ABSTRACT
The experiment was carried out and three osmotic solutions were prepared,
“hypertonic solution 60% concentrated, hypotonic solution 40% concentrated and
isotonic solution 50% concentrated” and oven drying was also carried in the
course of the experiment, the effect of sodium chloride (osmotic agent)
concentration, temperature and immersion time on overall mass transfer
coefficient, effective diffusivity, drying rate weight loss and shrinkage ratio
on oven drying and osmotic dehydration of Pumpkin and bitter leaf. Results showed that both pumpkin and bitter leaf had a highest mass transfer coefficient in oven drying at highest temperature of 80oC,
for pumpkin leaf 0.149(m/min), bitter leaf was
0.149(m/min), the results were also obtain for osmotic dehydration at 80Oc
at highest concentration (Hypertonic solution) had the highest mass transfer
coefficient, for pumpkin leaf was 0.015(m/min) for bitter leaf was obtained to
0.032(m/min). For osmotic dehydration, both samples weight loss percent (WL%)
for hypertonic solution at 800C for 90mins had the highest weight
loss percent, but the shrinkage ratio decrease with increase in time.The mass
transfer during oven drying of pumpkin and bitter leaf was described using
Fickian equation of diffusion with drying taking place in the falling rate
period, the effective moisture diffusivity value showed temperature dependence
on both samples. Effective diffusivity values were also determined for oven
drying at different temperature, and the
values increases as the temperature
increases, for pumpkin and bitter leaf at 600C, 700C and
800C, the effective diffusivities were 1.0E-09, 1.87106E-09 and
2.1843E-09m2/min and 8.52966E-10, 1.00015E-9 and 2.45308E-08m2/min.
TABLE OF CONTENTS
Page
Title Page: i
Certification: iii
Dedication iv
Acknowledgement: v
Table of Content vi
List of Figure xiii
List of Tables: xv
Abstract: xvi
CHAPTER
ONE: INTRODUCTION
1.1 Background: 1
1.2 Mass transfer phenomena during
osmotic dehydration: 2
1.3 Condition for drying 3
1.4 Statement of the research problem: 3
1.5 Propose solution 3
1.6 Aim 4
1.7 Objectives of the study: 4
1.8 Relevance of study 4
1.9 Method and scope 4
CHAPTER
TWO: LITERATURE REVIEW
2.1 General over view 6
2.2 Basic terminology in drying terms: 10
2.2.1 Adiabatic saturation
temperature 10
2.2.2 Bound moisture 10
2.2.3 Constant rate drying period: 10
2.2.4 Dew point: 11
2.2.5 Drying bulb temperature 11
2.2.6 Equilibrium moisture content: 11
2.2.7 Critical moisture content 11
2.2.8 Falling rate period: 11
2.2.9 Free moisture 11
2.2.10 Humid heat 11
2.2.11 Absolute humidity 11
2.2.12 Relative humidity 11
2.2.13 Unbound moisture 11
2.2.14 Water 11
2. 2.15 Wet bulb temperature: 11
2.3 Advances in food drying 11
2.3.1 Uses of advanced computational
tools: 12
2.4 Quality change during drying: 12
2.4.1 Browing: 14
2.4.2 Case hardening: 14
2.4.3 Rehydration 14
2.5 Classification of industrial
dryers 14
2.5.1 Conduction and convection dryer 15
2.5.2 Radiation and convection dryers 16
2.6 Description of dryer 17
2.6.1 Tray dryer 17
2.6.2 Band (belt) Dryers 17
2.6.3 Rotary dryers 17
2.6.4 Roller dryers 18
2.6.5 Fluidized bed dryers 18
2.6.6 Spray dryers 18
2.7 Osmotic dehydration 19
2.8 Application of osmosis in food
processing: 20
2.9 Parameters influencing the
osmotic process 20
2.10 Raw materials characteristics
for osmotic dehydration: 21
2.10.1 Quality of raw material 21
2.10.2 Shape, size and thickness of the fruit pieces 21
2. 11 Type of osmotic agent 21
2.12 Contacting time: 22
2.13 Osmotic process parameter 22
2.13.1 Immersion time 23
2.13.2 Temperature of the osmotic
solution 23
2.13.3 Concentration of osmotic
solution 24
2.13.4 Agitation / circulation 24
2.13.5Fruit pieces to osmotic
solution ratio: 24
2.14 Kinetic of osmotic dehydration 24
2.15 Mass transfer phenomena during
osmotic dehydration 25
2.16 Drying behavior of osmotic concentrated fruits 25
2.17 packaging of osmotic dehydrated
products 25
2.18 Storage of osmotic dehydrated
products 26
2.19 Microbial studies of osmotic
dehydrated products 26
2.20 Advantages of osmotic
dehydration 26
CHAPTER THREE: APPARATUS/ EQUIPMENT
AND METHODOLOGY
3.1 Osmotic dehydration 28
3.2 Method of osmotic dehydration 28
3.3 Oven drying 29
3.4 Method of oven drying 30
3.5 Moisture Ratio (MR) 31
3.6 Estimation of effective
diffusivity 31
3.7 Drying model 31
CHAPTER FOUR: RESULT AND DISCUSSION
