department department of food science and technology the science behind food preservation: dr. renee...
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DepartmentDepartment of Food Science and Technology
The Science The Science Behind Food Behind Food Preservation:Preservation:
Dr. ReneeDr. Renee Boyer Boyer
Extension Extension SpecialistSpecialist
May 21, 2009May 21, 2009
DepartmentDepartment of Food Science and Technology
Why Preserve FoodsWhy Preserve Foods ? ?
Prevent Spoilage of Foods & Extend Shelf Prevent Spoilage of Foods & Extend Shelf LifeLife
Types of Spoilage:Types of Spoilage:– MicrobiologicalMicrobiological
Molds, yeast, bacteriaMolds, yeast, bacteria
– ChemicalChemical Enzymatic changesEnzymatic changes
– PhysicalPhysical Bruising, water lossBruising, water loss
DepartmentDepartment of Food Science and Technology
Microbiological Food Microbiological Food Spoilage:Spoilage:
Microorganisms can get onto a food Microorganisms can get onto a food product from anywhere in the product from anywhere in the environment…environment…– People, animals, dirt, insects, other surfacesPeople, animals, dirt, insects, other surfaces
Spoilage microorganismSpoilage microorganism: cause food to spoil: cause food to spoil
NOT pathogenic!!NOT pathogenic!!
Pathogens: Pathogens: make you sickmake you sick
What Bacteria Need to What Bacteria Need to GrowGrow
FFoodood
AAciditycidity
TTemperatureemperature
TTimeime
OOxygenxygen
MMoistureoistureFIGHT BAC!
What Bacteria Need to What Bacteria Need to GrowGrowFFoodood
AAciditycidity– pH = Amount of aciditypH = Amount of acidity– Low acid food = pH > 4.6Low acid food = pH > 4.6
TTemperatureemperature
TTimeime
OOxygenxygen
MMoistureoisture
DepartmentDepartment of Food Science and Technology
Bacteria Inhibited by pHBacteria Inhibited by pH
Min Max Optimum
Gm +
Gm -
4.5
3.8
>9.0 >7.0
Yeast 1.5-3.5 8 4.5-6.8
Mold 1.5-3.5 11 4.5-6.8
Most Inhibited
Least Inhibited
What Bacteria Need to What Bacteria Need to GrowGrow
FFoodood
AAciditycidity
TTemperatureemperature
TTimeime
OOxygenxygenMMoistureoisture
Aerobic: most spoilage Aerobic: most spoilage organismsorganisms
Facultatively anaerobic: Facultatively anaerobic:
5% Oxygen5% Oxygen
pathogenspathogens
Anaerobic: No OxygenAnaerobic: No Oxygen
Clostridium botulinumClostridium botulinum
DepartmentDepartment of Food Science and Technology
What Bacteria Need to What Bacteria Need to GrowGrowFFoodood
AAciditycidity
TTemperatureemperature– Danger zone = 40°F to 140°F Danger zone = 40°F to 140°F
(41°F - 135°F)(41°F - 135°F)
TTimeime
OOxygenxygen
MMoistureoisture
DepartmentDepartment of Food Science and Technology
What Bacteria Need to What Bacteria Need to GrowGrow
FFoodood
AAciditycidity
TTemperatuemperaturere
TTimeime
OOxygenxygen
MMoistureoisture
Microbial Group Example aw
ProductsAffected
Normal bacteriaSalmonella species
Clostridium botulinum0.91
Fresh meat, milk
Normal yeast Torulopsis species 0.88Fruit juiceconc.
Normal molds Aspergillus flavus 0.80 Jams, jellies
Halophilic bacteria
Wallemia sebi 0.75 Honey
Xerophilic molds Aspergillus echinulatas 0.65 Flour
Osmophilic yeastSaccharomyces
bisporus0.60 Dried fruits
aw target = 0.85
DepartmentDepartment of Food Science and Technology
Food Preservation Goal:Food Preservation Goal:
Control microbial growth / destroy Control microbial growth / destroy microorganisms by:microorganisms by:
High temperature (Heat)High temperature (Heat) Low temperature (Cold)Low temperature (Cold) No oxygenNo oxygen Low pHLow pH Low Aw (water activity)Low Aw (water activity)
DepartmentDepartment of Food Science and Technology
Methods of Home Food Methods of Home Food Preservation:Preservation:
Heat Processing/CanningHeat Processing/Canning– Boiling Water BathBoiling Water Bath– Pressure CanningPressure Canning
FreezingFreezing DryingDrying
DepartmentDepartment of Food Science and Technology
DepartmentDepartment of Food Science and Technology
Canning = Preservation by Canning = Preservation by HeatHeat
Destroys microorganismsDestroys microorganisms
Inactivates enzymesInactivates enzymes
Seals container during the process to Seals container during the process to prevent recontaminationprevent recontamination
DepartmentDepartment of Food Science and Technology
Of the growth factors Of the growth factors that we discussed, that we discussed, which is the most which is the most important to know important to know
before proceeding to before proceeding to canning?canning?
