CONTENTS. Chapter 1 Introduction 1 Chapter 2 Review of Literature Composition of Onion 7

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1 CONTENTS Sections Description Page No. Title Page Dedication Approval of the Viva-Voce Board Certificate Declaration Acknowledgement Biodata List of Tables List of Figures List of Symbols and Abbreviations Abstract Chapter 1 Introduction 1 Chapter 2 Review of Literature Composition of Onion 7 i ii iii v vii viii ix xiv xvii xxi xxiv 2.2 Processed Onion Onion Varieties Suitable for Dehydration Dehydration Practices for Onion Vacuum Drying as a Potential Drying Method Pretreatments Quality Characteristics Non-enzymatic browning Flavour or pungency Rehydration ratio Scanning electron microscopy Texture Thermo-physical properties Fuzzy Sensory Analysis Storage Study Mathematical Modelling Modelling used for onion dehydration 24 x

2 Modelling used for vacuum drying Computational fluid dynamics modelling for drying CFD on vacuum drying 29 Chapter 3 Theoretical Considerations Determination of Moisture Transport Mechanism Constant diffusivity approach Variable diffusivity approach Modelling of Thin Layer Vacuum Drying Numerical Modelling of the Vacuum Drying Process for Onion Description of the system Physical model Mathematical model Computational fluid dynamics model formulation Computing the solution Model validation 55 Chapter 4 Materials and Methods Sample Preparation Vacuum Dryer Experimental Set Up and Design Design of experiment Data analysis and optimization Quality Evaluation of Dehydrated Onion Determination of moisture content Determination of colour Determination of flavour Determination of rehydration ratio Sensory Evaluation of Vacuum Dried Onion Slices Preparation of score card and training of the judges Fuzzy comprehensive modelling of Sensory scores xi

3 4.6 Scanning Electron Microscope Analysis Texture Analysis True Density Thermal Conductivity Storage Study 79 Chapter 5 Results and Discussion Drying Kinetics of Vacuum Dried Onion Slices Moisture profile analysis Drying rate variation Moisture ratio variation Modelling of drying characteristics Determination of diffusivity value Numerical Simulation of Drying Process of Onion Slice Temperature profile of onion slice during drying Pattern of isotherm in the slice Moisture profile of onion slice during drying Moisture concentration contour at different time of drying Comparison of experimental and simulated data Quality Analysis of Dried Onion Slices Moisture content Colour development Flavour content Rehydration ratio Optimization of the Parameters of Vacuum Dried Onion Slices Statistical analysis Optimization Fuzzy Sensory Analysis Triplets for overall sensory scores of onion - tomato paste samples Overall membership functions of sensory 147 xii

4 scores on standard fuzzy scale Similarity values of onion-tomato paste samples and their ranking Quality attributes ranking of onion-tomato paste samples in general Quality factor ranking of individual oniontomato paste samples Characterization of the Final Vacuum Dried Onion Microstructure analysis Texture analysis True density Thermal conductivity Storage Study 158 Chapter 6 Summary and Conclusions 163 References 171 Appendix A Specifications of the instruments used for study 183 Appendix B ANOVA for Quality Parameters 186 Appendix C MATLAB Program for Sensory Analysis using Fuzzy Logic 188 Appendix D Drying Data for Vacuum Drying of Onion 192 Appendix E Sensory Score Card for Fuzzy Logic Modelling 197 xiii

5 LIST OF TABLES Table Description Page No. 1.1 Yearwise Status of Area, Production, and Yield of Onion in India 2.1 Proximate Composition and Energy Values of Raw and Dehydrated Onion 3.1 Models for Predicting Vacuum Drying Characteristics of Onion Slices 3.2 Boundary Conditions Applied to the Vacuum Drying Model for Heat Transfer in COMSOL 3.3 Boundary Conditions Applied to the Vacuum Drying Model for Mass Transfer in COMSOL 3.4 Various Process Constants Assigned to the Drying Model in COMSOL 3.5 Variable Expressions Assigned to the Drying model in COMSOL 4.1 Experimental Design for Vacuum Drying of Onion Slice Triplets Associated with Different Sensory Scales Model Coefficients and Coefficient of Determination of Polynomial Model for Drying Rate Data 5.2 Statistical Results Obtained from Various Thin Layer Drying Models for Untreated Onion Slice 5.3 Statistical Results Obtained from Various Thin Layer Drying Models for Treated Onion Slice 5.4 Estimated Values of Parameters of Page Model Used for Thin Layer Drying Modelling of Onion Slices at Different Sample Thicknesses and Temperatures 5.5 Values of Constant Moisture Diffusivity for Vacuum Drying of Onion Slices 5.6 Percentage Error Values for Diffusivity Models Reaction Rate Constant for NEB Kinetics and R 2 Values for VDOS 5.8 Activation Energy Values for Browning Kinetics of VDOS Percentage Error in Predicted Optical Index Reaction Rate Constant for Thiosulphinate Loss Kinetics and R 2 Values xiv