4.1 Water loss (WL%) during osmotic
dehydration of the samples 33
4.2 Mass shrinkage ratio during
osmotic dehydration of the samples 36
4.3 The mass transfer coefficient
during osmotic dehydration 37
4.4 Oven drying 40
4.5 The mass transfer coefficient
during oven drying 45
CHAPTER FIVE: CONCLUSION AND
RECOMMENDATION
5.1 Conclusion 46
5.2 Recommendation 46
REFFERENCE 46
APPENDIX 50
LIST OF FIGURE
PAGE
Fig
1:Response of weight loss (WL%) to different solute concentration and immersion
time for dehydration of bitter leaf: 33
Fig
2: Response of weight loss (WL%) to different solute concentration and
immersion time for dehydration of pumpkin leaf: 34
Fig3:
Response of mass shrinkage ratio (SR) to different solute concentration and
immersion time for dehydration of bitter leaf: 35
Fig4:
Response of mass shrinkage ratio (SR) to different solute concentration and
immersion time for dehydration of pumpkin leaf: 36
Fig5:
Effect of moisture content on drying
rate at different temperatures
for
pumpkin leaf 40
Fig6:
of moisture content on drying rate at
different temperatures
for
bitter leaf 40
Fig7:
Effect of moisture ratio IN(MR) with time respect with temperature for pumpkin
leaf 41
Fig8: Effect of moisture ratio IN(MR) with time
respect with temperature for pumpkin leaf 41
Fig9:
Effect of moisture ratio with time respect with temperature for bitter leaf 42
Fig10: Effect of moisture ratio with time respect
with temperature for pumpkin leaf 42
LIST OF TABLES
Page
Tab
1: The mass transfer coefficient of bitter leaf during osmotic dehydration
(hypertonic solution) 37
Tab
2: The mass transfer coefficient of bitter leaf during osmotic dehydration
(hypotonic solution) 37
Tab
3: The mass transfer coefficient of bitter leaf during osmotic dehydration
(Isotonic solution) 38
Tab
4: The mass transfer coefficient of pumpkin leaf during osmotic dehydration
(hypertonic solution) 39
Tab
5: The mass transfer coefficient of pumpkin leaf during osmotic dehydration
(hypotonic solution) 39
Tab
6: mass transfer coefficient of pumpkin leaf during osmotic dehydration
(Isotonic solution) 39
Tab
8: Effective Diffusivity of pumpkin leaf at
different temperature 39
Tab
9: Effective Diffusivity of bitter leaf at
different temperature 43
Tab
10: R2 and k constant value of lewis model for oven drying of
pumpkin leaf 44
Tab
11: R2 and k constant value of lewis model for oven drying of bitter
leaf 44
Tab
12: The mass transfer coefficient during
oven drying of pumpkin leaf at different temperature 45
Tab
13: The mass transfer coefficient during oven drying of bitter leaf at
different temperature 45
CHAPTER
ONE
1.0 INTRODUCTION
1.1 BACKGROUND
Fruits
and vegetables contribute a crucial source of nutrients in daily human diet, the
world fruit production is estimated to be 434.7 million metric tones and
vegetables 90.0 million metric tones. India is the second largest fruits and
vegetable producer and its annual production is 44 million metric tones from an
area of 3, 949, 000 haduring 2000-2002 (Srivastava& Kumar, 2002). Fruits
and vegetables losses in the developing countries are considerably high. In
India, post harvest losses of fruits and vegetables are estimated as more than
25 percent. Many processing techniques can be employed to preserve fruits and
vegetables by drying and dehydration is one of the most important operations
that are widely practiced because of considerable saving in packaging,
storageetc
Vegetables contain
nearly 70% to 95% of moisture which make them highly perishable. If this
moisture is reduced to some extent, bulk transportation of the final product
can be made to other parts of the country where it is not available. Also the
shelf life of the product is increased. Conventionally sun drying and hot air
drying is used to dry and preserve the product. This produced discolored and
shrieked products which were of not interest to patronage. When osmotic
dehydration is used prior to drying steps it is evident that it conserves
energy and reduces the heat damage to the product in terms of color, flavor and
aromaetc
Osmotic
dehydration aims at extending life of food by removing water without phase
transition [Kowalska and Lenart 2001, Matuska et al. 2006]. The process is
carried out by immersing the raw material in a hypertonic solution (solution
with high concentration of sugars, sodium chloride, etc.).
