February 1, 2000
Understanding Process Cheeses
By: Kimberlee J. Burrington
Every product developer loves a cheese that performs exactly the way they want it to in a specific application. Not only does that cheese consistently melt when required, but it also has a uniform cheese flavor and texture. Imagine, for example, a cheese that melts, but doesn't flow, spreads at cold temperatures, and maybe even has fun flavors such as salsa or wine.
This type of cheese product has actually been available for a long time, but is now becoming a major part of prepared foods. In fact, production of pasteurized process cheese and process cheese foods and spreads has increased about 30% in the last two decades, according to the USDA.
These specialized cheese products fit under the category of process cheese products. Process cheeses could be considered the first "designer" cheeses, because they convert natural cheeses (primarily Cheddar) of different ages, compositions, flavors and weights into a uniform product with a desired standard and the stability to withstand elevated temperatures for extended periods without spoiling. Understanding the formulating tricks that fit particular cheese applications requires a look at the standards of identity and an understanding of the basic food chemistry behind process cheese products.
Before deciding which type of cheese product to develop, product designers need to know the ingredients and processing conditions allowed in specific categories. These standards are listed in 21 CFR sections 133.169 through 133.180 (available online at www.access.gpo.gov/nara/cfr/waisidx/21cfr133_99.html) under the main categories of pasteurized process cheese, pasteurized process cheese food and pasteurized process cheese spread.
Pasteurized process cheese is made by pasteurizing, emulsifying and blending natural cheese. This process cheese can have only 1% more moisture than the natural cheese it comes from, and no more than 43% total moisture. The fat content cannot be less than the minimum required in the natural cheese, and, in most cases, should not be less than 47%. Fat may only be added in the form of cream, anhydrous milkfat or dehydrated cream. Other ingredients allowed include emulsifying salts, acids, water, salt, artificial color, enzyme-modified cheese (EMC), antimycotic agents and lecithin (an anti-sticking agent).
The other categories branch out from the process-cheese definition:
Pasteurized process cheese food may contain other dairy ingredients such as milk, condensed milk, skim milk, nonfat dry milk, whey, skim-milk cheese, albumin from whey and EMC. Cheese food's moisture cannot exceed 44%, and the fat content must not be less than 23%. It must also contain at least 51% cheese, not including skim-milk cheese and EMC.
Pasteurized process cheese spread must have a moisture of greater than 44%, but not more than 60%. Fat content must be at least 20%. This product must also contain at least 51% cheese ingredients. All ingredients allowed for process cheese food are also allowed in spreads, with the addition of hydrocolloids, sweeteners and acidifying agents.
All three of the above categories can also contain fruits, vegetables or meats. In this case, they would be labeled as "Pasteurized process cheese (food, spread) with ___," the blank being filled in with the common or usual name(s) of the fruits, vegetables or meats used, in order of predominance by weight.
Understanding the basics of cheese chemistry requires a knowledge of emulsification properties. Cheese products consist of an oil phase (containing fats and oil-soluble substances) and a water phase (containing a solution of water-soluble proteins and minerals). These two phases are not compatible without some intervention. In cheese, the surface-active proteins are soluble in both the oil and water phases, and collect at the interfaces between the two, creating an emulsion. If the emulsion is just efficient enough to prevent phase separation, it will have large droplets of one phase floating within the other phase. As emulsification improves, the droplets get smaller, increase in surface area and eventually reach a state of total homogenization.
Emulsification is linked closely with a cheese's textural attributes. Modifying the emulsion helps achieve the desired textural properties in a process cheese. Variables such as cheese type, age and pH; amount of calcium in the calcium phosphate; and the temperatures experienced during processing all affect emulsification properties.
The emulsifying proteins in cheese are casein and casein fragments. Most caseins contain calcium phosphate groups on one end, which are water-soluble and carry the majority of the protein's charge. (The organic, nonpolar groups on the other end of the molecule are fat-soluble.) Calcium affects emulsification by influencing overall solubility - the more calcium, the less soluble the water-soluble end of the protein, and the less the protein's ability to emulsify.
