ABSTRACT
An experimental investigation, using three varieties of Colocasia esculenta was conducted. Sun-dried cocoyam corms (achicha) and leaves (mpoto) are invaluable sources of nutrients, which are consumed mainly in the South Eastern Nigeria. This study therefore, aimed at evaluating the effect of processing and storage of achicha and mpoto for a period of three months on chemical, functional, physicochemical properties, microbiological and sensory evaluation. The sun-dried cocoyam corms (achicha) and leaves (mpoto) were produced from matured cocoyam. The proximate composition of achicha and mpoto samples showed a increase of 3.93 to 5.77% and 14.7 to 16.83% in crude protein respectively as storage period progressed. The functional properties of achicha samples did not differ significantly (p>0.05) in the parameters considered. Potassium content was most abundant both in achicha (285.77 to 405.87mg/100g) and mpoto (325.87 to 485.52mg/100g) samples in the mineral composition. Vitamin composition of achicha and mpoto samples showed a increase of (2.47 to 4.14mg/100g) and (8.61 to18.46mg/100g) in vitamin C content respectively as storage period progressed. Alkaloid levels of both achicha and mpoto ranged from 1.19 to 1.63mg/100g and 1.52 to 1.85mg/100g respectively. Sugar and starch contents of achicha samples ranged from 1.94 to 4.15% and 51.64% to 65.06% respectively. Total viable counts (TVC) of achicha and mpoto samples ranged from 1.60 x 104 to 3.40 x 104 and 1.20 x 104 to 2.70 x 104 respectively. Total fungal counts (TFC) of achicha and mpoto ranged from 0.30 x 104 to 1.70 x 104 and 0.1 x 104 to 1.00 x 104 respectively. The microbiological counts of samples increased with increase in the storage time. Achicha meal and mpoto soup did not show any significant (p>0.05) difference in the sensory evaluation.
TABLE OF CONTENTS
Title
page i
Declaration ii
Certification
page
iii
Dedication iv
Acknowledgement v
Table
of contents vi
List of
Tables ix
List of
Figures
x
List of
Plates xi
Abstract xii
CHAPTER 1: INTRODUCTION 1
1.1 Background Information 1
1.2 Statement of the Problem 4
1.3 Objectives of the study
4
1.4 Justification
of the study
5
CHAPTER 2:
LITERATURE REVIEW
2.1 Origin
of Colocasia esculenta 6
2.2 Spoilage of Cocoyam 6
2.3 Storage of Cocoyam 7
2.4 Factors Affecting Storability of Roots
and Tubers 8
2.5 Physiological Factors. 9
2.5.1 Respiration 9
2.5.2 Dormancy and Sprouting 9
2.5.3 Skin
permeability 10
2.5.4 Temperature effect on dormancy 10
2.5.5 Damage by Extremes of Temperature 11
2.6 Nutrition and other Importance of Taro 11
2.6.1 Health benefits 12
2.6.2 Vitamins 15
2.6.3 Vitamin C 17
2.7 Phytochemicals 18
2.7.1 Phenolic Acids 21
2.8 Anti-nutritional factors limiting utilization
of taro 21
2.8.1 Mucilage 22
2.8.2 Oxalic acid and oxalates 22
2.8.3
Protease (trypsin and chymortrypsin) inhibitors 23
2.8.4 Lectins 23
2.8.5 Alpha-
amylase inhibitors 24
2.9 Processing of taro into different
products 24
2.9.1 Colocasia
esculenta flour 25
2.9.2 Uses 26
CHAPTER
3: MATERIALS AND METHODS 28
3.1 Sample
collection 28
3.2 Preparation of samples 28
3.2.1 Preparation of achicha meal and mpoto