Osmotic dehydration is used for foods with a
tissue structure, such as shredded fruit and vegetables [Torreggiani 1993]. The
method is based on the natural phenomenon of osmosis through cell membranes of
biological material [Shi and Le Maguer 2002]. In the osmotic dehydration the process
of water flow to the outside of food material takes place, and entering of
substances dissolved in a hypertonic solution into the product. Since the cell
membrane is not perfectly selective, the solutes present in cells (organic
acids, sugars, minerals, fragrances, and colorants) can pass with water into
the hypertonic solution [Derossi et al. 2008].
1.2
Mass transfer phenomena during osmotic dehydration
There are
three major types of counter current mass transfer in osmotic concentration
process (Karthiayani, 2004;Tiwari, 2005) (Figure 2).
1.
Important water out flow from product to solution.
2. A
solute transfer, from the solution to the product; it makes thus possible to
introduce the desired amount of an active principle, a preservative agent, any
solute or nutritional interest, or a sensoryquality improvement of the product.
3.
Leaching out of products own solutes (sugar, organic acids, minerals, vitamins
etc.), which is quantitatively negligible when compares with the first two
types of transfer, but essential with regard to the composition of final
product/
Drying of fruits and vegetables such as pumpkin, fruit pepper and bitter
leaves e.t.c is one the most time and energy consuming process in the modern
food industry [sunjka et al 20004]. However these fruit and vegetable are
usually in short supply during dry season because they are perishable crops
which deteriorate within a few days afterharvest (which occur mainly in rainy
season). Preserving these crops in their fresh state for months has been a
problem that is yet unsolved [famurewa et al 2006; Agarryetal 2006]. Drying
processes play an important role in the preservation of agricultural products.
They are defined as a process of moisture removal due to simultaneous heart and
mass transfer in which energy must be supplied [waewsak et al 2006]
1.3CONDITIONS FOR DRYING
The general condition include the following:
1)
Heat is
transfer by evaporation of liquid or moisture from the surface of the solid
2) Mass is equally transferred
1.4STATEMENT OF THE RESEARCH PROBLEM
Most of the work done on this subject have
been on the change that occur in the nutritional properties and mass transfer
at different temperature, immersion time and concentration of the solution
1.5 PROPOSE SOLUTION
This works tends to do proper investigation
on the drying rate and mass transfer characteristic in different osmotic
solution and thermal drying of
vegetable to bring it to the awareness
of the public, this work tends to bring out the importance of choosing the best
optimum temperature and best osmotic solution for thermal drying and osmotic
dehydration
1.6AIM
The aim of this research work is to
investigate the mass transfer characteristic of pumpkin and Bitter leaf
1.7 OBJECTIVES OF THE STUDY
The following objectives were use to achieved
the aim.
1) To
investigate the effect of temperature on drying rate of pumpkin and bitter leaf
2) To
investigate the effect of osmotic concentration
of pumpkin and Bitter leaf
3) To investigate
the effect of time for drying rate and osmotic dehydration for Pumpkin and
Bitter leaf
4)
To determine the optimum condition of thermal
drying and osmotic dehydration.
.1.8 RELEVENCE OF
STUDY
This is necessary to
determine the suitability of the drying process that will help in mass
transfer, and it also provide a suitable method that will help reduce crop loss
in Nigeria.
1.9METHOD AND SCOPE
The method used in this work include;
1). Osmotic solution
(hypertonic, Isotonic and hypotonic solution) using NaCL as the osmotic agent ,
were prepared at different temperature interval the solution was stirred until
complete dissolution, the samples were pumpkin and bitter leaf
2). Samples of
pumpkin and bitter leaves were weight and spread on a metal tray which was then
place in a laboratory oven. The drying was carried out at different temperature
of 600C, 700C and 800C
3). The effective diffusivity was determine
by using fickian equation
The scope of this research is limited to the
study of mass transfer coefficient during thermal drying and osmotic
dehydration of pumpkin and Bitter leaf
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