The Science Behind Food Preservation:

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The Science Behind Food Preservation

• Dr. Renee Boyer
• Extension Specialist
• May 21, 2009

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Why Preserve Foods ?

• Prevent Spoilage of Foods Extend Shelf Life
• Types of Spoilage
• Microbiological
• Molds, yeast, bacteria
• Chemical
• Enzymatic changes
• Physical
• Bruising, water loss

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Microbiological Food Spoilage

• Microorganisms can get onto a food product from
  anywhere in the environment
• People, animals, dirt, insects, other surfaces
• Spoilage microorganism cause food to spoil
• NOT pathogenic!!
• Pathogens make you sick

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What Bacteria Need to Grow

• Food
• Acidity
• Temperature
• Time
• Oxygen
• Moisture

FIGHT BAC!
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What Bacteria Need to Grow

• Food
• Acidity
• pH Amount of acidity
• Low acid food pH gt 4.6
• Temperature
• Time
• Oxygen
• Moisture

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Bacteria Inhibited by pH
Most Inhibited
Min Max Optimum
Gm Gm - 4.5 3.8 gt9.0 gt7.0
Yeast 1.5-3.5 8 4.5-6.8
Mold 1.5-3.5 11 4.5-6.8
Least Inhibited
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What Bacteria Need to Grow

• Food
• Acidity
• Temperature
• Time
• Oxygen
• Moisture

• Aerobic most spoilage organisms
• Facultatively anaerobic
• 5 Oxygen
• pathogens
• Anaerobic No Oxygen
• Clostridium botulinum

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What Bacteria Need to Grow

• Food
• Acidity
• Temperature
• Danger zone 40F to 140F
• (41F - 135F)
• Time
• Oxygen
• Moisture

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What Bacteria Need to Grow
Microbial Group Example aw Products Affected
Normal bacteria Salmonella species Clostridium botulinum 0.91 Fresh meat, milk
Normal yeast Torulopsis species 0.88 Fruit juice conc.
Normal molds Aspergillus flavus 0.80 Jams, jellies
Halophilic bacteria Wallemia sebi 0.75 Honey
Xerophilic molds Aspergillus echinulatas 0.65 Flour
Osmophilic yeast Saccharomyces bisporus 0.60 Dried fruits

• Food
• Acidity
• Temperature
• Time
• Oxygen
• Moisture

aw target 0.85
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Food Preservation Goal

• Control microbial growth / destroy microorganisms
  by
• High temperature (Heat)
• Low temperature (Cold)
• No oxygen
• Low pH
• Low Aw (water activity)

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Methods of Home Food Preservation

• Heat Processing/Canning
• Boiling Water Bath
• Pressure Canning
• Freezing
• Drying

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Canning Preservation by Heat

• Destroys microorganisms
• Inactivates enzymes
• Seals container during the process to prevent
  recontamination

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Question 1

• Of the growth factors that we discussed, which is
  the most important to know before proceeding to
  canning?

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Question 2

• What is the target organism associated with this?

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Acidity the most important factor!

• Clostridium botulinum
• Spore-former spores ubiquitous in the
  environment
• Cant make you sick
• Infant botulism
• ONLY Under anaerobic conditions (commonly
  created during preservation), spores germinated
  into vegetative cells
• Vegetative cells produce toxin

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Botulism

• Ingestion of toxin in foods
• Neurotoxin
• Causes paralysis and death
• if medical attention isnt
• found quickly
• Very rare in U.S. now
• Primarily associated w/
• improperly home canned

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Question 3

• Name one high acid and one low acid food

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High Acid Foods (pH lt 4.5)

• Lemons
• Grapefruit
• Pineapple
• Apricots
• Cherries
• Figs
• Plums
• Raspberries

• Apples
• Oranges
• Peaches
• Strawberries
• Pears
• Sauerkraut, pickles
• Blueberries
• Rhubarb

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Low Acid Foods (pH gt 4.5)

