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The Principles of ProteinThe Principles of Protein

February 1, 2000

22 Min Read
The Principles of Protein

The Principles of Protein
February 2000 -- Cover Story

By: Ronald C. Deis, Ph.D.
Contributing Editor

  Proteins - long-chain molecules made up of amino acids - are essential to life. They provide the building blocks of cellular structures, are necessary for human metabolism, and also supply the body with energy. Protein from both animal and vegetable sources is abundant in this country, so protein deficiency is not a health problem for the average American, although this isn't the case in many other parts of the world. Because many manufacturers are incorporating protein ingredients as a means to ensure optimal healthfulness of their products, protein types and their recommended consumed amounts are important issues for food product designers to understand.Diet craze  Protein has leapt past fat as a subject for the popular press in the past couple of years, becoming the center of controversy between diet "gurus" and the medical community. The drive for this is obvious - 55% of U.S. adults (97 million people) are overweight or obese, and they are spending $33 billion a year in the quest to shed those excess pounds. Another $70 billion a year is spent by the U.S. health-care system to treat medical conditions related to obesity. And since it's often hard to lose weight, dieters naturally respond to any diet that looks easy or allows them to eat foods they like.  Enter the high-protein diets. Almost everyone has either tried one or knows someone who has lost 20 to 30 pounds as a result of one. Examples include the Atkins diet; the "Zone" diet, promoted by Barry Sears; and "Protein Power," developed by Michael Eades. Collectively, these are often referred to as 40/30/30 regimens, because caloric distribution is close to 40% carbohydrate, 30% fat and 30% protein. This limits caloric intake, to between 1,200 and 1,700 calories per day.  High-protein diets do work, but cannot (and should not) be maintained for a long period of time. The Atkins diet is based on placing the dieter in ketosis, severely restricting carbohydrates so that stored body fat is burned more quickly. At the same time, the dieter is losing a great deal of water and often consumes a larger amount of cholesterol and saturated fat.  Some concerns associated with this type of diet include hypoglycemia in diabetics; liver and kidney problems; an increase in loss of calcium through urine; and potential heart disease due to increases in cholesterol- and saturated-fat intake. While many have attacked the Atkins diet, others note that it can jump-start a weight-loss plan, which can be advantageous to the psyche of the dieter. Also, the plan does recommend exercise and a pre-diet medical evaluation.Amino-acid scoring  While excess protein can be negative in the long term, protein is essential to nutritional well-being, and it also acts as a functional food ingredient. Food proteins are made up of about 20 common amino acids, nine of which are known to be essential to human nutrition. These are histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine.  Foods have different mixtures of amino acids, and some may be high in one amino acid, but limited in others. Meat, dairy, eggs and soy have sufficient quantities of amino acids to provide complete nutrition. In general, vegetables are lower in lysine, methionine and tryptophan, but combining vegetables and grains can balance the deficiencies in both. Health organizations generally recommend meat, poultry, fish, eggs, cooked dried beans, soy products, dairy products, peanuts, nuts and seeds as good sources of protein.  How is a protein's quality determined? For 80 years, the standard was the Protein Efficiency Ratio, or PER. This value is based on the weight gain of rats fed the test protein. The standard protein, casein, has a PER of 2.7. Anything with a PER greater than 2.7 is regarded as an excellent-quality protein. However, rats have different amino-acid requirements than humans, so this score is not always an accurate predictor of a protein's value to humans.  In 1993, the FDA replaced the PER with the Protein Digestibility-Corrected Amino Acid Scoring, or PDCAAS, method. Several criteria are needed for the determination of the PDCAAS - proximate nitrogen composition, essential amino-acid profile, and a food's true digestibility (obtained from animal assay data). An uncorrected amino-acid score is calculated by dividing the amount in milligrams of each essential amino acid in 1 gram of the test protein by the amount in 1 gram of reference protein (obtained from the 1985 FAO/WHO required amino-acid profiles for 2- to 5-year olds; see sidebar entitled "Amino Acid Requirements"). The PDCAAS is then calculated by multiplying the lowest uncorrected amino acid score by the true digestibility. (For more information on this process, see sidebar entitled "Evaluating Proteins - the PDCAAS Method" in Food Product Design's October 1997 Applications feature.)  