Foods Poli Age
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Transcript of Foods Poli Age
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8/14/2019 Foods Poli Age
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Food spoilage
What causes it
How to minimize it
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Mahalo.comInmagine.com
You know it when you see it
Or smell it
Or taste it
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What are the steps of food spoilage?
Introduce microbes to food
Food environment is favorable for growth
Food is stored at a temperature that favros
growth Enough time elapses
Thermoduric microbes survive heat treatment
Heat-stable enzymes can degrade food
Bacteria, molds, and yeasts cause most foodspoilage
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Microbes and food
Most nonsterile foods contain many types of
microbes
Spoiled foods have one or a few- that outgrew
the others (much more slowly than in
laboratory conditions!)
Aerobic foods: Pseudomonas
Anaerobic foods: Lactobacillusor Leuconostoc
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Animal muscle tissue contains few
bacteria
Hide, hair, hooves, GItract
Hide removal
Breaching GI tract Processing
environment andtools
Staphylococcus,
Micrococcus,
Pseudomonas
Scienceblogs.com
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Poultry
Skin, feathers, and
feet
Feces and litter from
coops
Potable water for
chilling
Goldcoastcommodities.com
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Finfish and shellfish
Water temperatureand feeding patterns
Warm vs cold
Psychrotrophic vsmesophilic microbes
Bottom feeders, filterfeeders (molluscs)
Harvesting methods Trawling vs line caught
Storage
Americanvision.org
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Recall types of microbes
Oxygen requirements Temperature optima
So different types of microbes can grow as conditions change
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Growth under storage conditions
Microbes were intrinsic or introduced by
processing
Generally few species grow
Aerobic conditions: Pseudomonas favored
Vacuum packed: lactobacilli if low pH
Bacillusand Shewanellacan grow at higher pH
Lowering awreduces microbial growth
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Meat, poultry, and fish are good food
sources for microbes
High aw Protein > lipids > carbohydrates
Microbial metabolism will lower pH
Slow cooling may favor the growth of anaerobesin deep tissue
Fungi may grow if surface gets dry
Fish vary in lipid content
Molluscs have higher carbohydrate content andare spoiled by fermenters
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Spoilage factors are diverse like the food
environment
Carbohydrates metabolized first, then lipids,then proteins (as microbial count increases)
Products from:
Carbohydrates- carbon dioxide or fermentationproducts
Lipids- aldehydes, ketones, short-chain fatty acids
Proteins- amino acids, amines, short peptides
Nonprotein nitrogenous compounds (usu.breakdown products from lysed cells)
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How does microbial metabolism adversely
affect food?
Volatile end products produce odor
Oxidation of pigmented products can change
color
Breakdown of tissues by degradative enzymes
can change texture
Production of dextran or sheer numbers can
produce slime
Water can be released (purge)
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Specific spoilage organisms: meats
High protein, low carbohydrate
High aw, pH tends to be acidic
Aerobes: Pseudomonas(grows fast), expends glucose
Acintobacterand Moraxellaprefer to utilize amino
acids
Facultative anaerobes and anaerobes if oxygen is
limited (vacuum-packed meats) Comminuted (ground) meats spoil faster due to
increased surface area
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Different issues with processed meats
Heat-resistant organismsIntroduced by handling
Preservatives often added
Lactobacillus
Leuconostoc
Amino acid metabolism
Putrefaction, odor, sliminess
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Eggshells do not protect against microbial infection!
Eggs do have natural protectionlysozyme, alkaline pH, chelators, protease inhibitors
Gram-negative motile rods
green, black, red rots
Dried eggs not susceptible
to spoilage
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Milk and milk products
Whats in milk?
Protein
Casein, lactalbumin, amino acids
Carbohydrate
lactose
Lipids
Degraded by milk lipases into butyric, capric, caproicacids
Minerals
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Pasteurization does not kill everything
Micrococcus, Enterococcus, and others can survive
Pseudomonas, spore formers,and others can be
introduced afterward
UHT (ultra high temperature, 150oC for a fewseconds) is essentially sterilized
Concentrated milk products are heat treated
Butter tends to be contaminated by yeasts and molds
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Fruits and vegetables
Vary in carbohydrates,
proteins, pH
What sorts of organisms
would spoil them?
Innate or introduced?
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Fermented foods are not immune to
spoilage
Generally yeasts and acidophilic bacteria
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Canned foods
Heat treated to kill microbes
Low acid: kill most spore formers
flat sour- no gasthermophilic anaerobe-gas
sulfide stinker- gas and
discoloration
High acid: all vegetative bacteria
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Refrigerated foods
Psychrophilic and psychrotrophic microbes
Handling introduces microbes
Some pathogens can grow at lowtemperatures
With long storage, microbes can increase to
disease causing levels
Competitive advantages: adaptation to cold. Low
O2, production of bacteriocins
Clostridiumgrow in vacuum-packed foods
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Summary
Why are different foods spoiled differently?
Available nutrients
Capability for rapid growth of microbes End products: organics, inorganics, gases?
Enzyme activity?