Healthy eating is a topic of conversation and objective for many populations and many market segments. Foodservice professionals, Registered Dietitians, Certified Dietary Managers, and chefs in all walks of food service understand that a healthy diet means focusing on high quality foods while maintaining a healthy balance of all of the food groups.
Optimizing the balance of macronutrients in the daily diet – carbohydrates, fats, and proteins – is a cornerstone of healthy eating. This course offers you a focus on proteins and their role in the diet, along with a basic understanding of protein composition and chemistry.
The high quality protein in eggs can support a variety of nutritional needs among nearly every demographic segment. It’s a good fit for many states of health, including for weight management, diabetes, fitness, healing and growth, and healthy aging.
Understanding egg science helps you tap into the nutritional benefits of eggs. It also helps you understand how to cook eggs and work with egg protein effectively for superb culinary results. The companion CE course from Michael Foods, Inc., Kitchen Science: Egg Culinary Techniques, provides culinary tips and techniques for cooking with eggs.
After completing this CE course, you’ll be able to:
Everyone knows that proteins are important. Cereal boxes and energy bars advertise protein for “building strong bodies,” “satisfying hunger longer,” and “long-lasting energy”.
While the marketing message from food organizations has many different implications from a dietary standpoint, what they all can agree on is that protein is important in the diet. Protein is critical to health in all phases of life from infancy through old age. Why?
Every cell in the human body contains protein. Next to water, proteins are the most abundant substance in a cell. Proteins typically account for almost 15% of a cell’s overall mass.
How much protein do we need? The Recommended Dietary Allowance (RDA) for healthy adults is 0.8 g per kilogram of body weight, generalized as 46 g/day for women and 56 g/day for men. The Institute of Medicine suggests an Acceptable Macronutrient Distribution Range (AMDR) of eating 10-35% of total calories in the form of protein, which can translate into higher numbers. For example, on an 1800-calorie diet, 35% of calories as protein is 158 g/day. The average American eats about 16% of calories as protein.
At the Protein Summit 2.0, more than 60 nutrition and health experts convened to explore dietary protein recommendations. They estimated that eating approximately twice the RDA may be advisable for weight management and a variety of health needs. And for older Americans, they noted that protein intake, along with exercise, has an impact on preventing muscle loss during aging. A science-based recommendation is 15-25% of calories as protein.
Note that someone with high physical activity or various health conditions may need more (or less).
A wide variety of proteins are essential for building and repairing tissues throughout the body. Some of these proteins are in solution in the blood and other fluids of the body, and some are in solid form as the framework of tissue, bone, and hair.
Proteins are major components of muscles and key to the work of muscles. Proteins also play a key role in immune function and in the acid-base balance in our bodies. Specialized protein molecules are important for digestion and a variety of chemical reactions throughout the body. Protein molecules help transport drugs, vitamins, and minerals throughout the body. And let’s not forget that protein is a source of energy (which makes it a macronutrient), and can assist in weight management.
Whereas the body can put away stores of excess carbohydrate and fat, this is not true for protein. For protein to function as we need it, the body needs a daily supply.
To learn more about egg nutrition, watch “Nutrition experts highlight protein” from the Egg Nutrition Center on YouTube.
A protein is a chemical compound that is similar to carbohydrates and lipids (fats). Every protein contains atoms of carbon (C), hydrogen (H), and oxygen (O). But what makes protein molecules unique is that they also contain nitrogen (N) atoms. Protein contains almost 16% nitrogen.
Proteins are composed of amino acids, which are smaller organic (life-based) chemicals that always contain nitrogen. Amino acids are linked together in many different ways to make proteins. It’s easiest to think of amino acids as the “building blocks” for the nearly 10,000 different proteins our bodies need to function.
Small chains of amino acids are called peptides. Large chains of (many) amino acids are called polypeptides. Protein molecules can indeed be very large, stringing together many amino acids.
