ABSTRACT
This work evaluated the effect of processing methods (boiling and sautering) on the chemical and antioxidant properties of some selected indigenous vegetables (scent leaf, garden egg leaf, utazi leaf, ukazi leaf and bitter leaf). Vitamins, antioxidant, anti-nutrient and mineral composition of the samples were determined. The vitamin composition of the samples varied from vitamin A (0.92 to 319.23mg/100g), vitamin B1 (0.01 to 10.67mg/100g), vitamin B2 (0.01 to 0.96mg/100g), vitamin B3 (0.04 to 0.88mg/100g). The antioxidant properties varied from % DPPH (18.90-82.40) %, The ABTS value ranged from 3.00 to 27.50 %, The FRAP value ranged from 3.42 to 21.89 %, The TPC value ranged from 2.45-116.74%, with cooked utazi leaf having the least value (2.45 %), whereas sautered scent leaf had the highest value (116.74 %). The TFC value ranged from 2.01-41.42 %, with cooked garden egg leaf having the least value (2.01 %), whereas sautered scent leaf showed the strongest power (29.89 %).The anti-nutrient varied from alkaloid content 0.06 to 6.38 %, with sautered garden egg leaf having the least value (0.06 %), whereas raw bitter leaf had the highest value (6.38 %).. The tannin content varied from 0.02 to 4.09 %, with sautered garden egg having the least value (0.02 %), whereas raw scent leaf had the highest value (4.09 %). The phytates content varied from 0.05 to 2.72 %. The saponin content varied from 0.01 to 4.73 %, with sautered garden egg leaf having the least value (0.01 %), whereas raw bitter leaf had the highest value (4.73 %).
TABLE OF CONTENTS
Title page i
Declaration ii
Certification iii
Dedication iv
Acknowledgement v
Table of Contents vi
List of Tables x
List of figures xi
Abstract xii
CHAPTER 1: INTRODUCTION
1.1 Background of the study 1
1.2 Statement of problem 3
1.3 Justification of the study 3
1.4 Objectives of the study 3
CHAPTER 2: LITERATURE REVIEW
2.1 Vegetables 5
2.2 Indigenous vegetables 6
2.3 Uziza leaf (Piper guineense) 7
2.3.1 Nutritional and health benefits of uziza leaf (Piper guineense) 7
2.4 Scent leaf (Ocimumgratissimum) 9
2.4.1 Nutritional and health benefits of scent leaf 9
2.5 Bitter leaf (Vernoniaamygdalina) 10
2.5.1 Nutritional value and health benefits of bitter leaf 11
2.6 Ukazileaf (Gnetumafricanum) 13
2.6.1 Nutritional value and health benefits of ukazi leaf 13
2.7 Garden egg leaf (SolanummelongenaL.) 15
2.7.1 Nutritional value and health benefits of garden egg leaf 15
2.8 Utazi leaf (Gongronemalatifolium) 16
2.8.1 Nutritional value and health benefits ofutazi leaf 16
2.9 Antinutrient factors in food 18
2.10 Antioxidants 19
CHAPTER 3: MATERIALS AND METHODS
3.1 Sources of raw materials 21
3.2. Sample preparation 21
3.2.1 Processing of leaf samples 21
3.3 Methods of analyses 25
3.4 Determination of mineral content of the vegetables 25
3.4.1 Determination of calcium and magnesium 25
3.4.2 Determination of potassium 26
3.4.3 Determination of zinc 26
3.4.4 Determination of iron 27
3.4.5 Determination of phosphorus 27
3.5 Determination of vitamin content of the vegetables 28
3.5.1 Determination of β-carotene 28
3.5.2 Determination of vitamin B1 28
3.5.3 Determination of vitamin B2 29
3.5.4 Determination of vitamin B3 30
3.5.5 Determination of vitamin C 30
3.6 Determination of antioxidant activity of the vegetables 31
3.6.1 Antioxidant activity determined by 2,2-Diphenyl-1-picrylhydrazyl (DPPH) 31
3.6.2 Antioxidant activity determined by Ferric Reducing Antioxidant Power 32
3.6.3 Antioxidant activity determined by ABTS+ radical cation 32
3.6.4 Determination of Total polyphenol Content (TPC) 33
3.6.5 Determination of total flavonoid content 33
3.7 Determination of antinutrient factors of the vegetables 33
3.7.1 Determination of phytate 33
3.7.2 Determination of saponin 33
3.7.3 Determination of tannin 34
3.7.4 Determination of phenol 35
3.7.5 Determination of alkaloids 35
3.8 Experimental design 36
3.9 Statistical analysis 36
CHAPTER 4: RESULTS AND DISCUSSION
4.1 Mineral composition of some indigenous vegetables 37
4.2 Vitamin composition of some indigenous vegetables 40
4.3 Antioxidant properties of some indigenous vegetables 42
4.4 Anti-nutrients composition of some vegetables 45
4.5 Correlation of total phenol, total flavonoids and vitamin C with antioxidant capacities of some raw, blanch and sautered indigenous vegetables. 47
CHAPTER 5: CONCLUSION AND RECOMMENDATION
5.1 Conclusion 50
5.2 Recommendation 50
REFERENCES 51
LIST OF TABLES
Table 3.1 Blanching 22
Table 3.2 Sautering 23
Table 4.1 Mineral composition of some indigenous vegetables 38
Table 4.2 Vitamin composition of some indigenous vegetables 41
Table 4.3 Antioxidant properties of some indigenous vegetables 43
Table 4.4 Anti-nutrients composition of some indigenous vegetables 46
Table 4.5 Correlation of total phenol, total flavonoids and vitamin C with antioxidant capacities of some raw, blanched and
sautered indigenous vegetables 48
LIST OF FIGURES
Figure 3.1: Flow chart for processing of bitter leaf, utazi leaf, garden egg leaf, scent leaf, uziza leaf and ukazi leaf. 24
CHAPTER 1
INTRODUCTION
1.1 BACKGROUND OF THE STUDY
Vegetables are vital in human nutrition, especially as sources of phyto-nutriceuticals like vitamins, minerals, dietary fiber and phytochemicals (Dias and Ryder, 2011) which are strongly associated with overall good health, reduced risk for some forms of diabetes, anemia, and other chronic diseases (Keatinge et al., 2010). Indigenous vegetables are valuable sources of nutrition in rural areas where exotic species are not available (Banerjee et al., 2015). They hold an important place in well-balanced diets and are within the reach of poor man (Dias and Ryder, 2011).In Nigeria, some of the common indigenous vegetables includes but not limited to bitter leaf, ukazi, scent leaf, garden egg leaf, utazi and uziza (Ndie et al., 2013).
