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Abstract

The nutrient and phytochemical assessment of ripe and unripe pulp and seeds of white rubber vine (Landolphia owariensis) was carried out. Ripe and unripe white rubber vine fruits were washed, cut open to obtain the seeds and pulps. The seeds and pulps were analyzed for proximate, dietary fibre, vitamins, mineral and phytochemical contents. The values obtained for the proximate compositions of the samples were within 15.22% to 31.85% (moisture); 0.57% to 2.87% (fat); 2.37% to 3.62% (ash); 2.61% to 3.58% (fibre); 6.31% to 9.03% (protein) and 55.95% to 66.13% (carbohydrate). The results revealed that seeds of white rubber vine contained higher quantity of fat, ash, fibre and protein while its pulps are richer in moisture and carbohydrate. The dietary fibre content of the samples ranged from 1.48% to 6.2%. The result revealed that the dietary fibre content of the seeds are higher than that of the pulp and ripening also reduced the dietary fibre content of both the pulp and seeds. The micronutrient contents of the white rubber vines were in the range of 3.44mg/100g to 5.87mg/100g (iron); 81.78mg/100g to 106.29mg/100g (potassium); 1.32 mg/100g to 1.73mg/100g (zinc); 84.02mg/100g to 90.50mg/100g (calcium), 9.77mg/100g to 18.54mg/100g (phosphorus), 2.74mg/100g to 19.79mg/100g (magnesium). Most of the minerals were higher in the ripe samples more than the unripe whereas the phytochemical contents reduced in the ripe seeds and pulps. The study generally proved that seeds and pulps of this lesser known and under-utilized fruit have the potentials of supplying nutrients and phytochemicals necessary for proper functionality of human cells and therefore, their consumption or incorporation in food formulation should be encouraged.

Introduction

Nigeria has a wide variety of plants which are both of nutritional and economic importance but are still classified as lesser known [1]. There are little or no information regarding the nutrient compositions of these lesser known fruits and seeds. However, analysis carried out on some of the lesser known fruits and seeds show that they are nutritionally useful and should be exploited further as source of food for man and animals [2]. Such foods include the Landolphia owarien- sis among others. According to [3]. Landolphia owariensis is a common African plant that has been found very useful due to its therapeutic potentials. It is a high climbing plant in the rain forest. The plant has brownish purples with simple terminal cymes of small white flowers which turn yellowish with age. It belongs to the family Apocynaceae. It’s commonly called white rubber vine and known locally by various names in Nigeria: Igbo – utu, Yoruba – mba and Hausa – Ciwa. L. owariensis is one of the plants whose leaves, bark and roots are used for the treatment of many ailments. The glabrous fruit which is 2–5cm in diameter is reddish yellow and spher- ical when ripe. The fruit is very popular among the peasant population in the South Eastern part of Nigeria where the ripe fruit can easily be obtained in the month of April [4]. The pleasantly flavoured ripe fruit is sometimes usually eaten by swallowing the juicy fleshy pulp containing the seed which are defeacated intact (Temple, 1998). The white rubber vine is among the indigenous foods considered lesser known fruit because there is little or no information about its nutrient and phytochemical properties. The fruit is only consumed during its season and of course due to lack of knowledge of its nutrient and phytochemical potentials, there’s has not been serious efforts towards its propagation and preservation. Neither the pulp nor seed of the Landolphia owariensis has any industrial application. This further reduces the economic value of the fruit. It is also worthy to note that the comparative evaluation of the juice and seeds from ripe and unripe white rubber vine has not been published in literature and or made widely known to the consumers of the fruit. This creates an important vacuum that needs to be filled. This study will reveal the proximate, dietary fibre, vitamins, minerals and phytochemical contents of the ripe and unripe fruit. The information will significantly contribute to the declassification of the fruit from the lesser known foods. The findings of the study can spike interest of researchers in the product towards its cultivation, domestication and preservation to widen its availability and use. It can also lead to industrial processing like production of white rubber vine juice or pulp. Also, from the results of this study, the consumers would be equipped with the criteria on which selection between the ripe and unripe can be made. The findings of this study will also reveal the nutrient composition of the seeds and this will obviously end their (seeds) being thrown away as wastes after consuming the pulp. This research is aimed at the assessment of the nutrient and phytochemical contents of pulp and seeds of ripe and unripe white rubber vine.

