Lecture 2-Food preservation Flashcards
How much food is lost to spoilage?
25%
What’s a big proportion of the food that is lost to spoilage?
Fruits and veggies
__% of landfill in US = food
20% of landfill in US = food
What speeds up decomposition?
Heat, light and oxygen speed up decomposition
What is lost due to decomposition?
Nutritive value is lost
Does food have to be contaminated to be spoiled?
No
What is obvious and detectable- decomposition or contamination or both?
Decomposition is both obvious and detectable. Contamination isn’t
Why is decomposition obvious and detectable?
Due to decreased quality- appearance, taste, texture, odour
Which qualities does the most perishable foods have?
High pro or/and water
What are the 3 types of changes that lead to food spoilage?
- Biological
- Chemical
- Physical
What are the biological changes in food due to yeast. Uses, actions
– Fungus (plant that lacks chlorophyll)
– Ferments sugars (CHO = CO2 and alcohol)
– Used for producing food products e.g. bread and alcohol
Give examples of biological changes in food
Yeasts, bacteria, molds
Give examples of chemical changes in food
Enzymes (naturally present)
Give examples of physical changes in food
Water loss (evaporation/dehydration), separation. damage/mechanical bruisign, tearing of tissues
What are the biological changes in food due to bacteria and molds
Difference between 2, actions
– Bacteria and molds can produce toxins
– Molds are visible; bacteria are not
– Bacteria can ferment sugars
How to destroy/inhibit factors behind biological changes in food
Boiling, refrigeration, drying, curing (high sugar/salt)
How are enzymes categorsied?
Based on substrate and mode of action
What are the 4 modes of actions of enzymes
– Protease (proteolytic enzyme): proteins-> AA
– Lipase: TG-> FA + glycerol
– Carbohydrase: CHO -> glucose
– Others (e.g. polyphenol oxidase (PPO))
Talk about proteases in fish
Proteases in fish start working straight away
Fish is more susceptible to spoilage
How can you slow down the action of proteases?
Cooler temperatures can do that
Downside of dry milk?
Lactose in dry milk can react with proteins and create new compounds
Bioavailability of protein in milk is also decreased
What can oxidation of fat lead to?
Can lead to off odors and flavors- rancid flavor
What are the non-enzymatic chemical changes in food
– Oxidation of fat
– Maillard reaction:
• May occur with long storage of non-fat dry milk (lactose + pro = nonenzymatic browning)
• BV of protein may decr: AA involved in reactions not readily released during digestion
What are the types of separation that cause physical damage?
– drip loss E.g. liquid from frozen meat- less moist product
– emulsion breakdown
– syneresis (gel)
Name 6 methods of food preservation
- High temp
- Low temp
- Removal/tying up of moisture
- Additional of chemical preservatives
- Keeping out microorganisms
- Ionizing radiation
What do high temperatures do in terms of food preservation?
High temperature to destroy microorganisms & enzymes
What do low temperatures do in terms of food preservation?
Low temperature to control growth of microorganisms
What do Removal/tying up of moisture do in terms of food preservation?
Removal/tying up of moisture to control microbial growth
What do Addition of chemical do in terms of food preservation?
Addition of chemical preservatives to inhibit
microbial growth
What do ionizing radiations do in terms of food preservation?
Ionizing radiations to destroy microorganisms & control enzyme activity
How does drying work?
- Removes water in food
- Inhibits growth of microorganisms
- E.g. sun-drying or commercial drying
Bacteria and mold need __% moisture to survive
Yeast needs __%
Bacteria and mold need 15% moisture to survive
Yeast needs 20%
What are the commercial ways of drying (4)?
• Conventional (uses heat)
– Drying room, tunnel drying, spray drying, drum drying
• Vacuum (uses low pressure)
• Osmotic (uses strong syrup that osmotically gets water out)
• Freeze-drying (ice crystals vaporize)
Benefit of vacuum drying
Doesn’t have to be heated-integrity is preserved
How does freeze-drying work? Benefits?
Most costly- premium products Ice is taken out instead of water High preservations of food qualities Camping and military rations Some instant coffees
How does curign work? Uses?
- Preservation with use of salt & drying
- Sugar, spices, nitrates may be added
- Meat/fish may also be smoked (for added flavour and preservation)
Downside of curing?
Overtime microorganisms still multiply. Curing doesn’t stop them, just makes it harder
What’s pickling?
Preservation by acidification (addition of acid/vinegar OR fermentation)
What’s edible coating?
A thin layer of edible material (CHO, PRO or FAT) used on fruits, vegetables, cheese, nuts, dried fruit, processed meats…
How does edible coating work? (4)
• Increases shelf life – Barrier to moisture, O2, CO2, volatile aromas • Improves handling – Less breaking/damage • Improves appearance – By increasing gloss, color • Vehicle for added ingredients – Flavours, antioxidants, antimicrobials
What are the 2 steps of canning?
- Food packed into sterilized containers &
sealed - Containers “canned”/heated to destroy
microorganisms & enzymes
– Extended boiling/ heating to temperatures much higher than regular boiling point
What are the 2 methods of canning?
