Proximate composition, minerals, vitamins, phytochemical constituents and anti-nutrient profile of Beilschmiedia mannii seeds and Combretum racemosum leaves for soup preparation

Abstract

Several vegetables are used in food preparation to improve the aroma, taste, appearance with less attention on the nutrient and anti-nutrient content. This study investigated the proximate, vitamins, minerals and anti-nutrients profile of Beilschmiedia manni seed and Combretum racemosum leaf. Proximate composition, vitamins, mineral analysis and anti-nutrient profile were determined using standard procedures. The proximate analysis revealed that C. racemosum contained high crude protein (19.18%), crude fat (22.20%) and energy value (449.11 kJ) but low carbohydrate (43.15%) compared to B. mannii with the high carbohydrate (64.25%) content. Phytochemical screening revealed the presence of active phytochemicals in both samples. Thiamine, riboflavin and niacin were significantly (p < 0.05) high in B. mannii compared to C. racemosum. The level of macro minerals in B. mannii seeds and C. racemosum leaves was in the order of K > Ph > Na > Mg > Ca. Beilschmiedia mannii seeds and C. racemosum leaves respectively contained 45.00 mg/100 g and 163.00 mg/100 g oxalate, 70.00 mg/100 g and 113.00 mg/100 g phytate, 58.00 mg/100 g and 209.00 mg/100 g of tannin. This study has revealed that B. mannii seeds and C. racemosum leaves are potential sources of essential nutrients, phytochemicals and could play important role in food enrichment, formulation of dietary supplements and in disease managements.

Introduction

Vegetables are plants with edible parts, especially seed, leaves or other fleshy parts that are used mainly for soups or salads, or to accompany main course. They have been explored and used in every facet of man’s existence to provide basic nutritional needs and health benefits for mankind (Muhammad and Amusa 2005). Phytochemicals and certain nutrients such as minerals, vitamins, proteins, and essential fatty acids found in vegetables are necessary for maintaining balanced nutritional diets (Muhammad and Amusa 2005). Deficiency or imbalance of these nutrients could result to measurable adverse effect on body physiology such as reduced muscle functions, cardiac muscle mass, altered gastrointestinal functions, impaired immunity and delayed wound healing process (Bello et al. 2014; Khomdram et al. 2014).

In Nigeria, several vegetables are often processed into different soup type since soup act as the main denominator for eating several other Nigerian foods. Common foods consumed include the popular fufu, eba (garri) and pounded yam that doesn’t go into the body system without a scrumptious plate of soup. Several other part of vegetables are usually added to soups as spices, condiments or adjuvants in order to improve its appearance, palatability, texture, taste and aroma (Luu et al. 2020).

Beilschmiedia mannii (Lauraceae) seed is popularly known as ‘gbokonisa’ among the Yorubas, Nigeria. The seed is about 1.5 inches in length, ovoid in shape with dark purple color coated with a thin green seed coat. Previous study showed that B. mannii seeds contained edible oil (Femi-Oyewo et al. 2009). Combretum racemosum (family: Combretaceae) commonly known as Christmas rose in English is locally referred to as ókósó (Edo), alagame (Igbo) and ògàn pupa (Yoruba) in Nigeria. Recent reports have revealed the anticancer, antiulcer, antimicrobial and in-vivo antioxidant potential of the leaf extract of C. racemosum (Idu et al. 2016). In South-western part of Nigeria, B. mannii seeds and C. racemosum leaves are used in large and small quantities respectively as condiment in preparations of ewedu (Corchorus olitorius) soup to majorly improve the mucilaginous quality of the soup.

Evaluation of the nutrients by assessing the proximate composition, minerals and vitamin content of vegetables and other edible plant play important roles in understanding the nutritional values and medicinal worth of plant species (Pandey et al. 2006). To the best of our knowledge, less attention is focused on the nutritional and the antinutrient quality of B. mannii seeds and C. racemosum leaves. The current study therefore investigated the proximate composition, minerals, vitamins, and phytochemical constituents of Beilschmiedia mannii seeds and Combretum racemosum leaves for soup preparation.

