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Effect of Different Drying Conditions on Ascorbic Acid
Content of Orange Fruit Using the Standard
Iodometric Method
Hanaa Mirghani Abdalla Elbadawi
B.Sc. (Honor) in Chemical Engineering Technology,
University of Gezira (2008)
A Dissertation
Submitted to University of Gezira in Partial
Fulfillment of the Requirements for the Award of the
Degree of
Master of Science
in
Chemistry
Department of Chemical Engineering and Chemical
Technology
Faculty of Engineering and Technology
April, 2017
2
Effect of Different Drying Conditions on Ascorbic Acid
Content of Orange Fruit Using the Standard
Iodometric Method
Hanaa Mirghani Abdalla Elbadawi
Supervision Committee
Name Position Signature
Dr. Mohammed Osman Babiker Main Supervisor …………..
Dr. Fathalrhman Abbas Elsheikh Co-Supervisor …………..
April, 2017
3
Acknowledgement
I wish to extend my thanks and gratitude to University of Gezira ,Facullty of Engineering and
Technology, Department of Chemical Engineering Technology. With sincere respect and deepest
gratitude I thank my advisorDr. Mohammed Osman Babikerfor his keen
supervision, support and guidance throughout this study. I would like to
express my grateful thanks to my co. supervisor Dr. Fathalrhman Abbas
Elsheikh. My thanks also to Ust. Hassan Anssariand all the staff of the Food Technology
Laboratories for their continuous help and encouragement. Finally Iwould like to thank all people whom
Ididn,t mention, but has contributed in one way or other to this work.
4
Effect of Different drying Conditions on Ascorbic Acid Content of
Orange Fruit Using The Standard Iodometric Method
Hanaa Mirghani Abdalla Elbadawi
Abstract
Ascorbic Acid (AA) vitamin C, is a valuable food component needed by all animals
and humans to prevent scurvy, a disease of the gums, bones and blood vessels.
The most prominent role of ascorbic acid is immune-stimulating effect, e.g.,
important for defense against infections such as common colds. Therefore, the
determination of ascorbic acid becomes increasingly important in Biochemistry,
pharmacology and nutrition. The aim of this study is to determine the effect of
different drying conditions on ascorbic acid content of orange fruit. The fruit
samples which were obtained from local market, were washed and cut into
pieces and dried in different conditions, room temperature, sunlight and in oven
at 60℃. After complete drying they were ground in mortar and packed in plastic
bags and labeled, AA content was analyzed in fresh and dried samples using
the standard idometric method, directly and by back titration. The results
obtained, in fresh peel samples AA was (9600mg/kg) and (9330mg/kg) for
direct and back titration methods respectively. Both results showed difference
with that reported for peel ( 9840 mg/kg ), in rag samples ( 5600mg/kg) and (
5330 mg/kg) for direct and back titration methods respectively, which also differ
from those reported in the literature (7860mg/kg). This could be due to the
climate, especially temperature which affects ascorbic acid content. On the other
hand for dried samples the AA was in order: room temperature-dried, sunlight-
dried and at 60 oven-dried samples, in peel samples AA was (6400 mg/kg &
6140 mg/kg(,)5860 mg/kg & 5600 mg/kg(and )5330 mg/kg & 5070 mg/kg ( for
direct and back titration methods respectively. For rag )4000 mg/kg & 3740
mg/kg(,)2930mg/kg& 2670 mg/kg ( and ) 2660 mg/kg & 2400mg/kg ( for direct
and back titration methods respectively. The results showed that as the
temperature increased the AA content decreased. It is concluded that there is
little difference in the results between direct and back titration methods. It is
recommended that, further work may be carried out to determine the ascorbic
acid content in orange using potentiometric methods to give a more comparative
results.
5
تأثير ظروف التجفيف المختلفة على محتوى حمض الاسكوربيك في فاكهة البرتقال باستخدام
الطريقه القياسية اليودية
هناء عبد الله البدوي ميرغني
الدراسةملخص
حمضضض الاسضضكوربيك ) فيتضضامي ي (ا هضضي مضضاد ذائ ةيمضضة غإاييضضة تحتضضاي اليهضضا ميضض الحيوا ضضائ و
الا سان لمن داء الاسقربوط ا وهو مضر ييضيا الل ضة والم ضام واةوعيضة الدمويضة والضدور اةبضر
لضدفا دضد لحمض الاسكوربيك هو تضأثير فضي تحفيضل الجهضا المنضاعي ا علضى سضبيل الم ضالا مهض ل
اةمرا م ل للائ البرد الشايمة. ولإلكا فإن تحديد حمض الاسكوربيك تلداد أهميته في الكيمياء
الحيويةا عل اةدويةا والتغإية. الهضدف مض هضإ الدراسضة هضو تحديضد تضأثيرظروف التجفيضف المختلفضة
سضضوغ غسضضل علضضى محتضضوى حمضضض الاسضضكوربيك فضضي فاكهضضة البرتقضضال. عينضضائ الفواكضضه ممضض مضض ال
وةطم الى ةط و فف في ظروف مختلفةا در ة حرار الغرفةا ودوء الشمس وفي الفرن على
م. بمد التجفيف الكامل طحن وعبأئ في أكياس بلاستيكية ورةمض ا تض تحليضل محتضوى حمضض 60
لمباشضر الاسكوربيك في المينائ الطا ة والمجففة باستخدام الطضرغ القياسضية اليوديضة ا بالممضاير ا
والر ميه. النتايج المتحيل عليها في عينائ القشور الطا ة فان محتوى حمضض الاسضكوربيك )
مضغ /كضغ ( مض الممضاير المباشضر والر ميضة علضى التضوالي ا هضإ النتضايج 9330مغ / كغ ( و 9600
5330مضغ / كضغ ( و) 5600مغ/كغ( أما عينائ اللضا )9840أظهرئ اختلاف ع المدروسة سابقا )
مغ/كضغ( 7860مغ/كغ ( م المماير المباشر والر مية على التواليا أظهرئ أيضا اختلاف عض )
ةد يمضلى هضإا الضي المنضااا خارضة در ضة الحضرار التضي تضوثرفي محتضوى حمضض الاسضكوربيك ا فضي
الجا ا الاخرا المينائ المجففة محتوى حمض الاسكوربيك و د بترتيا: في در ة حضرار الغرفضة
5860مضغ /كضغ (ا ) 6140مضغ / كضغ 6400م فضي القشضر ) 60أشمة الشمس وفي الفرن علضى ا
مضضغ / كضضغ( مضضض الممضضاير المباشضضضر 5070مضضغ / كضضضغ 5330مغ/كضضضغ ( و) 5600مضضغ / كضضغ
مضضغ / كضضغ 2930مضضغ / كضضغ( ا) 3740مضضغ /كضضغ 4000والر ميضضة علضضى التضضوالي. فضضي اللضضا )
مغ/كغ( م المماير المباشر والر مية على التوالي. 2400مغ/كغ 2660مغ / كغ( و) 2670
هإ النتايج أودح ا ضه كلمضا ارتفمض در ضة الحضرار فضان محتضوى حمضض الاسضكوربيك يضنخفضا
يتلخص م الدراسة أن هنالك اختلاف طفيف بي تضايج الممضاير المباشضر والر ميضة . تورضي هضإ
تحديد محتوى حمض الاسكوربيك في البرتقال باسضتخدام الطريقضة اللو يضة الدراسة بمليد م الممل ل
لمقار ة النتايج.
