Food Process Engineering Explained

Food Process Engineering Explained

Food Process Engineering Explained

Anagh Deshpande

Food Process Engineering Explained

Anagh Deshpande

ISBN - 9789361529153

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Preface

Food, as we know, it is one of the essential components of life. Since the dawn of time, human beings have progressed from raw to cooked food to processed food. We have come a long way, advancing from eating food in its raw form to making it more consumable and palatable by removing the inedible parts of the food and cooking it before we consume it. After the consumption, we introduced ourselves to the preservation and storage of food. The progression of the ideas and techniques has turned themselves into a fully-fledged industry called the Food processing industry. Technological advancement has contributed to this cause to enhance the food products along with their consumption, preservation, transformation, and storage globally.

The manufacturing process of the food products initiates with the raw materials, ending in the products and the by-products. There are various processes to ensure the proper processing and preservation of the food products elaborately discussed in this book.

Along with the processing, preservation, and consumption of food products, packaging also forms an important aspect of the food processing industry, contributing to the health and hygiene of the food items. Thus, this consists in a descriptive nature, the start of the food processing industry with raw materials to the end of the mechanisms resulting in the products and the by-products along with comprehensive examples and solved numerical problems and formulae which shall help you to grasp a better understanding of the calculations, procedures and an overall summation of the modern-day food processing industry and the technology involved.

