This research was conducted to determine the concentrations of heavy metals and proximate composition of different cereals (maize, millet and rice).Two different samples each sold in two different markets (Ogbete and Gariki) in Enugu, were used for this work, using atomic, absorption spectrophotometer. The heavy metal screening of the cereal samples showed the presence of arsenic in the range of 0.456ppm-0.955ppm but was not detected in sample E and f which are the two different rice I purchased from Ogbete market, then mercury in the range of 0.024ppm-0.124ppm, lead in the range of 0.554ppm-1.083ppm, cadmium in the range of 0.087ppm-0.565ppm, copper in the range of 0.050ppm-0.245ppm and zinc in the range of 1.448ppm-66.954ppm which is the highest and is discussed. The result of proximate composition analysis indicated ash: 1.0%-19.0%, moisture: 8.6%-12.6%, fat: 0.2%-20.0%.
1.0 BACKGROUND OF THE STUDY
Cereals are enriched with niacin, iron, riboflavin and thiamine, and most cereals have abundant fiber content, especially barley, oat, and wheat. Cereals also have soluble bran that aid in lowering blood cholesterol level and keeping heart diseases at bay. Cereals consumption also means an intake of high amounts of protein; breakfast cereals are often eaten with milk that makes for a protein-rich meal. For infants, iron-fortified cereals are said to be the premium solid food.
A cereal is any grass cultivated for the edible components of its grain (botanically, a type of fruit called a caryopsis), composed of the endosperm, germ, and bran. Cereal grains are grown in greater quantities and provide more food energy worldwide than any other type of crop; they are therefore staple crop.
In their natural form (as in whole grain), they are a rich source of vitamins, minerals, carbohydrates, fats, oils, and protein. When refined by the removal of the bran and germ, the remaining endosperm is mostly carbohydrate. In some developing nations, grains in form of rice, wheat, millet, or maize constitutes a majority of daily substance. In developed nations, cereal consumption is moderate and varied but still substantial. The growth of civilizations, or development in the human diet patterns, the cultivation of cereal grains has played a significant role. The word ‘cereal’ is derived from ‘ceres’- the name of the Roman goddess of agriculture and harvest. It is said that almost 12,000 years ago, ancient farming communities dwelling in the Fertile Crescent area of southwest Asia cultivated the first cereal grains. The first Neolithic founder crops that actually initiated the development of Agriculture include einkorn wheat, emmer wheat and barley. Cereals are the important sources of many essential or beneficial components to the human diet. For example, the National Diet and Nutrition Survey of the UK showed that cereal products contributed 29/30% of the total daily energy intake of adult males/females, 22/21% of the intake of protein and 39/37% of the intake of non starch polysaccharides (the major components of dietary fiber, DF) (NDNS, 2011).
Cereals are probably the greatest source of energy for humans. Providing almost 30% of total calories in a regular diet, cereals are probably the most widely consumed caloric food in America. This percentage rises in places like rural Africa, Asia and India where cereals are reported to supply almost 70 to 80% of energy requirements (since people in these regions cannot afford to eat other food product like fruits, vegetables, meat, or milk products. Cereals are inexpensive and a widely available source of energy; this is probably the prime reason why people from all budgets prefer cereals as the major energy provider in their diet. Cereal intake tends to be quite high almost poor income families as they attain good amount of energy through mineral expenditure.
In cereal, around 95% of minerals are the sulphates and phosphates of magnesium, potassium and calcium. A good amount of phosphorous in cereals is present, called phytin. The phylates present in the cereals considerably reduce the activity of iron absorption. The unrefined cereals have more phytates as compared to refined cereals. After the cereals germinate, phytates diminish due to the breakdown of enzymes, and then the iron content is enhanced. This is the reason why molted flours of cereals are said to have more nutritional value than raw flour. Zinc, copper and manganese are also present in cereals in very small quantities. Cereals hardly have and calcium and iron, but ragi is an exception to this. Amongst cereals, rice is the poorest source of calcium and iron. Ragi, millets, jowar and bajra have high amounts of minerals and fiber.
Whole wheat products reduce the chances of breast cancer. Cereals are rich in phytosterols or plant based steroids plant estrogen that stimulates hormone estrogen. Phytosterols binds to estrogen receptors present in the tissues of the breast and blocks human oestrogen that promotes the growth of breast cancer. many studies have shown that colon cancers can be avoided by consuming whole wheat products or any fiber-rich cereals. Phytosterols increase the stool movement through the intestines, thereby constricting the re-absorption time of the estrogen into the blood through the colon wall.
Cereals have both soluble and insoluble fibers like cellulose, pectin, and hemicellulose. These fibers are present in the bran and pericarp, which often gets demolished while processing, thus it is advisable to consume whole cereals to cure extreme constipation troubles. Cereals also effectively improve peristalsis in the intestine and increase the bulk of the stools, thus keeping your internal system clean. Ragi is high in cellulose and has excellent laxative properties that relieve constipation. Brown rice is also helpful for treating this disorder.
