Studies focused on the chemical composition of wild edible plants and how these chemicals contribute to the nutrition of local communities are increasing in the recent years

Studies focused on the chemical composition of wild edible plants and how these
chemicals contribute to the nutrition of local communities are increasing in the recent years
(Salvi & Katewa 2016). Wild edible plants are rich in nutrients such as proteins, lipids and fatty
acids, carbohydrates, vitamins, and minerals. These plants provide several health benefits
and reduce the risk of diseases (Islary et al. 2016).Proteins and amino acids
Proteins are one of the components essential to the diet of humans and other
organisms (Medak & Singha 2016). Proteins repair muscle tissues and transport molecules
needed in the body. Studies revealed that wild edible plants serve as moderate sources of
protein (Medak & Singha 2016; Nabatanzi et al. 2016; Seal et al. 2017a, 2017b).
The leaves of wild edible plants are rich in protein (Odhav et al. 2007), with values
ranging from 13.24% to 35.13% (Nabatanzi et al. 2016; Seal et al. 2017a, 2017b). Though
these leaves are only consumed when nothing is available, high protein content makes these
plants desirable for consumption and possible cultivation. These plants already supply more
than 11% of the regular daily protein allowance (Glew et al. 1997, 2005, 2004)
Fruits and seeds of wild edible plants have low protein content. Proteins represent only
a small fraction of the total fruit and seed mass. Values range from 3.17% to 7.15% protein
(Murray et al. 2001; Mahapatra et al. 2012; Ayessou et al. 2014), a large difference from the
protein content on the leaves of wild edible plants.
In analyzing protein in wild edible plants, there are instances when nitrogen
compounds that do not contribute to protein composition are present (Sotelo et al. 2007).
When such instances occur, the protein is said to be crude. Nevertheless, this measure
provides a good estimate of the available protein in wild edible plants.
Carbohydrates and dietary fiber
Carbohydrates are the most abundant biomolecules on Earth and are the dietary staple
in most parts of the world (Nelson & Cox 2008). The oxidation of these carbohydrates
produces high-value energy that humans need for daily activities. Carbohydrate content
analysis is necessary to determine the nutritional value of wild edible plants.
According to Ayessou et al. (2014), carbohydrates in wild edible plants are
concentrated in fruits and are predominated by glucose and fructose. These sugars are
evident in the taste of these wild fruits. However, sugar content varies from one wild edible
plant to another.
Sugar in wild edible plants commonly range from 20% to 40% (do Nascimento et al.
2011; Mahapatra et al. 2012; Ayessou et al. 2014). However, Murray et al. (2001) reported
that sugar content in wild baobab fruits in Africa reach as high as 61.73%. At this amount, the
fruits provide high energy, from 1329kJ to 1430 kJ per 100 grams of fruit consumed (Murray
et al. 2001).
Sugar content in wild edible plants is higher than that of cultivated fruits like
pomegranate 17.17%, mango 17.00%, and grapes 16.25% (Mahapatra et al. 2012). Thus,
wild edible plants can be potential sources of sugar needed in the body.Dietary fibers are another class of carbohydrates reported in literature. These are
substances commonly found in cell wall of plants, particularly in stalks, stems, and leaves
(Nelson & Cox 2008). Fibers are essential for a smooth running of the digestive tract.
Wild edible plants contain 9.7% to 53.3% dietary fiber (Murray et al. 2001; Nabatanzi
et al. 2016). However, Medak & Singha (2016) found that previous studies reported crude fiber
on wild edible plants, rather than total dietary fiber. Direct measurement of dietary fiber should
be done because fiber is not digested in the human body. Crude fiber underestimates the fiber
content of wild edible plants and apparently increases the amount of digestible carbohydrate.
As a result, there is an overestimate of the calculated energy content of the food.
Lipids and fatty acids
Biological lipids are a chemically diverse group of compounds that are insoluble in
water. Fats and oils are lipids that serve as principal forms of stored energy in many organisms,
including plants (Nelson & Cox 2008). Consumption of lipids is necessary for humans and is
part of the balanced nutrition that humans need.
Most studies concerning fatty acid analysis focused on linoleic acid omega-3 and
alpha-linolenic acid omega-6. These fatty acids constitute the lipids essential to humans
(Glew et al. 1997, 2005).
