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FREEZE DRYING OF FOOD PRODUCTS An accessible guide to safely dehydrating food Freeze drying, or lyophilization, is a method for dehydrating food or other substances through the use of pressure instead of heat. This allows for the preservation and storage of high-value food products without altering their essential properties or causing a reduction in quality or value. For these reasons, freeze drying is the most reliable method for preserving and distributing high-quality products. Freeze Drying of Food Products provides a concise, accessible overview of freeze-drying techniques and their modern applications. Beginning with the basic principles and processes of freeze drying, it incorporates specific discussion of freeze-drying different categories of food products, before moving to an analysis of recent developments in freeze-drying technology. The result is a key publication in the fight to extend the shelf-life of food products and expand the distribution of high-quality freeze-dried foods. Freeze Drying of Food Products readers will also find: * An editorial team with a wide range of pertinent research experience * Detailed discussion of different freeze-drying processes such as vacuum drying, atmospheric drying, and spray drying * Commercial applications of freeze-dried food products Freeze Drying of Food Products is ideal for researchers and industry professionals involved in food production, food distribution, or food biotechnology, as well as students studying these and other related fields.
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Veröffentlichungsjahr: 2024
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Table of Contents
Cover
Table of Contents
Title Page
Copyright Page
List of Contributors
Preface
Acknowledgments
1 Freeze‐Drying: Basic Principles and Processes
1.1 Introduction
1.2 Principle of FD Process
1.3 Basic Components of a Typical Freeze‐Dryer System
1.4 Types of FD Processes
1.5 Characterization of FD Samples
1.6 Applications of FD in Food Processing
1.7 Advantages of FD
1.8 Limitations of FD
1.9 Commercial Status
1.10 Conclusion and Future Perspectives
References
2 Mathematical Modeling of Freeze‐Drying Process
2.1 Introduction
2.2 Principle of Freeze‐Dryer
2.3 Mathematical Model for Freezing
2.4 Mathematical Expression of the Progress of Freeze‐Drying
2.5 One‐Dimensional Model (
R
p
–
K
v
Model)
2.6 Three‐Dimensional Model (
K
cc
Model)
2.7 Conclusion
References
3 Freeze Drying of Fruits and Vegetables
3.1 Introduction
3.2 Physical Characteristics of Freeze‐Dried Fruits and Vegetables
3.3 Biochemical Characteristics of Freeze‐dried Fruits and Vegetables
3.4 Freeze Drying for Encapsulation
3.5 Applications of Freeze‐dried Fruits and Vegetables
3.6 Advantages and Disadvantages of Freeze Drying
3.7 Conclusion
References
4 Freeze‐Drying of Meat and Seafood Products
4.1 Introduction
4.2 Principles of Freeze‐Drying Technology
4.3 Effect of Freeze‐Drying on the Sensory Attributes of Meat and Seafood Products
4.4 Stability of Freeze‐Dried Meat and Seafood Products
4.5 Conclusions
Acknowledgments
References
5 Freeze‐Drying of Dairy Products
5.1 Introduction
5.2 Application of Freeze‐Drying in Different Dairy Products/Ingredients
5.3 Application of Freeze‐Drying of Other Dairy Products
5.4 Spray Freeze‐Drying
5.5 Advanced Freeze‐Drying Methods
5.6 Conclusion
References
6 Freeze‐Drying of Probiotics for the Incorporation in Functional Foods: Drying Process, Viability, and Powder Properties
6.1 Introduction
6.2 Functional Foods
6.3 Cultivation and FD of Probiotics
6.4 Protection of Probiotics During FD
6.5 Stability and Viability Assessment After FD
6.6 Properties of Freeze‐Dried Probiotic Powders
6.7 Rehydration of Freeze‐Dried Probiotics
6.8 Conclusion and Future Trends
References
7 Freeze‐Drying Effect on Nutrients and Their Stability
7.1 Introduction
7.2 Vitamin
7.3 Minerals
7.4 Bioactive Compounds
7.5 Future Perspective
7.6 Conclusion
References
8 Packaging of Freeze‐Dried Products
8.1 Introduction
8.2 History of Freeze‐Dried Foods
8.3 Industrial Process of Freeze Drying
8.4 Need for Good Packaging for Freeze‐Dried Food Products
8.5 Selection of Packaging Material
8.6 Types of Packaging for Freeze‐Dried Foods
8.7 Quality Consideration During Packaging
8.8 Case Studies of the Packaging of Freeze‐Dried Food Products
8.9 Market Scenario
8.10 Sustainability Aspects
8.11 Safety Aspects of Freeze‐Dried Product Packaging
8.12 Principal Instrumental Techniques Employed for Packaging Controls
8.13 Conclusion and Future Scope
References
9 Advances in Freeze Drying to Improve Efficiency and Maintain Quality of Dehydrated Fruit and Vegetable Products
9.1 Introduction
9.2 Challenges in Freeze Drying
9.3 Novel Freeze Drying Systems
9.4 Conclusion and Future Prospects
References
10 Commercial Applications of Freeze Drying in Food Processing
10.1 Introduction
10.2 Commercial Applications of Freeze‐Dried Products
10.3 Cost Analysis of Freeze‐Dried Food Products
10.4 Industries Freeze‐Drying Operation
10.5 Industrial Freeze‐Drying Device
10.6 Future Prospects
10.7 Conclusions
References
Index
End User License Agreement
List of Tables
Chapter 1
Table 1.1 Effect of freeze‐drying (FD) on physicochemical properties of dif...
Chapter 2
Table 2.1 Values applied to the simulation shown in Figures 2.20 and 2.21....
Chapter 3
Table 3.1 Polyphenolic content of dried fruit and vegetables.
Table 3.2 Ascorbic acid content of different freeze‐dried fruits and vegeta...
Table 3.3 Application of freeze drying as encapsulation technique.
Chapter 4
Table 4.1 Influence of freeze‐drying process on sensory quality parameters ...
Table 4.2 Ability of the freeze‐drying process to stabilize meat and seafoo...
Chapter 5
Table 5.1 Effects of freeze‐drying on different cultures.
Table 5.2 Application of freeze‐drying in different bioactive products.
Table 5.3 Effect of spray freeze‐drying on various dairy products.
Chapter 6
Table 6.1 Probiotic microorganisms (Song et al. 2012).
Table 6.2 Some examples of probiotic bacteria used in food products.
Table 6.3 Different cryoprotectants and their effect on the survival rate o...
Chapter 7
Table 7.1 Sources, stability, and functions of fat‐soluble and water‐solubl...
Table 7.2 Effect of freeze drying (FD) on vitamins in various food material...
Table 7.3 Effect of freeze drying on the mineral content of camel’s milk.
Table 7.4 Effect of freeze drying on various food materials on bioactive co...
Chapter 8
Table 8.1 Different operating parameters for freeze‐dried foods.
Table 8.2 Packaging materials for different types of freeze‐dried food prod...
