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NF2016_Preservation_1cd

Covers pasteurization, UHT, sterilization, evaporation and drying
by

Richard Marshall

on 25 June 2013

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Transcript of NF2016_Preservation_1cd

Food Preservation 1c, 1d
Heat treatments of milk (and other beverages
Pasteurization
UHT processing
Sterilization
Evaporation
Drying
Pasteurization
Can be carried out at 65 - 90 C
Milk mostly at 72 C/20 s, HTST
Destroys vegetative pathogens
Mycobacterium avium subsp. paratuberculosis (MAP) - probable link to Ulcerative Colitis and Crohn's Disease
Brucella (brucellosis
Staphylococci
Salmonellae

Lactococcus & Lactobacillus spp.may survive
Testing for successful pasteurization
Microbiological testing takes too long
Heating inactivates the enzyme 'alkaline phosphatase
Has approx. same heat sensitivity as MOs
Tests measure enzyme activity
If no activity, pasteurization is OK
How to pasteurize?
In bucket - 65 C/30 - 60 mins
In plate-type pasteurizer
Plate-type pasteurizer
Pre-heat milk to avoid cooked flavour
In-coming milk heated by out-going (hot) milk
= regeneration
Regeneration recovers almost all of the heat
Plants therefore very efficient (>90%)
Pasteurization - named after Louis Pasteur
Who was Louis Pasteur?
http://www.bbc.co.uk/history/historic_figures/pasteur_louis.shtml
Pasteurizer animation
http://learning.londonmet.ac.uk/TLTC/connorj/HHSResources/pasturiser/pasteuriser.html
Pasteurizer schematic
UHT Processing
"Ultra high temperature"
135 - 141 C/1 - 2 s
Very little flavour change in milk, juices
Aspetic product (but packaging just also be aseptic)
Long shelf-life
Uses: juice, wine, beer, soups, other beverages
BUT equipment is more difficult to clean
Sterilized milk
Much more severe
Destroys all MOs and spores
Has strong cooked flavour
Browning due to Maillard reaction
Process same as canning
Evaporated milk
Developed from process for condensed milk
Milk fore-warmed to 50 C
Concentrated to 25% solids using heat
Na citrate or Na phosphate added to prevent granular texture
Canned, sterilized
Typical 'creamy' product
2
Video of falling film evaporator
http://www.gea-wiegand.com/GEAWiegand/cmsdoc.nsf/WebDoc/webb899cfe
High efficiency evaporators
Food industry tries to save as much energy as possible
Evaporators with multiple stages
Mechanical Vapour Recompression (MVR)
Thermal Vapour Recompression (TVR)
TVR
Part of steam evaporated from product is recompressed by a steam jet
Returned to steam chest of evaporator
Can give 2 to 1 improvement in economy or better with multiple effects
Economies with TVR
Roller drying
Rotating stainless steel drum
Heated inside by steam
Conc. milk picked up on outside
Dried flakes scraped off on opposite side
Heat damage - Maillard reaction
Loss of heat volatile vitamins
Decrease of protein quality
Poor dispersability
Spray-drying makes a better product
Spray drying
Fine, atomised spray
Heated in conical chamber
Flash stripping of water
Some bacteria may survive
Heat process before drying
Makes very fine powder - poor dispersibility

Improved by wetting with steam
Agglomerates the particles - spongy
Dried in warm air - fluidized bed
http://learning.londonmet.ac.uk/TLTC/connorj/TestArea/sprayDryer/SD0704.html
Freeze drying
Makes use of thermal properties of water
Water is sublimed from frozen
Under vacuum
Latent heat of vaporisation keeps product frozen
Minimal damage to product

Water phase diagram
Freeze dried products
Instant coffee, premium grade
Fruits, as in some breakfast cereals
Soups
Vegetables
Meat

http://www.gea-wiegand.com/GEAWiegand/cmsdoc.nsf/WebDoc/webb899cfe
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