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EVALUATION OF THE NUTRIENT CONTENTS IN ADVANCED GENERATIONS OF INTERSPECIFIC HYBRIDS OF TWO SOLANUM SPECIES

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INTRODUCTION

 

Tomato, Solanum esculentum has become the most popular grown vegetables in the world. Tomato contains health promoting vitamins such as vitamins A and C, and disease fighting phytochemicals known as carotenoids essential for cancer prevention and it is a good source of protein (Briggs and Saunders, 1979). Recent studies have shown that prostate cancer is a chronic disease whose incidence is believed to be reduced by beneficial effects of carotenoids (Anonymous, 2001).

Tomato also contains several other components that are beneficial to health including vitamin E, trace elements, flavonoids, and several water soluble vitamins (Beecher, 1998). Lycopene, a carotenoid found in tomato fruits prevent oxidation of low density lipo protein (LDL) cholesterol and reduces the risk of developing other osteoporosis and coronary heart disease. Tomato is cholesterol free. This explains why people who eat diets high in tomato have a lower risk of heart disease.

Tomato is highly beneficial in the treatment of diabetes, eye disorder, urinary disorder, obesity, intestinal and liver disorders, respiratory disorder and painful joints (Gyan, 2000). Tomato has been reported to be a kidney stimulant and thus helps to clean toxic substances in the system. The cultivation of tomato has some problems. High relative

humidity predisposes tomato to fruit and foliage diseases arising from fungal infections.  This makes the cultivation of tomato in high humid environment very difficult. The use of chemical control is also environmentally unsafe. The use of disease resistant cultivars therefore becomes the most sustainable measure of control even though they are not readily available.

Although tomato breeding has undoubtedly been very successful in advanced economies, a great deal of efforts are needed in the under developed countries to develop varieties that are adapted to the local environmental conditions. It is therefore very necessary to improve the cultivated tomato with respect to quality to meet the nutritional needs of the people of Africa. Thus, one of the major challenges in any tomato breeding programme is to increase the yield and nutritional quality through plant breeding and hybridization programmes. These considerations prompted the initiation of the present study with the following objectives:

  1. to assess the nutrient composition of advanced interspecific hybrids generated from crosses between the cultivated and wild tomato lines and
  2. to determine the differences in nutrient contents between the hybrids and their parents.

 

LITERATURE REVIEW

          Tomato (Solanum esculentum) is one of the most widely cultivated vegetable crops in the world. Tomato is of the family solaneceae and is believed to have originated in Peru and Mexico, in present day central and south America (Purseglove, 1968). Tomato production has risen to 3.58 million tons/ha worldwide (FAO, 2000). Tomato ranks as one of the top two vegetable crops in the United States. It is the most popular home garden vegetable. Tomato reached Europe from Mexico in the 16th century, and was initially used as an ornamental plant. At the end of 18th century, tomato was produced as an edible cultivated plant for household use.

Tomato plant is generally branched with weak trailing stems when young. Most varieties grow erect but eventually slump as they age and are unable to carry their weight (Uguru, 1996). Tomato is day –length neutral and can be planted at anytime of the year provided temperature, humidity and light conditions are favourable. It grows in many kinds of soils. However, it does best in well-drained rich loamy soils (Uguru, 1996). It requires high day temperature of 21-28 0C and cooler night temperature of 15-20 0C (Grubben, 1977).

The tomato fruit contains some health giving compounds such as lycopene.  Lycopene is a bioflavonoid that is closely related to β-carotene. It is the most prominent carotenoids in tomato (Beecher, 1998). Lycopene has hydrocarbon carotenoids that give tomatoes their characteristic colour. Lycopene do not have pro-vitamin activity but it is a good dietary anti-oxidant. High plasma lycopene level resulted in reduced incidence of prostate cancer (Gann et al, 1999). Lycopene is the main carotene accumulated in ripe tomato fruits (Carlo, 2000). In addition to the antioxidant activity, lycopene’s biological activities include control of cell to cell communications. Cooking fresh tomatoes with little oil greatly increases lycopene absorption (Hollie, 2003). Lycopene from tomato such as tomato juice (processed tomatoes) are better absorbed from intestine than raw tomatoes (Bohm and Bitch 1999). Tomato serves as an excellent source of vitamin A and C. Thiamine, niacine, riboflavine and ati-pellegra factor. Lycopene in the presence of vitamin C can repair itself and other antioxidants to restore their antioxidant qualities. The growing importance of tomato diet helps in preventing chronic diseases, such as cardiovascular disease, certain cancers, osteoporosis and diabetes. Solanum pimpinellifolium is closely related to the cultivated tomatoes and it possesses a number of desirable horticultural characteristics including salt tolerance, disease and high fruit quality (Chen and Foolad, 1998). Solanum pimpinellifolium was reported to be resistant to many tomato diseases like fusarium wilt, bacterial spot, bacterial wilt, bacterial canker, bacterial speck, tomato yellow leave curl virus (TYLCV) (Alexander and Hoover, 1955; Andrus et al., 1942).

