Post Mortem Factors That Affect Toughness or Tenderness of Meat

The most important factors affecting tenderness are cooking methods and heat.

The heat of cooking affects tenderness in two ways:

• Heat tenderizes connective tissue if moisture is present and cooking is slow.
• It toughens protein. Meat can turns tough and dry if cooked at excessively high heat for too long.

(Wayne Gisslen , 2004)

Because high heat toughen and shrinks protein and causes excessive moisture loss, low heat cooking should be the general practice. Among the cooking method preferred are low heat roasting, broiling and simmering. For this reason, our experiment is done by frying at 150 degree Celsius.

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Rigor Mortis

To know how muscle turns into meat, we must first understand what is rigor mortis.

When an animal dies, aerobic glycolysis stops since no oxygen is available. As the muscle attempts to maintain homeostasis, muscle glycogen is metabolised via anaerobic glycolysis, thus phosphorylating ADP to supply ATP.

Anaerobic glycolysis generates lactate that accumulates, lowering the intracellular pH, so that by 24 hours post mortem the pH has fallen to an ultimate pH of about 5.4–5.7.
Muscle is highly sensitive to both ATP and Ca2+, which are both involved in the contraction–relaxation process. Consequently, as ATP levels are reduced and Ca2+ levels rise, irreversible cross bridges form between myosin head and actin. This formation is associated with an increase in toughness.
It was also reported that meat with low ph is likely to be poorer eating quality as the enzymes involved in post mortem tenderization are inhibited by the acidification. (Maltin et al, 2003)

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Juiciness of meat

The Juiciness Factor

Juiciness is a very subjective measurement. One person’s definition of juiciness may differ from the other.

Three main factors affect the perception of juiciness:

- Internal fat – Fat makes meat juicy and we all know that. Lean meat taste drier and lack succulent than of marbled meat.

- Gelatin – Converted from connective tissue in muscle, it readily binds to water molecule and holds them in meat.

- Protein coagulation – as mentioned earlier, protein coagulates when cooked and looses water. The more it is cooked, the more it contracts and forces out the moisture. Also, extreme pH may cause protein coagulation too, which we will see later in our discussion of results ( Wayne Gisslen , 2004)

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Ingredients

1 x 500mL tub of yogurt








300gm Ritz crackers





Corn oil




corn flour

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Production of chicken nuggets -- Day 1

1) Wash chicken breasts thoroughly with running water to remove any unwanted material

2) Put the chicken breasts one at a time into a freezer bag so that they lie flat

3) Bash with a roller pin until the chicken is quite thin

4) Take it out and slide into few slices and repeat with other chicken breast.

5) Separate the chicken slices into 3 parts
The 1st part - chicken slices, unmarinated into freezer bag(control)
The 2nd part - chicken slices with water into freezer bag
The 3rd part - chicken slices with yogurt

6) Store all the 3 bags of chicken slices into chiller for one day

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Production of chicken nuggets-- Day 2

1) After marinating for 24 hours, the chickens are ready to be fried. Fill the deep fryer with oil and heat the oil in a deep fryer at 150°C.

2) Put the Ritz crackers into a bag, seal the end, then bash and roll them with a rolling pin until they have broken down into little pieces

3) Placed the crushed biscuits into a wide shallow bowl

4) For chicken soaked and none soaked with water, coat them with corn flour before frying so crackers can adhere to chicken

5) For chicken soaked with yogurt, shake off the excess yogurt from the chicken slice and dip them into the crumbs. Coat them well before laying gently into the hot oil

6) Cook til the surface of the chicken turns golden brown in a deep fryer

7) Transfer them to kitchen towel to blot the excess oil

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Sensory Analysis

Acceptance testing was chosen because this is the most suitable feedback format to be used to measure the degree of likeliness of individual products. In our feedback format, Hedonic Scaling is used. Hedonic 9-point scaling format is considered the most sensitive or facial scaling. The data will be summarized using histogram.

Consumer testing is carried out to assess the acceptability or preferences for the product. It is divided into 2 categories- large, untrained, subjective consumer panel and intermediate subjective panel. The panel we chosen are from large, untrained, subjective consumer panel.

Therefore, random 20 classmates were chosen which consist of 5 males and 15 females age ranged from 20 to 22 years old.

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Results from sensory

Based on the feedback results obtained, the chicken slices marinated with water shows that, no one chose the category of dislike, 4 panels in the category of like extremely, 7 panels in the category of like very much, 6 panels in the category of like moderately, 2 panels in the category of like slightly and only 1 panel in the category of neither like nor dislike.



As for the chicken slices marinated with yogurt, shows that none choose the category of dislike, 7 panels in the category of like extremely, 8 panels in the category of like very much, 3 panels in the category of like moderately, 2 panels in the category of like slightly and none in the category of neither like nor dislike.



As for chicken slices which are not marinated with any medium, are taken as control. Therefore, we do not emphasize on the panels preferences and are not evaluated. Therefore, from the overall acceptance of colour, aroma, flavour, texture and mouth-feel, we can summarize that based on the histogram, the consumers prefer chicken marinated with yogurt.