Question #1: Question #1:
DepartmentDepartment of Food Science and Technology
What is the target What is the target organism associated organism associated
with this? with this?
Question #2: Question #2:
DepartmentDepartment of Food Science and Technology
Acidity: the most important Acidity: the most important factor!factor!
Clostridium botulinumClostridium botulinum Spore-former: spores ubiquitous in the Spore-former: spores ubiquitous in the
environmentenvironment– Can’t make you sick Can’t make you sick – Infant botulismInfant botulism
ONLY: Under anaerobic conditions ONLY: Under anaerobic conditions (commonly created during preservation), (commonly created during preservation), spores germinated into vegetative cellsspores germinated into vegetative cells
Vegetative cells produce toxinVegetative cells produce toxin
DepartmentDepartment of Food Science and Technology
Botulism:Botulism:
Ingestion of toxin in foodsIngestion of toxin in foods NeurotoxinNeurotoxin
Causes paralysis and deathCauses paralysis and death
if medical attention isn’t if medical attention isn’t
found quicklyfound quickly Very rare in U.S. now Very rare in U.S. now Primarily associated w/ Primarily associated w/
improperly home cannedimproperly home canned
DepartmentDepartment of Food Science and Technology
Name one high acid Name one high acid and one low acid foodand one low acid food
Question #3: Question #3:
DepartmentDepartment of Food Science and Technology
High Acid Foods (pH < 4.5)High Acid Foods (pH < 4.5)
ApplesApples OrangesOranges PeachesPeaches StrawberriesStrawberries PearsPears Sauerkraut, picklesSauerkraut, pickles BlueberriesBlueberries RhubarbRhubarb
LemonsLemons GrapefruitGrapefruit PineapplePineapple ApricotsApricots CherriesCherries FigsFigs PlumsPlums RaspberriesRaspberries
DepartmentDepartment of Food Science and Technology
Low Acid Foods (pH > 4.5)Low Acid Foods (pH > 4.5)
Meat, fishMeat, fish CarrotsCarrots Green beansGreen beans PotatoesPotatoes PeasPeas CabbageCabbage CornCorn SquashSquash
PumpkinPumpkin OkraOkra TurnipsTurnips Snap BeansSnap Beans Sweet potatoesSweet potatoes OnionsOnions OystersOysters Ripe olivesRipe olives
DepartmentDepartment of Food Science and Technology
Tomatoes:Tomatoes: Usually considered Usually considered
an acid foodan acid food
Some now known Some now known to have a pH to have a pH slightly above 4.6slightly above 4.6
Boiling water bath Boiling water bath …MUST be acidified…MUST be acidified
DepartmentDepartment of Food Science and Technology
Canning FoodsCanning Foods Low acid foods: Low acid foods:
– pHpH >4.6 >4.6 – Processing Processing Pressure canner!Pressure canner!
High acid foods:High acid foods:– pHpH <4.6 <4.6 – Boiling water bathBoiling water bath
Acidified foods:Acidified foods:– pH is decreased to <4.6 by pH is decreased to <4.6 by addingadding
acidacid– Pickling, salsas, tomatoes!Pickling, salsas, tomatoes!– Boiling water bath Boiling water bath
DepartmentDepartment of Food Science and Technology
DepartmentDepartment of Food Science and Technology
Destruction of Spores in Destruction of Spores in Low Acid foods:Low Acid foods:
Spores are very difficult to destroy at Spores are very difficult to destroy at boiling temperaturesboiling temperatures
Boiling water bath: 212°FBoiling water bath: 212°F– 7 – 11 hours depending on the food7 – 11 hours depending on the food
Pressure canning: 240 – 250°F (10-15 psi)Pressure canning: 240 – 250°F (10-15 psi)– 20 – 100 minutes depending on the food20 – 100 minutes depending on the food
DepartmentDepartment of Food Science and Technology
DepartmentDepartment of Food Science and Technology
Time/Temperature Time/Temperature DependencyDependency
FoodFood Acid, salt, sugar, starch, fatAcid, salt, sugar, starch, fat Size of PiecesSize of Pieces ConsistencyConsistency Convection heating in liquidsConvection heating in liquids Conduction heating in solidsConduction heating in solids
DepartmentDepartment of Food Science and Technology
Time/Temperature Time/Temperature DependencyDependency
Combination of bothCombination of both Fullness of packFullness of pack Container size and materialContainer size and material Initial temperature of foodInitial temperature of food Microorganisms presenMicroorganisms presen
WHEN CANNING ALWAYS USE A RECIPE WHEN CANNING ALWAYS USE A RECIPE FROM A REPUTABLE SOURCE!!!FROM A REPUTABLE SOURCE!!!
