TOTAL MICROBIAL LOAD OF FERMENTED MANIHOT ESCULENTA
Manihot esculenta is a woody shrub of the spurge family, Euphorbiaceae, it is extensively cultivated as an annual crop in tropical and subtropical regions for its edible starchy tuberous roots, a major source of carbohydrates. Manihot esculenta when dried to a powdery (or pearly) extract is called tapioca; its fermented flaky version is named garri. Manihot esculenta is the third largest source of food carbohydrate in the tropics, after rice and maize(Fargette Denis,1999).Manihot esculenta is a major staple food in the developing world, providing a basic diet for over a billion people. It is one of the most draught tolerant crops, capable of growing on marginal soil and heat stress. The Manihot esculenta is not labour intensive crop and produces well on marginal soils. In many of the Manihot esculenta growing region of the world, however, the Manihot esculenta does not achieve its yield potential, due primarily to disease and limited input such as fertilizer and irrigation (Siritunga and Sayre, 2004). Manihot esculenta is referred to as a food security crop (Barratt et al., 2006), which can be left in the ground for extended period of up to 2 years, until required. Manihot esculenta is used mainly as fresh food item, but is also processed into various food and noon food products such as starch, flour, beverages, animal feed, biofuel and textiles. There is much variation in the nutrient quality of the Manihot esculenta root (Chaves et al., 2005). In the tropical regions, Manihot esculenta is the most important root crop and as a source of energy, the calorific value of Manihot esculenta is high, compared to most starchy crops (Okigbo, 1998). The starch content of the fresh Manihot esculenta root is about 30%, and gives the highest yield of starch per unit area of any crop known (Tonukari, 2004). The protein content is extremely low, however, and ranges between 1-3% (Buitrago 1990). The Manihot esculenta root contains a number of mineral elements in appreciable amounts that are useful in the human diet. The root contains significance amounts of iron, phosphorus and calcium and is relatively rich in vitamin c (Enidiok, et al.,2008).
There are several thousand varieties of Manihot esculenta and about 100 related wild species, with hydrogen cyanide (HCN) contents of their root ranging from 1-1550 part per million (PPM). Manihot esculenta plants are generally categorized as bitter or sweet, depending upon their cyanide content. The low-HCN, of sweet Manihot esculenta, has less than 50ppm of the cyanogenic equivalents, while the high-HCN or the bitter Manihot esculenta has more than 100ppm (Wilson and Dufour, 2002). According to Adepoju et al., (2010), the food value of Manihot esculenta is greatly compromised by its toxic hydrogen cyanide content. The sweet Manihot esculenta can be cooked and eaten as they are, while the bitter Manihot esculenta needs to be processed before being consumed, as improper processing of Manihot esculenta before consumption may leave enough residual cyanide to cause acute cyanide intoxication, goitres, and even ataxia or partial paralysis. A large amount of variation exists among the Manihot esculenta leaf, stem, and root characteristics. These characteristics, which include leaf morphology, stem colour, branching habit and storage root shape and colour, may influence Manihot esculenta yield (Ntawuruhunga and Dixon, 2010).Other, not so obvious, characteristic include resistance to insect pest and disease. A proper understanding of these variations in plant characteristics would assist the selection of Manihot esculenta types with the desired traits.
Several health disorder and diseases has been reported in the Manihot esculenta-eating populations. Consumption of 50 to 100mg of cyanide has been associated with acute poisoning and has been reported to be lethal in adults. (Yeoh and Sun, 2001).The consumption of lower cyanide amounts are not lethal but long term intake could cause severe health problem such as tropical neuropathy, glucose intolerance and, when combined with low iodine intake, goitre and cretinism (Delange et al., 1994; Harris and Koomson, 2011). There are also very few reports on the microbial quality and fate of the various food borne pathogens during the storage of Manihot esculenta cultivars. The level of microorganism in food items is essential as some of them are hazardous to health. For instance ,if the number of Bacillus cereus and Staphylococcus aureus exceeds 106cfu/ml, it is suspected to cause food poisoning and Listeria monocytogens which causes meningitis abortion (Gray and Killinger, 2012).
Manihot esculenta was first cultivated more than 4000 year ago in Brazil. It was introduced into Africa in the 17th century and only reached Asia about 150 years ago. Today about 40% of the global output originates from Africa, the rest being produced almost equally by Asia and Latin America (Nestle, 2008). In Africa, 68.9million tons of fresh roots were harvested from 8.9 million hectares (Dahniya, 2004). On average, farmers worldwide produce about 10 tons of Manihot esculenta per hectare, but yields can reach 40 tons. It is estimated that the production of high-yield varieties, improved pest and disease control and better processing methods could increase Manihot esculenta production in Africa by 150%.
