Preservation

Question 1

What is the purpose of preservation?

Answer 1

• All foods begin to spoil as soon as they are harvested or slaughtered
• Some spoiling is caused by microorganisms as bacteria and mold
• Other spoilage results from chemical changes within the food itself due to natural processes such as enzyme action or oxidation

Question 2

What is the pH of most foods?

Answer 2

• pH of virtually all foods is less than 7.0
• Will be dealing mostly with acidic side of pH scale
• No food is on the pH of 1 (usually chemicals)

Question 3

What are some common organic acids in foods?

Answer 3

• Lactic acid (yogurt, sour cream, buttermilk)
• Oxalic acid (spinach, rhubarb)
• Citric acid (citrus fruits, other fruits)
• Malic acid (apples)
• Tartaric acid (apples, grapes)
• Acetic acid (vinegar)
• Ascorbic acid (vitamin c)

Question 4

What is water quality?

Answer 4

Extent to which water is available in foods, particularly for microbial growth (does not equal the water content of food). Measured on a scale from 0-1 (pure water), most are 0.7 or above

Question 5

What are the 5 growth conditions of microorganisms?

Answer 5

1. Oxygen
   - Aerobic (oxygen required)
   - Anaerobic (oxygen must be absent)
   - Facultative (can grow with or without oxygen)
2. Water activity (aw)
   - High (nothing added to make water unavailable)
   - Low (little water available due to addition of large amounts of sugar, salt, pectin binding to water or by freezing)
3. pH
   - Low acid (pH 6-7): milk (6.8), meat, butter, eggs, fish, seafood
   - Medium acid (pH 4.5-6): bread, bananas, vegetables, cheese
   - High acid (pH < 4.5): fruits, soft drinks, citrus fruits (2.5), sour cream, yogurt, buttermilk
4. Temperature
5. Food source

Question 6

What are the optimal growth conditions of molds?

Answer 6

• Oxygen: aerobic
• Water activity: lower than for bacteria and yeasts
  o Ideal range is 0.78-1.0
  o Extreme minimum 0.61
• pH: 2 to 8.5
• Temperature: wide range (ideal is 20-30 C)
  o Readily destroyed by heat (100 C)
• Food source: almost any food

Question 7

What are the optimal growth conditions of yeasts?

Answer 7

• Oxygen: grow best in aerobic situations
  o Fermentative yeasts grow slowly in anaerobic conditions
• Water activity: fairly high
  o Ideal range: 0.82 to 1.0
  o Extreme minimum: 0.69
  o Osmophillic yeasts can grow in very low water activity
• pH: acidic conditions (<4.5)
  o Ideal: 4.0-4.5
  o Range: 4.0-6.5
• Temperature: room temperature
  o Ideal is 25-30 C
  o Readily destroyed by heat (>100 C)
• Food sources: foods which contain sugar
  o If added sugar is close to 1:1 ratio to fruit then only osmophilic yeast can survive

Question 8

What are the optimal growth conditions of bacteria?

Answer 8

• Oxygen: aerobic, anaerobic, or facultative (grow in either condition)
• Water activity: highest level
  o Ideal range: 0.94-1.0
  o Extreme minimum is 0.85
• pH: non-acidic conditions
  o Ideal: 7.0
  o Range: 5.0-8.5
• Temperature: wide range
• Food sources: foods low in sugar, salt and acid concentrations (neutral foods)

Question 9

What are the types of bacteria?

Answer 9

1. Psychrophilic (cold-loving)
   - Can survive at 0 C or below
   - Ideal: 15-20 C
2. Mesophilic (room-temperature)
   - Range: 20-45 C
3. Thermophilic (heat-loving)
   - Can survive at > 45 C
   - Ideal: 15-20 C
4. Thermoduric
   - Ideal: 20-40 C
   - Can also survive longer heat treatments > 55 C

Question 10

Discuss the thermophilic bacteria with deadly spores

Answer 10

• Clostridium botulinum spores require temperatures of 116 C or higher to be destroyed (can survive > 6 hours at 100 C)
• Requires anaerobic conditions, pH > 4.5 AND water activity is > 0.90
• This toxin is one of the deadliest known, causes botulism food poisoning
• Food can contain toxin without showing signs of spoilage until 12-72 hours after ingestion
• Symptoms include blurred, double vision, difficulty swallowing, speaking, and breathing
• Anti-toxin is available, but recovery is slow and permanent nerve damage is possible
• To destroy anaerobic spores you must use pressure canner and reach temperatures of > 116 C

Question 11

What are the forms of bacteria?

Answer 11

1. Vegetative cell: grows, multiplies and maintain life cycle
2. Spores: dormant state produced under adverse conditions (extreme heat or cold conditions)
   - Spores have thick cell walls which protect cell contents (nucleus) from environment
   - Spores are one of the most resistant forms of life (protective, heat resistant)
   - When spores germinate they form toxin-producing cells

Question 12

What is pasteurization?