• Meat, fish
• Carrots
• Green beans
• Potatoes
• Peas
• Cabbage
• Corn
• Squash

• Pumpkin
• Okra
• Turnips
• Snap Beans
• Sweet potatoes
• Onions
• Oysters
• Ripe olives

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Tomatoes

• Usually considered an acid food
• Some now known to have a pH slightly above 4.6
• Boiling water bath MUST be acidified

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Canning Foods

• Low acid foods
• pH gt4.6
• Processing Pressure canner!
• High acid foods
• pH lt4.6
• Boiling water bath
• Acidified foods
• pH is decreased to lt4.6 by adding acid
• Pickling, salsas, tomatoes!
• Boiling water bath

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Destruction of Spores in Low Acid foods

• Spores are very difficult to destroy at boiling
  temperatures
• Boiling water bath 212F
• 7 11 hours depending on the food
• Pressure canning 240 250F (10-15 psi)
• 20 100 minutes depending on the food

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Time/Temperature Dependency

• Food
• Acid, salt, sugar, starch, fat
• Size of Pieces
• Consistency
• Convection heating in liquids
• Conduction heating in solids

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Time/Temperature Dependency

• Combination of both
• Fullness of pack
• Container size and material
• Initial temperature of food
• Microorganisms presen
• WHEN CANNING ALWAYS USE A RECIPE FROM A REPUTABLE
  SOURCE!!!

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What are reputable sources?

• National Center for Home Food Preservation
• http//www.uga.edu/nchfp/
• USDA Complete Guide to Home Canning
• http//www.uga.edu/nchfp/publications/publications
  _usda.html
• Ball Blue Book

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Methods of canning NOT recommended

• Open-kettle canning
• Processing in conventional ovens, microwaves,
  dishwashers
• Do no prevent all spoilage risks
• Steam canners
• Do not heat as effectively
• Canning at pressures greater than 15
• Use of glass caps or one piece zinc/porcelain-line
  d caps
• Failure to seal properly

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Boiling water bath canning

• Large covered cooking pot with a rack
• Must be deep enough to cover 1 inch above jars
• Processes foods at boiling temp. (212F)
• Acid / acidified foods
• Heat destroys m/o
• that spoil acid foods

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Pressure Canning

• Heavy pot, lid can be sealed fitted w/ vent and
  pressure dial or weighted gauge
• Processes foods at 240F (10-11 pds pressure)
• ONLY safe way to process low acid foods

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Question 4

• True or False Altitude affects the canning
  process

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The Effects of Altitude

• Water boils at lower temperatures as altitude
  increases.
• Lower temps are less effective, so
• Boiling water bath processing time increased
• Pressure canning pressure increased
• Altitudes in WV
• vary greatly
• Morgantown 960 ft
• Beckley 2421 ft

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Weighted vs- Dial gauge

• Weighted gauges

• Dial Gauges

• 0-1000ft 10 lbs pressure
• Over 1000ft must be operated at 15 lbs pressure

• 0-2000ft 11 lbs pressure
• Over 2000ft corrections must be made
• Ex
• 2001ft-4000 12 lbs
• 4001 6000 13 lbs

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Ensuring Quality

• Use only high quality foods, free of bruises and
  blemishes
• Can/preserve w/in 6-12 hours of harvest
• Hot pack (especially acid foods)
• Helps to remove air from the food
• Keeps food from floating in jar
• Increases the vacuum seal
• Helps food maintain color during storage

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Importance of headspace

• Jams/jellies ¼ inch
• Fruits / tomatoes (boiling water bath) ½ inch
• Low acid 1-1 ¼ inch
• Needed for expansion
• of the food
• Higher the temperature, the greater the expansion
• Forming vacuum in cooling jars

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Appropriate Jars/Lids
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Important notes Fruit

• Some recipes call for ascorbic acid dip
• Apples, pears, nectarines, apricots, peaches
  etc.
• Pure powdered form
• Vitamin C tablets
• Commercially prepared mixes
• This dip prevents the fruit from
• browning while preparing jars