DepartmentDepartment of Food Science and Technology
What are reputable What are reputable sources?sources?
National Center for Home Food National Center for Home Food PreservationPreservation– http://www.uga.edu/nchfp/
USDA Complete Guide to Home CanningUSDA Complete Guide to Home Canning– http://www.uga.edu/nchfp/publications/publicat
ions_usda.html
Ball Blue BookBall Blue Book
DepartmentDepartment of Food Science and Technology
Methods of canning NOT Methods of canning NOT recommended:recommended:
Open-kettle canningOpen-kettle canning Processing in conventional ovens, microwaves, Processing in conventional ovens, microwaves,
dishwashersdishwashers– Do no prevent all spoilage risksDo no prevent all spoilage risks
Steam cannersSteam canners– Do not heat as effectivelyDo not heat as effectively
Canning at pressures greater than 15Canning at pressures greater than 15 Use of glass caps or one piece zinc/porcelain-lined Use of glass caps or one piece zinc/porcelain-lined
capscaps– Failure to seal properlyFailure to seal properly
DepartmentDepartment of Food Science and Technology
Boiling water bath canning:Boiling water bath canning:
Large covered cooking pot with a rackLarge covered cooking pot with a rack Must be deep enough to cover 1 inch Must be deep enough to cover 1 inch
above jarsabove jars Processes foods at boiling temp. (212°F)Processes foods at boiling temp. (212°F) Acid / acidified foodsAcid / acidified foods Heat destroys m/oHeat destroys m/o
that spoil acid foodsthat spoil acid foods
DepartmentDepartment of Food Science and Technology
DepartmentDepartment of Food Science and Technology
Pressure Canning:Pressure Canning:
Heavy pot, lid can be sealed: fitted w/ vent Heavy pot, lid can be sealed: fitted w/ vent and pressure dial or weighted gaugeand pressure dial or weighted gauge
Processes foods at 240°F (10-11 pds Processes foods at 240°F (10-11 pds pressure)pressure)
ONLY safe way to process low acid foodsONLY safe way to process low acid foods
DepartmentDepartment of Food Science and Technology
DepartmentDepartment of Food Science and Technology
True or False: True or False: Altitude affects the Altitude affects the canning process canning process
Question #4: Question #4:
DepartmentDepartment of Food Science and Technology
The Effects of Altitude:The Effects of Altitude:
Water boils at lower temperatures as Water boils at lower temperatures as altitude increases.altitude increases.
Lower temps are less effective, so:Lower temps are less effective, so:– Boiling water bathBoiling water bath: processing time increased: processing time increased– Pressure canningPressure canning: pressure increased: pressure increased
Altitudes in WV Altitudes in WV
vary greatly:vary greatly:Morgantown: 960 ftMorgantown: 960 ft
Beckley: 2421 ftBeckley: 2421 ft
DepartmentDepartment of Food Science and Technology
DepartmentDepartment of Food Science and Technology
Weighted –vs- Dial gauge:Weighted –vs- Dial gauge:
Weighted gauges:Weighted gauges:
0-1000ft: 10 lbs 0-1000ft: 10 lbs pressurepressure
Over 1000ft: must be Over 1000ft: must be operated at 15 lbs operated at 15 lbs pressurepressure
Dial Gauges:Dial Gauges: 0-2000ft: 11 lbs 0-2000ft: 11 lbs
pressurepressure Over 2000ft: Over 2000ft:
corrections must be corrections must be mademade
Ex: Ex: – 2001ft-4000: 12 lbs2001ft-4000: 12 lbs– 4001 – 6000: 13 lbs4001 – 6000: 13 lbs
DepartmentDepartment of Food Science and Technology
Ensuring Quality:Ensuring Quality:
Use only high quality foods, free of bruises Use only high quality foods, free of bruises and blemishesand blemishes
Can/preserve w/in 6-12 hours of harvestCan/preserve w/in 6-12 hours of harvest
Hot pack (especially acid foods)Hot pack (especially acid foods)– Helps to remove air from the foodHelps to remove air from the food– Keeps food from floating in jarKeeps food from floating in jar– Increases the vacuum sealIncreases the vacuum seal– Helps food maintain color during storageHelps food maintain color during storage
DepartmentDepartment of Food Science and Technology
Importance of headspace:Importance of headspace:
Jams/jellies: ¼ inchJams/jellies: ¼ inch Fruits / tomatoes: (boiling water bath): ½ inchFruits / tomatoes: (boiling water bath): ½ inch Low acid: 1-1 ¼ inchLow acid: 1-1 ¼ inch
Needed for expansion Needed for expansion
of the foodof the food– Higher the temperature, the greater the expansionHigher the temperature, the greater the expansion
