ABSTRACT
African pear (Dacryodes edulis) fruit was dried through different drying methods (sun drying, oven drying, microwave drying and toasting) and was assessed for functional, proximate, mineral, dietary fibre, vitamin compositions, peroxide value and sensory characteristics. The functional properties ranged from 0.71 to 0.75 g/ml bulk density, 3.31 to 5.08 ml/g water absorption capacity, 22.26 to 28.12 ml/g oil absorption capacity, 5.03 to 6.19 ml/g, 117.50 to 124.50 ml/g wettability, 1.01 to 1.18 ml/g solubility index and 62.35 to 70.85 °C gelation temperature. Toasting gave better functional properties. Sun dried samples had the highest fat (12.44 %), protein (13.25 %) and moisture content (10.03 %), while toast dried samples had the highest higher fibre (1.26 %) and carbohydrate (68.28 %) contents. Microwave dried samples recorded the highest concentration of minerals with respect to calcium (0.03-0.05 mg/100 g), magnesium (0.02-0.03 mg/100 g), iron (0.00-0.01 mg/g), sodium (0.00-0.01 mg/100 g) and potassium (0.06-0.09 mg/100 g) contents. Oven dried samples had the highest total dietary fibre (2.66 %) and insoluble dietary fibre (1.79 %) while sun dried samples had the highest soluble dietary fibre (0.93 %). Sun drying resulted to samples with better vitamin contents; pro-vitamin A (1.06 mg/100 g), vitamin C (8.86 mg/100 g), vitamin E (197.00 mg/100 g) and lowest peroxide value (2.99 meq O2/kg). The various drying methods did not significantly (p<0.05) alter the dryness, texture, aroma and general acceptability of the African pear flour samples while oven dried samples appeared darker in appearance. Conclusively, African pear fruits can be dried using different drying methods with respect to the desired properties of the end product, hence, exhibiting the potential of a viable industrial raw material.
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
List of plates xii
Abstract xiii
CHAPTER 1: INTRODUCTION
1.1 Background of the study 1
1.2 Statement of the problem 2
1.3 Justification of the study 3
1.4 Objectives of the study 3
CHAPTER 2: LITERATURE REVIEW
2.1 Description OF AFRICAN pear (Dacryodes edulis) 5
2.2 Origin and varieties of African pear (Dacryodes edulis) 6
2.3 Nutritional composition of African pear (Dacryodes edulis) 7
2.4 Health benefits of African pear (Dacryodes edulis) 8
2.5 Uses of African pear (Dacryodes edulis) 8
2.6 Drying 10
2.6.1 Drying methods 10
2.6.1.1 Sun drying 11
2.6.1.2 Solar drying 11
2.6.1.3 Microwave drying 12
2.6.1.4 Toasting 13
2.6.1.5 Oven drying 14
2.7 Impact of different drying methods on the quality characteristics of food 14
2.8 Influence of different drying methods on the oxidative rancidity of flour 17
2.8.1 Microwave drying 17
2.8.2 Oven drying 17
2.8.3 Sun drying 18
2.8.4 Toasting 18
CHAPTER 3: MATERIALS AND METHODS
3.1 Sources of raw material 19
3.2. Raw material preparation 19
3.3. Determination of functional properties 22
3.3.1 Gelation capacity 22
3.3.2 Water absorption capacity 22
3.3.3 Oil absorbtion capacity 23
3.4 Swelling index 23
3.3.5 Bulk density 24
3.3.6 Wettability 24
3.3.7 Foam capacity 25
3.4. Proximate analysis 25
3.4.1 Moisture content determination 25
3.4.2 Determination of crude fibre 26
3.4.3 Determination of crude protein 27
3.4.4 Determination of fat 27
3.4.5 Determination of ash content 28
3.4.6 Carbohydrate determination 28
3.5 Mineral contents 29
3.5.1 Determination of calcium and magnesium 29
3.5.2 Determination of iron 30