Table of CONTENT

Chapter 1. Physical Properties Of Food Material 1

1.1 Introduction 1

1.2. Mechanical Properties 5

1.3. Thermal Properties 8

1.4. Electrical Properties 10

1.5 Structure 11

1.6. Water Activity 12

1.7. Phase Transition Phenomena in Foods 14

1.8 Exercise 16

Chapter 2. Fluid Flow 18

2.1. Introduction 18

2.2. Computational Fluid Dynamics 22

2.3. Flow Properties of Fluids 24

2.4. Transportation of Fluids 25

2.5. Flow of Particulate Solids (Powder Flow) 26

2.6 Exercise 27

Chapter 3. Heat and Mass Transfer, Basic Principles 28

3.1. Introduction 28

3.2. Basic Relations in Transport Phenomena 29

3.3. Conductive Heat and Mass Transfer 30

3.4. Convective Heat and Mass Transfer 32

3.5. Heat Exchangers 33

3.6 Microwave Heating 34

3.7. Ohmic Heating 36

3.8 Exercise 37

Chapter 4. Elements of Process Control 39

4.1. Introduction 39

4.2. Basic Concepts 40

4.3. Basic Control Structures 42

4.4 Input, Output, and Process Dynamics 44

4.5 Control Modes (Control Algorithms) 44

4.6 Exercise 48

Chapter 5. Size Reduction 50

5.1. Introduction 50

5.2. Particle Size and Particle Size Distribution 51

5.3. Size reduction of Solids, Basic Principles 59

5.4. Size Reduction of solids, Equipments, and Methods 62

5.5 Exercise 70

Chapter 6. Mixing 73

6.1. Introduction 73

6.2. Mixing of Fluids (blending) 74

6.3 Kneading 81

6.4. In-flow mixing 83

6.5 Mixing of Particulate Solids 83

6.6 Homogenization 88

6.7 Exercise 93

Chapter 7. Centrifugation 96

7.1 Introduction 96

7.2 Basic Principles 97

7.3 Centrifuges 106

7.4 Cyclones 110

7.5 Exercise 111

Chapter 8. Extraction 113

8.1 Introduction 113

8.2 Solid-Liquid Extraction (Leaching) 115

8.3 Supercritical Fluid Extraction 125

8.4 Liquid-Liquid Extraction 129

8.5 Exercise 130

Chapter 9. Spoilage and Preservation of food 133

9.1. Mechanisms of Food Spoilage 133

9.2. Food Preservation Processes 134

9.3. Combined processes (the hurdle effect) 135

9.4. Packaging 135

9.5 Exercise 136

Chapter 10. Crystallization and Dissolution 137

10.1. Introduction to Crystallization 137

10.2. Crystallization Kinetics 139

10.3. Crystallization in the Food industry 144

10.4. Dissolution 150

10.5 Exercise 150

Chapter 11. Refrigeration, Chilling, And Freezing 153

11.1 Introduction 153

11.2 Effects of Temperature on food spoilage 154

11.3 Freezing 159

11.4 Exercise 163

Chapter 12. Refrigeration, Equipments, And Methods 166

12.1. Sources of Refrigeration 166

12.2. Cold Storage and Refrigerated Transport 172

12.3. Chillers and Freezers 173

12.4 Exercise 178

Chapter 13. Freeze Drying (Lyophilisation) And Freeze Concentration 180

13.1. Introduction 180

13.2. Sublimation of Water 181

13.3. Heat and Mass Transfer in Freeze Drying 182

13.4. Freeze Drying, in Practice 186

13.5. Freeze concentration 188

13.6 Exercise 190

Chapter 14. Frying, Baking, Roasting 192

14.1. Introduction 192

14.2. Frying 193

14.3. Baking and Roasting 196

14.4 Exercise 198

Chapter 15. Food packaging 200

15.1 Introduction 200

15.2. Packaging Materials 203

15.3. The Atmosphere in the Package 212

15.4. Environmental Issues 214

15.5 Exercise 214

Chapter 16. Cleaning, Disinfection, And Sanitation 217

16.1. Introduction 217

16.2. Cleaning Kinetics and Mechanics 218

16.3. Kinetics of Disinfection 224

16.4 Cleaning of Raw Materials 225

16.5 Cleaning of Plants and Equipments 227

16.6 Cleaning of Packages 228

16.7 Odor Abatement 228

16.7 Exercise 229

Chapter 17. Challenges Faced during Food Process Engineering 232

17.1. Sustainability 232

17.2. Population Growth 236

17.3 Human Health 237

17.4 Exercise 239

Appendix 242

Tables 242

Figures 243

Glossary 247

Index295

Chapter 1. Physical Properties Of Food Material

1.1 Introduction

Food materials have some physical properties. Physical properties can be observed or measured without changing the chemical makeup of the material. Physical properties can give us clues about chemical composition and processing characteristics.

Physical characteristics of raw, unprocessed, as well as processed food materials include particle size and shape, particle and bulk density, porosity, and surface area. The size and shape of a raw food material can vary widely. The variation in the shape of a product may require additional parameters to define its size. The size of spherical particles like peas or cantaloupes is easily defined by a single characteristic such as its diameter.

The size of non-spherical objects like wheat kernels, bananas, pears, or potatoes may be described by multiple length measurements. The longest diameter (major) and shortest diameter (minor) will adequately describe the size of an ellipsoidal object such as a grain kernel or potato. The two dimensions are usually measured perpendicular to one another. The size of pear-shaped objects such as pears, carrots, or beets can be expressed by the diameter or circumference of the largest part and an overall length in the direction of the stem. The size of irregular-shaped materials like bananas, okra, or squash requires more extensive considerations.

Particle size is used in sieve separation of foreign materials or grading (i.e., grouping into size categories). Particle size is particularly important in grinding operations to determine the condition of the final product and determines the required power to reduce the particle’s size. Small irregular-shaped objects can be sized with sieves by expressing particle size as the smallest sieve opening through which the particle passes. The size of larger objects may be expressed only in terms of their largest diameter or circumference. The size of the banana might be given only in overall length. Precise methods incorporating optical, light, or lasers in machine vision systems exist to define the shape and size of irregular-shaped objects.

These systems are costly; their use is warranted in applications of high-value materials more commonly found in highly processed, final products rather than raw, unprocessed materials. Ultimate use will dictate which physical characteristic properly represents size. The size of a carrot may be expressed only in length or in diameter of its large end. Size may be indicated by weight since it is so easily determined by simply placing it on a scale. Thus, the physical property size is actually related or correlated to the property weight. There is often a compromise between ease or cost of measurement and the usefulness or value of that property in the market channel in practice. Shape affects the grade given to fresh fruit. To make the highest grade, a fruit or vegetable must have the commonly recognized expected shape of that particular fruit/vegetable. Misshapen fruit and vegetables will be down-graded and may sell at a lower price in high-volume markets.

The shape of an irregular object can be described by terms such as the following:

Some physical properties of food:

Freezing Point:

The freezing point is the temperature at which a liquid turns into a solid. We can also define it as freezing refers to the phase change of a substance from the liquid state to a solid state. This is a phase change phenomenon which means that a substance is transformed from one state of matter to another state.

