food preservationlibvolume4.xyz/foodtechnology/bsc/semester6/technologyofmeatpou… · spoilage...
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Food Preservation
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Conditions for Spoilage
•Water
•pH
•Physical structure
•Oxygen
•temperature
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Microorganism Growth in Foods
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Intrinsic Factors
• composition
• pH
• presence and availability of water
• oxidation-reduction potential
– altered by cooking
• physical structure
• presence of antimicrobial substances
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Composition and pH
• putrefaction
– proteolysis and anaerobic breakdown of proteins,
yielding foul-smelling amine compounds
• pH impacts make up of microbial community and
therefore types of chemical reactions that occur
when microbes grow in food
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Water availability
• in general, lower water activity inhibits microbial growth
• water activity lowered by:
– drying
– addition of salt or sugar
• osmophilic microorganisms
– prefer high osmotic pressure
• xerophilic microorganisms
– prefer low water activity
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Physical structure
• grinding and mixing increase surface area
and distribute microbes
– promotes microbial growth
• outer skin of vegetables and fruits slows
microbial growth
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Antimicrobial substances
• coumarins – fruits and vegetables
• lysozyme – cow’s milk and eggs
• aldehydic and phenolic compounds – herbs
and spices
• allicin – garlic
• polyphenols – green and black teas
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Extrinsic Factors
• temperature
– lower temperatures retard microbial growth
• relative humidity
– higher levels promote microbial growth
• atmosphere
– oxygen promotes growth
– modified atmosphere packaging (MAP)
• use of shrink wrap and vacuum technologies to
package food in controlled atmospheres
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Microbial Growth and Food
Spoilage
• food spoilage
– results from growth of microbes in food
• alters food visibly and in other ways, rendering it unsuitable for consumption
– involves predictable succession of microbes
– different foods undergo different types of spoilage processes
– toxins are sometimes produced
• algal toxins may contaminate shellfish and finfish
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Food Spoilage
•Approximately 1/3rd of all food manufactured in
world is lost to spoilage
•Microbial content of foods (microbial load):
qualitative (which bugs) and quantitative (how many
bugs)
•Shelf life
•Non-perishable foods (pasta)
•Semiperishable foods (bread)
•Perishable foods (eggs)
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General Principles
•Minimize contamination by:
•Good management processes
•Acceptable sanitary practices
•Rapid movement of food through processing
plant
•Well-tested preservation procedures
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Spoilage•Meat
•Cutting board contamination
•Conveyor belts
•Temperature
•Failure to distribute quickly
•Fecal bacteria from intestines
•Fish
•Polluted waters
•Transportation boxes
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Spoilage•Poultry and Eggs
•Human contact
•Penetration by bacteria
•Milk and Dairy Products
•Lactobacillus and Streptococcus species that survive
pasturization (sour milk)
•Breads
•Spores and fungi that survive baking
•Grains
•Fungi produce toxins
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Food-Borne Diseases
• two primary types
– food-borne infections
– food intoxications
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Preventing Foodborne Disease
•Food infections (microbes are transferred to
consumer)
•Food poisoning (results from the toxin
consumption)
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Food-Borne Intoxications
• ingestion of toxins in foods in which
microbes have grown
• include staphylococcal food poisoning,
botulism, Clostridium perfringens food
poisoning, and Bacillus cereus food
poisoning
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Toxins
• ergotism
– toxic condition caused by growth of a fungus in
grains
• aflatoxins
– carcinogens produced in fungus-infected grains
and nut products
• fumonisins
– carcinogens produced in fungus-infected corn
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Controlling Food Spoilage
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Removal of Microorganisms
• usually achieved by filtration
• commonly used for water, beer, wine,
juices, soft drinks, and other liquids
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Low Temperature
• refrigeration at 5°C retards but does not stop
microbial growth
– psychrophiles and psychrotrophs can still cause
spoilage
– growth at temperatures below -10°C has been
observed
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High Temperature
• canning
• pasteurization
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Canning
• food heated in
special containers
(retorts) to 115 °C
for 25 to 100
minutes
• kills spoilage
microbes, but not
necessarily all
microbes in food
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Spoilage of canned goods
• spoilage prior to
canning
• underprocessing
• leakage of
contaminated water
into cans during
cooling process
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Pasteurization
• kills pathogens and substantially reduces
number of spoilage organisms
• different pasteurization procedures heat for
different lengths of time
– shorter heating times result in improved flavor
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Water Availability
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Chemical-Based Preservation
• GRAS
– chemical agents “generally recognized as safe”
• pH of food impacts effectiveness of
chemical preservative
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Radiation• ultraviolet (UV) radiation
– used for surfaces of food-handling equipment
– does not penetrate foods
• Gamma radiation
– use of ionizing radiation (gamma radiation) to
extend shelf life or sterilize meat, seafoods,
fruits, and vegetables
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Detection of Food-Borne
Pathogens
• must be rapid and sensitive
• methods include:
– culture techniques – may be too slow
– immunological techniques - very sensitive
– molecular techniques
• probes used to detect specific DNA or RNA
• sensitive and specific
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comparison of PCR and
growth for detection of
Salmonella
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nucleic acid can be detected
even when plaque-forming
ability is lost
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Surveillance for food-borne
disease
• PulseNet
– established by Centers for Disease Control
– uses pulsed-field gel electrophoresis under carefully controlled and duplicated conditions to determine distinctive DNA pattern of each bacterial pathogen
– enables public health officials to link pathogens associated with disease outbreaks in different parts of the world to a specific food source
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Surveillance…
• FoodNet
– active surveillance network used to follow nine
major food-borne diseases
– enables public health officials to rapidly trace
the course and cause of infection in days rather
than weeks
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Helpful Suggestions
•Refrigerate quickly
•Wash hands
•Clean cutting boards
•Leftovers
•Avoid home-canned foods
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Microbiology of Fermented
Foods
• major fermentations used are lactic,
propionic, and ethanolic fermentations
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Fermentation
Any partial breakdown of carbohydrates taking
place in the absence of oxygen.
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Meat and Fish
• sausages
• hams
• bologna
• salami
• izushi – fish, rice and vegetables
• katsuobushi – tuna
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Wine
White vs. Red: juice or juice and skin
Yeasts: Ferment when no oxygen around.
Saccharomyces species
Dry
Sweet
Sparkling
Fortified
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Production of Breads
• involves growth of Saccharomyces cerevisiae
(baker’s yeast) under aerobic conditions
– maximizes CO2 production, which leavens bread
• other microbes used to make special breads (e.g.,
sourdough bread)
• can be spoiled by Bacillus species that produce
ropiness
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Other Fermented Foods
• silages
– fermented grass, corn, and other fresh animal feeds
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Microorganisms as Foods and
Food Amendments
• variety of bacteria, yeasts, and other fungi
are used as animal and human food sources
• probiotics
– microbial dietary adjuvants
– microbes added to diet in order to provide
health benefits beyond basic nutritive value