Selected Physicochemical Properties of Flour from the Root of African Fan Palm (Borassus aethiopum)

Abstract

Chemical composition of African fan palm (Borassus aethiopum) root and some physicochemical properties of the flour obtained from the root were investigated. It was found that the root was relatively high, on dry weight basis, in protein content (13.41%), starch (65.12%), crude fibre (7.72%), and total phenolics (1.94%). The processing characteristics of the root showed that the flour fraction obtainable from it ranged from 14.7–16.3% (on whole root basis) while the energy value of the flour (17.23 KJ/g) was relatively high. The elemental composition of Borassus aethiopum root revealed that it was high in potassium (812.21 ppm) and phosphorus (736.33 ppm), while it was low in iron (8.23 ppm) and manganese (4.41 ppm). Elements such as copper, zinc, aluminum, and silicon were not detected. The functional properties of the root flour showed that it had relatively high water absorption capacity (241.24%), moderate oil absorption capacity (192.42%), moderate bulk density (1.22g/cm³), and foaming capacity (2.31%). The maximum solubility and swelling power of the root flour were 15.7 and 18.9%, respectively, at the highest temperature of 95°C. The pasting characteristics of the flour revealed that the peak viscosities at different concentrations were 260 B.U. (5%), 340 B.U. (8%), and 520 B.U. (10%), and these peak viscosities were attained after reaching 95°C. Other pasting characteristics of flour from Borassus aethiopum root revealed that the flour could be used in such composite applications as those flours from other crops (i.e., maize, cocoyam, water yam, and plantain).

Keywords:

• African fan palm
• Borassus aethiopum
• Physicochemical properties
• Root flour

INTRODUCTION

African fan palm (Borassus aethiopum) is a tall palm with huge fan-shaped leaves and has separate male and female trees. The female ones bear a number of fruits called nuts which, at maturity, normally contain a sweet sap usually taken as a refreshing drink while the male counterpart is naturally fruitless. The palm is widespread in West Africa particularly, in countries such as Nigeria, Senegal, Togo, and Guinea; it is mostly found in the wild, especially in marshy areas and by streamsides in the savannah and coastal regions.[1,2] The nut from the female palm also contains a maximum of three soft seeds[2] that can be eaten directly or when a seed is replanted it produces enlarged starchy root that is edible especially after boiling. The starchy roots are usually harvested after about 3 to 4 months of planting the soft seeds. The root is locally called “muruchi” in the Hausa language of the West-African sub-region. The root is normally cooked in order to improve its palatability and digestibility, while there have been instances when the root was consumed raw without cooking with no obvious health hazard. However, due to the fibrous nature of the fleshy part of the root, it is normally eaten when cooked, as this improves its flavour and taste. The root is usually eaten as a snack, while the raw roots can be stored for a year or more after harvesting provided it is stored under airy and dry environment at tropical ambient temperature. One major storage problem peculiar to Borassus aethiopum root is that of drying-out that usually occurs when the storage temperature is above 34°C for a substantial prolonged period.[3]

The utilization of the starchy roots of Borassus aethiopum is presently limited in Nigeria. Its food use has not gone beyond mere cooking for ultimate consumption, while it also serves as an article of commerce in the rural areas as a form of income-generating produce for the farmers. It has, however, been observed that the potential use of the starchy roots as a food and as an income-generating produce in the rural areas needs to be emphasized,[4] yet the exploitation of the utilization potentials of the roots has received little attention. For the utilization diversification of the roots to be practically feasible, therefore, there is the need to examine the physicochemical properties of the root and its flour, which is the general objective of this article.

MATERIALS AND METHODS

Acquisition of Materials

The roots of African fan palm (Borassus aethiopum) were obtained from Yola main market, Yola, Adamawa State, Nigeria. The roots were about 1 to 2 months old after harvesting when purchased.

Proximate Analysis

The moisture, crude protein, lipid, ash and crude fibre contents of freshly peeled root were respectively determined using the standard methods of analyses.[5] The quantitative determination of starch was carried out according to the colorimetric method of Dubois et al.[6] The content of other carbohydrates in the root was determined by difference by subtracting the sum of the percentages of crude protein, lipid, crude fibre, ash, and starch content from 100.

