1. Introduction
Tree species play a significant role by contributing immensely to the food, income, and health needs of a large proportion of the population of Africa [1] [2] . Sub-Saharan Africa contains high flora of which many of the species are believed to possess high food and medicinal properties thereby contributing enormously to the food and health needs of the people [3] . Throughout Africa, wild tree products do not only contribute significantly to the food requirements of the majority of people but also to income security in rural areas where they are harvested for consumption and for sale to provide supplementary income for households [4] .
The genus (Pterocarpus) belongs to the family Fabaceae and the subfamily (Faboideae). More than 60 of the species are believed to exist in different parts of the world including Africa and Asia. Approximately 20 species are believed to be native to Africa [2] . The species (Pterocarpus erinaceus) commonly known as Barwood, African Kino, African rosewood, or African teak is an averaged-sized tree that grows up to the height of about 15 - 25 m. The crown is rounded but opens with long shoots bending toward the ground. The tree bole can be branchless or straight and can be up to 10 m high under good environmental conditions [5] [6] .
The plant is widely distributed across West and Central Africa and is specifically native to the following countries; Guinea, Gambia, Ghana, Benin, Senegal, Nigeria, and the Central African Republic [5] [7] . Rosewood is widely acclaimed to produce very high-quality timber for both local and foreign consumption. In recent years, the species is overly exploited in many Sub-Saharan African countries owing to the high demand for its timber and other related products in both local and international timber markets [2] [8] [9] .
Pterocarpus erinaceus foliage is known to provide excellent fodder for livestock. In many Sub-Saharan African countries, the foliage and immature pods of the plant are harvested for feeding livestock, especially during the dry season when livestock feed becomes increasingly scarce [1] [5] . In Sub-Saharan Africa, Pterocarpus erinaceus is known to be one of the most exploited plant species for traditional medicinal purposes. Various parts of the plant are harvested by traditional healers for the treatment of many ailments in many rural communities across Africa [8] . Leaves of P. erinaceus are used for the treatment of severe fever, the bark for the treatment of toothache and mouth-related diseases, and the exudates or resins are used for the treatment of stomach ulcers, diarrhea, dysentery, and intestinal worm infections. In North America and Europe, P. erinaceus was widely used for the treatment of chronic diarrhea until the middle of the 20th Century [1] [10] [11] . Figure 1 below depicts the image of P. erinaceus.
The nutritional composition of various leguminous tree species in Sub-Saharan Africa including P. erinaceus has long been studied and reported [2] [12] . Studies have indicated that plant nutrients such as proteins, carbohydrates, and fats are necessary to the lives of humans and all living organisms. Vitamins and minerals are equally essential for tissue functioning, the prevention of various diseases, and hormonal regulations [1] [13] . Proximate analysis of Pterocarpus erinaceus leaves revealed that the plant contains average nutritional attributes
such as Carbohydrates, Crude proteins, Crude fat, Fatty acid, Total ash, Crude fibre, Dry matter, and Moisture content [2] [5] [8] . The stem bark of Pterocarpus erinaceus is also known to produce moderate nutritive values of Carbohydrates, Proteins, Dry matter, and fats including essential vitamins and minerals [1] .
Studies have shown relative variations in nutritive values between fresh and dry leaves of some plant species [10] [14] [15] . P. erinaceus has been extensively used in traditional herbal medicine, the wood industry, and the livestock industry as one of the top browse species for livestock in Sub-Saharan Africa including Ghana [8] [10] [16] . Despite the extensive research on the nutritional, phytochemical, vitamin and mineral compositions of the leaves and bark of the plant [1] [2] , presently there is insufficient information on the nutritive composition between the fresh and dry leaves of the plant. This study was therefore conducted to provide information on the proximate composition between the fresh and dry leaves of P. erinaceus.
2. Materials and Methods
2.1. The Study Area
The study was conducted in the Tamale Metropolis. Geographically, the Tamale Metropolis lies between latitudes 9˚16' and 9˚34' North and longitudes 0˚36' and 0˚57' West of the equator [17] . Tamale has a tropical climate with summers being much rainier than winters. The average annual rainfall of Tamale is around 893 mm per annum and the average annual temperature is 28.4˚C [18] . The most important economic trees in the area are Parkia biglobosa, Azadirachta indica, Acacia spp, Khaya senegalensis, Vitellaria paradoxa, and Adansonia digitata (see Figure 2). The main soil types that have resulted from natural phenomena include sand, clay, and laterite ochrosols. These soil types are inadequately protected resulting in serious erosion during the rains [19] . The area is poorly endowed with natural water bodies. The only natural water systems are a few seasonal streams that contain water during the rainy season and dry up quickly during the dry season each year [20] . Agriculture is the main occupation in the area followed by the service and sales sectors which are mostly done by people in urban and suburban areas [17] .
2.2. Methods
2.2.1. Collection and Preparation of Plant Materials
Fresh but matured leaves of Pterocarpus erinaceus were harvested at the midsection of the tree in the outskirt of the Tamale Municipality in July 2022 at coordinates; 9˚24'27"N 0˚51'11.999"W and were mixed together thoroughly. The plant was taxonomically identified in the Department of Biodiversity and Conservation Management, University for Development Studies Tamale. The leaves were sorted out and washed under running tap water and left to dry at room temperature for about 2 hours. They were spread on a tray and placed in an Oven-Air dryer (Memmert F110) at 60˚C for about 4 - 5 hours and homogenized using (MISTRAL 50L art. 650P grinding mill) into fine flour. The homogenized samples were kept in a plastic film containment for proximate analysis at the Savanah Agricultural Research Institute (SARI) laboratory in Nyankpala, Tamale.
