ABSTRACT
This study evaluated the physicochemical, antioxidant activity, glycemic index and glycemic load of mixed fruit juice produced from Monkey kola (Cola lepidota) and Golden apple (Spondias dulcis). Fresh juices extracted from monkey kola and golden apple fruits were mixed at different proportions (100:0, 80:20, 70:30, 60:40, 50:50, 40:60, 30:70, 20:80, 0:100). Both fruits and mixed juice samples were subjected to analyses (proximate analysis, physicochemical properties, antioxidant activity, glycaemic index and load, and sensory evaluation). Completely randomization design was the experimental design used for this study, while t-test and one-way statistical tools were used to determine significant different between and among the fruits and mixed juices respectively at p<0.05. The result of the analyses showed that there was significant difference in the proximate composition of the fruits except in fibre (p>0.05). The proximate composition of the mixed juices showed that the moisture content ranged from 87.23 to 94.52%, ash (0.15 to 0.25%), fibre (0.00 to 0.33%), protein (0.09 to 0.31%), fat (5.02 to 9.21%), and carbohydrate (0.09 to 2.89%). The result of the physicochemical composition showed that the total soluble solid ranged from 43.50 to 87.00 brixo, total titratable acidity (0.03 to 0.22%), and pH (3.79 to 6.92). The result of the antioxidant composition of the fruits showed that there was significant difference (p<0.05) in the total carotenoid, total flavonoid and total phenolic contents of the fruits. The antioxidant composition of the mixed juices showed that total carotenoid ranged from 0.21 to 0.51 mg/100g, total flavonoid (0.74 to 2.82 mg/100g), total phenol (9.11 to 13.16 mg/100g), and ascorbic acid (6.19 to 10.79 mg/100g). The result of the antioxidant activity of the fruits showed that there was significant difference (p<0.05) in the free radical scavenging activity (ABTS), but there was no significant difference (p>0.05) in the ferric reducing power (FRAP). The antioxidant activity of the mixed juices showed that the percentage free radical scavenging activity ranged from 33.00 to 50.29%, while the percentage ferric reducing power ranged from 21.67 to 39.86%. Furthermore, the result of the glycaemic index (GI) and glycaemic load (GL) of the fruits showed that both fruits had low GI at p<0.05. Monkey kola has low GL, while golden apple has moderate GL. The mixed juices also had low GI and low GL at p<0.05. The result of the sensory evaluation of the mixed juices showed that mixed juices with higher proportions of golden apple juice were the most preferred in terms of appearance, taste, aroma, consistency and general acceptability than others. Thus, inclusion of the golden apple juice increased the consumers’ acceptability of the mixed fruit juices. Therefore, this study showed positive synergistic effects of the mixed fruit juices on the nutritional value, improved antioxidant activity and as well as glycaemic index and glycaemic load. The mixed fruit juices are therefore recommended for these functional attributes in modern food systems.
TABLE
OF CONTENTS
Title page i
Declaration ii
Certification iii
Dedication iv
Acknowledgements v
Table of Contents vi
List of Tables x
List of Figures xi
List of Plates xii
Abstract xiii
CHAPTER 1:
INTRODUCTION
1.1 Background of the Study 1
1.2 Statement of Problems 3
1.3 Justification 5
1.4 Objectives of the Study 6
CHAPTER 2:
LITERATURE REVIEW
2.1 Fruits 7
2.1.1 Fruit juices 8
2.1.2 Physicochemical characteristics
of fruit juices 9
2.2 Monkey Kola (Cola lepidota) 10
2.2.1 Chemical composition of monkey kola 11
2.2.2 Health benefits of monkey kola 12
2.3 Golden Apple (Spondias dulcis) 13
2.3.1 Chemical composition of golden apple 14
2.3.2
Health benefits of golden apple 14
2.4 Antioxidants 14
2.4.1
Importance of antioxidants 16
2.4.2
Classification of antioxidants 17
2.4.3
Common antioxidants in fruits 18
2.5 Glycemic Index (GI) 20
2.5.1 Measurement of glycemic index 21
2.5.2
Factors that affect the glycemic index of a food 21
2.6 Glycaemic Load (GL) 25
2.7 Role of
