ABSTRACT
This research work was designed to investigate the effect of different integrated soil nutrient management methods and storage period on the nutrient content and carotenoid profile of two orange fleshed sweet potatoes (OFSP). There were eight levels of integrated soil nutrient management: control, poultry manure at 10 t/ha, poultry manure at 5 t/ha, NPK:15:15:15 at 400 kg/ha, Agrolyser at 5.3 t/ha, poultry manure at 2.5 t/ha plus NPK at 200 kg/ha, poultry manure at 5 t/ha plus NPK at 200 kg/ha, Agrolyser at 2.7 kg/ha plus NPK at 200 kg/ha, poultry manure at 2.5 t//ha plus NPK at 200 kg/ha plus Agrolyser at 2.7 kg/ha and two varieties of orange fleshed–sweet potato: Umuspo 1 and Umuspo 3. Mineral, vitamin, anti-nutrient and proximate composition of the tubers were also analysed using standard methods. High performance liquid chromatography (HPLC) was used to determine the carotenoid profile in two varieties of orange fleshed sweet potato as influenced by integrated soil nutrient management and storage period. Integrated soil nutrient management significantly (p < 0.05 ) increased the mineral, vitamins, anti- nutrient, proximate content. Ipomea batatas grown on soils treated with poultry manure at
2.5 t/ha plus NPK at 200 kg/ha plus Agrolyser at 2.7t/ha had the best nutrient composition for the two varieties. There was significant (p< 0.05 ) increase in the Lutein (2.37 μg/100g to 4.83 μg/100g); zexanathin (2.03 μg/100g to 3.84 μg/100g); β-cryptoxanthin (7.31 μg/100g to 10.99 μg/100g); all-trans (84.41 μg/100g to 89.88); total β-carotene (89.89 μg/100g to 94.24 μg/100g) after 6 weeks of storage in almost all the potato samples. Alpha-carotene, 13-cis and 9-cis decreased significantly (p> 0.05) after 6 weeks of storage. The percentage retention of carotenoid was better in Ipomea batatas grown of soil subjected to Agrolyser at 5.3 t/ha for Umuspo 1 variety while in Umuspo 3, higher percentage retention of carotenoid was from Ipomea batatas treated with poultry manure at 5 t/ha plus NPK at 200 kg/ha, and poultry at 2.5 t/ha plus NPK at 200 kg/ha plus Agrolyser at 2.7 kg/ha. Storage significantly (p< 0.05) increased the mineral, fat, ash, carbohydrate and fibre content of the sweet potato samples while anti-nutrients and vitamins content decreased significantly (p< 0.05) with increase in storage period.
TABLE OF CONTENTS
Cover Page i
Title Page ii
Certification iii
Declaration iv
Dedication v
Acknowledgements vi
Table of Contents vii
List of Tables xii
List of Figures xiv
Abstract xvi
CHAPTER 1: INTRODUCTION 1
1.1 Introduction 3
1.2 Problem Statement 4
1.3 Justification 4
1.4 Objective of the Study 4
CHAPTER 2: REVIEW OF RELATED LITERATURE
2.1 History of Sweet Potato 6
2.2 Sweet Potato Varieties 6
2.3 Effect of Organic Manure on Crop Production 7
2.4 Animal Manure and Chemical Fertilizers 9
2.5 Effect of NPK Fertilizer on Plant Yield 11
2.6 The Effect of Poultry on Plant Yield 13
2.7 The Effect of Variety on Sweet Potato 15
2.8 The Effect of Storage on Sweet Potato Nutrients 16
2.9 Storage Methods for Sweet Potato 16
2.10 Carotenoids 18
2.11 Chemical and Physical Properties of Carotenoids 22
2.12 Functions and Health Benefits of Carotenoids 23
2.13 Antioxidant Activity of Carotenoid 25
2.14 Functions of Vitamin A 28
2.15 Degradation of Carotenoids 30
2.16. Vitamin A Deficiency 30
2.17 Quantification of Carotenoids. 31
CHAPTER 3: MATERIALS AND METHODS 33
3.1 The Study Site 33
3.2 Root and Tuber Samples 33
3.3 Experimental Design and Treatments 33
3.4 Storage of Sweet Potato Tuber 34
3.5 Sample Preparation 34
3.6 Determination of Moisture Content 34
3.6.1 Determination of ash content 35
3.6.2 Determination of crude fiber 35
3.6.3 Determination of crude fat 36
3.6.4 Determination of protein content 37
3.6.5 Determination of carbohydrate 38
3.7 Determination of Mineral Content 38
3.7.1 Determination of calcium and magnesium 39
3.7.2 Determination of phosphorus 40
3.7.3 Determination of potassium and sodium 40
3.8 Determination of Tannin 41
