Food preservation and processing methods and related products Flashcards
Name the 3 main processes in the conversion of muscle to meat
- Acidification
- Rigor mortis
- Conditioning
Describe acidification in the presence of oxygen
Glycogen breaks down to pyruvic acid and then to CO2 i H2O (with synthesis of ATP)
Describe acidification in the absence of oxygen (postmortem)
Glycogen breaks down to lactic acid – no blood to remove LA – acidification (from pH 7.2 to pH 5.5)
Describe acidification of meat
- pH drops in beef muscle 36-48 hours, pig 4-8 hours
- Protein denaturation, meat paler and more opaque - its ability to bind water decreases
- pH drop is critical for meat qualities
What is the ultimate pH for normal meat?
5.6-6.2
Describe PSE acidification and its characteristics
Pale soft exudative
- accelerated anaerobic glycolysis: fast and excessive drop in pH to 5.2-5.4
- Characteristics: poor water holding capacity, pale colour, soft texture, cooking losses (lower processing yield), poor colour in cured products
Describe DFD acidification and its characteristics
Dark firm dry
- Not enough glycogen (6.0-6.2 or up to 6.8)
- Characteristics: dark, dry surface (high water holding capacity), shorter shelf life and poor consumer perception of quality
What is the onset of rigor mortis solely controlled by?
The availability, or not, of ATP
Describe how rigor mortis occurs
ATP can no longer be generated by glycolysis and is eventually exhausted, the muscles lose this relaxed state and pass into rigor
How is rigor mortis different in stressed animals?
Stressed animals: less glycogen and ATP = more rapid rigor
Why is rigor important for meat quality?
Rigor is important because it fixes the lengths of the sarcomeres, and therefore the muscle’s length and the potential texture of the meat:
- Muscles entering rigor in a very contracted state tend to produce tough meat
- Those entering rigor in a relaxed, or stretched, state will produce tender meat
Muscles should enter rigor mortis at what temperature for optimum tenderness
10-15°C
What is the effects of fast chilling of carcasses after slaughter?
Cold shortening - the resulting meat is tough
What is the main objective of electrical stimulation?
Accelerate the pH decline after death in order to be able to implement a chilling system without any risk of cold contraction
- An electrical current is passed through a carcass to ensure that the meat is tender under rapid carcass chilling.
- It accelerates the normal PM changes (depletion of glycogen and ATP) so that muscle sets in rigor mortis sooner and carcasses can be chilled without fear of cold-shortening and toughening.
Describe the process of conditioning
- Natural process which improves eating quality of beef: flavour and tenderness
- Conversion of muscle to meat: natural enzymes from muscle degrade specific proteins from muscle fibers
- Enzymatic proteolytic degradation results in an increase of meat tenderness
What are the different recommended ageing times before meat is consumed?
- Poultry 1 day
- Pork 4-10 days,
- Lamb 7-14 days,
- Beef 10-21 days
What is meat chilling critical for?
Meat hygiene, safety, product shelf-life, appearance and eating quality
When should carcass chilling start, at what temp?
Within 1hr of exsanguination and occur so that a temp of 4°C or less is reached within 24hrs
What are the 3 mechanisms of dry chilling?
- Slow air refrigeration
- Rapid air refrigeration
- Ultra-Rapid air refrigeration
Describe Slow air refrigeration
Used rarely, in small abattoirs with traditional technologies, three steps:
• carcass ‘draining’ or ‘drying’ at ambient temperature for a few hours,
• pre-refrigeration (around 10°C; 75% relative air humidity) and
• refrigeration (4–7°C, 85–90% relative air humidity).
Describe rapid air refrigeration
Most common, carcasses are exposed to air at 1 to -1°C, 90% relative air humidity and 1–3 m/sec circulation for 24–36 h (cattle) or 18–24 h (pigs, lambs); weight loss is around 1.5–2.0%.
Describe the 2 phases of ultra rapid air refrigeration
- Carcasses exposed to intensive circulation (2–4 m/sec) of very cold (-4 to -6°C, even -20°C) and humid (90–100%) air in special tunnels for 1–3 h
- Then, refrigeration at -1 to 2°C for 18–22 h (cattle) or for 14–16 h (pigs) with slow air circulation (0.1 – 0.3 m/s). Weight loss only 1%.
- Problem – “cold shortening”
Which two problems are associated with wet chilling
Cross contamination and water absorption
What is the problem associated with spray chilling
Surface stays wet, better survival of microorganisms
Which meat has the longest and shortest shelf life
Longest = Beef carcasses – 3-4 weeks Shortest = Offal – 3 days
What are the main signs of meat spoilage?
Meat greening (with or without fluorescence) and slime layer
What is the purpose of aerobic packaging?
Prevents secondary contamination, but doesn’t extend shelf life
Bacteria and yeasts in meat are inhibited at what temperature when freezinf?
Bacteria inhibited at –7°C, yeasts at –12°C
How does slow vs rapid freezing affect bacteria
Slow freezing - better survival of bacteria
Rapid freezing – water inside bacterial cell crystallises leading to cell death
Name some other food preservation and processing methods
- cooking
- salting and curing
- smoking and drying
- fermentation
- thermal treatments
Describe the methods of drying meat
Removal of the water
- Most often carried out by keeping the product suspended in air
- Lyophilization (“Freeze drying”) - the meat is first frozen and then exposed to a very low pressure of around 5–6mbar (‘in vacuum’) at -20°C to -40°C, then removing the ice by sublimation
Based on their final aw values, dried foods can be divided into which three groups?
- High moisture products
- Intermediate-moisture products
- Low-moisture products
Describe smoking as a food preservation treatment
- A result of aerobic or anaerobic pyrolysis of woods
- It starts at around 170°C, and at temperatures up to 270°C is endothermic, and above that has an intensive exothermic nature
- Cold (30oC), warm (40-60oC) or hot (70-80oC) smoking
- Can be hardwood smoke or liquid (injected)
- It should not be higher than 300°C
Define fermentation
Phase of intensive growth and metabolism of lactic acid bacteria accompanied with rapid fall of pH
or: Any partial breakdown of carbohydrates taking place in the absence of oxygen
Which factors affect the microbial growth in food?
- Intrinsic – associated with the food itself
- Extrinsic – related to the environment where the food is placed e.g. temp, humidity
- Factors related to the microorganisms themselves
Name some food additives
- Polyphosphates - increase the ability of meat proteins to bind water. Enable incorporation of additional water
- Antioxidants (Ascorbic acid)
- Food colours
- Preservatives
- Sweeteners
- Flavour enhancers
- Emulsifiers
Which foodborne pathogen is most sensitive to dry chilling?
Campylobacter jejuni
What is the water activity (Aw) of food?
Proportions of available water in food for microorganisms needs
How does adding salt affect microbial growth and survival in food?
Reduced water activity in food
Microorganisms that can grow in dry food are called?
Xerophilic
How are pasteurised products stored?
Refrigeration
