Nutritional composition of five food trees species products used in human diet during food shortage period in Burkina Faso

Laboratoire de Biologie et d’Ecologie Végétales, UFR Sciences de la Vie et de la Terre, Université de Ouagadougou, 03 B.P. 848 Ouagadougou 03, Burkina Faso. Département Technologie Alimentaire/Institut de Recherche en Sciences Appliquées et Technologies, 03 BP 7047 Ouagadougou. Institut de l'Environnement et de Recherches Agricoles, BP 10 Koudougou, Burkina Faso. Département de Biochimie/Microbiologie, Laboratoire de Biochimie Alimentaire, Enzymologie, Biotechnologie Industrielle et Bioinformatique, UFR Sciences de la Vie et de la Terre, Université de Ouagadougou, 03 B.P. 848 Ouagadougou 03, Burkina Faso. Embrapa Amapa Rodovia Juscelino Kubitschek, km5, N°2600CEP 68903-419 Caixa Postal 10 Macapa, DF68906-970 BR Brazil.

. In several African countries, natural tree products constitute an important part of human diets and are also an important source of income (Falconer, 1990;Shackleton et al., 1998;Ayessou et al., 2009;Lamien et al., 2009).They are excellent source of minerals and vitamins; and also contain carbohydrates in form of soluble sugars, cellulose and starch (Nahar et al., 1990;Ayessou et al., 2009;Lamien et al., 2009).Mainly crudely consumed, they improve the daily food ration as an energy source and through their content in micronutrients (Parkouda et al., 2007;Ayessou et al., 2009;Kouyaté et al., 2009).Indeed in Africa, they constitute the most affordable and dietary sources of vitamins, trace elements and other bioactive compounds.Thereby, they form common ingredients in a variety of traditional native dishes for the rural population in developing countries (Humphrey et al., 1993).Consumption of indigenous trees products is among strategies to supplement diets (Falconer, 1990;Ayessou et al., 2009;Thiombiano et al., 2012).Several tree products which play pivotal role exist but undervalued and are seasonal (Ambé, 2001;Ayessou et al., 2009).Studies identified some of these food tree species (Arbonnier, 2004;Lamien et al., 2009;Thiombiano et al., 2012) and initiated studies of their nutritional potential (Glew et al., 1997;Parkouda et al., 2007;Ayessou et al., 2009;Kouyaté et al., 2009;Compaoré et al., 2011).However, most of these products have received little research attention, particularly their nutritional compositions.Their contribution to local diets is less understood and quantified.Therefore, the study was done to determine the proximate composition, minerals and amino acids content of five top wild trees products consumed during food shortage by rural population in Burkina Faso.

Proximate composition
Proximate analysis of samples was conducted using the conventional procedures described by the Association of Official Analytical Chemists (AOAC, 2005): Dry matter by drying at 105°C overnight, ash by incineration at 550°C for 12 h, crude protein (N × 6.25) by the Kjeldahl method and crude fat content by Soxhlet extraction using n-hexane.Metabolizable energy values (kcal/100 g) were calculated by multiplying the grams of protein, fat, and carbohydrate by the factors of 4, 9, and 4 kcal/ g, respectively.The pH was established using HANNA pH-meter (Hanna HI 991300) at 25°C.Titrable acidity was determined by titrating 2.0 g of samples in 100 ml of water with 0.1 M NaOH using phenolphthalein as the indicator and was calculated as percentage citric acid.The total sugars were measured according to the sulfuric orcinol method as described by Montreuil and Spik (1969).

Mineral content
Mineral elements of the samples were determined according to procedures described by Walinga et al. (1989).The sample (1 g) was digested with 4 ml of a mixture (ratio 7:1) of perchloric acid (HClO 4 , 60%) concentrated sulfuric acid and 15 ml of concentrated nitric acid.After complete digestion, the product was cooled, filtered and the volume adjusted to 50 ml.For determination of calcium, 0.2 ml of the filtered solution was diluted with 4.8 ml of lanthane (La 2 O 3 , 1%).For the other minerals, the dilutions were made with distilled water.Potassium was measured using a flame photometer (Corning 400, Essex, England); phosphorus was determined with a Skalar auto analyzer (Skalar, Breda, The Netherlands) and all other minerals with an atomic absorption spectrophotometer (Perkin Elmer Analyst 100).

