating global efficiency of a dehuller. Theoretical values of I_D lied within [-1, +1] interval. It’s equal to -1 in case of a total break of seeds and +1 when perfectly dehulling i.e. without any broken cotyledon and unshelled seed.[26]

 

Estimated Limit and Reference Values for Performance Parameters:

A survey was carried out among thirty (30) randomly selected afitin producers distributed as follows in respective cities: 9 producers located at Porto-Novo, 5 at Adjarra, 2 at Banigbé, 2 at Sakété, 2 at Dangbo, and 10 at Abomey. Afitin production and sale are the main activity of these producers.

 

Determination of Breakage Rate indicator:

Samples of cotyledons, with breakage rates of 0%, 5%, 10%, 20% and 25% respectively, were assessed by those afitin processors. Each of themes had indicated acceptable samples and reasons for their operated choice. To constitute each sample, 150 g of whole or divided cotyledons were added to specific quantities of the broken almonds in order to obtain the respective breaking rates mentioned above. Mass of the broken cotyledons, to be added in order to obtain the corresponding degree of breaking, is determined from formula (5).

 

Determination of Dehulling Rate:

Nine (09) different samples of 100%, 95%, 90%, 85%, 80%, 75%, 70%, 65% and 60% respectively of hulling rate were tested by the respondents. They indicated which samples they consider acceptable to characterize the good performance of this motorized hulling machine. To constitute each of these samples, 65 g of shells and quantities of unseeded seeds were added to 150 g of cotyledons, so as to obtain the samples having these mentioned dehulling rates. The mass of undehulled seeds added to each sample is obtained from formula (4).

 

Determination of Dehulling Index:

Ten (10) different samples, each with a hulling index of 1; 0.95; 0.90; 0.85; 0.80; 0.75; 0.70; 0.65; 0.60 and 0.55, were presented to respondents for the realized survey. To make up each sample, 65 g of shells and determined amounts of unshelled seeds and broken cotyledons were added to 150 g of cotyledons, so as to form the samples having these indicated hulling indices. According to their experiences in this field, the women indicated the samples that showed the good hulling indexes, thus marking a good performance of this motorized huller. Respective masses of the unshelled seeds and broken cotyledons added to obtain these shown corresponding values of the husking indexes are calculated from formula (3).

 

Determination of Dehulling Yield values:

One hundred and fifty (150) grams of cooked seeds, manually dehulled, make it possible to obtain a certain quantity of cotyledons. This assessed quantity of cotyledons was gradually reduced so as to constitute the respective samples giving yields of 70%, 60%, 50%, 40% and 30%. Respondents indicated the samples disclosing the correct Hulling Performance according to their practices in field. Respective masses of the broken cotyledons, added to entire ones, to arrive to each of these considered hulling yield values, have been thus determined from formula (3-4).

 

Determination of hourly capacity indicator:

The hourly capacity determination was carried out on the basis of a form in which respondents indicated the number of pans, owing 40 kg cooked seeds capacity, that the devised equipment was able to dissect  per hour, so that its  rhythm’s judged satisfactory for them.

 

For each of these performance parameters, the analyzed sample offering the highest score determined the limit-value of subsequent indicator. Similarly, the reference-value was that obtained experimentally through application of the known traditional method of feet-crushing.  In case of hourly capacity parameter, reference-value was the one used for design calculations of this realized equipment.

 

Statistical analysis:

The values acquired for the various measured parameters were processed in descriptive statistics, through calculations of the mean values, standard deviations and frequencies, using SPSS 12.0 software. Results of the taste tests were analyzed through the designed graphs from application of Microsoft Office Excel 2010 version. [28, 29, 30].

