CHAPTER ONE INTRODUCTION
Tomato (Solanum lycopersicon L.) is a horticultural crop produced and consumed throughout the world (Nunes, 2008). Worldwide consumption is second only to potato as a vegetable (FAO, 2012; Javanmardi and Kubota, 2006). Tomato belongs to the Solanaceae family and has its origin in the South American Andes (Naika et al., 2005). Though botanically it is a berry, it is usually considered as a vegetable due to its savoury flavour.
The health benefits conferred by certain vegetables and fruits have been the result of the presence of health-promoting phytochemicals with potent antioxidant properties such as carotenoids, flavonoids, phenylpropanoids, tocopherols, and ascorbic acid (vitamin C). Ripened fruit of tomato (Solanum lycopersicon L.) contains significant amounts of these compounds and are the principal dietary source of the carotenoid lycopene in the human diet (Giovannucci, 2002).
Tomato fruits are versatile; they can be consumed fresh in salads or cooked in sauces, soups and meat or fish dishes. They can be processed into purées, juices, ketchup, powders, canned whole or chopped.
Tomatoes contribute to a healthy, well-balanced diet. The fruit is mainly composed of water, soluble and insoluble solids (Nikbakht et al., 2011; Pedro and Ferreira, 2007). Total solids are the summation of soluble and insoluble solids with soluble solids made up of mainly sugars, like sucrose and fructose, and salts and the insoluble solids mainly constituted by fibres, such as cellulose and pectin (Pedro and Ferreira, 2005). Usually, excluding seeds and skin, tomato presents 4.5-8.5% total solids, depending on variety, soil and climatic conditions (Pedro and Ferriera, 2005).
Tomato contains organic acids (mostly citric acid) and such micronutrients as carotenoids, and vitamins A and C (Nikbakht et al., 2011; Pedro and Ferreira, 2007). They are also rich in minerals, essential amino acids, sugars and dietary fibres. Tomato contains much vitamin B, E and K, iron and phosphorus.
As a tomato fruit ripens, its colour changes from green in the immature fruit to deep dark red in the fully mature fruit. Most of the orange, yellow and red colours of leaves, fruits and flowers are due to carotenoids. Carotenoids, such as beta-carotene and lycopene, are important components of antioxidant defence against lipid peroxidation in living cells (Bunghez et al., 2011). They are essential nutrients in the human diet that are thought to provide health benefits by decreasing the risk of various diseases, particularly certain cancers, cardiovascular and eye diseases.
In tomato, fruit quality is an important factor that contributes to consumer acceptability. In addition to colour and firmness, measurements of acidity, total soluble solids content, and sugar-to-acid ratio, are factors that are used to select desirable sweet and sour flavour attributes in tomato fruit (Nikbakht et al., 2011; Shao et al., 2007).
Tomato is considered a low-high acid food with a pH value of between 3.7- 4.5.The pH of a food is one of several important factors that determines the survival and growth of microorganisms during processing, storage and distribution, thus the final safety of the food product. Therefore, determining the pH of foods helps to prevent product deterioration and spoilage. Canned and dried tomatoes are economically important processed products (Naika et al., 2005).
As a whole product, tomato maintains a delicate tissue structure that is extremely susceptible to chilling injury, mechanical damage and the presence of microorganisms. It is highly perishable with shelf life stability ranging from three days to three weeks depending on the time of harvest and/or variety (Prakash et al., 2002; Ellis et al., 1998). Kader (1992) stated that post – harvest losses in tomato as a result of improper storage and handling are enormous and can range from 20-50 % in developing countries.
In Nigeria availability of tomato fruit on the market is variable depending on the season and hence, the inability to meet manufacturing demands and an all-year-round production of the fruit for consumers. Market women usually display the fruits on table tops, in plastic baskets or wooden boxes and leave them in the sun till the close of day. This renders the fruit short-lived, due to the action of microorganisms and the inappropriate storage conditions under which the fruits are kept. During the peak seasons, the problem of glut sets in due to lack of appropriate methods/facilities for long term preservation of the fruits in their unprocessed state. Shortages of fresh tomato fruits occur during the lean season immediately following the glut, leading to a rise in the price of the fruit. Consequently, Ghana imports tomato fruits from neighbouring countries.
The shelf life, fruit quality characteristics as well as the optimum storage conditions and post – harvest treatment of common tomato fruits in Nigeria need to be identified to curb the problem of postharvest losses. Irradiation has been known to inhibit microbial growth, delay ripening and extend the shelf life of minimally processed fruits and vegetables (Prakash et al. 2002; Hagenmaier and Baker, 1998). In addition edible coatings create a modified atmosphere within the fruit and thus help to preserve it for a longer time. Calcium chloride has been proven to reduce post – harvest decay, controls the development of physiological disorders, and improves quality and delay aging or ripening (Stanly et al., 1995). Low temperature is also effective in delaying the onset of senescence and decay.