ABSTRACT
Aerial yam (Dioscorea bulbifera) and cocoyam (Xanthosoma sagittifolium) were evaluated for the proximate, functional, anti-nutrient properties and volatile constituents as affected by processing treatments. The proximate, functional and anti-nutritional properties of the processed flour showed significant (p<0.05) variations. The proximate results ranged as follows: protein (5.54-7.92%), fat (2.29-3.53%), fibre (1.53-2.41%), ash (1.93-3.72%), moisture (6.52-10.17%) and carbohydrate (75.34-80.22%) respectively. There were significant increases in the fat and ash contents of the roasted flour (1.40 and 2.40%). The functional property values ranged as follows: bulk density (0.49-0.74 g/mL), water absorption capacity (1.79-2.13 ml/g), oil absorption capacity (1.32-1.74 g/ml), foam capacity (10.23-15.35 ml/ml) and gelatinization temperature (60.52-75.630C) respectively. The result of the anti-nutritional factors (oxalate, alkaloid, tannin, and saponin), reveals that the boiled flour samples had lower values (aerial yam; 0.09-1.95%, cocoyam; 0.02-1.46%) while the unprocessed flour samples had the highest values (aerial yam; 0.49-2.93%, cocoyam; 0.33-2.30%). Volatile constituents of Dioscorea bulbifera and Xanthosoma sagitifolium play an important role in the flavour quality characteristics of these roots and tubers. In this study, volatile aroma components of Dioscorea bulbifera and Xanthosoma sagitifolium were analyzed using gas chromatography-mass spectrometry (GC-MS). A total of 150 volatiles were identified in raw, boiled and roasted Dioscorea bulbifera and Xanthosoma sagitifolium. The compounds identified were amines, acid and esters, hydrocarbons, alkanes, carboxylic acids, amides, aldehydes, ketones, alcohol compounds and other additional compounds. The predominant volatile compounds in the two cultivars (unprocessed, roasted and boiled) were the alkanes followed by hydrocarbons, carboxylic acids, acid and esters, ketones, alcohol, aldehyde, amine, amide and other additional volatiles. Methylene chloride, Acetic acid, dichloro, Methane-d, trichloro, Octane. 2-methyl, 1, 10-diaminodecane and Propanoic acid, 2-hydroxy-2-methyl- were detected in all the samples studied. These volatile components had different retention times with different percentage peak area. Propanoic acid, 2-hydroxy-2-methyl- had 3.555mins, 3.557mins, 3.563mins, 3.566mins and 3.566mins retention time, at percentage peak area of 0.22, 0.68, 0.32%, 0.26% and 0.30% respectively for aerial yam and cocoyam (Ede uhie) samples. The major volatile components obtained for the unprocessed Dioscorea bulbifera and unprocessed Xanthosoma sagittifolium are the Methylene chloride and Acetic acid, dichloro, which increased consistently at different retention times.
TABLE
OF CONTENTS
Title
Page i
Declaration
ii
Certification
iii
Dedication
iv
Acknowledgment v
Table
of Contents vi
List
of Tables ix
Abstract
x
CHAPTER 1:
INTRODUCTION 1
1.1 Background of Study 1
1.2
Scope of Study 2
1.3
Problem Statement 2
1.4
Justification 4
1.5
Objective of Study 4
CHAPTER
2: LITERATURE REVIEW 5
2.1
Background of Study 5
2.2. Aerial Yam 7
2.2.1 Uses of Aerial Yam 9
2.2.2 Aerial Yam and its Importance 10
2.3
Cocoyam 11
2.4
Post-harvest Operations, Processing and Uses of Cocoyam 11
2.4.1
Storage of Cocoyam 13
2.5.0 Flavor 14
2.5.1 Gas Chromatography- Mass Spectrometry (Gc-Ms) 14
CHAPTER 3: MATERIALS AND
METHODS 16
3.1 Source of Material 16
3.2 Sample Preparation 16
3.3 Determination of Proximate Composition 18
3.3.1 Determination of Moisture Content 18
3.3.2 Determination of Crude Protein 18
3.3.3 Determination of Crude Fiber 20
3.3.4 Determination of Crude Fat 20
3.3.5 Determination of Total Ash Content 21
3.3.6 Determination of Total Carbohydrate 22