When we eat protein, our bodies digest the protein into amino acids, and absorb these amino acids into the bloodstream. Within our bodies, many metabolic processes come into play, building the various proteins we need from these amino acids. Fortunately, we do not need to consume every specific protein we need; we only need to consume the building blocks so our bodies can get to work.
In all, there are 20 different amino acids our bodies use to build proteins. Some are essential, and some are non-essential or conditional.
An essential amino acid is a building block we must include in our diets. Without this essential compound in adequate amounts, we can’t produce all the proteins we need. Essential amino acids earn their name because they are essential in our diets. Nine of the 20 amino acids are essential.
A non-essential amino acid is one our bodies can make through its own chemical reactions. The body can convert other amino acids into these crucial building blocks for body proteins.
Some amino acids are called conditional, meaning they are not usually essential, but can become essential when the body is under stress or in a state of illness.
As you can imagine, it’s important to include varied sources of protein in the diet, and to ensure that we eat enough of each essential amino acid to maintain strong protein nutrition.
Every food has its own complement of amino acids. In general, animal foods tend to be excellent sources of all the essential amino acids. The amino acid profiles of plant foods vary.
We don’t need to consume all essential amino acids from a single food. The body breaks down all the protein we eat into its own “pool” of amino acids. It draws from this pool to build the proteins we need.
A food that provides significant amounts of all the essential amino acids is said to provide complete protein. This is also called high quality protein, offering a complete complement of essential amino acids. In general, animal foods provide complete protein. Think of meat, seafood, milk, cheeses, yogurt, and eggs.
A food that lacks one or more of the essential amino acids is called an incomplete protein source. Generally, grains, vegetables, fruits, and any plant-based food provide incomplete protein.
Complementary protein sources are two foods that complement each other. One may provide an essential amino acid that another lacks. In the diet, then, all the essential amino acids are present. For example, beans and rice complement each other for a healthy profile of essential amino acids.
Nutrition scientists used to say we need to eat “complementary proteins” at the same time when eating foods that were not high in all the essential amino acids. Today, this is no longer considered necessary. Eating all the right essential amino acids any time during the day is effective in helping the body build the proteins it needs.
Eggs are a great example of a food that provides all the essential amino acids as a complete protein source. In addition, eggs are considered the standard for bioavailability. Bioavailability is a term that describes how well the nutrients in a food can be absorbed and used by the body. The amount of a nutrient in a food that the body actually uses or that can become bioavailable is influenced by age and physiologic conditions.
Egg protein offers nearly the highest bioavailability of protein of any food. In fact, egg protein is used as a standard for measuring protein quality of other foods.
Cooking with any high-protein food leads to chemical changes in the food’s protein molecules. These changes affect flavor, texture, and culinary quality. Basically, what happens during cooking is a re-organization of the protein molecules.
Let’s take a closer look. Remember that many protein molecules are huge. They take a three-dimensional form, first folding upon themselves, and then wrapping around to create what are called secondary and tertiary configurations. This three-dimensional form of a protein affects how it functions.
Cooking a high-protein food breaks down some of the protein’s three-dimensional form; the protein molecule changes shape and functions differently. When the protein changes form because of cooking (or other factors, such as acid), we say the protein is denatured. It is still nutritious; it may even be more digestible. But the food looks different due to a change in the protein’s form.
As an egg protein is heated, the structure of the protein reacts to the heat. As a common kitchen term, we may call eggs “scrambled”. But really what is happening is that there is a change in protein structure.
Essentially, the egg protein denatures (becomes uncoiled or rearranged) and begins to change how it bonds. Once heated, the protein coagulates or changes from a liquid to a solid. The protein structure is changing and new bonds are occurring. Some of the bonds hold the molecules together differently, transforming the egg from a liquid to a semi-solid. So scrambled eggs are simply another term for “coagulated eggs”.
To truly understand what is happening to proteins in eggs with any cooking methodology, it helps to first understand the composition of the egg. Within the very porous shell of an egg, there are two distinct components—the egg white and the egg yolk—which each behave quite differently.
