Transcript Food Preservation

13
Food Preservation and Safety
The Competition
Food Spoilage(식품부패)
• General principles
– 33% of all food manufactured worldwide lost to spoilage
– Qualitative aspects: which microbes are present
– Quantitative aspects: overall microbial count
• Sometimes, count must be zero
• Sometimes there is an acceptable limit because microbes can be
killed during cooking
– Shelf life(유통기간)
• Non-perishable foods
• Semi-perishable foods
• Perishable foods (썩기 쉬운 식품)
Food Spoilage
• General principles(일반적인 원리)
– Product coding
– Microbial load (미생물부하)
• Load can be high, as long as not pathogenic
– Microbial contamination is impossible to avoid
– Control is the goal
– Good food management practices
• Sanitation
• Rapid movement through processing plants
• Well tested preservation techniques
Food Spoilage
• General principles
– Human handling
• Inadvertently mixing intestines with meat
• Washing poultry(가금류), fish, or meat with untreated water
• Handling of raw vegetables in supermarkets by consumers with dirty
hands
– Rework(재가공)
– Intentional contamination: bioterrorism
Food Spoilage
• The conditions for
spoilage
– Food is a good culture
medium for microbes
– Water content
– pH range
– Physical structure
– Oxygen availability
– Temperature
Figure 13.2: Food Spoilage
Food Spoilage
• The conditions for spoilage
– Detecting spoilage
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Alcoholic taste to fruit juice
“Rotten egg” smell
Souring of foods through acid production
Swelling of sealed cans by gas production
Color
Food Spoilage
• Meats
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Cannot be pasteurized
High nutrient supply for microbes to thrive
Escherichia coli O157:H7 (1993년 용혈성 설사현상 발생)
Sources of contamination
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Cutting boards
Conveyer belts
Improper temperature control
Failure to distribute meat and meat products quickly
Observable as brown color with surface slime(표면의 점질물질)
Fecal contamination(배설물에 의한 오염)
Lactobacillus
Leuconostoc
Food Spoilage
• Meats
– Choke points(관문)
– Processed meats (e.g., sausages, frankfurters)
• Handled often
• Contain variety of meat products
• Sausage and salami casings made from animal intestines
– Cured meats (e.g., ham, corned beef)
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Large doses of salt
Lactobacilli still survive
Souring of meat
Gas production
Red meat turns green
Food Spoilage
• Fish
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Microbes adapted to grow in cold
Shellfish concentrate microbes because they are filter feeders
Looser tissue than red meat
Polluted water
Microbes in gills
Storage boxes as source of microbes
Preservation methods
• Salting
• Heating
• Drying
– Thrimethylamine production(생선 부패 취의 원인물질)
Food Spoilage
• Poultry and eggs(가금류와 계란)
– Bacteria that have infected the bird
– Commonly Salmonella
– Bacteria enter foods such as
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Chicken pot pie
Whole egg custard
Mayonnaise
Egg nog
Egg salad
– Eggs normally sterile
– Shell and waxy membrane can be
penetrated by microbes
– Proteus causes black rot and awful
smell
– Serratia marcescens causes blood
red appearance of yolk
Reprinted with permission from the American Society for
Microbiology (Thomas, C.J. and McMeekin, T.A.; Appli.
Environ. Microbiol, 1981 February; 41(2): 492-503.)