 

 

3. RESULTS AND DISCUSSION:

3.1Limit and reference values of dehuller’s technical performance parameters

The results of afitin processors survey, illustrated by the logged data in Table 2, showed that ideal value that can take dehulling index is 1. At this value, all the seeds are dehulled and there is no broken cotyledon is recorded. On the other hand, the minimum acceptable value for this parameter is 0.85. The majority of respondents believe that, when dehulling index is lower than 0.85, the devised dehuller delivers many unshelled seeds with broken cotyledons. An equipment that giving these characteristics is not likely to remove the viewed constraints relating to efficiency and harshness of the dehulling process. The reference value is that obtained from seeds hulling by foot-pressing. A designed equipment that provides a value of dehulling index closed to 0.93 will be acknowledged by the interviewed processors. The dehulling rate remains one of the reference parameters for dehulling operation. Most of afitin processors estimate that the dehulling process is perfect when all the hosted seeds are shelled at 100%. For these surveyed afitin processors, acceptable minimal value of hulling rate is 90%. They justify it as the limit condition not to accumulate many losses, but rather to be able to make the hulling activity profitable in the afitin field. In practice, African locust bean seeds which are not shelled through a first crushing are annealed and crushed again

 

Table 2. Limits and reference values of dehuller’s performance parameters

Item	Minimum accepted value	Référence value	Maximum accepted value	Score (%)
Dehulling index (-)	0.85	0.93	1	90.04
Dehulling rate (%)	90	95	100	91
Breaking rate (%)	0	5	10	89.4
Dehulling yield (%)	40	48	60	78.6
Throughput (kg/h)	500	800	1,000	75

 

The breaking rate is a decisive factor for characterizing the dehulling operation. In the processors opinion, its particularity resides in the fact that it occupies a very important place in the requirements of consumers. Indeed, the consumers emphasize that they are looking for traditional alike afitin exhibition made of whole cotyledons. They also think that, when the breaking rate is high, many losses are recorded during sorting phase in the succeeding bath using earth-bar. They justify these losses by the fact that, broken cotyledons, in mix with mud and hulls, are therefore difficult to recover. On the other hand, whole cotyledons and some broken, float on surface of the earth-bar bath and are then easily recovered using a convenient basket. For majority of the surveyed afitin processors, a value of breaking rate between 0 and 10% is considered as acceptable. The reference value of breaking rate is of 5%.

 

The dehulling yield is admitted within interval limits of 40 to 60% by majority of the surveyed afitin processors: 78.6%. The latter fraction consider that, if their requirements related to limit values of the dehulling rate and breaking rate are met, it’s then possible to remain within. A dehulling process, that provides a yield’s value of less than 40%, causes to afitin processors a lot of shortfall. They are very demanding on this parameter, especially during periods of high cost of ALB seeds (90,000 FCFA a bag of 100 kg against 45,000 FCFA usually). The reference value for feet dehulling process is 48%. The introduction of power-motorized equipment to improve the traditional method aimed, among other things, at reducing the workload and increasing the productivity in afitin field. Just like the corn mills and condiment mills, a locust bean dehulling machine, to be profitable, must be introduced in form of services delivery. It must have a significant capacity of processing the whole quantity of the produced locust bean seeds by groups and villages. These considerations motivated the respondents to choose the limit values of output capacity between 500 kg/h and 1,200 kg/h, i.e. 12.5 to 30 basins of 40 kg in one hour.

 

3.2 Effect of the gap between the grids on theoretical value of dehulling rate:

On figure 3 were disclosed the results of effect studying of theoretical gap, between mobile and fixed grids, on the dehulling rates. Analysis of the results shows that, when the inter-grids gap adjustment increases from 1.5 to 11 mm, theoretical values of the dehulling rate increase too from 0 to 100%. However, technological conditions impose that the dehulling rate must take its values in the following interval: [minimal = 90; maximal = 100%] as previously shown in Table 2. These interval’s limit values, are theoretically delivered by values of the inter-grids gap adjustment between 3 and 11 mm. An inter-grids gap value established to 3.75 mm, marked by B-point on figure 3, permit to obtain reference value of the dehulling rate: 95%. The evolution of  the dehulling rate (T_{D %}) as function of  grids gap (x; mm) can be described adequately by equation of the obtained trend curve, a polynomial function of degree 3 expressed by:

 

T_Dt= 0.779x³-16.64x²+113.21x-143.58 (%)   R² = 0.95                                                                                                    (7)

 

Figure 3: Evolution of theoretical dehulling rate versus inter-grids gap adjustment

 

3.3 Effect of the inter-grids gap adjustment on theoretical value of breaking rate 

 

Figure 4: Evolution of theoretical breaking rate versus inter-grids gap adjustment

 