Uziza (Piper guineense) is a spice plant from the family, piperaceae (Echo et al., 2012). It possess amino acid, vitamins, and minerals like calcium, magnesium, potassium, and phosphorus (Dike, 2010).The major phytochemicals present in uziza leaf are flavonoids, alkaloids, saponins and tannins which have therapeutic and anti-oxidant potentials (Dibulo et al., 2017).
Scent leaf (Ocimum gratissimum)is one of those plants consumed as a leafy vegetables and the nutritional importance of this plant center on its usefulness in seasoning because of its aromatic flavour (Nduche and Otaka, 2019).Scent leaf possess crude fibre and micronutrients like magnesium (Paul et al., 2018). It also contains some bioactive substances like phenols and flavonoids, also referred to as phytochemicals (Agholor et al., 2018).
Bitter leaf (Vernonia amygdalina) is one of the most famous plants found in Africa (Egharevba et al., 2014). It is a source of protein, micronutrients and amino acids (Alara et al., 2017). Bitter leaf consists of medicinal properties which include antioxidant properties, and anti-diabetic effects among others (Egharevba et al., 2014).
Ukazi (Gnetum africanum) is an edible tropical crop, native in south Eastern part of Nigeria (Oguwike et al., 2018). Ukazi leaf contains crude protein, crude fibre (Ekpo et al., 2012), and micronutrients like potassium, vitamin A and C (Okerulu and Onyema, 2015).The leaves of ukazi possess the potential to be used as a remedy for nausea and sore throats (Ali et al., 2011).
Garden egg (Solanum melongena L.) is of economic importance throughout the world (Caruso et al., 2017). Its leaf possess micronutrients like vitamin A and iron (Tamègnon et al., 2012) which aids in minimizing anaemia (Egbi et al., 2018). Dry garden egg leaves are beneficial in the treatment of stomach bloating, while consumption of the fresh leavesaids to strengthen bones, control diabetes, prevent paralysis and helpful in teeth related problems (Cassidy et al., 2013, Krisban, 2013).
Utazi (Gongronema latifolium) leaf is popularly known for its nutritional and medicinal values (Balogun et al., 2016). Utazi leafhave been shown to be a source of carbohydrates, proteins, vitamins, minerals (Mgbeje et al., 2019) and amino acid (Balogun et al., 2016). Utazi leafpossess sufficient active principles that confirm it as an important medicinal vegetable with rich free radical scavenging properties (Enemor et al., 2014).
The proportion at which nutrients in these vegetables is retained relative to the amount of nutrient present in a known weight of the raw food (i.e. before processing) refers to as nutrient retention. The retention of food quality is important to ensure the consumption of food with high nutritional values for proper human growth and development (Sharif et al., 2017).
1.2 STATEMENT OF PROBLEM
Utazi leaf, garden egg leaf, scent leaf, uziza leaf, ukazi leaf and bitter leaf are usually utilized in raw and cooked forms. During processing of these vegetables, nutrients are lost by degradation, solubilization or leaching, hence the need to evaluate their chemical and nutrient retention. Besides, frequent consumption of such vegetables has the tendency to result to improve immune competence.
1.3 JUSTIFICATION OF THE STUDY
Different types of delicacies like African salad are prepared with Utazi leaf, garden egg leaf, scent leaf, uziza leaf, ukazi leaf in Nigeria. Assessing nutrient retention of raw and processed forms of these vegetables will go a long way to give information on the nutrient availability. More so, findings of this study will be incorporated in Nigeria’s food composition table so that provision of dietary guidance using such food composition database as a reference material could be more effective.
1.4 OBJECTIVES OF THE STUDY
The main objective of this study was to evaluate the chemical and nutrient retention of some indigenous vegetables (utazi leaf, garden egg leaf, scent leaf, uziza leaf, ukazi leaf and bitter leaf).
The specific objectives were to:
i. Determine the mineral and vitamin content of the raw, blanched and sautered indigenous vegetables
ii. Evaluate the antioxidant activity of the raw, blanched and sautered indigenous vegetables.
iii. Determine the anti-nutrient factors of the raw, blanched and sautered indigenous vegetables.
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