2.6. TIGER NUT
2.6.1. Introduction
Table 5: Scientific Classification of Tiger nut
Kingdom: Plantae
Order: Poales
Family: Cyperaceae
Genus: Cyperus
Species: esculentus
(Source: Belewu and Belewu, 2007)
The tiger nuts also called chufa sedge, nut grass, yellow nutsedge, or earth almond is a crop of the sedge family widespread across much of the world (Odemelan, 2003). It is native to countries like Southern Europe, Africa, Madagascar, the Middle East and the Indian Subcontinent. This plant is found wild, as a weed or as a crop (Sanchez-Zapata et al., 2012). It is a tuber crop that grows in the soil and cultivated by continous irrigation. It is known in Nigeria as ‘Aya’ in Hausa, ‘Ofio’ in Yoruba and ‘Akiausa’ in Igbo where three varieties (black, brown and yellow) are cultivated. The yellow variety is preferred to all other varieties because of its inherent properties like its bigger size, attractive colour and fresher body (Okafor et al., 2003). Tiger nuts can be eaten raw, roasted, dried, baked or be made into a refreshing beverage called Horchata De Chufas or tiger nut milk.
2.6.2. History of tiger nut
Tiger nuts have been cultivated by man for many centuries with, evidence of the same having been found in the sarcophagus and tombs of the early Egyptian dynasties. It was believed that tiger nuts were highly appreciated in an age in which people buried their dead with belongings that were meant to provide enjoyment in the after-life. The tiger nuts were also used medicinally taken orally, as an ointment, or as an enema and used in fumigants to sweeten the smell of homes or clothing (Defelice, 2002).
Presently, the cultivation of tiger nuts have gone widespread over many countries like Spain, Nigeria, Niger, Congo, USA, Brazil, Iran, Iraq etc.
2.6.3. Cultivation and Harvesting of tiger nut
Planting is normally done on flat soils where ridges to favour the coming irrigations have previously been done. The separation between ridges is approximately 60cm and seeds are planted manually and are separated at 15-20cm (Pascual-Seva et al., 2012).They are planted between April and May and must be irrigated every week until they are harvested in November and December. Tubers develop about 6-8weeks after seedling emergence and grow quickly during July and August. The maturing is around 90-110days (Pascual-Seva et al., 2012).
With a combines harvester the tiger nuts are pulled out of the ground and immediately harvesting, they are washed with water in order to remove sand and small stones from it. The drying occurs usually in the sun and can take up to three months. The temperature and humidity levels are monitored carefully to ensure uniform drying of the tiger nuts. This is done to prevent rot or any bacterial infection and to ensure the quality and high nutritional value of it (Abano et al., 2011).
2.6.4. Nutritional values of tiger nut
Tiger nuts have long been recognized for their nutritional values as they have a high content of soluble glucose and oleic acid, along with high energy content, they are rich in minerals like phosphorus, potassium, calcium, magnesium and iron which help in bones, tissue repair, muscles, the blood stream and for body growth and development and they are also rich in vitamins E and C. Their nutritional values include the following:
- Tiger nuts are rich in fibre which provides the body with relief and prevents constipation and also aids in weight maintenance.
- Tiger nuts milk is rich in calcium which helps in bone building and growth supporting mineral.
- They help in the control of blood pressure and also act as antioxidants (Sowonola et al., 2005).
2.7. MICRO ORGANISMS ASSOCIATED WITH CONTAMINATION OF FRUITS.
Consumption of fruits and vegetables is commonly viewed as a potential risk factor for infection with pathogens such as Salmonella species and Escherichia coli O157:H7. Microorganisms form part of the epiphytic flora of fruits and vegetables and many will be present at the time of consumption. The majority of bacteria found on the surface of plants is usually Gram-negative and belong either to the Pseudomonas group or to the Enterobacteriaceae (Lund, 1992). Many of these organisms are normally non-pathogenic for humans. The numbers of bacteria present will vary depending on seasonal and climatic variation and may range from 104 to 104 per gram. The inner tissues of fruits and vegetables are usually regarded as sterile (Lund, 1992). However, bacteria can be present in low numbers as a result of the uptake of water through certain irrigation or washing procedures. If these waters are contaminated with human pathogens these may also be introduced. About two thirds of the spoilage of fruits and vegetables is caused by moulds. Members of the genera Penicillium, Aspergillus, Sclerotinia, Botrytis and Rhizopus are commonly involved in this process.
