ABSTRACT
Non Communicable diseases such as diabetes, obesity and cardiovascular complications have steadily been on the rise over decades. One of hall mark of diabetes mellitus is hyperglycemis which is compounded by consumption of goods with high glycemic indices. In this study, in vitro starch digestibility and glycemic indices of cocoyam accessions were evaluated. Six accessions of cocoyam both (Colocasia esculenta) Nce001, Nce012, Nce011 and (Xanthosoma maffafa) (Nxs001, Nx002, Nxs003) were harvested, samples were cleaned and oven dried at 500C and processed into flour. Proximate analysis, phytochemical determination, amylose determination, total starch and in vitro starch digestion were carried on each of these accessions. Appropriate statistical tools were used for data analysis. The result of proximate analysis shows that the accessions NCe001 (8.47 0.03a) had the highest moisture content and was significantly(P>0.05) higher than other accession; for crude fibre content, there was no significant (P<0.05)difference
NXs003(3.72±0.02e) and NXs 002(2.48±0.02e) while accessions NCe001(74.58±0.02c) was significantly (P<0.05) lower among Carbohydrate accessions . The phytochemical analysis revealed significant difference (P<0.05) between all the accessions. While NXs001 had the highest saponins(46.3±0.02a), Nce 001(2.16±0.02a ) had the highest phytate value. Total starch content was significantly (p<0.05 higher in all accessionsrNxs001 (77.64±3.38c) and NXs002(99.65±0.07c); Nce012(210±14±1.81a) Nce011(200.14±1.81b),NXs003 (206.05±6.73ab) and NCe001 (85.55±2.22d) when compared with white bread(217.39±1.88f) which served as control. Acession NXs001 (19.01±0.15a) had the highest and was significantly (p<0.05) higher than other accessions . The result fronm in vitro hydrolysis showed the control had significantly (P<0.05) higher values compared to the accessions used NXs001 (0.30) gave the highest equilibrium const ant while NXs003 (0.03) gave the lowest. The GI was low in all the accessions studied and ranged from NXs003(2.97)- white bread(26.96). The highest G.I was recorded in NCe001. This findings suggest that the cocoyam accessions studied could be recommended for use in the management of diabetes milletus and individuals seeking to control their blood sugar level.
TABLE OF CONTENTS
Title Page i
Declaration ii
Certification iii
Dedication iv
Acknowledgements v
Table of Contents vi
List of Tables ix
List of Figures x
Abstract xi
CHAPTER 1:
INTRODUCTION 1
1.1
Background of the Study 1
1.2
Aim and Objective of the Study 3
CHAPTER 2: REVIEW OF RELATED LITERATURE 4
2.1 History of
Cocoyam 4
2.2 Botanical Classification 5
2.3 Uses of
Cocoyam 7
2.3.1 Uses of cocoyam flour and 8
2.4 Nutritionalcomposition 9
2.4.1 Proximate
composition 9
2.4.2 Phytochemicals
and antinutrients in cocoyam 10
2.5 Classifications
of Carbohydrates 13
2.5.1 Types of
starch 14
2.5.1.1 Amylose 14
2.5.1.2 Amylopectin 15
2.6 Enzymes
Involved in Carbohydrate Hydrolysis 16
2.6.1 Amylase 16
2.6.2 Amyloglucosidase 17
2.7 Starch
Digestion Rate 18
2.8 Glycemic
Index and Slowly Digestible Starch 19
2.9 Benefit of
Slowly Digestible Starch Consumption 21
2.10 In Vitro Digestion 23
2.11 Synergism between Amylase and
Amyloglucosidase 25
CHAPTER 3: MATERIALS AND METHODS 26
3.1 Materials 26
3.1.1 Apparatus
and equipment 26
3.1.2 Reagents 27
3.1.3 Chemicals 27
3.1.4 Enzymes 27
3.1.5 Kit 27
3.2 Methods 27
3.2.1 Collection
and preparation of sample 27
3.3 Biochemical
Assays 27
3.3.1.1 Determination
of moisture content 28
3.3.1.2 Determination
of ash content 28
3.3.1.3 Determination
of crude fibre content 28
3.3.1.4 Determination
of fat content 29
3.3.1.5 Determination
of protein content 30
3.3.1.6 Determination
of carbohydrate content 31
3.3.2 Phytochemical
analysis 31
3.3.2.1 Determination
of Alkaloids 31
3.3.2.2 Determination of Saponins 31
3.3.2.3 Determination of Tanninsfollowed the Folin Dennis
colorimeter method 32
3.3.2.4 Determination
of Flavonoid content 33
3.3.2.5 Determination of Oxalate content 33
3.4 Amylose
Determination 34
3.4.2 Amylopectin
content 34
3.5 Assay 34
3.5.1 Total
starch 34
3.5.2 In vitro starch digestibility 35
3.6 Statistical
Analysis 36
CHAPTER 4: RESULTS AND DISCUSSION 37
4.1 Results 37
4.2 Discussion `42
CHAPTER 5: CONCLUSION AND RECOMMENDATIONS 49
5.1 Conclusion 49
5.2 Recommendations 50
References 51
School of
Applied Sciences, RMIT University, City Campus, Melbourne, Victoria Australia
Anna Bannikova, Phone:
+61-3-99252720
+61-3-99252720,
Fax: +61-3-99255241, Email: ua.ude.timr@avokinnab.anna.
Corresponding
author.
