ABSTRACT
This study investigated the effect of different cooking methods on glycemic index (GI) of three yam cultivars commonly eaten in Nigeria namely: Dioscorea rotundata, Dioscorea alata and Dioscorea dumentorum. Yam tubers were processed by, frying, pounding and boiling, and then immediately consumed by twenty-seven normal healthy adults comprising of males and females. Capillary blood samples were taken at the fasting state and at different intervals of 15, 30, 45, 60, 90 and 120 minutes from the consumption of each meal. The blood samples were analysed for plasma glucose concentration and incremental areas under plasma glucose curves were calculated. The GI varied between 22.31 –72.78 for the yam cultivars studied. Samples prepared by boiling recorded Dioscorea alata as low GI (22.31) and Dioscorea rotundata as high GI (72.78). While those processed by frying and pounding, recorded a low GI (20.95 – 44.35) and Dioscorea dumentorum having the least GI value (20.95). The study indicates that the glycemic index of the three yam cultivars (Dioscorea rotundata, Dioscorea alata and Dioscorea dumentorum) varies significantly by their methods of preparation and variety differences. Consumption of boiled and pounded Dioscorea alata could minimize postprandial blood glucose spikes and therefore, may prove to be more efficacious in the management of type 2 diabetes mellitus. Proximate composition (moisture, protein, fat, ash, fibre and carbohydrates) were determined for the raw and processed samples prior to glycemic analysis. The functional properties and amylose /amylopectin ratio of the flour sample were determined. The result of this study showed a significant difference (p<0.05) in the functional properties of the yam flour samples, the moisture content significantly differed (p<0.05) in different cooking methods and various varieties. There was no significant difference in the protein content of the different yam varieties. Low protein values observed in this study suggested that yam is not a good source of protein. At different levels of processing there was a significant difference in the fat content when compared to the raw samples with an increase on the fried samples and a decrease on boiled and pounded samples. There was a significance difference (p<0.05) in the crude fiber content of the different yam varieties at its raw state with Dioscorea dumentorum having the highest value (1.30). No significance difference was seen on the ash content of the boiled Dioscorea rotundata and Dioscorea dumentorum. The carbohydrate content differed significantly (p<0.05) amongst the yam varieties and their various processing methods. The variety main effect were significantly different (p<0.05) while the processing method main effect were also significantly different (p<0.05).
TABLE
OF CONTENTS
Title
page i
Declaration ii
Certification
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 Background
of the Study 1
1.2 Statement of Problem 3
1.3 Justification
of Study 4
1.4 Objectives
4
CHAPTER 2:
LITERATURE REVIEW
2.1
Glycemic Index 5
2.2 History of Glycemic Index 7
2.3 Coining of the Concept of Glycemic Index 8
2.4 Classification of Glycemic Index 9
2.5 Measurement and Interpretation of
Glycemic Index 12
2.6 Factors that Affect the Glycemic Index of
a Food 13
2.6.1 Cooking method 13
2.6.2 Processing method 13
2.6.3 Type of starches 14
2.6.4
Fibre 14
2.6.5
Sugar 15
2.6.6
Fat 15
2.6.7
Acidity 15
2.6.8
Physical entrapment 15
2.7
Carbohydrate Metabolism 16
2.8
Role of insulin in Diabetes Mellitus 17
2.8.1
Type 1 diabetes mellitus 18
2.8.2
Type 2 diabetes mellitus 18
2.9
Application
and Clinical use of Glycemic Index Values 20
2.9.1
Glycemic index and obesity 20
2.9.2 Glycemic index and diabetes 21
2.9.3
Glycemic index and heart disease 24
2.9.4
Glycemic index and cancer 25
2.9.5
Enhancing satiety 25
2.10
Yam 26
2.10.1
Background of yam 26
2.11
Botanical
and Agronomic Characteristics of Yams
27
2.12
Origin and Current Distribution of
Major Food Yam Species 28
2.13
Nutritional
Value of Yam 30
2.14
Chemical
Composition of Yam 31
2.15
Distribution
of Yam in Nigeria 32
2.16
Constraints to Yam Production 33
2.17
Prospects of Yam Production 34
2.18
Yam Food Preparation Method in West
Africa 35
2.19 Production Process of Yam Flour 35
2.20
Yam Minisett Technology 37
2.21
Development of Non-Stake Yam Genotypes 38
CHAPTER 3: MATERIALS AND METHODS
3.1
