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Pre-preparation of Raw Materials (SIZE REDUCTION (PURPOSE (increase…
Pre-preparation of Raw Materials
CLEANING
TYPES OF CLEANING
2. WET CLEANING
ADVANTAGES
Effective removal of firmly adhered soils
Dustless
Result in less damage to foods than dry cleaning
TYPES OF WET CLEANING
Soaking
Spray washing
Spray drum washers
Spray belt washers
Flotation washing
Ultrasonic cleaning
Dewatering
DISADVANTAGES
Use of large amounts of clean water
Wet surface prone to spoilage
High effluent disposal charges and chemical oxidation demand
1. DRY CLEANING
ADVANTAGES
Does not add extra moisture to raw materials
Equipment generally smaller and cheaper
No effluent disposal
Lower chemical and microbial deterioration
DISADVANTAGES
Possibility of health and explosive hazard from dust
Additional cost to control dust
Possibility of product recontamination due to dust
Less effective in cleaning efficiency
TYPES OF DRY CLEANING
Physical method
Screening
Drum screen
Flat bed screen
Abrasion
Aspiration
Magnetic/Electromagnetic
What is cleaning?
Purpose of cleaning
Reduce food wastage
Protect consumers
Improve economics of processing
A unit operation of removing/separating contaminating materials from foods
SORTING & GRADING
SORTING
What is sorting?
Separation of raw materials based on single measurable property
PURPOSE
Aesthetic and marketing advantages
Ease of process control
Better control over weight filling operations
Necessary for uniform heat transfer
SIZE SORTING
Variable aperture
Step-wise diverging apertures
Continuous diverging apertures
Stationary or rotating
Fixed aperture screen
Flat bed screen (sieve)
Drum screen (rotary screen)
WEIGHT SORTING
Most precise method
Types of devices
Spring-loaded
Electronic weighing device
Not suitable for small items due to long process per unit
SHAPE SORTING
Raw materials are separated base on it's shape
Useful for materials that are contaminated with particles of similar size and weight
Using disc/cylinders with specific indentation to pick up seeds of correct shape when the materials are rotated and other shapes will remain in the feed
GRADING
Assessment of overall quality using several attributes or classification based on quality
More expensive than sorting due to higher costs of skilled operators
SIZE REDUCTION
What is it?
A unit operation whereby average size of food is reduced as the raw materials are often too large to be used directly
3 Categories:
Solid
- Cutting, chopping, slicing and dicing
Solid
- Milling to powders and fine paste
3.
Liquid
- Emulsification, homogenisation and atomization
PURPOSE
increase surface area to volume ratio of foods thus increase rate of heat transfer, improves efficiency and increase rate of soluble components extraction
Reduce particle size to allow more complete/uniform mixing of ingredients
Ore-determined range of particle size increase screening process efficiency
Similar size of dispersed liquids increase product stability
Smaller particle size enable easier packaging
Increase product range
DISADVANTAGE
Potential increase in nutrient loss due to increase surface area
Promote degradation (eg. oxidation)
SOLID FOODS
Fracture of foods
Application of a force
Compression force
Apply force over a period of time
Fracture friable, brittle and crystalline foods such as grains of wheat, roasted coffee beans
Shear force
Forward and backward movement
Fibrous and softer foods such as vegetables, fruits, bread and meat
Impact force
Short and compact
Hard and highly brittle material such as sugar crystal, spices and roast nuts
Deformation
Result in permanent deformation of food if exceeds critical level (enough force to cause it to tear)
Flow
If stress continues, the food will flow once the strain reaches a yield point.