soup 33
3.3 Proximate
Analysis 41
3.3.1 Determination
of moisture content 41
3.3.2
Determination of total ash content 42
3.3.3 Determination of crude protein 42
3.3.4 Determination
of Crude Fibre 43
3.3.5 Determination
of fat content 44
3.3.6 Determination of Carbohydrate 45
3.3.7 Determination of Dry matter 45
3.4 Functional
Properties
46
3.4.1 Determination
of Bulk Density
46
3.4.2 Determination of Swelling Index
46
3.4.3 Determination of water/oil absorption
capacity
47
3.4.4 Determination of Wettability 48
3.4.5 Determination of Gelation capacity 49
3.4.7 Determination of foam stability 49
3.4.8 Determination
of Foam Capacity 49
3.4.9 Determination
of Viscosity 50
3.4.10 Determination of pH 50
3.5 Mineral Analysis 50
3.5.1 Extraction by wet-acid Digestion for
multiple nutrients 51
3.5.2 Determination of Heavy metals by the Atomic
Absorption
Spectrophotometer (AAS) 51
3.5.3 Determination of phosphorus by the Molybdate
yellow
Method using Spectrophotometer 52
3.5.4 Determination of Potassium and Sodium using
the
Flame photometer 52
3.5.5 Determination of Calcium and Magnesium by
the Versenate
EDTA Complexometric 52
3.6 Phytochemical Analysis 53
3.6.1 Determination of Alkaloid Content 53
3.6.2 Determination of Tannin content 53
3.6.3 Determination of saponins content 54
3.6.4 Determination
of flavonoid content 55
3.6.5
Determination of polyphenol 56
3.6.6 Determination of oxalate 57
3.6.7 Determination of Phytate 58
3.7 Vitamin Analysis 59
3.7.1 Determination of Vitamin A 59
3.7.2 Determination of Vitamin B1
(Thiamin) 60
3.7.3 Determination of Vitamin B2
(Riboflavin) 60
3.7.4 Determination of Vitamin B3
(Niacin) 61
3.7.5 Determination of Vitamin C (Ascorbic acid) 62
3.8
Carbohydrate Analysis 63
3.8.1 Determination of Amylose content 63
3.8.2 Determination of Starch content 64
3.8.3 Determination of Sugar content 64
3.9 Microbiological Analysis 65
3.9.1
Isolation of microorganism from
the samples, characterization
and culturing of the samples 65
3.9.2 Purification of
isolate 65
3.9.3 Characterization of
isolates (bacteria) 66
3.9.4 Characterization of
isolates (fungi) 66
3.9.5 Determination of the microbial load 66
3.9.6 Counting of colonies 66
3.9.7 Calculation of microbial load (cfu/g) 67
3.10 Sensory Evaluation 67
3.11
Statistical Analysis 67
CHAPTER 4: RESULTS AND DISCUSSION
4.1: Proximate
and dry matter Composition of Achicha stored
from
Zero to three
Months (%) 68
4.1.1 Moisture
content 68
4.1.2 Ash
content 66
4.1. 3 Crude Protein 66
4.1.4 Crude
Fat
67
4.1.5 Crude
Fibre Content
67
4.1.6 Carbohydrate Content
68
4.1.7 Dry matter
68
4.2: Functional
Properties of Achicha Stored for Three
Months 73
4.2.1 Bulk
Density (g/ml)
73
4.2.2 Swelling
index (ml)
74
4.2.3 Water absorption capacity (WAC) (ml/g) 75
4.2.4 Oil
absorption capacity (ml/g)
77
4.2.5 Wettability
(sec)
78
4.2.6 Gelation
capacity (g/5ml)
78
4.2.7 Gelation
Temperature (oC)
79
4.2.8 Foam
Stability (%) 79
4.2.9 Foam Capacity (%)
80
4.2.10 Viscosity (mpa) 81
4.2.11 pH 82
4.3:
Mineral Composition of Achicha stored forThree Months
(mg/100g) 84
4.3.1 Calcium
(Ca) content 84
4.3.2 Sodium
(Na) content 85
