Food Preservation Methods Flashcards
what is food preservation
the science of extending the shelflife of food to maintain its nutritional quality and avoid the growth of unwarned microorganisms
how is shelf-life labeled
- date of minimum durability (best before)
2. expiration date (use by)
what is food spoilage
undesirable changes occurign in food due to airt, heat, light or moisture that motivates microorganism growth
how is food mainly spoilt
- microorganisms
- enzymes
- insects
two ways bacterial infections are caused
infections
intodications
carrier issues
healthy subjects hosting pathogens working in food industry might contaminate/transmit pathogens
main cause of food posioning?
cross contamination
how can one avoid cross contamination
avoid letting raw meats/animal products/raw veggies touch other food
always clean utensils/board
clean worktops with detergent
types of bacteria
cause spoilage
can be useful (health, fermentation)
dangerous (toxins/pathogens)
3 main sources of food contamination
- raw matieral I.e. meat, egg shells, fresh milk
- environment: storage of food, breeding, cultivation
- manufacturting practice: failure of HAACP
types of preserved foods
- stored products [frozen/dried/canned]
- semi preserved products [pasteurized, chilled]
- processed [fermented, salted, seasoned, smoked]
methods of preservation
phsyical
chemical
biological (fermentation)
physical preservation methods
refridgeration freezing modified atmosphere packing 9MAP) high temperature pasteurization sterilization packaging (tetrapak/aspeptic) dehydration concentraiton lyophillization (free drying)
chemical prservation methods
salting sugaring vegetabale oils vingegar ethyl alcohol food smoking/liquid smoke use of preservatives
explain the process of refrigeration
- 1 to 8.C
1. food is refrigerated during transport/storage and sold at room temp (fruit/veggies)
2. food fully sold/distributed in fridge
i. e. meat, milk, fish, salads, etc.
explain the process of: CA (controlled atmosphere)
oxygen kept at 5%
carbon dioixe at 1-3$
temperature dependign on food
used to extend post-harvest life of fruits
how does CA extend the harvest life of fruits
- reducing oxygen= reduces microbial contamination
- hydrating in water and creating acidic environment by carbnon dioxide= kills them
- inhibits enzymes/tissue metablism
where is oxygen icnreased in CA
for red meat storage to increase myoglidoin red pigment meat colour
why is adding oxygen bad to food
promotes enzymatic/chemical oxidation
activates beta-carotene degradation
substrate of respiration of plant/microbial cells
explain the process of: MAP (modified atmosphere packaging)
extends shelf life by creating barrier using packaging (to gas/contaminants) or vacuum packaging
example of MP matieral
polyvinyl chloride
polypropylene
polyethylene
vacuum packaging
where/which foods is MAP used
fresh apsta
baked goods
meats
frest cut fruts coffee
proces of vaccum packaging
pressure put below atmopshreic value
- stored in CRYOVAC (waterpoof vaccum)
- bags sealted under vaccum
- pacakge immersed in water at 90C
- hearable film adheres to film
types of freezing methods
flash freezing
industrial flash freezing
deep freezing
explain flash freezing
food quickly frozen at extreme cold temperature between -0.5/4 degrees which stops enzymatic reactions when water is solidifed
is fast to create smaller icecrystals that don’t damange the food
what is industrial flash freezing
forms smaller chrystals at fast temprature
how does flash freezing occur
sample placed in sample with liquid nitrogen/dry ice + ethanol
or
product pressed between 2 plates at -40/50 c (spinach cubes)
or
bulk subjected to jet of air in tunnel/freezing cells (peas, carrots)
or
product sealed in wterpoof packaged in placed in non freezable liquids (poultry)
or direct use of freezing product
what is the cold chain?
how products are frozen from raw matieral to consumers to fridege/freezer in the supply chain in :
procurement, trasnport, storage and customer retail
cons of just deep freezing
creates larger chrystals that when thawing, might damage the nutritional properties of food
high temperature methods
blanching
pasteurization
what is blanching
slighly cooking food (veggies) to inactivate enzymes/slow them down and:
clean surface from dirt and mold
brighten colour
make it easier to cook/pack
what is pasterurization
heat prevents bacterial flora to ferment
other proesses often used with it (chemicals, vaccuum packaging, freezing)
types of pasteuriziation
high temperature (70-75 c for few minutes)
low (60-65 for 30 minutes)
HTST: high temperature and fast time (liquid for few seconds)
how is milk pasteruized
HTST applied isuing steel plates
kills lactophillus bacteria which need sto be added in after pasteurization for lactose fermentation
two types of milk
extended shelf-life milk (extremment HTST)
raw unpasteruzied milk (special outlets and filtering rules)
pasteurized
what is sterilization
kills all microboial forms to can them/jar them
how does commercial sterilization occur
temperature related to acidity of the food for canning
(if pH lower than 4.5 100 c used, if higher: 115-120)
especially for meat products
compromise in sterliziation
high temperature: microbio safety
moderate temp: product quality
method of sterilization
- pressure cookers used (autoclaves)
- steam injected at high temperature
- indirect UHT (ultra high tempt), direct UHT
- cooling
- aspeptive pacakging in sterile containers
packaing methods
tetrapak
aspeptic packaing
tetrapak composition
paper (75), plastic (20), aluminum (5)
aspeptic packaging process
sterilized food placed into sterile containers
superior nutritional quality but shorter duraiton and prevents additive use
must be santiized by hydrogen perodixe vapour (which is ecological as split into oxygen and water)
dehydration method
water encourages micro/enzyme activity: hence:
total dehydration for milks/cereal
partial dehydraiton for tomato juice/fruitjuise
often combined by other tech
methods of dehydration
- cold
- hot (special evaporater machines or industrial ovens)
- concentration
- lyiphillization
pros of dehydration
long shelf life
reducton of volume and weight
lower tranpsort costs
concentration method aim
reduce foods weight to make less expensive, easier to store and easier to transport
dehydration types
evaporation cyroconcentraion (lowers coneglation point) membrane technology (filtration and reverse osmosis)
lyophillization method
freeze drying method; preserves biomatierals for extended perio to be used at room temperature using the process of sublimation (solid to vapour state)
proces of lyophilliziation
rapid freezing of food at -30/40 and then dehydraiton by sublimiation in vaccum
common food types lyophilized
coffee fruit and juice veggies meat fish eggs dairy
salting process
dry salting (fish, sausages) wet salting (for smoking, fridge, saline solutions, etc. )
salting= kills pathogens due to NaCl dehyrating them
sugaring
use of sucrose to dehydrate microrganisms
vegetable oils
protect food from air (like olive oil)
issue with oils
clostridium bacteria can still develop anaerobically so contamination still possible
food smoking process
exposesd cured meats, fish and dairty to aromatic wood to:
- increase palatabiltiy
- presreve food
types of chemical preservatives
sulphates sorbic acid ntirates benzoic acid salts ascorbic acid