Fatty acids are concentrated on different parts of wild edible plants that include pods,
seeds, fruits, flowers, and parts with sticky raw membrane. These parts contain the highest
absolute amounts of the essential fatty acids (Glew et al. 1997, 2005).
Most wild edible plants contain 0.23% to 8.07% fatty acids (Odhav et al. 2007;
Nabatanzi et al. 2016; Seal et al. 2017a). These levels are at par with leafy vegetables
cultivated for consumption (Uddin et al. 2014). Surprisingly, Vitex doniana black plum does
not contain linoleic and alpha-linolenic acids. These undomesticated edible plants form an
important constituent for traditional subsistence in local communities. Odhav et al. (2007) and
Medak et al. (2016) suggested that wild edible plants are healthy foods because of its low
levels of fatty acids.
Studies on wild edible plants relative to omega-3 and omega-6 fatty acids are still being
carried out. However, the general trend is the enormous variation in the fatty acid content of
these plants (Aberoumand 2009). Possible cultivation of wild edible plants will lead to
increased production of these fatty acids and reduce the risk of chronic diseases.
Vitamins
Vitamins are organic substances essential in small quantities for human nutrition.
However, vitamins do not provide energy or serve as building units (Kennedy 2009). These
substances support normal growth and body processes throughout the human life span.Vitamin A is a fat-soluble vitamin identified through its retinyl functional group. This
vitamin supports the eyes, skin, hair, and bones. It also plays a role in the immunity of a person
(Kennedy 2009).
Studies regarding vitamin A in wild edible plants is limited. Nabatanzi et al. (2016) is
among the few that reported vitamin A composition of wild edible plants. It was found that
Physalis angulata contains 1.86% vitamin A. The low percentage of this vitamin is attributed
to the processing of P. angulata before consumption. This resulted to the possible
decomposition of vitamin A in P. angulata.
Studies of Glew et al. (1997, 2005) and Martins et al. (2011) reported the presence of
carotenoids in wild edible plants. Carotenoids serve as provitamins for vitamin A. These are
substances that convert to vitamin A upon intake. Amaranthus vidis, Asparagus acutifolius,
and Stellaria media contain carotenoids from 4.2 mg to 23.3 mg for every 100 grams of the
wild plant.
Vitamin C, also known as ascorbic acid, have been a target for many wild edible plant
studies. According to Guil et al. (1997), ascorbic acid content is very high in several plant
families, with values over 100 mg / 100 g. These plants belong to the following families:
Amaranthaceae, Chenopodiaceae, Compositae, Cruciferae, Polygonaceae, and Umbelliferae.
In these families, the vitamin C of the wild species is higher compared to that of their respective
cultivated counterparts (Guil et al. 1997; Shaheen et al. 2016). Malvaceae, Plantaginaceae,
Portulacaceae, and Verbenaceae have high ascorbic acid content, but lower than that of its
respective cultivated counterparts (Guil et al. 1997; Yildirim et al. 2001; Sekeroglu et al. 2006).
Generally, wild edible plants have ascorbic acid content similar or superior than the ascorbic
acid content of their cultivated counterparts.
Among plant parts, the fruit has the most vitamin C. Wild fruits contain high amounts
of bioactive compounds with antioxidant potential, particularly vitamin C (Dembitsky et al.
2011). Wild edible fruits that are good sources of vitamin C include Phyllantus acidus, Solanum
torvum, Terminalia citrina, and Ziziphus mauritiana. Vitamin C content of these fruits range
from 26.27 mg to 142.2 mg per 100 grams of the fruit (Murray et al. 2001; Martins et al. 2011;
Nabatanzi et al. 2016). Ascorbic acid content of these fruits are comparable to contemporary
cultivars such as papaya and strawberry, and are richer in vitamin C content compared to that
of banana, apple, pomegranate, and mango (Mahapatra et al. 2012).
The preparation of these wild plants affects its vitamin C content. Sánchez-Mata et al.