3.8.1 Determination of alkaloid 42
3.8.2 Determination of flavonoid 43
3.8.3 Determination of oxalate 43
3.9 Determination of Vitamin B1 44
3.9.1 Determination of vitamin B2 45
3.9.2. Determination of niacin (Vitamin B3) 45
3.9.3. Determination of vitamin A 46
3.9.4. Determination of vitamin C 47
3.10 Determination of β-Carotene 48
3.10.1 Conversion of pro-vitamin A carotenoid 50
3.11 Statistical Analysis 50
CHAPTER 4: RESULTS AND DISCUSSION 51
4.1 Effect of Integrated Soil Nutrient Management on Carotenoid Content of
Ipomea batatas Umupos 1 and Umuspo 3 Varieties 51
4.2 Effect of Different Soil Nutrient Management Treatments on the Pro-vitamin A Content of Ipomea batatas of Umuspo 1 and Umuspo 3 Varieties 57
4.3 Effect of Integrated Soil Nutrient Management on the Proximate Composition
of Ipomea batatas of Umuspo 1 and Umuspo 3 Varieties. 59
4.4 Effect of Integrated Soil Nutrient Management on the Mineral Composition of Ipomea batatas Umuspo 1 and Umuspo 3 Varieties. 64
4.5 Effect of Integrated Soil Nutrient Management on the Anti-Nutritional composition of Ipomea batatasof Umuspo 1 and Umuspo 3 Varieties. 69
4.6 Effect of Integrated Soil Nutrient Management on Vitamin Content of
Ipomea batatas Variety for Umuspo 1 and Umuspo 3 Varieties. 72
4.7 Effect of Storage Period on the Carotenoid Profile of Ipomea batatas
Umuspo 1 and Umuspo 3 Varieties. 75
4.8 Effect of Storage Period on the Proximate Composition of Ipomea
batatas Umuspo 1and Umuspo 3 Varieties. 81
4.9 Effect of Storage Period on the Mineral Composition of
Ipomea batatas Umuspo 1and Umuspo 3 Varieties. 89
4.10 Effect of Storage Period on the Anti-Nutritional Composition of
Ipomea batatas Umuspo 1and Umuspo 3 Varieties. 91
4.11 Effect of Storage Period on the Vitamin Composition Ipomea
Batatas Umuspo 1and Umuspo 3 Varieties. 96
4.12 Chromatograms of Ipomea batatas Varieties (Umuspo 1 and Umuspo 3) 100
CHAPTER 5: CONCLUSION AND RECOMMENDATIONS 117
5.1 Conclusion 117
5.2 Recommendations 118
Reference 120
Appendices 133
LIST OF TABLES
2.1 : Relative bioactivity of some provitamin a 24
2.2 : Absorption coefficient (a1 %) of common food carotenoids 31
4.1 : Effect of integrated soil nutrient management on the carotenoid content
of ipomea batatas of umuspo 1 and umuspo 3 varieties. 56
4.2 : Effect of integrated soil nutrient management on the provitamin a
content of ipomea batatas of umuspo 1 and umuspo 3 varieties. 58
4.3 : Effect of integrated soil nutrient management on the proximate composition of ipomea batatas of umuspo 1 and umuspo 3 varieties. 63
4.4 : Effect of integrated soil nutrient management on the mineral composition (mg/100g) ipomea batatas umuspo 1 and umuspo 3 68
4.5 : Effect of integrated soil nutrient management on the anti-nutritional composition (mg/100g) of ipomea batatas of umuspo 1 and umuspo 3 71
4.6 : Effect of integrated soil nutrient management on vitamin content
(μg/100g) of ipomea batatas umuspo 1 and umuspo 3 74
4.7 : effect of storage period on the carotenoid content (µg/g) of umuspo i
ipomea batatas variety 79
4.8 : Effect of storage period on the carotenoid content (µg/g) of ipomea
batatas umuspo 3 80
4.9 : Effect of storage period on the proximate composition (%) of umuspo
1 ipomea batatas variety 84
4.10 : effect of storage period on the proximate composition (%) of
ipomea batatas umuspo 3 85
4.11 : Effect of storage period of the mineral composition (mg/100g) of
ipoema batatas umuspo 1 89
4.12 : Effect of storage period on the mineral composition mg/100g of
ipomea batatas umuspo 3 90
4.13 : Effect of storage period on the anti-nutritional composition (µg/100g)
of ipomea batatas umuspo i 94
4.14 : Effect of storage period on the anti-nutritional composition (µg/100g)
of ipomea batatas umuspo 3 95
4.15 : Effect of storage period on the vitamin composition (mg/100g) of ipomea batatas umuspo 1 98
4.16 : Effect of storage period on the vitamin composition (mg/ 100g)
of ipomea batatas umuspo 3 99
LIST OF FIGURES
2.1 : Structures and characteristics of common food carotenes 20