Amino acids
The profile and the amount of total amino acids were determined by reverse phase HPLC, using the Pico-Tag system described by Bidlingmeyer et al. (1984).Samples were first defatted and hydrolyzed.For hydrolysis, 0.4 g of defatted sample placed in a flask and 15 ml of 6 M HCl added and the whole placed in an oven at 110°C for overnight.The sample are subsequently cooled to room temperature and transferred to a 50 ml volumetric flask and filled with Milli-Q water.Approximately, 1 ml of the diluted solution is homogenized and filtered through a filter of 0.45 µm.An aliquot of 10 µl of the solution is placed in reaction tube and dried for 15 min with the Picotag Workstation.The sample was then re-dissolved in 10 µl of re-drying solution (ethanol: water: triethylamine, 2:2:1 volume).They were dried again for 15 min and finally derivatized with 20 µl phenylisothiocyanate reagent (ethanol: water: triethylamine: phenylisothiocyanate, 7:1:1:1) for 20 min at room temperature.Excess reagent was removed with the aid of vacuum for 45 min in Pico-Tag Workstation.Derivatized samples were dissolved in 100 µl PicoTag Sample diluent solution (WAT088119).Analysis (identification and quantification) of amino acids performed using a Waters C18 column under the conditions described by Bidlingmeyer et al. (1984).
Briefly, 40 µl of aliquot was injected onto the column.Quantitation of amino acids was performed using a Waters C18 column (3.9 × 150 mm) with gradient conditions as described elsewhere.Derivatized amino acids were eluted from the column with increasing concentrations of acetonitrile.The eluate was monitored at 254 nm and the areas under the peaks were used to calculate the concen-   trations of the unknowns using a Pierce Standard H amino acid calibration mixture (Rockford, IL).

Data analysis
Data were computed in Excel and analyzed with XLSTAT version 7.5.2.Statistical analysis was focused on principal component analysis (PCA) and analysis of variance (ANOVA).These analysis were performed with the software "XLSTAT Version 7.5.2"with a risk of error p = 5%.

RESULTS
The  seeds are reported in the Table 4.

Proximate composition and energy value of the food tree species
In general, variability in the chemical content are reported to be dependent on soil (habitat), climatic variations, genetic factors, maturity and the storage conditions of the samples as reported elsewhere by Chadare et al. (2009); Diop et al. (2005); Osman (2004).The ash content of the pulp of A. digitata in a current study is similar with the 4.97±0.02reported by Compaoré et al. (2011) in an earlier study in Burkina Faso.For the pulp of P. biglobosa, the value found was similar to the value reported by Compaoré et al. (2011).The ash content of the fruits of D. microcarpum is fairly similar to 3.04 to 3.1 reported by Parkouda et al. (2007).For G. erubescens, the ash content (2.54±0.08)found was lower than that of the value (3.69-4.56)reported by Parkouda et al. (2007).The leaves of A. digitata had ash content (11.76±0.1) between the values of 8 and 16 g/100 g reported by Diop et al. (2005).
Statistically, the protein content of the products analyzed was significantly different.Among the studied products, A. digitata leaves and B. senegalensis seeds had good level of protein (Table 1) and B. senagalensis seeds can be considered as potential source of protein.The leaves of A. digitata protein content is similar to that value (10.3 to 15 g/100 g) reported by Diop et al. (2005) but higher than the value (10.3 g/100 g) found in an earlier study in Burkina Faso by Glew et al. (1997).The pulp of A. digitata has protein content lower than that of the value (5.23±0.03)reported by Compaoré et al. (2011).The protein content of P. biglobosa pulp was similar to the result reported by Parkouda et al. (2007) and lower than the value (5.37±0.07)reported by Compaoré et al. (2011).The B. senegalensis seeds proteins content is higher than the value (20.62) reported by Parkouda et al. (2007).The protein content of D. microcarpum fruits pulp are similar to the value reported by Kouyaté et al. (2009) but higher than the value (2.86) found earlier in Burkina Faso by Parkouda et al. (2007).As shown in Table 1, the lipids content ranged between 1.11±0.08 to 4.65±0.12with the B. senegalensis seeds having the lowest value while the leaves of A. digitata had the highest content.Apart from A. digitata leaves, all the samples had fairly similar content of lipids.The P. biglobosa and A. digitata pulps lipids content are similar to the results reported earlier by Compaoré et al. (2011).D. microcarpum and G. erubescens pulp had lipid levels about ten times higher than previous study (Parkouda et al., 2007) who reported value of 0.1%.Lipid content of B. senegalensis seeds is similar to the previous reported by Parkouda et al. (2007) but lower than the value (3.7±0.8 g/100 g) reported in B. senegalensis seeds study in Niger by Kim et al. (1997).The leaves of A. digitata have a fat content between the values (2.3 to 10 g/100 g) reported by Diop et al. (2005).
The pulp of P. biglobosa and A. digitata from this study had higher levels than those reported by Compaoré et al. (2011) who found respectively 67.66±0.05 and 67.8±2.1.The pulp of D. microcarpum and G. erubescens had total carbohydrates content lower than those reported by Parkouda et al. (2007) while the B. senegalensis seeds had total carbohydrates content similar to that found by Parkouda et al. (2007).The total carbohydrates content of the A. digitata leave found (57.04±1.59) between the values (13.8 to 70) reported by Diop et al. (2005).The value of calculated metabolizable energy was comprised between 41.9 to 351.9 kcal/100 g.The metabolizable energy found in A. digitata pulp is lower than the value (320.3±4.4 kcal/100 g) reported by Osman (2004)