4.3.3 Magnesium (Mg) content 85
4.3.4 Potassium
(K) content 85
4.3.5 Phosphorous
(P) content 86
4.3.6 Iron
(Fe) content 87
4.3.6 Zinc
(Zn) content 87
4.3.7 Manganese
(Mn) content 88
4.3.8 Iodine
(I) Content 88
4.4:
Vitamin Composition of Achicha from Zero to Three Months
(mg/100g) 90
4.4.1 Total
carotene (ug/100g) content 90
4.4.2 B1
(Thiamin) mg/100g content 90
4.4.5 B2
(Riboflavin)Mg/100g content 90
4.4.4 B3
(Niacin) mg/100g content 91
4.4.5 Vitamin
C (Ascorbic Acid) mg/100g content 91
4.4.6 Vitamin
E (Tocopherol) mg/100g content 91
4.5:
Phytochemical Composition of Achicha stored for Three Months
mg/100g) 93
4.5.1 Alkaloid
content 93
4.5.2 Oxalate
content 93
4..5.3 Phytate content 93
4.5.4 Saponin
content 94
4.5.5 Flavonoid
Content 94
4.5.6 Polyphenol
content 94
4.5.7 Tannin
content 94
4.6: Carbohydrate Analysis of Achicha stored for Three Months (%) 97
4.6.1
Amylose content 97
4.6.2 Amylopectin
content 97
4.6.3 Starch
content 97
4.6.4 Sugar
content 98
4.7: Total Viable Count (TVC) of Achicha stored for Three Months
(cfu/g) 100
4.8: Total
Fungal Count (TFC) of Achicha stored
for Three
Months (cfu/g) 102
4.9: Sensory
Evaluation of Achicha from Three
Varieties
of Colocasia esculenta 104
4.9.1 Aroma 104
4.9.2 Appearance
104
4.9.3 Texture 105
4.9.4 Taste 105
4.9.5 Overall
acceptability 105
4.10: Proximate and Dry Matter Compositions of Mpoto stored for
Three Months (%) 107
4.10.1 Moisture content 107
4.10.2 Dry Matter Content 107
4.10.3 Ash Content 107
4.10.4 Crude Protein content 107
4.10.5 Crude Fat Content 108
4.10.6 Crude Fibre content 108
4.10.7 Carbohydrate Content 109
4.11:
Mineral Composition of Mpoto stored for Three Months
(mg/100g) 111
4.11.1 Calcium (Ca) content 111
4.11.2 Sodium (Na) Content 111
4.11.2 Magnesium (Mg) Content 112
4.113 Potassium
(K) Content 112
4.11.4 Phosphorus (P) Content 112
4.11.5 Iron (Fe) Content 112
4.11.6 Zinc (Zn) Content 113
4.11.7 Manganese (Mn) Content 113
4.11.7 Iodine (I) Content 113
4.12:
Vitamin Composition of Mpoto stored for Months (mg/100g) 115
4.12.1 Total Carotene (ug/100g) Content 115
4.12.2 B1 (Thiamin) mg/100g Content 115
4.12.3 B2 (Riboflavin) mg/100g Content 115
4.12.4 B3 (Niacin) mg/100g content 116
4.12.5 Vitamin C (Ascorbic Acid) mg/100g Content 116
4.12.6 Vitamin E (Tocopherol) mg/100g content 117
4.13
Phytochemical Composition of Mpoto
stored for Three Months
(mg/100g) 119
4/13.1 Alkaloid Content 119
4.13.2 Oxalate Content 119
4.13.3 Phytate Content 119
4.13.4 Saponin Content 119
4.13.5 Flavonoid Content 120
4.13.6 Polyphenol Content 120
4.13.7 Tannin Content 120
4.14 Total Viable Count (TVC) of Mpoto stored for Three Months
(cfu/g)
122
4.15: Total Fungal Count (TVC) of Mpoto stored for Three Months
(cfu/g) 124
4.16: Sensory Evaluation of Mpoto Soup from Three Varieties of
Colocasia esculenta 126
4.16.1 Aroma 126
4.16.2 Appearance 126
4.16.3 Texture 126
4.14.4 Taste 127
4.16.5 Overall acceptability 127
CHAPTER 5:
CONCLUSION AND RECOMMENDATION
5.1 Conclusion 129
5.2 Recommendation 130
REFERENCES 131
APPENDICES 147
Appendix 1 147
Appendix 2 148
Appendix 3
149
Appendix 4
150
LIST
OF TABLES