3.5.3 Determination of sodium and potassium 31
3.6 Determination of vitamins 32
3.6.1 Determination of retinol 32
3.6.2 Determination of vitamin C 33
3.6.3 Determination of vitamin E 33
3.7 Dietary fibre determination 34
3.7.1 Total dietary fibre 34
3.7.2 Soluble (SDF) and insoluble (IDF) dietary fibre 35
3.8 Determination of peroxide value 35
3.9 Sensory evaluation 36
3.9 Statistical analysis 36
CHAPTER 4: RESULT AND DISCUSSION
4.1 Functional composition of African pear (Dacryodes edulis)
flour samples 38
4.1.1 Bulk density 38
4.1.2 Water absorption capacity 40
4.1.3 Oil absorption capacity 40
4.1.4 Foam capacity 41
4.1.5 Wettability 42
4.1.6 Swelling index 42
4.1.7 Gelatinization temperature 43
4.2 Proximate compositionvof African pear (Dacryodes edulis)
flour samples 44
4.2.1 Moisture content 44
4.2.2 Fat 44
4.2.3 Ash 46
4.2.4 Crude fibre 47
4.2.5 Protein 47
4.2.6 Carbohydrates 48
4.3 Mineral composition of African pear (Dacryodes edulis)
flour samples 49
4.3.1 Calcium 49
4.3.2 Magnesium 49
4.3.3 Iron 51
4.3.4 Sodium 51
4.3.5 Potassium 52
4.4 Dietary fibre of African pear (Dacryodes edulis) flour samples 52
4.4.1 Total dietary fibre (TDF) 52
4.4.2 Soluble dietary fibre 54
4..4.3 Insoluble dietary fibre 54
4.5 Vitamin composition of African pear (Dacryodes edulis)
flour samples 55
4.5.1 pro-Vitamin a content 55
4.5.2 Vitamin c 57
4.5.3 Vitamin e 57
4.6 Peroxide value of African pear (Dacryodes edulis)
flour samples 58
4.7 Sensory evaluation of African pear (Dacryodes edulis)
flour samples 60
4.7.1 Appearance 60
4.7.2 Aroma 60
4.7.3 Texture 60
4.7.4 Dryness 62
4.7.5 General acceptability 62
CHAPTER 5: CONCLUSION AND RECOMMENDATIONS
5.1 Conclusion 63
5.2 Recommendations 63
REFERENCES 65
LIST OF TABLES
3.1: Codes representing each drying method.
4.1: Functional Properties of African pear (Dacryodes edulis) Flour Sample. 39
4.2: Proximate Composition of African pear (Dacryodes edulis) Flour Sample 45
4.3: Mineral Composition of African pear (Dacryodes edulis) Flour Sample 50
4.4: Dietary Fibre Composition of African pear (Dacryodes edulis) Flour Sample 53
4.5: Vitamin Composition of African pear (Dacryodes edulis) Flour 56
4.6: Peroxide Composition of African pear (Dacryodes edulis) Flour Samples 59
4.7: Sensory Evaluation of African pear (Dacryoles edulis) Flour Sample 61
LIST OF FIGURES
Figure 1: Flow chart for African pear (Dacryodes edulis) flour production 22
LIST OF PLATES
Plate 1: Matured and ripened African pear (Dacryodes edulis) fruit. 19
Plate 2: Sun dried 20
Plate 3: Oven dried 20
Plate 4: Microwave dried 20
Plate 5: Toasted dried 20
CHAPTER 1
INTRODUCTION
1.1 BACKGROUND
African pear (Dacryodes edulis) belongs to the family Burseraceae. In this family, there are resinous trees and shrubs with alternate leaves composed of many leaflets. According to Jecinta (2015), they are of the order Sapindales, subclass Rosidae and class Magnoliopsida. African pear (Dacryodes edulis) is a fruit tree native to Africa, sometimes called Safou (Cameroon), Atanga (Gabon), Ube (Nigeria) (Wikipedia, 2020). African pear (Dacryodes edulis) tree can attain heights of 18-40 meters in the forest but generally not exceeding 12 meters in plantations and it is an evergreen tree. It generally has low branches and has a dense crown (Ajibesin, 2011). Although the preferred habitat for African pear (Dacryodes edulis) is shady, humid tropical forests. It adapts well to changes in soil type, humidity, temperature, and day length.
