He has worked in large pharmaceutical and multi- national food companies in Greece for 5 years and has at least 14 years experience in the public sector. Since , he has served as an assistant and associate profes- sor in the Department of Food Technology, Technological Educational Institute of Peloponnese ex Kalamata , Greece, specializing in issues of food technology, food processing, food quality, and safety.
He has written more than 90 research papers and reviews and has presented more than 90 papers and posters at national and international conferences. He has written two books in Greek, one on geneti- cally modified food and the other on quality control in food. Varzakas has participated in many European and national research programs as a coordinator or scientific member.
Tzia has more than 70 articles in international scientific SCI journals, 2 books in the Greek language, 1 book editor , and 6 chapters in international scien- tific books.
She has more than presentations at international conferences and more than at Greek conferences. She has participated in European research proj- ects and has coordinated many national research projects and projects in cooperation with Greek food industries.
She has been a reviewer in many international journals. The most recent and advanced information required for the efficient design and development of processes that are used in the manufacturing of food products has been described. The audience for this handbook includes practicing engineers in food and related industries, students preparing for careers as food engi- neers or food technologists, and other scientists and technologists seeking informa- tion about design and development of processes.
Although the first three chapters focus primarily on mass and energy balances, thermodynamics of foods, and food formulation, the chapters that follow are orga- nized according to traditional unit operations associated with the manufacturing of foods. Three key chapters cover the basic concepts of heat transfer, heat exchangers, and steam generation distribution.
Two additional background chapters focus on the basic concepts of diffusion and mass transfer in foods as well as modeling. The chapter on membrane processes deals with liquid food concentration but provides the basis for other applications of membranes in food processing. As demands for safe, high-quality, nutritious, and convenient foods continue to increase, the need for the concepts presented will become more critical.
In the near future, the applications of new technologies such as nanotechnology in food manufacturing will increase, and the role of engineering in process design and scale-up will be even more visible. Finally, the use of engineering concepts should lead to the highest quality of food products at the lowest possible cost.
The editors wish to acknowledge the authors and their significant contributions to this edition of the handbook.
Zogzas Mass and energy balances are powerful tools for the design and optimization of food manufacturing plants. They are based on the application of mass and energy conser- vation laws to an individual part or the whole food process. The aim is to determine the mass flow rate and composition of any stream of raw material, intermediate or the final product, by-product, waste, or effluent encountered in the process along with the amounts of energy mainly heat that must be supplied or rejected. The basic steps that are followed are the construction of the process flow diagram along with any available information, the consideration of the suitable system boundaries, and the establishment and solving of the set of independent equations resulting from the suitable mass and energy balance application.
The above mentioned will be discussed in detail in the following sections along with comprehensive examples and problems collected from a variety of existing food process applications. The law can be applied for the total amount of mass entering, leaving, or accumulating within the system, as well as, for any individual component.
Typical examples of mass bal- ance applications in food processing can be found in mixing, blending, separation, dilution, concentration, drying, evaporation, and crystallization. The boundary can be real or imaginary and separates the system from its surroundings. Let us consider a can in atmospheric air that contains concentrated milk. The outer surface of the can could be considered as the boundary between milk and the atmospheric air. We could also draw an imaginary boundary around the can Figure 2. Whatever be the case, the system consists of milk and the can walls. A typical example is that of a heat exchanger shown in Figure 2.
If we draw a boundary around the body of the exchanger, we can easily notice that there are hot and cold fluid streams entering or leaving the system. In the majority of food engineering operations, the systems that we deal with are actually open systems, since continuous and semibatch processes are of common practice. Closed systems are rare and can be met mainly in batch processes i. The definition does not exclude any component transforma- tion within the system and in the case of a chemical or a biochemical reaction the total mass of the reactants equals the total mass of the products at any time point.
Note that in the case of mass depletion the second part of Equation 2.
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A continuous process is by definition an open system in which the total mass of the feed entering is continuously removed by the form of products and wastes. In this case, there is no accumulation or depletion of mass within the system and Equation 2. The above equation also holds for a batch process in terms of a total mass balance at the beginning and at the end of the process. That is, the total mass of the feed entering the system at the beginning of the process equals the total mass of the products at the end. In general, the total mass flow rate that enters or leaves a system may consist of several streams.
Equation 2. Under this condition Equation 2. Physical properties of fluids such as water, steam, air, and other liquid foods are provided.
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For an incompressible fluid, that is, for a fluid that does not change its density under the processing conditions, Equation 2. However, this equation is rarely applied to food processing practices since systems are complex involving solid, liq- uid, and gas mixtures, phase transitions, and material transformations with density change. Constructing the flow diagram of the process 2. Defining the suitable boundaries 3.
Collecting all available data for the streams of materials entering or leaving the boundaries 4. Selecting a basis for calculations 5. Applying of mass balance Equations 2. Solving the system of equations to estimate the unknowns There are four types of flow diagrams used in food process design and optimiza- tion.
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The first is the simplest and shows all streams of raw materials, products, side products, and wastes. It is made of blocks that symbolize all individual unit opera- tions needed to complete the process. Conventional international symbols are used to depict the vari- ous types of equipments along with process parameters such as temperature, pres- sure, composition, flow rate, level, and any other property necessary to describe the process. The third is a layout of the machinery arrangement on the floor or in space [3D] of the plant showing the dimensions of equipment.
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This type of diagram is use- ful in estimating the necessary surface and space of the food plant. The fourth dia- gram is focused on the details of connections and control of process equipment such as piping including pumps, fans, ducts, regulating and safety valves, steam traps, and other fittings and instrumentation such as gauges, sensors of temperature, pres- sure, level, flow, moisture and others, signal transducers, controllers, and wiring.
Of the above diagrams, the first two types are useful for applying mass and or energy bal- ances.
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In fact, the PBD is used for overall mass and energy balances across each unit operation and PFD is used for more detailed calculations within a specific operation, for example, estimating the operating conditions, flows, and composition in a triple effect evaporator. Boundaries can be drawn around the whole or an individual part of the process.
Usually, an overall mass balance along with some selected individual parts is ade- quate. The choice of the suitable boundaries, as well as, the set of mass balance equa- tions depends on the number of unknowns, the available data, and the easiness of calculations. Collecting the suitable data such as material compositions, mass or volumetric flow rates, process conditions pressure and temperature , and any other information provided by the flow diagram is essential for solving the set of mass balance equa- tions. Process conditions can be used to estimate thermophysical properties of food materials including water and air.
For example, the pressure of saturated steam is necessary to estimate its temperature, specific volume, and other thermodynamic properties from the available literature steam tables. In a generalized approach, food materials can be said to consist of water and total solids, with the latter comprising soluble and insoluble matter. In this way, composi- tion can be expressed in a wet or a dry basis. That is, Xi,w. Obviously, Equation 2. The basis of calculations is kg of oranges. Reprinted with permission from Maroulis, B.
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