Answer 12

Pathogenic (disease-producing) microorganisms only are destroyed

Eg. commercial milk and juice products

Question 13

What is sterilization?

Answer 13

All microorganisms and their spores are destroyed

Results in a sterile product

Question 14

How do you preserve jams/jellies?

Answer 14

• Not a sterile process
• Require pectin and acid to form gel
• High sugar concentration means sugar binds water so less water activity
• Microorganisms lose water due to osmosis, dehydrate, and die
• Only osmophilic yeasts can survive

Question 15

How do you preserve pickles?

Answer 15

• Not a sterile process unless processed in boiling water bath
• Mixture is heated and filled into sterilized containers

1. Acid (usually vinegar) inhibits growth of some but not all microorganisms
2. Salt or sugar reduces water activity so microorganisms die

Question 16

What are the methods of preservation?

Answer 16

• Canning (packing/filling, processing)

- Freezing

Question 17

Discuss the first stage of canning.

Answer 17

Packing (filling) the containers using either: your choice

1. Raw/cold pack method
   - Advantages: easier to fill containers, food keeps shape and texture better, better heat circulation
   - Disadvantages: longer processing time
2. Hot pack method
   - Advantages: shorter processing time
   - Disadvantages: food shrinks more, has softer texture

Question 18

Discuss the second stage of canning.

Answer 18

Processing of the filled containers in order to destroy all microorganisms and spores (STERILIZATION): no choice, depends on pH

1. Boiling water bath: pH < 4.5
   - Foods high in acid, low pH
   - Eg. fruits and tomatoes
   - Microorganisms and spores are less heat resistant in acidic conditions, therefore more readily destroyed at 100 C
2. Pressure canner: pH > 4.5
   - Temperatures goes up to > 116 C
   - Must be used for foods that are medium or low in acid (medium or high pH)
   - Eg. vegetables (if boiling, then add vinegar), meat, fish, poultry, dairy products
   - No steam escapes and increase pressure and temperature

Question 19

Discuss the headspace for canning.

Answer 19

Space between food and jar top, only finger-tight because hot food will increase pressure in jar

Too little: food may bubble out under lid during processing
- Deposit on rim may prevent hermetic seal from forming, leads to food contaminated in storage, can put in fridge and consume fast

Too much: food may discolour (oxygen)

• Jar may not seal properly because not all air forced from jar during processing
• Venting process: during processing food expands and pushes oxygen out, when cooled food shrinks and low pressure pulls lid in (hermetic seal)

Question 20

What is freezing?

Answer 20

• Not sterile
• Only slows microbial growth
• Microbial growth slows below -18 C and psychrophilic bacteria still grows at slow rate
• Low temperature slows down microbial growth and water to ice, reduce water activity which means less for microorganisms

Question 21

What are the ways of freezing?

Answer 21

• Fast freezing (commercial -35 C): many small ice crystals within cells so less damage to cell walls meaning better texture in thawed and cooked food
• Slow freezing (home -18 C): fewer larger ice crystals between cells so cell walls rupture meaning a softer texture in thawed and cooked food

Question 22

What is freezer burn?

Answer 22

• White or grey dried out patches on frozen food due to losses of water which forms food surface sublimation (solid to gas, ice to freezer air)
• Caused by improper packaging that is not moisture or vapour proof
• No flavour or odour changes, or colour fading
• The reason why foods shouldn’t be frozen for a long time

Question 23

How do you freeze fruits?

Answer 23

In order to prevent oxidative enzymatic browning in fruits, add ascorbic acid (antioxidant, reduce pH), acid (reduce pH), sugar (exclude oxygen) but no not blanch

Sometimes frozen in sugar to preserve colour and flavour

Question 24

How do you freeze vegetables?

Answer 24

• Vegetables must be blanched before freezing (boiling to denature enzymes)
• If not blanched, enzymes will continue to function at freezing temperatures
• Leading to off-flavours, tough texture, faded colour (chlorophyll to pheophytin), musty and hay-like odours, and nutrient loss (if frozen for 3+ months)

Question 25

Which microorganisms are likely to grow on which specific foods?

Answer 25

• Aerobic microorganisms usually found growing on surface of food
• Anaerobic microorganisms found in closed canned goods
• Fruits are usually spoiled by molds and yeasts due to acidic nature
• Molds and osmophillic yeasts are likely to cause spoilage of jams and jellies due to low moisture content

Question 26

What is canning?

Answer 26

A high heat treatment to sterilize food to keep indefinitely

However reactions between food may occur over time

Done in air-tight sterilized (aspetic) container