Evaluation of Bacterial Contaminants and the Level of Aspergillus Flavus Present in Peanuts Sold in (Abakiliki Metropolis)

Evaluation of Bacterial Contaminants and the Level of Aspergillus Flavus Present in Peanuts Sold in (Abakiliki Metropolis)

Peanut (Arachis hypogaea), is one of the species in the legume or beans family (fabaceae). Peanuts are also known by many other local names such as earthnut, goober peas, pygmy nuts and pig nuts.
Peanuts occupy a vital position in the economy of developing nations. The major peanut producing countries are India, china and the United States. It was introduced into Nigeria in the 16th century and it has been estimated that about 14 million hectares are cultivated for peanut in Nigeria (Salunk et al.; 1985; Irvine 1970).

Peanut is a nutrient dense agricultural product, which is very high in energy due to its fat and protein content. The carbohydrate content of peanut is relatively low, being under 30% of the whole nut. The nut has relatively high content of fiber. It is an industrial crop whose major utilization is a source of oil (Elegbede, 1998).
Peanut is widely consumed in Nigeria as roasted or boiled nuts, which could be cooked or eaten with cooked maize in the Western and Southern parts of the country. Peanut cake “kulikuli” is the residue obtained after extraction of oil and it is high in protein and serves as supplement in feed and food. The peanut cake is usually fried in oil and as a delicious snacks or food supplement.

Peanut flour is obtained by grinding groundnut into fine size, which can be used in making soup or stew, sauce, confectioneries, pudding and bakery products. “Dankwa” is peanut flour that has been mixed with roasted cereal flour in which some spice, like dried grinded alligator pepper are added. Sugar and salt are also added to the mixture before been pounded and molded into small balls that can be eaten without further processing (Adebesin et al, 2001).
As a result of improper processing and storage conditions, peanut and its products which includes cooked and uncooked peanut may be contaminated with microorganisms. The number and type of microbes present on the produce is vital in deterioation and numerous mold formation. Bacterial are among the possible contaminant and the most commonly isolated bacterial species are Bacillus, Salmonella, Pseudomonas, Staphylococcus and Escherichia coli (Abalaka et al,1981). Fungi are among the possible contaminants of peanut and the most common species are Aspergillus, penicillium and Fusarium (Frazier et al, 1978). Mold development on peanuts before, during or after harvest is hazardous, particulary Aspergillus flavus, which produces aflatoxin that is carcinogenic (Shewfelt et al, 1977). It was reported that Aspergillus flavus and Aspergillus parasiticus grow and produce aflatoxin on peanut (Salunkhe et al, 1985). The major factor which leads to high contaminant level of peanuts are shell damage, and kernel splitting (usually induced by insects) poor harvesting and drought (Elebgede, 1998). Aflatoxin was found in peanut products sold in Tokyo between 1986-1990 (Tabata et al, 1993).

To isolate and determine the level of microbial contaminants of cooked(boiled) and uncooked(raw) peanut that are sold in Abakiliki metropolis
To analyze raw and boiled peanut to determine their degree safety for consumption.
To enlighten the public on the possible microbial flora present in raw and boiled peanut


Peanut was probably first domesticated and cultivated in the valleys of Paraguay. It is an annual herbeceaous plant growing 30 to 50cm tall. The leaves are opposite, pinnate with four leaflets (two opposite pairs; no terminal leaflet), each leaflet is 1 to 7cm long and 1 to 3cm broad. The flowers are a typical pea flower in shape, 2 to 4cm across, yellow with reddish veining. After pollination, the flower stalk elongates causing it to bend until the ovary touches the ground. Continued stalk growth then pushes the ovary underground where the matured fruit develop into a legume pod. The peanut is a classic example of geocarpy. The pods are 3 to 7cm long, containing 1 to 4 seed (Michael 2006).

