Class 2: Food Preservation Flashcards
How much food is wasted every year around the globe? How much of it is from human consumption?
1.3 billion of tones
1/3
Food lost and wasteages amounts to which squandering of resources? name 4
water
land
energy
labour and capital
How much food lost and waste is lost to spoilage?
25%
What is food spoilage?
• Decomposition, loss of nutritive value
Who consumes the spoiled food?
rodents, flies, microorganisms…
food spoilage vs food contamination
FS: Obvious & detectable
– Due to decreased quality (appearance, taste, texture,
odour)
FC: not obvious and dangerous for health
What food is most likely to spoil?
high pro +/or water
Name 3 types of changes that lead to food spoilage and give examples
• Biological – Yeasts, bacteria, molds • Chemical – Enzymes (naturally present) - non enzymatic • Physical – Water loss, separation
Changes that lead to food spoilage=> Biological=>Yeast=> 1. what is it 2. function 3. utility
– Fungus (plant that lacks chlorophyll)
– Ferments sugars (CHO = CO2 and alcohol)
– Used for producing food products e.g. bread and alcohol
Changes that lead to food spoilage=>
Biological=>Bacteria and Mold
1. what do they produce
2. mold vs bacteria appearance and function
– Bacteria and molds can produce toxins – Molds are visible; bacteria are not
– Bacteria can ferment sugars
How to destroy/inhibit yeast and bacteria and mold
boiling, refrigeration, drying, curing (high sugar/ salt)
Changes that lead to food spoilage=>
Chemical=> enzymes=>
1. how are they categorized
2. mode of action
– Categorized by • Substrate • Mode of action – Protease (proteolytic enzyme): proteinsàAA – Lipase: TGàFA + glycerol – Carbohydrase: CHOàglucose – Others (e.g. polyphenol oxidase (PPO))
Changes that lead to food spoilage=>
Chemical=> non enzymatic=>
1. what is it
2. mode of action
– 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
Changes that lead to food spoilage=>
Physical=>
2 types
+ consequences
• Evaporation / dehydration
• Separation: – drip loss
– emulsion breakdown – syneresis (gel
consequence: damage/mechanical bruising, tearing of tissues
6 Methods of food preservation
Methods of food preservation
• Hightemperaturetodestroymicroorganisms& enzymes
• Lowtemperaturetocontrolgrowthofmicroorganisms
• Removal/tyingupofmoisturetocontrolmicrobial
growth
• Additionofchemicalpreservativestoinhibit
microbial growth
• Keepingoutmicroorganisms
• Ionizingradiationstodestroymicroorganisms& control enzyme activity
Methods of food preservation: curing
- What?
- With what?
- For what?
- Preservation with use of salt & drying
- Sugar, spices, nitrates may be added
- Meat/fish may also be smoked (for added flavour and preservation)
Methods of food preservation: pickling
- What?
- With what?
- Preservation by acidification (addition of acid/vinegar OR fermentation)
- Spices/herbs may be added for flavour
Methods of food preservation: drying
- What?
- Example
- conventional uses (4) ?
1. • Removes water in food • Inhibits growth of microorganisms 2. E.g. sun-drying or commercial drying of Pandanus, seaweed, fish 3. • Conventional (uses heat) – Drying room, tunnel drying, spray drying, drum drying • Vacuum (uses low pressure) • Osmotic (uses strong syrup) • Freeze-drying (ice crystals vaporize)
Methods of food preservation: drying
- What?
- Function
- A thin layer of edible material (CHO, PRO or FAT) used on fruits, vegetables, cheese, nuts, dried fruit, processed meats…
- • 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
Methods of food preservation: drying
- for what?
- process
- two methods
1.
