High-Powered Protein Drinks
By Kimberlee J. Burrington
Whether you’re interested in meal replacement, bodybuilding, endurance, weight loss or supplementation, there is a protein drink formulated for your specific nutritional goals. Among one of the fastest growing areas of functional foods, high-protein beverages have evolved from doctor-prescribed diet products to a mainstream grocery product. Fortified with everything from intact proteins from every source imaginable all the way down to individual amino acids, these drinks come with benefits ranging from “beefing up” to “slimming down” and “immunity enhancement” to “increased endurance.” Whether a drink should deliver 15 or 50 grams of protein per serving, there are tricks to fulfilling product claims. Picking the right protein sources and taking a hard look at their nutritional and functional properties are the keys to formulating a protein-packed beverage that consumers will buy again and again.
The normal level of protein in the diet is 12% to15% of the total energy expenditure. The U.S. Recommended Daily Allowance (RDA) for protein is 0.8 gram per kilogram body weight to maintain overall health and fitness with a sedentary lifestyle. If the RDA is met, over a 24-hour period the protein ingested in the diet will be metabolized and nitrogen balance will be maintained.
In some cases, exercise can increase the protein requirement, but to a smaller degree than energy needs. Most of the energy requirements of training are met by fat and carbohydrate oxidation, with only a small contribution from protein. The relative contribution of protein during exercise depends on the exercise intensity and duration, as well as the level of fitness and nutritional status of the individual. Exercise, regardless if it is long-distance running, aerobics or weight training, causes some increase in the protein-oxidation rate relative to the resting state. The relative contribution of protein oxidation to energy production during exercise may decrease to about 5% of the total energy requirement, but the protein-degradation rate is increased during exercise. As a result, strenuous exercise leads to an increase in the minimum daily protein requirement and nutrition experts recommend an intake of 1.2 to 1.7 grams per kilogram of body weight per day for athletes. Those involved in bodybuilding, weightlifting, wrestling or self-defense may require levels of up to 2.0 grams per kilogram of body weight per day to remain in positive nitrogen balance.
The daily stresses of living do not call for increases in the daily protein requirements. However, extreme environmental or physiological stresses increase nitrogen loss from the body. Surgical stress, fevers, infections and burns result in an increased loss of nitrogen through the urine, and require an increased dietary protein intake to replace this loss. Other diseases, such as AIDS, HIV, cancer and others which compromise the body’s immune system, also qualify as conditions creating an increased nitrogen loss. No known health problems develop from protein intake that is moderately above requirements. Evidence from animal studies suggests that high dietary protein intake may cause kidney damage. The National Research Council, an agency of the National Academy of Sciences, Washington, D.C., suggests an upper limit of twice the RDI for protein.
One more thing to consider when determining the protein requirement is that the body does not utilize any protein 100%. A high-quality protein will have a 30% loss of efficiency while a lower-quality protein will have a 60% loss. Ingesting a high protein level increases metabolic stress to the body’s organs. A much better idea is to consume high-quality proteins having the best biological value.
Several measurements of protein quality are used. The one method that measures protein quality based on human amino-acid requirements is the Protein Digestibility Corrected Amino Acid Score (PDCAAS). Factors needed for PDCAAS include: true digestibility, approximate nitrogen composition and essential amino-acid profile. The ideal protein that meets all the essential amino-acid requirements of the human body is given a PDCAAS score of one. “The earlier protein-quality methods distinguish more between the high-end proteins than the PDCAAS,” says Eric Bastian, Ph.D., director of research and development, Glanbia Ingredients, Richfield, ID. The PDCAAS yields a score of 1.0 for whey protein, casein, milk protein isolate, soy protein isolate and egg-white powder — all protein sources that can be found in high-protein drinks. Using an earlier method, the biological value, scores for the same proteins range from 74 for soy protein to 104 for whey protein. Regardless of the protein source, they all have unique functional and nutritional characteristics that make them especially suited for beverage applications.
Wheying the options
“Whey proteins are typically the proteins of choice for high-protein sports-drink applications,” says Julie Wagner, director of applications, Century Foods International, Sparta, WI. Whey protein ingredients often used in high-protein drinks include whey protein concentrate with 80% protein (WPC-80), whey protein isolate (WPI) containing greater than 90% protein, hydrolyzed WPC-80 and WPI, lactoferrin and glycomacropeptide. Whey proteins represent 20% of the milk proteins. Whey protein ingredients are produced by filtration and concentration of whey, the group of proteins and other nutrients that do not remain with the curd formed during cheesemaking.