Glycemic Index (GI) and Glycemic Load (GL) in preventing
diseases 26
2.7.1 Diabetes 27
2.7.1.1 Relationship between diabetes
and obesity 28
2.7.2 Type
2 diabetes mellitus 29
2.7.3 Obesity 31
2.7.4
Cardiovascular disease 33
2.7.5
Cancer 35
2.7.6
Gallbladder disease 36
CHAPTER 3: MATERIALS AND METHODS
3.1 Sources
of Raw Materials 38
3.2 Preparation of Samples 38
3.2.1 Extraction of monkey kola juice 38
3.2.2 Extraction of golden apple juice 40
3.3 Formulation of Mixed Fruit Juices 40
3.4
Proximate Analyses of the Fruits and Mixed Juices 43
3.4.1
Determination of moisture content 43
3.4.2
Determination of ash content 44
3.4.3
Determination of fat content 44
3.4.4
Determination of crude fibre content 45
3.4.5
Determination of crude protein content 45
3.4.6
Determination of carbohydrate content 46
3.5
Physicochemical Analyses of the Mixed Fruits Juices 46
3.5.1 Total
soluble solid (TSS) 47
3.5.2
Titratable acidity 47
3.5.3 pH 47
3.5.4 Ascorbic acid (AA) 47
3.6
Antioxidants Analyses of the Fruits and Mixed Juices 48
3.6.1 Total
carotenoid content (TCC) 48
3.6.2 Total
flavonoid content (TFC) 48
3.6.3 Total
phenolic content (TPC) 49
3.7 Antioxidant Activity of the
Fruits and Mixed Juices 49
3.7.1 Free
radical scavenging activity (ABTS) 49
3.7.2
Ferric reducing antioxidant power (FRAP) 50
3.8
Determination of Glycemic Index (GI) and Glycemic Load (GL) 51
3.9 Sensory
Analysis 52
3.10
Experimental Design 53
3.11
Statistical Analysis 53
CHAPTER 4: RESULTS AND DISCUSSION
4.1
Pictorial Representation of the Juice Samples 54
4.2
Proximate Composition of the Fruits 56
4.3
Proximate Composition of the Mixed Fruit Juices 59
4.4
Physicochemical Composition of the Mixed Fruit Juices 64
4.5
Antioxidant Content of the Fruits 67
4.6
Antioxidant Content of the Mixed Fruit Juices 70
4.7
Antioxidant Activity of the Fruits 73
4.8
Antioxidant Activity of the Mixed Fruit Juices 75
4.9
Glycemic Index (GI) and Glycemic Load (GL) of the Fruits 78
4.10 Glycemic
Index (GI) and Glycemic Load (GL) of the Mixed
Fruit Juices 80
4.11
Sensory Evaluation of the Mixed Fruit Juices 82
CHAPTER 5: CONCLUSION AND RECOMMENDATIONS
5.1
Conclusion 87
5.2
Recommendations 88
5.3
Contribution to Knowledge 88
References 89
Appendices
LIST
OF TABLES
2.1: Proximate composition of
endocarp and exocarp of Cola lepidota 11
2.2: Energy and
proximate composition of monkey kola (C. parchycarpa
and C. lepidota) juice 12
2.3: GI and GL of some common fruits 36
2.4: GI and GL of some common fruit
juices 37
3.1: Formulation of mixed fruit juice 41
4.1:
Proximate composition of the mixed fruit juices 60
4.2:
Physicochemical Composition of the Mixed Fruit Juices 65
4.3:
Antioxidant content of the mixed fruit juices 71
4.4:
Antioxidant activity of the mixed fruit juices 76
4.5:
Glycemic index (GI) and glycaemic load (GL) of the fruits 79
4.6: Glycemic
index (GI) and glycaemic load (GL) of the mixed
fruit juices 81
4.7:
Sensory evaluation of the mixed fruit juices
83
LIST
OF FIGURES
3.1: Flow chart for the preparation of mixed fruit juice 42
4.1:
Proximate composition of the fruits 57
4.2: Antioxidant content of
the fruits 68
4.3:
Antioxidant activity of the fruits 74
LIST
OF PLATES
1: Monkey kola fruit 39
2: Golden apple fruit 39
3: Monkey
kola juice 54
4: Golden
apple juice 54
5: Mixed fruit juices (samples MG1,
MG2, MG3, MG4) 55
6: Mixed fruit juices (samples MG5,
MG6, MG7, MG8, MG9) 55
CHAPTER
1
INTRODUCTION
1.1
BACKGROUND OF THE STUDY
Fruits are the structural parts of
plants that contain seeds. Fruits, usually fresh and edible in the raw state
are also plant parts which have aromatic fragrant characteristics and are
usually sweet or sweetened before eating (Mauseth et al., 2003). Most fruits are eaten as deserts and they can be
processed into liquid products which include fruit juices, fruit wine and other
preserves like marmalade, jams, jellies etc. There are also different kinds of
tropical fruits available for the production of fruit juice. These tropical
fruits include pineapple, grape, lime, lemon, orange, paw-paw, guava, tangerine,
monkey kola, golden apple and others.