Fruits, vegetables & meats
2.
process:
a) Food packed into sterilized containers & sealed
b) Containers “canned”/heated to destroy microorganisms & enzymes
– Extended boiling/ heating to temperatures much higher than regular boiling point
3. 2 methods: 1. Boiling water process - good for low pH items 2. Pressure canning - for higher pH items - boiling at higher temps under pressure - to destroy Clostridium botulinum
Canning – high acid foods
- for what
- process
1.
For fruits & tomatoes (pH 4.5 or below)
2.
• 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
Canning – low acid foods
- for what
- process
1.
For vegetables, meat, fish, poultry & milk (pH above 4.6)
2.
• 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
3 types of heat preservation methods
- Boiling:
• simplest method; 10 minutes - Pasteurization:
• Liquids are heated to a certain T for a certain period of time
• Eg 71°C (160°F) à 15 sec OR 138oC (280oF) à 2 sec
• Kills bacteria, yeasts, molds - Ohmic heating:
• Electrical current passed through food, generating heat that destroys microorganisms
• Liquid eggs, fruit juices
2 types of cold preservation methods, just name them
Refrigeration
Freezing
Cold preservation Refrigeration=> 1. function 2. for what 3. temperature 4. when should it be applied
- 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
Cold preservation Freezing=> 1. temperature 2. for what 3. function 4. problems (5)
• -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
what changes occur during the freezing and frozen stage?
- Recrystallization:
Formation and growth of ice crystals: - Freezer burn
- Reactions still continue (O2 present), so shorter life than canned goods: oxidation
- Development of off-odors
Whats medium is most likely to be dispersed in frozen foods?
water
What happens during the formation and growth of ice crystals:
if rapidly frozen? Slowly frozen?
• Rapidly frozen: ice crystals are small and numerous, mostly intracellularàgives superior food quality
• Frozen slowly: ice crystals are large and fewer in number, form in extracellular spaces
– Upon thawing, loss of juices occurs
What happens during freezer burn stage?
What is it due to? Explain
– Dehydration on the surface of frozen food (white or
greyish patches)
– Inadequate packagingà water evaporates and may recrystallize on surface of food
what can be oxidized during freezing & frozen stage?
Explain
- Oxidation of polyphenolic substances in plant tissues by polyphenolases may occur during frozen storage
– Results in undesirable browning
– Blanching vegetablesàdestroys enzymes that
cause browning - Oxidation of fat
- Oxidation of ascorbic acid
• Ascorbic acid is oxidized during frozen storage • Blanching vegetables inhibits this oxidation by
inactivating ascorbate oxidase
• Some loss of ascorbic acid occurs during the
blanching process
• Additional ascorbic acid is lost with long periods
of frozen storage
What changes occur in colloidal substances during frozen storage?
• 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)
How do off odours develop during freezing & frozen stage?
What would be a valid solution?
- Accumulation of volatile carbonyl compounds in
unblanched or underblanched frozen vegetables - Blanching before freezing, using boiling water or
steam:
• 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
Irradiation: also called: 1. what? 2. function (3) 3. what foods are approved by health Canada? 4. types of irradiation
cold pasteurization
1. Treatment of food with ionizing radiation
2. To reduce microbial load on spices and dehydrated seasoning preparations, meaning it destroys bacteria, molds and yeast which cause food to spoil
• To control insects in wheat, flour and whole wheat flour
• To increase shelf life by preventing sprouting or
germination in potatoes and onions
3. potatoes, onions, wheat, flour, whole wheat flour, whole and ground spices, dehydrated seasoning preparations and fresh and frozen raw ground beef
4. Gamma rays, x rays or electrons
Aseptic packaging
- What?
- Temperature?
- For what?
– Sterilized, packed and sealed in sterilized container
under sterilized conditions
– Can sit at room temp
– Juice boxes, puddings, baby foods, UHT milk…
MAP
- Stands for:
- What?
- For what?
- Modified-Atmosphere Packaging
- Composition of surrounding air is changed (usually decr
O2, incr CO2 – but depends on food product) - Fruits & Veg, meat/poultry, baked goods