Whey proteins work in high-protein drinks for a number of reasons. Functionally speaking, whey protein ingredients have high solubility over a wide pH range. “Whey proteins are acid stable but they have the best solubility outside of the pH range of 4 to 5 because their isoelectric point falls in this range,” says Laurie Nelson, applications manager, Davisco Foods International, Inc., Eden Prairie, MN. When considering a dry-mix drink or a ready-to-drink product, whey proteins contribute to a smooth mouthfeel and a mild dairy flavor that blends well with the popular flavors: vanilla, chocolate and strawberry.
A unique property of these proteins is their ability to make a high-clarity beverage. Generally speaking, whey protein ingredients have good dispersibility in water but certain processing modifications can optimize their dispersibility. “Agglomeration is the key to good dispersibility in a high-protein dry mix,” says Wagner.
Good emulsion stability and foam stability are also included on whey protein’s list of important attributes in drink applications. “Most high-protein sports drinks are dry mixes because it is difficult to process a high amount of protein through the retort or UHT process required by a ready-to-drink (RTD) beverage for a good, stable and palatable finished product,” says Wagner.
One functional property of whey proteins that makes them very good at forming gels and, in general, good at protein-protein interactions, is their reaction upon heating above 70°C. “These proteins are heat sensitive; you can’t go in and change the characteristic of the protein because that is dictated by the primary structure of the protein,” says Bastian. “You have to try to control the environment that the whey protein is in, in order to improve the heat stability of the protein.” In this case, the environment includes the amount of water, presence of ions such as calcium, pH, and the levels of other ingredients in the drink formulation.
Cellulose- and carageenan-type hydrocolloids work well with whey proteins to provide some stability in an RTD application at a more neutral pH. Pectins can stabilize whey proteins in a low-pH RTD product. Homogenization will also aid the long-term solubility of whey proteins in an acid beverage.
Choosing acidulants for a low-pH protein drink requires care; some organic acids taste better than others. “To achieve the best flavor in a low-pH whey protein drink, an 85% solution of phosphoric acid works well as the acidulant,” says Nelson. If it is important to pack as much protein as possible into an RTD product, many companies play with the serving size to optimize the functional limitations. “You can easily add 6% to 8% whey protein to a ready-to-drink product, which could translate into 40 grams of protein in a 22-oz. serving size,” says Nelson. Beyond functionality, the interest in whey proteins quickly becomes a matter of nutrition.
The nutritional whey
Whey proteins have the highest concentration of branched-chain amino acids (BCAA), leucine, isoleucine and valine, available from any natural protein source. A whey protein isolate would typically supply 26 grams of BCAA per 100 grams protein. Whey has 10 grams of leucine, 6.5 grams of isoleucine and 5.5 grams of valine per 100 grams of protein. The amino-acid composition of whey protein ingredients will vary with the processing methods used to isolate the proteins. Whey protein isolates manufactured by ion exchange or microfiltration contain higher levels of Beta-lactoglobulin, a protein naturally high in BCAA.
Whey proteins are also a good source of the sulfur-containing amino acids, cysteine and methionine, compounds responsible for maintaining the body’s antioxidant levels. The high levels of arginine and lysine in whey are thought to stimulate growth-hormone release promoting an increase in muscle mass and decline in body fat. One study published in 1992 in the Journal of Applied Physiology (volume 72) by Zawadzki et al., indicated that adding whey protein to a carbohydrate meal resulted in greater muscle glycogen stores four hours after recovery. The proposed mechanism for this resynthesis of glycogen is that the simultaneous ingestion of protein and carbohydrate winds up augmenting the action of insulin.
“Some athletes with over-training syndrome tend to get respiratory infections that they have been able to ameliorate with whey protein consumption,” says Bastian. The high level of glutamine in whey proteins might prevent this decline in immune function from overtraining.
Two other proteins with bioactive properties unique to whey are glycomacropeptide and lactoferrin. Lactoferrin makes up about 0.1% of the whey proteins. It can be isolated from whey by ion exchange and added to a protein drink to provide additional benefits. It is classified as an iron-binding protein from the transferrin family. Transferrins bind iron in the blood for energy production and the regulation of red cells and hemoglobin. An iron shortage can hamper an athlete’s aerobic performance. Lactoferrin can be added as an iron supplement to boost oxygenation.
Lactoferrin has even more benefits. “Typically we think of lactoferrin primarily as an iron-binding protein,” says Bastian. “Research presented by the Baylor College of Medicine (Houston) at the 2001 Lactoferrin Conference suggested that the transferrin present in rat milk is able to deliver the iron that infants need. They discovered that lactoferrin is a protein that keeps free iron very low in body tissues, which is more of an antioxidant role.” Free iron is one of the free radicals that can injure an athletes’ muscles. One other characteristic of lactoferrin that might benefit medical drinks for patients with compromised immunity is its role in the cellular defense system. Lactoferrin may regulate the macrophage activity and stimulate the proliferation of lymphocytes.