2.2 Structures and characteristics of common food xanthophylls 21
2.3 Important physical and chemical properties of carotenoids 23
2.4 : Health- promoting function of carotene. 27
25: The role of vitamin a (retinol) in the visual cycle 28
4.1: Chromatogram of carotenoid of umuspo 1 ipomea batatas treated with poultry manure at 2.5 t/ha plus npk at 200 kg/ha plus agrolyser at 2.7 kg/ha 974.2: chromatogram of carotenoid of umuspo
1 ipomea batatas treated with npk at 400 kg/ha 105
4.3 : Chromatogram of carotenoid of umuspo 1 ipomea batatas treated with agrolyser at 5.3 kg/ha 106
4.4 Chromatogram of carotenoid of umuspo 3 ipomea batatas
treated with poultry manure at 2.5 t/ha plus npk at 200 kg/ha plus agrolyserat 2.7 kg/ha 107
4.5 Chromatogram of carotenoid of umuspo 3 ipomea batatas treated with poultry manure at 5 t/ha plus npk at 200 kg/ha 108
4.6 Chromatogram of carotenoid of umuspo 3 ipomea batatas treated with npk at 400 kg/ha 109
4.7 Chromatogram of carotenoid of umuspo 1 ipomea batatas treated poultry manure at 2.5 t/ha plus npk at 200 kg/ha plus agrolyser at 2.7 kg/ha after six weeks of storage 110
4.8 Chromatogram of carotenoid of umuspo 1 ipomea batatas treated npk at 400 kg/ha after six weeks of storage 111
4.9 Chromatogram of carotenoid of umuspo 1ipomeabatatas treated with agrolyser at 5.3 kg/ha after six of storage 112
4.10 Chromatogram of carotenoid of umuspo 3 ipomea batatas treated with poultry manure at 2.5 t/ha plus npk at 200 kg/ha plus agrolyser at 2.7 kg/ha after six weeks of storage 113
4.11 Chromatogram of carotenoid of umuspo 3 ipomeabatatas treated with poultry manure at 5 t/ha plus npk at 200 kg/ha after six weeks of storage 114
4.12 Chromatogram of carotenoid of umuspo 3 ipomeabatatas treated with npk at 400 kg/ha after six weeks of storage 115
CHAPTER 1
1.0 INTRODUCTION
Sweet potato (Ipomea batatas (L) Lam) is a starchy root crop grown in tropical and subtropical countries like China (Onuh et al., 2004). Sweet potato is a perennial crop but usually grown as an annual and belongs to the family Convolvulaceae. It ranks fifth as the most important food crop after rice, wheat, maize, and cassava in developing countries (Som, 2007). A very large number of sweet potatoes existed; the number is larger than for yams, cassava, or cocoyam (Onwueme and Charles, 1994). Many of these cultivars have developed through systematic breeding efforts, and through natural hybridization and mutations. Sweet potato cultivars also differ from one another in the colour of the root skin (usually white, brown, yellow, or reddish purple), colour of the root flesh (white, yellow, purple or orange), shape of tuber, shapes of leaves, depth of rooting, time of maturity, and several other vegetative characteristics (Woolfe, 1992).
Sweet potato is an important crop with versatile utility. It is valued for its roots which are boiled, fried, baked, or roasted for humans or treated and fed to livestock as a source of energy (Udoh et al., 2005). The roots are also source of industrial materials for the production of starch, alcohol, pectin, (Ukom et al., 2009). In Nigeria, the flour is utilized in sweetening local beverages like kunun-zaki, burukutu, and for fortifying baby foods, foo foo and pounded yam (Truong, 1989; Tewe et al., 2003). Sweet potato leaves are used as vegetables (Nwinyi, 1991). Besides being energy provider, it is a good source of minerals such as K, Na, Cl, P, and Ca and vitamins A, B and C (Watt and Merill, 1975).
Sweet potato, depending on cultivar is quite high in carotenoid, the β-carotene. The mean β-carotene content of sweet potato cultivars ranges from 10- 26,600 µg/100g (Hagenimana et al., 1999; Almedia-Muradian and Penteado, 1992; Rodriguez-Amaya, 1993; and K’ Osambo et al., 1998). β-carotene predominates particularly in the yellow- orange fleshed cultivars (Woolfe, 1992). β-carotene is the most important provitamin A both in terms of its bioactivity and widespread occurrences (Rodriguez-Amaya, 1997).
