The Science Behind Food Preservation Dr Renee Boyer
The Science Behind Food Preservation: Dr. Renee Boyer Extension Specialist May 21, 2009 Department of Food Science and Technology
Why Preserve Foods ? Prevent Spoilage of Foods & Extend Shelf Life n Types of Spoilage: n – Microbiological § Molds, yeast, bacteria – Chemical § Enzymatic changes – Physical § Bruising, water loss Department of Food Science and Technology
Microbiological Food Spoilage: n 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 Department of Food Science and Technology
What Bacteria Need to Grow n Food n Acidity n Temperature n Time n Oxygen n Moisture FIGHT BAC!
What Bacteria Need to Grow n Food n Acidity – p. H = Amount of acidity – Low acid food = p. H > 4. 6 n Temperature n Time n Oxygen n Moisture
Bacteria Inhibited by p. H Most Inhibited 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 Least Inhibited Department of Food Science and Technology
What Bacteria Need to Grow n Food n Acidity n Temperature Aerobic: most spoilage organisms n Time Facultatively anaerobic: 5% Oxygen pathogens n Oxygen Anaerobic: No Oxygen n Moisture Clostridium botulinum
What Bacteria Need to Grow n Food n Acidity n Temperature – Danger zone = 40°F to 140°F (41°F - 135°F) n Time n Oxygen n Moisture Department of Food Science and Technology
What Bacteria Need to Grow Products Affected n Food Microbial Group n Acidity Normal bacteria n Temperature Normal yeast Torulopsis species 0. 88 Fruit juice conc. n Time Normal molds Aspergillus flavus 0. 80 Jams, jellies Wallemia sebi 0. 75 Honey Xerophilic molds Aspergillus echinulatas 0. 65 Flour Osmophilic yeast Saccharomyces bisporus 0. 60 Dried fruits n Oxygen n Moisture Example aw Salmonella species Clostridium botulinum 0. 91 Fresh meat, milk Halophilic bacteria aw target = 0. 85 Department of Food Science and Technology
Food Preservation Goal: Control microbial growth / destroy microorganisms by: n n n High temperature (Heat) Low temperature (Cold) No oxygen Low p. H Low Aw (water activity) Department of Food Science and Technology
Methods of Home Food Preservation: n Heat Processing/Canning – Boiling Water Bath – Pressure Canning Freezing n Drying n Department of Food Science and Technology
Department of Food Science and Technology
Canning = Preservation by Heat n Destroys microorganisms n Inactivates enzymes n Seals container during the process to prevent recontamination Department of Food Science and Technology
Question #1: Of the growth factors that we discussed, which is the most important to know before proceeding to canning? Department of Food Science and Technology
Question #2: What is the target organism associated with this? Department of Food Science and Technology
Acidity: the most important factor! n Clostridium botulinum n Spore-former: spores ubiquitous in the environment – Can’t make you sick – Infant botulism ONLY: Under anaerobic conditions (commonly created during preservation), spores germinated into vegetative cells n Vegetative cells produce toxin n Department of Food Science and Technology
Botulism: Ingestion of toxin in foods n Neurotoxin n Causes paralysis and death if medical attention isn’t found quickly n Very rare in U. S. now n Primarily associated w/ improperly home canned n Department of Food Science and Technology
Question #3: Name one high acid and one low acid food Department of Food Science and Technology
High Acid Foods (p. H < 4. 5) n n n n Apples Oranges Peaches Strawberries Pears Sauerkraut, pickles Blueberries Rhubarb n n n n Lemons Grapefruit Pineapple Apricots Cherries Figs Plums Raspberries Department of Food Science and Technology
Low Acid Foods (p. H > 4. 5) n n n n Meat, fish Carrots Green beans Potatoes Peas Cabbage Corn Squash n n n n Pumpkin Okra Turnips Snap Beans Sweet potatoes Onions Oysters Ripe olives Department of Food Science and Technology
Tomatoes: n Usually considered an acid food n Some now known to have a p. H slightly above 4. 6 n Boiling water bath …MUST be acidified Department of Food Science and Technology
Canning Foods n Low acid foods: – p. H >4. 6 – Processing Pressure canner! n High acid foods: – p. H <4. 6 – Boiling water bath n Acidified foods: – – – p. H is decreased to <4. 6 by adding acid Pickling, salsas, tomatoes! Boiling water bath Department of Food Science and Technology
Department of Food Science and Technology
Destruction of Spores in Low Acid foods: n Spores are very difficult to destroy at boiling temperatures n Boiling water bath: 212°F – 7 – 11 hours depending on the food n Pressure canning: 240 – 250°F (10 -15 psi) – 20 – 100 minutes depending on the food Department of Food Science and Technology
Department of Food Science and Technology
Time/Temperature Dependency n n n Food Acid, salt, sugar, starch, fat Size of Pieces Consistency Convection heating in liquids Conduction heating in solids Department of Food Science and Technology
Time/Temperature Dependency n n n 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!!! Department of Food Science and Technology
What are reputable sources? n National Center for Home Food Preservation – http: //www. uga. edu/nchfp/ n USDA Complete Guide to Home Canning – http: //www. uga. edu/nchfp/publications_ usda. html n Ball Blue Book Department of Food Science and Technology