Table 8.3 Advantages and disadvantages of packaging freeze‐dried food produ...
Chapter 9
Table 9.1 Some recent studies conducted on vegetables and fruits using infr...
Table 9.2 Some recent studies conducted on some vegetables and fruits using...
Table 9.3 Some recent studies conducted on some fruits and vegetables using...
Chapter 10
Table 10.1 Leading Industries Producing Freeze‐Dried Products.
List of Illustrations
Chapter 1
Figure 1.1 Freeze‐drying process, presenting freezing, primary drying, and s...
Figure 1.2 Basic components of a typical freeze‐dryer system. (Freeze‐dryers...
Figure 1.3 Atmospheric spray freeze‐drying apparatus.
Figure 1.4 Flow illustration of spray freeze‐drying.
Figure 1.5 Diagram of four‐fluid nozzle.
Figure 1.6 SEM pictures of the surface (A–D) and interior (a–d) of freeze‐dr...
Figure 1.7 Major food applications of freeze‐drying.
Chapter 2
Figure 2.1 Shelf‐type freeze‐dryer equipped with temperature controllable sh...
Figure 2.2 Radiation‐type freeze‐dryer.
Figure 2.3 Atmospheric freeze‐dryer (heat pump dryer).
Figure 2.4 Mass balance of gas in a freeze‐dryer.
Figure 2.5 Computational fluid dynamics (CFD) simulation of water vapor flow...
Figure 2.6 Modeling heat transfer of solutions in vials frozen by shelf cool...
Figure 2.7 Example of simulation results of solution freezing.
Figure 2.8 Simulated temperature history, temperature distribution, and prog...
Figure 2.9 Optical microscope image of the ice microstructure and ice crysta...
Figure 2.10 Variations of mean ice crystal size depending on the cooling rat...
Figure 2.11 Dried layer permeability values estimated from the ice crystal s...
Figure 2.12 Progress of freeze‐drying.
Figure 2.13 Mass transfer within the drying layer during the primary drying ...
Figure 2.14 Classification of progress of freeze‐drying.
Figure 2.15 Schematic of
R
P
–
K
v
model.
Figure 2.16 Schematic of freeze‐drying proceeding with radiative heat.
Figure 2.17 Approximation of mean layer thicknesses by the hollow sphere mod...
Figure 2.18 Schematic of
K
cc
model.
Figure 2.19 Experimentally obtained sublimation and bottom surface area duri...
Figure 2.20 Comparison of experiment and simulation (Nakagawa and Ochiai 201...
Figure 2.21 Contour line of the total drying time as functions of heater tem...
Chapter 3
Figure 3.1 Cubes of different freeze‐dried fruit and vegetable.
Figure 3.2 The representative microstructure of 12 fresh and freeze‐dried fr...
Figure 3.3 Physical appearance and size comparison of the baked oil containi...
Figure 3.4 Oil‐free bread samples showing transverse structure and loaf size...
Figure 3.5 Appearance of milkshakes prepared using freeze‐dried fruit and ve...
Chapter 4
Figure 4.1 Schematic representation of freeze‐drying process.
Figure 4.2 Scheme of how the freeze‐drying process can affect meat.
Figure 4.3 Scheme of how the freeze‐drying process can affect seafood produc...
Chapter 5
Figure 5.1 Changes in the cells at different freezing rates. (a) Slow freezi...
Figure 5.2 Schematic diagram of atmospheric spray freeze‐drying apparatus....
Figure 5.3 Schematic diagram of microwave freeze‐drying.
Chapter 6
Figure 6.1 Categories of functional foods.
Figure 6.2 SEM images of freeze‐dried probiotic powder particles (protective...
Figure 6.3 The comparison of processing steps of SD, FD, and SFD.
Chapter 7
Figure 7.1 Schematic diagram of freeze drying.
Figure 7.2 Effects of freeze drying on tomatoes.
Chapter 8
Figure 8.1 Freeze‐drying storage conditions.
Figure 8.2 Process flow chart for industrial manufacturing of freeze‐dried p...
Figure 8.3 Barrier properties of packaging against environmental factors dur...
Figure 8.4 Freeze‐drying packaging requirements.
Figure 8.5 Common types of packaging material for freeze‐dried food products...
Figure 8.6 Market freeze‐dried products available globally.
Chapter 9
Figure 9.1 Advantages of microwave/ultrasound/infrared‐assisted freeze dryin...
Chapter 10
Figure 10.1 Schematic of the phase for triple points.
Figure 10.2 Steps involved in freeze drying, from sample preparation to fina...
Figure 10.3 Step involved in the industrial freezing process.
Guide
Cover Page
Table of Contents
Title Page
Copyright Page
List of Contributors
Preface
Acknowledgments
Begin Reading
Index
WILEY END USER LICENSE AGREEMENT
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Freeze Drying of Food Products
Fundamentals, Processes and Applications
Edited by
Roji Balaji Waghmare
Department of Food Engineering and Technology, Institute of Chemical Technology, Mumbai, India
Manoj Kumar
Chemical and Biochemical Processing Division, ICAR ‐ Central Institute for Research on Cotton Technology, Mumbai, India
Parmjit Singh Panesar
Department of Food Engineering and Technology, Sant Longowal Institute of Engineering and Technology, Longowal, Punjab, India
This edition first published 2024© 2024 John Wiley & Sons Ltd
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The right of Roji Balaji Waghmare, Manoj Kumar, and Parmjit Singh Panesar to be identified as the the editorial material in this work has been asserted in accordance with law.
