There is a growing awareness that plant based foods make for healthy living. Much of the evidence so far has come from observations of cultures in which the diet comes mainly from plant sources, and which seem to have lower rates of certain types of cancer and heart disease. For instance, the relatively low rates of breast and endometrial cancers in some Asian cultures are credited, at least in part, to dietary habits. These cancers are much more common in the United States, possibly because the typical American diet is higher in fat and lower in fruits, vegetables, legumes, and grains (American Cancer Society, 2013).
Green vegetables are an imperative component of a nutritious diet. The varieties of leafy vegetables are diverse, ranging from leaves of annuals and shrubs to tree leaves (Sood,et al., 2012). They play a significant role in human nutrition, especially as sources of vitamins, minerals and dietary fiber; they offer a high concentration of micronutrients for low contents of calories and fat (Lintas, 1992). The benefits of a diet rich in fruits and vegetables are also provided by the complex mixture of chemicals present in whole foods. In the science of food, no change has been bigger than the discovery of phytonutrients and their unique place in our health. Phytonutrients include all of the unique substances that give foods their brilliant colors, their delicious flavors, and their unique aromas. They are also the nutrients most closely linked to prevention of certain diseases (Lintas, 1992), many chronic diseases associated with cancer, inflammation, atherosclerosis, and aging caused by free radicals (Liu, 2003, 2004).
The major plant-derived chemical groups now recognized as having potential health-promoting effects are the flavonoids, alkaloids, carotenoids, pre- and pro-biotics, phytosterols, tannins, fatty acids, terpenoids, saponins, soluble and insoluble dietary fibres (Basu et al., 2007). These chemicals are strong antioxidants and function to modify the metabolic activation and detoxification/disposition of carcinogens, or even influence processes that alter the course of the tumor cell. The higher the average daily intake of fruits and vegetables, the lower the chances of developing cardiovascular disease (Hung et al., 2004).
The key fruits and vegetables in human nutrition both in the developed and developing countries of the world are the yellow corn, spinach, green leafy vegetables, fruits, tomato, watermelon, pink-fleshed guava, red-fleshed papaya, red pepper, mango, orange, carrot, melon, yellow and orange-fleshed sweet potato, nuts, tea, wine, flaxseed, sesame seed, grapes, peanuts, cereals and pulses. Evidences of the benefits to human-health associated with their consumption have caused an increase in the demand for fresh-like fruits and vegetables (Oms-Oliu et al., 2012). Hence, the need for the identification and exploitation of other novel plants to fulfill the growing need of plant based chemicals. The emphasis therefore shifted to the underutilized plant foods which as a result of lack of attention from research and development has meant that their potential value to human well-being and income is underexploited (IPGRI, 2002). While such crops continue to be maintained by sociocultural preferences and the ways they are used, they remain inadequately documented and neglected by formal research and conservation (IPGRI, 2002). Irvingia gabonensis (Family: Irvingiaceae) commonly known as the African bush mango, Dika nut, bush mango or wild mango, and manguier sauvage in French is one of such crops, with the leaves only known to be used as food for livestock by farmers (Ayuk et al., 1999).
African bush mango (Irvingia gabonensis) belongs to the Irvingiaceae plant family (Lamorde et al., 2010). It is a wild forest tree 15 – 40 m with a bole slightly buttressed, possessing dark green foliage and yellow flowers (Kuete et al., 2007). The ripe fruit is green while the edible mesocarp is soft, juicy, and bright orange. The fruits are sometimes referred to as ‘Mangoes’ (hence the synonym of African Bush Mango) although they are unrelated, since the true Mango fruits are borne from the plant Mangifera indica of the plant family Anacardiacea (Bally, 2006). The pulp of this fruit is eaten fresh and can also be used for the preparation of juice, jelly and jam as well for a good quality wine (Akubor, 1996). The mango-like fruits of bush mango are especially valued for their dietary-fiber, fat- and protein-rich seeds (Jianghao and Pei, 2012). The bark of the Irvingia gabonensis tree (rather than the seeds, which are commonly used as fibrous supplements) appears to be traditionally used by the Mende tribe of Africa for pain relief (Okolo et al., 1995). Studies have shown that the seeds of Irvingia gabonensis could be effectively used as an ingredient in health and functional food to ameliorate certain disease states such as diabetes (Dzeufiet, 2009). And the leaves of plants have been shown to be richer in chemical compostion than the fruit pulps and seeds (Nwofia et al., 2012). Bush mango leaf/root extracts have documentary inhibitory activity against several bacteria and fungi. Aqueous leaf extract significantly protected mice against diarrhoea induced experimentally by castor oil in terms of severity and onset and the population of animals with diarrhoea (Abdulrahman et al., 2004). As reported by Kuete et al. (2007), the aqueous maceration of the leaves is used as anti-poison. And when taken in combination with palm oil, the leaves are also used to stop hemorrhages for pregnant women in Cameroon.