Materials and methods

Plant materials and preparation

The wet seeds of Bielscmeidia mannii were collected from Okitipupa main market, Okitipupa, Ondo state while Combretum racemosum leaves were freshly harvested from a local farm in Okitipupa, Ondo State.

Both specimens were air dried for a period of 3 weeks and pulverized to powder form prior analysis.

Proximate analysis

Proximate chemical composition (ash, moisture, crude protein, crude fat, crude fiber and carbohydrate) of Beilschmiedia manni seed and combretum racemosum leaf were determined using the method of AOAC (2000) and the analysis were carried out in triplicates. Ash content was determined by incineration in a muffle furnace at 550 °C for 6 h. Crude protein content was determined by micro- Kjeldahl method. The crude fat content of samples (5 g) were firstly extracted with petroleum ether (b.p 40–60 °C) using the Soxhlet extraction method. Flask containing the fat was placed in hot oven for total removal of residual petroleum ether, cooled and weighed. Crude fiber was determined by initial digestion of samples under reflux in 0.25 N H₂SO₄ and 0.25 N NaOH followed by successive rinsing with hot water, acetone and 50% ethanol. Obtained residues were transferred into an empty crucible, dried in hot oven at 130 °C for 2 h, cooled and weighed. Thereafter, the sample was placed in a muffle furnace at 550 °C for 30 min, cooled in a desiccator and weighed. Total carbohydrate content was estimated by difference using the formula

$$\text{Carbohydrate}\left(\%\right)=100-\left[\text{Moisture}\left(\%\right)+\text{Ash}\left(\%\right)+\text{Crude protein}\left(\%\right)+\text{Crude fat}\left(\%\right)\right].$$

Total energy value was calculated by the Atwater factors as:

$$\text{Energy value}=\left(\%\text{crude protein x 4}\right)+\left(\%\text{carbohydrate x 4}\right)+\left(\%\text{crude fat x 9}\right)$$

Phytochemical screenining

Preliminary phytochemical analysis to detect the presence of phytochemical constituents in B. manni seed and C. racemosum leaves were carried out using the methods of Sofowara (1993); Trease and Evans (1989).

Analysis of vitamins

Thiamin, riboflavin and niacin were determined follwing AOAC (2005) method. Analysis was performed in triplicate and final results were expressed in mg/100 g of sample.

Vitamin B₁ (thiamin)

Portion (1.5 g) of sample was added to 100 mL of HCl (0.1 N) solution and heated in a water bath at 100 °C for 30 min. After cooling, the flask content was made up to mark with 0.1 M HCl solution, filtered using Whatman No 1 filter paper and further centrifuged at 5 000 × g for 5 min. Thereafter, the residue was treated with 5 ml of absolute alcohol and 5 ml of potassium ferricyanide solution (prepared in NaOH) to form pink color. To the solution was added 20 ml of toluene, stirred and centrifuge 5 000 × g for 10 min obtained a clear pink colour. Thiamine was used as standard and treated as above. The standard and sample solutions were read at 530 nm wavelength using the TTO 30UV spectrophotometer (UV/VS) the amount of thiamin present in the sample was calculated as thus:

$$\text{Thiamin mg}/100\text{g}=\frac{\text{Abs of sample}}{\text{Abs of standard}}\times \frac{\text{wt}.\text{of sample}\left(\text{mg}\right)}{\text{wt}.\text{of sample}\left(\text{g}\right)}\times 100$$

Vitamin B2 (Riboflavin)

Aliquot (1.5 g) of sample was mixed with 100 mL of acetic–water mixture (v/v 50:50) and heated in a boiling water bath at 100 °C for 30 min. The mixtures in the flask was cooled and then made up to the mark with acetic-water solution. The mixture was stirred for 10 min using the magnetic stirrer and then filtered in the dark. The fluorescence of the standard and sample solutions was read using T70 PG spectrophotometer at 460 nm wavelength. Riboflavin (0.5 mg) solution used as standard was treated as sample and amount of riboflavin in sample was calculated as follows:

$$\text{Riboflavin mg}/100\text{g}=\frac{\text{Abs of sample}}{\text{Abs of standard}}\times \frac{\text{wt}.\text{of sample}\left(\text{mg}\right)}{\text{wt}.\text{of sample}\left(\text{g}\right)}\times 100$$

