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Y3 Public health > Food preservation and processing methods and related products > Flashcards

Food preservation and processing methods and related products Flashcards

1
Q

Name the 3 main processes in the conversion of muscle to meat

A
  • Acidification
  • Rigor mortis
  • Conditioning
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2
Q

Describe acidification in the presence of oxygen

A

Glycogen breaks down to pyruvic acid and then to CO2 i H2O (with synthesis of ATP)

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3
Q

Describe acidification in the absence of oxygen (postmortem)

A

Glycogen breaks down to lactic acid – no blood to remove LA – acidification (from pH 7.2 to pH 5.5)

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4
Q

Describe acidification of meat

A
  • 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
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5
Q

What is the ultimate pH for normal meat?

A

5.6-6.2

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6
Q

Describe PSE acidification and its characteristics

A

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
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7
Q

Describe DFD acidification and its characteristics

A

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
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8
Q

What is the onset of rigor mortis solely controlled by?

A

The availability, or not, of ATP

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9
Q

Describe how rigor mortis occurs

A

ATP can no longer be generated by glycolysis and is eventually exhausted, the muscles lose this relaxed state and pass into rigor

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10
Q

How is rigor mortis different in stressed animals?

A

Stressed animals: less glycogen and ATP = more rapid rigor

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11
Q

Why is rigor important for meat quality?

A

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
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12
Q

Muscles should enter rigor mortis at what temperature for optimum tenderness

A

10-15°C

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13
Q

What is the effects of fast chilling of carcasses after slaughter?

A

Cold shortening - the resulting meat is tough

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14
Q

What is the main objective of electrical stimulation?

A

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.
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15
Q

Describe the process of conditioning

A
  • 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
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16
Q

What are the different recommended ageing times before meat is consumed?

A
  • Poultry 1 day
  • Pork 4-10 days,
  • Lamb 7-14 days,
  • Beef 10-21 days
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17
Q

What is meat chilling critical for?

A

Meat hygiene, safety, product shelf-life, appearance and eating quality

18
Q

When should carcass chilling start, at what temp?

A

Within 1hr of exsanguination and occur so that a temp of 4°C or less is reached within 24hrs

19
Q

What are the 3 mechanisms of dry chilling?

A
  • Slow air refrigeration
  • Rapid air refrigeration
  • Ultra-Rapid air refrigeration
20
Q

Describe Slow air refrigeration

A

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).

21
Q

Describe rapid air refrigeration

A

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%.

22
Q

Describe the 2 phases of ultra rapid air refrigeration

A
  • 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”
23
Q

Which two problems are associated with wet chilling

A

Cross contamination and water absorption

24
Q

What is the problem associated with spray chilling

A

Surface stays wet, better survival of microorganisms

25
Q

Which meat has the longest and shortest shelf life

A 
Longest = Beef carcasses – 3-4 weeks
Shortest = Offal – 3 days
26
Q

What are the main signs of meat spoilage?

A

Meat greening (with or without fluorescence) and slime layer

27
Q

What is the purpose of aerobic packaging?

A

Prevents secondary contamination, but doesn’t extend shelf life

28
Q

Bacteria and yeasts in meat are inhibited at what temperature when freezinf?

A

Bacteria inhibited at –7°C, yeasts at –12°C

29
Q

How does slow vs rapid freezing affect bacteria

A

Slow freezing - better survival of bacteria

Rapid freezing – water inside bacterial cell crystallises leading to cell death

30
Q

Name some other food preservation and processing methods

A
  • cooking
  • salting and curing
  • smoking and drying
  • fermentation
  • thermal treatments
31
Q

Describe the methods of drying meat

A

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
32
Q

Based on their final aw values, dried foods can be divided into which three groups?

A
  • High moisture products
  • Intermediate-moisture products
  • Low-moisture products
33
Q

Describe smoking as a food preservation treatment

A
  • 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
34
Q

Define fermentation

A

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

35
Q

Which factors affect the microbial growth in food?

A
  • 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
36
Q

Name some food additives

A
  • 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
37
Q

Which foodborne pathogen is most sensitive to dry chilling?

A

Campylobacter jejuni

38
Q

What is the water activity (Aw) of food?

A

Proportions of available water in food for microorganisms needs

39
Q

How does adding salt affect microbial growth and survival in food?

A

Reduced water activity in food

40
Q

Microorganisms that can grow in dry food are called?

A

Xerophilic

41
Q

How are pasteurised products stored?

A

Refrigeration

Y3 Public health (19 decks)

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