department department of food science and technology the science behind food preservation: dr. renee...

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


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


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


TTimeime

OOxygenxygen

MMoistureoisture


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


FFoodood

AAciditycidity


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


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



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


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)


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


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


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:


What is the target What is the target organism associated organism associated

with this? with this?



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


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


Name one high acid Name one high acid and one low acid foodand one low acid food



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


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


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


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


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


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


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!!!


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


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


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


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


True or False: True or False: Altitude affects the Altitude affects the canning process canning process



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


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


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


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


Appropriate Jars/LidsAppropriate Jars/Lids


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


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


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


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)


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


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


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


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


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


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


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


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


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


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?



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)


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

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