β-carotene is a potent provitamin A with 100% activity. Carotenoids are very important in nutrition and health. Simpson (1983) estimated about 82% dietary vitamin A in developing countries to come from provitamin A. β-carotene has also been linked with enhancement of immune function and decreased risk of degenerative disease such as cancer and cardiovascular disease (Mathews-Roth, 1985; Bendich and Oslon, 1989; Bendich, 1990, 1994).
Despite the importance and potential of sweet potato as a food security crop, the crop has received comparatively little attention, and yields are low in farmers field (Njoku, 2008). Low soil fertility is profound and remains a major constraint to sweet potato in ultisols which constitute the main agriculture lands of South Eastern Nigeria (Njoku et al., 2001; Okpara et al., 2011).The problem of nutrient deficiency is exacerbated by erratic rainfall distribution, which results in non availability or insufficiency of moisture for nutrient uptake and leaching of nutrients due to excessive precipitation, with consequent loss of growth.
Poultry manure is a readily available organic material that can be utilized to supplement the quantity of mineral fertilizer needed for sweet potato production. Poultry manure contains both macro and micronutrients and, in contrast to inorganic fertilizer, it adds organic matter to soil which improves soil structure, soil aeration, nutrient retention, soil moisture holding capacity and water infiltration (Amanuallah et al., 2010).
Nutrients contained in organic manures are released more slowly and are stored for a long period in the soil, thereby ensuring a long residual effect. The potato plant assimilates nutrient from both organic and inorganic fertilizer relatively due to its long vegetative growth period (Harris, 1992). Type of fertilizer forms, rates and their combined application can increase or decrease dry matter, starch, protein and sugar content in sweet potato tuber (Makaravicutte, 2003). Sweet potato response to fertilizer in Nigeria has been concentrated on the white fleshed type, while little is known about nutrient management for orange fleshed sweet potato (Njoku et al., 2001; Okpara et al., 2009). Element of best practices in integrated nutrient management involves the right sources, rates and timing of fertilizer to ensure optimum crop performance and sustainability.
The storage behavior of potato tuber depends on many factors. The physiological age of the seed tuber, the cultivar, the soil type, climate conditions during the growing period as well as agronomic factors like foliage killing before maturity and date of harvest influence weight losses and changes in the chemical composition of stored tuber (Firman and Allen, 2007). Thus Rodriguez-Amaya (1997) emphasized the need to accompany β- carotene content result with pertinent information such as the variety, stage of maturity, season and method used.
1.2 PROBLEM STATEMENT
Post harvest handling of sweet potato is a challenge due to its perishable nature, and losses in nutrient composition after harvest has been a major problem that reduces farmer’s income. Hence, farmers need to maintain the quality of the crop, until sale or consumption under suboptimal traditional storage condition, which is also limited by attack from sweet potato weevils. Hence, this study will evaluate nutrient composition of sweet potato tubers from the time of harvest to six (6) weeks of storage in order to determine the best soil nutrient management system that will prolong the shelf life of harvested tubers during ambient temperature of storage.
1.3 JUSTIFICATION
The storage behavior of potato tuber depends on many factors: the physiological age of the tuber, the soil type, climate condition during the growing period as well as date of harvest. There is need to determine the changes in nutrients of freshly harvested sweet potato grown under different soil nutrient management conditions. This will highlight the optimal storage period of orange fleshed sweet potato in relation to the soil nutrient management type used in growing the tubers.
1.4 OBJECTIVE OF THE STUDY
The objective of the study was to determine the effect of post harvest storage on nutrient content of two orange-fleshed sweet potato varieties as influenced by integrated soil nutrient management.
The specific objectives of this research are to;
1. To evaluate the effect of integrated soil nutrient management on the chemical, mineral, vitamins and anti-nutrient content of orange-fleshed sweet potato varieties (Umuspo 1 and 3).
2. To determine the effect of integrated soil nutrient management on the carotenoid profile of orange-fleshed sweet potato varieties (Umuspo 1 and 3).
3. To determine the effect of integrated soil nutrient management and storage on the carotenoid profile of the orange -fleshed sweet potato varieties (Umuspo 1 and 3)
4. To determine the effect of integrated soil nutrient management and storage on the chemical, mineral, vitamins and anti-nutrient content of orange-fleshed sweet potato varieties (Umuspo 1 and 3).
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