Controlling Micro organisms File

Controlling Micro‐organisms / Preservation / Extending Shelf Life Food producers and manufacturers need to control the growth of bacteria in order to keep food in its best condition. By changing the conditions that bacteria need to grow food can be kept in good condition for longer, thus reducing waste and saving money. By controlling the following, the shelf life of food can be extended: Time: Moisture: Oxygen Bacteria
needs
O2 time to
multiply
Temperature: Bacteria grow
best at 37ºC
although
between 3ºC
and 63ºC
is considered
the ‘danger
zone
pH level: Bacteria
like moist
conditions
, most
foods are
moist.
Bacteria grow
best in a
neutral pH
between 6.6
and 7.5
Some
bacteria
but not all
require
oxygen to
reproduce
Some foods are more prone to bacterial growth, they are known as High risk foods Examples of high risk foods are:‐ • Raw or cooked meat • Raw or cooked fish • Raw eggs and egg products • Cooked rice and lentils • Gravies and soups • Unpasteurised foods e.g. milk Examples of low risk foods are:‐ • Fats and oils • Jams and marmalades (high sugar foods) • Chutneys and pickles (high acid foods) • Foods that are cooked before you eat them In food manufacturing high risk foods are kept separate from uncooked or raw foods. Workers working with raw foods wear different coloured clothing so they can be seen if they accidentally move to the high risk area of the factory. Application of Heat to help extend shelf life /prolong quality Method Main principles Pasteurisation • Liquid is heated and held at a high temperature for short time (HTST) • Pathogenic micro‐organisms destroyed(72ºC for 15 seconds) • Short term method of preservation‐shelf life extended for days not months • Milk is heated to 71ºC for 15 seconds and cooled quickly to below 10ºC Sterilisation • Food is heated to a higher temperature for longer 104ºC for 40 minutes • Most micro‐organisms are destroyed • Changes flavour and colour of milk slightly as caramelisation occurs. Milk is heated to 110ºC and held for 30minutes. • Extends storage period /shelf life Ultra heat • Heated to a very high temperature for a very short time treated (UHT) • Kills all known bacteria • Milk is heated to 133ºC for 1 second • It is a long term method of preservation • Very little colour or taste change • Extends storage period of milk for up to 6 months (unopened) Canning • Is a form of sterilisation • Food can be packed in cans and then sterilised or • Sterilised and packed in ASEPTIC(sterilised cans) • Containers are sealed with a double seam to prevent re‐contamination • Temperature and time varies according to food • Baked beans are heated to 120ºC for 35 minutes and cooled quickly Irradiation • Process involving passing strictly controlled x –rays from a radioactive or electron beam through food • Food absorbs the energy and radicals develop and destroy bacteria Suitable for: Milk, fruit juices, soups, liquid eggs, ice‐cream Wide variety of food such as milk, fruit juices Food sold in airtight cartons such as milk, soups, Sauces Used for a range of foods‐soups, fruit, meat, fish Strawberries, tomatoes, herbs, meat • Delays ripening of food e.g. strawberries • Destroys small insects found in cereal Removal of heat to help extend shelf life /prolong quality Cold temperatures slows down the rate at which the bacteria multiplies but it does not destroy them Bacteria are dormant at low temperature. When food is thawed or becomes warm the bacteria will start to multiply Method Main principles /How it works Suitable for Chilling • Chilled foods stored between 1ºC and 8ºC Salads, • Optimum temperature for chilled foods is sandwiches, pies 4ºC as this prevents listeria • Food is kept for a short time • Chilling reduces enzyme activity Cook –Chill • Prepared dishes are cooked and chilled quickly to between 0ºC and 3ºC in 90 minutes or less • Cook‐chill products have a shelf life of 5 Single raw food days e.g. meat, fish • Chilled foods are sold from chilled cabinets Mixture of raw 8ºC maximum legal chiller temperature foods –coleslaw, (5ºideal chiller temperature) stir‐fry • Dishes must be re‐heated to at least 72ºC Made from before eating cooked ingredients • They should be