Nutraceutical qualities of Cucurbita, Vernonia amygdalina Del and Ocimum gratissimum leaves vis-à-vis- vitamins A and C: a source of health benefits

The inadequate information on the nutritional values associated with the consumption of vegetables by the people in our communities demands from the researchers to evaluate the benefits and recommend the highly nutritious vegetables to the host communities. The study was aimed at quantifying the vitamins A and C contents of the three selected indigenous vegetables widely consumed in Akure, Nigeria. Three vegetables were obtained from a local market in Akure, the leaves were processed into powdered form by drying and blending using laboratory scale grinder (Sumeet CM/L 2128945) and sifted through 300 μm sieve. Vitamin C and A were determined according to the recommended procedure. The vitamin A contents were in the range (8.03±0.10 to 21.55±0.04 mg/100 g) with the composite being the highest. The vitamin C contents were recorded in the descending order of composite (10 g of mixture of powdered leaves), Cucurbita, Vernonia amygdalina Del and Ocimum gratissimum. It was interesting to uncover that the composite formulation was highly rich in vitamins A and C and this mixture of vegetables for consumption should be encouraged.


Introduction
Vitamins are essential building blocks for various pharmacological activities in the human body system and their roles in human health cannot be overemphasized. Vitamins are organic compounds essentials for the physiological functions of human systems and can be classified as soluble or insoluble. Nutritionists have placed a high premium on diets high in vegetables and fruits because of the prevalence of vitamins especially vitamins A and C and they are recommended for their health-promoting properties (Slavin and Lloyd, 2012). The nutritional qualities and health benefits of vegetables have been well reported and this includes among others, sources of provision of vitamins (C, A, B 1 , B 6 , B 9 , E) and mineral elements such as iron, zinc (Quebedeaux and Eisa, 1990;Craig and Beck, 1999;Wargovich, 2000;Dias and Ryder, 2011). Furthermore, vegetables have been found to be rich in phytochemicals, their function as strong anti-oxidants and they have the potentials to reduce the risk of chronic diseases (Craig and Beck, 1999;Wargovich 2000;Southon, 2000;Herrera et al., 2009;Dias and Ryder, 2011). Other health benefits associated with the consumption of vegetables include reducing risk for some forms of cancer, heart disease, stroke, diabetes, anaemia, gastric ulcer, rheumatoid arthritis, and other chronic diseases (Prior and Cao, 2000;Hyson 2002;Golberg, 2003;IFAVA, 2006;Keatinge et al., 2010). A vegetable is common and affordable to humans of all categories. Vegetables are locally cultivated either at subsistence or mechanized levels and available throughout the season period in Akure, Nigeria, as the plants can be grown in swampy areas and irrigation can be adopted.
Bitter leaf (Vernonia amygdalina Del) belongs to the family called Asteraceae, it is described as a small shrub with dark green leaves growing in tropical and subtropical Africa (Igile et al., 1994;Erasto et al., 2006;Erasto et al., 2007a;Erasto et al., 2007b;Tsado et al., 2015). It is a perennial plant with a height between 1 m and 6 m (Nwosu et al., 2013). Tsado et al. (2015) had reported that fresh V. amygdalina grew in Baddegi, Niger state, Nigeria to have high vitamin C and low Vitamin A contents. In addition, Bob et al. (2019) reported the high vitamin C content and low vitamin A of V. amygdalina purchased in Calabar, Nigeria and other nutritional qualities have been reported by (Igile et al., 1994;Okafor, 2005). In addition, Ogunlesi et al. (2010)  Furthermore, Scent leaf (Ocimum gratissimum) (African basil) belong to the group called Lamiaceae and it is a herbaceous perennial plant available in tropical Africa and Asia. The plant has a special aroma which has made it useful as spice and condiments (Akinmoladun et al., 2007) and the essential oil present has been found useful industrially (Lachowicz et al., 1996;Machale et al., 1997). Bob et al. (2019) found a low level of vitamin A content in African basil leave and a moderate level of vitamin C contents harvested from local farms in Cross River State, Nigeria.
Cucurbita moschata generally called pumpkin belongs to the species of plants Cucurbitaceae and very common in the Andes and Mesoamerica (Burrows and Tyrl, 2008). It is also widely grown in African countries, Nigeria inclusive. There are five various species cultivated worldwide and their fruits are edible, and the leaves are good sources of nutrients such as vitamins A and C, Aruah et al. (2011) reported low vitamin C contents for various Cucurbita species investigated across five states in Nigeria. The three selected vegetables are widely common in Akure, Nigeria and inadequate information on the health benefits associated with the consumption necessitated the study.

Laboratory
The samples were analyzed in the chemistry laboratory, Afe Babalola University Ado Ekiti, Nigeria between the periods of 20th February 2020 to 30th April 2020.

Sample preparation
Three different vegetables were purchased from local market in Akure, Ondo state, Nigeria on the 19 th of January, 2020. The leaves were separated from the stock, washed and air dried for 8 days at room temperature. The dried leaves were powdered using a laboratory scale grinder (Sumeet CM/L 2128945) and sifted through 300 μm sieve to obtain the powdered samples. For the composite (uniform single sample); 10 grams of the powdered samples each were blended together to obtain a single uniform sample.

Reagent preparation for the analysis 2.3.1 5% Metaphosphoric acid-10% acetic acid
Fifteen grams of solid metaphosphoric acid (E. Merck) were dissolved in mixture of 40 mL of glacial acetic acid (BDH) and 450 mL of distilled water in a 500 mL volumetric flask. The solution was filtered and collected.