If the PDCAAS is greater than or equal to 1.00, the protein is a good source of essential amino acids. Since excess amino acids are excreted by the body, all proteins with a score of greater than or equal to 1.00 are considered equivalent and of high quality. PDCAAS values have been determined in general for a number of protein sources: casein, 1.00; egg white, 1.00; isolated soy protein, 1.00; ground beef, 1.00; tuna, 1.00; lentils (canned), 0.52; peanut meal, 0.52; and wheat gluten, 0.25.Protein requirements  How much protein do we actually need in our diets? A certain amount is essential to the body for building and maintaining muscles, repairing muscle damage, maintaining fluid and electrolyte balance, buffering acid/base fluctuations, providing energy, boosting the immune system, and maintaining hair, fingernails and skin. Protein is also required for production of red blood cells, enzymes and hormones.  To maintain fitness and overall health, the U.S. RDA for protein is 0.8 gram/kg body weight; at 154 pounds, for example, this equals 56 grams of protein per day. However, an individual's protein requirements also depend on lifestyle, physical condition, overall health and age. In general, the RDA is sufficient for a sedentary lifestyle, but exercise and age cause protein needs to increase. Most of us can achieve the recommended protein levels without supplementation, but this can change depending on physical condition and the presence of disease.  The American Dietetic Association (ADA), Chicago, and the Dietitians of Canada (DC), Toronto, have reported data suggesting that 1.5 grams protein/kg body weight, which is considered an adequate amount for athletes, are required for maximal protein deposition (70 to 105 grams protein per day for a 154-lb. individual). According to an ADA/DC position paper on nutrition for physical fitness and athletic performance for adults, "even the highest protein requirements can be met easily with a balanced diet that includes a variety of foods." This means that, for the most part, amino acid and protein supplements are not required for athletes, because excess dietary protein is either stored as energy (fat) or is oxidized. Fat storage is contrary to what most view as exercise's goal, and oxidation leads to additional excretion and possible dehydration.  Extra protein might also be required by older adults. Requirements for those 51 years or older are estimated at 1.00 to 1.25 grams/kg of body weight, rather than 0.8 grams. According to the ADA, 33 million adults (13% of the U.S. population) were 65 years and older in 1994. By 2030, this is projected to increase to 70 million, or 20% of the population.  Factors other than age also account for the older population's protein requirement. According to the U.S. Census Bureau, close to 20% of adults are relatively poor, which may result in malnutrition, for example. Medical or mental problems such as chronic disease, chewing or swallowing problems, dementia, depression, function disability and anorexia may also be factors. In all cases, inadequate protein intake can mean loss of muscle mass, reduced immunity to disease and decreased reserves for trauma and infection.  Children have their own special protein needs. Infants, for example, require more essential amino acids per gram of crude protein than adults, according to the FAO/WHO statistics. Supplementation with infant formula is a good way to achieve these levels. For children, it's important to provide adequate energy in the form of calories, and this can be achieved with a well-balanced diet including sufficient amounts of protein coming from various animal and plant sources.  Protein deficiency in children can be observed in under-developed countries, usually coupled with malnutrition. These problems are manifested in the form of marasmus, a condition of general wasting away due to caloric malnutrition. Kwashiorkor, a severe disease in which protein malnutrition is even more evident, can occur from infancy to about 5 years of age. If not treated, the child can become mentally and physically retarded, and the condition may deteriorate to coma and/or death.  Not all problems occur from lack of protein, however. A life-long, phenylalanine-avoiding diet is necessary for those affected by phenylketonuria, or PKU. This is a relatively rare protein-related disease inherited through an autosomal recessive gene, meaning that both parents must be carriers. PKU individuals lack the enzyme phenylalanine hydrolase, which converts phenylalanine to tyrosine. Phenylalanine is toxic to the central nervous system if this conversion does not occur. If treatment for PKU is not started early, mental retardation and other neurological problems result.Protein potential  Protein can be added to foods for nutritional and functional purposes. Important protein characteristics include varied solubility, gelation, adhesion/cohesion, water-binding, viscosity control, emulsification and foaming. Proteins can be denatured by heat, or hydrolyzed to enhance capabilities, reduce allergenicity or increase bioavailability. Commercial proteins can be derived from either animal or plant sources. Animal-protein sources include milk proteins, gelatin, fish proteins and egg products. Probably the most prevalent plant proteins are derived from soybeans, but protein is also extracted from corn, peas and wheat.  Milk proteins are common in food formulations due to their nutritional quality, immunoglobulin content and range of functional characteristics. The major proteins in milk are casein and whey proteins.  