The domesticated peanut is an amphidiploid or allotetraploid, meaning that it has two sets of chromosomes from two different species thought to be A. duranensis and A. paensis. These likely combine in the wild to form the tetraploid species A. monticola, which give rise to the domesticated peanut (Seijo et al, 2007). This domestication might have taken place in Paraguay or Bolivia, where the wildest strains grow today. Many pre-columbian cultures, such as the Moshe, depicted peanut in their art (Berrin et al,1997). Archeologists have dated the oldest specimen to about 7600 years, found in Peru (Dellehay et al, 2007). Although the peanut was mainly a garden crop for much of the colonial period of North America, it was mostly used as animal feed stock until the 1930s (Putnam et al, 1991)
In the United States, a US department of agriculture program to encourage agricultural production and human consumption of peanuts was instituted in the late 19th and early 20th centuries. George Washington carver is well known for his participation in that program in which he developed hundreds of recipes for peanuts.
China and India together are the World’s leading peanut producers accounting for nearly 60% of the production and 52% of the crop area.

India cultivates about 7.74 million hectares and produces 7.61 million tones of peanut with the productivity level of 991.8kg ha-1. South Africa is the major produer in Africa, while in latin America almost one half of the total peanut produced in that region may be credited to Argentina. Among the developing coutries, Egypt has the highest productivity and capacity to produce peanut. In most developing countries, the productivity level is lower than in the United States of America, solely due to a number of difficulties encountered during production such as cultivation of the crop on marginal lands under rain fed conditions; occurrence of frequent drought stress due to vagaries of monsoo; and higher incidence of disease and pest attacks; low input-use and factors related to socio-economic infrastructure. Especially in the developing countries, peanuts has to play a vital role both as oil and food crop. For example in India about 10kg peanut per capita are available for domestic consumption. Fat and oil consumption averages less than 5% kg per capital per year. It has been estimated that in the year 2000, approximately 34 million metric tones(mt) of peanut were produced worldwide of which 15 million metric tones were produced in China, 6 million metric tones in India, 2 million mt in Nigeria, 1.5 million mt in United States of America and the rest mostly in other countries (freeman et al, 1999).
Similary in other developing countries, most of the peanuts are used for extraction of oil for domestic consumption and export. For instance, Sudan accounted for 17% of the world peanut export trade. Peanuts are important component of Nigerian diet and about 5% of the estimated 58.9g of crude protein available per head per day is contributed by peanut (Abulu,1978). In most of the developing countries it provides high quality cooking oil and is a vital source of protein for both human and animal diet and also provides much needed foreign exchange by exporting the kernel and cake. In the literature peanut role as a cash crop is found to completely dominate its role as subsistent food crop.

Peanuts are rich in nutrients, providing over 30 essential nutrients and phytonutrients. Peanuts are good source of niacin, folate, fiber, vitamin E, magnesium and phosphorus. They also are naturally free of trans-fat and sodium, and posses about 25% protein (a higher proportion than in any true nut). Peanuts are good source of niacin, and thus contribute to brain health and blood flow. Recent research on peanut has shown the presence of antioxidants and other chemicals that may provide health benefits. New research shows that peanuts rivals the antioxidant content of many fruits. Roasted peanuts rivals the antioxidant content of blackberries and strawberries, and are far richer in antioxidant than carrots or beets. Peanuts contain high concentration of antioxidant polyphenols, primarily a compound called p-coumaric acid, and that roasting process can increase peanut’s p-coumaric acid level, boasting their overall antioxidant content by as much as 22% (journal of food chemistry,1981). Peanut is nutrient dense agricultual produce which is very high in energy due to its high fat and protein content. The carbohydrate content of peanut is relatively low, being under 30% of the whole nut. The nut has relatively high content of fiber. It is an industrial crop whose major utilization is a source of oil (Elegbede,1998).
Peanut have a desirable fatty acid profile and are rich in vitamins, minerals and bioactive materials.

The contain several known heart healthy nutrients including mono-unsaturated and poly-unsaturated fatty acid, potassium, magnesium, copper, niacin, arginine, fiber, alpha-tocopherol, folates, phytosterols, and flavonoids. Peanut consumption has been related to improved overall diet quality and nutrient profile (Kris et al,1999). The American Heart Association (AHA) has indicated that cardiovascular disease (CVD) remains the common cause of death among Americans (Lloyd-jones et al,2008). Peanuts and peanut oil have been demonstrated to reduce CVD risk and or risk factors in epidemiological and clinical studies(Fraser et al,1992).
Peanut can be consumed directly as cooked or boiled peanut, roasted peanut, processed into oil or cake/meal, or further processed into confectionary products or snack food. Every part of the peanut plant is used in some way; kernel for human consumption , vines as food for cattle and nitrogen fixed from its roots as nutrients for the soil. While valued in most countries primarily for its oil, the abilty to improve soil fertility is being grown to break the rice monoculture , as well as adding to export sales needed to secure income. Peanuts are used to help fight malnutrition. Plumpy nut, MANA nutrition and Medika Mamba are high protein, high-energy and high –nutrient peanut –based pastes developed to be used as a therapeautic food to aid in famine relief (Ramond et al,2011).