However, due to the varied growing and harvesting seasons of different vegetables at different locations, the availability of fresh vegetables differs greatly in different parts of the world. Thus necessitating processing, which can transform vegetables from perishable produce into stable foods with long shelf lives and thereby aid in the global transportation and distribution of many varieties of vegetables. Processing of leafy vegetables can have a major impact on the sensory attributes, nutrients and antinutrient constituents in the final product (Ramaswamy and Marotte, 2006). The anti-nutritional factors interfere with the bio-availability of nutrients and constitute a major factor limiting the wider food use of many tropical plants. This would also apply to the leaves of African bush mango. Thus the focus of this work was to determine the effect of processing methods on the chemical, nutrient, vitamin, mineral content and microbiological quality of vegetable drink extract of African bush mango.
1.1 Statement of problem
In spite of the growing awareness that plant based foods make for healthy living, there is inadequate consumption of fruits and vegetables. The recommendation is five to ten servings of fruits and vegetables each day in at least three different colours such as dark green, yellow, orange (BC Cancer Agency, Care and Research, 2002). The world health organization (WHO) recommended a minimum daily intake of 400 g of fruits and vegetables (WHO, 2003).
Owing to the perishable nature of fresh produce and the varied growing and harvesting seasons of different vegetables at different locations, the availability of fresh vegetables differs greatly in different parts of the world. This has necessitated processing and thus the determination of the effect of processing on the nutritional interest in vegetable species.
Despite the health benefits associated with intake of vegetables, the risk of microbiological contamination on leafy greens is of concern, and the microbiology of functional and specialty beverages as well as novel beverage ingredients has been poorly studied (Juvonen et al., 2011).
1.2 Justification of study
Reliance on conventional fruits and vegetables as sources of nutrients as well as of other health promoting bioactive components in our present community may not be considered appropriate. In general, such fruits and vegetables which are valuable for vitamins and minerals are only cultivated on small farmers’ holdings. However, African bush mango (Irvingia gabonensis), which has reportedly been used locally to control such conditions as obesity, elevated cholesterol and blood pressure among others, is an underutilized plant in Nigeria. It has been classified as one of the lesser known seeds which were mainly grown for mitigating deforestation and environmental degradation due to the size and height of its tree in the sub-sahara African region from where it originated (Leakey et al., 2003). Thus determination of the potentials of such plant species to improve the lifestyle of local communities, such as we are in, is invaluable.
Leafy vegetables are known to abound in their seasons and vanish out of season. This makes processing an indispensable tool in the agricultural world, hence the need to determine the effect of processing on the nutritional and chemical value of the final product.
1.3 Aims and objectives
The broad aim of this research was to produce and evaluate the effect of processing methods on the chemical composition and microbiological quality of vegetable drink extract from African bush mango.
The specific objectives were:
- To process the leaves of African bush mango (Irvingia gabonensis).
- To produce vegetable drink extract from the processed leaves of African bush mango.
- To determine the chemical composition and microbiological quality of the vegetable
- To evaluate the effect of the processing methods on the chemical composition and
microbiological quality of the drink extract.
1.4 Significance of the study
Fresh leafy vegetables are seasonal and this affects availability of vegetables out of season thus making leaf processing inevitable both in the homes and in the industries. Fruits and vegetables are therefore processed to supply wholesome, safe, nutritious and acceptable food to consumers throughout the year (Mircea, 1995). Research on the effect of processing methods on the chemical composition and microbiological quality of the vegetable drink extract of Irvingia gabonensis would add to the existing knowledge of the processing methods to adopt to meet specific and desired needs. Also, the knowledge of the microbiological quality would guide in the selection of process controls to apply to vegetable drink extracts prior to consumption.