The fiber content in cereals decreases the speed of glucose secretion from food, thereby maintaining sugar levels in the blood.
Proteins are present in every tissue of the cereal grain. the concentrated protein-rich areas are scutellum, embryo and alleurone layer and moderate amount can be found in the endosperm, pericarp and testa. The concentration of proteins becomes denser in the endosperm from the center to the borderline. The cereal protein are of different types; like albumins, prolamines gliadins, globulins and glutelins. These type of proteins are called ‘’gluten’’ protein. This gluten has extraordinary elasticity and mobile properties mainly present in wheat grain, but also in some other types of cereals. Cereals usually have 6-12% protein but lack in lysine. The protein content varies in each type of cereals. For instance, rice contains less protein in comparison to other cereals. In fact, the protein percentage even varieties with different varieties of the same cereals. Although less in amount, the quality of rice protein is better than the protein of other cereals. When you consume cereals with pulses, the protein quality automatically improves, owing to the mutual supplementation. Pulses have high lysine content and are deficient in methionine; on the other hand cereals have an abundance of methionine.
Recent research suggests that greater consumption of vegetable, whole grain products and fruits may lower the risk of multimorbidity. If you are suffering from a deficiency in the vitamin B complex, add whole grain cereal to your diet. Most of the vitamins of cereals are present in the outer bran, but the refining process usually reduces the vitamin B content, and thus it is advisable to consume whole grain cereals. Cereals are usually devoid of either vitamin A or vitamin C; only maize has small amounts of carotene. The cereal grains are processed to extract oils that are rich in vitamin E. Rice bran oil has more concentrated amounts of vitamin E than other oils available on the market. Cereals grains are rich in enzymes, particularly protease, amylase, lipases and oxido-reductases. After the seed germinates, amylase actively increases. The germ encloses the protease enzymes. Cereals are undoubtedly full of nutrition, but unfortunately, the refining process degrades their quality. The degree of milling, polishing and refining to some extent decides the nutrition content of cereals. Some nutrients are lost during food preparation, especially vigorous washing, soaking and cooking methods, which results in the depletion of the nutrients on the skin of the grains. Heavy metal of cereals cannot be underestimated as these foodstuffs are important component of human diet. However, heavy metal contamination of food items is one of the most important aspects of food quality assurance (Marsshall, 2004; Radwan and Salama 2006; and Khan et al., 2008).
Though heavy metals are naturally present in soil, geology and anthropogenic activities increase the concentration to a harmful mount (chibuike and obiora, 2014). In many ways living plants can be compared to solar driven pumps which can extract and concentrate several elements from their environment. From the soil, all plants have the ability to accumulate heavy metals which are essential for their growth and development like magnesium, iron, manganese, zinc, copper, molybdenum and nickel (Langille and Maclean, 1976) certain plant also have the ability to accumulate heavy metals which have no biological function. These include cadmium, chromium, silver, selenium, and mercury (Hanna and Grant, 1962: Baker and Brooks, 1989). it is also well known that the growth and economic yield of plants is significantly depressed when they are raised on soils contaminated with heavy metals (Foy et al., 1978; Lepp, 1981; Woolhouse,1983).
The prolonged consumption of unsafe concentrations of heavy metals through foodstuffs may lead to the chronic accumulation of heavy metals in the kidney and liver of humans causing disruption of numerous biochemical processes, leading to cardiovascular, nervous, kidney and bone diseases (WHO,1992 and Jarup, 2003).
STATEMENT OF PROBLEM
Metals have important and wide ranging role in biochemistry, being both essential and toxic (Guengerich 2009). Deficiency of micronutrient in soils and plant is a global nutritional problem as the major food staples are highly susceptible to such deficits (Imtiaz et al. 2010) for example, essentiality of Zn in the diet and its deficiency in humans was recognized in 1963 (Prasad 2012). However among all the environmental stresses, the effect of the metal accumulation has been considered one of the most disturbing factors arising in the late 19th and early 20thcenturies (Azevedo et al. 2012) in addition to their essentiality for plant growth and human nutrition, some micronutrients may also be toxic to animals, including humans, at high concentrations (Wang et al 2008). For example, Cu or Zn. An important component of seed quality is its chemical composition, including the concentration of micronutrients such as Fe, Zn, and Cu (Waters and Sankaran 2011). Clearly, plants are the first step of a metal’s pathway from the soil to heterotrophic organisms such as animals and humans, so the micronutrient content in their edible parts makes a major contribution to human intake. Zhao and McGrath (2009) suggested that micronutrient in humans and environmental contamination with heavy metals or metalloids are both global and challenging problems that require concerted efforts from researchers in multiple disciplines, including plant biology, plant breeding as well as biotechnology, nutrition and environmental sciences, such as soil fertility and chemistry.