Elemental Composition

Two grams of dried and ground sample of Borassus aethiopum root were put in a porcelain crucible and then subjected to dry ashing in a muffle furnace set at 550°C. The resultant ash was dissolved in 5ml of HNO₃/HCl/H₂0 (1:2:3, v/v/v) followed by heating on a hot plate at the boiling temperature of the solution until brown fumes disappeared. Five millilitres of deionized water were later added to the remaining content in the crucible, and the mixture was heated until a colourless solution was obtained. The colourless solution was then filtered into a 100-ml volumetric flask using a Whatman No. 42 filter paper, and the volume made to the mark with deionized water. The concentration of the following elements: Ca, Mg, Mn, Zn, Al, Si, Fe, Li, and Cu was then determined from the filtered solution using atomic absorption spectrophotometer (Model SP9 Pye Unicam, UK), having initially prepared a standard curve for each element under investigation. The concentration of each element was calculated as mg/kg of sample (ppm).

The analysis of sodium and potassium concentrations of the sample was carried out using flame photometry while the phosphorous content of the filtered solution was determined colorimetrically according to the method described by Egan et al.[7] To 5 ml of the filtered solution in a 100-ml volumetric flask, 50 ml of deionized water was added followed by neutralization with a dropwise addition (2–4 ml) of 0.88 ammonia in order to attain a pH of 7.0. The mixture was then made just acidic with dilute nitric acid (1:2) followed by the addition of 25 ml vandate-molybdate reagent and then diluted to the mark. The solution was allowed to stand for 10 minutes and absorbance reading was recorded at 470 nm. The content of phosphorus in the filtered solution was determined using a standard curve obtained for potassium dihydrogen phosphate (KH₂PO₄) and expressed as mg phosphorus per kg of sample (ppm).

Phenolic Content

The method of Shahidi and Naczk[8] was used for the isolation of the phenolics. One gram (wet weight basis) of the fleshy part of the root was extracted three times with 10 ml of 70% (v/v) aqueous acetone at ambient temperature using a Polytron homogenizer (model PT3000, Kinematika AG, Littau, Switzerland) for one minute at 10,000 rpm. The slurry was centrifuged at 5000 × g for 10 minutes; the supernatants were collected, combined, and evaporated to dryness at 30°C under vacuum. The extracted phenolics were then dissolved in 25 ml of methanol, centrifuged again, and the content of phenolics in methanol was determined colorimetrically using the method of Swain and Hillis.[9] To 0.5 ml of a methanolic solution of phenolics, 0.5 ml Folin-Denis reagent, 1 ml saturated solution of sodium carbonate, and 8 ml distilled water were added and mixed properly. Absorbance reading was recorded at 725 nm after 30 minutes standing at ambient temperature. The content of phenolics was determined using a standard curve obtained for trans-sinapic acid and expressed as trans-sinapic acid equivalents, on a dry weight basis.

Amylose Content

The amylose content of the root was determined using the colorimetric method of William et al.[10] Twenty milligrams (20 mg) of dried and ground sample were weighed into a 100 ml beaker followed by the addition of 10 ml of 0.5N KOH solution. The mixture was then subjected to magnetic stirring for 5 minutes until fully dispersed. The mixture was transferred into a 100 ml volumetric flask and diluted with distilled water to the mark with careful rinsing of the beaker. Ten millilitres (10 ml) of aliquot of the test flour solution was pipetted into a 50 ml volumetric flask; 5 ml of 0.1N HCl was added followed by the addition of 0.5 ml of iodine reagent. The whole mixture was finally diluted up to 50-ml mark with distilled water and the absorbance value measured at 625 nm after 5 minutes standing with a spectrophotometer (Model 80–2088–64, Pharmacia Biotech.). The amylose content in the root was determined using a derived standard formula [ i.e., amylose content (%) = (85.24 × A) − 13.19 ]; where A = absorbance value.[10]

Physical Characteristics

The colour of the peel of freshly purchased Borassus aethiopum root was subjectively evaluated. The length of the root was measured using a fixed vertical measuring rule by which the root was made to stand vertically and the length measured. The diameters of the roundish and tapered ends of the root were respectively measured using a vernier caliper. The proportion of the peel with respect to the whole root was determined by weighing the peel having carried out the peeling manually.