The fruit is the major part utilized for food and it is widely used among Yoruba and Igbo speaking people of Nigeria (Conrad, 2012). It can be eaten alone or with a number of other foods. Common edible oils are sometimes substituted with oil derived from African pear (Dacryodes edulis) pulp. It has been touted to have medicinal properties and locally, the plant has been used alone or combined with other plants to treat some illnesses and diseases some of which include malaria, dermatological issues, oral and ear conditions, hypertension, leprosy, labor pain, retarded growth and epilepsy in children (Conrad, 2012). African pear (Dacryodes edulis) has some socio-cultural and religious uses in some areas where it is viewed as a symbol of fruitfulness, and of peace. In such areas the plant parts are used for both religious and sociocultural activities including warding off evil spirits, worship of gods, communal festivals, marriage and naming ceremonies (Conrad, 2012). Other sectors where the plant has been very useful include in carpentry, road and shelter construction. According to Conrad (2012), exudates from the stem act as glue, and can be used for production of cosmetics alongside the fruit oil.
African pear (Dacryodes edulis) has the potential to boost food security as it rich in edible oil and other essential food nutrients (Ajibesin, 2011). Improved cultivation and utilization of the plant can foster rural development by improving the economic status of local farmers and support sustainable land-care. The most utilized part of the African pear (Dacryodes edulis) plant is the fruit, which can be eaten either raw, cooked in salt water or roasted. Cooked flesh of the fruit has a texture similar to butter. The pulp contains 48% oil. The fat content of this fruit is higher compared to fruits such as apple, guava and pawpaw (Omogbai and Ojeabuni, 2010).
Kengue (2011), reported that it is as a highly perishable with a shelf-life of 2-3 days after harvest at ambient conditions. Poor harvesting, handling and storage of the fresh fruit is complicated since value chain actors have limited knowledge and resources to ensure product quality and increased shelf life (Ndindeng et al., 2012). Production of flour from African pear (Dacryodes edulis) will be an alternative way of prolonging its shelf life. However, some drying procedures are believed to accelerate the process of product rancidity, therefore, it is important to determine which drying procedure is more acceptable in producing a dried African pear (Dacryodes edulis). Thus, various methods of drying should be considered to know which is suitable for the production of African pear (Dacryodes edulis) flour.
1.2 STATEMENT OF PROBLEM
African pear (Dacryodes edulis) is a good security crop with important nutritional and economical relevance. However, it is prone to a lot of postharvest losses because it is highly perishable in nature which leads to limitations in utilization of the crop. It is mostly consumed after roasting or boiling with little or no commercial value. Processing it into other forms which will improve its utilization, industrial value, reduce postharvest losses and make African pear (Dacryodes edulis) derived product available all year round would be beneficial. It is therefore necessary to investigate the best drying method that would be suitable for obtaining flour from African pear (Dacryodes edulis) fruit with the intent of creating valuable raw materials for domestic and commercial purposes.
1.3. JUSTIFICATION OF THE STUDY
Upon completion of this study, it is expected that, a suitable drying method that would be sufficient in processing African pear (Dacryodes edulis) fruit to flour with minimal nutrient losses would have been uncovered. Achieving this purpose would improve its utilization and minimize postharvest losses that is associated with African pear (Dacryodes edulis) fruit during its on-season period. Local farmers involved in its cultivation may experience an increase in their earnings because of increase in demand. This would also encourage the use of locally sourced food materials for flour production as well as minimize the volume of wheat flour that comes into the country. Thus, economic growth with respect to agricultural produce will be achieved.
1.4. OBJECTIVES OF STUDY
The main objective of this study was to evaluate the effect of different drying methods on the quality characteristics of African pear (Dacryodes edulis) flour.
The specific objectives include:
i. To process African pear (Dacryodes edulis) fruit into powder using sun drying, microwave drying, oven drying and toasting methods
ii. To evaluate the functional properties, proximate, vitamin, mineral, peroxide value and dietary fibre composition of African pear (Dacryodes edulis) flour.
iii. To evaluate the sensory characteristics of African pear (Dacryodes edulis) flour.
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