From meat to muscle

1. Breaking down meat
The process begins in your mouth with mechanical digestion of food: your teeth cut, shred, and mash the steak into smaller particles. Mix with saliva to form a semi-solid mass.

2. Digesting Protein
Once swallowed, ground beef travels down the esophagus and lands in the stomach. Here, enzymes such as pepsin chemically break down the steak into amino acid chains. The whole mess is now more like a liquid called chyme.

3. Create usable portions
Chyme passes from the stomach into the small intestine. Here, additional enzymes—trypsin and chymotrypsin—act on the amino acid chains, breaking them down into smaller parts until only single and double amino acids remain.

4. Preparing for transport
The amino acids are then transported through the cells of the intestinal wall and into the bloodstream, a process called absorption. They are now ready to be sent through the blood vessels to your muscles.

5. Strengthen muscles
After the amino acids reach the muscles, they will be transported to the cells through capillaries. There, amino acids help repair damaged fibers. In fact, muscle protein synthesis won't occur unless the amino acids are readily available - all the more reason to eat some protein with every meal.

Overview

1. Animals are slaughtered.
2. When oxygen is depleted, metabolism switches from an aerobic state to an anaerobic state.
3. Glycogen is converted to lactic acid, lowering muscle pH from ~7 to 5.6.
4. Creatine phosphate (rephosphorylates ADP to ATP) and ATP decrease.
5. Without ATP for relaxation, myosin heads form tight bonds with actin.
6. The muscles enter rigor mortis.
7. Protein hydrolysis begins, causing muscles to become tender.

The isoelectric point of muscle and its pH value

• Greatly affects water holding capacity
• Water Holding Capacity WHC – The ability of meat to retain moisture under external forces such as cutting, heating, grinding or pressing.

Calpain and calpain inhibitors

• Calpain degrades proteins during colder aging
• The role of calpain inhibitors in inhibiting calpain

Thus, if an animal has higher levels of calpain, calpain activity is lower, and colder aging has less of an effect on muscle tenderness. Brahman cows are naturally tougher due to higher levels of calpain.

PSE and DFD muscles

• Poultry and pigs carry one or two genes for malignant hypothermia (halothane)
• The muscles of these animals tend to be pale, soft, and exudative (PSE).
• Antemortem stress often increases the severity of PSE.
• The pH value of the muscle drops rapidly and the body temperature rises, resulting in pale meat, soft texture, and water exudation.
• The negative impact on consumer sales appeal and shrinkage is greatly increased.
• PSE can be induced in animals without halothane

Dark, firm, dry (DFD) meat

• Caused by glycogen shortage at slaughter (chronic stress).
• If there is not enough glycogen converted to lactic acid, muscle pH will remain high, near 7.0 (living muscle pH)
• Antemortem stressors can lead to DFD.
• Results in excessively dark muscle color, firm texture, and dry muscle surface (opposite of PSE muscle); sweeter.
• Beef has the most DFD problems.
• Rare among poultry

Thaw the severe event

The muscle is frozen before rigor mortis (a phenomenon in which muscles contract after death) occurs: ATP has not been used for rigor mortis events and will be high when muscles are frozen.

Freezing damages the sarcoplasmic reticulum (SR).

When thawing occurs, calcium is released from the sarcoplasmic reticulum, causing massive contractions due to higher ATP levels. The result is toughening.

Cold shortening

• A similar event occurs when cold muscles shorten but do not freeze (rigor mortis occurs at freezing temperatures below 15°C – 16°C b/f).
• Because it cools too quickly, the sarcoplasmic reticulum cannot retain calcium.
• While ATP is still available, the muscle contracts.
• Electrical stimulation consumes ATP during contraction, helping to prevent cold shortening.

Thermal Loop

Occurs in thin-skinned carcasses (lean carcasses that have not been cooled properly).

Beef carcasses require at least 0.25 inches of backfat, while lambs require at least 0.10 inches of backfat.

The outer ring of the muscle becomes cold too quickly

• Glycolysis rate is slow
• The pH value decreases slowly
• It takes longer to develop rigor

The result is an unwelcome ring around the muscle that is darker in color and rougher in texture.

Blood splatter

• Caused by ruptured capillaries, usually between periods of stun; blood pressure spikes after stunning.
• The result is small blood spots in the muscles; the most common problem is in pigs and poultry.
• Stunning: Too long a time between sticks will cause blood splashing, and the excitement before stunning will also cause blood splashing.
• If it is fat, it is called "fire fat".
• Quality Solutions

Electrical stimulation

• Electricity makes fire "exceptionally" soft.
• Running an electric current through the body causes the muscles to contract and consume ATP...thus, inducing rigor mortis.
• Reduce hot rings and cold shortening and may increase tenderness of lower grade carcasses.
• Brighter muscle color will better show marbling.
• ES will improve overall carcass quality

Hot deboning

• Hot deboning is ideal because hot bones have a higher water-holding capacity.
• Prevents rapid decline in muscle pH.
• Without skeletal restraint, muscles will shorten and become tougher if they are put through the rigors rather than grinding.
• Intramuscular injections of salt and PO4 can reduce tenderness problems.

Delayed freezing

• After trimming, let the carcass sit at room temperature for 2 to 4 hours.
• There is a microbiological problem.
• The higher the temperature, the faster glycolysis occurs, ATP is used up, and cold shortening is prevented. Aging speed is accelerated.