How does freezing occur?

●The molecules in the liquid state are loosely bound, and the intermolecular forces of attraction are lower than that of solids.

●This is because the heat energy transferred to the molecules during the process of conversion from solid to liquid state is larger than the potential energy of the molecules holding them together in the crystal lattice of a solid.

●This potential energy is also indicative of the lattice energy of the solid.

●When the substance’s temperature is lowered by extracting heat from the substance or lowering the pressure, the molecules lose their kinetic energy and come close to each other.

●Gradually they gain potential energy and become stable. At this stage, they get converted to solid—this one of the stable forms of water.

As with the melting point, increased pressure usually raises the freezing point. The freezing point is lower than the melting point in mixtures and for certain organic compounds such as fats. Once the mixture freezes, the solid that is formed first usually will have a composition different from the liquid, and the formation of the solid changes the composition of the liquid in such a way that it steadily lowers the freezing point. This principle is used in purifying mixtures, successive melting and freezing, gradually separating the components. The heat of fusion is the heat that must be applied to melt a solid, must be removed from the liquid to freeze it. Some liquids can be cooled below the freezing point without solid crystals forming. This property is called supercooled.

Theoretically freezing point and the melting point of any substance should be equal. For many substances, it is equal also, but for few substances, there are few differences. It is because few substances can be cooled below their freezing point without changing into a solid state.

These substances are known as supercooled liquids. This is because few solids have special crystal lattices that require nucleation sites to initiate crystallization which finally results in solidification.

Putting a seed crystal into supercooled liquid triggers freezing; after that, the release of the heat of fusion raises the temperature rapidly to the freezing point.

Factors Affecting Freezing Point

The main factors are the type of molecules the liquid is made up of.

1. If the intermolecular forces between its molecules are strong, then there is a high freezing point.

2. If the forces are weak, the freezing point is relatively low.

3. The freezing point of a liquid or melting point of a solid occurs at the temperature at which the solid and liquid phases are in equilibrium.

Freezing preservation retains the quality of agricultural products over long storage periods. As a method of long-term preservation for fruits and vegetables, freezing is generally regarded as superior to canning and dehydration, concerning retention in sensory attributes and nutritional properties. The safety and nutrition quality of frozen products are emphasized when high-quality raw materials are used, good manufacturing practices are employed in the preservation process, and the products are kept at specified temperatures.

The need for freezing and frozen storage

●Freezing has been successfully employed for the long-term preservation of many foods, providing a significantly extended shelf life. The process involves lowering the product temperature generally to -18 °C or below. The physical state of food material is changed when energy is removed by cooling below freezing temperature. The extreme cold simply retards the growth of microorganisms and slows down the chemical changes that affect the quality or cause food to spoil.

●Competing with new technologies of minimal processing of foods, industrial freezing is the most satisfactory method for preserving quality during long storage periods. Compared to energy use, cost, and product quality, freezing requires the shortest processing time. Any other conventional preservation method focused on fruits and vegetables, including dehydration and canning, requires less energy compared with energy consumption in the freezing process and storage. However, when the overall cost is estimated, freezing costs can be kept as low (or lower) as any other method of food preservation.

Advantages of freezing technology in developing countries

●Developed countries, mostly the US, dominate the international trade of fruits and vegetables. The US is ranked number one as both importer and exporter, accounting for the highest percent of fresh produce in world trade. However, many developing countries still lead in the export of fresh, exotic fruits and vegetables to developed countries.

●For developing countries, the application of freezing preservation is favorable with several main considerations. From a technical point of view, the freezing process is one of the most convenient and easiest food preservation methods, compared with other commercial preservation techniques. The availability of different types of equipment for several different food products results in a flexible process in which degradation of initial food quality is minimal with proper application procedures. As mentioned earlier, the high capital investment of the freezing industry usually plays an important role in terms of the economic feasibility of the process in developing countries. As for cost distribution, the freezing process and storage in terms of energy consumption constitute approximately 10 percent of the total cost. Depending on the government regulations, especially in developing countries, the energy cost for producers can be subsidized using lowering the unit price or reducing the tax percentage to enhance production. Therefore, in determining the economic convenience of the process, the cost related to energy consumption (according to energy tariffs) should be considered.

