Lecture 30: Meat Quality

What is meat quality

Properties that identify what the consumer cares about when purchasing or eating meat product

Visual components: Colour, marbling

Palatability components: tenderness, juiciness, flavour

Factors impacting meat quality

Genetics/breed

Nutrition

Maturity (age)
Animal stress (lower pH)

Post-slaughter handling → cooling, aging

Review of conversion of muscle to meat

Starts when animal is harvested

Attempt to maintain cellular homeostasis

ATP production

• Through Phosphagen system

• Glycogenolysis

• Glycolysis

Acidification of muscle

Hydrolysis of ATP → H ions produced and accumulated in muscle

Lowers pH

How energy production affects pH

Normal meat is around 5.5

DFD (Dry, firm, dark) meat is over 5.5

PSE (pale, soft, exudative) is under 5.5

Energy production in meat after slaughter

Met pH can interact with electrical charges on muscle proteins

Influences Water Holding Capacity

PI = Isoelectric point

• Number of positive and negative charges are equal

This will be lowest water holding capacity

DFD Meat

Limited energy available

pH very high and stay high

Muscle glycogen deficiency

Chronic exposure to pre-slaughter stress

Glycogen stores are used up prior to slaughter because of stress

PSE meat

Rapid metabolism immediately after slaughter

Carcass temperature still elevated

pH drops in muscle

Low pH and high temperature leads to extreme denaturation of sarcoplasmic myofibrillar proteins in muscle

Gives meat cloudly look

Preslaughter stress

Effects of stress on meat quality both acute and long term, arise from release of stress hormones → Epinephrine

Once released, hormones initiate series of biochemical reactions

Mobilize energy to meet demands of stress

Acute stress

Accelerates glycogenolysis

Rapid decline pf pH

Chronic stress

Glycogen stores consumed

Lack sources for glycolysis postmortem

Temperature

Temp of muscle immediately after slaughter affect metabolic reactions that critically impact two meat quality development

Associated with low muscle temperature prior to onset of rigor mortis

• Thaw Rigor

• Cold-shortening

Temperature and Ca release

Colder temp causes changes is capacity of sarcoplasmic reticulum to control Ca in sarcoplasm

Causes Ca to stay stuck is SR

If it occurs before all glycogen is depleted, more severe contraction

Causes more long lasting contracting because Ca is stuck

Thaw rigor

Muscle frozen before going into rigor mortis

Then thawed (glycogen is still present)

During freezing

• Ice crystal form

• Crystals damage sarcoplasmic reticulum

When muscle saws, damaged SR releases a lot of Ca

Causes greater muscle contractions because glycogen still present

Tougher meat

Cold shortening

Meat chilled to quickly before rigor mortis

Ca will leak out of sarcoplasmic reticulum

Ca builds up in muscle cell

ATP still available

Muscles will contract but cant relax properly

Less severe than thaw rigor

Tougher meat

Cold shortening

Red muscles are more likely to cold shorten

• Because less developed SR

White muscles

• Better developed SR

Beef and lamb have less fat so they cool down too quickly

Pig carcass has more fat

How electrical stimulation help prevent cold shortening

Electrical stimulation makes muscle use up ATP quickly

Break down glycogen faster

Glycogen is used up and no ATP left

Stop the strong contractions

Aging: Meat

Let meat rest after slaughter to make it more tender

Between slaughter and eating

Done in the fridge

What makes meat tender

Proteolysis

Proteins get broken down into smaller constituents → Polypeptides or amino acids

Aging and proteolysis of myofibril

Myofibrils weaken

Breakage or structural damage near Z line in I band