Do you know the secrets of chicken tenderness?

The smell of succulent fried chicken wafts through the air, awakening a sensation of pure bliss. While vegan food becomes increasingly popular, the yearning for chicken’s succulence remains. Here, we unlock the secrets to chicken tenderness that satisfy any poultry lover’s cravings.

It’s a common misconception that we know our chickens better than the breeder. Well, in a way, that is true, as we are the ones who choose all the pieces with care. Cook it to perfection with all the skills we have honed over time. Still, many more parts of this chicken’s story are unknown. A chain of processes makes it tender before it can find us, and we can eat it.

Tenderness in chicken results from two primary elements: stiffness and aging. Stiffness is highly impacted by glycogen, oxygen, and muscle contraction. The upcoming sections discuss the influence of all three factors on chickens after slaughter.

Table Of Content

What makes an animal alive?

How do you say a chicken is dead or alive? It is simple if the chicken is breathing normally, moving its neck, having its heartbeat, and so on. When all these activities stop, we declare them dead.

During their lives, chickens require approximately 10 kg of food. It provides the chicken with all the essential nutrients it needs to survive. The chickens get their energy from the glucose present in the feed. This energy circulates in the body as ATP, or adenosine triphosphate. All the glucose does not go into making ATP. The spare one is stored as glycogen in muscle and liver. When the chicken is resting, the muscle breaks from all the hard work and relies on blood glucose. But as the chicken starts running, the muscle puts in all the effort and needs extra energy. It starts using glycogen for that extra energy.

Glycogen breakdown

Glycogen returns to its original form, glucose. At first, the muscle breaks down the glucose into pyruvic acids. This acid enters either an aerobic or an anaerobic pathway to generate ATP. It chooses the aerobic path when the muscle is resting. During this period, the body has a high reserve of oxygen. As the muscle starts working, the oxygen demand increases (oxygen debt). In such scenarios, the muscle generates ATP anaerobically. But the amount of ATP produced is less than that of aerobic metabolism. The muscle uses the creatine shuttle to fill the gap.

Glycogen= Glucose + abundant Oxygen = Aerobic breakdown = Carbon dioxide + Water + ATP

Glucose + Oxygen debt = Anaerobic breakdown = Lactic acid + ATP

Creatine Shuttle

Creatine always comes to the rescue of the muscle during a crisis. But it is not part of the muscular system. The liver is the creator of creatine. It travels to the muscles and becomes phosphocreatine by accepting the inorganic phosphate group. The bond between creatine and phosphate is a high-energy bond. It can store 43.3 kJ per mole of energy. The phosphocreatine gives the energy to the ADP (a low-energy form of ATP) to create a bond with one of its inorganic phosphates. A shift in the energy gradient happens from PC to ADP to ATP.

Creatine + Pi = Phosho-(43.3kj/mole)bond-creatine= PC + [ADP + Pi] = [Creatine + Pi] + ATP

Muscle Contraction and relaxation

When do the body’s muscles contract? I asked one of my cousins this question, and he replied, “Dude! when I flex my muscle in the gym.” He didn’t stop there, and he flexed his biceps in response. I laughed and had to give this reason.

Muscle contraction and relaxation happen every time. The time when you are trying to stand or sit. When holding that morning coffee mug, the muscle won’t put in that effort. These actions are, most of the time, involuntary. The challenge starts when you are on a fitness spree and decide to cycle daily to work. The muscle starts working to make that happen for you.

If you see it from the chicken’s perspective, it’s the same for them. During the struggle, high muscle activity is observed. Before we get into muscle contraction and relaxation, let’s talk about muscle fiber and the architect. In the section below, we will discuss the skeletal muscles, as they are the ones we eat. The smooth muscles are removed during processing.

Muscle Fiber in Skeletal Muscles

Imagine a long power cable. How do you define it? It is a cylindrical tube with several cables inside, each carrying many wires. A muscle is a collection of bundles of fascicles. These are bundles of muscle fiber. So, the muscle fibers are like wires encased in tiny cables or fascicles. These collectively form the power cable or the muscle.

Muscle fibers are multinucleated cylindrical muscle cells, meaning they have many nuclei. It also contains the protein fibers myosin and actin, together called myofibrils. These two play a crucial role in the contraction and relaxation of muscles.

Myosin is the thick filament. It looks like a log of wood with mushroom-like growth on it. These are the heads of myosin. Actin is a thin filament. It appears to be one parallel line drawn above the other.

Contraction

The myosin head has two attaching sites. One for the actin and another for ATP or ADP + Pi. Myosin forms a bond with actin, where ADP and Pi are still attached to the head. This bond is the cross-bridge. When the cross-bridge formation starts, the ADP + Pi leaves the second site. The myosin-actin bond becomes more robust. The myosin head moves and pulls the actin toward it. The myofibril shortens. This causes the muscles to contract.

Relaxation

The relaxation phase occurs when the cross-bridge between actin and myosin is broken. The ATP attaches to the second site of the head, and myosin releases the actin. Then ATP transfers the energy to the myosin head and reduces itself to ADP and Pi. The charged myosin head restarts the process. The cross-bridge remains in place if the ATP fails to connect to the head. The myosin-actin bond never breaks down.