Table 1.1. The frozen food industry in terms of annual sales in 2001

1.2. Mechanical Properties

The mechanical properties of foods are important to their processing, storage, distribution, and consumption behavior. Information on various compositional factors on mechanical properties and their dependence on temperature and water content is needed for choosing proper equipment required, e.g., for transportation, mixing, and size reduction, as well as for the evaluation of the tolerance of mechanical stress during manufacturing. Food packaging is often used to protect foods from mechanical stress or water transfer between the product and its environment. Mechanical properties also affect the perceived texture of foods during consumption.

Several compositional and processing parameters affect the mechanical properties of foods. The overall mechanical properties may be defined by cell structure which is typical of various vegetables and fruits, resulting from the physical state, flow properties, or porosity. However, the physical state of food solids is one of the most important factors that affect the mechanical properties of low-moisture and frozen foods in which small changes in temperature or water content may significantly affect the physical state due to phase transitions. Therefore, the physical state may affect the overall quality of products starting from changes that may occur during processing, e.g., cookies, to the final stage of consumption, since the mechanical properties define product texture and sensory properties, e.g., perceived crispness. It should also be remembered that the mechanical properties of fatty foods are almost exclusively defined by the physical state and crystallinity of the lipid fraction.

Mechanical properties of food packaging, including deformability, TS, elongation at break (EAB), and elastic modulus (EM), are critical since food-packaging materials must keep up their integrity during storage, distribution, and handling. The maximum stress that the film can withstand while being stretched or pulled before failing or breaking is known as TS and EM, which indicate the flexibility and intrinsic stiffness of the films, respectively.

The mechanical properties of biopolymer films depend both on their composition and environmental conditions. For instance, the addition of plasticizers causes higher mobility of polymer chains, which leads to expanded elongation and diminished TS of the plasticized films. The embedding of different additives, such as cross-linking materials or lipids, can improve film strength and extensibility.

Moreover, the humidity and moisture of the environment influence the mechanical properties of polymer/biopolymer films. For example, hydrophilic films absorb humidity more promptly at higher moisture levels, consequently enhancing the plasticizing impact of water, which subsequently decreases the TS and increases the extendibility of the films. Also, the contact between polymer/biopolymer packaging materials and packaged products can likewise influence the functioning of packaging films.

In recent years, the incorporation of NPs has turned into a well-known way to improve the properties of different films since the utilization of NPs typically gives them improved mechanical properties. This result is due to the increased surface interaction between the matrix and NPs with a high surface area and the hydrogen bond formation between them. EAB has a reverse relation to TS in most cases, and YM is directly related to TS. Furthermore, the mechanical properties of films are closely associated with the density and distribution of the intra- and intermolecular interactions between polymer chains in the film matrix.

• Density

Density is defined as mass per unit volume and is used in process calculations and characterizations of food products.

Mass is defined as the amount of matter in a body. The international prototype kilogram is a simple cylinder of platinum-irradium alloy with a height equal to the diameter. It is important to distinguish between mass and weight. Weight is defined as the force acting on an object as a result of gravity. Consequently, the weight of an object changes as the gravitational force changes, whereas the mass remains constant. Density is one of the most important mechanical properties and thus is widely used in process calculations and product characterization.

It is defined as mass per unit volume: Mass Density Volume = (1) SI unit of density is kg m-3

• Porosity

Porosity indicates the volume fraction of void space or air in a material and is defined as:

Porosity = Air or Void Volume / Total Volume....(1.2)

Different forms of porosity are used in food process calculations and food product characterization.

These are defined below:

1. Open Pore Porosity

Open-pore porosity is the volume fraction of pores connected to the exterior boundary of a material and is given by (εop):

Open-pore porosity = Volume of open-pore / Total volume of material....(1.3)

εop = 1 - (ρa/ρp)

There may be two types of open pores: one type is connected to the exterior boundary only, and another type is connected to the other open pores and the exterior geometric boundary. The level of open and closed pores depends on what component (helium, nitrogen, toluene, or mercury) is used in the measurement.