Whey protein contains glycomacropeptide (GMP) because of the reaction of chymosin with kappa-casein during the cheesemaking process. Whey proteins contain about 15% to 20% glycomacropeptides. These proteins stimulate the synthesis and release of cholesystokinen in the body, a regulator of digestive functions. “GMP could be added to a protein drink for its potential appetite-suppressing properties,” says Nelson.
GMPs also play a role in providing growth factors for bifidobacteria in the intestine, antiviral activity, modulating digestion, improved calcium absorption, antibacterial properties, and immune-system enhancement. “Glycomacropeptide is involved in stimulating the release of certain interleukins that tone down the immune system using an anti-inflammatory mechanism,” says Bastian.
Enzyme hydrolysis of whey proteins increases the digestibility, nitrogen absorption and retention, and decrease the allergenicity of the protein. Many high-protein drinks utilize hydrolyzed whey proteins to deliver these benefits. Keep in mind that the nutritional benefits will increase with the level of hydrolysis, but that bitterness from peptides also will increase accordingly.
One example of an application for a highly hydrolyzed product is for enteral feeding. “Enteral feeding serves to stimulate the proliferation of cells and to re-establish the integrity of the gut. This type of feeding can be used on surgical patients in counteracting multiple organ failure, which typically results in death for critical patients,” says Bastian.
If you are looking for a vegetable protein source, soy protein might be the answer. Generally, vegetable proteins don’t provide as high a quality protein as animal sources, but soy proteins are an exception. Soy proteins also deliver nutritional and functional attributes appropriate for high-protein drinks.
Soy protein isolates containing 90% protein are most widely used in high-protein drinks. Modifications to soy protein isolates can customize them for either a dry mix or RTD product. “A low level of hydrolysis in a soy protein isolate will yield a low-viscosity product with good emulsification properties,” says Russ Egbert, Ph.D., director of protein research applications, Archer Daniels Midland Company (ADM), Decatur, IL. A high-viscosity isolate will provide a soy shake with a smoothie consistency, while a low-viscosity isolate will result in a protein drink with milk-like consistency.
Similarly to whey proteins, processes such as agglomeration, lecithination and changes in the protein solubility will improve the protein’s dispersibility in a dry-mix application. Lower solubility will actually improve the dispersibility of the protein. “In a liquid beverage, it is essential that the soy protein be properly hydrated in order to achieve the desired results,” says Egbert. Added food gums provide mouthfeel and protein stabilization in liquid applications.
Carrageenan, xanthan, locust bean, guar and cellulose gums work well in neutral-pH drinks. Pectins, xanthan and guar are designed for acid beverages. Homogenization is critical to maintain protein solubility in an RTD product. Stabilization needs will go up with the heat processing required for a RTD product.
Low levels of soy protein will produce a slightly cloudy drink. Currently no commercially available soy proteins produce a clear beverage. “Clear beverages would require highly hydrolyzed protein products and there is no evidence to support the heart-health benefits with a highly hydrolyzed product,” says Egbert.
When it comes to flavor, soy proteins continue to have some flavor that may be a negative for some consumers, although soy-processing technologies have made strides in improving flavor through processes such as alcohol-washing. In addition, the flavor industry has developed several very effective masking flavors for soy proteins that improve the sensory attributes of a high-protein soy drink. “There is also a move in the soy market for beverages to include masking-flavor technology in the powdered soy proteins,” says Egbert. This should simplify the formulation of high-quality soy drinks for beverage manufacturers.
If a consumer is looking for soy they are looking for the nutritional claims associated with soy proteins. Their amino-acid profile make soy protein ingredients high-quality sources of protein. Their high lysine content, approximately 63 mg per gram of protein, make them unique among vegetable proteins. Despite a small deficiency of the sulfur-containing amino acids methionine and cystine, the quality of soy proteins as measured by PDCAAS compare favorably to beef, egg white and casein. In addition, the FDA recently has approved a label health claim for soy-containing products. “You need to have 6.25 grams of soy protein (per serving) in your drink to make the claim that it will improve cardiovascular health,” says Laurent Leduc, vice president of sales and marketing, Schouten USA, Minneapolis, MN.
