Composition of Protein in Meat
Proteins are the main component of meats and are also found in the bones and knuckles in the form of
cartilage. The building blocks of proteins are amino acids and all proteins are made of chains of amino
acids. These chains can vary greatly in length, shape and complexity. There are about 21 or 22 amino
acids depending on who you talk to. Think about the letters of the alphabet; there are 26 letters in the
alphabet and look at how many words we can make with 26 letters. So, think about how many proteins
can be made with 22 amino acids. Not all animal proteins contribute equally to the preparation of a
stock. It is important to understand the different proteins and their basic composition in order to
manage them during the production of quality stocks. Let’s take a look at how the different types of
protein contribute to, and detract from, the production of a quality stock.
The Structure of Animal Proteins
You can find out more about proteins in the nutrition section where you will see that the building blocks
of protein are amino acids.
Animal proteins can be grouped into three main types: oxygen-carrying, muscle tissue, and connective
tissue. Within each of these three types we will further categorize these proteins and discuss how each
subgroup impacts the characteristics of a stock. Choosing appropriate ingredients and cooking
procedures will enable you to produce a stock with excellent body, colour, clarity and flavour.
The three main types of animal proteins and their relative proportions are shown in the table below.
Oxygen Carrying & Storing Proteins
(water soluble)
hemoglobin
myoglobin
albuminoid
etc…
(approx. 30%)
Muscle Tissue
(fiber)
Connective Tissue
Fibrils

(myosin + actin)
elastins
reticulins
collagens
(approx.50%)
(approx.20%)
Oxygen Carrying & Storing Proteins
Hemoglobin and, myoglobins are basically the red protein in muscle tissue. They carry and store the
oxygen to produce energy. If you want to picture these proteins, think about a drop of blood that gets
dropped into water. The water will turn pink. You can see the blood that will dissolve into the water and
the water itself will turn pink to the point of being red. If you were to heat that water, that blood will
turn gray and adversely affect the clarity of a stock.
Muscles that receive sustained activity, like the muscles of a cow or the breast of ducks or geese, or the legs of
chickens are called slow-twitch fibers. In order to keep activity at appropriate levels, the muscles need a
constant supply of oxygen.
Myoglobins is a protein that stores oxygen in the muscle cells and has quite a bit of pigment, resulting in a
darker colored muscle.
Note: fast-twitch muscles (in general white meat) rely on glycogen, a polysaccharide of glucose (sugar), as
an energy source; they don’t have the myoglobin pigment
. So,. I tell a story.
These proteins are very short and will dissolve and stay suspended in water and cause the stock to be
cloudy. Because clarity is one of the main characteristics of a well made stock we need to do eliminate
or remove these proteins.
The albuminoids (or albumen) commonly found in egg white is also found in bones, meats and other
foods. These proteins play an important role in the clarification process. They tend to be much longer
protein chains than hemoglobin and myoglobin which are very short. These proteins are also water
soluble.
If we were to look at the protein (chains of amino acids) through the microscope, we would see the
protein being all coiled up. These proteins must first be added with cold water to allow them to disperse
throughout. When the water is heated (or energized), the proteins will denature, or uncoil in a straight
line and start firming up or coagulating. In doing so, the albuminoids (long proteins) form a sort of mesh
which traps the shorter hemoglobin and myoglobin molecules (referred to as impurities).
As the stock heats up,an upward pressure is created by the rising steam bubbles, and pushes the
trapped proteins to the surface where they can be skimmed off.
Muscle Fiber (filaments)
The second group of protein is the muscle fiber. This type of protein (composed of myosin and actin)
has a rather elongated shape, which resembles fibers but should not be confused with the fibers found
in plant foods (referred to as dietary fiber). We will refer to this type of protein as fibrils. The fibrils are
the muscle tissue itself. This protein enables the muscles to extend and contract during movement.
There is more information in the text book if you are interested
Connective Tissues
Connective tissues can be further divided into three main types.
Elastins (tendons and ligaments); reticulins (veins and arteria); and collagens (connective tissue within
the muscle, silver skin and cartilages). Elastins and reticulins are very tough and will not dissolve through
the cooking process. For this raison, they are usually removed during the meat cutting or trimming
process.
Collagens play a very important part in stock making. When exposed to low heat for a long time,
collagens break down into water-soluble protein called gelatin. This is the ingredient that most
contributes to excellent body in a stock. Bones with the most collagen are from younger animals as their
bones contain a higher proportion of cartilage than bones from older animals. Specifically the bones
with the most collagen are the knuckles, shank and leg bones in veal and beef; the neck and back in
chicken. We will look at stock ingredients in more detail later in this lesson and you can look in your
textbook for recipes for different stocks.