Table 4.1: Proximate and dry matter Compositions of Achicha stored for
Three Months (%) 72
Table 4.2: Functional Properties of Achicha
stored for Three Months 83
Table 4.3: Mineral Composition of Achicha stored for Three Months (mg/100g) 89
Table 4.4: Vitamin Composition of Achicha stored for Three Months 92
Table 4.5: Phytochemical Composition of Achicha stored for Three Months 96
Table 4.6: Carbohydrate Analysis of Achicha stored for Three Months (%) 99
Table 4.7: Total
Viable Count (TVC) of Achicha stored for Three Months (cfu/g) 101
Table 4.8: Total Fungal Count (TFC) of Achicha stored for Three Months (cfu/g) 105
Table 4.9: Sensory Evaluation of Achicha from Three Varieties of
Colocasia
esculenta 106
Table 4.10: Proximate and Dry Matter
Compositions of Mpoto stored for
Three Months (%) 110
Table 4.11: Mineral Composition of Mpoto stored for Three Months (mg/100g) 114
Table 4.12: Vitamin Composition of Mpoto stored
for Three Months 118
Table 4.13: Phytochemical Composition of Mpoto stored for Three Months 121
Table 4.14: Total Viable Count (TVC) of Mpoto stored for Three Months (cfu/g) 123
Table 4.15: Total Fungal Count (TFC) of Mpoto stored for Three Months (cfu/g) 125
Table 4.16: Sensory Evaluation of Mpoto Soup from Three Varieties of
Colocasia esculenta 128
LIST OF FIGURES
Figure
1: The Flow chart of the production of achicha 30
Figure
2: The Flow chart of the production of mpoto 32
LIST OF PLATES
Plate 1: Colocasia esculenta corms/cormel 29
Plate 2: Colocasia
esculenta leaves 31
Plate 3: Achicha
meal 36
Plate
4: mpoto soup 37
LIST
OF EQUATIONS
Equation 2.5.1:
Respiration 9
Equation
3.3.1: Determination of moisture content 38
Equation 3.3.2:
Determination of total ash
content 39
Equation 3.3.3:
Determination of crude protein 40
Equation 3.3.4:
Determination of Crude Fibre 41
Equation 3.3.5:
Determination of fat content 42
Equation 3.3.6:
Determination of
carbohydrate 42
Equation 3.4.1:
Determination of bulk
density 43
Equation 3.4.2:
Determination of Emulsification
Capacity 43
Equation 3.4.3: Determination
of Swelling Index 44
Equation 3.4.4: Determination
of water/oil absorption capacity 44
Equation 3.4.7: Determination
of foam stability 46
Equation 3.4.8:
Determination of Foam Capacity 46
Equation 3.6.1:
Determination of Alkaloid Content 50
Equation 3.6.2:
Determination of Tannin content 51
Equation 3.6.3:
Determination of saponins content 52
Equation 3.6.4:
Determination of flavonoid
content 52
Equation 3.6.5:
Determination of polyphenol 53
Equation 3.6.6:
Determination of oxalate 54
Equation 3.6.7:
Determination of Phytate 55
Equation 3.7.1:
Determination of Vitamin A 56
Equation 3.7.2:
Determination of Vitamin B1
(Thiamin) 57
Equation
3.7.3: Determination of Vitamin B2 (Riboflavin) 58
Equation
3.7.4: Determination of Vitamin B3 (Niacin) 59
Equation
3.7.5: Determination of Vitamin C
(Ascorbic acid) 59
Equation 3.8.1: Determination
of Amylose content 60
Equation
3.8.2: Determination of Starch content 61
CHAPTER 1
INTRODUCTION
1.1 BACKGROUND INFORMATION
In
the region of West and Central Africa, the term cocoyam is attributed to two
members of the Araceae family,
namely, Colocasia esculentum (L.)
