Lecture 8: Quality Optimization in Thermal Processing Flashcards
what is the aim of techniques in quality enhancements?
improving heat transfer to the product
what is heat transfer in canned foods driven by?
- convective heat transfer: the rate of heat transfer from the heating medium to the can
- heat transfer within: can be mixed convection and conduction rate heat transfer
what factors are involved with a shorter rate of heat transfer?
- shorter process time/quicker turnover
- more uniform temp
- less overcooking of product
- bettwe quality retention
what is the heat transfer equation?
q= h * A * deltaT = k * A * deltaT * x
the graph of relative D value vs. temperature provides what data?
relative resistance of bacteria to thermal destruction
in the relative D vs temp graph, what has the highest D value? why?
nutrients b/c they are more stable than microorganisms
do nutrients or microorganisms have a higher z value?
nutrients have a higher Z value
are nutrients or microorganisms less sensitive to changes in temperature? how can this be seen?
nutrients are less sensitive, which can be seen by their flatter slope in the relative D vs temp graph
in the relative D vs temp graph, what does a steeper slope indicate?
more sensitive to change in temp
vegetative bacteria has a very ___ slope
steep
what does HTST stand for?
high temperature short time
what does UHT stand for?
ultra high temperature
everything on the left of the thermal destruction curve is _____
everything on the right of the curve is ____
underprocessed
overprocessed
(process times should be right on the curve)
what are some different types of heat exchangers?
- plate and frame
- tubular
- swpet (Scrapped) surface
what are some process benefits from HTST and UHT?
- hats rapidly for liquids
- involves packaging in thin profile forms
- for cans that undergo agitation during processing (either liquids or semi-solids)
- for aseptic processing and packaging
what is HTST not suitable for?
conduction heating type of products in large containers
what does HTST do in thin profile processing?
- increases surface area
- reduces thickness
what is thin profile processing use for?
conduction heating foods
what are the three layers in a retort pouch used in thin profile processing?
what is the role of each layer?
- outer layer: strength and printability
- middle layer: barrier properties
- inner layer: heat sealability and food contact
in the retort pouch used in thin profile processing, which layer is used for heat sealability?
inner layer
in the retort pouch used in thin profile processing, which layer is used for strength and printability?
outer
in the retort pouch used in thin profile processing, which layer is used for barrier properties?
middle
what is over pressure processing used to process?
- retort pouches
- flexible containers
- glass containers
what is over-pressure processing used for?
- to protect package integrity (prevents pressure build up in packages at the beginning of cooling)
- promotes better heat transfer during heating (better contact between package and contents)
what determines the degree of over pressure?
proportion of steam and air
in over pressure processing, higher steam content provides _____
better heat transfer
in over pressure processing, higher air content provides ____
better overpressure protection
what kind of turbulent conditions are used in over-pressure processing to achieve better heat transfer?
- continuous venting (positive flow retorts)
2. turbo fans (through mixing)
how does overpressure processing change the pressure profile of a process?
pressure profile with NO overpressure has higher pressure than the retort during cooling. Thus, this creates a danger zone
pressure profile WITH air overpressure has lower pressure than the retort during cooling. Thus, the whole process is in the safe zone
what happens when there is no over-pressure to compensate for the high pressure inside a pouch compared to if overpressure is present?
if no overpressure: pouch will expand from the inside
if overpressure is present: expansion will be supressed
what are advantages of HTST?
- high quality
- easy opening and disposal
- easy reheating
- easy storage
what are disadvantages to HTST?
- slow speed (sealing limitation)
- incomplete air removal
- package failure (fragility)
- more manual labor
- needs overpressure processing
why is rotational/agitation processing is used to optimize food processing?
to improve heat transfer by improving mixing and heat transfer coefficient
what are the type types of rotation and agitation processing?
- end over end
- axial agitation
- reciprocation agitation
what kind of operation is axial rotation used for?
continuous operation
what kind of operation is end over end rotation used for?
batch operation
what are advantages of rotation/agitation processing?
- results in mixing of content
- rapid heat transfer
- uniform temperature
- less overcooking of product
- better quality retention
- shorter process time/quicker turnover
what type of container is end over end good for?
cans, semi rigid containers, glass containers
what type of container is axial rotation good for?
only for cans
what type of container is reciprocation agitation good for?
all types
what are factors that influence rotary sterilization?
- product viscosity
- can size
- type of product
- agitation speed
- retort temp
- head space
- ratio of liquid to particles
what is aseptic processing applied to?
liquid and acidic foods
what is the main concept behind aseptic processing?
heat, hold and cool concept
what are advantages to aseptic processing?
- high speed
- continuous process
- less damage to product
- shorter processing time
- uniform and high quality
- reduced energy consumption
what needs to be sterilized for aseptic processing?
- equipment
- container
- product (HTST)
- environment
what are disadvantages of aseptic processing?
- high initial capital investment
- complexity of system
- sophisticated instrument
- need highly qualified personnel
- can’t be used for solid food or conductive products
- process is not long enough to inactivate enzymes
what is SSHE?
security, safey, health, environment management
what is laminar and turbulent flow?
laminar: slow
turbulent: high speed
which fluid viscosity gives better flow for particulates: lower or higher viscosity?
- low density moves along top surface and has resistance with the bottom
- high density moves along the bottom and has resistance with the top
- fluid with equal density with liquid moves down the middle and moves fastest
