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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.




Title Page:                                                                                                                               i

Certification:                                                                                                                           iii

Dedication                                                                                                                              iv

Acknowledgement:                                                                                                                 v

Table of Content                                                                                                                     vi

List of Figure                                                                                                                          xiii

List of Tables:                                                                                                                           xv

Abstract:                                                                                                                                 xvi      


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


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


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


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



5.1 Conclusion                                                                                                                 46

5.2 Recommendation                                                                                                      46

REFFERENCE                                                                                                              46

APPENDIX                                                                                                                     50







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









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













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]


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


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


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


The aim of this research work is to investigate the mass transfer characteristic of pumpkin and Bitter leaf




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.


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.


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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