The white of the egg contains close to 88% water, 11% protein, and 1% minerals. The yolk, approximately 1/3 of the volume of the egg, contains 50% water, 34% lipids (fats) and 16% protein. Because they have different compositions of water, proteins and fat, the two parts of an egg behave and react differently to heat.
Let’s illustrate protein denaturing and coagulation with an egg. When eggs are raw, they have protein strands that we call “tangled,” and interspersed in the protein molecular structure is water. As an egg is heated, the water begins to turn to steam and dissipate.
As this occurs, the protein strands unfold. They begin to stick together and form a lattice type of network. Heat causes the protein strands to align and bond together. The lattice network of protein strands can maintain the water molecules – and cause cooked eggs, for example as in scrambled, to remain light and fluffy due to the retained water.
As cooking continues and the temperature continues to rise, water is squeezed out from among the strands. At this point, an egg can quickly become dry.
For scrambled eggs, many recipes call for fat or milk. Fat can slow down the process of the proteins unfolding and allow the coagulation process to occur much more slowly. Moisture will remain with the eggs, as the protein strands do not tighten as rapidly and squeeze out the water molecules.
This same process occurs with meat. Protein is denatured or reconfigured as heat is applied to the proteins. With, for example, a steak, the protein structures unwind and then form or coagulate into cohesive bonds. The muscle tissue of meat, as it is heated, becomes more rigid, and again, water or juices are squeezed out of meat. This exemplifies how high heat can dry out either an egg or a meat protein as the proteins are denatured at high temperatures.
Denaturing of proteins is illustrated two ways. First: when an egg white (concentrated source of albumin) is poured onto a hot surface, the clear albumin begins to change to a solid that has a jelly-like consistency. This same denaturing occurs with meat juices in that when a hamburger is placed on a griddle, the clear red juices start to become brown and initially turn into brown jelly-like strands.
Protein denaturing is important from a digestive standpoint in that “cooked” proteins can be more readily digested. Digestive enzymes can work on this denatured protein more easily because the protein coils have already been unraveled (denatured).
Getting back to eggs, if an over easy egg is the entrée of choice, temperature again plays a clear role in protein denaturation.
Keep in mind that the yolk and white will coagulate at different temperatures, given their composition. Therefore, as an egg is put into production, the egg white will begin to cook and coagulate at around 142°F. Typically, the egg white will become a complete solid, close to 180°F. With the egg yolk, typically 158°F will completely solidify the yolk.
We’ve already examined how heat denatures protein. Did you know that other factors can denature protein, too? Here’s a quick overview.
|Denaturing Agent||Mode of Action|
|Heat||Disrupts the hydrogen bonds of molecules. When frying an egg, produces coagulation.|
|Microwave||Molecules will vibrate and disrupt the hydrogen bonds, similar to adding heat|
|Whipping or shaking||Think of egg meringues. The molecules will form globular shapes and extend to longer lengths.|
|Acids (e.g., lemon juice) and bases||Disruption of the hydrogen bonds and salt bridges of the protein molecules.|
|Ultraviolet radiation||Disrupts hydrogen bonds but can make molecules vibrate too violently.|
Protein is a key nutrient for people of all ages and is used in every cell of the body for a broad range of metabolic functions. Its building blocks, amino acids, can be categorized as essential, non-essential, or conditional. Nine of the 20 amino acids used by the body are essential. Protein sources labeled “complete” provide all the essential amino acids.
During cooking, the three-dimensional structure of protein molecules is changed through a process called denaturation. As it cooks, an egg—one of the best quality sources of protein—traps moisture in the new shapes the protein molecules form. Applying too much heat results in a dry egg.
Yolks, with their higher fat content, cook quicker than whites. A perfect illustration of this is an over-easy egg.
Denaturation makes protein foods more digestible. In addition to heat, microwaving, whipping or shaking, chemical factors, and ultraviolent radiation can lead to denaturation of protein.
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