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List of Contributors
Rubén AgregánCentro Tecnológico de la Carne de GaliciaSan Cibrao das Viñas, OurenseSpain
Shalini S. AryaDepartment of Food Engineering and TechnologyInstitute of Chemical TechnologyMumbaiIndia
Kalyan BarmanDepartment of HorticultureInstitute of Agricultural Sciences Banaras Hindu UniversityVaranasi, Uttar PradeshIndia
Surya N. ChaurasiaDivision of Vegetable ProductionICAR‐Indian Institute of Vegetable ResearchVaranasi, Uttar PradeshIndia
Tanuva DasDepartment of Food Engineering and TechnologyInstitute of Chemical TechnologyMumbaiIndia
Ruben DominguezCentro Tecnológico de la Carne de GaliciaSan Cibrao das Viñas, OurenseSpain
Noemí EchegarayCentro Tecnológico de la Carne de GaliciaSan Cibrao das Viñas, OurenseSpain
Ertan ErmişDepartment of Food Engineering Faculty of Engineering and Natural SciencesIstanbul Sabahattin Zaim UniversityIstanbulTurkey
Yogesh GatDepartment of Food Engineering and TechnologyInstitute of Chemical TechnologyMumbai, MaharashtraIndia
Papiha GawandeDepartment of Food Engineering and TechnologyInstitute of Chemical TechnologyMumbai, MaharashtraIndia
Mouandhelmamou HassaniAmity Institute of Food TechnologyAmity University RajasthanJaipurIndia
Hatice E. KırtılDepartment of Food Engineering Faculty of Engineering and Natural SciencesIstanbul Sabahattin Zaim UniversityIstanbulTurkey
Hare KrishnaDivision of Vegetable ProductionICAR‐Indian Institute of Vegetable ResearchVaranasi, Uttar PradeshIndia
Manoj KumarChemical and Biochemical Processing DivisionICAR‐Central Institute for Research on Cotton TechnologyMumbaiIndia
Shiv KumarMMICT&BM (HM)Maharishi Markandeshwar (Deemed to be a University), MullanaAmbala, HaryanaIndia
Yogesh KumarDepartment of Agricultural and Food SciencesUniversity of BolognaCesena, FCItaly
Yasemin Ş. KüçükataDepartment of Food Engineering Faculty of Engineering and Natural SciencesIstanbul Sabahattin Zaim UniversityIstanbulTurkey
Jose M. LorenzoCentro Tecnológico de la Carne de GaliciaSan Cibrao das Viñas, OurenseSpain
Área de Tecnología de los Alimentos Facultad de Ciencias de OurenseUniversidad de VigoOurenseSpain
Rahul MehraMMICT&BM (HM)Maharishi Markandeshwar (Deemed to be a University), MullanaAmbala, HaryanaIndia
Anuradha MishraMMICT&BM (HM)Maharishi Markandeshwar (Deemed to be a University), MullanaAmbala, HaryanaIndia
Arun S. MujumdarDepartment of Bioresource Engineering, Macdonald CollegeMcGill UniversityMontreal, QuebecCanada
Paulo E.S. MunekataCentro Tecnológico de la Carne de GaliciaSan Cibrao das Viñas, OurenseSpain
Kyuya NakagawaDepartment of Chemical Engineering Faculty of EngineeringKyoto UniversityKyotoJapan
Donald Lyngdoh NonglaitDepartment of Food Engineering and TechnologyInstitute of Chemical TechnologyMumbaiIndia
Arun Kumar PandeyAmity Institute of Food TechnologyAmity University RajasthanJaipurIndia
Parmjit Singh PanesarDepartment of Food Engineering & TechnologyS.L. Institute of Engineering & TechnologyLongowal, PunjabIndia
Mirian PateiroCentro Tecnológico de la Carne de GaliciaSan Cibrao das Viñas, OurenseSpain
Research and Development DepartmentIdaho Milk ProductsJerome, IDUSA
Devraj RajputDepartment of Food Engineering and TechnologyInstitute of Chemical TechnologyMumbaiIndia
Gunvantsinh RathodFood Science InstituteKansas State UniversityManhattan, KSUSA
Research and Development DepartmentIdaho Milk ProductsJerome, IDUSA
Suchismita RoyFood Science InstituteKansas State UniversityManhattan, KSUSA
Swati SharmaDivision of Vegetable ProductionICAR‐Indian Institute of Vegetable ResearchVaranasi, Uttar PradeshIndia
Rajat SuhagFaculty of Agricultural, Environmental and Food SciencesFree University of BolzanoPiazza UniversitàBolzanoItaly
Roji Balaji WaghmareDepartment of Food Engineering and TechnologyInstitute of Chemical TechnologyMumbaiIndia
Preface
Freeze‐drying, also known as lyophilization, has been a significant breakthrough for the food industry, particularly for the dehydration of sensitive and high‐value foods. This technique gained prominence after World War II as a method of preserving and storing food products without the need for refrigeration. Compared to conventional drying methods, freeze‐drying offers several advantages, including the preservation of morphological, biochemical, and immunological properties, structure, surface area, and stoichiometric proportions. This book aims to serve as a reference for anyone interested in using freeze‐drying to extend the shelf life of food, whether for academic or practical applications.
The book describes the fundamentals and practices used in freeze‐drying areas with respect to different food products. It also discusses the applications of freeze‐drying in the preservation of different food products such as fresh produce, meat and poultry, dairy products, functional foods besides the effect on nutrients and their stability. The summary also includes advances in the conventional freeze‐drying process through the application of more advanced freeze‐drying setups and other techniques that aim to reduce drying time and increase drying rate.
The book comprises 10 chapters, which are contributed by experts in their area of research. Chapter 1 deals with a fundamental understanding of freeze‐drying, its principles, and the process involved. The mathematical modeling of freeze‐drying, presenting a mathematical approach to the freezing and drying of food products, has been discussed in Chapter 2. Chapter 3 has been focused on the application of freeze‐drying for preserving fruits and vegetables, highlighting its effectiveness in retaining the quality characteristics of fresh produce.
Chapter 4 discusses the use of freeze‐drying to increase the shelf life of meat and seafood products, while Chapter 5 focuses on the freeze‐drying of dairy products. Chapter 6 deals with the freeze‐drying of probiotics for incorporation into functional foods, with a particular focus on the stability and viability of probiotics during and after the freeze‐drying process.
Chapter 7 describes the effects of freeze‐drying on vitamins, minerals, and bioactive compounds, while Chapter 8 discusses the criteria required for packaging materials for freeze‐dried foods and the various types of commercially available packaging for such products. Chapter 9 sheds light on advances in freeze‐drying technology to reduce energy consumption and improve energy efficiency, while the final chapter has been focused on the commercial applications of freeze‐drying in the food industry.
In summary, this book provides a comprehensive overview of freeze‐drying as a drying technique for food products, offering insights into the fundamentals, principles, and process involved, as well as highlighting its applications and advancements. The book would be highly useful for the faculty, research students, and industry personnel involved in food processing, dairy technology, food microbiology, food biotechnology, and allied fields.
Roji Balaji Waghmare, Manoj Kumar, Parmjit Singh Panesar
October 2023
Acknowledgments
We are indeed grateful to the contributors to all the chapters for their input and timely revision of the manuscript. We also acknowledge the various sources of illustrations used in the book that have been given in the form of figures, tables, and references.
We are especially obliged to Rebecca Ralf, Commissioning Editor, Kelly Labrum, and Ashik Melvin, Managing Editor, John Wiley & Sons Limited, UK, for all their support in bringing out this volume. We also extend our thanks to the production team at John Wiley & Sons Limited, UK, for their efforts in the production of this volume.
Last but not least, we acknowledge the support of our family members while preparing this volume.
