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Topic 4.1 Food spoilage and contamination - Coggle Diagram
Topic 4.1 Food spoilage and contamination
food spoilage happens when food is contaminated by yeasts, moulds or bacteria. food spoilage can also be caused by enzyme activity that causes colour and flavour changes.
most food spoilage is caused by microorganisms. microorganisms are tiny living things that can only be seen with a microscope. they need food, moisture, warmth and time to grow.
yeasts
yeasts are single-celled fungi which reproduce by budding.
most yeasts grow best in the presence of exygen ( aerobic ) but they can grow without oxygen ( anerobic )
yeasts prefer moist acid foods but can also grow in high concentrations of sugar.
yeasts grow best in warm conditions 25-29C but can grow in temperatures of 0C and below so refrigeration won't completley stop the growth of yeast.
yeasts are destroyed at above 100C and cannot grow when there is insufficient water available.
yeasts often spoil foods like jam, honey, fruit, yoghurts and fruit juices.
yeasts ferment sugars in foods which produces carbon dioxide and alcohol. foods will develop off flavours and may be fizzy.
enzymes
enzymes are bioligical catylists usually made from proteins.
enzymes speed up chemical reactions. the action of enzymes can cause browining of foods that are bruised or cut open.
browning caused by enzymes is called enzymic browning
blanching food by quickly boiling and cooling down food can prevent enzymic action by destroying the enzymes. foods like bean sprouts and corn on the cob benefit from this.
freezer temperatures are not enough to prevent enzyme activity so some foods must be blanched before freezing like corn on the cob and apple slices.
acids can be used to prevent enzymic browning because acids can denature enzymes (destroy)
enzymes can also cause oxidation which is the loss of water-soluble vitamins b and c
moulds
moulds are tiny fungi that produce thread like filaments that help them spread around food and extract nutrients.
moulds grow on many foods but prefer temperatures between 20 and 30C. they also like high humidity.
mould growth can be prevented by storing food in a cool, dry place, storing food in the fridge, heating or cooking food and storing in acid conditions.
moulds often grow on bread and bakery products
bacteria
macteria are single celled microorgansims. they can be divided into three groups. harmless, pathogenic and food spoilage bacteria
bacteria that cause food poisoning are called pathogenic
bacteria need food, warmth, moisture and time to grow. they grow best in neutral conditions
bacterial growth can be slowed down by: storing perishable food in the fridge at between 0C and below 5C, cooling cooked perishable food to room temperature within 90 minutes before putting it into the fridge, reheating leftover food only once and useing hight concentrations of salt, sugar and acid to remove most bacteria.
bacteria often spoil foods with high protein content that are moist
foods that bacteria often spoil are: cooked meat and poultry, cooked meat products such as gravy, soup and stock, milk and eggs and dishes made from them, eggs and dishesmade from them,shellfish sucha s mussels and cooked rice
signs of food spoilage
enzymic browning can be identified if the food has turned brown
yeasts can make liquids appear fizzy and can appear as a thin layer of dust on foods like grapes
moulds can be identified by blue or green patches on foods
use of yeasts in food production
yeasts are often used as a raising agent in bakery products
yeasts are used to ferment foods into alcohol and make drinks fizzy in foods like wine and beer.
use of moulds in food production
some cheeses are made with moulds to improve their colour and flavour such as stilton cheese
moulds are used on the surface of some sausages to improve their smell and extend their shelf life
soy sauce is made by mixing soya beans with mould and yeast and leaving it to ferment. this process produces monosodium glutanate which is popular in east asian dishes.
use of bacteria in food production
cheese making
the raw ingredients for cheese making are milk, a starter culture of bacteria, rennet and salt
milk used for cheese making is usually pasteurised to kill harmfull/pathogenic bacteria
the starter culture changes lactose found in the milk into lactic acid and begins the cheese making process
rennet causes the milk to separate into curds and whey
the curds are pressed into molds and then the cheeses are put into storage for the necessary time to age and develop flavour.