Break
Fracture alone along weakness lines
FACTORS SELECTING EQUIPMENT
Mechanical properties of feed
Moisture content of Feed
Temperature sensitivity of feed
Types of Machine
Hammer mill - impact force
Roller mill - Compression force
Slicing equipment - shear force
Dicing equipment - shear force
LIQUID FOODS
A process of creating a stable emulsion by the intimate mixing of 2 or more immiscible liquids so that one (dispersed phase) is dispersed in the form of very small droplets (often sub-micro meter) within the second (continuous phase)
2 Types
Emulsification
Homogenisation
Severe size reduction of liquid particles in the dispersed phase
Types of dispersions
Oil-in-water (O/W)
Milk
Ice cream
Water-in-oil (W/O)
Margarine
Butter
Influencing Factors
Type and quantity of emulsifying agent
Size of globules in the dispersed phase
Interfacial tension
Viscosity of continuous phase
Density difference between dispersed and continuous phases
4 MAIN TYPES OF EQUIPMENT
Pressure homogenizers
Colloid mills
Ultrasound homogenizers
High speed mixers
EFFECTS ON FOOD
Affect product texture
Losses of nutritional compounds and oxidation of fatty acids due to exposure to surrounding environment
Dispersed particle size can affect the colour
SEPARATION
A unit operation used for the physical removal of food components from another
To aid processing and has no preservation effects
PURPOSE
Remove of specific components (e.g. flavour components, essential oil, undesirable microorganism (m/o)]
Form of cleaning , sorting and grading
Retrieval of high value compounds
Purification of fractions
2 MAIN SEPARATION PROCESSES
Mechanical/physical separation
e.g. force/pressure) to the fluid of concern
eg. Filtration, centrifugation, expression, solvent extraction
Equilibrium/Diffusion
Equilibrium of mixtures of different components in the solid, liquid or gas states
Bring two phases together into contact
E.g. Solvent Extraction, Reverse Osmosis, Evaporation
FILTRATION
Clarify liquids by the removal of small amount of solid particles (e.g. wines, beer, edible oil, granulated sugar) or to separate liquids from the solid part of a food (fruit juice)
RATE OF FILTRATION
Driving force
Resistance to flow
EQUIPMENT
Pressure filters (e.g. Plate and Frame Filter Press
Separate components based on partied / molecular size
CENTRIFIGUATION
PURPOSE
use of centrifugal force to separate materials
Separation of immiscible liquids
Separation of insoluble solids from liquids
Separation of immiscible liquids
Separation of insoluble solids from liquids
Machine
Liquid-Liquid Centrifugal Separators
Tubular bowl centrifuge
Disk bowl centrifuge
Solid-Liquid Centrifugal Separators
APPLICATION
Production of cream and/or skimmed milk from separation of milk. (Disk bowl centrifuges are commonly used.)
Fruit juice processing e.g. removal of pulp in citrus juices or production of oils from citrus fruits. (Tubular bowl centrifuges commonly used)
EVAPORATION
PURPOSE
• uses heat to remove water from liquid foods
• final product remains in liquid state
• Source of Steam & Heat exchanger (calandria) to transfer heat from steam to food
• Energy is boiled off as water from food
MACHINES
Raising film evaporator
• Suitable for low viscosity of foods
• Liquid rises inside tubes by vapour formed near the bottom of the heating tubes; and a thin liquid film quickly moves upward;
• Residence time 3-4 min.
Falling Film Evaporator
• Suitable for relatively viscous foods
• A thin liquid film moving downward under gravity on the inside of the vertical tubes
• Short residence time (20- 30 seconds)
EFFECTS ON FOOD
• Loss of nutrients (e.g. vitamin)
• loss of volatile and heat sensitive components
• Reduction in water activity
• Darkening of colour (e.g. maillard reaction)
• Increase shelf life (e.g. reduction of microbial counts)
APPLICATION
Evaporation is used to concentrate
Fruit juice
Vegetable juice or purees
Sugars
Salt from sea water
Dairy: milk, whey
DEHYDRATION
Removal of the majority of water in foods by evaporation through application of heat under controlled conditions
Removal of moisture from food products to very low level will inhibit microbial deterioration (↓ Aw) and prevent deteriorative reactions (enzymatic actvities)
Water in foods
Bound water
Partly bound water
Free water
WATER ACTIVITY
Measures the availability of water for microbial, enzymatic or chemical activity within food system
FACTORS AFFECTING DEHYDRATION
Processing conditions
Pressure
Relative humidity
Air velocity
Temperature
Properties of food
Surface
Constituent orientation
Cellular structure
Type and concentration of solutes
EFFECTS ON FOOD QUALITY
Texture - Loss of firm texture of fresh material
Flavour & aroma - loss of volatile compounds
Colour - Pigment loss, browning
TYPE OF EQUIPMENTS
Hot air dryers
Solar drying
Advantages
Most energy efficient
Most environment friendly (no pollution)
Disadvantages
Weather dependent
↓ productivity due to long process
Large space requirement
Fluidized-bed drying
Advantages
Very rapid heat transfer
Uniform drying from product surface
Disadvantages
Requires minimum air velocity to fluidize particles
Not suitable for very large/heavy particles
Difficult for sticky particles
Spray dryer
Extremely ↑ surface contact area between food & hot air
very ↑ rate of mass transfer
short residence time
↑ product quality
mostly suitable for ↓ viscosity fluid materials
Heated surface dryers
Drum drying
Advantages
↑ drying rates and ↑ energy efficiencies
Disadvantages
Damage to heat sensitive components
↑ capital cost
MATERIAL BALANCE
:star: STEPS
Draw flow diagram
Write given information on flow diagram
Symbolize unknown items
Choose basis of calculation (1hr? 100kg? *if not indicated, assume 100kg)
Material balance equation (i. overall mass balance, ii. individual components)
Total mass of material entering the plant must equal to total mass of material leaving the plant less any accumulation left in the plant