Influence of hot-air,microwave--vacuum,and far-infrared catalytic drying on drying kinetics and quality of tomato slices

摘要

干燥是农产品收获后保藏的最古老和最常见的方法之一。目前使用的干燥方式有很多，如热风干燥、真空微波干燥、红外干燥等，研究的重点集中在干燥工艺参数的优化及设备的研发上，而针对各种干燥方法的干燥动力学过程及其对产品品质影响的对比性研究较少。因此本研究进行了热风干燥、真空微波干燥和红外干燥三种干燥方式对番茄片的干燥动力学和品质影响的对比性研究。
　　首先，本研究采用电热干燥方法对番茄片进行干燥处理，研究不同干燥温度(50℃、60℃、70℃和80℃)对干燥动力学参数和产品品质的影响，其中考察的产品品质指标包括非酶褐变指数、番茄红素含量、颜色和气味的变化。研究结果显示:随着干燥温度从50℃增加到80℃，干燥时间从1140 min缩短到540 min。在80℃下干燥后番茄片的非酶促褐化指数由新鲜番茄的0.051升高到1.40。在50℃、60℃、70℃和80℃下干燥后，番茄红素含量均显著增加(P＜0.05)，由新鲜番茄的11.46 mg/100g（干基含量）分别上升至61.23 mg/100g、59.10 mg/100g、60.88 mg/100g和65.28 mg/100g（干基含量）。所有干燥样品的颜色值介于51.81°和61.95°之间，颜色均为黄色，由此推断干燥过程中样品均发生了褐变反应。采用电子鼻系统检测发现所有干燥样品的气味与新鲜番茄相比均有所下降;采用4个常见的干燥模型进行实验数据拟合，研究结果显示Page模型是预测番茄片电热干燥动力学过程的最佳模型。有效水分扩散系数随着干燥温度的增加而增加，在50℃、60℃、70℃和80℃下，分别为5.13×10-10 m2s-1、6.45×10-10 m2s-1、8.44×10-10 m2s-1和10.26×10-10 m2s-1，得出干燥活化能为22.28 KJ/mol。
　　其次，本研究采用真空微波干燥方法对番茄片进行干燥处理，研究不同微波功率（200W、300W、500W和700W）和不同真空度(0.04 MPa、0.05 MPa和0.06 MPa)对干燥动力学参数和产品品质的影响，其中考察的产品品质指标包括非酶褐变指数、Vc含量、番茄红素含量、颜色和气味的变化。研究结果显示:随着微波功率从200W增加到700W，干燥速率不断提高，干燥时间从84 min缩短到14 min。非酶褐变指数随微波功率的增加而增加。在干燥实验中，Vc含量均显著降低(P＜0.05)，从新鲜番茄的2.74±0.29mg/g下降到最低值1.87±0.13 mg/g，与新鲜番茄相比，番茄干的Vc含量下降最大值为32％，样品在200W和0.06 MPa的干燥条件下具有最大的Vc保留率。番茄红素含量均显著增加(P＜0.05)，在700W和0.04MPa下干燥后由新鲜番茄的11.46 mg/100g（干基含量）上升至25.44 mg/100g（干基含量）。观察发现，所有干燥样品的亮度和黄色度与新鲜番茄相比均有所增加，但是红色度有略微的减小。所有干燥样品的气味与新鲜番茄相比均有所下降，气味指标比新鲜番茄减少了18.99％-20.80％;采用13个常见的干燥模型进行实验数据拟合，研究结果显示Midilli模型是预测番茄片真空微波干燥动力学过程的最佳模型。有效水分扩散系数随着微波功率的增加而增加，在200W、300W、500W和700W下，分别为7.22×109 m2s-1、9.10×10-9 m2s-1、14.99×10-9 m2s-1和25.19×10-9 m2s-1。
　　再次，本研究采用风机辅助的热风干燥方法对番茄片进行干燥处理，通过响应面优化实验研究热风温度(40～60℃)、风速(1～2 m/s)和样品厚度(7～11 mm)对产品品质的影响。研究确定的最佳热风干燥条件为:温度44℃、风速2m/s、样品厚度7.72 mm。在此最佳条件下，干燥时间为527±76min，番茄红素含量为62.7±4.3mg/100g（干基含量），Vc含量为3.07±0.14 mg/g（干基含量），亮度值为62.92±2.18，红色度值与黄色度值的比例为0.78±0.05，非酶褐变指数为0.55±0.06。最后，本研究采用催化式红外干燥方法对番茄片进行干燥处理，考察了样品厚度(7mm、9 mm、11 mm)和红外辐射距离(38cm、44cm、50 cm、56 cm)对产品品质的影响。建立了随辐照距离（红外辐射板与样品之间的距离）与样品厚度之间的干燥动力学模型。随着番茄片厚度的减小和辐射距离的缩短番茄的水分有效扩散率增加，并呈现三次多项式的关系。只有催化式红外干燥番茄片干燥速率呈现下降趋势，而没有干燥速率稳定期。相对远红外干燥的样品与新鲜番茄相比，58.3％的干制品的风味有所提升，增加值为3.0％-36.6％之间，而41.7％的干制品风味有所下降，减少值为3.1％-14.1％。通过对薄层干燥模型与干燥数据进行拟合，Midilli模型能够最好的预测干燥过程中的水分变化。研究结果表明，真空微波和远红外辐射干燥是一种高效的干燥方法，其能够很好的保持产品颜色和维生素C含量，有效防止产品发生褐变，以及增加番茄红素的保留率。在真空微波干燥番茄过程中，应避免较高的微波功率(例700W)。
　　本研究能够为工业化生产高品质产品提供有效信息及最优干燥条件。