The same explanation goes for the rigor mortis. You will find out in the next section.

How does a Rigor mortis affect tenderness?

After the slaughter, a gradual stiffness develops in the chicken’s muscles. The changes won’t be visible suddenly, but it takes a few hours for the process to complete. Stiffness, also known as rigor mortis, occurs within three hours of chicken slaughter.

It has four stages: delay, rapid, post, and resolution.

In delay, the glycogen breakdown continues, and ATP is available for the myosin. After the slaughter, most blood drains out of the blood vessels. So, there remains no blood to provide oxygen. As the oxygen level drops, the glycogen breakdown switch to an anaerobic process.

Rapid phase, the muscles use all the glycogen for the ATP, and there is no more glycogen or ATP, left to release the cross-bridge.

The number of cross-bridges increases and the myofibril is stuck in the contracted phase. When enough myofibrils contract, the muscle toughens and reaches the peak of rigor mortis. It is the post-rigor stage.

The resolution comes much later when the lysosomes feed on the contracted myofibril. It breaks the cross-bridges, and the muscle again gets pliable. The resolution stage breaks down muscle protein, fat, and other pigments.

Effect of Lactic acid on Rigor Mortis

Lactic acid is produced in large quantities during rigor mortis. This increases the acidity of the muscle. We will take the pH as the unit of measurement for the acidity. The higher the acidity, the lower the pH, and vice versa. If the food is neither acidic nor alkaline, it is neutral, and the pH stands at 7. For sour, it is below 7; for alkaline, it is above 7.

Until the post-rigor, the muscle pH drops to 5.6 from 7 or above. As the pH gains a value of 6.5 somewhere in the middle of the rigor mortis stage, one of the phosphates enzymes degrades phosphocreatine and ATP. It makes them unavailable to form energy bonds. This could be another reason for the less ATP.

Resolution or Aging

After slaughter, it takes 12 to 24 hours for the chicken to regain flexibility. The drop in pH causes a series of changes in cells. The trigger of enzymatic digestion is the one that causes protein breakdown. Once the protein loses its strength, the water-holding capacity also goes down. The water is bound to the protein network. As the web is disturbed, the bonds become weak. The ability of meat to hold water is essential in determining whether it is tender or tough. However, too much holding can cause the meat to become dry, and too much dripping can make it leaky. It can become one of the defects of the meat.

Which defects can alter the tenderness of meat?

It amused me that chickens can go through stress as well. They can be temporary or permanent. It’s also worth noting that these stress levels have an effect on glycogen storage. The chicken is starved for 12 hours to adjust the glycogen level and achieve the desired rigor mortis. As a result, the glycogen content of a slaughtered chicken is already lower. Any additional stress can change the status and cause an abnormal breakdown.

Pale, Soft, and Exudative Meat (PSE)

When a chicken faces stress, like struggle before slaughter or during handling gives rise to PSE. They start showing an abnormal rate of glycogen breakdown. As a result, the pH drops fast.

The pH of a well-rested, healthy chicken requires a minimum of 6 hours to reach 5.6. In a PSE chicken, the reaction accelerates by many folds. The pH reduces within an hour. The lower pH accelerates the protein breakdown. It occurs before time. The meat loses its water-holding capacity. The broken-down protein starts leaking into the water. The meat appears soft, exudative, and pale.

Upon cooking, the PSE meat shrinks and is hard to bite.

Dark, Firm, and Dry Meat (DFD)

This condition arises when the birds face stress for an extended period. It may happen during long transportation or a prolonged struggle. These reduce the glycogen reserve before slaughter.

The glycogen reserve depletes to such a level that the pH never increases above 6.5 or 6.8. This low pH hinders the normal process of protein breakdown. As a result, the protein becomes more rigid, and the water becomes wholly trapped within. The surface becomes dry due to a lack of drip. The meat appears dry, hard, and dark in color.

Cold Shortening

The myofibrils get shorter than usual if the meat is chilled before post-rigor. There are a vast number of cross-bridges. It makes the meat very tough. The chilling must be done after the chicken has fully attained its rigor mortis state.

What are connective tissues, and how does it affects tenderness?

The connective tissue is the casing that holds the bundles of muscle fibers. Collagen, elastin, and ground matter make up each connective tissue. Collagen gives strength, and elastin is for elasticity. The amount varies depending on the type of connective tissue. Collagen is more abundant in muscles and forms interconnections. It increases with the age of the bird. The more collagenous linkages there are, the tougher the meat is. During the resolution period, these break down and decrease the number of linkages. Thus, the tenderness also depends on how much collagen linkage exists after rigor mortis.

The secret to tender chicken meat is the achievement of a proper rigor mortis graph coupled with perfect aging. But one should not leave behind the water-holding capacity of the meat. Too little or extremely leaky meat is not acceptable. I hope next time you can explain why your meat is more tender than your neighbor’s. But ensure it’s from a good manufacturer who can take care of PSE, DFD, and shortening.