ABSTRACT
The drying characteristics of Dioscorea bulbifera flour at different drying temperatures (55°C, 65°C, 75°C, 85°C and 95°C) and varied drying time (60 minutes, 80 minutes, 100 minutes, 120 minutes and 140 minutes) at a constant air velocity of 1.0 m/s were investigated. The moisture content of the dried flours ranged from 5.76 to 8.31%, 5.11 to 7.76%, 4.60 to 7.27%, 4.11 to 6.81% and 3.55 to 6.20% for samples dried at 55, 65, 75, 85 and 95˚C for between 60 to 140 minutes respectively. The ash content of the dried flours ranged from 2.64 to 2.87 %, 2.66 to 2.90%, 2.70 to 2.94%, 2.75 to 2.99% and 2.81 to 3.03% for samples dried at 55, 65, 75, 85 and 95˚C for between 60 to 140 minutes respectively. The protein content of flours dried between 55 to 95˚C ranged from 7.05 to 7.17% (60 minutes), 7.02 to 7.16% (80 minutes), 6.97 to 7.11% (100 minutes), 6.91 to 7.06% (120 minutes) and 6.85 to 7.00% (140 minutes) respectively. The fat content of the flours was quite low with the control recording 1.54% while those of the dried flours ranged from 1.36 to 1.51% (60 minutes), 1.32 to 1.49% (80 minutes), 1.27 to 1.47% (100 minutes), 1.23 to 1.44% (120 minutes) and 1.18 to 1.40% (140 minutes) respectively. The crude fibre content of the control was obtained as 1.28% and it was significantly (p<0.05) lower than those of the dried flours which ranged from 1.29 to 1.36 (60 minutes), 1.30 to 1.37% (80 minutes), 1.32 to 1.40% (100 minutes), 1.35 to 1.44% (120 minutes) and 1.37 to 1.47% (140 minutes). The carbohydrate content was observed to increase in the dry flour, ranging from 79.08 to 81.16%, 80.00 to 82.27%, 80.65 to 82.88%, 81.22 to 83.41% and 81.66 to 83.92% in flours dried at 55, 65, 75, 85 and 95˚C (for 60 to 140 minutes). WAC ranged between 2.70 to 3.38 ml/g, 2.73 to 3.42ml/g, 2.78 to 3.47ml/g, 2.88 to 3.60ml/g and 2.96 to 3.73ml/g in flours dried at 55, 65, 75, 85 and 95˚C at intervals of 60 to 140 minutes respectively. OAC ranged between 2.35 to 2.56 ml/g, 2.38 to 2.63ml/g, 2.44 to 2.71ml/g, 2.50 to 2.76ml/g and 2.56 to 2.84 ml/g for flours dried at 55, 65, 75, 85 and 95˚C at intervals of 60 to 140 minutes respectively. Gelatinization temperature increased from 72.10 to 73.70°C, 72.20 to 73.90°C, 72.40 to 74.20°C, 72.60 to 74.60°C and 72.90 to 75.10°C for flours dried at 55, 65, 75, 85 and 95˚C for intervals of 60 to 140 minutes, respectively, while pH values ranged from 6.30 to 6.50, 6.00 to 6.40, 5.60 to 6.20, 5.30 to 6.00 and 4.90 to 5.80 in flours dried at 55, 65, 75, 85 and 95˚C for intervals of 60 to 140 minutes, respectively. Generally, the dried D. bulbifera flours were found to be of good quality nutrient and could serve as good ingredients in infant food formulation.