Figure 13.4: A SEM of
unidentified flagellated bacteria
growing on the skin of a chicken
carcass (Bar = 2 μm)
Food Spoilage
• Milk and dairy products
– Nutritious fluid
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87% water
2.5% casein
5% carbohydrates, mostly lactose
Butterfat
– Spoilage often occurs while milk is refrigerated
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Lactobacillus or Streptococcus that survived pasteurization
Fermentation of lactose
Acid changes structure of casein to create sour curd
Breakdown of casein creates sweet curdling
– Whey
– Cheese
Food Spoilage
• Milk and dairy products
– Ropiness(점착성)
• Alcaligenese
• Enterobacter
– Red pigment
• Serratia marcescens
– Gray rot
• Clostridium
– Pink, orange, yellow discoloration
• Yeasts
– Inside of udder(젖통) is sterile
– Acquisition of microbes from duct leading to teat(젖꼭지)
• Lactobacillus
• Streptococcus
• Campylobacter
Food Spoilage
• Breads and bakery products
– Sources of spoilage
• Eggs
• Flour
• Sugar
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Bacterial and fungal spores
Bacillus spp,
Cream fillings
High sugar chocolate toppings and sweet icings
Food Spoilage
• Grains
– Aspergillus flavus
• Aflatoxins
– Wheat
– Peanuts
– Soybeans
– Corn
– Claviceps purpurea
• Ergot poisoning
– Neurological disorder
– Rye
– Wheat
– Barley
Food Preservation
• Objectives
– Reduce microbial count
– Maintain at low level
– Until food can be
consumed
• Heat
– Changes physical and
chemical nature of
proteins
Figure 13.6: Important temperature ranges in
food microbiology
Food Preservation
• Heat
– Canning
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Steam heat foods 3-5 minutes (blanching)
Food is processed (e.g., peeled, cored)
Food is canned
All air removed from can
Commercial sterilization
– Heat
– Pressure
– Designed to inactivate Bacillus and Clostridium spores
• Contamination may also come from Gram-negative coliforms
Food Preservation
• Pasteurization(저온살균법)
– Holding method
• Milk kept at 62.8 °C for 30 minutes
• Cream kept at 68.3 °C for 30 minutes
– Flash method (more modern)
• 71.7 °C for 15-17 seconds in hot cylinder
• Rapid cooling
– Ultrapasteurization
• 82.2 °C for 3 seconds
– Also important for fruit juices
Food Preservation
• Pasteurization
– Bacteria that survive may spoil product, but generally no other
harm
• Streptococcus lactis
– Up to 20 million per milliliter
– Enough lactic acid to sour milk, but not enough to be harmful
• Thermoduric microbes
• Thermophilic microbes
– Sterilization can also be accomplished with high pressure steam
• 140 °C for 3 seconds
• Milk with indefinite shelf life
Food Preservation
• Low temperatures
– Refrigerators and freezers
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Slows growth rate of microbes
Extends shelf life of foods
Microbes not killed
Refrigerators are 4-5 °C
– Psychotrophic bacteria
• Freezers at -20 to -5 °C
– Ice crystals form and burst microbes
• Deep freezing at -80 to -60 °C
– Smaller ice crystals
– Freezer burn
Food Preservation
• Drying
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Complete removal of moisture, an essential condition for life
Sun drying
Freeze drying
Heated drum
Belt heater
Lyophilization
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Frozen food
Water drawn off from solid to gas phase, without liquid intermediate
Food sealed in foil
Reconstitute food with water
Means for creation of bioterrorist weapons
Food Preservation: Industrial Lyophilization
Figure 13.8: An Industrial lyophilizer
Food Preservation
• Osmotic pressure
– Large quantities of salt or sugar
– Water flows out of microbes
– Examples
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Jams
Jellies
Fruits
Maple syrup
Honey
Ham
Cod( codfish : 대구)
Bacon
Beef
Sauerkraut
Food Preservation
• Chemical preservatives
– Must inhibit microbes
– Must be easily broken down and eliminated by people
– Organic acids
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Sorbic acid
Benzoic acid
Propionic acid
Interfere with the uptake of certain essential organic substances
– Smoking with hickory or other woods
• Dries out food
• Deposits antimicrobial byproducts of smoke
– Aldehydes
– Acids
– Phenols
– Sulfites
Food Preservation
• Radiation
– Gamma rays
• Destroys microbial proteins and DNA
• Does not impart radioactivity to food
Preventing Foodborne Disease
• Typical foodborne illnesses
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Typhoid fever
Salmonellosis
Cholera
Shigellosis
Ameobiasis
Giardiasis(편모충증)
Hepatitis (from hepatitis A)(간염)
Staphylococcal food poisoning
Botulism
Clostridial food poisoning
Preventing Foodborne Disease
• Helpful suggestions
– Leftovers as major source of foodborne illness
– Foodborne illness during the summer
• Outdoor picnics with no refrigeration
• Do not opt for egg-containing dishes
– Custards
– Cream pies
– Pastries
– Deli salads
• Use one plate for all raw meats
• Use different plate for all meats once cooked
– Over 90% of botulism cases traced to home canning
– Discard bulging or leaking cans
Preventing Foodborne Disease
• HACCP systems(식품위해요소 중점관리기준 체계)
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Hazard Analysis Critical Control Points
Federal safety regulations for seafood, meat, and poultry
Overseen by USDA
Eight key sanitation areas
• Safety of water and ice that contacts food
• Condition and cleanliness of utensils, gloves, clothes, and food
contact surfaces
• Prevention of cross contamination
• Maintenance of hand-washing and toilet facilities
• Protection of food and food surfaces from hazardous chemicals
• Proper labeling, storage, and use of toxic compounds
• Control of employee health conditions that could contaminate food
• Exclusion of pests from food