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Important notes Pickling

• Pickled foods are acidified, therefore they can
  be heat processed in a boiling water bath
• Prevents spoilage organisms and inactive enzymes
• Fermentation
• Dill pickles/saurkraut 3 weeks
• Refrigerated dill pickles 1 weeks
• Quick process not fermented

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Important notes Pickling

• Level of acidity should not be altered
• Recipe MUST be followed
• Use canning/pickling salt
• Other salt has non-caking material added which
  can make brine cloudy

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Important notes Jams and Jellies

• Ingredients
• Fruit, pectin, acid, and sugar
• Pectin
• Form a gel when in the right combination of acid
  and sugar
• All fruits contain some pectin
• Fully ripened fruit has less pectin (when not
  adding pectin, ¼ fruit should be under-ripe)

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Important notes Jams and Jellies

• Acidity
• Too much gel wont set
• Too little gel with lose liquid
• Low acid fruits must have lemon juice added
• Commercial pectins contain acid to help w/
  gelling
• Reduced sugar
• Must be made w/ low-methoxy pectin (requires
  addition of calcium to gel)
• Typically need to be processed longer

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Jams/Jellies and Mold

• Low water activity acidity typically prevents
  most spoilage
• Except MOLDS
• Mycotoxins have been found in jellies/
• jams which have surface mold growth
• Known to cause cancer
• PROCESS in boiling water bath
• 5 minutes
• Do not use paraffin or wax seals

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Freezing

• Easiest, most convenient quickest methods
• Freezing is the safest method, but may not
  produce the best quality
• Does not sterilize foods
• Retards the growth of m/o and slows down chemical
  changes that affect the quality of the foods

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Control of Enzymatic Spoilage

• Enzymes are slowed down considerably, but not
  eliminated during freezing.
• For best quality
• Vegetables Blanched
• Quick treatment in boiling water (2-3 min)
  inactivates enzymes prior to freezing
• Fruits Ascorbic acid is added
• Vit. C, lemon juice, citric acid added to prevent
  browning before freezing

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Changes during freezing

• Water in food freezes and expands
• Ice crystals formed cause cell water to rupture
  rendering the product softer when defrosted.
• Quicker freezing decrease amount of cell wall
  rupture
• Rapid freezing many small ice crystals form
• Slow freezing few large ice crystals
• Most commercial products are frozen VERY rapidly
  in blast freezers

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Importance of temperature

• Frozen foods should be stored below 0F to
  prevent deterioration of the product and improve
  quality
• Example

Storage Temperature Storage Life
0F One year
10F Three months
20F Three weeks
30F Five days
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Foods that dont freeze well

• Foods that have high water content or are
  typically consumed raw
• Tomatoes
• Lettuces
• Celery
• Potatoes
• Sour cream
• Fried foods
• Milk sauces

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How drying preserves food

• Drying preserves food by removing the moisture
  (80-95) to prevent microbial growth
• Slows down enzymes
• Removing the moisture lower Aw
• Drying process is slowed down if humidity is high
• Best done at temp 140F

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Drying

• Outdoors
• Only for fruits (high acid, sugar content)
• Must be treated for insects after drying is
  complete
• Indoors
• Dehydrator BEST METHOD!
• Oven use oven thermometer to monitor temperature
• Leave door cracked 2 6 inches for air
  circulation

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Question 5

• What sort of treatments do you think fruits and
  vegetables might need before drying?

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Treatments for foods to be dried

• Fruits Dips
• Sulfite, Ascorbic acid, fruit juice, honey
• Vegetables Blanched
• Meat safety measures
• Pork or wild game meat should be frozen for 30
  days before use to kill trichinella
• Heat in marinade before drying
• Heated in oven after drying (to reach 160F)

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New Technologies that may/may not help consumers

• Home vacuum packagers
• Removing oxygen can increase quality of food
  therefore extending shelf-life BUT
• Less likely for spoilage organisms to grow
• MORE likely for pathogens to grow
• Can make perishable foods unsafe
• Safe for foods that will be frozen
• BUT they should be thawed
• using safe practices