Food Preservation Flashcards
Food spoilage
Food is organic and spoils when enzymes and microbes that are present in food are given the ideal conditions to cause damage
Obvious- mould on surface, slimy texture, foul odour- discard whole product
Microbial- need to slow growth to a halt, alter the environment
Mould- small fungi, produces antibiotics, toxins and enzymes- some beneficial
Yeasts- small fungi that have an affinity for sugars and grapes. Wine is fermented grapes - yeast digest natural sugar in grape
Bacteria- single cell organisms, capacity to form spores when environment not favourable, bacteria will lag dormant with a protective outer layer and wait till enviro facilitates growth- produce toxins again
Food poisoning
Infective- caused by eating live bacteria within the food such as salmonella listeria and E. coli
Minimise risk by preventing growth of the bacteria
Toxic- caused by toxins produced by bacteria. Often cannot be removed or inactivated by cooking eg staph, clostridium
To overcome: hydration (salt and water), prebiotic and starch to feed new bacteria- helps regenerate gut microbiota
Ideal growth conditions
Warmth Moisture Food (sugar for yeast, protein for bacteria) Time Varied oxygen Varied pH
Enzymes- accelerate food spoilage
Desirable: accelerate bacterial fermentation eg in cheese and yoghurt making
Undesirable: enzymatic browning of apples, bananas
Drying
Dehydration, evaporation
Inhibits growth of microorganism- bacteria and moulds need 15% and yeast needs at least 20% (not only moisture by available water within food)
Drying makes light for transport, reduced storage
Can be eaten as is or rehydrated to change size, colour flavour and texture
Sun drying
Provides natural heat for evaporation
Commercial drying
Commercial drying: conventional
Uses heat to evaporate water.
Food is spread on a surface made of slats/Latrice/ mesh within kiln or drying room
Hot air passed over and through the food or food isnon a conveyor moved through a tunnel of hot air
Liquids are spray dried (liquid dries mid air) or drum dried (liquid is poured over a drum and then peeled off, ground and packed)
Commercial drying: vacuum
Sucks the water out
Pulls water out to obtain moisture levels of 1-3% in final product
Food or liquid is placed in a chamber and the surround pressure is reduced to below atmospheric pressure, which lowers waters boiling point. Water is more easily boiled off at this lower boiling temp. Commonly used for concentrating milk, tomato paste, orange juice and coffee
Conventional drying: osmotic
Water removed by osmosis
Involves reusing a strong syruonwith a high sugar concentration that osmotically draws water from the objects being dried
Eg. Craisins
Conventional drying: freeze
vapourises ice crystals
Food initially being frozen and then jd placed in a vacuum. The frozen foods ice crystals are sublimated to a vapour
Does not alter foods flavour, colour or structure as it is not subjected to heat
Produces high quality foods that can be stored indefinitely and reconstituted easily
At low pressure move from solid to vapour by increasing temp. If pressure is too high, solid product will go through liquid phase and result in product deterioration
Conventional drying: concentration
Liquid removed/ evaporated by applying heat, producing a paste eg tomato/ quince
Produced concentrated form of food. Many traditional pastes do not contain salt or sugar and thus rely on removal of water as their preservation method often preferred over sun drying as not susceptible to weather or insects.
Foods included- lentils, chickpeas, sun dried tomatoes, herbs and spices c teas, mushrooms ect
Some are rehydrated
Drying pre treatment
Blanching- to prevent enzymatic browning
Sulphur- exposure to sulphur dioxide or sulphite solution to preserve colour, flavour and act as antimicrobial
Checking- dipping fruits in very hot water to crack the skin and improve texture
Salting/ sugar or spice and nitrates for preservation
Cold smoking-dries but not cooks, hot smoking dries and cooks
Fermentation
natural process where sugars in the food become fermented by microorganism producing lactic acid
Eg. Milk fermented to cheese, yoghurt
Starch provides source of sugar- maltose and glucose
Fermented by yeast (candida) and bacteria of which depends on pH, alcohol, salt, moisture etc
Yoghurt
Fermented milk product
Lactose and it’s conpibents glucose and galactose metabolised by starter bacteria to produce lactic acid, thus decreasing pH
Microorganism used:
- mesophillic
- thermophillic
- probiotics
Basic components: raw milk, skin milk, cream, sugar, bacterial cultures, milk concentrate, milk powder, fruits, stabiliser, flavour and colour
Made by stirring water
Improve gel and reduce syneresis- low viscosity.
Caesin micelles have large number of negative charges on protein strands. Charge in pH due to lactic acid neutralises negative charges. Soft gel formed. Calcium phosphate released and gel becomes firmer 3.6-4.3
Heating or cooling to stop process
Volatile carbonyl compounds, acids, alcohols and non-volatile acids provide flavour
Sugaring
Create a physical barrier between atmosphere and food
Binds up much of water content of food making it unavailable to microorganisms
Pickling
Acidifying the food product via the addition of acid, salt or via fermentation- difficult for bacteria to survive
Vinegar commonly used
Food is covered with vinegar, boiled and sealed in a container. Left to stand for at lest 3wk so vinegar penetrates entire food
Lowers pH
Encasing foods also extends shelf life
Cooking foods
Causes of a series of chemical ranges related to high temp that destroy the microbes that cause food spoilage Application of heat through: Sterilisation through canning Pasteurisation Boiling Blanching Baking Cooking on stove or microwave All work to deactivate microbes Reach min temp 74