3.3.7 Determination of Energy Value 22
3.4 Determination of Functional Properties 22
3.4.1 Gelation
Temperature 22
3.4.2 Foam
capacity (FC) 22
3.4.3 Bulk density 23
3.4.4 Oil absorption capacity 23
3.4.5 Water
absorption capacity 23
3.5 Determination of Anti-Nutrients 24
3.5.1 Determination of Saponin 24
3.5.2
Determination of Tannins 24
3.5.3
Determination of Alkaloid 25
3.5.4
Determination of Oxalate 25
3.6 Determination of the Volatile Components 27
3.6.1 Sample Preparation 27
3.6.2 Analysis 27
3.6.3 Interpretation 27
3.7 Statistical Analysis 28
CHAPTER 4: RESULTS
AND DISCUSSION 29
4.1 Proximate Composition of the Different Processed
Cocoyam and Aerial
Yam Flour
Samples 29
4.2 Functional Properties of the Different Processed
Cocoyam (Ede Uhie) And
Aerial Yam
Flour Samples 32
4.3 Anti-Nutrient Composition of the Different
Processed Cocoyam (Ede Uhie)
and Aerial
Yam Samples 36
4.4 Number of differently grouped volatile compounds identified
in unprocessed (control), boiled and dry-roasted Aerial yam (%) and Ede Uhie (Xanthosoma sagittifolium) 38
4.5
Identified volatiles in Unprocessed, Boiled and Roasted Aerial yam (%) 44
4.6
Identified volatiles in Unprocessed, Boiled and Roasted
Xanthosoma sagittifolium (%) 50
CHAPTER
5: CONCLUSION AND RECOMMENDATIONS 54
5.1 Conclusion 54
5.2
Recommendations 55
References 56
Appendices 62
LIST
OF TABLES
Table 4.1: Proximate
Composition of Cocoyam and Aerial yam flour samples (%) 31
Table 4.2. Functional
properties of Xanthosoma sagittifolium
and Dioscorea
bulbifera flours.
35
Table 4.3. Quantitative
Analysis of the Anti-nutrient constituents of Xanthosoma
sagittifolium
and Dioscorea bulbifera
37
Table 4.4:
Percent composition of different volatile compounds identified in
unprocessed (control),
boiled and dry-roasted Aerial yam (%)
40
Table 4.5:
Percent composition of different volatile compounds identified in
unprocessed (control), boiled
and dry-roasted Ede Uhie (Xanthosoma
sagittifolium)(%)
43
Table 4.6:
Identified volatiles in Unprocessed, Boiled and Roasted Aerial yam (%) 46
Table 4.7:
Identified volatiles in Unprocessed, Boiled and Roasted Xanthosoma
sagittifolium (%)
50
LIST
OF PLATES
Plate 1; Aerial Yam (Dioscorea bulbifera) 29
Plate 2; Cocoyam (Xanthosoma sagittifolium) 29
Plate
3; Xanthosoma sagittifolium 30
Plate 4; Dioscorea bulbifera 30
CHAPTER 1
1.0 INTRODUCTION
1.1
BACKGROUND OF STUDY
Roots and tuber crops such as
yams, cassava, cocoyam and sweet potatoes rank next in importance to the cereal
grains in providing the major part of the daily caloric needs of people in the
tropics. Yams make a major contribution to the nutrition of West Africans as a
source of carbohydrate before and after the introduction of cassava and sweet
potatoes. However, aerial yam (Dioscorea bulbifera L.) and Chinese yam
(Dioscorea esculenta) are considered less important and are grown in little
quantities. Cocoyam is a perennial crop grown in Nigeria mainly for its edible
roots. It is the third most important root and tuber crop grown and eaten in
Nigeria, behind cassava and yam. It belongs to the monocotyledonous family
Araceae (the ariods) which consists of several plants which are cultivated and
used for food in various parts of the tropics (Amadi, 2015). It is apparent
that cocoyam is very nutritious when compared to cassava and yam. Those on
dietary prescriptions needing low starchy foods prefer cocoyam to cassava.
Cocoyam is used as a source of food for man and livestock. Cocoyam may be made
into fufu, roasted, achicha, and boiling cocoyam, among other things. It may
also be dried after being cut into chips. The dried chips are then rehydrated and
combined with veggies, palm oil, and oil bean to make a porridge. Alcohol,
medications, flour, and starch may all be made from cocoyam (Igbozulike, 2015).