Vitamin B3 (Niacin)

Exactly 1.5 g of sample was mixed with 5 ml of HCl (5 N), followed by 5.0 ml dichloromethane and 90 ml deionized water in a 200 ml volumetric flask. The mixture was stirred thoroughly, boiled in water bath at 100 °C for 30 min, cooled and the content was made up to mark with distilled water. The solution was filtered using whatman no 1 filter paper and absorbance was taken at 410 nm wavelength using spectrophotometer. Niacin standard solution of 0.5 mg was prepared and analyzed as above

$$\text{Niacin mg}/100\text{g}=\frac{\text{Abs of sample}}{\text{Abs of standard}}\times \frac{\text{wt}.\text{of sample}\left(\text{mg}\right)}{\text{wt}.\text{of sample}\left(\text{g}\right)}\times 100$$

Vitamin C (Ascorbic acid)

Ascorbic acid was determined using AOAC (2014) method. Exactly, 5 g of sample was extracted with 50 ml of 3% metaphosphoric acid and filtered using whatman no. 1 filter paper. Thereafter, 10 ml of filtrate was dispensed in 50 ml conical flask and titrated against 0.25% of 2, 6-dichlorophenolindophenol dye solution (DPIP) dye to faint pink colour which should persist for 15 s. The ascorbic acid content was calculated as follows:

$$\text{Ascorbic acid}(\text{mg}/100\text{g})=\{(CA\times \text{VD}\times 10)/(\text{VA}\times \text{VB}\times \text{W})\}\times 100$$

where CA = Concentration of the Standard Vitamin C (mg/ml).

VD = Titre value for the sample (ml).

VA = Titre value for Standard Vitamin C (ml).

VB = Volume of the sample used (ml).

W = Weight of the sample (mg).

Minerals analysis

The method of AOAC (2005) was adopted for the mineral analysis. Exactly, 0.5 g of each sample was weighed into the beaker and 10 ml of an acid mixture of ratio 1:2 (Nitric perchloric acid) was added. The content was allowed to undergo digestion in a fume cupboard using hot plate for about 30 min until the color changes to colorless. The digest was allowed to cool and was then measured on buck scientific atomic absorption spectrophotometer model 210/211 VCP to determine the minerals in the samples.

Anti nutrients

Determination of Phytate

Phytate determination was carried out using Reddy and Love (1999) method. Fraction (2 g) of sample was soaked in 100 mL of 2% HCl for 3 h and then filtered. Exactly 25 ml of the filtrate was placed in a 100 ml conical flask and add 5 ml of 0.03% NH₄SCN solution as indicator. About 50 ml of distilled water was added to give it the proper acidity. This was titrated with ferric chloride solution containing 0.005 mg of Fe³⁺ per ml. The phytate content was expressed in mg/100 g.

Determination of Tannins

The tannins content was determined by the modified method of Trease and Evans (1989). After reconstitution of the sample, 0.5 ml of the filtrate was added to 0.5 ml of 0.5 M ferric solution in and allowed to stand for 30 min for colour development. The absorbance was read at 760 nm and the amount of tannin was calculated from a tannin standard calibration curve.

Determination of Oxalate

Oxalate determination was done using the method of Day and Underwood (1986). Portion (1 g) of the sample was weighed into 100 mL conical flask. About 75 ml of 3 M sulphuric acid was added and the solution was carefully stirred intermittently with a magnetic stirrer for about 1 h and then filtered using Whatman No 1 filter paper. About 25 ml of the filtrate was collected and titrated against 0.1 M KMnO₄ until a faint pink colour appeared which persisted for 30 s.

$$\text{Oxalate}\left(\text{mg}/\text{g}\right)=\text{Titre value}\times 0.9004$$

Statistical analysis

Data were expressed as mean ± standard error of mean. Statistical significance was evaluated by one-way analysis of variance using Statistical Package for Social Sciences (SPSS) version 17. Differences between means were considered to be significant at (p < 0.05) using Least Square Difference post hoc test.