"Casein from the base cheese is the primary emulsifier in a process cheese product," says William Wendorff, Ph.D., professor of food science at the University of Wisconsin, Madison. An important factor in formulating a process cheese is determining the relative casein content (RCC) of the base cheese. "The relative casein content is the ratio of the amount of casein nitrogen divided by the total nitrogen in the base cheese," continues Wendorff. "Swiss cheese provides better emulsification than Cheddar because it has a higher relative casein content."
As a cheese ages, fats and proteins break down into shorter, simplified units via bacterial and/or fungal action. These units are more soluble than their predecessors, which increases their flavor strength. (Insoluble substances have no flavor because they can't interact with taste receptors in the mouth.) Aging's effects on protein also influence emulsification and finished texture. "As a cheese ages, it decreases in RCC, thus decreasing its emulsifying ability," says Wendorff. "The RCC recommended for a spreadable-type process cheese is 60% to 80%."
Protein associations at a given level of emulsification determine process-cheese texture. Short proteins have fewer chances than long proteins to interact with each other. As a result, an aged cheese tends to produce a shorter, more crumbly texture. The proteins become more water-soluble as protein-protein interactions weaken. This situation can temporarily enhance emulsification, but as proteins continue to break down, the decrease in protein-protein interactions leads to a general loss of structure and poor emulsification. To solve this problem, young cheese or rennet casein could be added. Too much of either of these, however, could result in a overly viscous product for processing.
A cheese's pH also affects the protein's configuration. Proteins roll up into spheres and reduce their interactions with other phases at specific pH values that correspond with the particular proteins and their isoelectric points. Additionally, heating can damage proteins and decrease their emulsifying ability.
Cheesemakers might find some of these variables difficult to control. Heating is needed for pasteurization, and aging is necessary for flavor development. However, pH and calcium levels can be controlled, and other ingredients such as whey protein, vegetable oil and water help achieve the desired texture of a process cheese product.
Emulsifying salts provide an effective way to control cheese properties. Some salts can modify pH, but as a group, they are primarily used for their calcium-binding ability. Phosphoric and citric acid salts are commonly used in process cheese including: sodium citrate, sodium aluminum phosphate (SALP), monosodium phosphate (MSP), disodium phosphate (DSP), trisodium phosphate (TSP), tetrasodium tripolyphosphate (TSTPP), sodium tripolyphosphate (STPP), sodium hexametaphosphate (SHMP), and insoluble metaphosphate (IMP). All of these salts have a natural tendency to bind calcium, including that in casein fragments.
"Emulsifying salts participate in an ion-exchange process by exchanging the calcium bound to casein with sodium, thus improving the emulsifying ability of the proteins," says Jeff Pfaff, senior technical advisor, BK Ladenburg, Simi Valley, CA. Because they are not fat-soluble, these salts do not interact with the fat-soluble portions of the proteins, and only affect the water-soluble portions.
Salts that bind weakly to calcium, yielding a weak emulsion, are most commonly used for soft, easily melted cheeses. Salts in this category include sodium citrate, SALP, DSP and TSP. They all bind calcium at a similar strength, but sodium citrate and SALP cannot bind as much calcium by weight as DSP or TSP. For this reason, sodium citrate and SALP have typical usage levels of 3%, while DSP and TSP are used at 2%. "As you decrease the amount of casein (or cheese) in a process cheese product, the amount of emulsifying salt required in the formula for physical destabilization decreases," says Pfaff.
TSP is usually used in combination with other salts because it also raises the pH of the cheese. MSP does not bind strongly to calcium either, but it isn't used often because it decreases cheese pH to unacceptable levels.
"It is recommended that the hydrated forms of DSP (duohydrate) and TSP (dodecahydrate) are used, as these are not heat treated to an extent where they might form polymers of phosphates," says Lulu Henson, Ph.D., research associate, FMC Corporation, Princeton, NJ. "The levels of pyrophosphates are kept to a minimum in these emulsifying salts, as the presence of pyrophosphates tends to change the melting characteristics of process cheese," she says.