TABLE OF CONTENT
Title
Page i
Declaration
ii
Dedication iii
Certification iv
Acknowledgement v
CHAPTER 1: INTRODUCTION 1
1.1 Background of the Study 1
1.2 Statement
of Problem 4
1.3 Objectives
of Study: 4
1.4 Justification 5
CHAPTER 2: LITERATURE REVIEW 6
2.1 Roots and Tubers 6
2.2 Yam
and Its Origin 7
2.3 Botanical and Agronomic Characteristics of Yams 7
2.4 Morphology
of Yam 8
2.5 Yam
Structure 9
2.6 Yam
Storage 9
2.7 Yam
Varieties 10
2.7.1 White
Yam (Dioscorea rotundata) 10
2.7.2 Yellow
Yam (Dioscorea cayensis) 11
2.7.3 Water
Yam (Dioscorea alata L.) 11
2.7.4 Bitter
Yam (Dioscorea dumentorum) 11
2.7.5 Chinese
Yam (Dioscorea opposita) 12
2.7.6 Air
Potato (Dioscorea bulbifera)- 12
2.7.7 Cush-Cush
Yam (Dioscorea trifida) 13
2.8 Aerial
Yam (Dioscorea bulbifera) 13
2.9 Botany of Aerial Yam (Dioscorea bulbifera) 14
2.10 Morphological Features 14
2.11 Nutritional
and Anti-Nutritional Aspects of Aerial
Yam (Dioscorea bulbifera) 15
2.12 Food Uses of Aerial Yam (Dioscorea bulbifera) 16
2.13 Medicinal Properties of Aerial Yam (Dioscorea bulbifera) 16
2.14 Phytoconstituents of Aerial Yam (Dioscorea bulbifera) 17
2.15 Pharmacological and Toxicological Studies 19
2.16 Drying 20
2.17 Drying
Behaviour 22
2.18 Drying Characteristics 24
2.19 Flour 28
CHAPTER
3: MATERIALS AND METHODS 29
3.1 Source
of Raw Materials 29
3.2 Production of Aerial Yam (D. Bulbifera)Flour 29
3.3 Determination of Drying Characteristics 29
3.3.1 Determination of
Moisture Content 29
3.3.2 Drying
Curves 31
3.3.3
Determination of Drying Rate 31
3.3.4 Mathematical
modelling 31
3.3.5 Equilibrium Moisture Content 32
3.3.6 Drying Models 33
3.4 Determination of Proximate Composition 34
3.4.1 Determination
of Ash Content 34
3.4.2 Determination
of Crude Fibre Content 34
3.4.3 Determination
of Fat Content 35
3.4.4 Determination
of Protein Content 35
3.4.5 Determination of Carbohydrate Content 36
3.5 Determination of Functional Properties: 36
3.5.1 Determination
of Gelatinization Temperature 36
3.5.2 Determination
of Bulk Density 36
3.5.3 Determination
of Water Absorption Capacity 37
3.5.4 Determination of Oil Absorption Capacity 37
3.5.5 Determination of pH 38
3.6 Experiment
Design of The Study 38
CHAPTER 4: RESULTS AND DISCUSSION 40
4.1 Proximate
Composition of Aerial Yam (Dioscorea bulbifera)
Flour
Dried atDifferent Temperatures 40
4.2 Functional Properties of Aerial
Yam (Dioscorea bulbifera)
Flour
Dried at Different Temperatures 45
4.3 Drying
Characteristics of Aerial Yam (Dioscorea
bulbifera)Flour 49
4.4 Mathematical Modelling Of Drying Kinetics of
Aerial Yam
(D. Bulbifera) Flour 52
CHAPTER 5: CONCLUSION AND RECOMMENDATION 54
5.1 Conclusion 54
5.2 Recommendation 55
REFERENCES 56
LIST OF TABLES
Table 3.1: Drying Models Used in D. bulbifera studies 34
Table 3.2: Layout of Experimental Design for Drying
Characteristics of Aerial Yam
Flour 40
Table
4.1: Proximate
composition (%) of D. bulbifera Flour
Dried at Different
Temperatures 42
Table
4.2: Functional
properties of D. bulbifera flour
dried at different temperatures 47
Table
4.3: Statistical
results obtained from the selected thin layer drying models
of Dioscorea
bulbifera flour 54
LIST OF FIGURES
Figure 2.1: A
Typical Drying Curve 25
Figure 3.1: Flow Chart Showing Production of D. bulbifera Flour 31
Figure 4.3: Effect of Drying Temperature
on the Moisture Content of D. bulbifera
Flour 50
Figure
4.4: Effect
of Drying Temperature on the Moisture Ratio of D. bulbifera Flour 51
Figure
4.5: Drying rate
curve of D. bulbifera Flour at
Different Temperature 52
CHAPTER
1
INTRODUCTION
1.1 BACKGROUND OF THE
STUDY
Dioscorea bulbifera, also
known as the air potato, is a variety of true yam in the yam family, Dioscoreaceae. It is a strongly climbing
vine, reaching 6 metres or more, with smooth stems ranging from 1 to 8 mm in
diameter, known as adu in Bende Local
Government Area of Abia State, where it is largely cultivated and consumed. It
is native to Africa, Southern Asia and Northern Australia (Wikipedia, 2016).
It is a
vigorously twining, long-stemmed herbaceous vine which may arise from an
underground tuber, although often tubers are inconspicuous or absent. The stems
are round to slightly angle in cross section and they twine counter-clockwise.
Conspicuous aerial tubers (called bulbils) are pale, round in shape, up to 13
cm wide and are formed in leaf axils. These bulbils give D. bulbifera
the common name "air potato" (Wikipedia, 2016).
The air
potato is becoming one of the most widely-consumed yam species. It can grow up
to 150 feet tall. According to Species
Inventory Homepage (2007), Dioscorea bulbifera is a perennial vine
with broad leaves that forms bulbils in the leaf axils of the twining stems.
These tubers are like small, oblong potatoes. Some varieties are edible and cultivated
as a food crop, especially in West Africa.