These tropical fruits can also be mixed to produce mixed fruit juice (Njoku et al., 2018).
Monkey
kola (Cola lepidota) is
an underutilized fruit found in South-East Nigeria. It belongs to the family Sterculiaceae; and genus cola. It is made up of three varieties;
red variety (Cola latertia), white
variety (Cola parchycarpa) and yellow
variety (Cola lepidota) (Singh et al.,
2010). Monkey kola (Cola lepidota)
fruit is edible, crunchy and tasty. Native people of Southern Nigeria
and Cameroun relish the fruits as well as primates like baboons, monkeys etc
(Essien et al., 2015). Monkey kola is identified by various local names
in South-eastern Nigeria (Achicha or Ohiricha in Igbo and Ndiyah in Efik). It is known as Obi edun in Yoruba language. Monkey kola
has nutritional and medicinal values (Singh et
al., 2010).
Golden apple (Spondias dulcis Forst or
Spondias cythera Sonnerat), also commonly referred to as Ambarella or June plum belongs to the family
of Anacardiaceae. It is a tropical
tree which is native from Melanesia through Polynesia and has been widely
spread in Sri Lanka, India, Indonesia, Malaysia and many other tropical and
equatorial countries (Mohammed et al.,
2017). The fruits are oval and 5 to 10 cm long, containing a fibrous flesh. The
colour of the fruit flesh changes from white to yellow, becomes softer and
flavour becomes musky with ripening. Fruit peel also changes from green colour
to golden yellow colour upon ripening (Ishak et al., 2005). The flesh of the golden apple fruit is juicy,
crunchy and mildly acidic and has a flavour and aroma closely related to
pineapple-mango. Golden apple has been used for indigenous medicine in
countries like Sri Lanka, India, Vietnam and Malaysia. The fruit is used to treat
anaemia, regulate blood glucose levels, and to treat digestive problems as it
contains high amount of dietary fibre (Mohammed et al., 2017). The consumption of fresh golden apple fruit is
increasing based on its nutraceutical properties against diabetes mellitus,
indigestion, urinary tract infections, hypertension and haemorrhoids (Islam et al., 2013)
Mixed
fruit juice blends can be produced from various fruits such as orange,
pineapple and among others in order to combine all the basic nutrients present
in these different fruits. This usually gives a better quality juice
nutritionally and organoleptically. Studies have shown that the practice of
mixing different exotic fruits positively impacted on the flavour and taste of
the fruit juice-mixes and fruit products (Nwachukwu et al., 2007; Ogiehor et al., 2008).
Most
fruits possess antioxidants, which are able to prevent or inhibit oxidation
processes in human body as well as in food products (Borowska, 2003). Antioxidants
occur in almost all edible plant products. Polyphenols are the most numerous
group of antioxidant components, and they are present in fruits and vegetables,
their products, leguminous plants, grains, teas, herbs, spices and wines
(Borowska, 2003). The oxidative reaction processes in food are the main cause
of its deterioration and are also responsible for the nutritional value losses,
as well as aroma, taste and texture degradation.
The
Glycemic index (GI) is said to be a measure of how fast a carbohydrate
containing food affects the blood glucose level after ingestion (Jenkins et al., 2002a; Astawan and Windowati,
2011). Most fruits fall into the low GI category, despite their relatively high
levels of sugar as a result of their high fibre contents (Ludwig, 2002). The GI
concept was introduced by Jenkins et al.
(1981) in the early 1980s as a ranking system for carbohydrates based on their
immediate impact on blood glucose levels. GI was originally designed for people
with diabetes as a guide to food selection, advice being given to select foods
with a low GI (Jenkins et al.,
2002a). Lower GI foods were considered to confer benefit as a result of the
relatively low glycemic response following ingestion compared with higher GI
foods. Jenkins et al. (2002b) defined
the Glycemic Load (GL) as the amount of carbohydrate present in a typical
serving of a meal. The concept of GI and GL was designed to determine the
quality and quantity of carbohydrate in food substances (Liu et al., 2001).