eaten within 2 hours and e.g. Quiches, pizza, left‐overs thrown away lasagne, soup, rice and pasta salads Freezing • Food is stored between ‐18ºC and ‐29ºC • Food is reduced from 0ºC to ‐18ºC in 12 minutes • Commercially frozen foods are quick frozen to produce small ice crystals which reduce cell damage • Food keeps for longer as water is not available for micro‐organisms • There is a great demand for frozen foods • Little change in nutritive value • May be structural changes Accelerated freeze drying (AFD) • A combination of freezing and drying • Food is frozen quickly and placed in a vacuum under reduced pressure • Heat vaporises the ice which turns to steam and leaves the food dry • Very little change to the colour, flavour, texture and nutritive value as very little heat is used • AFD foods more expensive dried fruits and nuts The use and function of chemicals in preservation methods Chemicals Function Used in Antioxidants Dried soup, fruit drinks, • Prevents fat going E300s stock cubes, cheese rancid(oxidation) Vitamin C and E • Protect fat soluble Vitamins A spreads (natural and D antioxidants • prevent fruit going brown Preservatives • Keeps food safe to eat for longer Processed foods, cured E200s meats, bacon, ham, dried by stopping bacterial growth fruit –raisins, sultanas Salt Ham, bacon, fish • Reduces moisture content by Brine solutions e.g.tuna osmosis • Destroys bacteria or prevents them from reproducing Pickles, chutneys Vinegar • Acetic acid has a pH of 3.5 Micro‐organisms cannot live below 4.5 Sugar • High concentration (60% of final Jams, marmalades jellies product) makes the water unavailable thus prevents bacteria from growing Emulsifiers and • Prevent emulsions separating Salad creams, salad Stabilisers dressings, mayonnaise, ice E.g. mixture of oil and water, E400s cream, low fat spreads, oil and vinegar. Lecithin (in cake mixes egg yolk) is an emulsifier which allows water and oil to mix • Stabilisers stop ingredients from Cook‐chill foods e.g. lasagne separating e.g. in a sauce. Xanthan gum is a stabiliser Task: Complete the statements by adding the correct ending to form the correct sentence. Drying food removes
food
must
be
kept
below
5ºC
or
above
62ºC
Freezing
preserves
food because
all the water and prevents the growth of micro organisms.
To reduce bacterial growth
water is changed from liquid to a solid and is
not available for the micro-organisms
ADDITIVES Additives are substances which are added to food to improve its keeping qualities, the colour, flavour and texture. Only a small amount is added. Other additives can be used to improve the texture, flavour or how the food looks. Additive Purpose Colours To give colour to foods e.g. jams, icing, drinks E100s Sweeteners Used in low calorie products such as yoghurts, drinks instead of sugar Flavourings To improve the flavour lost as a result of processing or to add taste to a manufactured food Natural Include herbs and spices flavourings Flavourings Are shown as flavouring e.g. raspberry flavouring in desserts (which do not have an E number) Flavour To make existing flavours stronger usually in savoury foods e.g. enhancers Monosodium glutamate (MSG) (E621) E600s Thickeners To improve the consistency of food during processing and storage. /Gelling agents They form a gel which thickens a product e. g. Jam, jelly, sweets, E44O (pectin) thick and creamy yogurts and desserts Anti‐caking To prevent dry ingredients from clumping together e.g. in cake agents mixes Facts Some people prefer to eat food without any chemical or artificial additives Some children become hyperactive as a result of eating foods with colouring e.g. tartrazine ref: http://www.sa‐wellbeing.com/2011/03/587/ Other methods of preserving food Method Main principles /How it works Suitable for Modified Bacon, ham, smoked • Removing air and sealing the Atmospheric fish, coffee, fruit packet Packaging and vegetables • Air is replaced by another gas (MAP) or which is a mixture of gases ‐ Controlled oxygen, nitrogen and carbon atmosphere dioxide packaging (CAP) • – this prevents growth of micro‐
Removal of Air organisms Vacuum Packing • Air is removed from a sealed Coffee packet in order to keep the flavour of the food