Results

Proximate composition and phytochemical constituents

The proximate composition of B. mannii and C. racemosum are presented in Table 1. The proximate analysis revealed that C. racemosum leaves contained significantly (P < 0.05) higher crude protein (19.18%), crude fat (22.20%), crude fibre (8.05%) and energy value (449.11 kJ) but low carbohydrate (43.15%) and moisture content (2.60%) compared to B. mannii with the high carbohydrate (64.25%) and moisture content of 15.92%. The phytochemical screening revealed that both B. mannii seeds and C. racemosum leaves are rich in medicinally active phytochemicals. Phytochemicals such as phenol, flavonoid, tannin, saponin, steroid and alkaloids were detected in both vegetables at different levels (Table 2).

Table 1.

Proximate composition of B. mannii and C. racemosa

	B. mannii	C. racemosa
Moisture (%)	15.92 ± 0.02a	2.60 ± 0.04b
Ash (%)	2.62 ± 0.05a	4.82 ± 0.03b
Crude Fiber (%)	2.49 ± 0.06b	8.05 ± 0.09c
Crude fat (%)	4.25 ± 0.09a	22.20 ± 0.01c
Crude protein (%)	10.46 ± 0.05a	19.18 ± 0.07b
Carbohydrate (%)	66. 75 ± 0.04b	51.20 ± 0.06c
Energy Value (KJ)	337.11 ± 0.07a	449.11 ± 0.47b

Values represent the percentage proximate composition of B. mannii seed and C. racemosa leaf and are mean ± SEM of three (3) independent determinations. Values with the different letters along the same column are significantly different (p < 0.05)

Table 2.

Phytochemical screening of B. mannii seed and C. racemosum leave

	B. mannii	C. racemosa
Phenol	+  +	+  +
Flavonoid	+	+  +
Alkaloid	+	+
Tannin	+	+  +
Saponin	+	+
Steroid	+  +	+  +

 +  +  = Highly Present

 +  = Moderately Present

– = Absent

Vitamins and mineral contents

Vitamin analysis of the vegetables revealed that seeds of B. mannii had higher value of thiamine (0.126 ± 0.01 mg/100 g), riboflavin (0.301 ± 0.02 mg/100 g) and niacin (0.223 ± 0.01 mg/100 g) compared to C. racemosum with thiamine (0.096 ± 0.01 mg/100 g), riboflavin (0.099 ± 0.03 mg/100 g) and niacin (0.121 ± 0.01 mg/100 g). There was no significant difference (p > 0.05) in the level of ascorbate in B. mannii seeds and C. racemosum leaves (Table 3).

Table 3.

B-Vitamins and vitamin C content of B. mannii and C. racemosa

Samples	Thiamine (mg/100 g)	Riboflavin (mg/100 g)	Niacin (mg/100 g)	Ascorbate (mg/100 g)
B. mannii	0.126 ± 0.01a	0.301 ± 0.02a	0.223 ± 0.01b	0.850 ± 0.04a
C. racemosa	0.096 ± 0.01b	0.099 ± 0.03b	0.121 ± 0.01c	0.92 ± 0.06a

Values are presented as mean ± SEM of three (3) independent experiments. Values with the different letters along the same column are significantly different (p < 0.05)

The mineral compositions of B. mannii seeds and C. racemosum are shown in Table 4. Calcium (26.00 mg/00 g) and phosphorus (580.33 mg/100 g) were significantly (p < 0.05) high in C. racemosum compared to B. mannii seeds that only showed a significantly high potassium (1617.10 mg/100 g). Sodium and magnesium in both samples showed no significant difference. B. mannii contained high amount of Fe (109.00 mg/100 g) compared to C. racemosum (101.50 mg/100 g). While manganese (5.96 mg/100 g) and zinc (2.14 mg/100 g) were higher in C. racemosum leaves relative to B. mannii seeds.

Table 4.