Physical parameters of aqueous fruit pulp
The most acidic was S. senegalensis and this may be responsible for the sour taste of this pulpy fruit.The low level of acidity in the V. paradoxa pulp can be explained by the fact that they do not contain enough free organic acids.Organic acids play an important role in the sensorial quality of product because the flavor is essentially a balance between sugar content and acidity (Neta et al., 2007).Indeed sugars and organic acids are two parameters used as indicators of maturity or ripeness of the fruit (Mahmood et al., 2012).

Mineral content of food tree species
The wide differences found in the chemical content of the current study can be attributed to soil (habitat), climatic variations, genetic factors, maturity and the storage conditions of the samples as reported by Chadare et al. (2009); Diop et al. (2005); Osman (2004).The pulp of A. digitata and P. biglobosa had higher levels of manganese compared to the report of Compaoré et al. (2011) who reported 0.6 and 78.5 mg/kg, respectively.The manganese content of the leaves of A. digitata is higher than the value 31 to 89 mg/kg and 31 mg/kg, respectively, reported by Diop et al. (2005); Glew et al. (1997).The iron content of the A. digitata pulp and P. biglobosa pulp are lower than those (149 mg/kg and 1030 mg/kg) respectively reported by Compaoré et al. (2011).The Iron content of the leaves of A. digitata was between the values (150 to 490 mg/kg) reported by Diop et al. (2005).The iron content of V. paradoxa pulp and D. microcarpum pulp are higher than those reported by Parkouda et al. (2007) respectively 45.8 and 61.5 mg/kg.The iron content of seeds of B. senegalensis was much higher that the values of 31.2 and 44.1 to 61.1 mg/kg reported respectively by Parkouda et al. (2007); Kim et al. (1997).This difference may be due to the processing methods applied by processors before storage; indeed collected seeds are generally extracted exhaustively with water to remove bitter components and possible toxic substances (Kim et al., 1997).
The zinc content of the leaves of A. digitata is lower than that reported by Glew et al. (1997); Diop et al. (2005) who found respectively 18.7 and 19 mg/kg.The pulp of P. biglobosa had a zinc content lower than that of (30.1 mg/kg) reported by Compaoré et al. (2011) while the zinc content of A. digitata was higher than that of the value (15.4 mg/kg) reported by Compaoré et al. (2011) and 18 mg/kg reported by Osman (2004).The zinc content of seeds of B. senegalensis and pulp of V. paradoxa are lower than those reported by Parkouda et al. (2007) respectively 33.5 and 22.3 mg/kg.The pulp of A. digitata and P. biglobosa had copper contents much lower than those values (67.3 and 252 mg/kg) reported by Compaoré et al. (2011).Osman (2004) reported value of 18 mg/kg for the A. digitata pulp.The copper content of the leaves of A. digitata was between the value (1 to 12 mg/kg) reported by Diop et al. (2005).The calcium content of P. biglobosa pulp are similar to the value (1.1 g/kg) reported by Compaoré et al. (2011).The calcium content (2.49 g/kg) of the pulp of A. digitata is similar to the value (2.9 g/kg) reported by Osman (2004) but lower than the values (3.1 g/kg) reported by Compaoré et al. (2011).For the leaves of A. digitata the value found (14.34 g/kg) is comprised between the values (3.1 to 40.2 g/kg) reported by Diop et al. (2005).The calcium content senegalensis), as a source of metabolizable energy (D. microcarpum, pulp of P. biglobosa and A. digitata) or minerals.Nutritionally, these products could contribute positively to the minerals intake.Most of the minerals determined are essential elements for normal body functioning.During food shortage period, consumption of these products will help to overcome nutrients deficiency in urban and rural areas.

Table 1 .
Proximate composition (g/100 g DM) and energy value (Kcal/100 g DM) of dried products of tree species.

Table 2 .
Physical parameters of aqueous fruit pulp.
a Values are Mean ± Standard Deviation for at least 6 samples in duplicate.Values with different letters in the same row are significantly different at P < 0.05.

Table 3 .
Minerals content of samples.
aValues are Means for at least 3 samples in triplicate.Values with different letters in the same row are significantly different at P < 0.05.

Table 4 .
Amino acids profiles of Adansonia digitata leaves and Boscia senegalensis seeds (mg/g of proteins).
proximate composition and Energy value, Physical samples.The leaves of A. digitata shown the highest content of lipids (4.65±0.12),while the seeds of B. senegalensis shown the lowest content (1.11±0.08).The results of the present study (Table3) revealed that the studied products are good source of minerals.The amino acids content of A. digitata leaves and B. senegalensis