Materials and Methods

Sample Collection and Laboratory Analysis

Mature fruits (ripe and unripe) of the white rubber vine fruit were plugged from a farmland in Umuisiama, Obokwu Avu, Owerri West Local Government Area. The fruits were washed, cut open to obtain the seeds and pulp. Then the seeds and pulps were analyzed for proximate, dietary fibre, vitamins, minerals and phytochemical contents according to [5].

Statistical Analysis

Data generated in this research were subjected to analysis of variance (ANOVA) as described by [6]. Tukey’s test was used to separate the means and the differences between the means was considered to be significant at p < 0.05.

Results And Discussion

Proximate Composition and Dietary Fibre of the White Rubber Vine Samples

The moisture content of the white rubber vine samples ranged from 15.22% to 31.85% (Table 1). There was a significant (p<0.05) difference among all the samples. Obviously, the ripe juice and seed contained higher moisture than the unripe samples. The fat content of the white rubber vine samples varied from 0.57% to 2.87%. The values were 2.42%, 0.57%, 2.87% and 0.91% for samples AWV, BWV, CWV and DWV respectively. It was observed that the fat values are low but the seeds of the white rubber vine contain more fat compared to the pulp.

Table 1: Proximate composition (%) and dietary fibre (%) of the White Rubber Vine Samples.

Values are means of triplicate analysis ± standard deviation. Values with different superscripts in the same row are significantly (p<0.05) different. AWV = Unripe white rubber vine seed, BWV= Unripe white rubber vine pulp, CWV = Ripe white rubber vine seed, DWV = Ripe white rubber vine pulp

The statistical analysis revealed that there were significant (p<0.05) difference among all the white rubber vine samples in terms of ash content. The pulp from ripe white rubber vine (DWV) had the lowest ash content (2.37%) followed in ascending order by the pulp from the unripe sample (BWV) which has 2.61%. The seed from the ripe sample (CWV) had 3.22% while the seed from unripe sample (AWV) had the highest ash content of 3.62%. The values for the ash contents in this study were low compared to 5.12% dry weight reported by [7]. According to [8] high content of ash indicates that the seed contains useful minerals. The results in Table 1 also revealed that fibre content of 3.58%, 2.76%, 3.55% and 2.61% was respectively obtained from AWV, BWV, CWV and DWV. It was observed that the seeds (unripe and ripe) contain more fibre compared to the pulp. The value (3.50%) obtained in the study by Nwaogu and Igwe (2010) is comparable to the values in this study. Crude fibre cannot be digested by man; rather, it plays an important role in providing roughage that aid digestion and reduces the accumulation of carcinogen in the body. Protein content in the range of 6.31% to 9.03% were obtained from the white rubber vine samples (both unripe and ripe). The results indicated that the seeds contain more protein than the pulp and the seed of the unripe white rubber vine was the highest source of protein among all the samples analyzed. This corroborates with [9]. The seeds of the fruit were found to contain higher carbohydrate than the pulps. The unripe seed had 66.13% which is significantly (p > 0.05) higher than 61.01% found in the ripe counterpart. This implied that ripening caused significant (p < 0.05) decrease in carbohydrate content of the seeds as well as the pulps where reduction from 59.18% to 55.95% was observed. However, the results of this work agrees with the assertion by [10]. that the major compounds of fruit pulps are carbohydrates. The values in this study are higher than 52.40% reported by Nwaogu and Igwe (2010). Amongst the white rubber vine samples analysed, the unripe seed sample (AWV) had the highest dietary fibre followed by the ripe seed. This difference may be attributed to the metabolic processes during ripening because according to[11], a key component of the cell wall, pectin is broken down by pectinase enzymes, which also include pectin methylesterase and polygalacturonase. Moreover, fruit softening is facilitated by the enzymes cellulase and hemicellulose, which break down the cellulose and hemicellulose in the cell wall. This results in reduction/alteration in fiber components. Fruit softening is primarily brought on by alterations in the content and structure of the cell walls, which affect the fruit’s flavor, texture, scent, and appearance [12]. Xyloglucan molecules connected to cellulose’s limited regions often make up cell wall [13]. It is well known that the ripening process of cell walls primarily affects pectin, hemicellulose, and cellulose. This is achieved through the coordinated and cooperative action of enzymes that modify the cell wall. These enzymes primarily consist of polygalacturonase, pectin methylesterase, cellulase, xylanase, β-galactosidase, α-arabinofuranosidase, and protease [14]. Extensive research has been conducted on the action patterns of cell wall modifying enzymes in various fruit varieties, including tomato, pears, zucchini fruit, apples, and so on, in order to investigate the internal relationship between textural properties and fruit softening. Protease enzymes break down proteins into amino acids, contributing also to the softening of fruit texture during ripening [15].