Editors
Roji Balaji Waghmare
Manoj Kumar
Parmjit Singh Panesar
1Freeze‐Drying: Basic Principles and Processes
Roji Balaji Waghmare1, Manoj Kumar2, and Parmjit Singh Panesar3
1Department of Food Engineering and Technology, Institute of Chemical Technology, Mumbai, India
2Chemical and Biochemical Processing Division, ICAR‐Central Institute for Research on Cotton Technology, Mumbai, India
3Department of Food Engineering & Technology, Sant Longowal Institute of Engineering & Technology, Longowal, Punjab, India
1.1 Introduction
It is possible that drying food is the earliest means of preserving it for an extended period of time, making it a crucial unit operation. Drying is most commonly used to turn a wet or liquid product into a powder, flake, or solid form without altering the product's physicochemical qualities (Maisnam et al. 2015; Assegehegn et al. 2019). Foods that have been dried have a longer shelf life because the drying process stops enzyme and microbial activity (Prosapio and Norton 2018). Traditional drying, on the other hand, degrades the physical and chemical properties of food, which can make it unpalatable to customers. As a result, enhanced drying methods are crucial for food and agro‐products to ensure the production of high‐quality goods with reduced drying times, increased capacities, enhanced process controls, reduced operational costs, and enhanced safety. Conventional drying processes can degrade nutrients, decreasing the overall quality of dried foods. In light of this, developing and researching innovative drying tools and methods are crucial.
“Altmann used freeze‐drying as early as 1890, his technique went unnoticed for over 40 years. …
… the optimism may have somewhat dimmed, the promise remains, and economic changes in the future may well stimulate another surge in development.”
Meryman (1976)
The above words are extracted from the abstract of the article “Historical recollections of freeze‐drying,” where author was optimistic about the future of freeze‐drying (FD) or lyophilization of food.
The age‐old Chinese and Peruvian Incas had some knowledge of FD. These people used to leave meat outdoor in the cold season to prolong storage and improve flavor. Prior to drying, the meat was first frozen. On the mountain tops above Machu Picchu, the ancient Incas kept potatoes and other harvests. The meal in the high altitudes' low pressure slowly sublimated the water inside due to the cold mountain temperatures that caused it to freeze. Food that has been freeze‐dried is lighter and stays longer than other dried samples (Hua et al. 2010).
In the nineteenth century, FD was widely used and employed in research and technology. Nevertheless, the uses of first industrial FD were not seen until after the Second World War. Initially, the medical business was the only one to use the FD procedure to produce medicines, cells, and other related items. The food industry did not begin to use FD until the middle of the twentieth century (Garcia‐Amezquita et al. 2015). This technique has quickly risen to prominence as a crucial method for the long‐term storage of food items, even among the many other types of drying methods. FD is frequently used in the food business since it results in superior quality dried food. FD relies on the fact that a product's solvent will eventually evaporate. In this process, the solvent – which can be water or an organic solvent – crystallizes at low temperatures before rapidly changing phase from solid to gas. Because FD is carried out at lower temperatures, the qualitative attributes of the food are preserved, and the damage to thermolabile food components is limited (Martínez‐Navarrete et al. 2019). Because of this, FD serves primarily to ship a product with a longer shelf life, and the quality of food is maintained after being reconstituted with water.
FD offers numerous advantages compared to conventional drying technology. The main advantages of FD are maintenance of morphological, biochemical, and immunological characteristics; high recovery of volatiles; maintenance of structure, surface area, and stoichiometric proportions; long time frame of realistic usability; and reduced weight for storage, shipping, and handling (Ciurzyńska and Lenart 2011; Isleroglu et al. 2018). Since FD is performed at low temperature, they present a lower risk for products labile to heat degradation. Therefore, FD can be applicable for valuable materials that are heat sensitive or samples sensitive to heat that cannot be treated using other processes involving high temperatures (Morais et al. 2016).
1.2 Principle of FD Process
To remove the solvent from a liquid formulation is the fundamental idea of FD, which is a method of preservation. As can be seen in Figure 1.1, there are typically three stages to the FD process: freezing, primary drying, and secondary drying. However, there are five crucial processes that must occur in order to fully comprehend the mechanics at play here: freezing, sublimation, desorption, vacuum pumping, and vapor condensation (Liu et al. 2008). At first, the liquid formulations are cooled to a low temperature, which freezes all of the water existing in the substance. In the sublimation drying process, the frozen solvent is first heated to a point where it leaves its solid state and enters the vapor phase (primary drying). After the initial freezing process, the unfrozen liquid is removed via desorption (secondary drying). Consequently, FD involves two equally important processes: freezing and drying (Tang and Pikal 2004).
Figure 1.1 Freeze‐drying process, presenting freezing, primary drying, and secondary drying stages.
Source: Morais et al. (2016)/Reproduced with permission from Elsevier.
The time and energy needed at each stage is highly dependent on the nature of the product, the dryer's design and configuration, and other process variables. In addition, moisture content standards of final product vary by type. While the necessity of proper storage of freeze‐dried products may not immediately jump out, it has a profound impact on the durability and safety of the dried goods. Most FD is intended for long‐term storage, which means that it must be packaged and stored in such a way as to prevent the deteriorating biochemical and microbiological reactions that would otherwise occur. Storage stability has been estimated using appropriate shelf‐life tests, which have included approaches incorporating accelerated shelf‐life testing.
1.2.1 Freezing of Raw Material
Freezing is the first phase and one of the essential steps during FD. All the food products such as fresh produce, beverages, and coffee should be subjected to freeze before primary drying (Nowak and Jakubczyk 2020). During the preliminary phase of freezing, the sample is reduced to a temperature below its eutectic point or glass transition temperature. It is the lowest point of the combination of composition and temperature at which the sample freezes. In this step, the primary focus is on freezing any liquid water that may be present in the sample. In this step, it is advised to cool the sample to a temperature lower than the glass transition temperature for each humidity concentration. Over this point, sample is in unstable rubbery form, whereas, under this point, sample changes into glassy or amorphous phase (Garcia‐Amezquita et al. 2015). This step transforms 70–90% of free liquid water present in food sample to solid frozen state. However, the remaining water is present in bound state (Bhushani and Anandharamakrishnan 2017). During FD, the suitable freezing rate relies on the type of food sample which could be solution, suspension, or biomaterials. Freezing rate depends on the temperature of the sample, temperature of the freezing medium, and also on the heat transfer resistance (Nowak 2017). To achieve the less primary drying time, it is necessary to maintain the big ice crystal size which results in less resistance to mass transfer in the final dried sample. However, development of several small ice crystals results in high resistance (Assegehegn et al. 2019). The temperature reducing the rate of cooling and freezing also has significant impact. Faster freezing results into the creation of limited glassy phase and inhibits extreme dehydration of food sample during freezing, whereas extremely fast freezing leads to the destructive changes, for example rupturing the cell wall and its other cellular components (Hua et al. 2010).