6 5.11 Activation Energy Values for Flavour Kinetics of VDOS Percentage Error in Predicted Flavour Loss Experimental Results for Vacuum Drying of Onion Slices ANOVA for the Selected Model and the Responses Regression Coefficients of the Selected Polynomials Relating the Responses with Variables 5.16 Sensory Scores and Triplets Associated with the Scores for Quality Attributes of Onion-Tomato Paste Samples in General 5.17 Triplets for Sensory Scores for Each of the Quality Attributes of the Samples 5.18 Similarity Values for the Three Samples Under Different Scale Factors 5.19 Similarity Values for the Quality Attributes of Onion-Tomato Paste Samples in General 5.20 Similarity Values and Ranking of Quality Attributes for Individual Onion-Tomato Paste Sample 5.21 Textural Property of Untreated and Treated VDOS True Density of Vacuum dried 5 mm Thick Treated Onion Slices 5.23 Thermal Conductivity of Onion Slices Dried Under Optimized Condition 5.24 Coefficient of Determination of the Fitted Model and Reaction Rate Constants for Colour and Flavour Kinetics During Storage B1 ANOVA for Moisture Content (Untreated) 186 B2 ANOVA for Moisture Content (Treated) 186 B3 ANOVA for Colour (Untreated) 186 B4 ANOVA for Colour (Treated) 186 B5 ANOVA for Flavour (Untreated) 187 B6 ANOVA for Flavour (Treated) 187 B7 ANOVA for Rehydration Ratio (Untreated) 187 B8 ANOVA for Rehydration Ratio (Treated) 187 D1 Moisture Content for 1 mm Thick Untreated Onion Slice 192 D2 Moisture Content for 1 mm Thick Treated Onion Slice 192 D3 Moisture Content for 3 mm Thick Untreated Onion Slice 192 D4 Moisture Content for 3 mm Thick Treated Onion Slice xv

7 D5 Moisture Content for 5 mm Thick Untreated Onion Slice 194 D6 Moisture Content for 5 mm Thick Treated Onion Slice 195 xvi

8 LIST OF FIGURES Figure Description Page No. 3.1 Drying Rate versus Free Moisture Content Curve Falling Rate Drying Plot for Diffusion Mechanism and Capillary Mechanism 3.3 Domain Geometry of Onion Slice Developed in COMSOL Meshing of the Geometry in COMSOL with Triangular Elements 4.1 Schematic Diagram of the Vacuum Dryer System Pictorial View of Vacuum Dryer Set Up UV-VIS Spectrophotometer (Model UV-1601) Values of Triplets Associated with Triangular Membership Distribution Function for Five-Point Sensory Scale 4.5 Graphical Representation of Triplet (a b c) and its Membership Function 4.6 Representation of Standard Fuzzy Scale Scanning Electron Microscope (Model - JSM-5800LV) Texture Analyser (Model TA-XT2i, UK) Air Comparison Pycnometer Thermal Conductivity Meter (Kemtherm QTM-D3) Variation of Moisture Content for Different Thicknesses Variation of Moisture Content for Different Temperatures Variation of Drying Rate with Time for Different Thicknesses Variation of Drying Rate with Time at 60 C Variation of Drying Rate with Moisture Content at Different Thicknesses 5.6 Variation of Drying Rate with Moisture Content for Different Temperatures 5.7 Moisture Ratio with Time at Different Slice Thicknesses for VDOS 5.8 Variation of Moisture Ratio with Time at 60 C Temperature Moisture Ratio versus Time Plot for 1 mm Thick Onion Slices Moisture Ratio versus Time Plot for 3 mm Thick Onion Slices Moisture Ratio versus Time Plot for 5 mm Thick Onion Slices xvii

