Questions and Answers
What is the definition of a 'process' in food engineering?
A set of actions in a specific sequence to a specific end.
Which of the following is a key feature common to all food processes?
Batch processing is usually more capital intensive but less costly to operate than continuous processing.
False
In continuous processing, materials pass through the system continuously, without __________ of a part of the material from the bulk.
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What is a typical example of a batch process in food engineering?
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What are flow diagrams used for in food process engineering?
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Which thermal property is defined as the quantity of heat needed to increase the temperature of one unit mass of a material by one degree at constant pressure?
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The specific heat of a solution is equal to the sum of the contributions of each component.
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What do we refer to when discussing 'mechanical properties' of food materials?
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Match the following types of deformation with their definitions:
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What are the two main electrical properties of foods relevant to food processing?
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What is a Sanitary pump primarily used for?
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Sanitary pumps operate differently than industrial pump versions.
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What material is most commonly used for sanitary pumps in the industry?
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The pipelines of a food plant can be divided into two categories: utility pipelines and _____ pipelines.
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What are utility pipelines typically made from?
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What is a drawback of pneumatic transport in the food industry?
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Hydraulic conveying is commonly used for transporting grain.
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What are the two types of systems classified for pneumatic conveying?
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The primary force that opposes movement of two touching bodies is called _____ .
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What is the main cause of particle-particle adhesion in dry powders?
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What is the process of gelation important for?
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What is the gelling agent used in jam production?
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Emulsions are thermodynamically stable systems.
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What distinguishes oil-in-water emulsions from water-in-oil emulsions?
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What is water activity (aw)?
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Match the following terms with their definitions:
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Bacterial growth occurs at water activity levels below 0.9.
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What happens to food quality when it loses water?
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What is a well-known model for predicting sorption isotherms?
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What is the main reason for the staling of bread?
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What type of phase transition is glass transition classified as?
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What effect does water have on amorphous food according to Roos and Karel?
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Which equation can be used to predict the glass transition temperature of a blend?
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The viscosity of liquids is strongly ______ dependent.
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The glass transition temperature is a fixed point for all materials.
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What is a common method for determining the glass transition temperature (Tg)?
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Which of the following fluids is described as shear thinning?
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Match the following types of pumps with their descriptions:
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Pumps are only used for moving liquids.
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What is a characteristic of Newtonian fluids?
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Study Notes
Food Process Overview
- A process involves a sequence of actions from raw materials to final products and by-products.
- Food processing industry utilizes various unit operations, categorized under similar principles and purposes.
- Material and energy balances in food processes adhere to conservation laws.
- Key exchanges in food processing include the transfer of materials, momentum, and heat, analyzed through transport phenomena.
- Knowledge of material properties is crucial due to the complexity of food materials and their reactions.
- Food safety and hygiene are central throughout product development, design, production, and distribution.
- Significant advancements are made in food process measurement and control systems, enhancing operational efficiency.
Batch and Continuous Processes
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Batch Processing:
- Involves treating a portion of materials separately; conditions change over time.
- Easier to control and suitable for small-scale production; often entails higher operational costs due to downtime.
- Example: Mixing ingredients to create bread dough.
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Continuous Processing:
- Materials pass through the system without separation, ideally maintaining constant conditions.
- Requires significant capital investment but optimizes production capacity at lower operational costs.
- Example: Continuous pasteurization of milk to eliminate harmful bacteria.
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Mixed Processes:
- Combine batch and continuous methods; buffer storage is essential between stages.
- Example: Strained infant food production involving continuous processing, followed by batch mixing and quality assurance before packaging.
Flow Diagrams and Equipment
- Flow diagrams visually represent process sequences, including raw materials, actions, and product outputs.
- Block diagrams simplify operations into rectangles.
- Equipment flow diagrams detail equipment used, utility lines, and information needed for physical plant layouts.
- Engineering flow diagrams serve as foundational elements for designing production lines.
Physical Properties of Food Materials
- Physical properties describe measurable characteristics of food, significantly impacting quality, stability, and engineering design.
- Mechanical properties include:
- Elastic Deformation: Immediate response proportional to applied stress.
- Plastic Deformation: Permanent change when stress exceeds yield stress.