1.2.2 Primary Drying – Sublimation
Following the freezing stage and during primary drying, ice is removed by sublimation. Sublimation begins at the ice surface and proceeds across the frozen–dry matter interface, mainly dependent on the temperature–pressure combinations maintained. The drying chamber's pressure and the drying process's heat intensity are crucial factors in the FD process (Rambhatla et al. 2006). If the pressure in the compartment or the partial pressure of vapor in the compartment is lower than the vapor pressure of ice, then the frozen solvent can be evacuated from the solid state and entered straight into the vapor phase. This has been suggested that the compartment pressure should be maintained in between one fourth to one half of vapor pressure of ice to achieve controlled sublimation process (Bhushani and Anandharamakrishnan 2017). For contact heating, maintaining the suitable temperature of shelf is essential. However, during radiation heating, the space between the radiation source and sample and the intensity of radiation are important factors to be maintained (Nowak and Lewicki 2005). The primary drying begins from the top layer of the material and it progresses to the bottom layer. Thus, the vapor is evacuated by diffusion or convection through the void area (Ingvarsson et al. 2011). It is an essential step which has a significant influence on the mass transfer rate. As the sublimation step progresses, the water from the sample is decreased and therefore the glass transition temperature also differed (Fellows 2009). Freeze‐dried products show low shrinkage and highly porous structures as the ice crystals in the samples get sublimated and the space which originally contained the ice is maintained (Jiang et al. 2017).
1.2.3 Second Drying – Desorption
During secondary drying, leftover moisture (in the unfrozen form) is removed by desorption, justifying higher time requirements. Desorption is performed by rising the temperature and decreasing the vapor pressure in the drying compartment of freeze‐dryer. The secondary drying temperature should be maintained in a proper range to prevent denaturation of the material (Cheng et al. 2017; Liu et al. 2022). When compared to primary drying, the time required for desorption is only about 30–50%. Lower drying rates are achieved in secondary drying by reducing the amount of water present in the material, increasing barrier to heat and mass transfer, and binding water particles to dry particles (Millman et al. 1985; Tang and Pikal 2004). When the majority of the water has been eliminated throughout the FD process, leaving a structurally stable dried food material with ideally less than 0.5–3% leftover water, the process is said to have finished (Bhushani and Anandharamakrishnan 2017; Liu et al. 2022).
1.3 Basic Components of a Typical Freeze‐Dryer System
A FD system is mainly composed of a drying chamber, a vacuum pump, a heat source, and a condenser. In order to achieve the maximum benefits of the FD system, these components must be properly selected and operated, and this depends on the specifications of every product material (Garcia‐Amezquita et al. 2015). The basic components of a typical freeze‐dryer system are shown in Figure 1.2. The food material must be placed in a drying chamber that can maintain full vacuum and has shelves that are temperature controlled. It is required that the drying chamber to be completely sealed. The latent heat of sublimation is supplied by the heat supply for the shelves during the first stage of drying. Depending on the model of freeze‐dryer, a number of different tray styles and heating options are available. Ribbed trays, for instance, are used in contact and conduction freeze‐dryers and sit on heater plates. Due to the uneven distribution of heat, drying time increases. An accelerated freeze‐dryer has superior heat transmission since the food is heated via expanding metal mesh, as opposed to being directly contacted by the dryer's heating element, as in a contact dryer (Rolfgaard 1987; Bhushani and Anandharamakrishnan 2017; Hua et al. 2010). The plates are often used to heat the materials inside the drying chamber. Conduction and radiation are the two methods used to heat food sample. Conduction is used to heat sample by the lower plate, whereas radiation is used to heat sample upper plate. It is possible to add an electric heater or heat exchanger inside the plates. A temperature control system can regulate the plates' temperature (Hua et al. 2010). For the best results from FD, it is important to control the drying stage's temperature so that it is not too high and denatures the product. The drying can be accelerated by raising the heating temperature, however, excessive heat will lead to denaturation of the food sample (Liu et al. 2022).
Figure 1.2 Basic components of a typical freeze‐dryer system. (Freeze‐dryers are equipped with a vacuum chamber that may chill and heat the containers and their contents, allowing for the drying of food products while they are stored on shelves. The vacuum chamber is linked to a vacuum pump, a refrigeration unit, and accompanying controls.)
There can be two possible sources of the noncondensable gases in the FD unit. Air can enter a vacuumed unit in two ways: first, it can leak in from external environment; second, gases can escape from food sample as they dry (Hua et al. 2010). Through the use of the vacuum pump, the drying chamber is emptied of any gases that cannot be condensed. This is essential in order to reach the vacuum level of less than 0.61 kPa. The dryer system's total volume can inform the design of the vacuum system, which in turn will inform the size, kind, and number of vacuum pumps utilized (Mellor 1978).
1.4 Types of FD Processes
The high price tag of implementing FD means that it cannot be used for a wide variety of everyday food items. Market success has been achieved with this technology for biological formulations and high‐value foods (Morais et al. 2016). However, with the development of cutting edge hybrid drying methods, FD is finding more and more uses in the food business. The following sections provide more detail on how FD is being utilized in tandem with a variety of other techniques, as well as some novel approaches that enhance FD procedures, to fulfill individual product needs. Common methods of FD food items include (1) vacuum FD, (2) atmospheric FD, and (3) spray FD.
1.4.1 Vacuum FD
Since the 1960s, the food industry has relied heavily on the vacuum FD technology to mass produce dried food items. This method has seen widespread use in recent years for drying a wide variety of high‐value foods, including fruits, vegetables, coffee, milk, meat, and more. It is the gold standard for making high‐quality dehydrated food items with minimum changes in texture, flavor, rehydration ability, nutritional value, and chemical makeup, and it is used all over the world (Ma et al. 2018). The process of vacuum FD combines the advantages of both vacuum drying and FD because it employs both of these methods simultaneously. This increases the rate at which water sublimates and helps to preserve the internal structure of particles (Shi et al. 2012).
To extract the water or solvent from a suspension using vacuum FD, the mixture is first frozen at a low temperature. Heat and mass are transferred concurrently in the vacuum FD process. Increases in heat and mass transfer rates during drying can be achieved through a number of different techniques (Patil et al. 2010). During the FD process, ice crystal size, drying rate, and heat and mass transfer rate can all be improved by annealing (Shi et al. 2012). For a set amount of time, a frozen liquid is kept above its final freezing temperature in the annealing process (Lim et al. 2018; Patil et al. 2010). Ice crystals form within and outside of the starch nanoparticles, thanks to the annealing process and the various cryoprotectants (Shi et al. 2012). Starch nanoparticles' glass transition temperature, particle size, and residual moisture content were all affected. To see how microbial transglutaminase (MTGase) might change the characteristics of gels made from vacuum freeze‐dried silver carp surimi (Guo et al. 2019), proteins can be dried in a vacuum without losing their gelling properties during the process (Danial et al. 2016). On the other hand, Guo et al. (2019) found that the gel texture of the surimi was diminished due to the vacuum FD process denaturing the proteins to some degree. The gel texture of the dried surimi is enhanced by heating it to 40 °C and the addition of MTGase. Pretreatment followed by vacuum FD results in surimi powder with a better gel texture. Grass carp (Ctenopharyngodon idella) fillets are dehydrated using vacuum FD to create high‐quality dried products with favorable nutritional quality, texture, flavor, color, little shrinkage, and high porosity. A partial least squares regression (PLSR) model was created for grass carp fillets to predict the percentage of mass loss during dehydration and the percentage of mass gain during rehydration (Ma et al. 2017).
