Subject: Leaving Certificate Home Economics Teacher: Ms Tracy McDonagh Week: Week 11 Lesson: Food Spoilage & Preservation

Microbiology- week 10 - Homework corrections

Part a) 4 conditions @ 4marks each = 16marks

1. Food: most moulds are saprophyte which means they feed of dead matter e.g. bread.

2. Warmth: most are mesophiles, freezing (-18̊ C) inactivates mould growth. 3. Moisture: is needed for growth, thus frozen foods are unsuitable. 4. Oxygen: moulds are aerobic, need oxygen, so they will grow on the surface of food

e.g. jam or through open structure foods e.g. bread.

b) 22 marks in total • Name of mould = 4marks • Description 2 points @ 3marks each = 6marks • Reproduction = 4 points @ 3marks each = 12marks

MUCOR: 4marks

Description 2 points @ 3marks each - Saprophytic feeds on dead matter. - Reproduces sexually and asexually - Has white hyphae with grey sporangia

Reproduction 4 points @ 3marks each

• When the mycelium becomes well established in the food source and when conditions for growth are favourable some hyphae begin to grow upwards from the surface of food.

• The tip of the hyphae develop a sporangium which is a round like structure that contains spores.

• When the structure is ripe; the sporangium bursts, releasing spores into the environment.

• These spores can be dispersed by air or water. When the spores find suitable conditions, the asexual reproduction cycle begins again.

• Causes of food spoilage • Types of food poisoning • Common symptoms of food poisoning • Groups vulnerable to food poisoning • Profiles of infectious food poisoning bacteria • Profiles of toxic food poisoning bacteria • Principles and advantages of food preservation • Methods of home preservation & commercial food preservation • Home freezing, heat treatments, chemical preservation and dehydration.

Week 11 Learning Intentions

Food Spoilage The main causes of food spoilage are: • Enzyme action • Moisture loss • Microbial contamination

Enzyme action: Enzymes are protein catalysts that speed up chemical reactions without being destroyed or changed. They are naturally found in food and play a role in food spoilage.

Ripening of foods All fruit and vegetables naturally contain enzymes. As enzymes ripen the: • Taste (sweetness) improves as the high starch content is converted to fructose. • Colour change e.g. tomatoes change from green to red • Texture changes e.g. hard bananas become soft and easy to digest.

Some fruit and vegetables e.g. apples, turn brown when cut as this releases an enzyme, oxidase, from the cell wall which reacts with oxygen in the air (oxidation). This eventually results in food spoilage.

Browning of food (enzymic browning)

1. Acids - The addition of acids lowers pH levels, inactivating enzymes as they generally work best at a neutral pH. For example squeezing lemon juice over a cut apple will prevent enzymic browning.

2. Heat - Enzymes are sensitive to high temperatures and become inactivated by cooking. This stops the browning and ripening of food e.g. stewing apples.

3. Additives - The preservative sulfur dioxide inactivates enzymes, reducing the spoilage. It is used commercially to prevent spoilage of dried fruits and juices.

4. Cold temperatures - Cold temps slow down enzyme activity in food, reducing the rate of spoilage and lengthening shelf life e.g. refrigerating fish @ 4ºC.

5. Blanching - e.g. broccoli must be blanched before freezing to prevent enzymatic spoilage as cold temperatures only slow down enzyme activity. Blanching involves immersing food in boiling water to kill enzymes and then plunging them in ice-cold water before freezing.

How to prevent / control enzymic spoilage

Food Poisoning Food poisoning is an illness caused by eating food contaminated with harmful substances. There are 3 types of food poisoning: 1. Chemical food poisoning 2. Biological food poisoning 3. Bacterial food poisoning

Profiles of Infections Food Poisoning Bacteria

1.

2.

3.

Profiles of Toxic Food Poisoning Bacteria

1.

2.

FOOD PRESERVATION PRINCIPLES OF FOOD PRESERVATION: • Preservation prevents enzyme activity in food • It inhibits the growth of microbes, often destroying them • Preservation prevents microbes from re-entering by sealing the food • It maintains as much nutritive value, colour, flavour and texture of the fresh food as

possible.

Advantages of Food Preservation

1. Saves money - home made preserves e.g. jams & chutneys are a lot cheaper than commercially produced variety.

2. It avoids waste - plentiful supply of garden produce e.g. fruit and vegetables can be preserved to prevent spoilage

3. It makes out of season foods available e.g. frozen rhubarb available at Christmas.

4. Preserved foods provides variety in the diet and are convenient and handy in emergencies

Freezing - Using low temperatures (below 0ºC) to inactivate microorganisms growth

and slow down enzyme activity. - Converting water in food into ice, making it unavailable to microorganisms. - Before freezing food should be wrapped well. This creates a barrier to

prevent the re-entry of microorganisms.