- Viscous Deformation: Instantaneous flow under stress, remaining altered.
Thermal Properties
- Thermal properties involve heating and cooling processes critical in food engineering.
- Key properties: thermal conductivity, specific heat, and latent heat of phase transition.
- Specific heat is quantifiable as the heat needed to raise a unit mass of material by a specific temperature at constant pressure.
Electrical and Structural Properties
- Electrical properties are vital for heating processes; primary focus on electrical conductivity and dielectric properties.
- Most foods are heterogeneous mixtures, influencing their properties:
- Cellular Structures: Turgidity in fruits and vegetables affects texture; engineered for specific qualities in products like bread.
- Fibrous Structures: Present in meat, influencing chewiness.
- Gels: Colloidal systems important for products like yogurt and jams, reliant on polymer interactions.
- Emulsions: Mixtures of two immiscible liquids (oil and water); stability requires emulsifying agents and energy input to create.
Summary
- Understanding food processes involves grasping the significance of unit operations, mechanical properties, thermal behavior, and structural components in food products.
- Advances in technology and control highlight the growing emphasis on efficiency, safety, and quality within the food engineering sector.### Emulsions and Foams
- Coalescence refers to the fusion of dispersed droplets into larger ones, while creaming involves the separation of the original emulsion into a more concentrated emulsion and some free continuous phase.
- Oil-soluble emulsifiers encourage the formation of water-in-oil emulsions.
- Foams are cellular structures comprising gas-filled cells and liquid cell walls, displaying solid-like behavior due to surface forces.
- Ice cream is an example of frozen foam, containing nearly 50% air.
- Important foam characteristics include bubble size distribution, density, stiffness, and stability, especially in milk-containing beverages and beer.
- Undesired foaming in products like skim milk can lead to engineering challenges, mitigated by equipment design or the use of food-grade antifoaming agents.
Powders in Food Engineering
- Powders consist of solid particles sized between 10 to 1000 micrometers; smaller particles are termed 'dust' and larger ones 'granules'.
- Common food products and raw materials exist as powders, produced through size reduction, precipitation, crystallization, or spray drying.
- Flow and transportation of particulate materials present challenges in food engineering.
Water Activity
- Water is the most abundant component in most foods, classified into high (e.g., fruits, vegetables), intermediate (e.g., bread, hard cheeses), and low moisture foods (e.g., dehydrated vegetables).
- Water's role in food quality extends beyond quantity, affecting texture, appearance, and microbial growth; loss of water leads to diminished quality.
- Water activity (aw) is a crucial parameter defined as the ratio of the water vapor pressure of a food to that of pure water at the same temperature.
- Water activity is judged as equivalent to the relative humidity of the air in equilibrium with the food.
Determination and Prediction of Water Activity
- Methods for measuring water activity often use hygrometric techniques to assess humidity in food samples.
- Solutions with high moisture content exhibit behaviors consistent with Raoult’s law, allowing calculation of water activity based on molar fraction.
- As water content decreases, factors like water binding and capillary forces significantly influence water activity.
- Water activity is temperature-dependent, particularly affecting low-moisture foods where molecular interactions change.
Water Vapor Sorption Isotherms
- Sorption isotherms illustrate the relationship between water content and water activity at constant temperatures, determined through static and dynamic methods.
- Hysteresis in sorption isotherms suggests that moisture adsorption and desorption can offer different water activity values for the same moisture content.
- Various mathematical models, such as the BET equation, help predict sorption isotherms, with the BET model being effective for up to 0.45 water activity.
Effects on Food Quality and Stability
- Bacterial growth is inhibited at water activity levels below 0.9; molds and yeasts have similar limits at 0.8–0.9.
- Many enzymatic reactions necessitate water activity levels of 0.85 or higher; reactions like Maillard browning and lipid oxidation have complex interactions with water activity.
- Water activity influences food preservation and quality by regulating microbial growth and chemical reactions.
Glass Transition Phenomena
- Foods can be seen as metastable systems, undergoing change reliant on rate, stabilization, and molecular mobility.
- The glassy state in foods, such as candies, is a result of concentrated solutions of solutes when cooled and concentrated in specific conditions.
- Glass transition temperature (Tg) varies with the concentration of components; it signifies the transition from a rubbery to a brittle glassy state, affecting texture.
