ABSTRACT
Four species of yam; white yam (Dioscorea rotundata), aerial yam (Dioscorea bulbifera), cocoyam (Xanthosoma robustum) and water yam (Dioscorea alata) were analysed for their glycemic indices, chemical and functional properties after subjecting them to four processing operations of boiling, sprouting, frying, roasting and a set was left untreated. Boiled cocoyam (Xanthosoma robustum) among the species was significantly (p<0.05) different in terms of glycemic index (40.215)%, total starch (52.29%), digestible starch (49.67%),oil absorption capacity (3.09%) and solubility (14.97%) whereas boiled aerial yam was significantly (p<0.05) different from all the samples in terms of water absorption capacity (4.21%), wettability (20.56%) and dispersibility (73.17%). Boiled white yam was significantly (p<0.05) different in terms of swelling power (9.21%) and bulk density (0.78%). Sprouted water yam was remarkably different (p<0.05) from all the samples in gelation capacity (12.00%), foam capacity (46.67%), foam stability (13.33%) and gelatinization temperature (88.30oC) while sprouted white yam was significantly (p<0.05) different in terms of protein content (3.50%) and moisture content (13.40%) while among the processing operations, boiling as a treatment was significantly (p<0.05) different from sprouting, frying, roasting as well as the untreated.
TABLE
OF CONTENTS
Title Page i
Declaration ii
Certification iii
Dedication iv
Acknowledgement v
Table of Contents vi
List of Tables vii
List of Plates viii
Abstract ix
CHAPTER 1: INTRODUCTION
1.1 Background
of the Study. 1
1.2 Statement
of Problem. 4
1.3 Justification
of the Study. 5
1.4 Objectives
of the Study. 6
CHAPTER 2: LITERATURE REVIEW
2.1. Origin
of Glycemic Index. 7
2.2 Background
Information and Nutritional Importance of the Selected
Tuber Flours.
9
2.2.1 Aerial yam (Dioscorea
bulbifera). 9
2.2.2 Cocoyam (Xanthosoma
robustum). ` 12
2.2.3 Water
yam (Dioscorea alata). 14
2.2.4 White
yam (Discorea rotundata). 15
2.3
Economic Importance and Utilization of the
Selected Tuber Crops. 17
2.3.1
White yam (Dioscorea rotundata). 17
2.3.2
Water yam (Dioscorea alata) . 20
2.3.3
Cocoyam (Xanthosoma robustum). 21
2.3.4 Aerial
yam (Dioscorea bulbifera). 22
2.4 Benefits of the Processing Methods used. 24
2.5 Starch Gelatinization. 26
2.6 Starch Hydrolysis 26
2.6.1 Factors
affecting starch digestibility. 28
2.6.2
Starch digestibility and health. 28
2.7 Factors
that can Affect the Glycemic Index of a Food 32
2.7.1 Method
of cooking. 32
2.7.2 Type of processing method. 32
2.7.3 Type of starch . 32
2.7.4 Solubility of fibre. 33
2.7.5 Type of sugar. 33
2.7.6 Acidity of a food. 33
CHAPTER 3: MATERIALS AND METHODS.