Schott and Xanthosoma sagittifolium (L.)
Schott, in the sub family Colocasioideae
according to Dahlgren et al. (1985). Aguegui
et al. (1992) reported, they are staple
foods for many people in developing countries of Africa, Asia and the Pacific. Cocoyam
(Colocassia and Xanthosoma spp.) is a stem tuber that is widely grown in the
tropical regions of the world (Eze and Okorji, 2003). Three other genera: Alocasia, Amorphophallus and Cyrotosperma
are common in the tropical regions of Pacific (Okaka, 1997).
This
plant ranks as the fourteenth most consumed vegetable worldwide, and is grown
widely in the tropical and sub-tropical countries (FAO, 1986). More so, it is third in importance after
cassava and yam among the root and tuber crops consumed in Nigeria as reported
by Udealor et al. (1996) and Onwueme (1978).
About
60% of the World’s cocoyam production (5.7 million ton) is in Africa and majority
of the remaining 40% in Asia and the Pacific (Mitra et al., 2007). Eze and Okorji (2003) also reported that Nigeria is
the largest producer of cocoyam in the world, accounting for about 40% of the
total world output.
According
to Manner and Taylor (2010) in other parts of the world, species of Colocasia are often referred to as taro,
while cocoyam or tannia is used for
species of Xanthosoma. In the Pacific Island countries where taro is
widely cultivated and consumed, two botanical varieties of Colocasia have been identified as C. esculenta var. esculenta,
many times called dasheen, and C. esculanta Var. esculenta, frequently called eddoe.
Purseglore (1972) stated that dasheen
varieties have very big central (middle) corms with suckers and or stolons,
whereas eddoes have a relatively small central corm and a large number of
smaller cormels. Colocasia is
believed to have originated in the Indo – Malaysian region, from where it
spread into the pacific Islands, the Eastern Mediterranean and finally to
Africa (Kay, 1987).
Cocoyam
without any doubt is an important food crop across many countries in South
Saharan region, specifically in Nigeria, Ghana and Cameroon. Cocoyam is a major
vegetable and source of income to farming household in Ghana. It is referred to
as the third important staple root crop after yam and cassava in Nigeria and provides
a cheaper yam replacement, especially during periods of food scarcity or
insufficient food supply (Onyeka, 2014).
According
to Wang (1983) cocoyam is rich in carbohydrates with nutritional value
comparable to potato. Also cocoyam is superior to cassava and yam in the
possession of higher protein, mineral and vitamin contents as well as easily
digestible starch (Parkinson, 1984, Splittstoesser et al, 1973). Cocoyam also contains higher noticeable quantities of
essential minerals (Ca, Mg and P) than cassava and yam. It is to a great extent
recommended for diabetic patients, the aged, children with allergies and for
persons with intestinal disorders (Plucknett, 1970). The corms and cormels of
cocoyam may be processed by boiling, baking or frying in oil. They may also be
processed into different food products in many parts of West and Central Africa.
All
major parts of cocoyam (corm, cormel and leaves) are edible. The young leaves
are nutritious spinach-like vegetable, which supplies a lot of minerals and
vitamins. This is particularly a major vegetable and source of income to
farming household in Ghana.
The
leaves from Taro (Colocosia esculenta)
are rich in vitamins and minerals. They are suitable sources of thaimine,
riboflavin, iron, phosphorus and zinc and a very good source of vitamin B6,
vitamin C, niacin, and exceptionally in the leaves, also it is highly
perishable that is it has high content of water. Leaves of new cocoyam are also
used in pig-feeding because of its nutritional benefits (Agrid, 2006).