Yam is a valuable commodity in the Nigerian food chain, and Nigeria is the
world's biggest producer of cocoyam, accounting for more than half of total
global production. According to Princewill-Ogbonna and Ibeji, (2015), some of
these food crops have been under exploited for their food values examples
Dioscorea bulbifera and Dioscorea dumentoum. Aerial yam and yams in general are
eaten boiled, fried or even roasted, though aerial yam (the wild form) is
generally feared to cause madness and in effect is inedible. Works on yams and
other tropical root tuber crops have been generated in the last 10-15 years
through the formation and subsequent activities of the International Society
for Tropical Root Crops (Princewill-Ogbonna and Ibeji, 2015). In Nigeria,
government awareness of the need to increase food production for feeding the
teeming population has led to support for studies on better methods of tuber
and root crops production. Currently, a large number of researches are being
done on root and tuber crops in research institutes and in Universities.
Dioscorea bulbifera has been sidelined over the years and is going extinct as a
result of its poisonous characteristic (Princewill-Ogbonna and Ibeji, 2015).
Improvement on the processing method and utilization of this crop (Dioscorea
bulbifera) will reduce food insecurity in Nigeria. While there are various
methods by which this crop can be made safe for consumption, a properly
scientifically researched method is yet to be known and publicized. Food
processing is an important aspect of agricultural production and marketing; it
adds value, removes anti-nutritional components increases the nutritional value
of foods thereby converting them into a form that is more acceptable
(Princewill-Ogbonna and Ibeji, 2015).
1.2
SCOPE OF STUDY
This work is limited to aerial yam, a
specie of Dioscorea bulbifera, and cocoyam (Xanthosoma sagittifolium cv “ede
uhie”), (an underutilized specie) consumed mainly in the eastern region of
Nigeria.
1.3
PROBLEM STATEMENT
Cocoyam suffers from extensive
post-harvest losses since it is stored mostly as fresh corms. Unfortunately,
cocoyam does not have a longer storage time, thus most of them are consumed
within a couple of months after harvest and its consumption is by boiling,
roasting, frying, chips and conversion into flours (semi-finished product) for
further use (Adegunwa, et al., 2011). Also, aerial yam (the wild
form) is feared to cause madness and in effect is inedible (Princewill-Ogbonna
and Ibeji, 2015). Aerial yam production is marred by many constraints, the key
among them being under-utilization, scarcity, unimproved varieties of the yam,
and high level of post-harvest losses. It belongs to the class of some
perishable foods owing to its relatively high moisture content and its
vulnerability to post-harvest deterioration. These obstacles bedeviling aerial
yam undermine its production, farmers’ ability to generate sustainable incomes,
and disproportionately impact on rural farmers. However, these crops can be
consumed with sauce after boiling, roasting or frying. It can also be mashed or
pounded into fufu after boiling. It is hypothesized that the processing methods
could affect the nutritional contents of these crops (Adegunwa, et al., 2011).
Thus, processing cocoyam (Xanthosoma saggitifolium cv “ede uhie”) and aerial
yam (Dioscorea bulbifera) for consumption or into less perishable forms is
essential. Generally, a lot of research works have been done on cocoyam and
aerial yam, but there is little or no information on the volatile profile of
flours obtained from different processing methods on the samples from aerial
yam (Dioscorea bulbifera) and cocoyam (Xanthosoma saggitifolium cv “ede
uhie”). Volatile compounds are responsible for the flavour and
aroma characteristics of foods. During roasting and other heating processes,
additional volatiles are formed from reactions between food components. Hence,
a study on the nutrient composition and classification of volatile compounds in
processed aerial yam and cocoyam extracts is essential.
1.4
JUSTIFICATION
With the growing emphasis on food
insecurity and malnutrition in Africa, diversification and sustainable
intensification of agricultural products would play an important role in
addressing these issues. Also, it is important for exploration of underutilized
starchy roots and tubers such as aerial yam and cocoyam, as information deduced
could be an alternative to help cob the problems of food insecurity and
malnutrition, underutilization of aerial yam and cocoyam (ede uhie), scarcity,
unimproved varieties of these roots and tubers and high level of post-harvest
losses. (Liu et al., 2006). The constancy of the volatile compounds
in starchy roots and tubers during processing are of increasing interest in the
food industry. Identification and quantification of the volatile compounds of
these underutilized tubers will extend our knowledge base and their
techno-industrial applications.
1.5
OBJECTIVE OF STUDY
The main objective of this research work
is to regulate the nutrient composition and classification of unstable
compounds in processed aerial yam (Dioscorea bulbifera) and cocoyam (Xanthosoma
saggitifolium cv “ede uhie”) cultivars.
The specific objectives are:
ü To
produce flour from raw, roasted and boiled aerial yam and cocoyam cultivars
ü To
determine the proximate structure of the processed flour samples.
ü To
determine the functional properties of the processed flour samples.
ü To
determine the anti-nutrient properties of the flour samples.
ü To
identify the volatile components of the flour samples.
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