Industrially, Manihot esculenta is used as a raw material for starch extraction, alcohol production, and incorporation in bread making and as sun-dried chips for animal feeds (Kimaryo, 2000). Manihot esculenta starch has an advantage over other types of starch in that; it has a particularly low level of impurities, giving it subtle flavour release. It is used in the production of beer, baby foods and other dried foods, as well as in meat products (Hunt, 2009). It is used in bakery products and be converted into dextrose, glucose, caramel or monosodium glutamate. It has good pasting viscosity, cost effective thickening properties for use in soups, gravies, sauces, baby food and binding properties that makes it highly suitable for use in extruded foods (Hunt, 2009). It is also used as an adhesive in corrugated cardboard manufacture, in foundries, in well drilling and in paper and textile industries. Brazil has begun substituting a portion of gasoline with Manihot esculenta alcohol (Almzon 2008). InAfrica ca.70% of total production of Manihot esculenta is processed into a wide range of products including pastes, chips/flour, granules, starch and alcoholic beverages (Nweke, 2004). Some of these products such as garri and flour can be stored for a long time under ambient condition (Danhiya, 2004). Despite these useful application of Manihot esculenta, hydro cyanide (HCN) occurs as a cyanogenic glucoside in the Manihot esculenta tubers (Kimaryo, et al, .2000), and is a major problem as it inhibits the enzyme involved in ATP production in animal cells. This inhibition results in an upper motto neuron disease known as ‘KONZO’, which is characterised by abrupt onset of spastic paralysis, nausea and vomiting (Kimaryo, et al 2000). The normal range of cyanide content in Manihot esculenta tubers is between 15 and 400mg HCN/kg fresh weight (Coursey, 2007). The concentration of cyanogenic glucosides has been found to increase from the centre of the tuber outwards, and generally the HCN content of the peel is substantly higher than that of the flesh (Onabolu, 2008). The cyanogenic glucoside of Manihot esculenta, linamarine and lotaustralin, usually found in the ratio of 10 to 100, are synthesised from the amino acids valine and isoleucine, respectively. Linamarin and lotaustralin are stored inside vacuoles in the cytoplasm, while the enzyme linamarase, a Beta-glucosidase that can hydrolysed them, is located on the cell wall. When plant tissue are crushed (e.g. when pounding the leaves or mashing the tuber), the plant cell structure may be damaged to such an extent that the enzyme can come into contact with and act on the cyanogenic glucosides. The action of linamarase on linamarin and lotaustralin is the hydrolytic release of acetone cyanohydrin and 2-butanone cyanohydrin, respectively. The latter compounds are relatively unstable at pH>5; they spontaneously decompose to the corresponding ketone and to HCN, which is lost by volatilization (the boiling temperature of HCN is 25.7co (Bokanga, 2005) thus providing detoxification of the Manihot esculenta tuber.
1.1 AIM OF THE STUDY
The aim of this work is to determine the total microbial load on fermented Manihot esculenta.
1.2 OBJECTIVES OF THE STUDY
The objectives of this research work include the following:
- To examine the microbial load of fermented Manihot esculenta on each day.
- To examine the different microorganism associated in fermented Manihot esculenta.
1.3 STATEMENTNOF THE PROBLEM
Manihot esculenta is classified as either sweet or bitter like other roots and tubers, both bitter and sweet varieties of Manihot esculenta contain anti-nutritional factor and toxins which may be harmful to the body with bitter varieties containing much larger amount of the toxin (Rome, 2012). Microorganisms are known to be involved in the process of Manihot esculenta fermentation which reduces the cyanides content of the Manihot esculenta and makes it un-harmful to the body when consumed by humans. Manihot esculenta must be properly fermented as improper fermentation and preparation of Manihot esculenta before consumption can leave enough residual cyanide to cause acute cyanide intoxication, goiters and even ataxia or partial paralysis.
1.4 SIGNIFICANCE OF THE STUDY
This work will be useful to farmers, students, producers and consumers of Manihot esculenta products (Garri and Fufu).
The outcome of this research will guide both users and producers of Manihot esculenta products on the best day to ferment Manihot esculenta for it not to be harmful to the
body and also to know the total microbial loads present during the process of fermentation.