2. Closed Pore Porosity

Closed pore porosity (εcp) is the volume fraction of pores closed inside the material and not connected to the exterior boundary of the material. It can be defined as:

Closed Pore Porosity = Volume of closed pores/ Total volume of material...(1.4)

εcp = 1 - (ρp/ρm)

3. Apparent porosity

Apparent porosity is the volume fraction of total air or void space in the material boundary and is defined as:

Apparent porosity = volume of all pores / Total volume of material....(1.5)

εa = 1 - (ρa/ρm)

4. Bulk Porosity

Bulk porosity (εB) is the volume fraction of voids outside the boundary of individual materials when packed or stacked as bulk:

Bulk porosity = volume of voids outside materials’ boundary / Total bulk volume of stacked materials .....(1.6)

εB = 1 - (ρb/ρa)

5. Bulk-Particle Porosity

Bulk-particle porosity is the volume fraction of the voids outside the individual particle and open-pore to the bulk volume when packed or stacked as bulk.

εBP = εB + εop...(1.7)

6. Total Porosity

Total porosity is the total volume fraction of air or void space (i.e., inside and outside of the materials) when a material is packed or stacked as bulk. (1.8)

εT = εa + εB = εop + εcp + εB....(1.5)

• Volume and Surface Area

Two types of surface area are used in process calculations: outer boundary surface of a particle or object and pore surface area for a porous material. An object can be characterized using Euclidian or non-Euclidian geometries. Euclidian geometric shapes always have characteristic dimensions and have an important common peculiarity of smoothness of surface; examples include spheres, cubes, and ellipsoids.

1.3. Thermal Properties

The thermal properties of foods are important in the design of food storage and refrigeration equipment and the estimation of process times for refrigerating, freezing, heating, or drying of foods. Because the thermal properties of foods are strongly dependent upon chemical composition and temperature, the most viable option is to predict these thermal properties using mathematical models that account for chemical composition and temperature.

Composition data for foods are readily available in the literature. These data consist of the mass fractions of the major food components: water, protein, fat, carbohydrate, fiber, and ash. Food thermal properties can be predicted by using these composition data in conjunction with temperature-dependent mathematical models of the thermal properties of the individual food components.

Thermal properties of foods and beverages must be known to perform the various heat transfer calculations involved in designing storage and refrigeration equipment and estimating process times for refrigerating, freezing, heating, or drying of foods and beverages. Because the thermal properties of foods and beverages strongly depend on chemical composition and temperature, and because many types of food are available, it is nearly impossible to experimentally determine and tabulate the thermal properties of foods and beverages for all possible conditions and compositions. However, composition data for foods and beverages are readily available from Holland et al. (1991) and USDA (1975). These data consist of the mass fractions of the major components found in foods. Thermal properties of foods can be predicted by using these composition data in conjunction with temperature-dependent mathematical models of thermal properties of the individual food constituents. Thermophysical properties often required for heat transfer calculations include density, specific heat, enthalpy, thermal conductivity, and thermal diffusivity. In addition, if the food is a living organism, such as fresh fruit or vegetable, it generates heat through respiration and loses moisture through transpiration. Both of these processes should be included in heat transfer calculations. This chapter summarizes prediction methods for estimating these thermophysical properties and includes examples of these prediction methods.

Equations for predicting the thermal properties of these food components have been developed as functions of temperature in the range of − 40 to 150 °C. These equations are presented in Table 1.2. Because water is the predominant constituent in most food items, the water content of food items significantly influences the thermophysical properties of foods. Therefore, equations for predicting the thermal properties of water and ice have also been developed.

Table 1.2. Thermal property equations for food components (−40 °C ≤ t ≤ 150 °C)

Table 1.3. Thermal property equations for water and ice (− 40 °C ≤ t ≤ 150 °C)

In general, the thermophysical properties of a food item are well behaved when the temperature of the food item is above its initial freezing point. However, below the initial freezing point, the thermophysical properties of a food item vary dramatically with temperature.

1.4. Electrical Properties

●Conductance

●Resistance

●Capacitance Soumitra Tiwari, Asst. Professor, Bilaspur University, Bilaspur (CG.)

●Dielectric properties

●Reaction to electromagnetic radiation

●Conductivity—The ability of seeds to hold a surface charge

There are two main electrical properties in food engineering: electrical conductivity and electrical permittivity. Electrical properties are important when processing foods involving electric fields, electric current conduction, or heating through electromagnetic waves. These properties are also useful in the detection of processing conditions or the quality of foods.

Electrical Conductivity and Permittivity Electrical conductivity is a measure of how well electric current flows through the food of unit cross-sectional area A, unit length L,