- Boiling water process
- good for low pH items - Pressure canning
- for higher pH items
- boiling at higher temps under pressure
- to destroy Clostridium botulinum
Describe canning for high acid foods
For fruits & tomatoes (pH 4.5 or below)
• Safely canned in a boiling water bath
• Heat resistance of microbes is decreased by the acidic pH can be destroyed in reasonable processing times
• Surviving organisms will not grow in acidic environments
Describe canning for low acid foods
• For vegetables, meat, fish, poultry & milk (pH above 4.6)
• Requires relatively high processing T° to destroy
all spore-forming organisms, particularly C. Botulinum
• Requires a pressure canner where T° > usual boiling point of water can be achieved
What are the 3 ways of heat preservation?
Boiling
Pasteurization
Ohmic heating
Describe boiling as a method of heat preservation
Simplest method; 10 minutes
Describe pasteurization as a method of heat preservation
- Liquids are heated to a certain T for a certain period of time
- Eg 71°C (160°F) à15 sec OR 138ºC (280ºF) ->2 sec
- Kills bacteria, yeasts, molds
Describe ohmic heating as a method of heat preservation
- Electrical current passed through food, generating heat that destroys microorganisms
- Liquid eggs, fruit juices
Describe refrigeration as a method of cold preservation. Guidelines
- Slows down biological, chemical, physical reactions that shorten shelf life of food
- Mostly high water content foods are refrigerated
- Temperature: just above freezing to ≤ 4ºC
- Refrigerate perishable foods as soon as possible, preferably during transport to prevent bacterial growth
Describe freezing as a method of cold preservation. Guidelines, problems
• -18ºC(0ºF) or lower = least damaging to flavor
• H2O unavailable to microorganisms
• Slows chemical & physical reactions (enzymes…)
• Problems:
– Reactions still continue (O2 present), so shorter life than canned goods
– Recrystallization
– Cell rupturing
– Fluid loss
– Freezer burn
Dispersion medium in most frozen foods is ___
Dispersion medium in most frozen foods is water
Benefits of rapid freezing
ice crystals are small and numerous, mostly intracellular -> gives superior food quality
Downsides of slow freezing
ice crystals are large and fewer in number, form in extracellular spaces
– Upon thawing, loss of juices occurs
What is freezer burn? Why does freezer burn occur?
– Dehydration on the surface of frozen food (white or greyish patches)
– Inadequate packaging-> water evaporates and may recrystallize on surface of food
What may happen when plant tissues freeze?
Oxidation of polyphenolic substances in plant tissues by polyphenolases may occur during frozen storage
What is the downside of oxidation of plant tissues upon freezing? How can that be resolved?
– Results in undesirable browning
– Blanching vegetables -> destroys enzymes that cause browning
How can ascorbic acid oxidation during frozen storage be resolved?
Blanching vegetables inhibits ascorbic acid oxidation by inactivating ascorbate oxidase
However, some loss of ascorbic acid occurs during the blanching process
Additional ascorbic acid is lost with ___ ___ of frozen storage
Additional ascorbic acid is lost with long periods of frozen storage
What are the changes in colloidal substances
during frozen storage (5)
• Retrogradation of starch & syneresis
• Toughening of cellulose
• Breaking of emulsion
• Nutritive value: no significant effects on macronutrients unless food kept for a long time
• Vitamins & minerals: 4% loss in drip
- Vit C, Vit B (especially folate)
Why does development of off-odors occur in frozen vegg?
Accumulation of volatile carbonyl compounds in unblanched or under blanched frozen vegetables
How does blanching before freezing, using boiling water or steam can resolve the problem of development of off-odors in frozen vegg? Downsides?
- Destroys enzymes responsible for development of “off ” flavors
- Controls undesirable changes in texture & color
- Inhibits conversion of bright green chlorophyll to olive green pheophytin
- But destroys some vitamin C and folate
What is another name for irradiation?
Cold pasteurization
What does irradiation do for spices and seasonings?
Reduces microbial load on spices and dehydrated seasoning preparations, meaning it destroys bacteria, molds and yeast which cause food to spoil
What is the purpose of irradiation do for wheat, flour and whole wheat flour?
To control insects in wheat, flour and whole wheat flour
What is the purpose of irradiation do for potatoes and onions?
To increase shelf life by preventing sprouting or germination in potatoes and onions
What is approved by Health Canada for irradiation?
potatoes, onions, wheat, flour, whole wheat flour, whole and ground spices, dehydrated seasoning preparations and fresh and frozen raw ground beef
How is food irradiation done?
foods are treated with low doses of Gamma rays, x rays or electrons
What is aseptic packaging? At what temp can it be stored?
– Sterilized, packed and sealed in sterilized container under sterilized conditions
– Can sit at room temp
Give examples of aseptic packaging
Juice boxes, puddings, baby foods, UHT milk
How is MAP achieved and what is it used for?
– Composition of surrounding air is changed (usually decr
O2, incr CO2 – but depends on food product)
– Fruits & Veg, meat/poultry, baked goods
What are hermetically sealed foods?
foods that have been packaged airtight by a commercial sealing process
