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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?