Appendix 66
LIST OF TABLES
1: Proximate analysis of six accessions of
NRCRI cocoyam 37
2: Phytochemical analysis of six
accessions of NRCRI cocoyam 38
3: Amylose content and total starch
analysis 39
4: Starch hydrolysis table with time 0min-.180
mins 40
5: Equilibrium constant, hydrolysis and
glycemic index table 41
LIST OF FIGURES
1: Corms
of xanthosomamaffafa ; Nxs 003
and Nxs 002 respectively 6
2: Corms
of colocasiasagituffollium; NCE012
and NCE011 respectively 7
3: Structure
of amylose (a) linear (b) helical 15
4: Structure
of amylopectin 16
5: A reaction amylase and amyloglucosidase
on starch to release maltose
and maltotriose 25
6: A graph
of in vitro starch hydrolysis of the
different accessions 42
CHAPTER 1
INTRODUCTION
1.1 BACKGROUND
OF THE STUDY
The
Glycemic Index (GI) is a dietary measuring system that ranks
carbohydrate-containing foods and relates the rate at which the blood sugar is
raised after two (2) hours or more of consuming the food
(post-prandialglycemia) to a reference food, usually glucose (Brand-Miller et
al., 2003). White bread may be used as a reference food in place of glucose
(Wolever, 1993; Anon, 2006; Ihediohanma et
al., 2012).Foods are classified into three categories
of glycemic index: low GI; ≤ 55, medium GI = 55-69, and high GI; ≥ 70 (Allen et al., 2012). Low glycemic index foods have been
shown to improve glucose and fat tolerance in diabetes mellitus patients and
improve insulin resistance. In addition they can also help in control of
appetite by slowing the emergence of hunger to help in weight control. (Regina,
2012) One of the ways of prevention of diabetes mellitus and obesity is by
choosing the right food for consumption. The functional food suitable for
application in people with diabetes mellitus and obesity is choosing a food
that has a low glycemic index (GI) (Margareth, 2006).
Carbohydrate
is the main energy source of food that is daily consumed, it provides
approximately 40-80% of total daily energy requirement in human (FAO/WHO,
1998).
Cocoyams
(Colocasia esculenta (L.) Schott and Xanthosoma sagittifolium (L.) Schott) are the
important species of edible aroids, grown in tropical and sub-tropical
countries. Cocoyams are used as subsistence staples in many parts of the
tropics and sub-tropics. Cocoyams are grown mainly for their edible starchy
corms, cormels, and their leaves that could serve as vegetables (Aregheore and
Perera, 2003). The corms could be processed into many products including poi
(fresh or fermented paste, canned, and canned-acidified), flour, cereal base,
beverage powders, chips, sun-dried slices, grits, and drum-dried flakes
(Owuamanam et al., 2010).Starch is
the main carbohydrate source in the diets (Chung et al., 2006). Starch
is one of the most abundant substances in nature, being renewable and an almost
unlimited resource, it is produced from grain and or root crops. It is mainly
used as food, but can also readily be converted chemically, physically, and
biologically into many useful products to date. The main sources of starch are
cereals, roots (tapioca and sweet potato) and tubers (potato and cocoyam). This
diversity of sources is reflected in their properties and functionalities
(Wurzburg, 1986); Starch plays special role in glucose homeostasis (Mann et al., 2007). Consumption of easily
digestible food results in a rapid rise in blood glucose and substantial
fluctuation of hormones, which places high stress on the regulatory system.
(Brownlee, 2001; Ludwig, 2002). Starch composition of food and its rates of
digestion are determinants of blood glucose, satiety and energy intake (Raben et al., 1996; Alderson et al., 2010). Starch digestion rate and its consequent
glycemic impact is greatly influenced by the food composition such as resistant
starch content, phosphorylated starch, phytonutrients, dietary fibre, protein,
and fat content (Absar et al., 2009).
Human and animal feeding trials is time consuming and expensive, besides the
differences in digestion rate in starch containing foods from human studies,
necessary research effort has been focused on developing in vitro models of starch digestion (Englyst et al., 1992; Slaughter et al.,
2001; Dona et al., 2010). The in vitro procedure allows the simulation
of starch enzymatic digestion at the best possible rate. This procedure uses a protease (pepsin) to
avoid protein-starch interactions and an amylase to hydrolyse starch and finally
amyloglucosidase to release glucose from the starch hydrolysis products (Jenkins
et al., 1987, Goñi et al., 1997).
The
diverse metabolic disorders prevalent in this day and age has made it
imperative for scientists, nutritionists and medical personnel to harness the
nutraceutical potentials of food sources within and around the tropic. Literature reveals that research works have
been carried out on the functional and proximate properties of cocoyam flours
and starch as well as some industrial application, cocoyam is still under-utilized
crop (Osisiogwu et al., 1974; Lawal,
2004), as there is paucity of informationon the phytonutrient profile on
accessions in Nigeria. The need to evaluate the glycemic indices of cocoyam
accessions to enable individuals living with diabetes make informed choices is
one of the major reason for this study.
1.2 AIM
AND OBJECTIVE OF THE STUDY
1.2.1 Aim of the study
The
present study is aimed at determining the proximate, phytochemical composition
and comparative evaluation of in vitro
digestibility of flour samples from six cocoyam accessions.
1.2.2 Objectives of the study
The
objectives of this study are to:
1. Determine
the proximate and phytochemical composition (Oxalate, Tannins, Saponins e.t.c.)
of the different accessions of cocoyam.
2. Evaluate the starch quality (Amylose,
amylopectin and total starch) in these accessions.
3. To determine the digestibility of the
cocoyam accessions by in vitro digestibility of each flour samples.
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