CH 28 - Food Preservation

What are the biological changes that occur in food?

- Bacteria: meat, eggs, milk, opened canned goods - Yeast: fruit, veggies, fruit preserves, can lead to fermentation - Molds: cheese and bread

What is Pickling?

- acidification and/or *fermentation* to acidity foods, lower pH, microorganisms cannot thrive - acid created is usually lactic acid - salt is added to draw out liquid (less water availability) and also prevent microbe growth - ex. cucumbers, beets, artichokes

What changes can occur in food?

- biological (bacteria, yeast, molds) - chemical (enzymes) - physical (evaporation, syneresis, separation)

What are the food preservation methods?

- drying - curing - fermentation - canning

What is curing?

- high concentrations of salt bind to H2O making it not available to microbes - ex. corned beef - smoking is often done to improve flavor (ex. ham)

What is fermentation?

- relies on microorganisms to transform the food into an easily preserved form - changes in flavor, color, and texture - examples — bacteria that produce lactic acid to preserve dairy, transform into yogurt, kefir, sour cream - yeast used to bread and beer-making turning sugars into CO2 and ETOH - ex. pickling

What is the drying food preservation method?

- removal of food's water - inhibits growth of microbes - makes food lighter to transport - to preserve food need water activity (Aw) < 0.6 - sun-drying — raisins - commercial drying — convention (heat), vacuum, and freeze-drying

What foods are approved for irradiation?

- wheat flour - white potatoes - seeds for sprouting - herbs & spices - red meats, shellfish, raw poultry, eggs

What is the food preparation for canning?

- Hot-pack • foods heated to 170 degrees F in syrup, juice, or water • poured into sterilized jars - Cold-pack • foods is placed in sterilized jars • jars filled with boiling liquid (in both cases headspace is left at the top)

What is irradiation?

- Irradiation disrupts DNA of microbes, prevents them from multiplying - Reduces spoilage, lengthens shelf life, protects from foodborne diseases - Many fruits and veggies cannot be irradiated - Much controversy surrounds irradiation

What is canning and what is involved in the process?

- 2 step process • food is packed into container • container is canned (heat to ensure microbes are destroyed) - canning destroys microbes by high heat and also destroys enzymes that could chemically spoil food

What is heat preservation?

- Boiling - 10 mins kills most microbes - pasteurization - milk, fruit juices - sous-vide - cooking in sealed, airtight plastic bags in water bath, low temp. but longer time - popular among gourmet restaurants

What are the canning methods?

- Boiling Water Method — fruits and tomatoes with pH below 4.6 (acidic), Clostridium Botulinum cannot survive - Pressure Canning — for pH above 4.6, allows higher temperatures to be reached

What are the ways you can use the drying food preservation method?

- Conventional — mashed potato flakes, instant oatmeal, powdered milk, instant coffee - Vacuum — tomato paste, OJ, coffee, contents under pressure, lowers H2O boiling point, evaporates more water - Osmosis — uses strong syrup to draw out water, Ocean Spray Craisins - Freeze-drying — freeze food, place in vacuum, ice changes to vapor (sublimates). • Most effective drying method (b/c no heat, no destroying of nutrients or texture). • Highest quality but more $ • Coffee, tea, fruit, herbs, instant meals for military or camping

What are the chemical changes that occur in food?

- Enzymes — catalyze reactions • proteases or proteolytic enzymes split proteins, more in fish • lipases break down lipids — rancidity • carbohydrates break down sugars • tyrosinase and polyphenolase cause browning on fruits and veggies

What are the physical changes that occur in food?

- Evaporation — improper storage, dried out appearance - Syneresis — gelatin, yogurt - Separation — of oil and water in dressing

What are some problems with freezing?

- Freezer burn - improperly packaged food or frozen too long - Cell rupturing - water expands when frozen, breaks cell walls; foods with high H20 content like lettuce, milk, tomatoes freeze poorly - Fluid loss - frozen meats lose fluid when thawed, dryer meats - Recrystallization - ice cream in freezer door

What is cold preservation?

- Refrigeration — slows down biological, chemical, and physical reactions that spoil food • Refrigerators between just above 32-40 degrees F • Product in crisper section, limits oxygen, lasts longer, better quality - Freezing — foods at 0 degrees F best for retention of flavor, nutrition, and texture • Makes water unavailable for microbes • Chemical and physical changes slowed by freezing • Shorter shelf life than canned goods

What is aseptic packaging?

- sterilized, packed and sealed in a sterilized container under sterile conditions - ex. juice boxes, lunch kits, puddings, soups, baby food, UHT milk - MAP (modified atmospheric packaging) changes to the air around the food reducing O2 and increasing CO2