1.4.2 Atmospheric FD
The process of atmospheric FD combines the benefits of both FD and convective drying. To facilitate the sublimation of the frozen solvent, a high vacuum must be applied to the frozen samples, which increases the energy requirements of the process and hence the cost. The diagram of atmospheric spray FD is shown in Figure 1.3. There is no need for a strong suction while drying frozen samples. Because of this, the original idea behind air FD was to reduce energy usage compared to vacuum FD while keeping the same high product quality. This can be done if the water vapor pressure in the drying chamber is less than that of the frozen sample. This state is attained by exposing a frozen sample to a stream of cold, dry gas (Ishwarya et al. 2015). Both atmospheric FD and vacuum freeze‐dried products share similar rehydration kinetics and hygroscopic properties. Antioxidant levels were reduced by 15% when air‐dried versus vacuum‐dried (Rahman and Mujumdar 2012; Taylor et al. 2010). The antioxidant capabilities of eggplant (Solanum melongena L.) samples were examined by Colucci et al. (2018), who looked at how various drying process variables affected the eggplant. Antioxidant capacity, total phenolic content, and ascorbic acid in atmospheric FD eggplant samples were observed to decrease with increasing drying temperature and air velocity. On the other hand, the antioxidant content of the eggplant sample is unaffected by the ultrasonic‐assisted atmospheric FD process.
Figure 1.3 Atmospheric spray freeze‐drying apparatus.
Source: Israel Borges Sebastião et al. (2016)/ Reproduced with permission from Elsevier.
1.4.3 Spray FD
With the advantages of both spray drying and FD, spray FD is a potential drying method that produces powdered materials (Anandharamakrishnan 2019). The spray FD methodology can be broken down into the following steps: (1) atomization, wherein the solution or suspension is broken up into minute droplets, resulting in a high surface‐to‐mass ratio; (2) solidification of the droplets (freezing), when the atomized liquid metals solidify upon coming into contact with a cryogenic medium (usually liquid nitrogen), and (3) sublimation of frozen particles at low temperature and pressure (Parthasarathi and Anandharamakrishnan 2016; Isleroglu et al. 2018). The flow diagram of spray FD is shown in Figure 1.4.
Due to the lower temperatures employed during the spray FD process, thermally sensitive materials can be processed with success. Microencapsulation of heat‐sensitive probiotic microbes and chemicals including vitamin E, bovine serum albumin, docosahexaenoic acid, and fish oil has been a popular use for spray FD in recent years (Parthasarathi and Anandharamakrishnan 2016; Isleroglu and Turker 2019). Spray FD was reported to be an efficient way of encapsulating Lactobacillus paracasei utilizing a maltodextrin–trehalose mixture as a matrix, with final viabilities more than 60% (Semyonov et al. 2010). Scientists noted that the atomizer is crucial to the production of high‐quality goods because it controls the spray's droplet size distribution. Ultrasonic‐aided spray FD (USFD) is the most recent development in the industry, and it has been used to achieve controlled particle size and shorter drying times (Ishwarya et al. 2015; Isleroglu and Turker 2019). Ultrasonic nozzles were found to be responsible for regulating the particle size and aerodynamic properties of spray FD particles when using USFD to create large, porous particles of mannitol, lysozyme, and BSA protein (D'Addio et al. 2012).
Figure 1.4 Flow illustration of spray freeze‐drying.
Source: Ishwarya et al. (2015)/Reproduced with permission from Elsevier.
Atomization can be accomplished with a variety of nozzle configurations, including those that use two fluids, three fluids, four fluids, and even ultrasonic waves. It has been reported that the ultrasonic nozzle provides very precise regulation of particle size, and that four fluid nozzles are well suited for medications with low aqueous solubility. Figure 1.5 depicts the recent use of four‐fluid nozzles for atomization in spray FD (Anandharamakrishnan 2019). There are two compressed air feeds, one for each fluid supply, that atomize the fluids independently. A thin film of liquid is formed over a fast‐moving gas when the streams collide. Around the epicenter of the impact, the shock wave disperses small droplets into a mist. Together with liquid nitrogen, these tiny droplets create a more uniform temperature field for heat transfer, which in turn encourages homogenous nucleation and the formation of fine ice crystals.
The comparative research on spray drying, FD, and spray–FD highlighted the significance of spray FD (Ishwarya and Anandharamakrishnan 2014). Authors compared the SFD‐grown coffee's physical attributes and aroma quality to those grown using the FD and spray drying procedures. Spray FD aids in preserving coffee's signature low‐boiling aromatic components, which are otherwise lost during the first stages of the FD and spray drying processes.
Figure 1.5 Diagram of four‐fluid nozzle.
Source: Anandharamakrishnan 2019/Reproduced with permission from Elsevier.
1.5 Characterization of FD Samples
To determine whether the process was effective and resulted in an appropriate freeze‐dried matrix, it is crucial to characterize the systems after they have been freeze‐dried. Additionally, it is important to determine if the process has not altered the sample's qualities (Morais et al. 2016). Freeze‐dried products are often associated with reduced shrinkage, greater porosity, and the retention of the original cellular structure. The FD method also does not significantly alter the structure of the sample (Ciurzyńska et al. 2022).
1.5.1 Color
Consumers' perceptions of a product's quality are greatly influenced by its visual qualities, making color one of the most crucial indicators of food quality (Waghmare 2021). The quality attributes of FD powder and spray‐dried bayberry powder can be determined using color evaluation (Cheng et al. 2017). The powder's browning index significantly enhanced during the period of the 50 days of storage at temperatures of 25 °C. ΔE for FD product was observed to be greater than spray‐dried product. In this study, it was found that the FD is suitable and effective technique to retain the superior quality of dried bayberry fruits. Carvalho et al. (2017) investigated the effects of FD and air‐drying methods on the color characteristics of whipped yogurt foam. Redness (a*) was the only color characteristic that did not indicate a significant variation between FD and AD foams. When compared to AD foams, which displayed an average L* of 79.7, FD foams displayed the lightest color, with L* value of 93.3. FD aids in preserving whipped yogurt foam's original color and flavor, whereas air‐drying promotes Maillard reactions, resulting in a browning exterior and toasted flavor.
1.5.2 Moisture
FD can decrease moisture level up to 2% (Deshwal et al. 2020). The effect of hot air‐drying and FD on kimchi powder preparation has been documented (Park et al. 2016). The amount of moisture of kimchi dried powder varied from 10.82% to 7.86%. The amount of moisture present in market product is lower than 10%. Hence, hot air‐drying and FD produces dried Kimchi powder as compared to market sample in moisture content. Drying methods for chives were investigated which included hot air‐drying (HAD), FD, catalytic infrared drying in combination with hot air‐drying (CIRD‐HAD), and catalytic infrared drying in combination with FD (CIRD‐FD) (Gu et al. 2022). The influence of catalytic infrared drying (CIRD) alone was also studied. The application of CIRD in addition to FD produces greater quality final dried product in less time and releases higher water from sample. It is difficult to preserve dried amorphous products in powdered form due to their ability for instinctive aggregation and caking, which lowers their quality. The damping of the particle surface results in plasticization and disintegration which leads to derivative variations in sample. Stępień et al. (2020) added greater molecular weight biopolymers such as maltodextrin and inulin to decrease hygroscopicity of freeze‐dried avocado powders but it was observed that addition of these biopolymers is not required to enhance its stability.