Flour production from Borassus aethiopum root. The freshly purchased roots of Borassus aethiopum (of known weight) were first soaked in cold water for 3 hours so as to soften the peel and facilitate its removal. The peel was carefully removed manually from the soaked roots followed by thorough washing and draining. The peel-free roots were then individually cut longitudinally into two equal halves which facilitated easy removal of finger-like tissue from the centre of the root. The left-over was then cut into rectangular pieces (about 1 cm × 2 m) and then spread thinly in a force draught oven at 55°C for 12 hours to obtain root pieces at moisture content of about 10%. After drying, the pieces were then subjected to milling using a disc attrition mill (Agrico model 2A, New Delhi, India) followed by sieving using a sieve size of 425 microns to obtain the ultimate flour. The percent quantity of the flour obtained was measured in relation to the initial weight of the roots used for its production.

Calorific Value

The calorific value of Borassus aethiopum root flour was determined using the Gallenkamp adiabatic bomb calorimeter (Gallenkamp CBB-330–010L), while the result was expressed as KJ/g.

Bulk Density

The bulk density of the root flour was determined by the method described by Narayana and Narasinga.[11] The flour was loaded into a 50 ml-graduated cylinder and tapped to determine mass and volume.

Water and Oil Absorption Capacities

The water and oil absorption capacities of the flour were determined by the procedure of Beuchat.[12] The values were expressed as percentages of water or oil absorbed by the flour.

Foaming Capacity and Stability

The procedure of Coffman and Garcia[13] was used. The percentage volume that increased immediately after whipping was used for capacity while that of stability was after 2 hours of standing, using 2% (m/v) flour concentration.

Viscosity

This was determined by methods as described by Beuchat[12] and Tagodoe and Nip.[14] Flour was dispersed in distilled water at 2.0 and 2.5% concentration using a magnetic stirrer at 1000 rpm and heated to 100°C in a waterbath for 30 minutes. The hot slurry obtained was stirred constantly and cooled at 20°C. The viscosity was measured using a rotary viscometer (Model LV-2020, Cannon, Pennsylvania, USA).

Swelling Power and Solubility

These were determined by a method as described by Schoch.[15] A weighed flour sample with known moisture content was mixed with a measured volume of distilled water and heated at varying temperatures of 55°, 65°, 75°, 85°, and 95°C respectively in a temperature controlled water bath for 30 minutes with intermittent stirring. After heating, the slurry was centrifuged, the clear supernatant drawn off and evaporated to dryness on steam bath to obtain a measure of the dissolved solids. The sedimented flour obtained after centrifugation was weighed to get the weight of the swollen flour particles. The values were expressed as percentages of total dissolved solids (solubility) and total swollen flour particles (swelling power) with respect to the weight of the flour sample used.

Pasting Properties of Borassus Aethiopum Root Flour

The pasting properties of the flour were evaluated using Brabender visco/amylograph. Flour slurry of 5%, 8%, and 10% solids (w/v, dry basis) were respectively prepared and each was gradually heated from 30°C to 95°C at the rate of 2.5°C/min., held at this temperature (95°C) for 15 minutes, cooled down to 50°C and finally held at this temperature for another 15 minutes.

Statistical Analysis

All determinations and /or measurements reported in this study were carried out in triplicates. In each case, a mean value and standard derivation were calculated. Analysis of variance (ANOVA) was also performed and differences in mean values determined using Duncan's test at p < 0.05 by employing ANOVA and Duncan procedures of statistical analytical systems.[16]