TSTPP, STPP and SHMP all bind calcium much more strongly than the salts mentioned above, and TSTPP binds most strongly. These salts provide excellent emulsification, and produce firm, non-melting cheeses. "Polyphosphates can provide a 'creaming effect' by their interactions with the proteins, which leads to a thicker, creamier texture," says Pfaff. "In very high-moisture spreads and sauces, monophosphates and citrates normally give you the least amount of emulsion stability, whereas the polyphosphates can increase the amount of emulsion stability." Henson notes: "A restricted-melt cheese, for a chicken cordon bleu application, would utilize a TSTPP or SHMP in combination with an alkaline salt to achieve the desired meltability and pH."
Strongly binding salts can cause over-emulsification, so they are usually used at lower levels in combination with a weaker salt. IMP is insoluble, so it's never used alone. Rather, it is combined with a more efficient salt such as DSP or TSP.
Emulsifying salts also have side benefits. "Phosphates have a bacteriostatic effect on process cheese products, which provides protection against the growth of Clostridium botulinum. This characteristic of phosphates creates a safer, shelf-stable product," says Henson.
The pH can alter a protein's solubility and configuration, as well as the ability of emulsifying salts to bind calcium. Proteins have multiple positively and negatively charged sites positioned along their length. An excess of one type of charge causes an open protein structure, due to repulsion between sites with like charges.
Protein charges become more balanced as the surrounding solution approaches the isoelectric point, and completely balance at that point. At this pH, the protein curls up, because the opposing charges attract, and because it greatly reduces other protein interactions and solubility.
Casein's isoelectric point is about pH 5. Normally, cheese pH is higher than this, producing an excess of negative charge on the protein. As cheese pH is reduced to 5, a crumbly texture can develop due to weakening of protein-protein bonds and the fat can start to demulsify. Increasing the pH to less than 6.5 improves solubility and strengthens protein bonds, creating a more elastic and better-emulsified cheese.
The effects of pH make it important to consider the pH of a cheese's emulsifier. MSP, with a pH of 4.2, produces a dry, crumbly cheese. TSP has a pH of 13, and produces a moist, elastic cheese. To adjust pH in process cheese products, the FDA allows organic acids such as vinegar, lactic acid, citric acid, acetic acid and phosphoric acid.
A cheese's protein:fat ratio determines to what extent the cheese's texture can be modified. In Cheddar-based process cheese, for example, this ratio determines hardness and non-melting properties. This ratio isn't a factor at any level of emulsification below the critical point, which is the point where the surface area of the fat becomes so large that there's not enough protein to cover it completely. The result is that some fat is well-emulsified within the body of the cheese, and some separates out as oil. This separation can be prevented by limiting the degree of emulsification. In other words, when Cheddar's emulsification passes a certain level, oil separation occurs. In cheeses that have different protein:fat ratios, this would happen at a different emulsification level.
An over-emulsified cheese is hard and non-melting, while the reverse is true of an under-emulsified cheese. Over-emulsification can occur when adding re-work cheese, due to the additional emulsifying salts contained within this cheese. It may be necessary to reduce the level of emulsifier salts when using a substantial amount of re-work.
Most natural cheeses have more fat than is needed for typical emulsification. Skim-milk cheeses such as Parmesan, however, have an excess of protein. In this case, there's not enough fat to take care of all the proteins, which separate into grainy or chalky water-phase deposits. Increasing the degree of emulsification with emulsifying salts can increase the available fat - the salts expand the surface area of the fat, without changing the amount of fat, potentially yielding a harder, higher-melting cheese. An additional fat source, such as vegetable oil, could also improve such a product.
Process cheese foods and spreads often require additional ingredients to bind the extra water added to these products. Hydrocolloids and gums bind water, control viscosity during processing, and contribute to the finished texture of the cheese product. Other ingredients, such as whey proteins, provide some of the same functionalities, and are very cost effective. These proteins add body and provide a smooth, creamy texture, but do not melt, stretch, spread or retain finished-cheese firmness, as caseins do.
The hydrocolloids permitted in a process cheese spread are carob bean gum, gum karaya, gum tragacanth, guar gum, gelatin, sodium carboxymethylcellulose, carrageenan, oat gum, algin, propylene glycol alginate and xanthan gum. Guar gum is commonly evaluated because of its low cost. Up to 0.8% hydrocolloids are allowed in a spread, but less are recommended. "Typical usage levels for gums in these applications are 0.1% to 0.5%," says Lee Jensen, applications manager, Texturant Systems Business Unit, SKW Biosystems, Atlanta.