Preliminary investigations have revealed that most vegetables are good source
of antioxidants, but some are definitely better than others. When it comes to
vitamins, minerals, carotenoids and cruciferous phytonutrients, which are all
virtually important to good health, the most potent vegetable are dark green
leafy vegetables, Green leafy vegetables are greatly used for food in many countries
of the world; they are good sources of β-Carotene, ascorbic acid, minerals and
dietary fibre (Moshaand and Gaga, 1999). However, dark vegetables are more
nutritious than those with lighter or yellowish leaves. They are in large
amount shortly after rainy season but become insufficient during the dry season,
these vegetables could be harvested at all stages in the process of growth or
could be consumed fresh, semi- processed or processed forms (Moshaand and Gaga,
1999).
Agrid
(2006) reported cocoyam is a well-known food plant, which has a long history of
cultivation. Its corms are important source of starch. They may also be cut up
and boiled in curries or fried to make crispy chips. The leaf stalks can also
be eaten. The leaves which are seldomly used for food must be cooked. Every
part of the raw cocoyam plant contains a toxic compound calcium oxalate, which
must be destroyed through cooking before eating (Fafunso and Baser, 1987).
Achicha (dried
cocoyam corms/cormels) is a pre-cooked, sun-dried cocoyam corms/cormels and it
lends its name to the vegetarian dish made with it. Achicha does not only have enjoyable taste and satisfying but also low
in calories. Achicha can be cooked in
combination with fiofio (pigeon pea)
or black beans (akidi oji), these are highly nutritional. Green leafy
vegetables can also be added to it, for example, green amaranth, ugu and scent
leaf. Dry fish is also added which is an optional ingredient.
Mpoto
(dried cocoyam leaves) is a vegetable used in preparing soup delicacy. This is
peculiar to the Igbo people of Eastern Nigeria.
1.2 STATEMENT
OF PROBLEM
The
cocoyam (Colocasia esculenta) is
highly perishable root and leaves, crop as high as 40-60% post harvest losses
have been found (Anaele
and Nwawusi, 2008). Nwufo and Atu (1987) stated that microorganisms
take the lead in post harvest rot. The high perishability of the harvested and
stored cocoyam roots and leaves is a major barrier to the wider utilization of
the crop and there is need to diversify the uses to enhance demand and increase
the rate of turn over or sale of the product. Lack of adequate cocoyam
processing technology inhibits production and processing. Over the years due to
the high perishable nature of cocoyam local farmers had adopted sun-drying as a
means of preserving the cocoyam. It becomes necessary to evaluate the effect of
these processes and storage methods on the the overall quality of the cocoyam
products.
1.3 OBJECTIVES
OF THE STUDY
The
main objective of this study is to evaluate the effect of storage period on the
quality of cocoyam based products.
The
specific objectives of this work are:
1.
To produce achicha (dried cocoyam corms/cormels)
and mpoto (dried cocoyam leaves)
2.
To evaluate the proximate/dry
matter compositions of achicha and mpoto for a period of three months storage.
3.
To evaluate the functional
properties of achicha for a period of
three months storage.
4
To determine the mineral
composition of achicha and mpoto for a period of three months
storage.
5
To evaluate the vitamins of achicha and mpoto for a period of three months storage.
6
To determine the phytochemicals composition present in achicha and mpoto for a period of three months storage.
7
To investigate the carbohydrate component of achicha for a period of three months
storage.
8
To determine the microbiological
load of achicha and mpoto for a period of three months
storage.
9
To evaluate the sensory
properties of achicha and mpoto after a period of 3 months.
1.4 JUSTIFICATION
Processing
of cocoyam corms/cormels and leaves into more shelf-stable dry products such as
achicha and mpoto will reduce post harvest losses of cocoyam, provide a market
for small scale farmers, and diversify the uses of cocoyam. Evaluation of the
quality and shelf stability of the achicha
and mpoto would give confidence to
the producers and consumers of these products.
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