The figure 4 shows results of effect studying of theoretical gap between the mobile and fixed grids on the breaking rates. Analysis of the results on figure 4 shows that when the grids gap adjustment varies between 0 and 11 mm, the breaking rate decreases 100% to 0%. The evolution of  breaking rate (T_{Bt %}) as function of inter-grids gap (x; mm) can be described adequately by equation of the obtained trend curve, a polynomial function of degree 4 expressed by:

 

T_Bt= 0.2527x⁴-6.747x³+64.486x²-259.55x+368.69                R²=0.966.                                                          (8)  

 

A grids gap, ranging between 3.5 and 11 mm, allows theoretically obtaining the recommended limit values of dehulling rate (T_Dt) and breaking rate (T_Bt). However, these values are determined from frequency of the seeds thickness. They do not take into account the effects of friction and seed-to-seeds shocks during hulling process. Taking effects of these factors into account could conduct to inter-grids gap effective value and locate it between theoretical and real. The experimental study will make it possible to determine the extent of this difference. Also, the technical behavior of dehuller when the gap adjustment is greater than 11 mm is not known. Experimentation will provide clarifications on these aspect.

 

3.4 Effects of the inter-grids gap adjustment on experimental values of dehulling and breaking rates

The figure 5 shows the influences of change of the gap between the fixed and mobile grids respectively on the dehulling and breakage rates. Analysis of these results shows that when the grids gap varies between 0 and 25 mm, the dehulling rate of seeds decreases from 100 to 0% while the breaking rate from 50.83% to 0%. Moreover, the gap adjustment in limits of 5 and 15 mm makes it possible to already obtain the beheld values for both these two performance parameters.

 

 

Figure5.Evolutions of dehulling and breaking rates versus the inter-grids gap adjustment

 

As previously displayed in Table 2, technological conditions require a dehulling rate located between 90 and 100% and a breakage rate of less than 10%. A setup of the inter-grids gap between 5 and 15 mm allows the manufactured equipment to comply with these conditions. However, adjustment of inter-grids gap value to 9 mm gives the best performance with dehulling rate of 99.1% and breaking rate of 1.33% respectively. These experimental results are very closed to those obtained theoretically which recommends an inter-grids gap value located between 3.5 and 11 mm. The evolutions of experimental dehulling rate (D_re) and breaking rate (B_{re; %}) as function of setting gap (x; mm) can be described adequately by equations of the obtained trend curves, a polynomial function of degree 2 and 4 respectively expressed by:

 

-T_De = -0.3824x²+6.6372x+74.017; R²=0.965                                                                                                                                                                                      (9)

-T_Be= 0.0032x⁴–0.2027x³+4.5496x²–42.252x+136.76;         R²=0.9 (10)

 

3.5 Effects of the inter-grids gap adjustment on the experimental value of dehulling index

The figure 6 illustrates the obtained results for the effect study of the inter-grids gap setup on the dehulling index of the devised machine. Those data showed that when the inter-grids gap varies from 3 to 25 mm, the efficiency index takes values from-0.7 to 0.97. If the reference value varies between 0.85 and 1, then the values of inter-grids gap that allows assessing to these are located between 5 and 15 mm. The highest value of dehulling index equal to 0.97 is obtained when the grids gap is adjusted to 9 mm.

 

This value is close to those provided by geometrical and arithmetic diameters of the African locust bean seeds cooked for 4 hours: respectively 8.47±1.0 mm and 8.84±0.98 mm as resulting from characterization studies. [19, 23] The chaotic movements of seeds on the grids (fixed and mobile) favor efficient husking of seeds in spite of the fact that, thesetup value for inter-grids gap is greater than the average thickness of seeds evaluated at 5.86 mm. [19, 23] When the space is greater than 15 mm, the gap between the two grids becomes larger. It can no longer ensure the pressure and friction necessary for an efficient dehulling, resulting gradually in dropping of the dehulling index. For the dehulling index (Die), obtained model was rather a second order polynomial function expressed as:

 

Die= -0.0084x2+0.1586x+0.2827; (11) R²=0.952                                                                                                                                                                                     (11)

 

 

Figure 6. Evolution of dehulling index versus the inter-grids gap

 

3.6 Effects of inter-grids gap adjustment on the dehulling yield

 

Figure 7. Evolution of dehulling yield versus the inter-grids gap adjustment

 