- Viscosity dramatically increases as Tg is approached, impacting food stability and quality assessment in food technology.### Glassy State and Glass Transition Temperature (Tg)
- The glassy state is characterized by minimal molecular mobility, impacting food properties and stability.
- Food stability is analyzed based on the difference between temperature (T) and glass transition temperature (Tg).
- Determining Tg can be performed through various methods, with differential scanning calorimetry (DSC) being the most common.
- DSC measures the heat capacity of a sample against a reference, revealing phase transitions through heat capacity changes.
- Glass transition is identified by a subtle change in the heat capacity curve rather than a sharp transition.
- The determination of Tg can vary based on interpretation; commonly, the mid-point of the inflection or the onset of the transition is used.
Fluid Dynamics in Food Engineering
- Fluid movement is integral to industrial food processes, affecting liquids like milk and juices, as well as foods in freezing and milling processes.
- Essential utilities such as water, steam, and gases require well-designed pipeline systems to function efficiently.
- The chapter covers fluid dynamics, rheology, pump mechanics, and the flow of particulate solids.
Viscosity
- Composed of fluid dynamics concepts, viscosity is the measure of a fluid's resistance to shearing actions.
- Viscosity is quantified in Pascal seconds (Pa.s) in the SI system and poise in the c.g.s system.
- Liquid viscosity is temperature-dependent while gas viscosity increases with pressure.
- Shear stress (τ) and shear rate (γ) are central to understanding fluid flow behavior; Newton’s law governs the relationship.
- Newtonian fluids exhibit constant viscosity independent of shear rate, while non-Newtonian fluids have variable viscosity depending on shear conditions.
Types of Fluid Flow Behavior
- Fluids are categorized based on shear stress (τ) and shear rate (γ) relationships.
- Newtonian fluids display linear behavior with zero intercepts; examples include water and low molecular weight solutions.
- Bingham fluids have a yield stress; they do not flow until a certain threshold is met.
- Shear thinning fluids reduce viscosity with increased shear, found in products like fruit juice concentrates.
- Shear thickening fluids increase viscosity under shear; honey exemplifies this characteristic.
- Thixotropic fluids (like ketchup) decrease viscosity over time with constant shear, while rheopectic fluids increase viscosity, though thixotropic behavior is more common.
Pumps in Fluid Transport
- Pumps are devices used to increase fluid head and can include any energy-converting apparatus like gas compressors and fans.
- Two main pump categories: kinetic pumps (like centrifugal pumps) impart kinetic energy to fluids while positive displacement pumps physically move fluid within a chamber.
- Centrifugal pumps exploit rotational energy; they function by drawing fluid to the center and pushing it outward.
- Positive displacement pumps (reciprocating, rotary, peristaltic) are effective for high pressure, low capacity applications and can handle viscous materials.
- Sanitary pumps are designed with smooth surfaces for easy cleaning, crucial in food processing to prevent contamination.
Piping Systems in Food Processing
- Two types of pipelines exist: utility fluid pipelines (for water, steam) and product pipelines (for transporting food materials).
- Utility pipelines are generally made of steel while product pipelines use stainless steel to prevent contamination.
- Pipeline design considers flow rate, pressure, and fluid properties; connections can be dismantlable for cleaning.
- The trend is toward using welded stainless-steel pipelines due to the advancement of clean-in-place (CIP) systems.
Flow Properties of Particulate Solids
- Powder flow involves the movement of powder particles influenced by forces such as gravity or mechanical agitation.
- Powder strength is defined by inter-particle forces, primarily van der Waals forces and liquid bridge forces in dry powders.
- Techniques to analyze powder flow also apply solid mechanics principles, treating the powder as a continuous medium.
Pneumatic Transport of Particulate Solids
- Pneumatic conveying transport solids through a gas stream, while hydraulic conveying uses liquids.
- Pneumatic systems offer advantages like contamination protection, ease of assembly and disassembly, and capability for long-distance transport.
- Both methods have different equipment setups but share fundamental operational principles.
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Description
This quiz covers the basic concepts of food engineering, focusing on the definition of processes in food manufacturing. It outlines the sequence of actions that lead from raw materials to finished products, and explores the key unit operations involved in the food process.