Mineral composition of B. mannii and C. racemosa

	B. mannii (mg/100 g)	C. racemosa (mg/100 g)
Calcium (Ca)	5.00 ± 0.57b	26.00 ± 0.15a
Potassium (K)	1617.10 ± 6.98a	1225 ± 2.52c
Sodium (Na)	175.30 ± 1.76a	205.00 ± 3.21a
Magnesium (Mg)	52.30 ± 0.75a	40.10 ± 1.11a
Phosphorus (Ph)	515.00 ± 2.08b	580.33 ± 5.61c
Manganese (Mn)	3.35 ± 0.01a	5.96 ± 0.07b
Zinc (Zn)	1.30 ± 0.03a	2.14 ± 0.00b
Iron (Fe)	109.00 ± 1.26a	101.50 ± 0.40b

Values are presented as mean ± SEM of three (3) independent experiments. Values with the different letters along the same column are significantly different (p < 0.05)

Anti-nutritional profile

The result of the anti-nutrient profile of B. mannii seeds and C. racemosum leaves is presented in Table 5. B. mannii seeds contained 45.00 mg/100 g of oxalate, 70.00 mg/100 g of phytate and 58.00 mg/100 g of tannin while C. racemosum leaves contained oxalate (163.00 mg/100 g), phytate (113.00 mg/100 g) and tannin (209.00 mg/100 g).

Table 5.

Anti-nutrient profile of B. mannii seeds and C. racemosa leaves

Samples	Oxalate (mg/100 g)	Phytate (mg/100 g)	Tannin (mg/100 g)
B. mannii	45.00 ± 2.08a	70.00 ± 3.06a	58.00 ± 1.53a
C. racemosa	163.00 ± 3.51b	113.00 ± 4.58b	209.00 ± 3.06b

Values represent the concentrations (mg/100 g) of oxalate, phytate and tannin in B. mannii seeds and C. racemosa leaves and are expressed as mean ± SEM of three (3) different experiments. Values with different letters along the same column are significantly different (p < 0.05)

Discussion

From this study, the percentage carbohydrate and moisture content showed significant increase (p < 0.05) in B. mannii seed compared to C. racemosum leaves. The high carbohydrate content obtained in B. mannii seed could be an indication that the seed is an excellent carbohydrate storehouse. The mucilaginous nature of Beilschmiedia spps could presumably contribute to the carbohydrate content since plant mucilage contains complex polysaccharides with highly branched structure (Femi-Oyewo et al. 2009). Both B. mannii seed and C. racemosum leaves demonstrated low carbohydrate content compared to 73.77% from Ficus capensis leaves (Achi et al. 2017). Carbohydrate is essential to body cells by supplying energy. The relatively high moisture content observed in B. mannii seed compared to C. racemosum leaves could be attributed to complex mucilaginous structure and water retention capacity of the seed cotyledon (Femi-Oyewo et al. 2009). High moisture content could result to activation of enzymes that breakdown medicinally active compound, increasing susceptibility of food substances to microbial activity thereby promoting spoilage (Oikeh et al. 2013). This study suggests that dry seed of B. mannii should only be grinded when about to be used as soup condiments in order to avoid spoilage due to microbial infection.

Percentage ash and crude fiber of C. racemosum leaves were significantly high than values obtained for B. mannii seed. The amount of inorganic compounds found in food materials after extreme burning is usually determined by its level of ash content. This study suggests that C. racemosum leaves could be possibly rich in minerals compared to B. mannii seed. Food materials that are rich in dietary fibers have been reported to improve digestion, reduced constipation, lower serum cholesterol level and the risk of hypertension, diabetes and cancer (Usunobun et al. 2014). The high value of crude fiber obtained in C. racemosum leaves compared to B. mannii seed could suggest potential ability to keep the digestive system healthy, reduce lipid accumulation, improved intestinal bowel movement, suppression of carbohydrate digestion and improve mineral absorption (Usunobun et al. 2014).