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Discussion based on sensory

According to the sensory results
Chicken marinated with yogurt is more flavourful. It gives the chicken sweeter and hence a bit of sour taste which most of the panels found it interesting and tasty. However, they are less tender and less juicy and appear darker than control. Chicken slices are easy to cook. In split second, the texture of chicken turns golden brown. However, the taste of the crackers is overcome by the taste of yogurt when it is combined. Therefore, the sweetness of the chicken is not come from the cracker, instead is come from the yogurt. For chicken marinated with water, it appears to be more tender and juicier, but lack of flavour. The taste of the chicken appears to be sweeter because of the sweetness of the crackers. Water is chosen to marinate the chicken and compare with yogurt because we want to compare whether soaking chicken with other medium will affect the texture, the taste and other sensory values of the chicken.

To measure tenderness ..........
Scientists measure the force needed to shear muscles. The more force needed, the tougher the meat is. This is known as the 'Warner-Bratzler shear force test'. It's units of measurement are kilograms of force needed to shear a 1 cubic centimeter muscle sample. The other method used is a straight sensory panel test, where ordinary people eat the meat and record their perception of it's tenderness. The latter method is used in our experiment. Likewise, the same method was used to measure the juiciness (Maltin et al, 2003)


Based on our results,
untrained panels were chosen and feedback is done in an uncontrolled condition, hence, it may not be that accurate. The results can be affected simply by physiological and psychological factors of the consumers.

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What happen Chicken marinated with pure water ???

Chicken marinated with pure water appears more tender and juicy, but lacks the flavor

If the meat is submerged in water, a physical and chemical process called osmosis will cause the meat to absorb the liquid.

Osmosis is the flow of water molecules from high water concentration to low water concentration.

In effect, osmosis causes the water from the outside to enter the meat and dilute the fluids in an attempt to equalize. At the same time, some of the fluids inside flow out. The end result is that osmotic pressure swells the meat with moisture. This produces a more tender and juicy meat.

Also, the increase juiciness is because water binds with gelatin and holds them in meat.

The lack of flavor can be attributed to diffusion of salt and other flavor molecules present in the chicken to the water solution (Exploratorium, n.d).

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What happen when chicken meet with yogurt???

Chicken marinated with yogurt is more flavorful, but less tender and less juicy and appears darker than control.

Why???

More flavorful and appears darker than control.

Yogurt contains:
- sweeteners provides the sweet taste
- lactic acid bacteria as starter culture for fermentation

Yogurt marinated meat has higher flavor. This may be due to the sweeteners present in yogurt. When poultry is cooked, flavor develops from sugar and amino acid interactions. This flavor development is due to Maillard reaction. The Maillard reaction occurs due to the denatured proteins on the surface of the meat interact with the sugars present which produces the "meaty" flavor and changes the color. This explains why yogurt marinade meat appears browner.

Less tender and less juicy than control.
The less tenderness is due to the high amount of LAB in yogurt creates a low pH and high LAB counts. This low pH causes protein in muscle to coagulate and contracts, forcing the water out of the meat. But if the protein is in a very acidic marinade, such as in our yogurt marinade, the protein bonds tighten, water is squeezed out, and the tissue becomes tough. It was also reported that meat with low ph is likely to be poorer eating quality as the enzymes involved in post mortem tenderization are inhibited by the acidification.

A related factor influencing water binding, and juiciness is meat pH. The rate and extent of pH decline during rigor development in muscle can influence myofibrillar protein functionality, thereby altering meat tenderness, color, WHC, and meat protein binding ability. As rigor develops, myosin combines with actin to form actomyosin. Actomyosin, although not a poor water binder, is not as good as myosin and not as readily solubilized. Additionally, lactic acid accumulates and muscle pH drops to 5.6 or 5.7 in normal tissue. As pH declines during rigor, there is an efflux of fluid from the myofibrillar space caused by the decrease in negative electrostatic repulsion between filaments. As rigor is resolved, the muscle pH approaches the isoelectric point for the myofibrillar proteins, which is approximately 5.1. Decreased WHC occurs because actin and myosin are near their isoelectric point in postrigor meat, and the net charges on the protein will be a minimum, as will space between filaments for water to be held or bound (Alvarado^, and S. McKee, 2007).

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References

1. Alvarado^,1 and S. McKee, 2007. Marination to Improve Functional Properties and safety of Poultry meat. Journal of Applied Poultry. 16:113-120

2. Charlotte Maltin*, Denis Balcerzak, Rachel Tilley and Margaret Delday, 2003. Determinants of meat quality: tenderness. Proceedings of the Nutrition Society (2003), 62, 337–347

3. Wayne Gisslen , 2004. Essentials of professional cooking. John Wiley and Sons Publications.

4. Exploratorium, n.a. What gives meat its flavor. http://www.exploratorium.edu/cooking/meat/INT-what-makes-flavor.html

5. Yohan Yoon, Avik Mukherjee, Keith E. Belk, John A. Scanga, Gary C. Smith and John N. Sofos, 2008. Effect of tenderizers combined with organic acids on Escherichia coli O157:H7 thermal resistance in non-intact beef . International Journal of Food Microbiology Volume 133, Issues 1-2, 31 July 2009, Pages 78-85

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