9 5.12 Comparison of Experimental and Predicted Moisture Ratio for Untreated and Treated Slices by the Page Model 5.13 ln(mr) versus Time Plot for 3 mm Thick Untreated Onion Slices Dried at 50 C 5.14 ln(mr) versus Time Plot for 3 mm Thick Treated Onion Slices Dried at 50 C 5.15 Diffusivity of Onion Slices versus Moisture Content at Different Thicknesses 5.16 Diffusivity versus Moisture Content at 70 C Temperature Temperature Profile at the Bottom Surface of the Onion Slice Temperature Profile at the Side Surface of the Onion Slice Temperature Profile at the Centre of the Onion Slice Temperature Profile at the Top Surface of the Onion Slice Temperature Profile after 30 min of Drying (1800 s) Temperature Profile after 90 min of Drying (5400 s) Temperature Profile after 180 min of Drying (10800 s) Temperature Profile after 240 min of Drying (14400 s) Moisture Concentration at Bottom (mid point) of Onion Slice Moisture Concentration at Top (mid point) of Onion Slice Moisture Concentration at Side (mid point) of Onion Slice Moisture Concentration at Central Mid Point of Onion Slice Moisture Concentration after 30 min (1800 s) Moisture Concentration after 90 min (5400 s) Moisture Concentration after 180 min (10800 s) Moisture Concentration after 240 min (14400 s) Diffusive Flux after 240 min of Drying (14400 s) Temperature Profile at the Central Surface of 3 mm Thick Untreated Onion Slice 5.35 Temperature Profile at the Top Surface of 3 mm Thick Untreated Onion Slice 5.36 Temperature Profile of at Side Surface of 3 mm Thick Untreated Onion Slice 5.37 Moisture Concentration of 3 mm Thick Untreated Onion Slice During Drying at Central Mid Point 5.38 Moisture Concentration at Different Locations of 3 mm Thick xviii

10 Untreated Onion Slice During Drying 5.39 Moisture Content of VDOS at Different Operational Conditions 5.40 Colour Change (OI) of VDOS at Different Operational Conditions 5.41 NEB (OI/g sample) in 1 mm, 3 mm and 5 mm Thick Untreated VDOS at Various Temperatures 5.42 Arrhenius Plot for NEB in Untreated VDOS Actual and Predicted Optical Index (OI/g sample) for VDOS Thiosulfinate Concentration ( mol/g sample) in VDOS Thiosulfinate Loss ( mol/g sample) in VDOS Change in Thiosulfinate for Untreated VDOS Change in Thiosulfinate for Treated VDOS Arrhenius Plot for Thiosulfinate Loss ( mol/g sample) in Untreated VDOS 5.49 Actual and Predicted Flavour Loss for 3 mm Untreated Onion Slices 5.50 Actual and Predicted Flavour Loss for 3 mm Treated Onion Slices 5.51 Rehydration Ratio of VDOS at Different Operational Conditions 5.52 Contour Plots of Moisture Content for (a) Untreated and (b) Treated VDOS 5.53 Contour Plots of Colour Change for (a) Untreated and (b) Treated VDOS 5.54 Contour Plots of Flavour Content for (a) Untreated and (b) Treated VDOS 5.55 Contour Plots of Rehydration Ratio for (a) Untreated and (b) Treated VDOS 5.56 Microstructural View of Onion Slices Produced Using SEM Texture Profile for 5 mm Thick Untreated Onion Slices Dried at 60 C under 50 mm Hg Pressure 5.58 Texture Profile for 5 mm Thick Treated Onion Slices Dried at 60 C under 50 mm Hg Pressure 5.59 Variation in True Density with Moisture Content Thermal Conductivity Variation of Onion Slices with Moisture xix

11 Content 5.61 Colour Change in Dried Onion Slices During Storage Flavour Change in Dried Onion Slices During Storage Colour Change Behaviour of Actual and Predicted Optical Index at a Water Activity of Flavour Loss Pattern of Actual and Predicted Thiosulfinate Content at a Water Activity of xx