目录

声明

ACKNOWLEDGMENT

ABSTRACT

摘要

TABLE OF CONTENTS

LIST OF TABLES

LIST OF FIGURES

DEDICATION

CHAPTER 1 INTRODUCTION

REFERENCES

CHAPTER 2 OBJECTIVES

CHAPTER 3 LITERATURE REVIEW

3．1 INTRODUCTION

3．2 Conventional drying

3．3 Disadvantages of conventional drying

3．4 Principle of microwave heating and drying

3．5 Advantages of microwave drying

3．6 Drawbacks in microwave heat treatment

3．7 Principles of the vacuum drying process

3．8 Advantages of vacuum drying

3．9 Principles of infrared drying

3．10 Influence of drying on quality characteristics of dried tomatoes

3．10．1 Influence of drying on colour characteristics

3．10．2 Influence of drying on sensory characteristics

3．10．3 Influence of drying on lycopene

3．10．4 Influence of drying on ascorbic acid

3．10．5 Influence of drying on nonenzymatic browning

REFERENCES

CHAPTER 4 INFLUENCE OF AIR TEMPERATURE ON THE DRYING KINETICS AND QUALITY OF TOMATO SCLICES

ABSTRACT

4．1 INTRODUCTION

4．2 MATERIALS AND METHODS

4．2．1 Materials

4．2．2 Drying equipment and drying method

4．2．3 Drying kinetics expressed in terms of empirical models

4．2．4 Calculation of moisture diffusivity and Activation Energy

4．2．5 Colour Measurements

4．Z．6 Flavour measurement

4．2．7 Non-enzymatic browning determination

4．2．8 Lycopene content determination

4．2．9 Statistical analysis

4．3 RESULT AND DISCUSSION

4．3．1 Influence of air temperature on drying kinetics of tomato slices

4．3．2 Moisture diffusivity and activation energy

4，3．3 Modeling of the Drying Curves

4．3．4 Influence of air temperature on colour parameters

4．3．5 Influence of hot air temperature on non-enzymatic browning

4．3．6 Influence of hot air temperature on lycopene content

4．3．7 Influence of hot air temperature on flavour

4．4 CONCLUSION

REFERENCES

CHAPTER 5 INFLUENCE OF COMBINED MICROWAVE-VACUUM DRYING ON DRYING KINETICS AND QUALITY OF DRIED TOMATO SLICES

ABSTRACT

5．1 INTRODUCTION

5．2 MATERIALS AND METHODS

5．2．1 Materials

5．2．2 Combined microwave-vacuum drying

5．2．3 Drying kinetics of tomato slices

5．2．4 Calculation of Activation Energy

5．2．5 Colour Measurements

5．2．6 Flavour measurement

5．2．7 Non-enzymatic browning determination

5．2．8 Statistical analysis

5．3 RESULTS AND DISCUSSION

5．3．1 Influence of microwave power and vacuum pressure on drying kinetics of tomato slices