6
List of Contents
Subject Page No
Acknowledgement i
English Abstract ii
Arabic Abstract iii
List of Contents iv
List of Tables v
List of Figures vi
List of Abbreviations vii
CHAPTER ONE
1.1 Introduction 1
1.2 Etymology 2
1.3 Problem of The Study 2
1.4 Objective 2
1.5 Methodology of The Study 2
CHAPTER TWO: LITERATURE REVIEW
2.1 Background Biochemistry 4
2.1.1 Vitamin C Functions 4
2.1.2 History 5
2.1.3 IUPAC Name 5
2.1.4 Chemical Formula: 5
2.1.5 Molecular Structure 5
2.1.6 Properties 6
2.1.7 Dietary Sources 6
2.1.7.1 Plant Sources
6
2.1.7.2 Animal Sources 6
2.1.8 Animal and Human Supplements 7
2.1.9 General Benefits 7
7
2.1.10
Daily Requirements
8
2.1.11 Deficiencies 10
2.1.12
Method of Determination of AA 10
2.1.12.1 Titrametric Methods
10
2.1.12.1.1 Redox Titration
10
2.1.12.1.1.1 Titration Using Iodine
11
2.1.12.1.1.2 Titration Using Dcip
11
2.1.12.1.2 Potentiometric Method
11
2.1.12.3 Fluorometric Method
12
2.1.12.3 Colorimetric Methods
12
2.1.12.3.1 Determination of Total Vitamin C
12
2.1.12.3.2 Determination of Ascorbic acid(only)
13
2.1.12.4 Chromatographic Methods
14
2.1.12.1 Tlc Method
14
2.1.12.3.2 Hplc Method 14
2.1.13 Vitamin C Degradation 15
2.1.13.1 Effect of Environmental Factors on Degradation 15
2.1.13.1.1 Effect of Oxygen 15
2.1.13.1.2 Effect of Temperature 16
2.1.13.1.3 Effect of Light 16
2.1.13.1.4 Effect of pH 17
8
2.1.13.1.5 Effect of Enzymes 17
2.1.13.1.6 Metallic Catalyzers 17
2.1.14
Effect of Drying Process 18
2.1.14.1 Effect of Water activity 18
2.1.14.2 Effect of Temperature 19
2.2 Previous studies on vitamin c stability 19
CHAPTER THREE : MATERIALS AND METHODS
3.1 Materials 24
3.1.1 Samples Collections 24
3.1.2 Apparatus 24
2.1.3 Chemicals 24
3.2 Methods 25
3.2.1. Preparation of Reagents 25
3.2.2 Preparation of Samples 26
3.2.3 Titrations 27
CHAPTER FOUR: RESULTS AND DISCUSSION
4.1Results 29
4.1 Results of Direct Titration Method 29
4.2 Results of Back Titration Method 31
4.2Discussion 33
4.2.1 Fresh Samples Results 33
4.2.2 Room temperature-dried Results 33
4.2.3 Sunlight-dried Results 35
9
4.2.3 At 6℃0 oven-dried Results 36
CHAPTER FIVE CONCLUSSION & RECOMMONDATION
5.1 Conclusion 37
5.2 Recommendations 38
References 39
10
List of Tables
Table
No
Table Name Page
No
Table 2.1 Infants and
Children Daily
Requirements
9
Table 2.2 Adolescents Daily
Requirements
9
Table
2.3
Adults Daily
Requirements
9
The Results of Previous Studies on AA Stability
Table
2.4
Degradation of vitamin C
content in different citrus
juice during storage, vitamin C
in mg/100g
21
Table 2.5 Degradation of vitamin C
content in different types of
fruits with time and
temperature, vitamin C in
mg/100ml of fruits juice
21
Table 2.6 Effect of temperature on
vitamin C content in different
types of fruits, vitamin C in
22
11
mg/L
Table 2.7
Effect of heating on vitamin C
content of some selected
vegetables, vitamin C
mg/100ml
22
Table 2.8 Vitamin C content in some fruit juices, vitamin c
mg/100ml 23
Table 2.9 Degradation of vitamin C content in some fruits at
different temperatures, vitamin C in mg/100ml. 23
12
List of Figures
Fig
(1.1
)
AA and DHA structure 5
Fig
(2.2)
Reaction of AA with DCIP 11
Fig (2.3) Reaction of AA with
Orthophenylene Diamine
12
Fig.
(2.4)
Reaction of AA with2.4 DNPH 13
Fig( 2.5) Environmental Factors that affect
Degradation
15
Fig (2.6) Reaction routes AA or
derivatives participate
16
13
List of Abbreviations
AA
Ascorbic Acid
BDH British Drugs House
DCG Diketogulonic Acid
DCIP Dichloroindophenol
DHA Dehydroascorbic Acid
DNPH Dinitrophenyl Hydrazine
HPLC High Performance Liquid Chromatography
IUPAC International Union of pure and Applied Chemistry
SPFCL SP Fine Chemical Limited
14
CHAPTER ONE
1.1 INTRODUCTION
Regular consumption of fruits and vegetables is associated with reduced
risk of several types of diseases and promote a healthy life for human
beings. Fruits have a high content of fibre and vitamins, and are low in
calories and fat. Fruits are beneficial because of their content of vitamins,
anti-oxidants, micro-nutrients and minerals. Vitamins are a group of small
molecular compounds that are essential nutrients in many multi-cellular
organisms, and humans in particular. They serve as essential components of
specific coenzymes participating in metabolism and other specialized
activities. Among the vitamins, vitamin C (ascorbic acid) is an essential
micronutrient required for normal metabolic function of the body. Human
and other primates have lost the ability to synthesize vitamin C as a result
of a mutation in the gene coding for L-gulono lactone oxidase, an enzyme
required for the biosynthesis of vitamin C via the glucuronic acid pathway.
