Food Production/ Preservation Flashcards
Refrigeration
Slows the biological, chemical and physical reactions that shorten the shelf life of food
(<4 degrees) prevents many bacteria from multiplying
Crisper sections of refrigeration have reduced oxygen levels which slows the metabolism of fresh produce, thus prolonging life and quality
Plastic bags used to store fruit and veg should have small holes to allow small amounts of oxygen inc to prevent cellular death (enzymes that break down cells released)
Freezing
Least damaging to the foods original flavour, nutrient content and texture, compared with most other preservation methods
Process;
Water in food made unavailable to microorganisms when frozen
Slows the chemical and physical reactions leading to food deterioration
As some oxygen still present, reactions do still continue, therefore shorter shelf life than canned foods
Flash freezing is very rapid freezing to very cold temp (<0) faster the food freezes, less damage that occurs
Ability to freeze and length of time frozen depends on composition of food
Foods that don’t freeze well
Fruit, beg and liquid dairy
Plant tissue of unblanched fruits and veg are irreversibly damaged during freezing
Diary products may have their original distribution of fat and water permanently altered to being unacceptable quality
Higher the foods fat content, the shorter it’s lifespan in the freezer as fat can become rancid even when frozen
Conversely foods containing Bery little water, such as dried fruits beans, grains, nuts and coffee can have usual lifespan doubled when frozen
Properties of water
Great heat capacity - 1 degree
Heat of vapourisation- 540calories/g
Density decreases as phases change from liquid to solid - 1000kg/mcube to 917kg/mcube
Adding solutes changes boiling and freezing points
Freezing water
Formation of ice crystals
Nucleation-> propagation -> maturation
Freezing turns a liquid/ rubbery mads to a solid/ glassy state
Crystalline microstructure determines the texture, appearance and quality of food
Ice cream
3 phase system of air, liquid and solid
Initial nucleation starts in the inside walls of the freezer barrel
Propagation and maturation occurs during storage
Recrystallisation occurs via accretion and migration
Stabilisers retard ice crystal growth during storage eg. Hydrocolloid polysaccharides such as gust and locust bean gum
Sweetness of different kinds effect crystallisation
Storage temp effects rate of recrystallisation
Freezing problems: cell rupturing
Ice crystals piece cell walls within food, rupturing them, resulting in food with an inferior texture
High water content foods should not be frozen eg. Lettuce, tomato, milk and cottage cheese
Minimise problem with rapid freezing which results in smaller ice crystals and therefore less cell rupturing and higher quality thawed product
Liquor nitrogen, air blast, plate or contact, immersion, cryogenic freezing are all methods of rapid freezing
Freezer problems: Freezer burn
When an opaque surface partially covers food that had been frozen too long or improperly
Alters the texture, colour and flavour of foods
Caused by a loss of moisture (through sublimation = solid to gas) that occurs when air spaces are left in package or that package is torn or moisture proof packaging is it used.
When freezer burn is thawed, the texture is spongy often needing to be discarded
Prevention- wrap foods properly in an air right vapour resistant material, lack tightly, date it. Use within optimal storage time. - frost free freezers and vacuum packaging reduced risk
Freezer problems: fluid loss
The water loss from cells when food is thawed eg the red fluid from thawed meat
Fluid loss can result in dryer foods compared with the fresh form of same food when cooked
Freezer problems: recrystallisation
Occurs with longer storage times and fluctuation in temp caused by opening and closing the freezer
Numerous small ice crystals melt, then combine on refreezing to form larger crystals, thus affecting the texture and quality of foods such as ice cream
Additives acting as preservatives
Can be antimicrobial or antioxidant
Help a variety of types of food spoilage
Foods that contain fats (especially unsaturated) react readily with oxygen to great peroxides that are responsible for the odd flavours in foods that contain fats that have become rancid
Other foods such as apples and potatoes turn brown when they oxidise resulting in change in their nutritional quality
Modified atmosphere packaging (MAP)
Slows normal respiration of the fresh produce thereby prolong shelf life
Minimises spoilage during distribution of fresh produce
Different mixes of gases are applied under specifically selected types of packaging material, eg it may seem that a piece of meat or a tray of vegetables is simply wrapped under a piece of glad wrap
Actually a particular gas combination pumped under a specifically chosen film designed especially to protect that particular food from the biological chemical and physical factors that spoilt it
Meat, fish and cheese are non respiring products and need very low gas permeability/ high barrier films
Fruit and veg are resourcing and need higher gas permeability (for o2 and co2) films as interaction bw packaging and material and food product is important
MAP continued
Vacuum packing is an example of MAP commonly used with fresh meat. Oxygen is removed by vacuum and nitrogen or CO2 may be flushed through before the package is sealed
The modified atmosphere prevents oxidative damage to the mhoglobin and thus the meat keeps a purple- red colour and prevents the grown of microbes that need oxygen to survive
Equilibrium modified atmosphere packaging (EMAP) is the packaging technology most commonly used today for fresh cut fruits and veg
The gas atmosphere of packaged vegetables and fruits is not air, however rather comprises low O2 and higher CO2
Other factors include portion size, extent of preparation, maturity and type of tissue all affect shelf life of MAP produce
Gases used in MAP:
Oxygen
Carbon dioxide
Nitrogen
Carbon monoxide
Sulphur dioxide
Ethanol
Argon
Irradiation
Ionising radiation can kill bacteria, moulds and insects in food
Ionising radiation damages the DNA of microorganisms leaving them unable to reproduce or kills them completely
Also disrupts enzymatic pathways- eg slows down the ripening of some fruits.
Has not been well received by consumers who wriggle believe that the food becomes radioactive
Sometimes referred to as cold pasteurisation as not heat is invoked
Benefits as irradiation is one of the main methods by which nutrients, especially vitamins are not destroyed
Despite widespread approval for the technology in food preservation within the scientific community it is only slowly adding to then tonnes of food preserved across the world each year
