Microbial Contamination Of Vended Fruit

2.0                        LITERATURE REVIEW

Fruits are well recognized for their vitamins and mineral contents as well as their high nutritive value (Chumber et. al., 2007). For their nutritive value, man has been utilizing fresh fruits for the production of varieties of consumables like juices, jams, beverages, wines and/or eaten directly as food (Little and Metchell, 2004). In many tropical countries, fruits are the common man’s food and are sold mostly in public places and road side shops. There have been reports of food borne illnesses associated with consumption of fruits and these diseases mainly affect the gastro-intestinal tracts and may be transmitted through the consumption of contaminated fruits (Ambekar et. al., 2008).

2.1 FRUITS
Broadly, fruit refers to the mature ovary of a plant, including its seeds, covering and any closely connected tissue, without any consideration of whether these are edible. As related to food, fruit refers to the edible part of a plant that consists of the seeds and surrounding tissues. This includes fleshy fruits (such as blueberries, cantaloupe, poach, pumpkin, tomato) and dry fruits, where the ripened ovary wall becomes papery, leathery, or woody as with cereal grains, pulses (mature beans and peas) and nuts (Stern, 1988). 

2.2 WATERMELON
2.2.1 Introduction
Table 1: Scientific Classification of Watermelon 
Kingdom:     Plantae
Order:         Cucurbitales
Family:     Cucurbitaceae
Genus:     Citrullus
Species:     lanatus
(Source: Dane and Liu, 2006)
Watermelon (Citrulluslanatus) is a warm season, vine-like flowering plant originally from Southern Africa. It is a large sprawling annual plant with coarse, hairy pinnately-lobed leaves and white to yellow flowers. It is an edible special kind of berry botanically called pepo. The fruit has a smooth hard rind usually green with dark green stripes or yellow spots and a juicy, sweet interior flesh usually deep red, orange, yellow or white with many seeds.

2.2.2. History
Watermelon was said to have originated from Southern Africa where it was found growing wild. In 19th century, Alphonse de Candolle considered the fruit to be indigenous to tropical Africa. Evidence of its cultivation in Nile valley and its seeds have been found at the Twelfth Dynasty sites in the tomb of Tutankhamun (Zohary et al., 2000). In the 7th century, watermelon was cultivated in India and by the 10th century had reached China, which is today the world’s single largest watermelon produce.

2.2.3. Cultivation and Harvesting
Watermelons are tropical plants that can survive under temperatures higher than 25°C. Seeds are firstly sown in pots under cover and transplanted into well drained sandy loam with a pH between 5.5-7.0 and medium nitrogen levels. If humidity is high, the plant is prone to insects and plant diseases like powdery mildew and mosaic virus (Brickell, 1992). Watermelons have a longer growing period than other melons and can often take 85days or more from the time of transplanting for the fruit to mature.

    Watermelons are considered optimum for eating when their flesh matures to produce a sweet flavour, crisp texture and deep red colour. Some newer cultivars, however, range in colour from light red to yellow. Determining maturity of melons without tasting each is not easy. External rind appearance does not always predict good internal flesh quality and full maturity. Harvesting and handling costs are much higher than growing costs. Therefore, melons must be harvested at the right stage of maturity and handled gently enough to avoid damage to ensure market quality (Brickell, 1992). 

    Watermelons are cut from the vine rather than pulled, twisted or broken off. Pulling stems out provides an entrance for bacteria and fungi that can cause souring and can decay the internal flesh. As melons are cut from their vines, the bottoms, which are subject to sunscald, are turned down. Direct sunlight can affect watermelon quality after harvest. Sunburn develops quickly on exposed melons whether on the ground or loaded in a truck. Temperatures above 90° F cause internal flesh breakdown and increase decay. These effects may require several days to become apparent. Shading is a necessary protection against direct sunlight and heat (Brickell, 1992). 

2.2.4. Diseases and Pests
Diseases are important in determining the success or failure of watermelon production. Certain diseases have destroyed entire watermelon crops in some areas when weather conditions favoured their development. If disease control practices are not followed, some loss can be expected every year from foliage and stem diseases. All watermelon foliage diseases spread in a similar manner. 

Some diseases can easily be brought into an area in or on the seed. Seed grown in dry, arid regions have the best chance of being free of seed-borne diseases. Locally grown seeds are more likely to be infested with diseases (Larkin and Fravel, 1998).
Disease-causing fungi can live from year to year on undecayed vines of watermelon and such fungi produce millions of spores on susceptible plants. The spores are sticky when wet, any time humans, animals or machines move through wet vines, these diseases can be spread. Splashing rain or runoff water can also spread these fungi from one area to another.
The amount of disease pressure in any given year is directly related to environmental conditions. 

Rain is the most important factor in the spread of foliage diseases. Under ideal weather conditions, some diseases can destroy entire fields within a few days. Watermelons suffer from similar diseases and pests like the cucumber like gummy stem blight, anthracnose, fusarium wilt, downey mildew, aphids, thrips, root maggots, wireworms etc.
    Damping-off is caused by a seedling disease complex that usually involves Phythium spp., Rhizoctonia spp. or Fusarium spp. The amount of damping-off is usually directly related to litter from the previous crop and to environmental conditions. In some years, seedling diseases reduce stands by 50 percent; in other years, seedling diseases are rare. 

Good cultural practices and seed treatment are essential in preventing damping-off of young watermelon seedlings. Root-knot nematodes are small eel-like worms that live in the soil and feed on plant roots. Root-knot nematodes cause serious damage to watermelons when planted to infested fields. All species of root-knot nematodes are capable of causing serious damage to watermelons. The lack of a good, easy-to-use nematicide for watermelons makes the worms a major problem. Although fumigants are excellent for reducing nematode populations, the waiting period required after application can cause delays in planting (Gordon and Martyn. 1997).
    Watermelon mosaic virus I and II are now known as papaya ringspot virus-watermelon type (PRSV-W) and watermelon mosaic virus (WMV), respectively. These are two common viruses found on watermelons. Several other viruses affect watermelon; all have similar symptoms. The most common symptom is mottling of the leaf. However, mottling may be difficult to see under certain weather conditions. 

Some plants are stunted with abnormal leaf shapes, shortened internodes and bushy erect growth habits of some runner tips. The first symptom on the fruits is usually a bumpy and mottled appearance of the fruit surface. This disease symptom is strongly expressed in periods of extended high temperatures, which occur just before watermelon harvests. These viruses are spread by aphids, which can spread through an entire planting during the growing season.

2.2.5. Nutritional values
Every aspect of the fruit of watermelon has nutritional value, including the rind and the seeds. The most common way watermelon is eaten, is the consumption of the pink or yellow flesh, eaten raw, the way it was grown. However, other common ways it is eaten include watermelon rind pickles, deep fried watermelon, watermelon cake, and watermelon lemonade (Tlili et al., 2011). 

 In southern Africa it has been cultivated since pre-colonial times with other crops such as sorghum and maize. The tender young leaves and fruits are cooked as green vegetables, while the fruit flesh may be cooked as porridge with maize meal. It is also a valuable stock feed, especially in times of drought. The hollowed fruit can be used as a container for cooking or storing berries. 

The pulp and seeds are prepared in a number of different ways for eating. The flat brown seeds have a much higher food value than the flesh and have a nice nutty taste. Significant amounts of vitamin C, minerals, fat, starch and riboflavin have been obtained from them. They can be dried, roasted and eaten as such or ground into flour to make bread. The flour is said to contain saponin and is also used as a detergent. The seed contains a high percentage of oil which is similar to pumpkin seed oil and can be used in cooking (Tlili et al., 2011).