Sources of Raw Material 39
3.2
Sample Preparation 39
3.3
Determination of Glycemic Index 42
3.4
Proximate Composition Analysis 42
3.4.1
Determination of moisture content 42
3.4.2 Determination of crude protein 43
3.4.3 Ash content determination 44
3.4.4 Crude fibre determination 44
3.4.5 Fat content determination 45
3.4.6 Determination of carbohydrate 45
3.5
Physicochemical Analysis 46
3.5.1
Determination of amylose/ amylopectin
content 46
3.6 Functional Properties 46
3.6.1 Bulk
density 46
3.6.2 Water absorption capacity 47
3.6.3
Swelling index 47
3.6.4 Gelatinization temperature 48
3.7 Statistical Analysis 48
CHAPTER 4: RESULTS
AND DISCUSSION
4.1
Bulk Density 50
4.2
Water Absorption Capacity 50
4.3 Swelling Index
Capacity 51
4.4
Gelatinization Temperature 51
4.5
Amylose and Amylopectin 54
4.6
Moisture Content 55
4.7
Protein Content 58
4.8
Fat Content 60
4.9 Crude
Fibre Content 62
4.10 Ash
Content 66
4.11 Carbohydrates 68
4.12
Glycemic Index 69
CHAPTER 5: CONCLUSION
AND RECOMMENDATIONS
REFERENCES
75
Appendices
LIST
OF TABLES
2.0: Glycemic Index classification 11
4.1: Functional properties of Dioscorea rotundata, Dioscorea alata
and Dioscorea dumentorum 49
4.2: Starch composition of Dioscorea rotundata, Dioscorea alata
and Dioscorea dumentorum
Flour 53
4.3: Percentage moisture content of Dioscorea rotundata, Dioscorea
alata and Dioscorea dumentorum
57
4.4: Percentage crude protein content of Dioscorea rotundata, Dioscorea
alata and
Dioscorea dumentorum 59
4.5: Percentage crude fat content of Dioscorea rotundata, Dioscorea
alata
and Dioscorea dumentorum 61
4.6: Percentage Crude Fiber content of Dioscorea rotundata, Dioscorea
alata
and Dioscorea dumentorum 63
4.7: Percentage ash content of Dioscorea rotundata, Dioscorea
alata and Dioscorea dumentorum 65
4.8: Percentage Carbohydrate content of Dioscorea rotundata, Dioscorea
alata and
Dioscorea dumentorum 67
4.9: Glycemic index of Dioscorea rotundata, Dioscorea
alata and Dioscorea dumentorum
70
LIST
OF FIGURES
2.1: Flow chart for yam flour production 36
3.1: Flow chart for production of yam samples 40
LIST
OF PLATES
1-3: Pounded Samples of Dioscorea rotundata, Dioscorea 41
alata and Dioscorea dumentorum
4-6: Fried Samples of Dioscorea rotundata, Dioscorea 41
alata and Dioscorea dumentorum
7-9: Boiled Samples of Dioscorea rotundata, Dioscorea
41
alata and Dioscorea dumentorum
CHAPTER
1
INTRODUCTION
1.1 BACKGROUND OF
THE STUDY
The
glycemic index (GI) is a dietary measuring system that ranks carbohydrate
containing food and relates the rate at which the blood sugar is increased
after two hours of consuming the food to a reference food usually glucose (Wolver,
1993).Consumption of low glycemic index foods is suggested to be effective for
the prevention and control of diabetes (Little, 2003). Until recently, it was
widely held that the blood glucose response to different diets is determined
solely by the quantity of carbohydrate they contain and sugars being swiftly
absorbed produce greater responses than starch during and after digestion
(Wolver, 1993). This consequently led to the traditional diabetes diet plans in
which the amount of food allowed were based upon their carbohydrate content
(American Diabetes Association, 2002; WHO, 1985). This concept was however
challenged by the findings of Jenkins et
al. (1981) that sugars raise blood glucose to the same extent as several
starchy foods and hence developed the glycemic index.
Glycemic
index is expressed as percentages on an absolute scale. According to this
system, carbohydrates containing foods are graded as either having low,
intermediate and high glycemic index depending on the rate at which blood sugar
level rises (Mendosa, 2000). This in
turn is related to the rate of digestion and absorption of sugars and starches
available in that food (FAO, 1998). The low GI foods are ≤ 55 while Intermediate
(medium) glycemic foods are those that are between 56 and 69 and high glycemic
index ranges from 70 and above on the glycemic scale.
New
studies have shown that the regular consumption of diets containing high
glycemic index foods increases the risk of type 2 diabetes mellitus (Salmeron et al., 1997) and coronary heart disease
(Ford and Liu, 2001). Type 2 Diabetes (previously known as non-insulin
dependent Diabetes) is the most popular form of Diabetes characterized by hyperglycemia,
insulin resistance and relative insulin deficiency (Maitra and Abbas, 2005).
