Protein dependent quality traits and water holding capacity

Question 1

Particularities of proteins in animal-source foods

Answer 1

Amino acid profile:
sequence and often single protein proportions are gentically fixed

Polymorphisms:
Occur in single proteins (genotypes) with small differences in amino acid sequence (important mainly in milk)

Question 2

What are the mors important proteins of muscles and fat tissue? (Meat proteins)

Answer 2

Myoglobin: Metalloprotein, red muscle colour, plasma protein

Hemoglobin: Metalloprotein, blood in muscle, plasma protein

Actin: Part of myofibrils (structure forming)

Myosin: Head-tail structure, part of myofibrils (structure forming)

Collagen: triple helix, most frequent connective tissue protein

Elastin: Connective tissue protein

Reticulin: Connective tissue protein

Question 3

What are struxtural elements of the muscle?

Answer 3

Muscle fibre
Glycogen reserves
Connective tissue covers

Question 4

Function of the muscle

Answer 4

p. 21 + 22

Question 5

What are two parts of physicochemical meat quality

Answer 5

water holding capacity / water binding capacity (extent to which tissue is intact)

Texture (mechanical resistance / structural state)

Question 6

Meat quality defects

Answer 6

Meat with discounitnuous deviations in physicochemical properties - associated with impairment in quality - which can be distinguished from normal meat by the measurement of certain traits

Question 7

Kinds of meat quality defects

Answer 7

Genetically determined types of abnormal meat quality (expression under certain environmental conditions)
e.g.
PSE (pale-soft-exudatice)
DFD (dark-firm-dry)
Acid meat (abnormal meat quality from Hampshire breed pigs)

Non-genetically determined types of abnormal meat quality
e.g.
Cold shorthening/thawing rigor mortis
musty ageing/decay
punctual bleeding

Question 8

PSE type of meat quality defects

Answer 8

Occurrence: pig, poultry, fish

Cause: Particularly fast anaerobic degradation of glycogen reserves to lactic acid

Characteristics: Low pH early-postmortem; low water-holding capacity; (giant fibres)

Question 9

DFD type of meat quality defects
(dark-firm-dry)

Answer 9

Occurrence: Cattle, wildlife (pig; mostly n shoulder; may occur at the same time as PSE in the back)

Cause: Lack of glycogen at slaughter (gene defect and/or environment)

Characteristics: Late postmortem pH is too high; impaired taste; short shelf-life

Question 10

Acid meat type of abnormal meat quality

Answer 10

Occurrence: Pigs fo the Hampshire breed

Cause: Genetic predisposition for a particularly high glycolytic potential: defect in the RN gene

Characteristics: Late postmortem pH is too low, low water-holding capacity

Question 11

Properties of PSE and DFD meat
(p. 43)

Answer 11

PSE
Taste: partially changed
Water holding capacity: bad, therefore appears exudative, higher weight loss during thawing, cooking etc.
Curing suitability: Changed; takes up more curing brine, sometimes spotty coloration
Emulsifying properties: reduced
Shelf life: normal

DFD
Taste: normal sour taste is missing
Water-holding capacity: very good, low weight losses
Curing suitability: Reduced; low uptake of curing salt and unfavourable coloration properties
Emulsifying properties: finde
Shelf life: Clearly reduced

Question 12

Suitability of PSE meat for processing

Answer 12

Fresh cuts: limited suitability

Scalded sausages: suitable, when PSE meat is mixed with other meat

Raw cured meat: limited suitability
Raw sausages: not really suitable

Cooked cured meat: not suitable

Question 13

Suitability of DFD meat for processing

Answer 13

Fresh cuts: limited suitability

scalded sausages: high suitability

raw cured meat: not suitable

raw sausages: not suitable

cooked cured meat: suitable

Question 14

cold shortening / thawing rigor types of meat

Answer 14

Occurrence:
Cattle/lamb (cold shortening)
Dissection of warm pig/lamb carcasses (thawing rigor)