Thus, vitamin C must be obtained through the diet. Vitamin C plays an
important role as a component of enzymes involved in the synthesis of
collagens .Vitamin C is the major water – soluble antioxidant within the
body. It lowers blood pressure and cholesterol level. Not only does a
vitamin C intake markedly reduce the severity of a cold, it also effectively
prevents secondary viral or bacterial complications. Numerous analysis
have shown that an adequate intake of vitamin C is effective in lowering the
risk of developing breast cancer, cervix, colon, rectum, lung, mouth,
prostate and stomach.This vitamin is especially plentiful in fresh fruit, in
particular citrus fruit, and vegetables. Because of its health benefits
therefore, the determination ofascorbicacidbecomes increasingly important in
Biochemistry , pharmacology and nutrition .
15
1.2 Etymology
The term vitamin was derived from "vitamine", acoined in 1912 by the
Polish biochemist Kazimierz Funk when working at the Lister Institute of
Preventive Medicine. The name is from vital and amine, meaning amine of
life, because it was suggested in 1912 that the organic micronutrient food
factors that prevent beriberi and perhaps other similar dietary-deficiency
diseases might be chemical amines, but after it was found that other such
micronutrients were not amines the word was shortened to vitamin in
English.
1.3 Problem of the Study
Ascorbic acid which is an effective reducing agent belongs to endiol group
it is easily degraded by atmospheric oxygen. Its oxidation can be
accelerated by excessive heat and light.
1.4 Objective of the Study
The main objective of the present study is to determine the effect of
different drying conditions on vitamin C content of orange fruit.
1. To process and dry fruit samples under different conditions
2. To determine which of the above method degrade more ascorbic acid
and therefore form the basis for recommendation to the public.
1.5 Methodology of the Study
On the basis of reducing property of ascorbic acid, it can be determined
chemically by titrating against an oxidizing agent such as iodine solution.
This method determines the vitamin C concentration in a solution by a
redox titration using iodine and sodium thiosulfate. As the iodine is added
to the sample solution
16
the ascorbic acid is oxidized to dehydroascorbic acid, while the iodine is
reduced to iodide ions.
Once all the ascorbic acid has been oxidized, the excess iodine is free to
react with the starch indicator, forming the blue-black starch-iodine
complex which is titrated with sodium thiosulfate to form colorless solution
and this is end point of titration.
Equation (1.1) : Reaction of Excess iodine with sodium thiosulfate
I2+ 2Na2s2o3 →2NaI + Na2s4o6
17
CHAPTER TWO
LITERATURE REVIEW
2.1 Background Biochemistry
Vitamin C is an electron donor (reducing agent or antioxidant), and
probably all of its biochemical and molecular functions can be accounted
for by this function.
2.1.1 Vitamin C Functions
Ascorbic acid ( vitamin C ), is a valuable food component needed by all
animals and humans to prevent scurvy, a disease of the gums, bones and
blood vessels. The most prominent role of vitamin C is its immune-
stimulating effect, e.g., important for defense against infections such as
common colds. It also acts as an inhibitor of histamine, a compound that is
released during allergic reactions. As a powerful antioxidant it can
neutralize harmful free radicals which are produced through biological
processes and it aids in neutralizing pollutants and toxins. Thus it is able to
prevent the formation of potentially carcinogenic nitrosamines in the
stomach (due to consumption of nitrite-containing foods, such as smoked
meat). Vitamin C lowers blood pressure and cholesterol level. Not only
does a vitamin C intake markedly reduce the severity of a cold, it also
effectively prevents secondary viral or bacterial complications. Numerous
analysis have shown that an adequate intake of vitamin C is effective in
lowering the risk of developing breast cancer, cervix, colon, rectum, lung,
mouth, prostate and stomach. This vitamin is especially plentiful in fresh
fruit, in particular citrus fruit, and vegetables. Because of its health benefits,
the determination of ascorbic acid becomes increasingly important in
Biochemistry, pharmacology and nutrition.
18
2.1.2 History
Vitamin C is a small carbohydrate molecule first identified in the 1920by
Albert VanSzent Gyorgyi, who discovered that it was able to prevent and
cure scurvy. Scurvy is a pathological life threatening condition suffered by
people who do not have access to fruits or vegetables for long periods of
time. A decade earlier, kazimierz Funk had prepared a list of nutritional
factors called vitamins, whose deficiencies cause severe diseases in
humans. In his list, Funk used the Letter “C” to designate a factor still
unidentified, but known to prevent scurvy. Later on, Szent Gyorgyi and
Haworth chemically identified C as Ascorbic acid, and named it so because
it is one of the most popular drugs in human history.
2.1.3 Iupac Name
5-(1,2-dihydroxyethyl)-3,4-dihydroxyfuran-2-one
2.1.4 Chemical Formula
Ascorbic acid is asix-carbon compound structurally relatedto
glucose(C6H8O6)
2.1.5 Molecular structure
L-ascorbic acid is a monobasic acid with an enediol group built into a five
membered heterocyclic lactone ring. The structure of dehydroascorbic acid,
the first oxidation product of ascorbic acid (Fig2.1)
Figure 2.1Ascorbic acid and dehydroascorbic acid. Ascorbic acid is the reduced form of vitamin C. The
oxidized form, dehydroascorbic acid
19
1.1.6 Properties
Ascorbic acid is a colorless and odorless crystalline substance, slightly
sour in taste and optically active. It is soluble in water and alcohol but
practically insoluble in chloroform, ether and light petroleum. Stable under
ordinary conditions and readily destroyed by exposure to heat, light, and
air. This vitamin is also rapidly destroyed by alkalis but is fairly stable in
weak acid solutions. It has melting point about 190ºC (374ºF), boiling point
about 553ºC (1027ºF), density 1.694 g/cm3 and molar mass
176.12g/molecular.
2.1.7 Dietary Sources
2.1.7.1 Plant Sources
While plants are generally a good source of vitamin C, the amount in foods
of plant origin depends on the precise variety of the plant, soil condition,
climate where it grew, length of time since it was picked, storage
conditions, and method of preparation.
Vitamin C is widely present in fruits and vegetables. Citrus fruits(e.g.
orange, lemons, grapefruit), peppers, green vegetables and soft fruits such
as strawberries, guava, mango, watermelon and kiwi are particularly rich
dietary food sources of vitamin C.
2.1.7.2 Animal Sources
The majority of animals synthesize their own vitamin C therefore, some
animal products can be used as sources of dietary vitamin C. Vitamin C is
mostly present in the liver and least present in the muscle. Since muscle
provides the majority of meat consumed in the human diet, animal products
are not a reliable source of the vitamin.
20
2.1.8 Animal and Human Supplements
Vitamin C is used in human and animal nutritional health. In animal
nutrition, it is used as supplements in the aquaculture industry for example.
Ascorbic acid is used in fish farming to prevent scurvy and enhance
immune response. For humans, Vitamin C is offered in the form of
conventional tablets, chewable tablets, syrups, powders, granules, capsules,
drops and ampoules, either alone or in multivitamin-mineral preparations.