One of the issues in utilizing a gum is dispersability. "It is recommended to pre-blend gums with other dry ingredients and to use a high-speed mixer, if possible, to incorporate them into a process cheese spread," says Jensen. Agglomerated gums with improved dispersibility are available, but they cost more.
It's important to consider processing conditions and formulation when selecting a gum. Some gums require high-temperature heating to function; for example, locust bean gum must be heated to 180° to 190°F. Also, some gums are more acid-tolerant than others. "Xanthan gum is considered acid-tolerant, while carrageenans are less so," says Jensen. Using xanthan gum above 0.2% to 0.3% can lead to a slimy-textured spread.
When it comes to special effects, gums have even more unique qualities. "Sodium alginate forms a non-thermoreversible gel in the presence of calcium, and gives a glossy look to process cheese spreads," says Jensen. "Pectins can be added to a low-pH product, such as a spread flavored with salsa, to prevent the dehydration of casein during heat treatment and the subsequent development of a gritty texture."
If meltability is undesirable, combining the right formula and process will give the best result. "A combination of polyphosphates, starches and/or hydrocolloids in the formula with slower cooling during production can reduce the re-meltability of a process cheese spread," says Pfaff.
The right combination of emulsifiers and gums also plays an important role when formulating reduced-fat or fat-free process cheese products. "Citrates will tend to promote the formation of larger fat globules in a process-cheese emulsion than a phosphate, so the cheese will tend to melt faster," says Henson. For this reason, citrates work well in reduced-fat applications. Kappa, iota and lambda carrageenans can provide these products with textures ranging from a strong gel to a paste.
Recent research conducted at the University of Wisconsin-Madison and funded by the Wisconsin Milk Marketing Board involved the interactions of ingredients and processing conditions in the development of a fat-free process cheese. This research revealed that the best meltability was associated with trisodium citrate, and the best spreadability with a combination of DSP and guar gum.
For creating a process cheese with a nice, characteristic cheese flavor, EMCs are the primary ingredient of choice. However, "process cheese products can only be flavored with an EMC made from the cheese variety for which it is used as a flavoring agent," says Gene Seitz, Ph.D., manager, flavor group, Chr. Hansen, Inc., Milwaukee.
EMCs provide the flavor bases, or "keys," used to build WONFs. "However, when certain flavorant molecules such as propionic acid (important for Swiss flavor) can be produced by fermentation, using Swiss cheese as the substrate, they can be used in process Swiss cheese," says Seitz. "Many flavor molecules may be used, such as butyric acid for English Cheddar and lactones for creamy, buttery cheese foods."
A typical process cheese contains about 15% to 20% barrel cheese (for flavor) and 75% young cheese, in combination with an EMC. Using aged cheese is not only functionally prohibitive due to emulsion-stability problems, but it's also cost prohibitive. "EMCs were developed to provide the flavor of an aged cheese without the expense of using an aged cheese in a process cheese product," says Seitz.
EMCs have their own set of economics. "The development of an EMC is analogous to the technology of accelerated cheese ripening," says Seitz. "Incubation time is a critical factor in the cost and flavor development of an EMC." New technologies point to even faster incubation times and new substrates. "A newer substrate used for EMC is called UF retentate," continues Seitz. UF retentate is made via ultrafiltration of milk and yields a product that contains whey proteins as well as casein. As with all ingredients, improving process efficiency is key.
Whether you are looking for that hint of a "goaty" note from branched-chain amino acids or for a flavor potentiator such as sodium glutamate, characteristic of Parmesan, there's an EMC for your formula.
So the next time you bite into a cheese-filled entree or spread a process cheese product on a cracker, think about all the factors affecting that cheese. When all the elements - protein:fat ratio, type of protein, pH and moisture levels, amount of re-work added, age of the cheese, type of emulsifier salts - come together correctly, it is indeed possible to have the ideal cheese for just about any application.
Kimberlee J. Burrington is the whey applications program coordinator for the Wisconsin Center for Dairy Research in Madison. She received her B.S. and M.S. degrees in food chemistry from the University of Wisconsin-Madison. Her industry background is in bakery and dairy.
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