Type 2 Diabetes arises from interaction between genetic, environmental and
behavioural risk factors (Chen et al., 2011).
Individuals living with type 2 Diabetes are more prone to various forms of both
short and long-term complications, which usually lead to their premature death.
In contrast, the inclusion of low glycemic index foods in diet without a change
in the total amount of carbohydrate consumed may improve blood glucose control,
Brand et al. (1992); reduce serum
triglycerols, Jenkins et al. (1981); prolong endurance during physical
activity and improve insulin sensitivity, Frost et al. (1998).
Yams (Dioscorea spp) are annual root tuber bearing plants
with more than 600 species out of which six are socially and economically
important in terms of food, cash and medicine (IITA,2009). Yam
production has increased steadily in the last decade, from 18 million metric
tonnes in 1990 to recent estimates of over 39 million (FAO 2006). Several
edible species which are common are white yam (Dioscorea rotundata), yellow yam (Dioscorea esculentum), three leaved yam (Dioscorea dumentorum), water yam (Dioscorea alata) and aerial yam (Dioscorea bulbifera) are the most important of those commonly
consumed in Nigeria and West African countries (Ihekoronye and Ngoddy, 1985;
Okonkwo 1985). Moreover, the glycemic indices of these yam species are not
quite known. Okonkwo (1985) opined that the recommendation of water yam and
some cocoyam varieties as tolerable energy sources to diabetics is worthy of
further investigation. Thus, it is important to have the knowledge of the
glycemic indices of these commonly consumed yam species processed in different
ways that yams are eaten (Dioscorea rotundata,
Dioscorea alata and Dioscorea dumentorum)
as it will aid in evidenced meal planning and optimum food selection in
West Africa and Nigeria in particular.
1.2 STATEMENT OF PROBLEM
Obesity
and metabolic diseases like diabetes mellitus and cardiovascular diseases (CVD)
are on the increase, especially in certain young individuals. The World Health
Organization reported 65% rise in world diabetic rate. In Nigeria, there are no
existing data on the glycemic index of various commonly consumed foods, which
leaves several individuals at risk as they consume both low and high glycemic
index foods without putting their health status into consideration. According
to experts, nutritional habits play an important role in increasing the burden
of these chronic conditions. Therefore, modifying dietary habits could be
beneficial in the prevention and management of these diseases. It has been
suggested that the state of hyperglycaemia that is observed following food
consumption under certain dietary regimes could be a risk factor for the
development of various metabolic conditions especially in individuals with a
poor glycemic control such as in diabetes mellitus and even healthy
individuals. Under such circumstances,
it would be important to be able to reduce the amplitude and duration of
hyperglycemia. Hyperglycemia or high blood sugar is a medical condition in
which there is an excess amount of glucose circulating in the blood plasma.
This is generally a blood sugar level higher than 11.1 mmol/l (200 mg/dl) while
Hypoglycemia, also known as low blood sugar, is when blood sugar declines to
below normal levels. Some carbohydrate rich foods cause less post-ingestive hyperglycemia
than others. Therefore, having the right kind of carbohydrate foods could
actually be a potential strategy in the prevention and management of chronic
metabolic disorder. Hence, the need to know the glycemic indices of the
commonly consumed foods in Nigeria. This will aid healthy people and patients
with various nutritional disorders to choose the class of food that will be
beneficial to their health status.
1.3 JUSTIFICATION OF STUDY
There
is lack of information about the glycemic index of foods consmed in many
African communities and this has led to the poor health conditions and associated
dietary related disoders. The Glycemic index has been identified as a vital
tool to measure biological and health effects of meal. The management
of dietary induced
disorders have created
fear of consuming certain foods by people suffering from metabolic
diseases, yet little or no information exist on the glycemic index status of
many commonly consumed foods. It is therefore extremely important for this
information to be available to all in other to maintain a healthy status.
1.4 OBJECTIVES
The
primary objective of this work is to produce flour from the different yam
cultivars and determine the blood glucose response.
Specific objectives of this research:
i. To process different yam cultivars
(Dioscorea rotundata, Dioscorea alata and
Dioscorea dumentorum) using different methods; boiling, frying and pounding.
ii. To determine the functional
properties of the yam flour samples.
iii. To determine the amylose/amylopectin
ratio of the yam flour samples
iv. To determine the proximate
composition of the both the yam flour samples and test products.
v.
To determine the glycemic index of boiled, fried and pounded yam samples.
Login To Comment