1.5.3 Scanning Electron Microscopy
The ability of a freeze‐dried sample to retain and preserve biologics, such as proteins, cells, and other fragile structures, depends on the stability of the sample's structure (Palmkron et al. 2023). The steps of FD are dehydration, freezing, and secondary drying. Powder's microporous surface is a result of the sample's water sublimating directly from ice to water vapor in the vacuum (Chen et al. 2023). Morphological variations were observed for FD and freeze‐dried powder with cryoprotectants for Lactobacillus rhamnosus (Chen et al. 2023). In FD sample, the cells are extremely damaged, whereas FD powder with cryoprotectants showed smooth surface and entirely coated by the cryoprotectants. Zhou et al. (2021) observed shrinkage dissimilarity among vacuum FD, and hot air‐dried garlic slices have presented in SEM images in Figure 1.6. In comparison to the vacuum FD slices, the surface of hot air‐dried slices was irregular and significantly distorted. Vacuum FD developed extremely wide pores because of the development of ice crystals in freezing step. While the quick evaporation of water caused the garlic structure to extreme shrinkage and deform during hot air‐drying, which resulted in the creation of a dense structure. In another research, the damaged surface layer with the invariable dispersion of minerals on the surface was visible with SEM images of FD bovine colostrum whey powder (Mehra et al. 2022).
Figure 1.6 SEM pictures of the surface (A–D) and interior (a–d) of freeze‐drying garlic with various slice thicknesses treated by vacuum freeze‐drying and hot air‐dried. (A) Vacuum freeze‐drying – 3 mm sample. (B) Vacuum freeze‐drying – 6 mm sample. (C) Hot air‐dried – 3 mm sample. (D) Hot air‐dried – 6 mm sample.
Source: Cunshan Zhou et al. (2021)/Reproduced with permission from Elsevier.
1.5.4 Thermal Analysis
In some FD processes, freezing is followed by a further annealing phase. The material temperature is raised during the annealing process above the glass transition temperature (Tg'), but lower the melting point of the frozen state. Improvement in ice crystal area and improved homogeneity inside and between vials in a FD are the two main aims of annealing (Palmkron et al. 2023). Glass transition temperatures (Tg) indicate the conversion in amorphous form of material from glassy form to rubbery forms. Greater Tg value is related to the greater stable product (Waghmare 2021). Examining the behavior of materials as they undergo thermal decomposition is vital to ensure safety, and this assessment can be achieved through a range of tests such as differential scanning calorimetry (DSC), thermogravimetry (TGA), microcalorimetry (C80), and adiabatic calorimetry (ARC) (Ding et al. 2022). Calorimetry examines thermal characteristics of material by observing its particular physical characteristics in relation to temperature. Differential scanning calorimetry evaluates the amount of heat absorbed in response to variation in temperature. This method is frequently employed to monitor variations in phase transformation, including freezing, melting, glass transition, boiling, crystallization, and deterioration (Morais et al. 2016). In addition, this method is crucial for evaluation the recrystallization that can develop with few cryoprotectants, which may cause the process to become unstable (Zhang et al. 2008).
1.5.5 Rehydration Characteristics
Due to the ability to signify the physical and chemical modifications in samples during drying, the rehydration property of the dried sample was used as a quality index (Yali and Dongguang 2018). The quality of the dry sample improves with increasing rehydration. Freeze‐dried pineapple, mango, guava, acerola, and papaya were analyzed by Marques et al. (2009) for their rehydration properties. These particular items were rehydrated in distilled water at a temperature of 25 °C over a time frame of six hours. In this study, it was observed that the rehydration of the FD fruits included an initial high water uptake rate, a subsequent low rate, and eventually a condition that was near to saturation. In contrast to acerola and guava, which had increased rehydration ratios at saturation, mango, papaya, and pineapple showed increased rehydration rates. The ability to absorb water was influenced by damages during moisture elimination and by structural disintegration brought about by the rehydration process. Aksoy et al. (2019) conducted research on dried minced beef and found that the rehydration ratio of FD samples was higher than that achieved by ultrasound‐assisted vacuum drying (USV) and vacuum drying (VD). The rehydration ratio was shown to be greater for FD and CIRD‐FD than for hot air‐drying and CIRD‐HAD by Gu et al. (2022).
1.6 Applications of FD in Food Processing
Freeze‐dried foods are extensively used in various field activities for example aeronautics, armed forces, climbing, and research. These dried materials can be preserved at ambient temperature for significant time period after packaging (Liu et al. 2022). Major applications of FD in food products are presented in Figure 1.7.
Figure 1.7 Major food applications of freeze‐drying.
1.6.1 Fresh Produce
Fresh produce might not always be readily accessible for consumer and increased shelf life of fresh produce may be difficult due to presence of high water, lack of cold‐storage devices (especially in developing and poor nations), and potential for quality degradation. As a result, drying of these fresh produce makes them easier to handle, transport, and increase shelf life. Fresh fruits have high water content and are crucial to dry using traditional drying methods because it causes considerable damages to the product (Bhatta et al. 2020). Feng et al. (2022) observed that the taro powder which primarily contains polysaccharides and apple powder which primarily contains mono‐/disaccharides prevent structural damages in selected 12 freeze‐dried fresh produce. It was also observed that the mono‐ and disaccharides, particularly fructose, enhances hygroscopicity, while polysaccharides decreased it in final FD samples. Wang et al. (2022) studied energy‐conservation technique of vacuum FD kiwi fruit by providing changes in primary drying step. The method in which material temperature is greater than eutectic point temperature reduces energy use by 35% when compared to alternative procedures. Schössler et al. (2012) also reported decrease in period of drying needed to achieve final moisture of 10–11.5% (on dry matter basis) using ultrasonic treatment to FD for red bell pepper cubes. Ultrasonic treatment reduces drying periods and hence has the ability to decrease production cost of final dried powder.
1.6.2 Animal Products
Due to their high levels of important nutrients like protein, vitamins, minerals, and vital fatty acids, foods derived from animals are widely regarded as healthy and of high quality. Nevertheless, due to their large water activity and nutrient content, animal foods are prone to microbial spoilage. Therefore, animal products are acknowledged as foods that spoil rapidly and have a short storage period (Zouaghi and Cantalejo 2016). A series of extraction procedures were used to create a land snail meat substance with higher protein content by eliminating mucus, ash, and lipids (Pissia et al. 2022). A freeze‐dried snail meat concentration was created from the remaining leftover part from the last extraction. However, the prepared snail meat powder needs further research to use it as a functional ingredient in food products. In another study performed by Cantalejo et al. (2016), four months storage life was achieved for FD raw chicken breast meat. The application of ozone on FD product presented a storage period of up to 8 months at 21 ± 1 °C. Similarly, condition of modified atmosphere packaging along with ozonated treatment retains the textural and sensorial characteristics of FD chicken meat samples.
