Proteins are a component of food products, either because they are naturally present, or because they have been added for a specific reason. The consumption of proteins is required as part of basic health. Beyond this essential requirement, various amino acid-based ingredients can be added to foods to improve specific aspects of our health and well-being. Proteins are also added to food to function in a manner that improves texture. By understanding protein chemistry and the environments the molecules will encounter, the final food product properties can be controlled.
Proteins from Many Sources
Proteins come to us in many forms from different plant and animal sources. In Prepared Foods’ Food Master, categories of protein (and peptides) include bovine milk proteins, casein hydrolysates, lactoferrin, milk protein concentrate and rice protein, among others. Individual listings include those for soy proteins, milk proteins, gelatin, a variety of forms of egg-based ingredients, numerous enzymes, gluten and so on.
Dairy proteins have been developed into a range of ingredients far beyond the milk from which they came. Eggs are another staple source of protein and have a long history of use in food products for their functionality. Today’s formulator has many options of egg products, beyond just an egg in the shell. Soy is a newer protein source, but the protein from this plant has been thoroughly studied and comes in many different forms. The processing that has been done to obtain the protein from the matrix from which it is naturally derived will determine how the ingredients will function. Another aspect to consider is the physical nature of the ingredient--liquid, dry (granular or powder), frozen, shelf-stable, etc. Choosing a protein-based ingredient for one’s application is a daunting task. Functions of proteins to build the structure of food products are listed in the chart “Soy Protein's Functional Characteristics.”
Proteins from other sources, besides soy, can have similar functionality. Knowing what one wants the label to look like, what the product characteristics will be and understanding how processing conditions will influence the behavior of the ingredients will help get the final product just right.
Often in food products, it is the proteins in the form of enzymes that can be the most useful, or detrimental, to a food product. Foods that utilize microorganisms (bacteria or yeast) will have enzymes present that are a byproduct of their metabolism. Proteases and lipases react with cheese protein and fat, determining the final texture and flavor. Enzymes are available for purchase to control characteristics of a food. Some 36 categories of enzymes are listed in the Food Master, a number with numerous suppliers. By understanding how the enzymes work and how their environment influences them, their effect on the food product can be controlled.
The Effect of Proteins on Texture
Proteins are composed of amino acids held together by peptide bonds. The composition of the side chains makes each amino acid unique, determines the acid or basic nature of the protein, and controls the higher levels of structure. The basic, or primary, structure is the order of the amino acids. Next is the secondary structure, which is the shape of the protein molecule, often a helix. This helix becomes ordered in space to form the tertiary structure, which is held in place by other kinds of bonds (e.g., hydrogen, covalent, disulfide, hydrophobic interactions). Finally, the quaternary structure is the formation by various polypeptide chains.
Denaturation is the term used to describe the usually irreversible changes in the structure of the protein, but not breakage of a peptide bond. There are many environmental factors that can denature proteins or change their chain conformation. (See chart “Factors Affecting Protein.”) How this change occurs can determine the textural characteristics of the food. The challenge to the food formulator is to understand these factors and work with them, using the right protein ingredient with appropriate additional ingredients, if required, to alter the environment.
The effect of pH can be beneficial; for example, cheese manufacture requires a specific pH (4.6) for the casein to come out of its stable formation in milk and form curd. This is called the pI, or isoelectric point. When formulating a beverage with soy protein, an acid level near the pI will cause undesirable separation (or curd) formation. While all whey proteins are stable across a wide range of pH, certain whey protein hydrolysates have been developed which have greater clarity at the low pH--the environment found in some juice beverages. The water-binding ability of proteins is important and is influenced by pH. For example, in meat products, phosphate salts increase the pH, which results in greater retention of water with cooking and freezing and, thus, a more moist product with more desirable textural properties.
Temperature is important for all proteins and especially needs to be considered for enzymatic reactions. The rate of enzymatic reactions rises with increasing temperature. But, if it gets too high, the proteins become denatured, so the enzyme can no longer facilitate the reaction. The coagulating of egg protein in baked goods, such as cakes, contributes to their structure and tenderness. The textural characteristics of muscle proteins are very much influenced by the rate of heating and the conditions (wet or dry). When other proteins are mixed with the muscle protein, the final product can have a much different character. Recent research has shown that the addition of whey protein isolates and concentrates to a blend of white/dark chicken meat nuggets gave a preferred product over white meat alone. The soy industry has also developed new technology to allow soy proteins to enhance the juiciness of cooked, formed meats.