The gram negative bacterial contaminants of peanut includes Escherichia coli, Klebsiella, Shigella, proteus e.t.c (Ezekiel et al,2011). These organisms are capable of food and water contamination and there sources are from faeces. Shigella, Klebsiella and Proteus have been implicated in several human infections (Collei et al,1997,Nzeako et al,2002). Some of these enterobacteria like E. coli and Salmonella are specially known for their potential to incite food poisoning and intoxication, some strains of which liberate enterotoxins (Lund et al, 2000). Enterobacteria also cause severe gastroenteritis. Shigella and Salmonella infections on peanut cake can causeshigellosis and Salmonella infection respectively caused by hemolytic strains such as Shigella dysentriae, Shigella flexneri and Salmonella enteric serovars typhi and paratyphii (Sharma et al, 2001).
Adebesin et al. 2001 reported in his journal of food microbiology, that the gram positive bacterial contaminants constantly isolated from hawked peanut products were Staphylococcus aureus which is indigenous or the normal flora of the skin is gram positive organism, which is positive to both catalase and coagulase test and they contaminate these nuts due to improper handling and hawking, also improper hygiene. Staphylococcus aureus is known to cause enterotoxigenicity due to the production of enterotoxin (Frazier et al,1978).
Aspergillus, Fusarium, Penicillium and Rhizopus are the major contaminating fungi of peanut on storage.

The species of Aspergillus, Rhizopus and Penicillium are mold contaminants that produce toxin (Gachomo et al,2004).
Salunke et al,(1985), reported that A. flavus and A. parasiticus grow and produce aflatoxin on peanut . Tobata et al,(1993) reported the presence of aflatoxins in peanut products collected in Tokyo between 1986-1990. Aspergillus species are able to survive in situation where free water is not available (Samson et al,1981).

Level of microbial contamination may be influenced by many factors such as contacting of edible nuts by contaminated hands, packaging of these nuts its products may be contaminated with microorganisms (Adebesin et al,2001).

The major factors which leads to high contamination level of peanut are shell damage and kernel splitting (usually induced by insects), poor harvesting and drought (Elegbede,1998).

Other sources of these microbial contaminants of peanuts are mainly from human, E. coli which is the normal flora of gastro intestinal tract indicates that the food is contaminated with pathogens of intestinal origin. It can be as a result of fecal contaminated handlers either directly or indirectly. Bacterial pathogenic contaminants and are ubiquitous in nature and as such could be found in soil, dust, bodies of insects, animals and human who handle the peanuts and its products (Frazier et al,1978).
Salmonella which is one of these bacterial pathogens is a gram negative organism indigenous to the intestinal tract of both human and animals cause food borne pathogens. Staphylococcus aureus is also a contaminant which is the normal flora of the skin and can be isolated from hawkers and hawked peanut products. Salmonella, E. coli and Shigella are known to incite food poisoning. These bacteria are usually conveyed into food, drinks or water by vectors or faecally contaminated handlers who maintain a low level of hygiene. Lund et al,(2000).

Care should be taken from the harvesting stage of peanut to prevent contamination. The hawkers of peanut should always maintain a high level of hygiene (Adebesin et al,2001).
Little et al,(2010). Journal on food protection recommended that to enhance human health and food safety, there is need to evaluate the microbial load of peanut available for human consumption, the packaging and handling of these nuts should be ascertained, this will help to determine food quality, nutrients depletion and possible health risk of consumers. Researchers because of the existence of aflatoxins in the samples that were taken from different regions, announced that contacting these foods by hands should be avoided and that the products which were to be stored for a long period of time should be well packaged. Also various measures should be taken by environmental officers to curtail the selling and production of contaminated peanut and peanut products.

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