The bacterial micro-organisms involved in the consumption of contaminated fruits include:
1. Escherichia coli
Escherichia coli O157:H7 can be isolated from the faeces of livestock; therefore, its presence in animal manures and slurries is inevitable (Kudva et al., 1998). In addition to farm animals, E. coli O157:H7 may be present in the faeces of wild birds, for example, starlings (Moller Nielsen et al., 2004) and gulls (Wallace et al., 1997). Leafy vegetables and fruits are most commonly linked to E. coli infection, but apple juice is an interesting vehicle, as the acidity of the product is considered inhibitory to bacterial proliferation. Escherichia coli O157:H7 is commonly recovered from the faeces of ruminants; therefore, livestock grazing in orchards may contaminate fallen apples with faeces and, as E. coli O157:H7 can proliferate in damaged apple tissue (Stopforth et al., 2004) and this can result to the contamination of unpasteurized fruit juices or ciders. Janisiewicz et al., (1999) also demonstrated that fruit flies were an important vector in the contamination of apples with E. coli O157:H7,both preharvest and in packing houses.
2. Salmonella spp.
Salmonella species are an important cause of gastrointestinal illness in humans. Salmonella enteritidis and Salmonella typhimurium are the most frequently reported non-typhoidal serotypes in many countries and outbreaks have been associated with a diverse range of food vehicles. Salmonellosis is characterised by diarrhoea, fever, abdominal cramps and vomiting usually lasting 4-7 days (Anon., 2001). Although most Salmonella infections are self-limiting, in a small proportion of cases these may lead to bacteraemia. The case-fatality rate in industrialised countries is less than 1% (Anon., 2001).
3. Shigella spp.
Shigella sonnei is primarily spread by the person-to-person route although food and waterborne transmission can occur. Shigellosis can be endemic in institutional settings such as prisons, markets, hospitals and nursing homes, where population densities are high and or poor hygiene conditions may be present. Shigella infection usually presents as abdominal cramps, fever and diarrhoea, which may contain blood and mucus. The duration of illness is 4-7 days (Anon, 2001).
4. Vibrio cholerae
Vibrio cholerae serogroups O1 and O139 are the causes of epidemic cholera. This is predominantly a waterborne infection and high numbers of organisms are necessary to cause infection. Nevertheless, a significant number of fruit and vegetable borne outbreaks have been reported (Wachsmuth et al. 1994; Faruque et al. 1998; Anon 2001). The characteristic profuse watery diarrhoea of cholera is due mainly to the effects of a heat labile enterotoxine laborated by the organism in the intestine. Cholera is of rapid onset and can lead to severe dehydration and death within hours if left untreated. The illness usually lasts for 3-7 days (Anon., 2001).
5. Pseudomonas species
Pseudomonas spp thrive in moist environments such as soil and water and can be found in large numbers on fresh fruits and vegetables. They invade fruits and vegetables through the use of sewage-contaminated water to wash or rinse the fruits and vegetables. Such species like P. syringae, and related species P. avellanae, P. avii, and P. savastanoi, collectively cause important diseases on numerous plant hosts including fruit trees. The significance of damage to fruit trees includes effects on crop yield due to blossom blast, fruit lesions, killing of scaffold branches, and cankers that can ultimately kill trees (Megan et al., 2007).
6. Staphylococcus aureus
S. aureus is one of the major pathogens that can cause food poisoning. Intoxication is caused by the ingestion of enterotoxins within foods, usually because the food has been left at room temperature (Walls and Scott, 1997). Therefore poor storage of fruits and vegetables could promote the growth of this organism. There are five major classical types of staphylococcal enterotoxins (SEs): SEA, SEB, SEC, SED and SEE, as well as new SEs or SE-like superantigens (Sags) such as SEG to SEU (Chiang et al., 2008). Fruits and vegetables requiring considerable handling during preparation and kept without refrigeration are usually involved in staphylococcal poisoning. This bacterium is able to grow in a wide temperature range (7–48 °C), with an optimal growth at 35–37 °C, a frequent value in warm climates (Baeza et al., 2007). Food-borne viruses causing human diseases originate from human faeces. Many enteric viral infections are mild and of relatively short duration. Most cases are probably not identified because specimens are not commonly examined for viruses and the detection methods used routinely identify only some of the viruses known to cause infectious intestinal disease (IID). Transmission is mainly by person-to-person contact by inhalation of airborne droplets and faecal contamination. Many outbreaks of viral gastroenteritis associated with fresh fruit and vegetables have been described (Hedberg and Osterholm, 1993; NACMCF, 1999).Based on epidemiological criteria described by Kaplan et al., (1982), it is estimated that 32-42% of food-borne enteric infections in the US are caused by viruses, especially the enteric viruses.