Cause:
Cold shortening: too rapid chilling; inhibitiom of the backflow of Ca from sarcoplasm by cold temp and still available ATP reserves
thawing rigor: Start of rigor mortis not before thawing

Characteristics: very tough because of muscle shortening (shortening of sarcomere length)

Question 15

musty ageing type of meat quality defects

Answer 15

Occurrence: insufficient chilling after slaughter (wildlife, on-farm slaughter)
high summer temperatures
lont time period between death and recovery
too late devisceration; dirty carcasses
transport without chilling

Cause:
Particularly extensive decline of pH associated with heating
no result of microbial activity
formation of butryc acid, H2S and porphyrines instead of lactic acid

Characteristic:
Sour-pungent to foul and musty flavour, coppery, red-brown discoloration
fragile meat structure

Question 16

Punctual bleeding type of meat quality defects

Answer 16

Occurrence: chops and shoulder (mostly) of pigs

Cause: broken backbones as a result of electrical stunning

Characteristics: not for sale due to non-appealing appearance

Question 17

Indirect traits realted to the water-holding capacity of meat
(trait and measurement methods)

Answer 17

pH, pH Meter

Conductivity, conductivity measurement device

meat luminosity, lab photometer; Göttingen photometer

Meat colour, lab photometer

Reflexion, Fat-o-Meat’er (FOM; carcass grading device)

Question 18

Direct traits related to the water-holding capacity of meat

Answer 18

without external influence:
Drip loss, determination of the drip loss in the refrigerator from a free hanging nylon bag

ageing loss, weighing before and after ageing

water uptake capacity, measurement of the spontaneous water uptake of meat

emulsifying capacity, measurement of the water uptake of meat homogenate

under pressure conditions:
loss under pressure, filter paper pressing method
loss when centrifuged, centrifugation with or without sieve

under cooking conditions:
cooking loss, weighing before and after cooking (boiling, grilling)

Question 19

Suitability of indirect and direct methods to assess the water-holding capacity of meat

Answer 19

indirect: fast postmortem identification of abnormal meat quality

direct: determination of the really relevant criterion; stepwise changes can be measured

Question 20

Requirements of indirect and direct methods to assess the water-holding capacity of meat

Answer 20

indirect:
high correlation with the true water-holding capacity and the “ideal” trait
can be performed at slaughter plant; fast, easy, well reproducible
can be done without or minor damaging of the meat at the slaughter plant
minimum waiting period 40 to 45 min postmortem with all methods

direct:
application of a strictly standardised protocol: sample shape and size, intensity and time of treatment, environmental conditions, terminal temperature
fast, well reproducible; close correlation with other methods

Question 21

Application of indirect and direct methods to assess water-holding capacity

Answer 21

indirect:
Applied in slaughter plant routine: pH, FOM, Conductivity (all 45 min)
Used for quality assessment especially in label programs
used for scientific studies

Direct:
rarely; routine control of the water-holding capacity
used in scientific studies

Question 22

Effects of genetics on the frewuency of meat quality defects and water-hoding capacity
p.69

Answer 22

Differences between breeds and breeding lines

Gender differences

Differences between body sites

Heritabilities (in pigs) rather low (0.1 - 0.3)

Selection

Genetic correlations

Age at slaughter

siehe s. 69

Question 23

Strategies for reduced frequency of DFD in pigs

Answer 23

Short transport distances, fasting period not too long
careful handling during transport and slaughter
dimmer light (less fights)
feeding of cachectic animals e.g. with carbohydrates (difficult at the slaughter plant)

Question 24

effects of chilling, ageing period, treatment and cooking method on frequency of meat quality defects

Answer 24

chilling:
weight losses by inappropriate handling
pig: reduced frequency of PSE by fast chilling
cattle, duck: increased water loss by cold shortening caused by too intensive chilling

Ageing period:
increasing water loss; effect of PSE gets smaller with increased water loss

treatment:
in meat processing, e.g. changes in pH, addition of salt etc.

Cooking method:
Type and duration, initially high temperature cooking