Because heat processing is often necessary for the shelflife of beverages, it can cause the protein to fall out of solution. Whey manufacturers have altered their protein hydrolysates so that they can stay in solution in beverages up to a level of 12%, even with retort or UHT heat processes. When considering protein ingredients, the manufacturing steps matter. If the protein is dried, heat is required to remove the water. How this heat treatment is done is critical to the final protein characteristics and how it will behave in a food system.
Bread would not be bread without the ability of gluten proteins to hold air and expand in the oven. It is the hydration of the protein during mixing and subsequent kneading that expands the protein chains. The texture is definitely unique and one that is hard to duplicate with other ingredients. For the millions of people with celiac disease, finding other ingredients that mimic wheat gluten has been a challenge. The ability of egg protein to bind ingredients together can be used in place of flour. Semolina flour provides the proteins which give pasta its texture. However, in gluten-free pasta, egg white provides the protein for the structure. A meringue utilizes the ability of egg albumin proteins to be mechanically expanded to hold air. Other proteins (such as specific components of milk protein) are also able to expand with shear energy and form a foam.
Because of their charge, ions such as Na+, K+, Ca++ or Mg++ will alter the protein’s conformation. A solution of high ionic strength is used to coagulate the collagen that forms the casing for co-extruded sausage production. In other applications, the ions need to be sequestered, because they can cause undesirable alterations to the protein structure. In some situations, the order of addition of the ingredients in a formulation is of utmost importance. Putting the protein in solution first, before the calcium source for fortification is added, ensures the protein is soluble before the cations can interfere.
The unique properties of some proteins allow them to be surface-active agents because of hydrophilic and lipophilic portions of the molecules, which permits them to stabilize oil and water emulsions. Formation of processed cheese when natural cheese is heated in the presence of phosphate or citrate salts causes a stable emulsion to form, and this resists separation upon heating. The processing conditions, the addition of salt and the inclusion of whey protein concentrates will also influence the texture of the cheese product. There are egg products that have been modified with enzymes to improve the emulsification properties, so less can be used, which reduces cost. Soy proteins are well-suited to this function, which is important in nutritional beverages.
Health Benefits of Certain Proteins
Research has already demonstrated that there is an association between soy protein and a reduced risk of coronary heart disease. Proteins are considered satiating and make people feel fuller longer, which may in turn reduce caloric intake. Scientists continue to study if there are fractions of traditional protein sources that have unique health benefits. Beta-lactoglobulin is responsible for much of whey’s gelling properties, according to Sharon Gerdes of Dairy Management Inc. Alpha-lactalbumin can be added for its unique health benefits (influence on cognitive performance, sleep efficiency and mood support during stress), but will also gel if given the right environment. Textured proteins are also available. This allows the consumer to obtain the protein from the source they want (either whey or soy) with the texture of meat, but a different nutritional profile.
Recently, domestic milk protein concentrates have entered the market. The FDA does not formally define these ingredients. The method of manufacture will determine how the concentrates function; many have a high level of solubility, so they can boost protein content in beverage applications.
Texture is a complex subject that describes the physical behavior of food. This is sometimes decided by touching food (for example, squeezing a loaf of bread) and ultimately determined when the food is bitten and masticated. Various terms are used to describe the texture of foods. (See chart “Texture Terms.”) Many of the characteristics are interconnected; when one changes, so does another, sometimes in the same direction, sometimes in the opposite direction. Texture properties can be reproducibly measured with equipment. By setting up the correct test protocol with an instrument, each characteristic can be repeatedly reproduced. Sensory panels can be trained using standards to measure textural characteristics. No matter how the food is evaluated, the terms used must be clearly defined for the food product. Government agencies, various laboratories that specialize in studying food commodities, equipment manufacturers and sensory consultants can be great resources.
Proteins are complicated macromolecules of food systems that have useful functional properties that can be critical to the composition of a food product. In particular, they can control the textural properties, which are critical sensory characteristics. When added for nutritional benefit, how they interact in the whole food system must be considered. An open discussion with the supplier, followed by experimentation in the most realistic conditions, will allow a formulator to obtain the final product desired.