yoghurt making
the selected bacteria are added to warm milk and left to multiply for hours
during the process of yoghurt making the milk turns into a thick yoghurt and becomes slightly tangy
bacterial contamination
raw food contamination
many raw foods carry a lot of bacteria
bacteria that lives in the intestines of animals can be transferred to the meat during the slaughtering process. these bacteria can cause food poisoning
other types of raw food that carry bacteria are raw eggs, mussels and oysters
plant foods such as rice and vegetables can be contaminated with bacteria from the soil
work surface and equipment contamination
bacteria cannot be seen without a microscope so it is essential to clean work surfaces before you begin food preparation
any work surfaces that have been in contact with raw meat should be thouroghly cleaned with hot, soapy water before they are reused for other foods
all equipment should be cleand regularly, before and after use
dish cloths pick up bacteria every time they are used to wipe surfaces. if these surfaces have been in contact with raw meats it is better to use a disposable cloth rather than a dishcloth
make sure dishcloths are cleaned daily with very hot soapy water
food handler contamination
you can contaminate food with bacteria that are naturally present on you
use tongs or other utensils to pick up food
use a clean teaspoon to check flavour and don't double dip
don't lick your fingers under any circumstances
avoid touching the parts of utensils that come into contact with food
pest contamination
pests such as flies, insects, birds, mice and rats cand contaminate food. they carry bacteria on their bodies and in the excresions.
keep all work surfaces clean so pests have no food source
wash up straight away
make sure the kitchen is very clean after each cooking session
don't leave food out overnight as some pests are nocturnal
empty bins regularly and clean bins at least once a week
domestic pets should not be allowed in food preparation areas
waste foods and rubbish contamination
bacteria can multiply in rubbish bins
only use bins with lids
use thick bin bags
empty bins as soon as they become full and always at the end of the day
foot operated bins are preferred
bins should be washed regularly, inside and out, and then disinfected
the floor area underneath the bin should be washed every day
common pathogentic bacteria
campylobacter
found in poultry, milk and milk products
comes from unclean water unpasteurised milk, raw poultry, bottled milk pecked by birds, sewage and in the guts of cattle pigs birds and pets
symptoms generally take 48-60 to show
most common type of food poisoning bacteria in the uk
can be transmitted by domestic pets
E. coli
found in undercooked meat and unwashed contaminated fruit
comes from raw and undercooked meat, dirty water and sewage
symptoms generally take 12-24 hours to show
usually comes from the intestines of animals and can be found anywhere where faecal contamination occurs
salmonella
found in undercooked meat, beansprouts, unpasteurised milk and foods made from imported poultry and eggs
comes from the intestines of ill people, animals, raw meat, unpasteurised milk and imported poultry and eggs
symptoms generally take 12-36 hours to show
listeria
found in pate, cooked chicken, prepared salads and soft cheeses
comes from sewage, decaying vegetation and unclean water
symptoms can take as long as 70 days to occur
1 in 20 people can carry listeria without knowing or showing any symptoms
it is dangerous for pregnant woment to get listeria as it can cause miscarriage
staphylococcus aureus
found in unpasteurised milk, meat and meat products
comes from human food handlers touching, coughing or sneezing on food as well as human to human contact
symptoms occur in 1-6 hours
is mainly transmitted by human handlers and is found on human skin and mucus membranes.
food poisoning
at risk groups
babies and very young children
pregnant women
elderly people
those with reduced immunity
causes
eating or drinking contaminated water
eating undercooked food
not storing food correctly eg. wrong temperature
not storing cooked foods in the fridge or storing them in the wrong place in the fridge
eating food touched by someone with a septic cut
cross contamination from raw foods
general symptoms
vomiting
diarrhoea
nausea
stomach pains
dehydration
symptoms can start within two hours after eating but could take many days depending on what type of pathogenic bacteria was ingested