D. bulbifera has African
varieties and also Asian varieties. The tubers of edible varieties often have a
bitter taste, which can be removed by boiling. They can then be prepared in the
same way as other yams, potatoes, and sweet potatoes.
Immature
bulbils may be harvested 3-4 months after planting, and picking may continue
for the life of the plant, up to 24 months.
Immature bulbils are handpicked. Mature bulbils
fall to the ground. Bulbils are formed
at leave’s armpit and harvested after senescence and death of the whole plant.
At that period of vegetable cycle of the plant, the bulbils fall down. For
farmers, the fall of bulbils is the only one indicator of their maturity.
Unfortunately, this fall is the cause of a major postharvest loss due to injuries
on the bulbils by wild animals, insects and other micro organisms (Libra et al., 2011). Both
bulbils and tubers are resistant to fungal infections and harvest wounds heal
quickly; storage under dry, cool conditions, away from sunlight, appears to
give moderate storage life.
The bulbils are normally
cooked and eaten in a manner similar to other starchy root crops, though many
African forms require detoxification by soaking in water or prolonged boiling
before they are safe to consume. A few are very succulent and may be eaten raw.
Some yellow fleshed varieties darken during cooking. However these yams have
popularity because of the convenient size of the bulbils for kitchen use. The
bulbils and tubers are also used for production of flour for use in making
other food forms.
Drying
is one of the most widely used primary methods of food preservation. The
objective of drying
is the removal of water to the level at which microbial spoilage and
deterioration reactions are greatly minimized (Akpinar and Bicer, 2004). It
also provides longer shelf-life, smaller space for storage and lighter weight
for transportation (Ertekin and Yaldiz, 2004). Sun drying is the most common
method used to preserve agricultural products in tropical and subtropical
countries. However, being unprotected from rain, wind-borne dirt and dust,
infestation by insects, rodents and other animal, products may be seriously
degraded to the extent that sometimes become inedible and the resulting loss of
food quality in the dried products may have adverse economic effects on
domestic and international markets. Therefore, the drying process of
agricultural products should be undertaken in closed equipment (solar or
industrial dryer) to improve the quality of the final product. The drying
process takes place in two stages. The first stage happens at the surface of
the drying material at a constant drying rate and is similar to the
vaporization of water into the ambient. The second stage drying process takes
place with decreasing drying rate (Midilli and Kucuk, 2003). When the drying
process is controlled by the internal mass transfer, mainly in the falling rate
period; modelling of drying is carried out through diffusion equations based on
Fick’s second law.
Drying
is a complex thermal process in which unsteady heat and moisture transfer occur
simultaneously (Sahin and Dincer, 2005). From engineering point of view, it is
important to develop a better understanding of the controlling parameters of
this complex process. Mathematical models of drying processes are used for
designing new or improving existing drying systems or even for the control of
the drying process. Many mathematical models have been proposed to describe the
drying process, of them thin-layer drying models have been widely in use.
Several
thin-layer drying models are available in the literature for explaining drying
characteristics of agricultural products. These models can be categorized as
theoretical, semi-empirical and empirical. Moreover, the drying kinetics of
food is a complex phenomenon and requires simple representations to predict the
drying behaviour, and for optimizing the drying parameters. Many investigators
have carried out mathematical modelling and experimental studies on the
thin-layer drying of various vegetables and fruits. For example, potato slices
(Aghbashlo et al., 2009), onion slices (Arslan and Özean, 2010), sweet
cherry (Doymaz and Ismail, 2011) and banana (da Silva et al., 2013).
However, there is limited information and research on drying kinetics of Dioscorea bulbifera (aerial yam) flour
in the literature.
1.2 STATEMENT
OF PROBLEM
Dioscorea bulbifera (aerial yam) has been established to have a good
nutritional potential. It is an under utilised crop and thus its food uses are
limited. (Sanful and Engmann, 2016) To date, one of the major sources of food in
Nigeria is cassava. The drying of D.
bulbifera flour, at different air conditions using different drying methods
need to be carried out in order to investigate its drying characteristics,
proximate and functional properties. This study will help to broaden its
utilisation base and promote its uses.
1.3 OBJECTIVES OF STUDY:
The general objective of the study was to
explore the drying characteristics of D.bulbifera
flour using oven drying.
Specific objectives of the study
The specific
objectives include to:
i.
produce flour from Dioscorea bulbifera.
ii.
evaluate the proximate and functional
properties of the flour samples.
iii.
evaluate the drying characteristics of the
process using oven drying.
1.4 JUSTIFICATION
Tropical
food crops are abundant at a particular period, when they are in season, and
are scarce during the off season. D.
bulbifera is an under utilised aerial crop, thus creating the need to make
its use more relevant. Thus, there is need to carry out studies on drying characteristics
of D. bulbifera flour at different conditions of drying, in order to
investigate its drying behaviour as well as enhancing the shelf life of the
flour.
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