Nutritional scientists agreed that increased intake of a range of fresh tomato produce can help improve the health standards of almost any human population. Spent lycopene is recycled to lycopene by vitamin C and hence the combination of lycopene and vitamin C may produce the best dietary antioxidants. Increased intake of tomato and their associated compounds including lycopene help to prevent DNA oxidative damage. There are a number of preclinical studies, which noted that dietary intake of lycopene is inversely proportional to prostrate cancer. There is a great interest in diet rich in fruits & vegetables, due to their potential health benefits. Diet modification is a first step in treating high blood pressure that accompanies cardiac and circulatory disorder. The result of short term treatment with antioxidant –rich, tomato extracts have been encouraging. They have been found to help reduce blood pressure in mild to moderate hypertensive cases within the limited extent of these traits.

Carotenoids are group of plant pigments responsible for many of the red, orange, yellow and blues of plant leaves, fruits and flowers, as well as colours of some birds, insects, fishes and crustaceans (Plander, 1992). About six hundred different carotenoids are known to occur naturally (Ong and Tee, 1992) and new carotenoids continue to be identified (Mercandante, 1999).

Recent research had shown that carotenoids are present in algae and photosynthetic bacteria where they play a critical role in the photosynthetic process. They are natural fat soluble pigments. The principal nutrient of tomato fruit are vitamins A and C. Tomato can be an important dietary source of these vitamins. The vitamin A activity of tomato fruit is determined by the β-carotene content (Atherton and Rudich, 1986). The cultivar with better colour has higher vitamin A activity. There is a great variation of pro vitamin A (β-carotene) concentration among several species, cultivars and strains. Carotenoids provide high protection for plant and can help prevent skin damage in humans. The canning process itself both librates lycopene from the cell wall, while protecting this valuable antioxidant from air and light.

The colour of the red tomato is determined by their lycopene and β-carotenoids contents. Lycopene and β-carotene are the principal carotenoids present in the red tomatoes and can be important factor in tomato colour under certain environmental conditions (Atherton and Rudich, 1986).

Nitrogen tends to delay maturity and ripening of fruits (Uzo, 1971). Tindal (1965) noted that nitrogen is an important nutrient element for stimulating healthy and good vegetative growth in tomato. Potassium promotes fruit yield. Vegetable growers use potassium fertilizers to improve yields, quality, colour, strength of stalk (Lucas, 1968). Barker et al. (1967) also reported that tomato performs well in soils with good proportions of potassium and nitrogen. According to Abou Azizi, (1968) sugar level in fruits always follow an inverse pattern with nitrogen level. They were always higher under low nitrogen levels. Sugar level starts to decrease at 45 days after planting in high nitrogen level, this never occurs under low level nitrogen. The decrease in sugar level was attributed to climatic rise (increase in respiratory activity) which took place in these fruits at this stage. Neubert (1959) reported that high nitrogen application was associated with decrease in monosaccharide. Takahashi and Nakayama (1962) found that deficiency of nitrogen, particularly in sand culture reduced plant vigour and yield but increased the sugar content of fruits. Fruits from plants treated with higher nitrogen levels were always higher in crude protein content than those from plant under low nitrogen level (Azizi, 1968). High nitrogen application caused an increase in total nitrogen which is directly proportional to crude protein increase (Neubert, 1959). Fruits from plants under the low nitrogen level were faster and earlier in gaining both carotene and lycopene. Tomatoes had been proved to contain numerous unsurpassable nutritional and health given qualities. Tomato was a rich source of foliate, vitamins A and C, potassium, and phytonutrients. It also contains several other components that are beneficial to health including vitamin E, trace elements, flavonoids phytosterols and several water soluble vitamins.

Tomatine is steroidal glycoalkaliod which is found in all tomato genotypes (Davies and Hobson 1981). Young developing tomato fruits accumulate tomatine but as ripening begins, allcaloid degeneration occurs and the tomatine concentration declines to less than 0.4 percent on fresh weight basis. Asiegbu and Uzo (1983) equally observed that tomato plant accumulate a lot of calcium, but tanslocate little through the abscission zone into the fruit, and thereby resulting in soft rot. Kohler et al., (1947) obtained a selection containing 20 times more β-carotene than most cultivars. Caro Red has 10 times more β-carotene than normal genotypes and is close to  that found in carrot. Tomato is also a source of fibre, and has almost no sodium and fat. Tomato like all other vegetables, has no cholesterol. In human beings, carotenoids can serve several important functions. The most widely studied and well understood nutritional role for carotenoids are their pro-vitamin A activity. Vitamin A which has many vital systemic functions in humans can be produced within the body from certain carotenoids, notably carotene (Britton et al.,1995). Carotenoids play an important role in human health by acting as a biological antioxidant, protecting the cells and tissues from damaging effects of free radicals. The oxidative potential of carotenoids include enhancement of immune system function (Bendich, 1989), protection from sunburn (Roth, and Fox 1990) and inhibition of development of certain types of cancers (Nishino, 1998).