3.1 Sources
of Raw Material. 34
3.2 Raw Materials Preparations. 34
3.3 In
Vitro Glycemic Determination of the Selected Food Crops. 38
3.1.1
Resistant starch (Rs) analysis. 39
3.3.2 Total
starch (Ts) analysis. 39
3.3.3
Digestible starch (DS). 40
3.3.4 Hydrolysis
index (HI) . 40
3.3.5 Glycemic index (GI). 40
3.4 Proximate Analysis. 41
3.4.1 Determination
of protein. 41
3.4.2 Determination of moisture content. 42
3.5.3 Determination of ash content. 42
3.4.4 Crude
fiber determination. 43
3.4.5 Fat content determination. 44
3.4.6 Carbohydrate
content determination. 45
3.5 Functional
Properties Determination. 45
3.5.1 Bulk
density (BD) (g/ml). 45
3.5.2 Water
absorption capacity (WAC) (g/ml). 46
3.5.3 Oil
absorption capacity (OAC) (g/ml) 46
3.5.4 Foam
capacity (FC) (%). 47
3.5.5 Foam
Stability, (FS) (%). 47
3.5.6 Emulsification
capacity (EC) (%). 48
3.5.7 Gelation
capacity (GC) (w/v). 48
3.5.8
Gelatinization temperature (GT) (oC). 49
3.5.9
Wettability (%)
49
3.5.10
Dispersibility (%). 49
3.5.11
Solubility (%) . 50
3.5.11
Swelling power (%). 50
3.5.12 pH
measurement. 51
3.6 Statistical Analysis of Data. 51
CHAPTER 4: RESULTS
AND DISCUSSION
4.1 The Effect of Processing Methods on the Glycemic Index
of the
selected Tuber Flours. 52
4.2 The Effect of Processing methods on the Total
Starch Content of the
selected Tuber
Flours. 54
4.3
The Effect of Processing methods on the Resistant
Starch Content of the
selected
Tuber Flours. 56
4.4 The Effect of Processing methods on the Rapidly
Digestible Starch
(RDS)
content of the selected Tuber Flours. 60
4.5
The Effect of Processing methods on the Proximate
Composition of the
selected Tuber Flours. 62
4.6
The Results of the Analysis on the
Effects of Processing methods on the
Functional
Properties of the selected Tuber Flours. 68
CHAPTER 5: CONCLUSIONS
AND RECOMMENDATIONS
5.1 Conclusion. 85
5.2
Recommendations. 86
REFERENCES 87
LIST OF TABLES
2.1: Similar research works using invitro glycemic index determination
and the effects of processing
methods on the glycemic index,
chemical and functional properties of tuber crops /flours. 9
2.2: Starch hydrolyzing enzymes 27
2.3: Extract of some Glycemic index values (GI)
and Glycemic Load
(GL) of Some Foods from the International Glycemic Table
29
2.4: Extract of some Glycemic index values (GI)
and Glycemic Load
(GL) of some foods from Revised International Table of Glycemic
Index (GI) and Glycemic Load (GY) values-2008 31
4.1: Effect of processing methods on the in vitro estimated glycemic
index
(%) of the selected tuber flours. 55
4.2: Effect
of processing methods on the Total Starch (TS) (%) content
of the
selected tuber flours. 57
4.3
Effect of processing methods on the
Resistant Starch (RS) % content
of the
selected tuber flours. 59
4.4 Effect
of processing methods on the Rapidly Digestible Starch (RDS)
(%)
content of the selected tuber flours. 61
4.5 Effect of processing methods on the
proximate compositions (%)
of
the selected tuber flours. 67
4.6 Effect of processing methods on
solubility, swelling power and
dispersibility of the
selected tuber flours 71
4.7
Effect of processing methods on the
bulk density, foam capacity and
foam stability of the
selected tuber flours 75
4.8 Effect
of processing methods on emulsification capacity, gelation
capacity
and gelatinization temperature. 79
4.9 Effect
of processing methods on the water absorption capacity, oil absorption
capacity,
wettability and pH of the selected tuber flours. 84
LIST OF PLATES
1: Cocoyam (Xanthosoma robustum) 35
2: Sprouted cocoyam (Xanthosoma robustum) 35
3: Sprouted white yam (Dioscorea rotundata) 35
4: Cross-section dissected/undissected white yam (Dioscorea rotundata) 35
5: Water yam (Dioscoreaa alata) 36
6: Sprouted wateryam (Dioscorea alata) 36
7: Aerial yam {Dioscorea
bulbifera) 36
8: Sprouted aerial yam (Dioscorea bulbifera) 36
CHAPTER 1
INTRODUCTION
1.1 BACKGROUND OF THE STUDY
The
choice of food should be taken into consideration, not only by their chemical
composition but also their ability to influence post prandial glycemia, (http://www.glycemicindex.com).
Diseases such as the second type of diabetes (Diabetes mellitus) are on the
increase and this seems to be directly related to the amount and type of carbohydrates
consumed in an individual’s daily diets (Jenkins et al.1981).
