Preface

This book discusses dehydration processes. Chapter 1 examines the significance of water and dehydration processes in general. It reviews the two dehydration processes of food dehydration and hydrogel dehydration. It presents the physical basics of dehydration and discusses the state of water in food and hydrogels. Regarding food dehydration, the chapter demonstrates the significance of controlling the structuralkinetic states of water and their effect on the structural and sensing properties of dehydrated food. Regarding hydrogel dehydration, the chapter discusses its practical and theoretical importance and suitability for modeling the kinetics of food dehydration. The chapter also presents novel kinetic models that can describe hydrogel dehydration with great precision and reliability.

Chapter 2 presents recent developments in energy-efficient drying technologies for food dehydration. The authors discuss conventional dehydration processes based on solar dehydration, trash drying, smoke, drum, spray dehydration, fluidized bed drying, and freeze drying. They also describe advanced drying processes that include infrared, microwave, ultrasonic and other non-conventional drying techniques. Innovative food dehydrating methods use less energy and therefore contribute to environmental protection. During the dehydration process, some changes in dried food products may occur. Novel dehydration methods better conserve the chemical structure, color, taste, flavor, and appearance of the dried product. The chapter shows that the various dehydration techniques do not affect the fundamental structure of polysaccharides and that certain foods subjected to dehydration processes exhibit increased total phenolic content.

Chapter 3 reviews the state of the art in dehydration assisted by microwave (MW), infrared radiation (IR), and radio frequency (RF) applied to food drying, specifically to foods such as bananas and apples. It discusses the advantages and disadvantages of each method compared to conventional drying systems. IR dehydration in comparison to conventional dehydration exhibits certain advantages, such as a higher heating rate, shorter drying time, and greater quality of the dried product. As such, IR drying techniques are increasingly being used method for drying food, vegetables, grains, fruits, and other high-value products. MW has also been widely applied in the drying of various foods and is a proven method for improving the drying process and quality of dried products. RF has also been studied and applied in food processing. Each of the methods discussed in this chapter can be combined with other drying methods, such as hot air drying, heat pump drying, vacuum drying, and freeze drying.

Chapter 4 presents the theoretical basis of hybrid drying techniques based on MW drying, which can be enhanced via combination with other drying methods such as hot air drying, freeze drying, vacuum drying, and fluidized bed drying. Using MW in hybrid drying significantly enhances drying rates, making it a novel approach to retaining the quality of dried products. Each hybrid drying method has its own advantages. For example, hot air drying speeds up the removal of moisture from

the core of the food to the surface, whereas freeze drying assists in preserving the bioactive compounds and nutritional status of products. Fluidized bed drying and vacuum drying are preferable techniques in cases when a better rehydration ratio and uniform heating of the products are required. The chapter describes why the holistic approach is crucial to developing smart hybrid drying systems that bring together the efficiency of drying and the quality of the dried products.

Chapter 5 examines the effects of pre-treatment by ultrasound (US) in different media (water and ethanol) in the convective drying of BRS Vitória grapes. The study shows that pre-treatment with the US increased the efficiency of convective drying of the grapes by reducing drying time up to 61% when using ethanol as media. The pre-treatment did not result in any significant effects of media on the texture, color, soluble solids, and water activity of the grapes. Pre-treatment with ethanol is thus revealed as effective in obtaining raisins, reducing drying time, maintaining the quality of the product, and promoting more retention of nutrients. There was no observed loss of phenolic content in grapes after drying. US combined with ethanol exhibited the highest phenolic content of the treatments. Regarding the kinetics of the investigated drying process, the chapter study establishes that the logarithm model is the best to describe the kinetics of the grape drying process when compared to other mathematical models.

Finally, Chapter 6 summarizes investigations in the kinetics of absorbed water dehydration from different hydrogels, including equilibrium swollen hydrogels of poly(acrylic acid) hydrogel (PAAH), poly(acrylic-co-methacrylic acid) (PAMAH), and poly(acrylic acid)-g-gelatin (PAAGH). The complex kinetics of dehydration of hydrogels are described by a series of novel kinetic models: distribution apparent energy activation model (DAEM), Webull's distribution of reaction times, the dependence of the degree of conversion (α) on the temperature defined by the logistic function, coupled single step-approximation, and iso-conversion curve. The chapter explains the complex kinetics of dehydration of hydrogels in terms of the fluctuating structure of the hydrogel, the phase state of the absorbed water, and the thermal activation of the hydrogel.

> **Jelena D. Jovanović** Research Professor, Institute of General and Physical Chemistry, Belgrade, Serbia

> > **1**

**Chapter 1**

**1. Introduction**

water removal from the material [4].

**2. Food dehydration**

properties), etc. [2]

Introductory Chapter: A

*Jelena D. Jovanović and Borivoj K. Adnadjević*

Comprehensive Review of the

Versatile Dehydration Processes

Water is the most abundant substance on the Earth and the main component of plant and animal tissues, in which it plays a role as a solvent and a reagent. The unique role of water in natural processes is related to its physical and chemical properties and its widespread. As a result, most materials in the natural conditions contain water either as chemically bound or retained in pores due to intermolecular interactions [1]. The presence of water in food and foodstuffs plays a significant role in the physico-

Dehydration is a complex reversible and endothermic physicochemical process of removing water from the material, which takes place under conditions of simulated energy exchange (especially heat) and mass transfer between the material and the external environment [3]. The removal of water is a kinetically complex process characterized by either rapid nucleation of water molecules at the reaction boundary phase (RBP) or nucleation at certain locations of the boundary phase (RBP), after which there is an increase in the size of the nucleus, which leads to the removal of water from the material. The most important feature of the dehydration process is the dominant influence of the dehydration product on the mechanism and kinetics of

The water content in food, fruits, vegetables, foodstuffs, and in agricultural products varies in a wide range from 60 to 98% by mass. The dominant content of water indicates the key role of water on the physicochemical, biological, and nutritional and sensing properties of the food. Water is, first of all, the most important medium in which chemicals (ions, salts, vitamins, etc.,) and biological reagents (sugars, proteins, lipids, DNA, enzymes, etc.,) move, collide, and react. In addition, water participates such as (a) reagent and coreagent in a series of degradation reactions (hydrolysis of lipids, Maillard reactions, enzymatic browning, vitamin degradation, etc.,); (b) stabilizes the most important biological structures, (enzymes, proteins, DNA, and cellular membrane); (c) control the growth of pathogens and other microorganisms; (d) significantly changes the physical and chemical properties of the material (thermal conductivity, thermal capacity, electrical and dielectric

chemical and biological processes that take place during their storage [2].

## **Chapter 1**