1.6.3 Dairy Products
Since spray drying can rapidly remove moisture from atomized milk droplets using hot air, it can be used with a wide variety of foods and is also a cost‐effective method, it is mostly used to manufacture powders of dairy products. Dairy products receives several benefits from FD, since it inhibits protein denaturation and the Maillard reaction, increases the preservation of thermally sensitive vitamins, and produces stiff and porous products that are shelf stable (Deshwal et al. 2020). Over the past several years, the interest for dairy products that are good for human health has increased due to increase in consumer demand (Mehra et al. 2022). As a result of its high microbial load and low coagulation temperature, bovine colostrum spoils quickly. Bovine colostrum has a short shelf life because of the high number of bacteria in it and the low temperature at which it coagulates. FD is preferred drying method for converting bovine colostrum whey into bovine colostrum whey powder. It helps to reduce degradation of heat‐sensitive compounds, mainly IgG, and increases storage period without changing its qualities. FD bovine colostrum whey powder presented a significant quantity of various nutrients such as IgG, protein, and total amino acids. Carvalho et al. (2017) investigated the impact of air‐drying and FD on the characteristics of yogurt foam. Water activity was higher in air‐dried samples than in freeze‐dried samples. In addition, freeze‐dried samples were much softer and less prone to cracking than their air‐dried counterparts.
1.6.4 Miscellaneous Applications
Because of its popularity, coffee is one of the world's most traded agricultural products. Ishwarya and Anandharamakrishnan (2015) examined the efficiency of spray drying, FD, and spray FD method for producing soluble coffee. Spray FD enhances instant solubility and flow characteristics of coffee powder. The electronic nose study revealed that the aroma profiles of spray FD and FD coffee granules were similar. The researchers demonstrated that the spray FD method may be used to develop soluble coffee with enhanced characteristics. Park et al. (2016) compared the physicochemical characteristics of vacuum freeze‐dried kimchi powder with those prepared by hot air‐dried. It was found that the vacuum FD is the most effective for preparing superior quality kimchi powder. Furthermore, sensory score was higher for FD product than hot air‐dried product. The water‐related quality in freeze‐dried multivegetable snacks was determined, specifically the effect of water activity on the structure and shrinkage of product (Ciurzyńska et al. 2022). Sodium alginate‐infused FD snacks have a compressed structure and without having more prominent pore. The effect of FD on physicochemical properties of different food products is presented in Table 1.1.
1.7 Advantages of FD
FD offers several benefits over conventional drying techniques in the food area. Following are the few advantages:
FD retains the original physical characteristics of food material as well as enzymatic and nonenzymatic reactions are also prevented.
The amount of water in FD sample can reach up to 2–3%, which permit higher shelf life of food products.
Significant benefits include high solubility and readily reconstituting dried product by rehydration, particularly for coffee or other instant foods. In this case, greater porosity and uniformly dispersed pores are also essential (Ciurzyńska et al.
2022
).
Table 1.1 Effect of freeze‐drying (FD) on physicochemical properties of different food products.
Food products
Sample
FD
FD model
Other drying methods
Key conclusion
References
Fresh produce
Garlic slices
Vacuum FD: prefrozen at −80 °C for 3 h; drying temperature – 18 °C; vacuum 0.518 mbar; cold‐trap temperature of −85 °C
Epsilon 2‐6D LSC plus, Martin Christ Ltd.
Hot air‐drying: temperature 60 °C; air speed 2 m/s
Vacuum FD product presented less moisture than hot air‐dried product.Vacuum freeze‐dried product showed increased water absorption rate than hot air‐dried product.
Zhou et al. (
2021
)
Pineapple, mango, guava, acerola, and papaya
Pressure 13 kPa and temperature −30 °C
Model L4KR, Edwards, Sao Paulo, Brazil
—
Mango, papaya, and pineapple showed increased rehydration rates in comparison to acerola and guava.
Marques et al. (
2009
)
Bayberry
Drying temperature −50 °C; drying time 48 h
FD‐1C‐50 (Boyikang, Beijing, China)
Spray drying: aspirator rate 100% (35 m
3
/h), entry temperature 160 °C, exit temperature 90 °C
Higher amount of bioactive compounds were found in FD sample than SD.FD is an effective and appropriate technique to retain bioactive compounds.
Cheng et al. (
2017
)
Chives
The prefreezing temperature: −20 °C; drying temperature: −80 °C
Epsilon 2‐6D LS C plus, Martin Christ Ltd., Germany
Hot air‐drying: temperature 70 ± 5 °C, catalytic infrared drying (CIRD): temperature70 ± 5 °C
CIRD‐FD most effectively retains quality characteristics.Highest retention of chlorophyll in CIRD‐FD and freeze‐dried samples.
Gu et al. (
2022
)
Avocado
Temperature −20 °C; pressure 0.035 mbars for 48 h
Alpha 1‐2LD plus Christ(United Kingdom)
—
Water activity of the FD powders including avocado, maltodextrin, and inulin were varying from 0.11 to 0.86.
Stępień et al. (
2020
)
Red bell pepper
Temperature −30 °C
EdwardsModulyo II, Edwards High Vacuum Int., UK
—
Ultrasonic treatment to the sample enhances temperature which helps in decrease of energy consumption.
Schössler et al. (
2012
)
Animal products
Minced meat
Drying temperature: −55 °C and 1 hPa for 72 h
Martin Christ, Beta 1‐8 LSC plus, Osterode am Harz, Germany
Ultrasonic vacuum drying: 25, 35, and 45 °CVacuum drying: 25, 35, and 45 °C; pressure 60 mbar; pump speed 2 l/s
Drying period remarkably reduced with increment in drying temperature.FD method leads to increased rehydration ratios, lesser shrinkage, and color variation.
Aksoy et al. (
2019
)
Dogfish skin gelatin gels
—
—
Spray drying
Maximum yield (8.67%) was found for oven‐pretreated FD and least (3.06%) for oven‐pretreated spray dried.Application as functional additive in various food production.
Salem et al. (
2020
)
Snail meat
—
—
—
Snail meat concentrate powder is high in protein and less in lipids content.The production of snail meat concentrate influences the physicochemical characteristics of snail meat protein.
Pissia et al. (
2022
)
Dairy products
Bovine colostrum whey powder
Cut into 1 cm
3
sized cubes and dried with lyophilizer
Free zone, Labconco, Kansas City, MO, USA
—
Significant quantity of protein, amino acids, and trace minerals.
