Leafy vegetables are grown mainly in the gardens and consumed as side dish or soup with starchy staples among many Nigerians. They are of special nutritional importance being good sources of fat and water-soluble vitamins1. They are highly beneficial for maintaining health and preventing diseases. Dark green leafy vegetables provide high amounts of micro-minerals which play vital roles in nutrient metabolism and retard degenerative diseases2. Gropper et al.3 suggested the need to consume high vegetable meals to prevent colon and stomach cancers. Ball4reported a high vitamin, dietary fibre and mineral content in vegetables and the role they play in maintaining alkalinity in the body. The high dietary fibres in green leafy vegetables help in regulating the digestive system, aiding bowel health and weight management5,6.

Several studies have shown that high dietary fibre intake may lower the risk of colon cancer5,6,7. Green leafy vegetables are generally low in calorie and contain low carbohydrate content but high in fibre. These make them important in promoting and maintaining healthy body weight and ideal for reducing the risk of developing type II diabetes. Quite a large number of African indigenous leafy vegetables have long been known and reported to have health promoting properties and uses8. Several of these indigenous leafy vegetables continue to be used for prophylactic and therapeutic purposes in rural communities.

Silk cotton (Ceiba pentandra) is a tropical tree of the order Malvalesand the family Malvaceae. It is the largest African forest tree and severally known among some Nigerian ethnic groups as Rimi (Hausa), Bamtami (Fulani), Araba ogungun (Yoruba) and Apu (Igbo)9. Kapok is the most commonly used name for the tree. The tree is also known as the Java cotton, Hara kapok, Silk cotton or Ceiba10. The leaves of Ceiba pentandra have been reported to have both nutritional and medicinal properties. In Nigeria, especially in some part of South-west and South-east geo-political zones, the leaves are cooked in form of slurry sauce comparable to Okra. The young leaves or the shoots are normally used for soup, and a powder prepared from its dried leaves is used to prepare sauce during the dry season11.

African leafy vegetables have long been reported and continue to significantly contribute to dietary vitamin and mineral intakes of local populations12. Copious consumption of vegetables treats hemorrhoids, gallstones, obesity and constipation; the antioxidants in vegetables decrease the risk of heart disease and vitamin K contents of dark green leafy vegetables provide a number of health benefits including bone protection from osteoporosis and protection against inflammatory diseases13 In Nigeria, insufficient efforts have been made in assessing the nutritional value of less utilized indigenous green leafy vegetables, and knowledge about their consumption is low, leading to many of them going into extinction unnoticed. Nutrient analysis of indigenous vegetables can lead to better understanding of their nutritional importance14 and improve biodiversity as well as dietary diversity. This study was therefore undertaken to evaluate the nutrient composition and micronutrient potential of raw and cooked Ceiba pentandraleaf as a means of promoting vegetable dietary diversity in Nigeria.

Table 2 shows the result of proximate composition of the four samples. The raw sample (sample 1) was very high in moisture content, low in crude protein, ash and carbohydrate, and very low in fat and gross energy. Steaming resulted in increase in the moisture content ofthe blanched sample (sample 2) with attendant reduction in other nutrients. However, preparing the vegetable into soup (sample 3) and sauce (sample 4) led to significant reduction in moisture and fibre content with significant increase in other nutrients (p<0.05), especially protein, fat and gross energy content of the products compared to the raw and blanched samples.

In Table 3, the raw sample contained substantial amount of potassium, calcium, magnesium, phosphorus and iron. There was a significant reduction in most of the macro-minerals in the blanched sample (sample 2) compared with the raw sample (p<0.05). Processing the leaf to soup and sauce led to significant increase (p<0.05) in all the minerals studied compared with both raw and blanched samples,no significant difference (p>0.05) in the manganese and selenium contents of the raw and processed samples was observed. The raw sample was rich in β-Carotene, vitamins B₁, B₃, B₆ and ascorbic acid. Blanching and cooking into soup and sauce resulted in significant reduction in values of the water-soluble vitamins (p<0.05). However, there was no significant difference in the β-Carotene values for samples 1 and 4 (Table 4).

The raw leaf contains appreciable amounts of phytochemicals, especially phytates, saponins, glycosides and alkaloids (Table 5). Significant reduction (p<0.05) was found in all the phytochemical components in the processed samples. The cooked sauce had the highest level of reduction of phytochemicals followed by cooked soup (p<0.05.). Both the soup and sauce were scored well by the sensory Assessors (Table 6). The soup (sample 3) was rated better in texture, while the sauce (sample 4) was rated higher in colour, odour, taste (p<0.05) and general acceptability (p>0.05).

The value obtained for the moisture content of raw Ceiba pentandraleaves (sample 1) was in line with the report of Enechi et al.10. High moisture content in vegetables is characteristic of the degree of its freshness, perishability and susceptibility to microbial attack. Generally, the processed samples (Samples 2, 3 and 4) were high in moisture content. The increase in moisture content of blanched sample above the fresh one could be due to water absorption by the fibres and other natural chemical component of the vegetables. The lower moisture content for the soup and sauce compared with the raw sample was believed to be due to the added ingredients.