Methods of canning NOT recommended: n n n 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-lined caps – Failure to seal properly Department of Food Science and Technology
Boiling water bath canning: n n n Large covered cooking pot with a rack Must be deep enough to cover 1 inch above jars Processes foods at boiling temp. (212°F) Acid / acidified foods Heat destroys m/o that spoil acid foods Department of Food Science and Technology
Department of Food Science and Technology
Pressure Canning: n n n Heavy pot, lid can be sealed: fitted w/ vent and pressure dial or weighted gauge Processes foods at 240°F (10 -11 pds pressure) ONLY safe way to process low acid foods Department of Food Science and Technology
Department of Food Science and Technology
Question #4: True or False: Altitude affects the canning process Department of Food Science and Technology
The Effects of Altitude: Water boils at lower temperatures as altitude increases. n Lower temps are less effective, so: n – Boiling water bath: processing time increased – Pressure canning: pressure increased n Altitudes in WV vary greatly: Morgantown: 960 ft Beckley: 2421 ft Department of Food Science and Technology
Department of Food Science and Technology
Weighted –vs- Dial gauge: Weighted gauges: 0 -1000 ft: 10 lbs pressure n Over 1000 ft: must be operated at 15 lbs pressure n Dial Gauges: n 0 -2000 ft: 11 lbs pressure n Over 2000 ft: corrections must be made n Ex: – 2001 ft-4000: 12 lbs – 4001 – 6000: 13 lbs Department of Food Science and Technology
Ensuring Quality: Use only high quality foods, free of bruises and blemishes n Can/preserve w/in 6 -12 hours of harvest n n 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 Department of Food Science and Technology
Importance of headspace: Jams/jellies: ¼ inch n Fruits / tomatoes: (boiling water bath): ½ inch n Low acid: 1 -1 ¼ inch n n Needed for expansion of the food – Higher the temperature, the greater the expansion n Forming vacuum in cooling jars Department of Food Science and Technology
Appropriate Jars/Lids Department of Food Science and Technology
Important notes: Fruit n Some recipes call for ascorbic acid dip – – n 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 Department of Food Science and Technology
Important notes: Pickling n Pickled foods are acidified, therefore they can be heat processed in a boiling water bath – Prevents spoilage organisms and inactive enzymes n Fermentation – – – Dill pickles/saurkraut – 3 weeks Refrigerated dill pickles – 1 weeks Quick process – not fermented Department of Food Science and Technology
Important notes: Pickling n Level of acidity should not be altered – Recipe MUST be followed n Use canning/pickling salt – Other salt has non-caking material added which can make brine cloudy Department of Food Science and Technology
Important notes: Jams and Jellies n Ingredients – Fruit, pectin, acid, and sugar n 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) Department of Food Science and Technology
Important notes: Jams and Jellies n Acidity – – n Too much – gel won’t 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 Department of Food Science and Technology
Jams/Jellies and Mold n Low water activity + acidity typically prevents most spoilage n 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 Department of Food Science and Technology
Freezing: n n 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 Department of Food Science and Technology
Control of Enzymatic Spoilage: n n n 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 n Fruits: Ascorbic acid is added – Vit. C, lemon juice, citric acid added to prevent browning before freezing Department of Food Science and Technology
Changes during freezing: n n n 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 Department of Food Science and Technology
Importance of temperature: n Frozen foods should be stored below 0°F to prevent deterioration of the product and improve quality Example: Storage Temperature Storage Life 0°F One year 10°F Three months 20°F Three weeks 30°F Five days Department of Food Science and Technology
Foods that don’t freeze well: n Foods that have high water content or are typically consumed raw: – – – – Tomatoes Lettuces Celery Potatoes Sour cream Fried foods Milk sauces Department of Food Science and Technology
How drying preserves food: n n n 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: 140°F Department of Food Science and Technology
Drying: n Outdoors – Only for fruits (high acid, sugar content) – Must be treated for insects after drying is complete n Indoors – Dehydrator: BEST METHOD! – Oven: use oven thermometer to monitor temperature § Leave door cracked 2 – 6 inches for air circulation Department of Food Science and Technology
Question #5: What sort of treatments do you think fruits and vegetables might need before drying? Department of Food Science and Technology
Treatments for foods to be dried: n Fruits: Dips – Sulfite, Ascorbic acid, fruit juice, honey Vegetables: Blanched n Meat: safety measures n – 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 160°F) Department of Food Science and Technology
New Technologies that may/may not help consumers: n 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 Department of Food Science and Technology
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