Mineral Composition of the White Rubber Vine Samples

The mineral contents of the white rubber vine samples are presented in Table 2. Results showed that the fruit contains iron varying from 3.44mg/100g to 5.87mg/100g. Iron was significantly found higher in the seeds than the pulp. According to [16] iron is essential for the biosynthesis of the oxygen-carrying pigment of red blood cells and the cytochromes that function in cellular respiration. Potassium was the most abundant mineral in the fruit. It was found in the range of 81.78mg/100g to 106.29mg/100g. This agrees with [17] that confirmed potassium as the dominant mineral constituent of white rubber vine. Potassium is very important in the maintenance of osmotic balance between cells and the interstitial fluid in animal systems, would be an excellent food source of lowering blood pressure, reducing the risk of osteoporosis and in maintaining bone health. Zinc was the least of all the mineral elements analyzed. It varied from 1.32mg/100g to 1.73mg/100g. The next to potassium in abundance is calcium. It was found most abundant in the unripe pulp (90.50mg/100g), followed by the ripe pulp (89.90mg/100g) while the seeds of the unripe and ripe fruit respectively contained 84.25mg/100g and 84.02mg/100g. The results imply that both the unripe and ripe seeds and pulps of the white rubber vine can be recommended where calcium is needed. Another important mineral in the fruit is phosphorus. It was found within 9.77 to 18.45mg/100g and it is higher in the seeds than the pulp. On the contrary, magnesium was discovered more in the pulp than in the seeds. The pulp of the unripe and ripe white rubber vine contains 18.49 and 19.79mg/100g each whereas the seed had 2.74 and 3.11mg/100g respectively.

Table 2: Mineral Composition (mg/100g) of the White Rubber Vine Samples

Values are means of triplicate analysis ± standard deviation. Values with different superscripts in the row are significantly (p<0.05) different. AWV = Unripe white rubber vine seed, BWV= Unripe white rubber vine pulp, CWV = Ripe white rubber vine seed, DWV = Ripe white rubber vine pulp

Vitamin Composition of the White Rubber Vine Samples

The vitamin A content of the white rubber vine samples is within 2.66µg/100g to 6.86µg/100g. There were significant (p<0.05) difference among all the white rubber vine samples. The result revealed that the highest (6.86µg/100g) vitamin A was recorded in the seed from ripe white rubber vine (sample DWV) followed by samples BWV and CWV that contains 4.41µg/100g and 3.17µg/100g respectively while the seed from unripe white rubber vine (AWV) had the lowest value (2.66µg/100g). The results proved that seeds and pulp from the ripe samples had enhanced vitamin A content more than the unripe counterpart. Vitamin A is required for good sight and deficiency of vitamin A could result in blindness. The values of the vitamin B1 content of the white rubber vine samples include 0.10mg/100g, 0.98mg/100g, 0.27mg/100g and 0.39mg/100g for samples AWV, BWV, CWV and DWV respectively. Vitamin B1 contents of the pulp were significantly (p<0.05) higher compared to the seed samples of the white rubber vine. The observed difference in thiamine content of the pulp and seeds was inherent and not induced by ripening. Ripening did not cause a significant increase of thiamine in the samples. Thiamine plays an important role in the utilization of carbohydrate for supply of energy, where it functions as the coenzyme thiamine pyrophosphate, or cocarboxylase, in the oxidation of glucose [18]. Absence of vitamin B1 results in a specific deficiency disease called beriberi. The vitamin B2 content of the white rubber vine samples varied from 0.04mg/100g to 0.08mg/100g. It was observed that the seed (both for unripe and ripe) of the white rubber vine contains more vitamin B2 compared to the pulp. The result showed that BWV which contains 0.04mg/100g had the least vitamin B2 followed in ascending order by samples AWV and DWV with the same value 0.06mg/100g while CWV had the highest value (0.07mg/100g). Ripening did not result in a significant (p < 0.05) increase in the vitamin B2 content of both the seed and pulps of the samples.