Forming vacuum in cooling jarsForming vacuum in cooling jars
DepartmentDepartment of Food Science and Technology
Appropriate Jars/LidsAppropriate Jars/Lids
DepartmentDepartment of Food Science and Technology
Important notes: FruitImportant notes: Fruit
Some recipes call for ascorbic acid dipSome recipes call for ascorbic acid dip– Apples, pears, nectarines, apricots, peaches Apples, pears, nectarines, apricots, peaches
etc….etc….– Pure powdered formPure powdered form– Vitamin C tabletsVitamin C tablets– Commercially prepared mixesCommercially prepared mixes
This dip prevents the fruit from This dip prevents the fruit from
browning while preparing jarsbrowning while preparing jars
DepartmentDepartment of Food Science and Technology
Important notes: PicklingImportant notes: Pickling
Pickled foods are acidified, therefore they Pickled foods are acidified, therefore they can be heat processed in a boiling water can be heat processed in a boiling water bathbath– Prevents spoilage organisms and inactive Prevents spoilage organisms and inactive
enzymesenzymes
FermentationFermentation– Dill pickles/saurkraut – 3 weeksDill pickles/saurkraut – 3 weeks– Refrigerated dill pickles – 1 weeksRefrigerated dill pickles – 1 weeks– Quick process – not fermentedQuick process – not fermented
DepartmentDepartment of Food Science and Technology
Important notes: PicklingImportant notes: Pickling
Level of acidity should not be alteredLevel of acidity should not be altered– Recipe MUST be followedRecipe MUST be followed
Use canning/pickling saltUse canning/pickling salt– Other salt has non-caking material added Other salt has non-caking material added
which can make brine cloudywhich can make brine cloudy
DepartmentDepartment of Food Science and Technology
Important notes: Jams and Important notes: Jams and JelliesJellies
IngredientsIngredients– Fruit, pectin, acid, and sugarFruit, pectin, acid, and sugar
PectinPectin– Form a gel when in the right combination of Form a gel when in the right combination of
acid and sugaracid and sugar– All fruits contain some pectinAll fruits contain some pectin– Fully ripened fruit has less pectin (when not Fully ripened fruit has less pectin (when not
adding pectin, ¼ fruit should be under-ripe)adding pectin, ¼ fruit should be under-ripe)
DepartmentDepartment of Food Science and Technology
Important notes: Jams and Important notes: Jams and JelliesJellies
AcidityAcidity– Too much – gel won’t setToo much – gel won’t set– Too little – gel with lose liquidToo little – gel with lose liquid– Low acid fruits must have lemon juice addedLow acid fruits must have lemon juice added– Commercial pectins contain acid to help w/ Commercial pectins contain acid to help w/
gellinggelling
Reduced sugarReduced sugar– Must be made w/ low-methoxy pectin (requires Must be made w/ low-methoxy pectin (requires
addition of calcium to gel)addition of calcium to gel)– Typically need to be processed longerTypically need to be processed longer
DepartmentDepartment of Food Science and Technology
Jams/Jellies and MoldJams/Jellies and Mold Low water activity + acidity typically Low water activity + acidity typically
prevents most spoilageprevents most spoilage
Except: MOLDSExcept: MOLDS– Mycotoxins have been found in jellies/Mycotoxins have been found in jellies/
jams which have surface mold growthjams which have surface mold growth– Known to cause cancerKnown to cause cancer– PROCESS in boiling water bathPROCESS in boiling water bath
5 minutes5 minutes Do not use paraffin or wax sealsDo not use paraffin or wax seals
DepartmentDepartment of Food Science and Technology
Freezing: Freezing:
Easiest, most convenient quickest Easiest, most convenient quickest methodsmethods
Freezing is the safest method, but may not Freezing is the safest method, but may not produce the best qualityproduce the best quality
Does not sterilize foodsDoes not sterilize foods Retards the growth of m/o and slows down Retards the growth of m/o and slows down
chemical changes that affect the quality of chemical changes that affect the quality of the foodsthe foods
DepartmentDepartment of Food Science and Technology
Control of Enzymatic Control of Enzymatic Spoilage:Spoilage:
Enzymes are slowed down considerably, Enzymes are slowed down considerably, but not eliminated during freezing. but not eliminated during freezing.