2.1.9 General Benefits
The uses of ascorbic acid or vitamin C depend on its chemical properties as
an antioxidant or on its health-related properties. The benefits of Vitamin C
include:
2.1.9.1 Allergy and Asthma Relief
Vitamin C is present in the lung’s airway surfaces, and insufficient vitamin
C levels have been associated with bronchial constriction and reduced lung
function. Some studies have associated vitamin C supplementation with
asthmatic symptom relief.( Sizer, Frances &Whiteny, Eleanor., 1997).
2.1.9.2 Cancer Prevention
A large number of studies have shown that increased consumption of fresh
fruits and vegetables is associated with reduced risk for most types of
cancer. (Muhammad et al., 2014).
2.1.9.3 Cataract Prevention
Decreased vitamin C levels in the lens of the eye have been
associated with increased severity of cataracts in humans. Some studies
have observed increased dietary vitamin C intake and increased blood
levels vitamin C to be associated with decreased risk of cataract.(
Muhammad et al., 2014).
21
2.1.9.4 Collagen Production
Vitamin C assists the body in the manufacture of collagen, a protein that
binds cells together Collagen is critical to the health of the skin, cartilage,
ligaments, corneas, and other bodily tissues.( M.A.Bakir., 2011).
2.1.9.5 Immune System Booster
Vitamin C increases white blood cell production and is important to
immune system balance. Studies have related low vitamin C levels to
increased risk for infection. Vitamin C is frequently prescribed for HIV-
positive individuals to protect their immune system.( Sizer, Frances
&Whiteny, Eleanor., 1997).
2.1.9.6 Hypertension Prevention
Individuals with high blood pressure(hypertension) are at increased risk of
developing cardiovascular diseases, several studies demonstrated a blood
pressure lowering effect of vitamin C supplementation. A study in
individuals with hypertension found that vitamin C supplementation with
500mg/day for six weeks slightly decreased systolic blood pressure.(
Muhammad et al., 2014)
2.1.10 Daily Requirements
The daily requirement of vitamin C varies according to age, sex, risk group
cigarette smokers, alcohol users, and subjects on certain drugs). The best
way to get the daily requirement of essential vitamins, including vitamin C,
is to eat a balanced diet that contains a variety of foods. Vitamin C should
be consumed every day because it is not fat-soluble and, therefore, cannot
be stored for later use. Acording to (Sizer, Frances &Whiteny, Eleanor.,
1997). The Food and Nutrition Board at the Institute of Medicine
recommends the following amounts of vitamin C:
22
Table 2.1 Infants and Children Daily Requirements:
No Age Mg/day
1 1 - 6 months 40
2 7 - 12 months 50
3 1 - 3 years 15
4 4 - 8 years 25
5 9 - 13 years 45
Table 2.2 Adolescents Daily Requirements:
Gender Age Mg/Day
Girls 14-18 65
Boys 14-18 75
Table 2.3 Adults Daily Requirements:
Gender Age Mg/Day
Women 19 and older 75
Men 19 and older 90
23
2.1.11 Deficiencies
First symptoms of early vitamin C deficiency are very general and could
also indicate other diseases. They include fatigue, loss of appetite,
drowsiness and insomnia, low resistance to infections. Severe vitamin C
deficiency leads to scurvy, characterized by weakening of collagenous
structures, resulting in widespread capillary bleeding. Infantile scurvy
causes bone malformations. Bleeding gums and loosening of the teeth are
usually the earliest signs of clinical deficiency. Nowadays this is rare in
developed countries and can be prevented by a daily intake of about 10-15
mg of vitamin C. However, for optimal physiological functioning much
higher amounts are required.
2.1.12 Methods of Determination of AA
There are many methods that are employed for the quantitative
determination of vitamin C such as titrimetric, fluorometric, colorimetric
and liquid chromatographic methods. All the methods have great limitation
in use for different purpose, because each samples type have its own
specific characteristics and properties in trems of extraction, purification,
interference of other compounds (such as color, presence of oxidizing,
reducing components etc). On the basis of reducing property of ascorbic
acid, it can be determined chemically by titrating against an oxidizing
agent.
2.1.12.1 Titrimetric Methods
2.1.12.1.1 Redox Titration
Redox titration is the common determination method of vitamin C in food.
This method shows better results than a normal acid-base titration due to
the presence of other acids, apart from ascorbic acid, which can interfere in
the oxidation of the primary acid and hence change the results.( David.A et
al., 1991).
24
2.1.12.1.1 .1Titration Using Iodine Solution
This method is the most common method in determination ascorbic acid
and is based on the calibration of iodine solution with the acid extract. As
the iodine is added during the titration, the ascorbic acid is oxidized to
dehydroascorbic acid, while the iodine is reduced to iodide ions.(see page 3
)(Muhammad et al. 2014).
ascorbic acid + I2 → 2 I− + dehydroascorbic acid
2.1.12.1.1.2 Titration Using Dichloroindophenol (DCIP)
The amount of vitamin C in a sample will be determined by redox titration
using the reaction between ascorbic acid and dichloroindophenol dye
(DCIP). DCIP is used as the titrant because it will act as a self-indicator in
the titration When the dye is added to the sample the blue colour
disappears. The solution will remain colorless, as long as there is vitamin is
not oxidized and if the end of all the vitamin we findthat the addition of
points of the dye turn it to pink colour and this is the end point of
titration.(Qasim Y. M.; Wali M. H.; Emad K.M; 2009)
Fig (2.2) : Reaction of A.A with DCIP
2.1.12.1.2 Potentiometeric Titration
This method is preferred in coloured or very diluted solutions. All we need
in this method is a guide electrode (glass electrode) that responds to the
hydrogen concentration and reference electrode (standard calomel
25
electrode) connects to ph meter. The voltage is recorded after each addition
of the standardized solution(iodine for example ) to the sample solution.
From the correlation curve between voltage and volume the concentration
of ascorbic acid in unknown sample can be measured.(Mohammed
Bastawisi& Mohammed Mahmoud., 2000 )
2.1.12.2 Fluorometric Method
The amount of ascorbic acid in unknown samples can be measured by
fluorescence. Ascorbic acid or vitamin C does not fluoresce. This method is
based on oxidation of ascorbic acid to dehydroascorbic, which reacts with
orthophenlene diamine in the presence of sulphuric acid to produce
quinoxaline ( fluorescent compound ). The fluorescent spectrophotometer
then is applied to determine the fluorescence intensity of the quinoxaline
generated. The fluorescence intensity is proportional to the concentration of
ascorbic acid. By reading the emission intensity of the standard solution and
sample, the concentration of ascorbic acid in the unknown sample can be
measured. (Mohammed Bastawisi& Mohammed Mahmoud., 2000 )
Fig (2.3) : Reaction of A.A with Ortho phenylene diamine
2.1.12.3 Colorimetric Methods
2.1.12.3.1 Determination of Total vitamin c
This is a simplified method for the simultaneous determination of the total
vitamin C. The method involves the oxidation of ascorbic acid to
dehydroascorbic acid by adding a few drops of bromine waterL-
26
dehydroascorbic acid formed reacts with 2,4- dinitrophenylhydrazine and
produces an osazone of red colour. ( Rahman ,Khan and Hosain., 2007 ).