(2012) reported that Silene vulgaris and Foeniculum vulgare retain most ascorbic acid when
eaten raw. However, Bryonia dioica, Humulus lupulus, and Tamus communis retain high levels
of ascorbic acid even when cooked. Aside from nutritional value, the antioxidant potential of
ascorbic acid was also studied in wild edible plants. This creates a basis for the
ethnopharmacological use of the same plants (Barros et al. 2011; Uddin et al. 2014).Major minerals
Calcium is one of the major minerals essential in the human body. It aids in building
red blood cells and maintaining body mechanisms (Mahapatra et al. 2012). The absence of
this mineral in the body leads to weak, stunted growth and poor bone development.
Wild edible plants contain considerably high amounts of calcium, particularly in fruits
(Mahapatra et al. 2012). Calcium content of wild edible plants range from 1.63 mg/g to 566
mg/g (Glew et al. 1997; Guil Guerrero et al. 1998; Mahapatra et al. 2012; Seal et al. 2017b;
Tunçtürk et al. 2017). These levels are higher than the calcium content of conventional fruits
like guava 0.18 mg/g and strawberry 0.22 mg/g (Mahapatra et al. 2012). This indicates that
wild edible plants could be alternative sources of calcium.
However, calcium bioavailability might be lower than these findings, due to the
presence of oxalic acid in wild plants (Guil Guerrero et al. 1998). High oxalic acid/calcium ratio
means that calcium readily absorbed by the body might be lower than indicated. High fiber
content also indicates that calcium found in these plants could hardly be absorbed by the body
(Guil Guerrero et al. 1998).
Magnesium is an element responsible for growth and maintaining body mechanisms
(Mahapatra et al., 2012). Wild edible plants contain high amounts of magnesium, ranging from
0.68 mg/g to 841 mg/g (Glew et al. 1997; Guil Guerrero et al. 1998; Uddin et al. 2014;
Nabatanzi et al. 2016; Tunçtürk et al. 2017). Like calcium, bioavailability of magnesium needs
to be checked because some plant species have high oxalic acid and high fiber content. Fiber
and oxalic acid interfere with the absorption of magnesium in the body (Guil Guerrero et al.
1998).
Relatively few studies present sodium as a major mineral needed in the body. Sodium
content varies from one species to the other, with high levels at halophytic plants (Guil
Guerrero et al. 1998). These values range from 55 mg/g to 290 mg/g sodium. Non-halophytic
plants tend to have lower sodium content from 0.21mg/g to 1.63 mg/g (Medak & Singha 2016;
Seal & Chaudhuri 2016a; Seal et al. 2017b).
Potassium is highly concentrated in fruits. The fruits of Eugenia rothii and Terminalia
citrina contained 20.09 mg/g and 14.61 mg/g potassium, respectively. Potassium in these
fruits is higher compared to that of cultivated fruits like guava 4.17 mg/g and banana 3.58
mg/g (Guil Guerrero et al. 1998). Most wild plant species contain potassium from 13.74 mg/g
to 47.31 mg/g, consistent among most studies (Seal & Chaudhuri 2016a; Seal et al. 2017a,
2017b; Tunçtürk et al. 2017).
Trace minerals
Iron is a mineral that aids in building red blood cells and maintains body mechanisms
(Mahapatra et al. 2012). Iron deficiency leads to stunted growth and poor bone development.Wild edible plants contain iron ranging from 1.7 mg/g to 589 mg/g (Glew et al. 1997; Guil
Guerrero et al. 1998; Valvi et al. 2011; Mahapatra et al. 2012).
Iron in wild edible plants is higher than that of cultivated plants like pomegranate 0.03
mg/g, banana 0.026 mg/g, and guava 0.026 mg/g (Mahapatra et al. 2012; Tunçtürk et al.
2017). Iron is also a potential antioxidant capable of reducing free radicals and chelating
harmful compounds (Valvi et al. 2011).
The richest sources of zinc are the fruits and seeds of wild edible plants. Values range
from 0.41 mg/g to 10 mg/g (Glew et al. 1997; Guil Guerrero et al. 1998; Tunçtürk et al. 2017).
These values suggest that most plant species have zinc content below levels of detection.
Similarly, wild plant species have copper and manganese only up to 20 mg/g and 1 mg/g,
respectively (Guil Guerrero et al. 1998)v