The effect of dehuller inter-grids gap adjustment on the dehulling yield is illustrated in figure 7. The analysis of these disclosed results confirms the trends obtained in the two preceding paragraphs. The inter-grids gap adjustment, in interval of 5 to 15 mm, allows obtaining the recommended values for dehulling yield which must be situated between 40% and 60%. In addition, a setup gap of 9 mm makes it possible to reach the maximal value of the husking yield. A gap value, greater than 15 mm, no longer provides good dehulling due to the weakness of the friction-forces, and resulting at that time in progressive reduction of the dehuller yield. The evolution of the dehulling yield (D_{ye; %}) as function of gap adjustment (x; mm) can be described adequately by equation of the obtained trend curve, a polynomial function of degree 2 expressed by:

 

D_ye= -0.2991x²+6.3159x+24.843; R²=0.9                         (12)

 

The 9 mm-gap adjustment, coupled with a rotating speed of the mobile grid of 666 rpm, and hopper opening diameter of116 mm, permit to obtain a throughput value of 773 kg/h. [22] These reached values are better than those of author [1] who published a value of dehulling rate of 98% with an hourly capacity of 10 kg/h of cooked seeds. Authors [27]  have previously obtained a lower result with an hourly capacity equal to 208 kg/h on their hulling machine tested using dry seeds of African locust bean [21] in Nigeria and [31] in Burkina Faso have respectively obtained dehulling index values of 29% and 28% on their developed decorticators. That from Burkina-Faso was developed by the assistance of CIRAD and tested by the Department of Food Technologies (DTA) of IRSAT. The constraint that emerges from this result is the ease of adjustment, especially in real environment, to respect this value of inter-grids gap. A direct reading table of the adjustment set must be introduced on the equipment to facilitate adjustment to the operator.

 

The experiments reported in this study made it possible to determine the optimal values of the adjustment gap between the fixed and mobile grids. The dehulling machine, designed for African locust bean, performs well when the seeds are cooked, especially for 4 hours, and the setup values for gap between the hulling grids are in the range of 5 mm to 15 mm. The best performance parameter values are obtained when adjustment of the gap is fixed at 9 mm. These results remain experimental and the real-world tests on production sites of afitin will have to be made to confirm these results.

 

4. CONCLUSION:

The experiments reported in this study made it possible to determine the optimal values of the adjustment gap between the fixed and mobile grids. The dehulling machine, designed for ALB, performs well when the seeds are cooked, especially for 4 hours, and the setup values for gap between the hulling grids are in the range of 5 mm to 15 mm. The best performance parameter values are obtained when adjustment of the gap is fixed at 9 mm. These results remain experimental and the real-world tests on production sites of afitin will have to be made to confirm these results.

 

5. ACKNOWLEDGMENT:

The authors would like to thank processors of African locust bean into afitin of Avrankou, Adjarra, Abomey, Porto-Novo, Sakété, and Saclo cities for active participation to this study. They send their words of gratitude to the authorities, respectively of the University of Abomey-Calavi, and Benin State, for funding the study through entitled project: '' Biodiversity and agro-food valorization of nere (Parkia biglobosa) in Benin.

 

6. NOMENCLATURE:

B_re   : Breaking rate

T_D    : Dehulling Rate

M_H  : Mass of hulls

x     : Setting gap

T_D   : Dehulling rate

D_ie,  : Dehulling index variation

D_{ye;           :} Experimental dehulling yield

I_D      : Dehulling Index

T_B    : Broken cotyledons Ratio

M_B   : Mass of broken cotyledons

D_re  : Experimental dehulling rate

T_br   : Theoretical values of the breakage rate 

M_U  : Mass of un-hulled or partially hulled seeds

R_D    : Dehulling Yield

T_dt    : Theoretical values of the hulling rate

X_n    : Number of seeds having half-thickness less than the adjusted gap value

Y_n    : Number of seeds having half-thickness greater than the adjusted gap value

V_n    : Number of cotyledons having half-thickness less than the adjusted gap value;

W_n   : Number of cotyledons having half- thickness greater than the adjusted gap value

 

7. REFERENCES:

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Received on 17.07.2018            Accepted on 19.08.2018            ©A&V Publications all right reserved Research J. Engineering and Tech. 2018;9(3): 241-252. DOI: 10.5958/2321-581X.2018.00033.8