Because some of the processes to improve the flavor of soy proteins can also diminish levels of specific soy components, such as soy isoflavones and other phytonutrients, product designers often need to find ways to add these components back. One source of these nutrients is from the soybean germ. “Soybean germ has 40% protein, 16% fatty acids and 34% carbohydrates,” says Leduc. “The soybean naturally stores a 20-times higher concentration of isoflavones, saponin and vitamin E in the germ vs. the rest of the bean.”
Soy isoflavones provide a number of health benefits, including heart-disease prevention and potential cancer risk reduction, including prostate cancer. Similar to isoflavones, saponins might also take part in lowering blood cholesterol by either blocking the absorption or increasing the excretion of cholesterol from the body. Vitamin E is, of course, a powerful antioxidant that may provide anti-cancer benefits, as well.
Science has not yet come up with a clear consensus for intake recommendations for these nutrients. “There is no official recommended dosage, but based on the Asian diet, 30 to 50 mg per day of isoflavones is recommended,” says Leduc. However, he does suggest levels for protein-drink applications. “You can add 1% to3% of this powdered germ product to a high-protein drink to provide the benefits from the phytonutrients,” he points out. Though bodybuilders may steer away from an ingredient described as a “phytoestrogen,” this ingredient fits into a number of health categories. “Customers who use this product are targeting women’s health, men’s health or cardiovascular health,” says Leduc.
The character of casein
Caseinates, another protein ingredient commonly used in high-protein drinks, are ultimately manufactured from skim milk by precipitation of casein with a rennet-type coagulant or by acid to produce acid or rennet casein. The acid or rennet casein is then neutralized with an alkali or alkaline salt, commonly sodium and calcium caseinate. The alkali treatment creates a water-soluble product. Caseinates have approximately 91% protein and are considered heat stable but not acid stable, an important factor for an acid beverage application. Their milk origins classify caseins as high-quality proteins.
When formulating beverages with caseinates, all forms do not exhibit the same properties. Sodium caseinate tends to have greater water absorption, higher viscosity, and greater foaming capabilities than calcium caseinate. In some cases, the choice between the two types of caseinate may come down to the added sodium or calcium that is associated with the ingredient. Caseinates typically are used in addition to other proteins in high-protein drinks. “Caseinates have good foaming properties and good foam stability, so combining a caseinate with a whey protein concentrate will provide even more enhanced foaming,” says Wagner.
Caseinates also are known for their good emulsifying ability. “You tend to see combinations of proteins, like whey protein concentrates, caseinates and soy protein isolates used in meal-replacement powders due to economics, in combination with functionality and amino-acid profile,” says Wagner. They also can provide some heat stability and help stabilize an RTD product.
A couple of other milk protein products that formulators might add to high-protein drinks are milk protein concentrates and isolates (MPC and MPI). MPC and MPI deliver the functionality and nutrition of both the casein and whey proteins. Like whey and soy proteins, MPC and caseinates can be hydrolyzed to improve their functionality and digestibility. Unlike whey and soy, it is not typical to find a high-protein drink made entirely from caseinate or concentrated milk proteins.
Another eggscellent choice
Another high-quality protein source that shows up on the ingredient legend of high-protein drinks is egg albumin. It typically follows the other proteins on the list of ingredients, but its presence is worth mentioning. Egg albumin has long been the gold standard to which other proteins compare their functionality and nutritional properties.
Liquid egg white consists of 88.5% moisture and 9.8% protein and contains no fat, but commercial dried products are dried down to approximately 8.5% moisture and pasteurized. Instantized products will provide the necessary dispersibility to a dry-mix drink. Like whey proteins, egg albumin is somewhat heat sensitive — it will coagulate at temperatures between 144° to 149°F, although the presence of dissolved solids raises these temperatures — so caution should be used in RTD products. Nutritionally, this protein complements the amino-acid profile of the others to supply high levels of phenylalanine and tyrosine, leucine, lysine, and valine. Egg white consists mainly of albumin (65.0%), but also contains conalbumin (14.0%), ovomucoid (9.0%), globulins (9.0%), lysozyme (3.4%) and ovomucin (1.6%). Lysozyme exhibits antimicrobial properties.
Amino acid answers
If the benefits of specific amino acids look like an avenue to explore, individual amino acids can supplement a drink. “More than 80 types of amino acids are found in nature, while about 20 amino acids are found in all natural proteins,” says Satoshi Yokota, manager sales and marketing, Ajinomoto USA Inc., Raleigh, NC.
Though protein only contributes a small portion of the total energy needs of active muscles, amino acids may provide between 5% and 10% of substrate supply during prolonged exhausting exercise. Amino acids released from muscle and other tissues can provide substrates to the liver for gluconeogenesis, the production of glucose from amino acids and other substrates. This glucose may be released from the liver, utilized by active muscle and oxidized for energy.
