Food Spoilage (High risk foods have ideal conditions for bacteria (High…
High risk foods have ideal conditions for bacteria
High risk foods are ready to eat foods that if not stored correctly could grow harmful bacteria
They are moist and high in protein ( protein = food for bacteria )
High risk foods have a short shelf life - can’t keep for long or bacteria might multiply to dangerous levels
A raw food e.g. chicken might have lots of bacteria but it’s not classed as a high risk food because you don’t eat it raw . Once it’s cooled and ready to eat it can be described as high risk..
Identify when a high risk food is spoiling- e.g. meat going slimy , milk smelling sour or cheese going mouldy
High risk foods: cooked meat, fish , poultry , dairy products ( eggs, cheese ) , gravies , stocks and sauces, shellfish and cooked rice
Pathogenic bacteria leave no signs - taste, colour, odour , texture aren’t affected
Check for no visible signs of spoilage when buying food: fresh meat - bright coloured, firm and fresh smell & fresh fish - shiny skin, red gills , clear eyes and smell clean or slightly salty
Mould and yeast can spoil food too
Moulds and yeast are microorganisms (fungi) - this means in the right conditions (warmth,moisture etc) they can grow and spread quickly
Moulds spoil bread, cheese,fruit - change look,smell and taste of food. Fuzzy appearance
Waste products from moulds cause food poisoning - even if scraped off, toxins may still remain
Yeasts commonly grow on the surfaces of fruit: grapes, blackberries and tomatoes
Yeast can spoil fruit by fermenting sugars turning them into alcohol and carbon dioxide.
Microorganisms grow in the right conditions
Microorganisms e.g. bacteria, moulds and yeasts need five conditions to quickly grow and multiply: warm temperature, a lot of moisture, food, the right pH , enough time ( ideal conditions bacteria split every 10-20mins )
Pathogenic microorganisms can spoil food and cause food poisoning
Changing any of these conditions will slow or stop the growth of microorganisms: use a fridge to change the temperature, pickle the food in vinegar to change the pH, add salt ( salt absorbs water and removes moisture from the food therefore dries it out.
Enzymes are biological catalysts
Enzymes are proteins that act as biological catalysts - they speed up chemical reactions.
Ripening: enzymes in fruit cause them to ripen which affects the sweetness, colour and texture of the fruit. E.g. unripe bananas are green and firm- enzymes break down starch inside them which makes the banana soft and sweeter.
Browning: when you slice fruits ( apples, pears ) the oxygen in the air turns the fruit brown. Enzymes inside the fruit speed up this process. Leaving some fruit ( banana & avocados ) to overripe will give them a brown colour
Slowing or stopping an enzyme from working
Adding an acid: enzymes work best at a certain pH. If you dip slices of fruit into lemon juice the acidic conditions will stop enzymic browning.
Blanching (plunging into boiling water for a short period) is used to prepare vegetables for freezing. Natural ripening enzymes will cause veg to lose colour, texture and flavour and nutrients overtime. Freezing will slow down the enzymes but not stop them completely. Blanching destroys the ripening enzymes, so the vegetables retain their colour, nutrients etc.