5．3．2 Moisture diffusivity and activation energy

5．3．3 Influence of microwave-vacuum drying on colour parameters

5．3．4 Influence of microwave-vacuum drying on flavour

5．3．5 Influence of microwave-vacuum drying on non-enzymatic browning

5．4 CONCLUSION

REFERENCES

CHAPTER 6 MICROWAVE-VACUUM DRYING EFFECT ON DRYING KINETICS，LYCOPENE AND ASCORBIC ACID CONTENT OF TOMATO SLICES

ABSTRACT

6．1 INTRODUCTION

6．2 MATERIALS AND METHODS

6．2．1 Sample preparation

6．2．2 Combined microwave-vacuum drying

6．2．3 Ascorbic acid analysis

6．2．4 Lycopene content analysis

6．2．5 Modeling of the experimental data

6．2．6 Calculation of moisture diffusion coefficient and Activation Energy

6．2．7 Statistical analysis

6．3 RESULTS AND DISCUSSION

6．3．1 Effect of microwave power and vacuum pressure on drying kinetics

6．3．2 Effect of drying parameters on coefficients of effective moisture diffusion

6．3．3 Etiect of microwave-vacuum on ascorbic acid

6．3．4 Effect of microwave-vacuum on lycopene content

6．3．5 Modeling of the Drying Curves

6．4 CONCLUSION

REFERENCES

CHAPTER 7 OPTIMIZATION OF DRYING CONDITIONS FOR QUALITY DRIED TOMATO SLICES USING RESPONSE SURFACE METHODOLOGY

ABSTRACT

7．1 INTRODUCTION

7．2 MATERlALS AND METHODS

7．2．1 Sample Preparation

7．2．2 Drying Equipment and Procedure

7．2．3 Experimental Design

7．2．4 Determination of Ascorbic Acid Content

7．2．5 Determination of Lycopene Content

7．2．6 Colour Measurement

7．2．7 Non-Enzymatic Browning Determination

7．2．8 Optimization of the Drying Process

7．2．9 Statistical Analysis

7．3 RESULTS AND DISCUSSION

7．3．1 Effect of Drying Parameters on Drying Time

7．3．2 Effect of Drying Condition on Lycopene Content

7．3．3 Effects of Drying Parameters on Ascorbic Acid Content

7．3．4 Effect of Drying Parameters on Colour Parameters

7．3．5 Effect of Drying Parameters on Non-Enzymatic Browning

7．3．6 Optimization of the Drying Parameters

7．4 CONCLUSION

REFERENCES

CHAPTER 8 CATALYTIC FAR-INFRARED DRYING EFFECT ON TOMATO SLICES PROPERTIES

ABSTRACT

8．1 INTRODUCTION

8．2 MATEIUALS AND METHODS

8．2．1 Sample Preparation

8．2．2 Drying Equipmentand Procedure

8．2．3 Experimental procedure

8．2．4 Experimental Design

8．2．5 Determination of Ascorbic Acid Content

8．2．6 Determination of Lycopene Content

8．2．7 Colour Measurement

8．2．8 Non-Enzymatic Browning Determination

8．2．9 Optimization of the Drying Process

8．2．10 Statistical Analysis

8．3 RESULT ANDDISCUSSION

8．3．1 Effect of FIR Drying on Drying Time

8．3．2 Effect of FIR Drying on Colour

8．3．3 Effect of FIR Drying on Non-Enzymatic Browning

8．3．4 Effects of FIR Drying on Ascorbic Acid Content

8．3．5 Effect of FIR Drying on Lycopene Content

8．3．6 Optimization of the FIR Drying Condition

8．4 CONCLUSION

REFERENCES

CHAPTER 9 THIN-LAYER CATALYTIC FIR DRYING AND FLAVOUR OF TOMATO SLICES

9．1 INTRODUCTION

9．2 MATERIALS AND METHOD

9．2．1 Sample preparation and drying

9．2．2 Experimental procedure

9．2．3 Experimental Design

9．2．4 Drying kinetics expressed in terms of empirical models

9．2．5 Effective moisture diffusivity

9．2．6 Flavour measurement

9．3 RESULT ANDDISCUSSION

9．3．1 FIR drying of tomato slices

9．3．2 Effective moisture diffusivity

9．3．3 Influence of FIR drying on flavour

9．3．4 Modeling of the FIR Drying Curves

9．4 CONCLUSION

REFERENCES

CHAPTER 10 GENERAL CONCLUSIONS

10．1 Conventional Drying

10．2 Blower-Assisted Convectional Drying

10．3 Combined Microwave-Vacuum Drying

10．4 Far-Infrared Catalytic Drying

Appendix Ⅰ some photos of the dried and powdered tomato slice