RESULTS AND DISCUSSION

The proximate composition of freshly peeled Borassus aethiopum root is presented in Table 1. The moisture content of the root was found to be relatively high (55.52%) but lower than that observed for fresh cassava root[17] and potato root.[18] The root was also found to be high in crude protein (13.41%), crude fibre (7.72%), and ash content (5.63%). The high protein content of the root implies that it can meet adult protein requirements[19] unlike most other root crops such as cassava as potato. The starch content (65.12%) in the root (on dry weight basis) compared favourably with other starch–containing crops such as cereals, potato, and cassava roots. The other carbohydrates, most likely made up of reducing and non- reducing sugars, constituted about 6.13% (dry weight basis) of the root. The lipid content of the root is low (2.13%), and this is typical of most root crops such as cassava and potato respectively.[17,20] The root was found to be high in total phenolics (1.94%). This high phenolic content is responsible for the bitter taste of the root after cooking coupled with the empirical observation that the root possesses a stimulating effect when consumed. It has, however, been observed that the higher content of phenolics may affect the nutritional value of the root as these and their oxidation products have a high tendency of interacting with free amino acids thereby making them nutritionally unavailable.[21] The starch amylose of the root (18.31%) was found to compare favourably with that of most other starch-containing crops such as maize, rice, and potato—of which amylose content usually falls within a range of 17–30% of the total starch.[22]

Table 1 Chemical composition of freshly peeled Borassus aethiopum root (% edible portion) ¹ .

Constituent	% Composition
Moisture content	55.52 ± 1.13
Crude protein (gN × 6.25)	13.41 ± 0.12
Lipid	2.13 ± 0.08
Crude fibre	7.72 ± 0.16
Ash	5.63 ± 0.11
Starch	65.12 ± 1.17
Other carbohydrate (by difference)	6.13 ± 1.14
Amylose	18.31 ± 2.19
Total phenolics	1.94 ± 0.18
^1Results are mean values of triplicate determination ± standard deviation. Results other than moisture content are on a dry weight basis.

The physical and processing characteristics of Borassus aethiopum root are given in Table 2. The root normally has a slightly bulb-like shape with the roundish end having a diameter range of 35.2–63.5 mm, while that of the tapered end was 18.5–27.8 mm. The total length of the root ranged from 112.2–165.5 mm, while the observed colour of the root ranged from brown to slightly dark brown. The peel fraction in the root was found to range from 0.73–1.34%, while the flour fraction (10% m.c., 425 microns) obtainable from the root was 14.71–16.34% (whole root basis). The calorific value of flour from the root was found to be 17.23 KJ/g. This implies that since the daily energy requirement for adults ranges between 10,000–12,600 KJ, depending on their physiological status,[23,24] an adult would require about 656 g of flour from African fan palm root to meet his average daily energy requirement.

Table 2 Physical and processing characteristics of Borassus aethiopum root.

Parameter	Observation/measurement
Colour of the root	Brown to slightly dark brown
Length of the root (mm)	112.2–165.5
Diameter of the roundish bottom (mm)	35.2–63.5
Diameter of the tapered end (mm)	18.5–27.8
Peel fraction of the root (%, whole root and wet basis)	0.73–1.34
Flour fraction of the root (%, whole root and wet basis)	14.71–16.34
Calorific value of the root flour (KJ/g)	17.23 ± 1.27

The mineral composition of Borassus aethiopum root is shown in Table 3. It was found that potassium (812.21 ppm) was the most abundant mineral present in the root followed by phosphorous (736.33 ppm), while minerals such as copper, zinc, aluminum and silicon were not detected. In general, the concentration of mineral elements in Borassus aethiopum root is relatively lower than those found in other root and tuber crops such as potato, cassava, and yam.[25] It has, however, been observed that the mineral composition of a food crop is directly related to its genetic origin, geographical source and soil conditions.[21]

Table 3 Elemental composition of Borassus aethiopum root ¹ .

Element	Composition (ppm)
Ca	242.11 ± 1.13
Mg	330.14 ± 1.35
P	736.33 ± 1.47
K	812.21 ± 1.15
Na	90.52 ± 0.43
Fe	8.23 ± 0.08
Mn	4.41 ± 0.05
Cu	ND ^2
Zn	ND
Al	ND
Si	ND
^1Results are mean values of triplicate determination (on dry weight basis) ± standard deviation. ^2ND = Not detected.

The functional properties of flour from the root of African fan palm are as shown in Table 4. The water absorption capacity of the root flour was 241.24%. This value is relatively high, and the flour may be relevant in certain food processing applications as a thickener. The water absorption capacity of flour has been observed to be dependent on the starch and protein concentration in the material coupled with the size of the particles.[26] Generally, the water absorption characteristics of the root flour is very important depending on the ultimate product to which the flour is intended to be converted which may include snack foods, extruded foods, and in bakery products.