Majority
of the carbohydrates that are commonly eaten are complex carbohydrates majorly
made up of starches of the amylose category.
For all of these starches to be broken down and go into the blood
stream, they have to be split down into glucose, the smallest unit of the sugar
molecules which starches are composed. Glycemic index therefore, classifies
foods with regard to their individual carbohydrate reabsorption time of the consumed
food. The resulting proprandial glucose levels are compared to those measured
after consumption of a standard food notably glucose or white bread which has
its glycemic index set as 100, (Englyst et
al.1982).
Glycemic
index (GI), therefore is defined as a measurement of the effect of carbohydrate
composition in food on levels of the glucose in the blood. According to
international glucose table, any food
rating less than 55 in glycemic index is
considered low while any food rating 56-69 is considered
medium while 70 or more is considered high,(Brand-Miller et al.2003;www.foodwatch.com). Foods with high glycemic index
promote higher insulin level thus increased risk of having type 2 diabetes. Glycemic
Index (GI) corresponds to carbohydrates potential to raise blood sugar levels.
In other words, GI tell us the extent to which some group of carbohydrates
induce our bodies to secrete insulin. Insulin is a pancreas hormone that
regulates the level of glucose released in the blood. Without insulin, the body
cells would not be able to use the energy released from glucose to perform vital
body activities. Glycemic index ultimately measures starch digestibility
through comparison to reference food; glucose or white bread. The proprandial
glycemic response of similar portions of carbohydrates from different plant
crops vary immensely depending on their rate of absorption. (http://www.montigac.com).
On
the other hand, Glycemic load (GL) can be defined as that value that accounts
for the amount of carbohydrate in a food and how much each smallest unit of
carbohydrate in the food raises blood glucose level. GL describes the quality
and quantity of the class of carbohydrate in a food,(www.foodwatch.com).The
GI values derived from many studies have been published in The International Tables
of Glycemic index (GI) and Glycemic load (GL) Values (Foster-Powell 2002,
Atkinson, 2008, David, 2008). The glycemic index of food can be determined
using in vivo or in vitro methods
(Jenkins et al., 1987).
The
measurement of glycemic index using the in
vitro method utilizes glycemic response to carbohydrate containing foods
after enzyme hydrolysis and allows the ranking of food depending on the rate of
their break down and assimilation of the carbohydrates contained inside of them
(Jenkins et al., 1987; Englyst et al.1982). Glycemic index evaluation in humans can be difficult
and costly, therefore studies measuring in
vitro digestion of starch foods have been done in order to use the result
and predict in vivo effects, (Grandfelt et al.1992; Englyst and Hudson 1996;
Bjorck 1996, Goni et al. 1997), while
Englyst and Hudson (1996) suggested the utilization of rapidly digestible starch
contained in foods as taken by subjects.
Goni et al. (1997)
developed a first order equation from the
in vitro kinetics of starch break
down of foods. This model has a high correlation with in vivo glycemic responses. In addition, for good reproducibility
and application in other studies, the in vitro methods have also been used to
classify foods based on their characteristics similar to the in vivo procedure and to identify slow
release of carbohydrate units in foods (Jenkins, et al., 1984; Schweizer and
Edwards, 1992)
Underutilized
plant, food crops such as aerial yam (Dioscorea
bulbifera), white yam (Dioscorea
rotundata), water yam (Dioscorea
alata) as well as cocoyam (Xanthosoma
robustum) have been selected for the determination of the effect of
processing operations on their glycemic index, chemical and functional
properties. These crops have been purported to have the ability to bring down
the level of blood glucose thus
controlling type 2 diabetes or even preventing it for persons who have not
developed it yet,(Evidence Based Complementary Journal, 2012; Elsevier, 2014; Ukom
et al. 2014) . These crops are
underutilized but quite affordable and available. A low glycemic rating relates
to lower break down and absorption of a food carbohydrate. This slower
absorption is linked to lower calorie consumption and weight loss. There is
therefore need to ascertain the authenticity of this hypothesis concerning
these crops with the view to recommending them for food use and in the processed
form that delivers the best hypoglycemic effect.