The reaction involves two reactions:
1. An addition-elimination Reaction
Dehydroascorbic acid react with 2,4dinitrophenyl hydrazine this step
contain nucleophilic addition of the -NH2 group to the C=O carbonyl
group which result in elimination of a water molecule from the
functional group
2. Coupling Reaction
Next step involves reaction of one equivalent of dinitrophenlosazone
formed with two equivalents of 2,4dinitrophenyl hydrazine (excess).
First 2,4dinitrophenyl hydrazine is involved in oxidizing the alpha
carbon to a carbonyl group, and the second 2,4dinitrophenyl hydrazine
involves in removal of one water molecule with the formyl group of that
oxidized carbon and forming the similar carbon nitrogen bond osazones
are highly colored compounds and can be easily detected fig (2.4).
Fig (2.4): Reaction of A.A with 2.4 DNPH .
2.1.12.3.2 Determination of Ascorbic Acid
This method is used to estimate the ascorbic acid of the sample extract. The
ascorbic acid is oxidized to dehydroascorbic acid with excess of 2,6
27
dichloroindophenol dye, which gives a red colour of reduced dye form. The
uv-visible spectrophotometer then is applied to determine the absorption. The
absorption of visible light is proportional to the amount of ascorbic acid in
the sample. From the calibration curve between the absorption of standard
solutions and their concentrations, the ascorbic acid in unknown sample can
be measured.(Reaction of AA with Dcip was explained on fig
2.2)(Mohammed Bastawisi& Mohammed Mahmoud., 2000 )
2.1.12.4 Chromatographic Methods
Chromatography technique for separating mixture components. Usually
prefered on other methods. Because of the quality and accurate separation it
is often used In biochemistry and analytical chemistry to separate, identify
and measure the compounds in a mixture.
2.1.12.4.1 Thin layer Chromatography (TLC )
The tlc method is used to identify the ascorbic acid. Ascorbic acid is
oxidized to dehyroascorbic acid with bromine water, which react with 2,4-
dinitrophenylhydrazine to form DAA-osazone. Other osazones are also
formed beside the osazone and tlc is used for their separation. Before tlc
separation the osazone precipitate must be filtered, washed, dehydrated and
dissolved in an organic solvent. The amount of DAA-osazoneis visually
determined by comparison of spot areas with calibration spots.(Ragaa
Elhassan. 2015).
2.1.12.4.2 High-performance liquid chromatography (HPLC )
High-performance liquid chromatography with spectrophotometric
detection has been used to separate and estimate ascorbic acid and
dehydroascorbic acid. These components of vitamin C are resolved on a
Lichrosorb-NH2 column (stationary phase). The technique is suitable for
assay of vitamin C in biological samples, foods, and pharmaceutical
vitamin preparations. The standard solutions and extracts must be filtered
through a membrane before their injection in the chromatograph. Ascorbic
28
Acid peak identify by comparing its uv-isible spectral characteristics and
retention time with a commercial standard of ascorbic acid(K.M. Phillips et
al., 2010).
2.1.13 Vitamin C Degradation
Ascorbic acid (AA) is an important component of our nutrition and used as
additive in many foods because of its antioxidant capacity. Thus, it
increases quality and technological properties of food as well as nutritional
value. However, AA is an unstable compound and under less desirable
conditions it decomposes easily depending on several variables. It has been
reported that the degradation kinetics are significantly affected by many
environmental factors such as pH, temperature, light, the presence of
enzymes, oxygen, and metallic catalyzers.This dependence is illustrated in
Fig. (2.5)
Fig. (2.5) : Environment factors that affect degradation kinetics
2.1.13.1 Effect of Environmental factors on Degradation
2.1.13.1.1 Effect of Oxygen.
Oxygen is the most destructive element in fruits causing degradation of
ascorbic acid. Depending on the conditions, two different types of
degradation occur: aerobic and anaerobic degradation. The mechanism of
anaerobic degradation is complex and has not been fully established. This
29
type of degradation is relatively insignificant in most food products. It is
observed in thermally preserved citrus juices. On the other hand, the
aerobic conditions characterized by the reversible oxidation of ascorbic acid
(AA) to dehydroascorbic acid (DHA), which also exhibits biological
activity. Further irreversible oxidation of DHA generates diketogulonic acid
(DCG),which has no biological function.(P.H.S. Santos and M. A. Silva.,
2010). The reactions in which ascorbic acid and its derivatives participate
can be summarized in the Fig ( 2.6).(David.A et al., 1991).
Fig( 2.6): Reaction routes in which vitamin C or derivatives participate
2.1.13.1.2 Effect of Temperature
Temperature is Important factor that also affects the degradation reaction
it has been described as one of the main factors that significantly influence
the stability of vitamin C in solution. The effect of the high temperature
may increase the motion energy of the particles, inducing a more collision
,thus allow to a greater number of particles to react which result in
increasing the rate of oxidation, and consequently more degradation on the
content of ascorbic acid.(P.H.S. Santos and M. A. Silva., 2010).
2.1.13.1.3 Effect of light
It has reported that, the light has influence on the degradation reaction.
When the light intensity was increased, ascorbic acid degradation enhanced.
Rohan V Tikekar.(2010) proposed that uv light processing of ascorbic acid
leads to formation of ascorbate radical that leads to the formation of
30
dehydroascorbic acid, which further degrades into 2.3-diket-gulnic acid this
can be attributed to the fact that lights can be also a source of energy to
promote the degradation.
2.1.13.1.4 Effect of pH
Many studies were carried out to determine the relationship between pH
and oxidation of ascorbic acid, (Gramlich, Zhang and Nau., 2002)
Investigated how does the pH value of a solution containing ascorbic acid
affect ascorbic acid conent in the solution due to oxidation by oxygen. At
low pH solutions, the H+ concentrations are high, the more H+ ions present
to oxidize the ascorbic acid, and hence more ascorbic acid degrades to
become dehydroascorbic acid. Their experiments results demonstrated that
vitamin C degrades (or is oxidized) more quickly at a low pH medium.
2.1.13.1.5 Effect of Enzymes
Enzymatic browning is very common at the cut surface of light-colored
fruits(apples, bananas ) and vegetables (potatoes). Browning takes place
when enzymes contain copper and iron, catalyze the oxidation of ascorbic,
to form dehydroascorbic. Further irreversible oxidation of DHA generate
furfural of brown pigments in the presence of oxygen .