Table 3: Vitamin Composition of the White Rubber Vine Samples

Values are means of triplicate analysis ± standard deviation. Means with different superscripts in the same row are significantly (p<0.05) different. AWV = Unripe white rubber vine seed, BWV= Unripe white rubber vine pulp, CWV = Ripe white rubber vine seed, DWV = Ripe white rubber vine pulp. There were significant (p<0.05) difference among all the samples in terms of vitamin C. Pulp from ripe white rubber vine (DWV) recorded the highest (17.69mg/100g) vitamin C content followed in descending order by BWV with the value 5.16mg/100g, CWV with the value 4,29mg/100g and (3.84mg/100g). Ripening led to remarkable enhancement of the vitamin C content of the samples. The results obviously proved that the pulp of ripe white rubber vine is a good source of vitamin C compared to the other samples analyzed. Vitamin C is the most thermolabile vitamin and is easily leached into water [19]. Vitamin C affects blood vessels, skin, gums and connective tissues, red blood cells and wound healing and its deficiency leads to scurvy [20].

Phytochemical Composition of the White Rubber Vine Samples

The flavonoid contents of the white rubber vine samples varied from 0.43mg/100g to 1.10mg/100g. The pulp from ripe white rubber vine (DWV) had the lowest flavonoid content (0.43mg/100g) followed in ascending order by the pulp from the unripe sample (0.78mg/100g), then seed from the ripe sample CWV which contains 0.81mg/100g while the seed from unripe sample (AWV) had the highest flavonoid (1.10mg/100g). The observed lower content of flavonoid could be attributed to ripening. Phytate was found higher in the seed whereas oxalate was more in the fruit pulp. Oxalate may be responsible for the sour taste of the fruit pulp and the results showed that its concentration was lower in the ripe samples. Fergusin et al. (1993)[21] reported that phytic acid intake of 4-9mg/100g is said to decrease iron absorption by 4-5 folds in humans while [22]. stated that a daily intake of 450mg of oxalic acid has been reported to interfere with various metabolic processes. The values obtained for phytate (2.10 – 3.10mg/100g) and oxalate (20.31 – 23.68mg/100g) are lower than the reported lethal dosage. Therefore toxic effect of these anti-nutrients may not occur when the fruits are consumed. Saponin was found to be more abundant than flavonoid and phytate in both the seed and pulp but also found to be lowered by ripening. Its values were in the range of 9.40mg/100g to 21.18mg/100g. The value 28.40mg/100g obtained by Nwaogu and Igwe (2010) is high compared to the values in this study. The seed and pulp of unripe white rubber fruit had 1.75 and 1.29mg/100g alkaloid each while those from ripe fruit had 1.66 and 0.92mg/100g respectively. Obviously, the ripe sample had lower alkaloid content than the unripe in both seed and pulp. This implies that ripening could impart slight reduction in the alkaloid content.

Table 4: Phytochemical Composition of the White Rubber Vine Samples (mg/100g)

Values are means of triplicate analysis ± standard deviation. Means with different superscripts in the row are significantly (p<0.05) different. AWV = Unripe white rubber vine seed, BWV= Unripe white rubber vine pulp, CWV = Ripe white rubber vine seed, DWV = Ripe white rubber vine pulp

Tannins was found to be the most abundant phytochemical in the fruit. Its value was in the range of 23.62 to 60.12mg/100g. The result showed that seed contained higher tannins than the pulp and ripening also caused a reduction the concentration of tannins discovered in both the seed and pulp. The values obtained in this study were lower than 100.50mg/100g obtained by Nwaogu and Igwe (2010).

Conclusion and Recommendation

The proximate composition, dietary fibre and mineral content of the ripe and unripe seed and pulp of white rubber vine clearly indicate that they are nutritious and could serve well as delicacies or incorporated in food formulations. The seeds are rich in protein, dietary fibre, ash, phosphorus and iron while the pulp is rich in magnesium, vitamins A, B1 and C. Both the seed and pulp have high quantity of potassium and calcium. The phytochemicals are within the range which makes the seeds and pulps of the fruit healthy. The results of this thesis should be disseminated to the society in order to widen people’s interest in white rubber vine. It is recommended that the cultivation of white rubber vine should be encouraged in a large scale so that there will be an all-year- round availability for consumers. Also, further study is recommended on the evaluation of vitamins, amino acids and phytochemical contents of the food material.

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