However,
the processing methods selected which are the common ways in which these tuber
crops are consumed or utilized are beneficial. Boiling is the cooking of foods in water or water based liquids up
to 100oC or 212oF. At this temperature pathogenic
organisms are inactive or destroyed, texture and colour of foods especially
starchy food are improved and digestibility of the food and the assimilation of
the nutrients is increased too. (,http://www.healthline.com). Sprouting which basically is a process
of allowing seeds, legumes and tubers to germinate either by soaking them in
water, sprinkling water on them or leaving them in a moist environment. Sprouting
increases the nutrient quality and quantity of the crop and provides better digestion
and aids in weight loss. It increases the protein, vitamin A and C, iron and
copper content. It shortens cooking time, provides antioxidants and alkalizes
the body (www.food.ndtv.com). Frying,
a method of cooking food in an oil or fat has the following benefits especially
to starchy foods: improves appearance, texture and palatability of the food. It
initiates browning process in foods that contain starch, (http://www.finecooking.com).
Roasting, a method of cooking over an open fire while controlling the temperature
to at least 150oC is active against disease causing organisms, softens
the food texture, induces browning and impacts characteristic taste and flavour
to the food, (http://www.foodroasting.com).
1.2 STATEMENT OF PROBLEM
The
prevalence of high blood sugar related diseases such as diabetes, stroke,
obesity and other related diseases which shorten life span of individuals are
on the increase and there is great need
to identify plant food crops with low value of glycemic index in order to
promote good health. Some crops which were of nutritional and health importance
consumed by our fore fathers such as aerial yam (Dioscorea bulbifera) and cocoyam (Xanthosoma robustum) have been abandoned for what may be called
“modern classy foods” which have health implications such as sugary foods and
unbalanced diets. The glycemic index, chemical as well as the functional
qualities of these underutilized crops need to be analysed after subjecting
them to the following processing operations: boiling, sprouting, frying and
roasting in order to determine their effective usage. In addition to these
underutilized crops are the commonly eaten tubers by diabetic patients as well
as older people such as water yam (Dioscorea
alata) and white yam (Dioscorea rotundata).
1.3 JUSTIFICATION OF THE STUDY
Literature
reviews reveal information about the therapeutic properties of aerial yam (Evidence
Based Complementary Journal, 2012) and cocoyam (Elsevier, 2014) as regards
reduction in high blood sugar and the prevention of other related diseases. Water
yam (Dioscorea alata) possesses good
nutritional compositions which promotes good health, (Otegbayo et al. 2001). White yam (Dioscorea rotundata) is regarded as the
most nutritively valued tropical root crops, (Wanasundera and Ravindran, 1994).
It contains approximately four times as much protein as cassava and is the only
major root crop that exceeds rice in protein content in proportion to
digestible energy, (Bradbury and Holloway, 1988). These crops are available and
affordable, it is therefore necessary to determine the glycemic index (which is
a health promoting factor) of these crops. Knowledge of the glycemic index as
well as the effect of using some processing methods on these selected tuber
flours would lead to a better understanding of their chemical composition and
their functionality which will aid in providing information on the implications
of their long term usage, their end use quality as well as increase their utilization
by individuals, industries that produce food products, hospitals as well as
health care providers.
1.4 OBJECTIVES OF THE STUDY
The
major objective is to determine the effect of processing operations on the
glycemic index, chemical as well as the functional properties of some selected tuber
flours: aerial yam (Dioscorea bulbifera),
white yam (Dioscorea rotundata) ,water
yam (Dioscorea alata) and cocoyam (Xanthosoma robustum).
The
Specific objectives of this research include;
i.
To determine the glycemic
index of these selected tuber flours using the in vitro method.
ii.
To determine the
proximate composition of these selected tuber flours.
iii.
To determine the functional
properties of the selected tuber flours.
iv.
To determine the effect
of using some processing methods on the glycemic index, chemical as well as the
functional properties of the selected tuber flours.
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