Ascorbic acid dehydroascorbicacid furfural
Brown color
2.1.13.1.6 Metallic Catalyzers
Iron(II) is oxidized by hydrogen peroxide to iron(III), forming a hydroxyl
radical and a hydroxide ion in the process. Ascorbic acid can recycle Fe(III)
to Fe(II) facilitating further generation of reactive oxygen species
1. 2 Fe2+
+ 2 H2O2 → 2 Fe3+
+ 2 OH• + 2 OH
−
2. 2 Fe3+
+ Ascorbate → 2 Fe2+
+ Dehydroascorbate
31
2.1.14 Effect of Drying Process
During the drying process of fruits and vegetables, several variables
influence the degradation, which makes this phenomenon quite complex.
These variables as shown below:
2.1.14.1 Effect of Water Activity
The important parameters that influence the ascorbic acid degradation
during drying process are water activity and temperature.( Lee and
Labuza,1975 ). According to the authors, the mechanism by which water
controls the degradation reaction is very complex and it might possibly
change depending on water content. High water activity, may dilute the
ascorbic acid concentration, inducing a low degradation rate. However,
increasing the water content, the aqueous phase becomes less viscous,
enhancing diffusion in the media. These effects facilitate the reaction of
oxidation and consequently the degradation.(P.H.S. Santos and M. A.
Silva., 2010).
2.1.14.2 Effect of Temperature
Effect of temperature was explained on page 16.
32
2.2 Previous Studies on Vitamin C Stability
Stability is a key problem of ascorbic acid analysis since this compound is
very unstable in aqueous solution. Temperature has been described as one
of the main factors that significantly influence the stability of vitamin C in
solution.
Degradation of vitamin C content in citrus juice concentrates during storage
(orange, lemon and tangerine) was investigated. All juices were stored in
darkness at 28, 37 and 45 _C for eight weeks. Ascorbic acid content was
determined every week. Results obtained(Table 2.4) showed that ascorbic
acid in citrus juice concentrates decreased with increasing
temperature.(FeryalKaradeniz et al,2006).
Degradation of vitamin C content in different types of fruits with time and
temperature was investigated. The results (Table 2.5)revealed that in both
boiled and stored juices there was a decrease in vitamin C content in
comparison with fresh juice, however the significant degradation was
observed in boiled one. From above it was concluded that high temperature
has effects on vitamin C content of fruits, blanching in hot water can cause
an appreciable loss in vitamin C that is thermally labile(Abubakar El-Ishaq,
Simon Obirinakem,2008).
Effect of temperature on vitamin C content in different types of fruits was
investigated. The juice from samples were extracted and analyzed at
different temperatures the results obtained (Table 2.6)showed that increase
in temperature generally reduced vitamin C content ( P.C.njoku, A.A. ayuk
,2011 )
Effect of heating on vitamin C content of some selected vegetables was
investigated .The heating time was varied (i.e. 5, 15 and 30 mins
respectively) while the temperature was kept constant (i.e. 60°C). The
results (Table 2.7) revealed that the vitamin C content of the raw vegetables
is generally high when compared with the heated. It was also observed that
heating affected the vitamin C content of all the vegetables, as the heating
33
time increased, the vitamin C content decreased.(N.C. Igwemmar, S.A.
Kolawole and I.A. Imran,2013)
Vitamin C content in some packed (industrial) fruit juices was investigated
to compare the values with that labeled on the packed fruit juices. The
results obtained (Table 2.8)revealed that there was a little difference
between the amount labeled and the amount calculated, in all cases the
amount calculated was less than labeled, that refers to unstable vitamin.
(Samira Ben Mussa and Intisar El Sharaa,2014).
Degradation of vitamin C content in some fruits at different temperatures
was investigated. The juice from samples were extracted and analyzed. The
results obtained (Table2.9) showed that as we increase the temperature the
vitamin C content decreases gradually ( Kaleem et al,2016).
34
2.3 The Results of Previous Studies on AA Stability
Table 2.4: Degradation of vitamin C content in different citrus juice during
storage, vitamin C in mg/100g.(Feryal Karadeniz et al,2006).
Fruit Temp Storage1 day Storage 60 day
Orange
28 232.9 194.9
37 232.9 52.4
45 232.9 39.3
Tangerine
28 97.9 65.0
37 97.9 23.1
45 97.9 14.8
Table 2.5 : Degradation of vitamin C content in different types of fruits
with time and temperature, vitamin C in mg/100ml of fruits
juice.(Abubakar El-Ishaq, Simon Obirinakem,2008).
Sample Room Tem Temperature of40 7 Days Storage
Pineapple 49.38 ±1.87 26.25 ±1.70 42.13 ± 0.87
Orange 39.75 ±1.00 23.00 ±1.52 31.50 ±1.00
Water melon 27.50 ±1.25 16.70 ±1.42 21.63 ±1.62
35
Table 2.6 : Effect of temperature on vitamin C content in different types of
fruits, vitamin C in mg/L.( P.C.njoku, A.A. ayuk ,2011 ).
Temp Grape orange Lemon
20 454.57 612.15 305.75
40 432.69 577.14 275.11
50 432.69 577.14 275.11
70 380.16 550.87 248.85
Table(2.7): Effect of heating on vitamin C content of some selected
vegetables, vitamin C mg/100ml.(N.C. Igwemmar, S.A. Kolawole and I.A.
Imran,2013).
Vegtable Raw sample 5 Mins 15 Mins 30 Mins
Peaper 61.56
54.32 39.84 21.72
Green Pea 43.44
38.84 28.96 18.12
Carrot 25.36
21.7 14.48 10.88
36
Table 2.8 :Vitamin C content in some packed fruit juices, vitamin c mg/
100ml.( Samira Ben Mussa and Intisar El Sharaa,2014)
Fruit amount labeled amount calculated
Apples 10 9.27± 0.00
Mixed Fruit 20 19.47± 0.42
Pineapple 30 26.88± 0.42
Orange 35 32.45± 0.10
Table 2.9 : Degradation of vitamin C content in some fruits at different
temperatures, vitamin C in mg/100ml. (Kaleem et al,2010).
Fresh fruits AA at 25°C AA at 50°C AA at max. heating
Lemon
10.0 6± 0.03
9.33 ± 0.09
52°C 6.66 ± 0.6
Apple
1.70 ± 0.00
2.50 ± 0.00
67°C
1.03 ± 0.03
Orange
1.96 ± 0.12
1.66 ± 0.02 55°C 1.53 ± 0.26
37
CHAPTER THREE
MATERIALS AND METHODS
3.1 Materials
3.1.1 Samples Collections
Orange fruits were purchased randomly from the market. The fruits were
washed with tap water, they cut into four pieces. The peel was separated
and the pulp was squeezed to remove the juice and obtain the rag. The
(peel & rag) dried at different conditions (room temperature, sun light and
60), until it dried completely. The dried samples were ground properly
using a mortar grinder to obtain the powdered form then they were packed
in plastic bags, labeled and transported to the laboratory.