The value for crude protein content of fresh Ceiba pentandraleaf was within the range of protein content of green leafy vegetables reported by Ball20, but lower than the value reported by Anosike et al.21. The crude protein decreased with blanching, and this agrees with what was reported by Komolafe and Obayanju22. The reduction in crude protein content of the blanched sample is believed to be due to leaching of soluble protein into the water. Preparing the vegetable to either soup or sauce however increased the protein content of the products, which might have resulted from the contribution of the added ingredients. The raw leaf was very low in fat content which is characteristic of most leafy vegetables. The fat value is comparable to the values reported in the literature for Solaneciobiafrae and Solanum nigrum with valuesof 0.92% and 0.96% respectively23. However, an increase was observed in the fat content of samples 3 and 4 due to addition of palm oil during cooking. Dietary fats function in increasing the palatability of food by absorbing and retaining flavours24.

The raw and processed samples’ crude fibre values are within the values reported for some commonly consumed vegetables such as Celosia argentea(1.8%)19, Ocimumgratissimum(3.89%), T. triangulaire(2.57%) and Telfariaoccidentalis(4.22%)1. The dietary fibre in green leafy vegetables helps to regulate the digestive system, aid bowel health and weight management6. The significant reduction in crude fibre content of the processed samples (samples 2, 3, 4) compared with the raw sample is suggestive of presence of soluble fibre content in the leaf.

The carbohydrate content of the studied leaf is lower than what was reported by Enechi et al.10 and Friday et al.11. The carbohydrate content of the leaf was significantly reduced (p<0.05) with blanching, and increased in samples 3 and 4 due to the added ingredients used in the cooking. The low carbohydrate content of the leaves could be of importance in the treatment of diabetes and its associated complications such as coronary artery disease25 as well as weight reduction. The gross energy content of the raw sample was observed to be slightly lower than what was reported by Raimi et al.26. The gross energy significantly increased in samples 3 and 4, which was believed to be a direct result of added ingredients which resulted in significant increase in their protein, fat and carbohydrate content.

The raw sample contained appreciable amount of essential minerals such as potassium, calcium, magnesium, iron, and moderate amount of sodium, and hence, can serve as good source of these minerals. However, blanching resulted in slight reduction in value of the minerals in sample 2, and this is similar to the findings of Shahnaz et al.27 and Oboh28, who observed that conventional food processing techniques such as blanching and cooking caused significant decrease in mineral content of vegetables. There was an increase in the mineral content of samples 3 and 4, with sample 4 having the highest values for all the minerals. Increase in the mineral content of samples 3 and 4 could have resulted from the ingredients added.

The raw C. pentandraleaf was rich in beta carotene, vitamins B_1, B₃, B₆ and ascorbic acid which were significantly reduced by processing. However, there was slight increase in the beta carotene content of the sauce. This observation is in line with the report of USDA29 that moderate cooking increases the availability of β-carotene in the vegetables as a result of breakdown of plant cell walls of the vegetables. Rickman et al.30 also stated that loss of soluble solids and release of protein-bound β-carotenes that occur during boiling may contribute to the observed increase in the pro-vitamin content. The significant reduction in B-vitamins and ascorbic acid content of samples 3 and 4 was believed to be due either to their destruction by heat or their leaching to washing water and blanching process before cooking.

The raw vegetable leaf contains substantial amounts of phytochemicals with health promoting benefits. The flavonoid in the fresh sample is much lower compared to the value reported by Friday et al.11. Phytochemicals such as beta carotene, ascorbic acid, flavonoids, alkaloids, tannins and saponins have antioxidant activity which protect body cells against oxidative damage, thereby reducing the risk of developing certain types of cancer. Phytochemicals also interfere with the replication of DNA cells, prevent the multiplication of cancer cells and play a role in prevention of some hormone-dependent cancers such as breast and prostate cancer31. A significant reduction was observed in the phytochemical content of processed samples, especially in soup and sauce. This finding is in support of the findings of Aganga and Tshwenyane32 and Ogbadoyi et al³³ who reported that boiling of vegetables in water ruptures the cell walls which can subsequently cause the leaching of the cell contents including the phytochemicals and toxic substances.

The Panelists rated both the soup and sauce highly in all the parameters tested. However, the vegetable sauce was rated higher for its colour, taste, aroma and general acceptability. This may be because the sauce contained more onions and palm oil, and was fried for a longer time than the soup.

The leaf of Ceiba pentandracontains significant quantities of essential micronutrients such as potassium, calcium, magnesium, phosphorus, iron, β-carotene, ascorbic acid, and the B-vitamins, and its nutrient content compares favourably well with that of commonly consumed vegetables. The presence of phytochemicals in the vegetable confers promotion of health and medicinal values on it. Its fibre content also qualifies it as a good and desirable vegetable for dietary diversity. Blanching the vegetable led to loss of more nutrients compared to the soup and sauce. Addition of some ingredients during processing significantly improved the nutrient content of the cooked samples; therefore, there is the need to popularise the consumption of this vegetable in the areas where it is available as a means of improving dietary diversity, health and nutritional status of people.