ADVANTAGES OF FREEZING DISADVANTAGES OF FREEZING

*Retains the nutritional value and sensory characteristics of food, e.g. texture, colour and flavour. *Saves time as people can bulk purchase foods on offer and freeze e.g. bread etc. *Saves money as people can bulk freeze meals for busy days, avoiding the need to impulse order takeaway. *Freezing makes out of season foods available all year e.g. freezing rhubarb to have at Christmas

*Initial cost of buying a freezer can be expensive to buy. *Bulk freezing can be time consuming *Packaging is needed for freezing, which can be costly. *Defrosting the freezer can be time consuming and laborious

• Turn on the fast freezer button to reduce the temp further to -25ºC this results in faster freezing of foods that retains the nutritional value and sensory characteristics of food.

• Cool foods first before freezing to avoid the internal temp of the freezer increasing.

• Avoid freezing more than 1/10 of the freezer capacity within any 24 hr period as it puts pressure on the condenser to keep the freezer cool.

• Freeze foods in usable quantities to avoid having to defrost more food than is needed.

1.Preparation:

~ Guidelines for home freezing ~

- Bring a pot of water to the boil in a large saucepan. - Wash, peel and dice your vegetable. - Place the vegetables into the boiling water for 3 - 5mins. Drain

using a colander. - Place the vegetables immediately into cold water with ice for 3 -

5mins. Drain using a colander. - Place the vegetables in freezer bags in usable portions and label the

food and date.

*BLANCHING* Vegetables are

blanched before

freezing to avoid enzymic spoilage over

time.

• Use good quality packaging that is strong, airtight and moisture proof. • Remove as much air as possible to save space in the freezer. • Seal packaging well, otherwise freezer burn may occur, resulting in

discolouration, toughening and drying out of protein foods. • If freezing liquid foods leave space at the top of the container for expansion.

2. Packaging & freezing

• Store similar foods together to avoid unnecessary searching and to make it easier to determine when additional food needs to be purchased.

• Use foods in rotation. • Keep the freezer full to capacity, as the majority of then energy a freezer uses is

spent cooling air between foods. • Avoid keeping the freezer door open for long periods or opening the door too

frequently in order to reduce the amount of warm air getting in.

3. Storing

Home Heat Treatments

1. Jam making Sugar

2. Chutney making Sugar and vinegar

3. Pickling Brine and vinegar

Home chemical Preservation

Home Dehydration • Dehydration is not a very popular method of home preservation. • It is usually carried out in a low temp. oven or in a hot press.

Removing moisture by heat, inhibiting microbial growth and inactivating enzymes. SUITABLE FOODS: • Herbs e.g. basil & rosemary • Fruit e.g. apples and banana chips • Vegetables e.g. chills, parsnips crisps etc

UNDERLYING PRINCIPLE

Commercial Preservation

- FREEZING - HEAT TREATMENTS - DEHYDRATION - CHEMICAL PRESERVATION - FERMENTATION - IRRIDATION

1. ASEPTIC CANNING Cans and food are sterilised separately

at high temps of 120 - 150 ºC Sterilised food is placed in cans and

then hermetically sealed. Cans are then cooled and labelled.

As this method has a short processing time the nutritional value and sensory characteristics of food are retained.

Methods of Canning

2. High acid food canning High acid foods e.g. fruit, requires a short processing time due to their

acidic pH of 4.5 or less, which already destroys many bacteria.

They are heated to 100ºC for less than 30minutes to destroy any

remaining bacteria.

3. Low acid food canning Low acid foods e.g. meat, fish and

vegetables requires a long processing time due to their low

acidic pH. They are heated to 115ºC for more

than 30minutes to ensure that bacteria are destroyed.

Commercial Chemical Preservation

• Sugar e.g. jam making • Salt e.g. pickling, preserving meat • Vinegar (acetic acid) e.g. chutney making • Sulfur dioxide e.g. dried fruit • Sorbic acid e.g. yoghurts • Antioxidants e.g vegetable oils • Alcohol e.g. pickling

FERMENTATION Breakdown of carbohydrates (sugar & starch) by microorganisms (yeast & bacteria) to

produce carbon dioxide, alcohol and energy.

• Used to preserve yoghurt e.g. lactic acid bacteria converts lactose into lactic acid.

• Yeast fermentation is used in baking and brewing. • The by products of fermentation e.g. alcohol and vinegar are used as chemical

preservatives.

IRRADIATION Preserves food by exposure to radiation energy as gamma rays pass through food and destroy microorganisms, kills pests, e.g. whiteflies and prevent sprouting on vegetables and ripening on fruit. Irradiation is used on more than 60 food types, including herbs, spices, fruit and veg in over 40countries. There are no irradiation facilities in Ireland. Any irradiated food products for sale on the Irish markets are imported.

ADVANTAGES OF IRRADITATION DISADVANTAGES OF IRRADIATION

• Extends shelf life as it destroys microorganisms.

• Kills insect pests • Delays ripening of fruit and sprouting of

vegetables

• Vitamins including B1 (thiamine) and C are reduced or eliminated.

• Can cause the chemical composition of food to change e.g. breaks down lipids causing them to become rancid.

• May mislead consumers as it can make food appear fresher by slowing microbial and enzymatic decay

EXAM PAPER QUESTIONS