3.1.2 Apparatus:
The equipments used in this research work include
1.1.1.1 Blender
1.1.1.2 Mortar and Pestle
1.1.1.3 Weighing balance
1.1.1.4 Oven.
2.1.3. Chemicals
1.1.1.1 Standard Ascorbic Acid was from BDH _ England
1.1.1.2 Potassium Iodide was from LT C _ India
1.1.1.3 Iodine Solid was from SPFCL_ India
1.1.1.4 Sodium Thiosulphate was from LT C _ India
1.1.1.5 Starch Indicator Solution
38
3.2. Methods
3.2.1 Preparation of Reagents
3.2.1.1 Standard Ascorbic Acid : ( 1mg/ml)
50 mg of standard ascorbic acid were weighed out and dissolved in 50 ml
distilled water.
3.2.1.2 Iodine Solution: (0.05 M)
10.7 g of iodine were placed in a 100 ml beaker. 2g of potassium iodide
were added to it, about 15 ml of distilled water were added and the
mixture was swirled for a few minutes. The resulting solution was
transferred quantitatively to a 500 ml volumetric flask and diluted to
volume with distilled water.
3.2.1.3 Starch Indicator Solution : (0.1%)
0.1 g of soluble starch was added to 100 mL of near boiling water in a 250
ml beaker, Stirred to dissolve and cooled before use.
3.2.1.4 Sodium Thiosulfate : (0.1M)
12.4 g of sodium thiosulfate were placed in a 500 ml volumetric flask, 100
ml distilled water were added and swirled until it dissolved then the volume
was completed with distilled water.
39
3.2.2 Preparation of Samples
3.2.2.1 Fresh Samples
20 g of each sample (peel & rag) grind in a mortar with 400 ml distilled
water. The juice obtained was filtered and 10 ml transferred into 250 ml
conical flask. 5ml iodine solution was added to the sample and stored in
dark for half an hour then titrated with sodium thiosulfate.
3.2.2.2 Room Temperature-dried samples
5g room temperature-dried of each sample (peel & rag) blended in a food
processor with 100 ml distilled water for two minute. The juice obtained
was filtered and 10 ml transferred into 250 ml conical flask. 5ml iodine
solution was added to the sample and stored in dark for half an hour then
titrated with sodium thiosulfate.
3.2.2.3 Sun light-dried samples
5g sunlight-dried of each sample (peel & rag) blended in a food processor
with100 ml distilled water for two minute. The juice obtained was filtered
and 10 ml transferred into 250 ml conical flask. 5ml iodine solution was
added to the sample and stored in dark for half an hour then titrated with
sodium thiosulfate
3.2.2.4 At 60 oven-dried samples
5g oven-dried of each sample (peel & rag) blended in a food processor
with100 ml distilled water for two minute. The juice obtained was filtered
and 10 ml transferred into 250 ml conical flask. 5ml iodine solution was
added to the sample and stored in dark for half an hour then titrated with
sodium thiosulfate.
40
3.2.3 Titrations
3.2.3.1 Direct Titration Method
In this method ascorbic acid was analyzed according to the method of
Muhammad et al, (2014)
1. 10 ml aliquot of the sample were pipetted into a 250 ml conical
flask. 1ml starch indicator solution was added.
2. The sample was titrated with .05M iodine solution. The
endpoint of the titration was identified by the appearance of
permanent trace of a dark blue_blackcolour due to the
starch_iodine complex.
3. The titration was repeated three times with further aliquots of
sample solution until concordant results (titers agreeing within
0.1 mL) was obtained
3.2.3.2. Indirect Titration Method (Back Titration).
In this method ascorbic acid was analyzed according to the method
of Samira Ben Musa and Intisar Elsharaa.(2014)
1. 10 ml aliquot of the sample were pipetted into a 250 ml conical flask
2. 5ml (.05 M) iodine solution was added to the sample and stored in dark
for half an hour.
3. 1ml starch indicator solution was added and titrated (Blue Solution) with
sodium thiosulfate (.1 M ).The end point of the titration was identified by
the appearance of colorless solution.
4.The titration was repeated three times with further aliquots of sample
solution until concordant results (titers agreeing within 0.1 mL) was
obtained.
41
Calculations
Ascorbic acid content was calculated from equation below:
C1 = ( V1÷ V2)× C2
Where :
C1 : Ascorbic Acid concentration of sample in ppm
V1: Iodine volume used for sample A.A
C2 : Standard Ascorbic Acid concentration in ppm
V2: Iodine volume used for standard A.A
For Direct Titration Method
V: Iodine volume obtained directly from burette.
For Indirect Titration Method
V= Total volume of iodine - (volume react with Sodium Thiosulphate)
2
42
CAHPTER FOUR
RESULTS AND DISCUSSION
4.1 Results of Direct Titration Method
4.1.1 Fresh Samples Results
Table 4.1 : Ascorbic acid content in fresh samples mg/kg
Sample
Iodine volume
(Average of three readings)
AA PPM
(Average of three readings)
Rag 2.1 5600
Peel 3.6 9600
4.1.2 Room Temperature-dried Results
Table 4.2: Ascorbic acid content in room temperature-dried samples mg/kg
Sample Iodine volume
Average of three readings
AA PPM
Average of three readings
Rag 1.5 4000
Peel 2.4 6400
43
4.1.3 Sun light-dried Samples Results
Table4.3: Ascorbic acid content in sunlight-dried Samples mg/kg
Sample Iodine volume
(Average of three readings)
AA PPM
Average of three readings)
Rag 1.1 2930
Peel 2.2 5860
4.1.4 At 60 C Oven-dried Samples Results
Table 4.4 : Ascorbic acid content in oven-dried samples mg/kg
Sample Iodine volume
(Average of three readings)
AA PPM
(Average of three readings)
Rag 1.0 2660
Peel 2.0 5330
44
4.2 Results of Indirect Titration Method
4.2.1 Fresh Samples Results
Table 4.5: Ascorbic acid content in fresh samples mg/kg
Sample
Thio volume
Average of three readings
Iodine volume
Average of three reading
AA PPM
Average of three readings
Rag 6.0 2.0 5330
Peel 3.0 3.5 9330
4.2.2 Room Temperature-dried Results
Table 4.6: Ascorbic acid content in room temperature-dried samples mg/kg
Sample
Thio volume
Averageof three readings
Iodine volume
Average of three reading
AA PPM
Average of three readings
Rag 7.2 1.4 3740
Peel 5.4 2.3 6140
45
4.2.3 Sun light-dried Samples Results
Table4.7: Ascorbic acid content in sunlight-dried Samples mg/kg
Sample Thio volume
Average of three readings
Iodine volume
Average of three readings
AA PPM
Average of three readings
Rag 8.0 1.0 2670
Peel 5.8 2.1 5600
4.2.4 At 60 C Oven-dried Samples Results
Table 4.8: Ascorbic Acid Content in Oven-dried Samples mg/kg
Sample Thio volume
Average of three readings
Iodine volume
Average of three readings
AA PPM
Average of three readings
Rag 8.2 0.9 2400
Peel 6.2 1.9 5070
The results of Ascorbic Acid contents were average of three analysis.