Table 4 Functional properties of flour from the root of Borassus aethiopum ¹ .

Functional property	Measurement
Water absorption capacity (%, m/m)	241.24 ± 3.37
Oil absorption capacity (%, m/m)	192.42 ± 2.35
Bulk density (g/cm^3)	1.22 ± 0.13
Foaming capacity (%)	2.31 ± 0.09
Foaming stability, after 2 hr (%)	0.0
Viscosity (2% flour, centipoise)	53.91 ± 0.16
Viscosity (2.5% flour, centipoise)	87.53 ± 0.22
^1Results are mean values of triplicate determination ± standard deviation.

The oil absorption capacity of the root flour was 192.42%. Good oil absorption capacity of flour predisposes it towards being useful in food preparations that require oil inclusion such as in bakery products. The oil absorption capacity of the root flour was found to be higher than that of most oil seed flours including full fat fluted pumpkin seed flour,[27] lipid seed flour,[28] and winged bean flour.[29] However, it had lower oil absorption capacity than plantain flour.[30]

The bulk density of the root flour was 1.22 g/cm³ implying that it might have packaging disadvantages as less weight would be packaged in a specific volume of container in comparison with flour (similarly obtained using a sieve size of 425 microns) from crop such as maize having a bulk density as high as 2.34 g/cm³.[31] It has, however, been observed that the functional properties of flour from root crops such as cassava could be influenced by the temperature of drying in the course of processing.[32] These functional properties include bulk density, gelation capacity, water absorption capacity, swelling index, and viscosity.

The foaming capacity of the flour (2.31%) and the foaming stability after two hours (0.0%) were found to be relatively poor when compared with higher values obtained for flours from taro, sunflower and Cajanus cajan.[30] Therefore, Borassus aethiopum root flour is not a good foaming agent and may not find any useful application in aerated foods.

The viscosity of the root flour at 2.0 and 2.5% (w/v) were 53.91 and 87.53 centipoises respectively. The relatively high viscosity value for the root flour has predisposed it towards not being appropriate in the preparation of a high nutrient density weaning food that requires a relatively low viscosity material.[33]

The swelling power and solubility of the root flour are shown in Fig. 1. The result indicated that the flour exhibited practically no swelling between 55 and 65°C, but there was a considerable increase between 65 and 85°C, while the maximum swelling was obtained between 85 and 95°C. The relatively high swelling power of Borassus aethiopum root flour is most probably due to the low percentage of lipid in the flour and, by extension, the near- absence of amylose-lipid complex.[34]

Figure 1 Swelling and solubility pattern of flour from Borassus aethiopum root.

The solubility of the root flour being a function of temperature revealed that the flour had initial insignificant solubility (55°–65°C), while there was a gradual increase in the solubility between 65 and 75°C. Highest solubility was however obtained at a higher temperature (85°–95°C) that was 15.7%.

The pasting properties of Borassus aethiopum root flour at different concentrations are shown in Table 5. The apparent gelatinization temperature (T_a) and gelatinization time for the flour showed a corresponding decrease as the flour concentration increased from 5% to 10%. The apparent gelatinization temperature and gelatinization time at 5% concentration were 82.2°C and 21 minutes respectively, while at 10% concentration, the values were 76°C and 18.4 minutes, respectively. The apparent gelatinization temperature is essentially the temperature at which the swollen granules of a starch solution undergoing heat treatment begin to burst thereby making the solution to lose its birefrigent quality and usually occurs within a temperature range.[22] Therefore, a higher T_a at lower concentration may be due to a wider intergranular distance which permits less hindered granular movement resulting in delayed bursting of swollen granules. The peak viscosities of the flour were 260, 340, and 520 B.U. at 5, 8, and 10% flour concentration, respectively, while the viscosities at 95°C at these concentration levels were 250, 325, and 480 B.U, respectively. The peak viscosity of the flour at all concentration levels was attained after reaching 95°C, which implies that the ease of cooking the flour, in practice, will be low as the cooking cycle must pass through 95°C temperature for a peak viscosity to be attained. The stability/breakdown values of the paste during cooking were + 10, −5, and − 45 B.U. at 5, 8, and 10% concentration levels, respectively. This means that at 5% concentration the paste was relatively stable (positive value), while it has the tendency to breakdown (negative value) at a higher concentration. The setback produced when the paste was cooled from 95°C to 50°C at 5, 8, and 10% flour concentrations were + 85, + 300, and + 305 B.U., respectively. The setback value tends to increase with increasing concentration of the flour.