For best quality:For best quality: Vegetables: BlanchedVegetables: Blanched
– Quick treatment in boiling water (2-3 min) Quick treatment in boiling water (2-3 min) inactivates enzymes prior to freezinginactivates enzymes prior to freezing
Fruits: Ascorbic acid is addedFruits: Ascorbic acid is added– Vit. C, lemon juice, citric acid added to prevent Vit. C, lemon juice, citric acid added to prevent
browning before freezingbrowning before freezing
DepartmentDepartment of Food Science and Technology
Changes during freezing:Changes during freezing: Water in food freezes and expandsWater in food freezes and expands Ice crystals formed cause cell water to Ice crystals formed cause cell water to
rupture rendering the product softer when rupture rendering the product softer when defrosted.defrosted.
Quicker freezing decrease amount of cell Quicker freezing decrease amount of cell wall rupturewall rupture
Rapid freezing: many small ice crystals form Rapid freezing: many small ice crystals form Slow freezing: few large ice crystalsSlow freezing: few large ice crystals Most commercial products are frozen VERY Most commercial products are frozen VERY
rapidly in blast freezersrapidly in blast freezers
DepartmentDepartment of Food Science and Technology
Importance of temperature:Importance of temperature:
Frozen foods should be stored below 0°F to Frozen foods should be stored below 0°F to prevent deterioration of the product and prevent deterioration of the product and improve qualityimprove quality
Example: Example: Storage Temperature Storage Life
0°F One year
10°F Three months
20°F Three weeks
30°F Five days
DepartmentDepartment of Food Science and Technology
Foods that don’t freeze Foods that don’t freeze well:well:
Foods that have high water content or are Foods that have high water content or are typically consumed raw:typically consumed raw:– TomatoesTomatoes– LettucesLettuces– CeleryCelery– PotatoesPotatoes– Sour creamSour cream– Fried foodsFried foods– Milk saucesMilk sauces
DepartmentDepartment of Food Science and Technology
How drying preserves food: How drying preserves food:
Drying preserves food by removing the Drying preserves food by removing the moisture (80-95%) to prevent microbial moisture (80-95%) to prevent microbial growthgrowth
Slows down enzymesSlows down enzymes Removing the moisture = lower ARemoving the moisture = lower Aww
Drying process is slowed down if humidity Drying process is slowed down if humidity is highis high
Best done at temp: 140°FBest done at temp: 140°F
DepartmentDepartment of Food Science and Technology
Drying:Drying:
OutdoorsOutdoors– Only for fruits (high acid, sugar content)Only for fruits (high acid, sugar content)– Must be treated for insects after drying is Must be treated for insects after drying is
completecomplete
IndoorsIndoors– Dehydrator: BEST METHOD!Dehydrator: BEST METHOD!– Oven: use oven thermometer to monitor Oven: use oven thermometer to monitor
temperaturetemperature Leave door cracked 2 – 6 inches for air circulationLeave door cracked 2 – 6 inches for air circulation
DepartmentDepartment of Food Science and Technology
What sort of What sort of treatments do you treatments do you
think fruits and think fruits and vegetables might vegetables might
need before drying?need before drying?
Question #5: Question #5:
DepartmentDepartment of Food Science and Technology
Treatments for foods to be Treatments for foods to be dried:dried:
Fruits: DipsFruits: Dips– Sulfite, Ascorbic acid, fruit juice, honeySulfite, Ascorbic acid, fruit juice, honey
Vegetables: Blanched Vegetables: Blanched Meat: safety measuresMeat: safety measures
– Pork or wild game meat should be frozen for 30 Pork or wild game meat should be frozen for 30 days before use to kill trichinelladays before use to kill trichinella
– Heat in marinade before dryingHeat in marinade before drying– Heated in oven after drying (to reach 160°F)Heated in oven after drying (to reach 160°F)
DepartmentDepartment of Food Science and Technology
New Technologies that New Technologies that may/may not help may/may not help
consumers:consumers: Home vacuum packagers:Home vacuum packagers:
– Removing oxygen can increase quality of food Removing oxygen can increase quality of food therefore extending shelf-life BUT:therefore extending shelf-life BUT:
– Less likely for spoilage organisms to growLess likely for spoilage organisms to grow– MORE likely for pathogens to growMORE likely for pathogens to grow– Can make perishable foods unsafeCan make perishable foods unsafe– Safe for foods that will be frozenSafe for foods that will be frozen– BUT they should be thawed BUT they should be thawed
using safe practicesusing safe practices