This study revealed that C. racemosum leaves contain high energy value, rich in crude protein and fat compared to B. mannii seed (Table 1). Using C. racemosum leaves as condiment in Corchorus olitorius (ewedu) soup preparations could add nutritive value by possibly influencing the quality of protein and fat in the soup. Dietary protein is necessary for maintenance of body tissues, act as a precursor for natural synthesis such as hormones, enzymes and immune functions (Princewill-ogbonna et al. 2019). Despite dietary fats are essential for food improvement and health, excessive consumption of fat (majorly saturated fat) could result to various cardiovascular disorders (Arun et al. 2013).

The presence of active phytochemicals in both B. mannii seed and C. racemosum leaves is an indication that both vegetables could possess significant therapeutic functions besides nourishing the body. Active secondary metabolites like alkaloids possess pharmacological properties such as antiasthma, analgesic and antimicrobial activity (Muhammad and Amusa 2005), Flavonoids and tannins are major class of phenols that act as antioxidant which protect the body cells from free radicals and reactive oxygen species (Saxena et al. 2013). The availability of these phytochemicals in B. mannii seed and C. racemosum leaves suggested that their extracts could be harness as lead compounds in pharmaceutical industry and in modern medicine.

Vitamins are class of essential nutrients that are obtained from diet and required by the body for diverse metabolic functions. The higher level of thiamine, riboflavin and niacin obtained in B. mannii compared to C. racemosum leaves could depicts that the seed of B. mannii is an excellent source of vitamin B. This study recommends that the use of B. mannii seed as condiment in soup could contribute immensely to required amount of thiamine, riboflavin and niacin that is needed for body function. These vitamins commonly function as coenzymes for optimal activities of metabolic enzymes that are required for energy generation. They are also important for normal appetite, healthy skin, red blood cell formation and nervous system (Princewill-ogbonna et al. 2019). This study revealed no significant difference in the level of vitamin C (ascorbic acid) in B. mannii seeds and C. racemosum leaves. Vitamin C belongs to the class of water soluble vitamins that play important roles as antioxidant for attenuating oxidative stress caused by free radicals (Khomdram et al. 2014). It facilitates the absorption of dietary iron in the intestine, maintenance of normal connective tissues and also assists in wound healing process (Khomdram et al. 2014).

Adequate dietary intake of minerals play important roles in maintaining proper body functions and good health while insufficient consumption in the diet has been linked to vulnerable immune system hence susceptibility to infectious diseases (Bello et al. 2014). The level of the macro minerals in B. mannii seeds and C. racemosum leaves were in the following order K > Ph > Na > Mg > Ca while the trace element in both vegetables were in order of Fe > Mn > Zn. The high minerals (Ca, Ph, Mn and Zn) obtained in C. racemosum leaves compared to B. mannii seeds could suggest that C. racemosum leaves is an excellent source. Potassium and Sodium are principal minerals of intra-cellular and extracellular fluids that help in maintaining fluid balance in the body and regulate blood pressure. Besides this role, potassium has also been reported to play crucial role in the utilization of iron, regulate acid–base balance in the body and improve muscle functions and nerve actions (Bello et al. 2014). The moderate amount of sodium and potassium in B. mannii seeds and C. racemosum leaves suggests that the vegetables could be beneficial in controlling hypertension through body fluid balance and prevent muscle paralysis (Bello et al. 2014).

Magnesium and phosphorus are important in diet for bone formation, hormonal activation and secretion, energy production and storage. Magnesium act as cofactor for over 300 enzymes and is also required for body osmotic balance and glucose homeostasis (Glasdam et al. 2016) while Phosphorus play vital role as energy intermediate, in synthesis and the overall architecture of DNA and RNA (Vance et al. 2003). It could be deduced from this study that 100 g of C. racemosum leaves could contribute ~ 46.4% of recommended daily allowance of 1250 mg/day phosphorus (USFDA 2020). Calcium was found to be present in low quantity in both vegetables although significantly (p < 0.05) higher in C. racemosum leaves compared to B. mannii seeds. The values obtained for the vegetables might be insufficient to meet the daily requirement of 1300 mg/day (USFDA 2020).