2.2.2. Proximate Composition Determination and Data Analysis
The proximate composition of the samples was determined using the standard methods of analysis of the Association of Official Analytical Chemists [21] . The following proximate compositions were determined; Protein, Fats, Moisture content, Total ash, Carbohydrates, and Dry Mather. Each proximate constituent was replicated three times (see Appendix I). The moisture content of the samples was determined by the air-oven dry method where 5 g of the sample in moisture was weighed and placed in a can or dish and dried to a constant weight at 105˚C in a dry oven. Moisture content% = weight of fresh sample – weight of dry samples/weight of fresh samples × 100.
Total ash content was determined using the muffle furnace maintained at 550 – 600˚C within four hours till grey ash was obtained. Ash% = Weight of ash/weight of sample × 100.
The crude fat was determined by the Soxhlet extraction method using ether as the extraction solvent. Crude fat (% of DM) = weight of fat/weight of sample × 100.
The crude protein of the samples was determined by the micro-Kjeldahl method.
Crude Protein (CP)% = Total Nitrogen (NT) × 6.25 (Protein factor).
Carbohydrate and dry matter contents were determined by taking the difference of the sum of all the proximate compositions from 100%. That is: 100% – (Fat% + moisture% + ash% + protein%).
The data obtained were analyzed using Microsoft excel and the results were presented and summarized using descriptive statistics (percentages).
3. Results and Discussion
The results of the proximate analysis of the leaf samples of Pterocarpus erinaceus are represented in Table 1. The highest nutritional value recorded from the analysis was for dry matter and this was obtained from the dry leaf samples. The least nutritional value recorded was for total fat and was obtained in fresh leaf samples.
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Table 1. Proximate composition values (%) of fresh and dry leaves of P. erinaceus.
The results presented are mean ± SEM (n = 3).
The crude protein content of the fresh leaf samples of P. erinaceous was lower at 11.01 ± 0.34 than that of the dry leaf samples at 22.14 ± 0.64. These values were higher than those reported for Amaranthus hybridus leaf samples at 3.56 ± 0.09 and Detarium microcarpum pulp at 4.65 ± 0.10 [12] [22] . Both values were however lower than those reported for P. mildbraedii leaves at 26.5 ± 0.4 (Akinyeye et al., 2010). The moisture value of the fresh leaf samples of P. erinaceus was 50.24 ± 0.15 higher than the value recorded for the dry leaf samples of 35.86 ± 0.07. The moisture content for both fresh and dry leaves was however higher than those reported for the stem bark of P. erinaceus 1.85 ± 0.26 and the leaves extract of P. mildbraedii 13.3 ± 0.0 [1] [2] .
The Carbohydrate value of the fresh leaf samples of P. erinaceus was slightly higher at 30.36 ± 0.34 than that of the dry leaf samples at 25.17 ± 0.82. These values are higher than those reported for Moringa oleifera seeds [15] . They were however lower than those reported for the edible leaves of Adansonia digitata at 57.04 ± 1.59 [12] .
The dry matter content of both the fresh and dry leaf samples of P. erinaceus was 49.75 ± 0.15 and 64.13 ± 0.07 respectively. These values are lower than those reported for Adansonia digitata leaf samples at 93.02 ± 0.8 [12] . They are however higher than those reported for the stem bark of P. erinaceus at 39.33 ± 0.05 [1] .
The total ash content of the fresh leaf samples of P. erinaceus was 4.81 ± 0.09 and that of the dry leaf samples was 9.66 ± 0.16 respectively. These values in this study are lower than those reported for Pterocarpus marsupium leaf samples at 12.4 ± 0.68. They are however slightly higher than the total ash values recorded for Rauwolfia serpentina leaf samples at 4.8 ± 0.23 [23] .
The total fat value of the fresh leaf samples of P. erinaceus was 3.56 ± 0.09 lower than the value recorded at 7.15 ± 0.18 for dry leaf samples. In the present study, these values are lower than those reported for Ipomoea aquatica and Achyranthes aspera leaves at 16.37 ± 0.67 and 23.26 ± 0.65 respectively [13] . They were however higher than the total fat values reported for P. erinaceus stem bark at 0.45 ± 0.50 [1] .
4. Conclusion and Recommendation
The study revealed that both fresh and dry leaves of Pterocarpus erinaceus are rich sources of vital food components such as crude protein, carbohydrates, dry matter, total ash, and fats. The values of these nutrients varied considerably between the fresh and the dry leaves of the plant. Higher values were recorded in the dry leaves of Pterocarpus erinaceus across all the food nutrients except for moisture and carbohydrates which recorded higher values in fresh leave samples. The presence of these food substances in both fresh and dry leaves of the plant makes it a potential food plant. It is recommended that; 1) further research should be done to compare the phytochemical composition between the fresh and dry leaves of P. erinaceus. 2) further research should be carried out to compare the minerals and vitamins composition of the fresh and dry leaves of P. erinaceus.
Acknowledgements
The authors wish to acknowledge all the staff of the Savannah Agricultural Research Institute laboratory for their contributions. We especially wish to thank the laboratory technician, Mr. Emmanuel Baako, and our research assistant, Miss Hikmatu Fuseini for their selfless assistance during the field and laboratory work.
Data Availability
All data and materials have already been included in this manuscript.
Abbreviations
P. erinaceus: Pterocarpus erinaceus;
P. mildbraedii: Pterocarpus mildbraedii.
Appendix
Raw Proximate Composition Values of Fresh and Dry Leaves of P. erinaceus