Antioxidants are substances that have the ability to inactivate harmful free radicals. Scientific evidence has shown that diet rich in antioxidants may help keep immune system healthy and reduce the risk for cancer and other diseases (Hollie, 2003). Substances in food with antioxidant activity that are not vitamins or minerals are sometimes referred to as phytonutrients. Lycopene and β-carotene are examples of phytonutrients in tomato. They are hydrocarbon carotenoids while oxygenated derivatives of this hydrocarbon are known as xanthophylls. β –carotene is the major dietary precursor of vitamin A, together with other carotenoids containing substituted β-ionone ring (Lakshman and Okoh, 1993). Dietary β-carotene is obtained from a number of fruits and vegetables such as tomatoes, carrots, spinach, sweet potatoes (Mangels et al., 1993).

In the human body system, β-carotene is converted to vitamin A. Pertinently, vitamin A deficiency is a major public health problem in over 75 countries, most of them localized in developing world. The supplementation of the diet with β-carotene reduces the risk of vitamin A deficiencys morbidity and mortality relating to several pathological conditions (Fawzl et al, 1993; Glasziou and Mackerras, 1993).

Vitamin A which has many vital systemic functions in humans is produced within the body from certain carotenoids, notably β-carotene (Britton et al.,1995). One medium–size fresh tomato provides 22% of the recommended daily allowance of vitamin A.

Vitamin A is a key nutrient, shortage of which may cause coronary heart diseases, some cancer and muscular degeneration and eye condition that can lead to blindness. It is essential and beneficial to reproduction, immune system and reduces skin damage by sunlight (Branmley, 2003). Anti-Nutritional Factors in Plant Foods

Antinutrients are nature and toxic chemical substances that militate against the absorption and utilization of food nutrients in the body. Antinutrients abound in plants and are more concentrated in plant seeds than other parts of plants. Some of these antinutrients include; tannins, phytates, haemogglutinin, saponin, flavoniod, e.t.c (Liener, 1981; Walker 1982). When consumed, they produce adverse physiological conditions in man and animals that precipitate mortality. Most of the antinutrients are heat labile (Nwokolo, 1996). Tannins are polyphenols found interacting with many plant proteins to form protein complexes. They are reported to be present in tomatoes and are also found in the testa of pigmented legumes, and millet (Deshponde et al.,1982). Little or negligible amount of tannins are found in the cotyledon of legumes (Elias et al.,1979). Tannin form complexes with protein, carbohydrate and other food components like polymers in food and certain metals such as iron under adequate concentration (Deshponde et al.,1984).

 

 

Phytates

          Phytates have 6 to 8 negative charges shared among the six phosphate esters per molecule (Raboy, 2000). It binds multivalent minerals such as calcium, iron, zinc, and magnesium and hinders their absorption and bioavailability (Nayini and Markalis, 1983; Potter, 1995; Anderson, and Wolf, 1995). The interaction between phytic acid and minerals lead to the formation of complexes that are insoluble at gut pH and hence, biologically unavailable for absorption (Endman, 1979). On the other hand, phytates form complexes that cannot dissolve easily by electrophoresis at pH greater than 9.0.However, it can dissolve at pH of 4.4 (O’Dell and de Boland, 1976). Cheryan (1980) reported that phytate protein complexes are formed by electrostatic interactions involving the terminal a-amino groups, the β-amino group of lysine, the inidazole group of histidine and the grandidyl groups , and the arginine. Most of these complexes are not soluble and are not biologically available under normal physiological conditions (Hariman, 1979; Fox and Tan, 1989). Furthermore, these proteins are less available for protelytic enzyme degradation than free proteins (Champagne and Philippy, 1989).

Phytic acid is widely distributed in plant kingdom. It is a major part of phosphorus in cereals and legumes (Khan et al., 1986). Graf and Eaton (1993) reported phytic acid to comprise 1 to 3% by weight of all seeds where it served as antioxidant and protect against oxidative charges during storage. Raboy, (2000) reported that cereal grains contain 2.5 to 4. 0 mg total phosphorus per gram dry weight. This would constitute 2 to 3 mg phytic acid, phosphorus or form 70 to 100mg phytic acid per gram dry weight. It is also found in most fruits, vegetables and grains (Mazzioda et al., 1986). Mature pinto dry beans contained about 1% phytic acid whereas immature beans contained approximately 0.13% (Markower, 1969). Lobs and Markakis (1975) found a range of 1.54 to 1.58% phytic acid levels in cultivars of phaseolus. Anderson and Wolf (1995) reported that phytic acid is concentrated in the cotyledon of soybean and about 1.6% is localized in the cotyledon.

Phytate has both positive and negative effects on humans. Apart from forming complexes, it can cause mineral deficiency in populations that depend on whole grain and legume based products as staple food (Brown and Solomon, 1991). It also acts as antioxidant during dormancy, storage of phosphorus cation and cell wall precursors and anti-cancer agent (Graf and Eaton, 1993). Phytic acids inhibit zinc absorption (Lonnerdal, 2000).

Haemogglutinins (Lectins)

Haemogglutinins are found extensively in plant kingdom. They are mostly found in legume seeds up to 1 to 3% dry weight (WHO, 1998). Legumes contain about 95% haemogglutinin. They are proteins of high molecular weight that have affinity for glycan

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