Unit processes
36 important questions on Unit processes
What are the 6 types of unit processes?
- Centrifugation: remove particles
- Homogenization: reduce particle size
- Heating: safety (denature proteins)
- Evaporation: remove some water
- Drying: remove all water
- Membrane processes: separate specific components
What is the Stokes' law
What does the Rotation velocities of fat globules with different diameters do?
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Separation and centrifuge together in one
Why is the centrifuge on 50*C
- All the milk fat is liquid
- You do not want to damage the fat particles
What is the effect of centrifuge on milk & product composition?
- Higher/lower fat content requires adaptations to centrifugation parameters
- Bactofugation (for e.g. Butyric acid spore removal in cheese milk), parameters need to be adapted
- Clarification (of e.g. Whey), although essentially the same type of precess, requires a very different setup
What is the effect of homogenisation of fat globule size?
- Homogenization causes disruption of fat globules in smaller ones
- Disruption of fat globules in first (1) and second (2) stage of homogenisation
- 2e stage is to break up the clusters --> a stable end product
Als er geen protein aanwezig zijn gaan de vet globules aan elkaar zitten
How does homogenisation process works?
4 disruption forces in the homogenising gap
- Elongation
- Shear
- Turbulence
- Cavitation
Distribution after 1st stage and distribution after 2nd stage of the homogenisation process
2 = loskoppelen
What is the effect of homogenisation on milk & product composition?
- Fat/protein ratio of the product influences risk of fat globule clustering: necessity of 2 stage homogenisation
- Different products require different fat globule size * fat globule size distribution; different homogenisation pressure and/or double homogenisation needed
Why do we use heat treatment?
- Heat treatment is used for virtually all dairy products
- Main objectives:
- Kill micro-organisms
- Inactivate enzymes
- Denature proteins
What are the purposes of heating?
- Safety
- killing the pathogens
- Keeping quality
- killing spoilage organism
- inactivation enzymes
- Product properties
- inactivate bacterial inhibitors
- improve consistency
Heating has 4 different intensity levels
- Thermalization
- Low pasteurisation
- High pasteurisation
- Sterilization
Optimization of time and temperature such that wanted effects are maximal, but undesired effects are minimal
Thermalization, what is the
- time/temperature
- purpose
- applied for
- important
- about 20sec at 65*C
Purpose
- reduction of vegetative micro-organisms (the normal bacterial cells and not the spores)
Applied
- For prolonged storage of milk
Important
- hardly any detectable protein denaturation
Low pasteurisation, what is the
- time/temperature
- purpose
- applied for
- important
- About 20 sec at 72*C
purpose
- Destroy pathogens and spoilage micro-organisms
- for consumption milk and cheese milk
- destroys alkaline phosphatase
High pasteurisation, what is the
- time/temperature
- purpose
- applied for
- important
- about 20 sec at 85*C
- kan ook langer en hoger
- to denature whey proteins and enzymes
- to inactivate bacterial inhibitors
- to improve product properties
- destroys lactoperoxidase
Sterilization, what is the
- time/temperature
- purpose
- applied for
- important
- about 30 min at 110*C or 30-1s at 130-145 *C
- dit kan ook ongewenst zijn, Maillard reactie
- to make ambient stable products
- for products stored outside fridge
- spored and heat stable enzymes may survive
What are the 4 consequences of heat treatment?
- Maillard reactions (reaction between protein & lactose)
Viscosity
- aggregation of whey proteins increases viscosity
Flavour
- development of cooked flavour; strongly dependent on time-temperature combination
Nutritive value
- some loss on vitamins
What is direct UHT
What is indirect UHT
It gives a slower cooling down and warming up than direct
What is the effect of heat treatment on milk & product composition?
- Fouling is important for both parameters of heating (t/T) and runtime:
- fat/protein ratio of the product influences risk of fouling
- Hygienic quality of milk influences risk of fouling
- Bacterial lead & presence of enzymes determine needed heating intensity --> hygienic quality of milk
- Bacterial inactivation rate depends on composition
Why do we use evaporation for dairy processing?
- increase dry matter and reduce water activity
- pre-concentration before drying
- concentration before crystallisation
- specific product - condensed milk (coffee milk/cream)
What are the evaporation limits for
- whole milk / skim milk
- whey
- whey protein concentrate
- permeate
- whole milk / skim milk - 48-50% d.m.
- whey - 58-65% d.m.
- whey protein concentrate - 35-48% d.m.
- permeate - 70-75% d.m.
(limitation) Water binding by casein/why protein main factor
What are the effects of evaporation on milk & product composition
- Fouling is even more important than for heating. It depends on parameters of heating (t/T) and is the main limiting factor in the runtime:
- fat/protein ratio & content os the product influences risk of fouling
- Hygienic quality of milk influences risk of fouling
- Higher required concentration degree increase fouling problems
- Dry matter content of the milk influences the amount of water to be removed
Why is drying important for dairy product?
- Milk
- Whey (components)
- Casein
- Infant formule
- Ice cream mix
Water removal needed for:
- promoting self-life
- reducing transport and storage costs
- application as ingredients
- Relative high investments
- removal of water by drying expensive - preconcentration by evaporation
- moisture content of end product low
- powders to be packed in water-vapour tight
- containers/paper bags
3 different drying methods
- some whole milk powder
- caseinate
- lactose
Spray drying
- most dairy powders
Fluid bed drying
- secondary drying for most powders
- primary drying for lactose
For fluid bed drying agglomeration is used for reconstitution properties
agglomeration is used
What is the effect of drying on milk & product composition
- Dry matter content of the (concentrated) milk influences the amount of water to be removed
- Larger preconcentration is energy efficient, but may increase fouling during evaporation stage
- concentrate composition (dry matter content, fat content, protein content, protein denaturation) all influence drying proces and powder particle properties
Why membrane processes?
- Remove bacteria
- Concentrate proteins
- Whey processing
Basics of membrane processes
- Membrane processes have a long history, with first industrial applications more than 50 years ago
- mainly used for way processing
- milk contains components of different size
Milk contains components of different size: from small to large
- Water
- Cl/Ca ions
- Lactose
- Whey proteins
- Casein micelles
- Fat globules
- Bacteria
- Somatic cells
- Cheese fines
What kind of different membrane processes exist, removing smaller and smaller particles:
Ultrafiltration
RO
NF
Most membrane processes are pressure driven
- Electrodialysis: electrical potential driven
- MF-MFF-UF-NF: sieving processes-like
- RO: osmotic pressure based
In these more sieving like processes, what are the characterisations (MF-MFF-UF-NF)
Characterizations
- Molecular weight cut-off
- NaCl retention
Membranes - electrodialysis, how does it works
Cathode (-) and Anode (+)
What is the effect of membranes on milk & product composition
- Limiting factor for runtime is membrane fouling. Composition and hygienic quality of the milk are important factors influencing fouling
- Hygienic quality also depends on temperature of membrane during processing
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