AGEN2002 Lecture Notes - Lecture 6: Exudate, Glycogen, Food Safety
15 May 2018
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6. Biochemistry of meat & animal products
Þ Muscle fibers are arranged in longitudinal bundles enveloped in connective tissue
Þ Collagen is made of 3 levels of connective tissue
What happens to carcass after death?
• Tissues move from aerobic to anaerobic
• Available energy & glycogen reserves depleted
• Metabolic pumps stop working in cells & leads to
o build up of lactic acid
o pH levels drop
o [Ca2+] rise
o protease start to break down muscle proteins
o sarcomere cross bridges become ridged & carcass appears stiff
Stress affecting meat quality
• Muscle glycogen content and ultimate pH level is related
o Less glycogen = longer food withdrawal times before slaughter = increase pHu
• Dark cutters – beef carcass subjected to undue stress before slaughter
o Dark in color, appear less fresh, undesirable to consumers
o Inconsistent EQ (eating quality)
o Short shelf life
o Low WHC (water-holding capacity)
o Coarser texture
Classification of meat quality (undesirable)
PSE (pale, soft, exudative)
• Acute stress
• Rapid acidification
• Low water holding capacity
DFD (dark, firm, dry)
• Chronic stress
• Reduced glycogen
• High water holding capacity
• Food safety issues
Carcass chilling (used to preserve meat)
BUT causes muscle shortening, which impacts meat quality
• Heat shortening
o Cooled too slowly pre rigor (>20’C)
o Prolonged maintenance of energy, leads to PSE
• Cold shortening
o Cooled too quickly (<10’C pre rigor)
o Caused by mass released of Ca
• Thaw shortening
o Freezing muscle pre rigor
o Shortens by 80%
Document Summary
Muscle fibers are arranged in longitudinal bundles enveloped in connective tissue. Collagen is made of 3 levels of connective tissue. What happens to carcass after death: tissues move from aerobic to anaerobic, available energy & glycogen reserves depleted, metabolic pumps stop working in cells & leads to, build up of lactic acid, ph levels drop. [ca2+] rise: protease start to break down muscle proteins, sarcomere cross bridges become ridged & carcass appears stiff. Inconsistent eq (eating quality: short shelf life, low whc (water-holding capacity, coarser texture. Dfd (dark, firm, dry: acute stress, rapid acidification, chronic stress, reduced glycogen. Low water holding capacity: high water holding capacity, food safety issues. Muscle shortening on meat quality: causes meat toughness, caused by overlapping of sarcomeres & muscle fibers making the meat twice as thick to cut through. Literal translation is death stiffening , a process that occurs when muscle is converted to meat.