Manganese is an important cofactor of many metabolic enzymes that are essential for the metabolism of carbohydrate, proteins and fat (Pandey et al. 2012). Despite the amount obtained from C. racemosum leaves was significant compared to B. mannii seeds, the values obtained from both vegetables are sufficient to meet human recommended daily dose of 2 to 9 mg/day (WHO 1994). This study revealed that C. racemosum leaves and B. mannii seeds are highly rich in iron (Table 4). Iron is important in the formation of blood and also acts as an essential component of hemoglobin, a protein which enables red blood cells to transport oxygen throughout the body. It also serves as an essential constituent of protein and some drug metabolizing enzymes requiring cytochrome P450. The high iron content observed in C. racemosum leaves and B. mannii seeds could suggest additional health benefit against anemia, dysfunction immune system and other diseases associated with iron deficiency (Trowbridge and Martorell 2002). However, caution should be observed since concentration of iron above daily recommended value could cause stomach upset, constipation and blackened stools (Trowbridge and Martorell 2002).

In the current study, oxalate, phytates and tannin present in C. racemosum leaves and B. mannii seeds were analyzed. The results revealed that B. mannii seeds contained less amount of anti-nutrients compared to its counterpart. Consumption of plants and plant products with high anti-nutrients has been linked to low bioavailability and utilization of nutrients in the body. Paradoxically, these chemical compounds can sometimes be advantageous to humans when consumed wisely (Gibson et al., 2018; Essack et al. 2017). C. racemosum leaves and B. mannii seeds could still be classified as low oxalate plant compared to 1000 mg/100 g reported for red Swiss chard, spinach, and rhubarb (Chai and Liebman 2005). The result of oxalate obtained from this study may not be harmful to humans after consuming the vegetables since the values were relatively low and processing (grinding, drying and boiling) of vegetables before consumption usually reduce oxalate in vegetables to about 60 to 180 mg/100 g (Essack et al. 2017). Phytate (inositol hexaphosphate) is naturally found in plants, unprocessed food substances such as grains, seeds, legumes, nuts and vegetables products. It represents about 50–85% of the total phosphorous in plants (Kumar et al. 2010). They chelate elements (calcium, iron and zinc) to form insoluble salt complexes in the upper gastrointestinal tracts thereby reducing the bioavailability, solubility and nutritive functions of the minerals and proteins (Gibson et al. 2018). High amount of phytates in diet could result to inhibition of proteolytic enzymes such as pepsin, trypsin and amylase (Kumar et al. 2010). Despite tannin exhibits anti-nutritional properties by impairing the digestion and absorption of various nutrients, it has been reported to possess definite health benefits such as antioxidant, antimicrobial and anti-inflammatory properties (Saxena et al. 2013).

Conclusion

The study has demonstrated that B. mannii seed contained appreciable amount of vitamins while C. racemosum leaves could serve as excellent source of some minerals such as calcium, phosphorus, manganese and iron. The proximate composition, nutritional and anti-nutritional profile suggested that both vegetables could be essential in food enrichment, formulation of different dietary supplements, pharmaceutical and cosmetic preparations. Despite the nutritional importance of the C. racemosum leaves and B. mannii seeds, they could also be harnessed for medicinal purpose since they are rich in phytochemicals.

Abbreviations

AOAC

Association of official analytical chemists;

H₂SO₄

Tetrahydrosulfate VI acid;

NaOH

Sodium hydroxide;

HCl

Hydrochloric acid;

UV/VS

Ultraviolet/visible;

DPIP

2, 6-Dichlorophenolindophenol dye solution;

DNA

Deoxyribonucleic acid;

RNA

Ribonucleic acid

Authors’ contributions

This work was collaboratively carried out between all authors. Authors ESA and FOA designed the study and supervised the work, ESA analyzed obtained data and wrote the first draft of the manuscript. ESA KOK and EOA performed the experiments, interpreted generated statistical data and performed literature search. All authors read, edited and approved the final manuscript.

Funding

None.

Availability of data and materials

All analyzed dataset to support the conclusions of this article is included as tables in the uploaded supplementary files.

Declarations

Conflict of interest

The authors declared no conflicts of interest.