Standard vitamin C (ascorbic acid) solution
Standard crystalline ascorbic acid (0.05 g) was dissolved in 100 mL of distilled water to prepare 500 ppm standard stock solution.

Sample preparation for estimation of vitamin C
Approximately 10 g of sample was homogenized with 50 mL of 5% metaphosphoric acid-10% acetic acid solution. Then it was quantitatively transferred into a 100 mL volumetric flask and was shaken gently until a homogeneous dispersion was obtained. Then it was diluted up to the mark by the 5% metaphosphoric acid-10% acetic acid solution. Then the solution was filtered and the clear filtrate was collected for the determination of vitamin C in that sample.

Estimation of vitamin C
Few drops of bromine water were added to the filtrate sample until the colour changes (to confirm the completion of the oxidation of ascorbic acid to dehydroascorbic acid). This was followed by the addition of few drops of thiourea to remove the excess bromine and cleared solution was obtained. To the colourless solution, 2, 4-dinitrophenyl hydrazine dye solution with vitamin C standard were added and reaction completed (Rahman Khan et al., 2006). A Shimadzu spectrophotometer (model UV-1800) with a pair of 1 cm quartz cells was used for the reading.

Vitamin A determination 2.5.1 β-carotene extraction and analysis
The β-carotene was determined by soaking 1 g of sample in 5 mL of methanol for 2 hours at room temperature under dark condition in order to get a complete extraction. The β-carotene layer was separated using hexane through separating funnel. The volume was made up to 10 mL with hexane and then this layer was again passed through sodium sulphonate through a funnel to remove any moisture from the layer. The absorbance of the layer was measured at 436 nm using hexane as a blank (Ranganna, 1999). The beta carotene was calculated using the formula: Where V = Total volume of extract, D = Dilution factor, W = Sample weight, Y = Percentage dry matter content of the sample.

Statistical analysis
The analyses were done in triplicates and ANOVA

Results and discussion
From the results of Table 1, the vitamin A content of composite (powdered mixture of the leaves) was the highest (21.55±0.04 mg/100 g) and Ocimum gratissimum was the lowest (8.03±0.10 mg/100 g). However, the vitamin A content of Cucurbita (18.15±0.12 mg/100 g) was higher than that of Vernonia amygdalina (11.27±0.03 mg/100 g). The vitamin A contents of these vegetables when compared to the previously studied plants as reported by Bob et al. (2019), it was observed that they were higher. The vitamin A content of V. amygdalina (11.27±0.03 mg/100 g) was higher than that reported by Bob et al. (2019) (1.2±0.9 mg/100 g) for the same vegetable. Also, the Vitamin A content of Cucurbita (18.15±0.12 mg/100 g) was higher than that reported by Mohammed et al. (2013) for the seed of Cucurbita (0.76.2±0.00 mg/100 g). Furthermore, the vitamin C content of Cucurbita leaves (43.47±0.10 mg/100 g) was higher than V. amygdalina (31.89±0.16 mg/100 g) and Ocimum gratissimum (23.28±0.13 mg/100 g) respectively. However, the composite had the highest (58.63±0.21mg/100 g). Bob et al. (2013) had reported the vitamin C content of V. amygdalina to be (43.4±0.10 mg/100 g) which was higher than that of the current study (31.89±0.16 mg/100 g). Past studies had also shown the rich content of vitamins C (197.5 mg/100 g) and A (13.41 mg/100 g) of V.amygadlina (Odukoya et al., 2007;Aregheore, 2012). The vitamin C content of Ocimum gratissimum in the study was lower when compared to the previously studied vitamin C content for the various Ocimum gratissimum collected from five different locations in the south-east part of Nigeria and the vitamin C contents recorded were in the range of (182.45-188.91 mg/100 g) as reported by Emeka and Chimaobi (2012). However, Aluko et al. (2012) had reported the vitamin C content of Ocimum canum Sims to be (0.05 g/kg).
The selected vegetables were all rich in vitamins and the various values recorded by different scholars may be due to varying climatic conditions. Health benefits associated with vitamins A and C have been well elaborated on and plants have been found to be a good reservoir of vitamins and minerals (Godber, 1990). Furthermore, studies have revealed a huge majority of vitamins with antioxidant activities from vegetables such as vitamins A and C (Godber, 1990). The role played by vitamins A and C cannot be over-emphasized as previous investigations had shown that they perform various functions in the human system. Mensah et al. (2008) had reported the physiological functions of vitamin C as antioxidant which serves as body defence against cancer, arthritis and type 2 diabetes mellitus and also serves as an immune booster. Moreover, Charttejea et al. (2005) had enumerated the functions of vitamin C to include the facilitation of iron absorption by its ability to lower ferric ions to the ferrous form. Ismail (2017), Cao et al. (1996) and Odukoya et al. (2007)   which was present in the highest composite had shown to have positive drug-likeness, an indication that it is a drug also and possess no toxicity, furthermore, vitamin A (βcarotene) had no toxicity and drug-likeness of -1.8704.

Conclusion
With the numerous health benefits associated with the consumption of vegetables such as V. amygadlina, Ocimum gratissimum and Cucurbita, the study had revealed the rich contents of vitamins A and C present and that of the composite. It is recommended that selective vegetables as composite are better for consumption for their health benefits than only one vegetable.