12 LIST OF SYMBOLS AND ABBREVIATIONS % Percentage C Degree Celcius 2D, 3D Two dimensional, Three dimensional A Absorbance a, b, c, d, A, B, C Coefficients of the equations Adeq Adequate Adj Adjusted ADOGA American Dehydrated Onion and Ginger Association ANOVA Analysis of variance ASHRAE American Society for Heating Refrigeration and Air Conditioning avg Average a w Water activity b Cell path used, cm c Moisture concentration of the domain at any instant, mol.m -3 c_0 Initial moisture concentration of onion slice, kg.m -3 c_b Bulk moisture concentration in the ambient, kg.m -3 C_m Specific moisture capacity C_p, C p Specific heat of onion c b Bulk concentration, mol.m -3 CFD Computational Fluid Dynamics CV Coefficient of variation cz Concentration gradient components dc/dz D Diffusion coefficient, m 2 /s D_m Surface moisture diffusivity, m 2.s -1 db Dry basis, kg water.(kg dry solid) -1 D e Effective moisture diffusivity, m 2.s -1 DOF Degrees of freedom e.g. Exempli gratia, for example E a Activation energy, kj.mol -1 et. al. Et alibi, and others exp Exponential eqn Equation F 0 Fourier number FAO Food and Agriculture Organisation FEM Finite element method FMC Final moisture content g Grams h Heat transfer coefficient, W.m -2.K -1 h_m Mass transfer coefficiemt, kg.m -2.s -1 h_ta Heat transfer coefficient of chamber air, W.m -2.K -1 Hg Mercury i.e. Ed set, that is ICAR Indian Council of Agricultural Research ITC International Trade Centre xxi

13 K Kelvin k Thermal conductivity tensor, W.m -1.K -1 k_c Mass transfer coefficient, m.s -1 k_m Moisture conductivity of onion slice, kg.m -1.s -1 k_t Thermal conductivity of vacuum dried onion kc Reaction rate constant for colour kinetics kcal Kilo Calorie k d Drying rate constant k f Reaction rate constant for flavour kinetics kg Kilo Grams kpa Kilo Pascal l, x Thickness of slice, m lda Latent heat of vaporization, J.kg -1 m Meter M 0 Initial moisture content, kg water.(kg dry solid) -1 M d Moisture content at any instant in dry basis, kg water.(kg dry solid) -1 M e Equilibrium moisture content, kg water.(kg dry solid) -1 min Minutes mm Millimeter MR Moisture ratio M v Mass flux vector, mol.m -2.s -1 m w Wet basis moisture content, kg water.(kg total matter) -1 M w Moisture content in percent wet basis N Force, kg.m.s -2 n Normal vector of the boundary N 0 Number of observation taken M v0 Inward mass flux normal to the boundary, mol.m -2.s -1 NAFED National Agricultural Cooperative Marketing Federation of India NEB Non-Enzymatic Browning NHRDF National Horticultural Research and Development Foundation nm Nanometer OI Optical index PDE Partial differential equation PE Percentage error pred Predicted q Heat flux vector, W.m -2 Q Heat source (or sink), W.m -3 q 0 Inward heat flux vector normal to the boundary, W.m -2 R 2 Coefficient of determination rho, ρ Bulk density of vacuum dried onion RMSE Root mean square error RR Rehydration ratio Rt Reaction rate, mol.m -3.s -1 s Seconds SEM T Scanning electron microscopy Temperature difference xxii

14 t Time, s T Temperature at any instant, K T_0 Initial temperature of onion slice, K T_a Chamber air temperature, K T_b Bottom temperature of onion slice, K TC Thiosulphinate concentration of the solution, μmol.g -1 Theo Theoretical T inf External temperature of domain, K TL Thiosulphinate loss T r Transmittance VDOS Vacuum drying of onion slices viz. Videlicet, namely w Weight of sample, g wb Wet basis, kg water.(kg total matter) -1 Y e Experimental values of response Y p Predicted value of the response z Number of constants in the model (eqn 3.18 ) ε Molar absorptivity of thiolsulphinate solution at 254 nm, g.μmol - λ μ χ 2 1.cm -1 Characteristics roots of the corresponding regression equation Micro Reduced chi-square xxiii