Oxidation of the branched-chain amino acids, leucine, isoleucine and valine, along with alanine, glutamate and aspartate also occurs in muscle and can function as a direct provider of a small amount of the ATP required for muscle contraction. The contribution of protein oxidation to energy metabolism increases when muscle glycogen stores are depleted, but the issue with using amino acids for energy production is that they must be retrieved from protein in skeletal muscle or from the tissues of the gut because there are no amino acid stores in the body. Most of the time, it is preferable to spare muscle protein.
One recent study published in the April 2001 British Journal of Sports Medicine by A.G. Williams et al. suggests that regular glucose/amino-acid supplementation immediately following resistance exercise is unlikely to enhance gain in muscle strength. They also concluded that supplementation may not affect the average person, but it may benefit well-trained athletes.
Supplementation of the three branched-chain amino acids during exercise has been examined for its ability to prevent fatigue which impairs physical performance. BCAA supplementation, in theory, blocks the uptake of tryptophan into the brain because both compete for the same blood-brain barrier transporter. Tryptophan is the precursor of serotonin, the chemical thought to be the inducer of fatigue.
Various studies on the effects of BCAA ingestion on physical performance discussed in the book “Sports Drinks: Basic Science and Practical Aspects” indicate no delay in the onset of fatigue during moderate- to high-intensity exercise. Specific amino acids provide a transportable solute in the gut, so addition to a beverage may enhance fluid absorption. Actively transported solutes generate an osmotic pressure that draws fluid across the intestinal membrane. The addition of glycine to a sports drink has been evaluated in one study with no increase in fluid absorption rate resulting.
“Glutamine is the most abundant amino acid found in the human body,” says Yokota. Glutamine intake has been evaluated for its prevention of overtraining in athletes. “L-glutamine has been shown to build up the immune system,” he notes. Glutamine acts as an important fuel for the immune system by providing the precursor for genetic material in cells, such as the white blood cell. When daily energy expenditure is consistently high, researchers believe that blood glutamine levels decrease because of an increased demand for energy throughout the body. Theoretically, addition of glutamine to a hydration beverage might decrease the risk of overtraining or impairment of the immune system in the athlete. Glutamine also has been examined for its enhancement of muscle glycogen recovery after intense exercise. No studies have been reported on the use of glutamine in sports drinks. Glutamine is readily converted to glutamate in the stomach or in an acidic beverage, a consideration for individuals who experience allergies or have a sensitivity to monosodium glutamate.
Arginine is a precursor of nitric oxide, a compound that regulates vasodilation and local blood flow. Arginine may accelerate recovery after exercise and inhibit protein breakdown during exercise. L-arginine hydrochloride is very soluble in water, making it easily added to drinks. However, it possesses a very bitter taste, making it difficult to mask in a drink application. Only a few studies have been performed using arginine in a hydration drink and they failed to show an effect on performance or recovery.
The leucine derivative, beta-hydroxy-beta-methylbutyrate (HMB) is considered a new ergogenic aid. HMB stimulates rate-limiting cholesterol synthesis and provides the keto-analogue to spare leucine oxidation. Some have made claims of enhanced recovery after training, but there is no clear consensus on the few studies done to date.
Addition of creatine elevates muscle creatine levels, which accelerate recovery of phosphagen concentrations. Creatine also serves as a stimulus for muscle hypertrophy. Creatine supplementation is used by many atheletes to enhance power or sprint capacity. Studies have indicated that creatine loading for several days may enhance performance in intermittent anaerobic efforts. Bodybuilding drinks also commonly contain creatine supplementation for its effects on increasing muscle mass. Studies are not clear on whether actual lean body mass is gained or if the muscle has just taken up more water. Creatine is readily hydrolyzed in acidic conditions so addition to an acid beverage would reduce the dosage delivered to the consumer.
Carnitine is involved in the transport of long-chain fatty acids across the mitochondrial membrane for oxidation. Most of the body’s carnitine is produced by the liver and transported into the blood stream and then transported into the muscle. Increasing the dietary intake of carnitine is supposed to improve fatty-acid transport across the inner mitochondrial membrane and enhance the capacity to oxidize fat and therefore enhance endurance.
Now that you have sufficiently stored this protein knowledge, you should have an adequate supply to fulfill all your formulating needs for your latest high-protein drink application. Food scientists can be assured that the protein ingredients available along with some formulating tips will be there for their next protein-packed drink project.
Kimberlee J. Burrington is the whey applications program coordinator for the Wisconsin Center for Dairy Research in Madison, WI. 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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