These result shows differences in values of AA content at different
conditions.
46
4.3 Discussion
The results of Ascorbic Acid contents were average of three analysis.
These results shows differences in values of AA content at different
conditions. The mean values of the AA contents were of the order, fresh
samples, room temperature-dried, sunlight-dried and oven-dried samples at
60℃.
4.3.1 Fresh Samples Results
The results showed that AA content in fresh peel samples from direct and
indirect methods 9600 mg/kg & 9330 mg/kg respectively, was higher than
fresh rag 5600 mg/kg & 5330 mg/kg. While the dried sample recorded the
lowest content of AA. All drying methods significantly cause loss of
vitamin C.
4.3.2 Room temperature-dried Results
4.3.2.1 Direct Titration Results
The AA content in room temperature-dried samples ( 6400 mg/kg ) and
(4000 mg/kg ) for peel and rag respectively, the results obtained showed
that there was degradation in AA content in both samples. The difference
in AA content of fresh peel samples and room temperature-dried samples
was (3200 mg/kg) however, in rag samples the difference in AA content
was (1600 mg/kg).
4.3.2.2 Indirect Titration Results
The AA content in room temperature-dried samples (6140 mg/kg) and
(3740 mg/kg) for peel and rag respectively, the results obtained also
showed that there was degradation in AA content. The difference in AA
content of fresh peel samples and room temperature-dried samples was
47
(3190mg/kg) however, in rag samples the difference in AA content was
(1590 mg/kg).
The degradation in AA content of fresh samples may return to effect of
many factors:
1. Preparation of Samples
The loss of AA can occur by chemical degradation during preparation step.
The water content of orange fruit is higher than 86% and because of the
high solubility of AA in water, there was potential for significant losses by
leaching from freshly cut fruit.
2. Exposure to oxygen ( see page 14)
The most degradation showed in peel samples, this may return to that
suggested the degradation of ascorbic acid described by first-order
reaction, which depend on:
1. The concentration of reactant
Since peel samples were higher in concentration than rag, inducing a more
collision with oxygen increasing the rate of oxidation, and consequently
more degradation on the content of ascorbic acid.
2. The time of reaction
Also, since peel is more thickness than rag it may need longer time until
complete drying of more exposure to oxygen consequently more
degradation of the AA content.
48
4.3.3 Sunlight-dried Results
4.3.3.1 Direct Titration Results
The AA content in sunlight-dried samples (5860mg/kg) and (2930mg/kg)
for peel and rag respectively. The difference in AA content of fresh samples
and Sunlight-dried samples was (3740 mg/kg ) and (2670mg/kg ) for peel
and rag respectively.
4.3.3.2 Indirect Titration Results
The AA content in sunlight-dried samples (5600 mg/kg) and (2670mg/kg)
for peel and rag respectively. The difference in AA content of fresh samples
and Sunlight-dried samples was (3730 mg/kg) and (2660 mg/kg) for peel
and rag respectively.
The results showed that both sunlight-dried samples had lower AA content
than shaded ones here, the combination between oxygen and sunlight
enhance AA degradation thus according to ( P.H.S, Santos and M.A.Silva.,
2010), the degradation of the vitamin C is not only dependent on the kind of
product but also on the drying procedure. They reported that shade drying
would be better to get a dried product richer in vitamin C.
Also, the concentration of oxygen in the drying atmosphere influences the
final content in the dried product.
49
4.3.4 At60℃ Oven-dried Results
4.3.4.1 Direct Titration Results
The AA content in oven-dried samples (5330mg/kg) and (2660 mg/kg ) for
peel and rag respectively. The difference in AA content of fresh samples
and 60 sample is (4270mg/kg ) and (2940 mg/kg) for peel and rag
respectively.
4.3.4.2 Indirect Titration Results
The AA content in oven-dried samples was (5070 mg/kg) and (2400mg/kg)
for peel and rag respectively. The difference in AA content of fresh samples
and at 60 samples was (4260 mg/kg) and (2930 mg/kg).
The results obtained showed that 60 samples had the highest vitamin C
degradation. At increased temperature, the samples were more susceptible
to oxidation and the effects of temperature and consequently experienced
more degradation of ascorbic acid.
50
CHAPTER FIVE
CONCLUSION & RECOMMENDATION
5.1 Conclusion
Peel samples presented higher quantity of ascorbic acid than rag sample
they lost their AA by exposure to different environmental conditions .
Losses of AA content occur not only during the drying process but also
during pre drying treatments. Because of the high solubility of vitamin C in
aqueous solution, there was potential for significant losses by leaching from
freshly cut fruits.
Among the environmental variables that affect the vitamin C degradation,
temperature and time are the most important parameters. Because of the
high sensibility of this nutrient to heat, the combination between these two
parameters determines the extent of decrease. Also, the concentration of
oxygen in the drying atmosphere influences the final content in the dried
product.
This study supports the common perception that fresh fruits is often best for
optimal vitamin C content, also its revealed that the effect of heat at
different temperatures has resulted in the degradation of AA. As
temperature increases, the amount of AA that is lost also increases,
therefore it is to be noted that consumption of fresh fruits is needed so as to
acquire an essential amount of vitamin C which is an important nutrient for
maintaining a healthy life. Moreover storage of fruits at higher temperature
should be avoided as this leads to degradation of AA.
51
5.2 Recommendations
In view of the results obtained from this study, the following
recommendations are hereby forwarded.
1. It is recommended that, people should be eating fruit in order to meet
up the recommended daily intake of vitamin C. And for optimum
consumption, people should add peel to the intake amount, either in
the form of fruit salads or juices.
2. It is also recommended that, consumption of uncooked fruit should
be strongly encourage because heating of fruit leads to a considerable
loss in ascorbic acid contents
3. people should avoid drying of fruits completely as a means of
preserving them because it also leads to a considerable loss in
vitamin C. And if it necessary, it can be dried at room temperature as
it is the least loss of vitamin C compared to other drying methods.
52
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