Protein dependent quality traits and water holding capacity Flashcards
Particularities of proteins in animal-source foods
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)
What are the mors important proteins of muscles and fat tissue? (Meat proteins)
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
What are struxtural elements of the muscle?
Muscle fibre
Glycogen reserves
Connective tissue covers
Function of the muscle
p. 21 + 22
What are two parts of physicochemical meat quality
water holding capacity / water binding capacity (extent to which tissue is intact)
Texture (mechanical resistance / structural state)
Meat quality defects
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
Kinds of meat quality defects
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
PSE type of meat quality defects
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)
DFD type of meat quality defects
(dark-firm-dry)
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
Acid meat type of abnormal meat quality
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
Properties of PSE and DFD meat
(p. 43)
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
Suitability of PSE meat for processing
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
Suitability of DFD meat for processing
Fresh cuts: limited suitability
scalded sausages: high suitability
raw cured meat: not suitable
raw sausages: not suitable
cooked cured meat: suitable
cold shortening / thawing rigor types of meat
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)
musty ageing type of meat quality defects
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
Punctual bleeding type of meat quality defects
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
Indirect traits realted to the water-holding capacity of meat
(trait and measurement methods)
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)
Direct traits related to the water-holding capacity of meat
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)
Suitability of indirect and direct methods to assess the water-holding capacity of meat
indirect: fast postmortem identification of abnormal meat quality
direct: determination of the really relevant criterion; stepwise changes can be measured
Requirements of indirect and direct methods to assess the water-holding capacity of meat
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
Application of indirect and direct methods to assess water-holding capacity
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
Effects of genetics on the frewuency of meat quality defects and water-hoding capacity
p.69
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
Strategies for reduced frequency of DFD in pigs
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)
effects of chilling, ageing period, treatment and cooking method on frequency of meat quality defects
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