Table 5 Pasting characteristics of flour from the root of Borassus aethiopum at different concentrations.

	Concentration (%, w/v)
Brabender variable	5.0	8.0	10.0
Apparent gelatinization temp (°C)	82.2	78.1	76.0
Gelatinization time (min)	21.0	19.2	18.4
Peak viscosity, Vp (B.U) ^1	260∗	340∗	520∗
Viscosity at 95°C, Va (B.U)	250	325	480
Viscosity at 95°C after 15 min. holding, Vb (B.U)	260	320	435
Viscosity at 50°C, Vc (B.U)	345	640	825
Viscosity at 50°C after 15 min. holding, Vd (B.U)	315	614	768
Stability/ Breakdown of the paste during cooking, (Vb − Va) (B.U)	+10	−5	−45
Setback value, (Vc − Vp) (B.U)	+85	+300	+305
Stability index of the cooked paste in actual use, (%)	+21.2	+80.6	+47.7
^1B.U = Brabender Unit. ∗Peak viscosity was attained after reaching 95°C.

Fig. 2 shows the comparative pasting characteristics of flour (8%, w/v) from Borassus aethiopum root and that of starches (approximately 8%, w/v) from some common tropical crops including maize, cocoyam, plantain, and water yam. The apparent gelatinization temperature of Borassus aethiopum flour was about 78.1°C, while that of starches from other botanical sources were between 71.5°C and 80°C. The peak viscosity of Borassus aethiopum flour (340 B.U.) was reached after attaining 95°C similar to that of starches from maize, plantain, and water yam, except that of cocoyam whose peak viscosity was reached before attaining 95°C. The final viscosity of flour from Borassus aethiopum root gave a higher value than its corresponding peak viscosity and this trend was similarly observed for starches from above-mentioned tropical crops, respectively.[35] This implies that the stability index values of their respective cooked pastes in actual use were positive. The stability index is a measure of the difference between the final viscosity of the paste after stirring for 15 minutes at 50°C, and its peak viscosity during cooking. The pasting characteristics of flour from the root of African fan palm (Borassus aethiopum) therefore revealed that they compared favourably with starches from the above-mentioned tropical crops.

Figure 2 Comparative pasting characteristics of flour (8%, w/v) from Borassus aethiopum root and that of starches (approximately 8%, w/v) from some common tropical crops (Adapted from Rasper[35]).

CONCLUSION

The investigation has revealed that the utilization of African fan palm (Borassus aethiopum) root can go beyond the present use of mere cooking for ultimate consumption. Some of the physicochemical properties of its flour are pointing to the fact that the flour could be used in such composite applications as those flours from other crops (i.e., maize (Zea mays), cocoyam (Xanthosoma sagittifolium), plantain (Musa paradisiaca), and water yam (Dioscorea alata)). However, it has a peculiar attribute of being bitter, which may be desirable in some forms of utilization. Nevertheless, more work need to be carried out in order to actually confirm the potential uses of the root flour particularly in areas such as bread and biscuit manufacture using composite flour, as well as in extruded food formulation.

Notes

3. Bello, S.B. Utilization Potentials of Borassus aethiopum Root. Department of Food Science and Technology, Federal University of Technology, Yola, Nigeria, B.Tech Thesis, 1999.

23. FAO/WHO/UNO. Technical Report Series 224; World Health Organization (WHO): FAO, Geneva, 1985.

31. Olotu, V.A. Varietal influence of maize on the quality and acceptability of maize tuwo. Department of Food Science and Technology, Federal University of Technology, Akure, Nigeria, B.Tech. Thesis, 2004.