1.2 STATEMENT OF PROBLEMS
In Nigeria, monkey kola is mostly
consumed fresh and like most fruits it has a very short life span probably due to
its high moisture content; its hard texture also limits its consumption
particularly among the vulnerable group (young children, aged) due to poor
dentition (Okudu et al., 2015).
Antioxidant activity of the leaf and stem bark extracts of monkey kola have been studied
(Oghenerobo and Falodun, 2013), but there is paucity of information as regards
the antioxidant potential of monkey
kola fruit and juice coupled with the increase in demand for the need to evaluate nature's repository of
chemicals in plants for their potential value in health care.
Due to poor keeping quality and
difficulties of transportation, processing, preservation and marketing
facilities, a huge quantity of these valuable fruits are being damaged, spoiled
and wasted specially during their peak seasons. Golden apple is a climacteric
fruit with high respiratory rate
(Graham et al., 2004). Fruits with
high rate of respiration tends to deteriorate and spoil easily. Golden apple is an underrated tropical fruit
and scientific research has proven that the fruit contain significant health
benefits and nutrients (Jayarathna et al., 2020). However,
with increasing consumption of the Golden apple fruit, considerable attention
is required for analyses of its nutrients and natural compounds that might be
found in the juice. The use of monkey kola and golden apple fruits is still neglected
and primitive. Normal physiological processes (in vivo) result in the production of
free radicals. Oxidative stress is created when there is an insufficient
capacity of the biological system to neutralize excess free radicals. These may
result in aging and disease conditions as reported by Sahreen et al. (2014). Thus, the Fruits with the
most suitable antioxidant composition for consumption should be identified. In
general, their recommended intake is based on their concentration of vitamins,
minerals, and fibre, while little attention has been given to their glycemic
effects (Jenkins et al., 2011;
Ballali and Lanciai, 2012; Balisteiro et
al., 2013).
The
lack of good database and poor knowledge of the nutrient composition and quality
of underutilized fruits are some of the reasons for low fruit juice consumption
in developing countries like Nigeria (Grivetti and Ogle, 2000). Tropical
African sub-regions are home for many valuable fruit species whose potentials
have not been fully realized. Most of them have not been identified and
evaluated for their chemical and antioxidant properties and therefore are
underexploited. Although considerable amount of literature exists on the
importance and usefulness of different parts of these plants, there is little
or no information about their juices which is usually consumed.
1.3 JUSTIFICATION
There is need to process monkey kola and
golden apple fruits into a more stable, easier to use forms like juice, jams
and jellies in order to derive maximum benefit from it. Secondly, in order to
reduce the wastage and to get reasonable price of these fruits, processing and
preservation are necessary. The values of these fruits can be increased by
processing them to juice. Thus, this research would provide valuable
information on the nutritional and health potentials of mixed fruit juices from
monkey kola and golden apple fruits in the country where they are being
neglected as abandoned or underutilized.
Mixing
of fruit juices are normally done to increase their nutritional quality and
acceptability of such fruits especially monkey kola which usually have a hard
texture thereby limiting its consumption particularly to vulnerable group. More
so, the fresh-made seasonal beverages would provide more cost-effective
alternative to meet daily recommended needs. Fruits contain antioxidants which
play an important role in reducing the risk of degenerative diseases such as
cardiovascular disease, various cancers and neurological diseases. Many of
these phytochemicals may help to protect cells against the oxidative damage
caused by free radicals as reported by Wada and Ou (2002).
Therefore,
in continuation of research on the health potential and nutritional composition
of the poorly studied and underutilized plants, this work provides the first
report on the glycemic index, glycemic load and antioxidant activities of mixed
juice produced from monkey kola and golden apple. This study seeks to
investigate their possible physicochemical, antioxidant activity and glycemic
effect, so as to unravel new information and warrant their use.
1.4 OBJECTIVES OF THE
STUDY
The main objective of this study was
to evaluate the physicochemical, antioxidant activity, glycemic indices and
sensory properties of mixed fruit juice produced from Monkey kola (Cola lepidota) and Golden apple (Spondias dulcis).
The
specific objectives were to:
i. produce Monkey kola and Golden
apple juices and formulate mixed juices.
ii. determine
proximate composition of the fruits and the mixed fruit juices.
iii. determine
the physicochemical composition of the fruits and the mixed fruit juices.
iv. analyze antioxidants present and
antioxidant activity of the fruits and the fruit mixed
juices.
v. determine
glycemic index and glycemic load of the fruits
and mixed juices.
vi. evaluate
the sensory attributes of the mixed fruit juices.
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