Caseins are phosphoproteins that constitute 2.5% to 3.2% of fluid milk, and about 80% of milk protein. Caseins can be precipitated from raw skim milk at pH 4.6 as casein micelles associated with calcium. Adding rennet causes casein aggregates to form an insoluble paracalcium caseinate. Raising the pH and forming a calcium, sodium, potassium or magnesium caseinate increases solubility. Caseinates are commonly used in coffee creamers, icings and toppings and to fortify cereals, flour and bread.  Whey, obtained after the extraction of casein in cheese production, contains about 6.5% solids, 1% of which is protein and 5% lactose. The two main whey proteins are beta-lactoglobulin and alpha-lactalbumin.  To form whey-protein concentrates (WPCs), which contain 35% to 85% protein, whey protein is either denatured by heating to form an insoluble protein or ultrafiltered to remove some of the lactose. The more denaturation occurs, the more viscosity the WPC imparts because of its increased water-binding activity. Denaturation also leads to increased opacity of the final product.  Whey-protein concentrates are used in a number of applications, including meat products, where they function as binders and fat reducers, and soups, where they emulsify cream varieties. WPCs can range from products that gel very firmly to products that impart very low viscosity, so they can be tailored to fit many targets, according to Gwen Bargetzi, communications and brand manager at NZMP, Inc., Santa Rosa, CA.  Whey-protein isolates (WPIs) contain >90% protein. "Whey-protein isolates are an extremely pure and valuable form of protein made up of peptide chains," says Marty Davis, general manager of Davisco Foods International, Eden Prairie, MN. "They are highly nutritional in value, containing essential amino acids within these peptides. They also offer great benefits for functionality in food applications, including emulsification, gelation, foaming and water-binding."  Milk-protein isolates (MPIs), also referred to as total milk protein, consist of whey proteins and caseins in one high-protein (90%) product. Milk-protein hydrolysates are manufactured via enzyme hydrolysis of casein, WPC or total milk protein. Enzymatic hydrolysis provides specificity; for example, Davisco uses an enzyme that specifically hydrolyzes the bond between arginine and histidine, producing a WPI with improved digestibility and intestinal absorption, decreased allergenicity, controlled functional characteristics, and improved bioactivity. "Hydrolyzed milk proteins, in which proteases are used to make the protein more easily assimilated by the body, are used in foods for immunocompromised individuals, for individuals with poor digestion, and in baby foods," notes Bargetzi.  "There are two valid reasons for fortifying with whey or milk protein," says Bargetzi. "The high-calcium advantage and the nutritional profile of the milk protein itself. By high-calcium advantage, I mean that the calcium is micronized and wedded to the milk protein, making it more suspendable, more dispersible, and more soluble." She also notes that milk protein provides many functional advantages, such as shape integrity and even browning in baked goods such as biscotti and cookies.  Individual milk proteins might provide even more benefits. For example, branched-chain amino acids from whey are thought to provide additional energy for athletes. Other whey proteins, including beta-lactalbumin, lactoferrin, lysozyme and others are being investigated for potential biological benefits. (For more information, see Food Product Design's October 1999 "Dairy Ingredients for Health.")Beyond dairy  Traditionally, gelatin is the product of hydrolyzed collagen, which is the chief protein in the hides, skins and connective tissues of animals. Animal gelatin may not be used in kosher products, but a fish gelatin has been derived from the skin of cold-water fish. Gelatin is used primarily in gelatin desserts, and also to a great extent in confections, dairy products and meats, where it functions as a binding agent and fat replacer. Although gelatin is a good source of protein, it's used chiefly for its functionalities, i.e., viscosity, stability and strong gelling at low concentrations.  Most of the proteins in eggs are glycoproteins, to which lipids may also be attached. Egg whites contain about 11% protein, and yolks about 17%. More than half of egg-white protein is ovalbumin. The yolk proteins are more complex, consisting, among others, of glycoproteins, lipoproteins and phosphoglycoproteins. Ovalbumin is easily denatured by heat, which contributes to the toughened structure of a cake as it bakes, for example, as well as the unique whipping ability of egg white or the structure enhancement of pasta. The protein in eggs is high quality and very functional, and inexpensive compared to meat-based proteins. It's more expensive than vegetable proteins, however, and for this reason is generally used at the lowest possible concentrations for functionality, and not generally for fortification purposes.Plant-protein power  By far the biggest vegetable-protein story is that of the soybean. Raw soybeans contain approximately 40% protein. Soybean protein is commercially available as isolated soy protein (90% to 92% protein, dry weight basis); soy-protein concentrate (65% to 72% protein); and soy flour (40% to 54% protein). Soybean protein is also available as hydrolyzed soy protein, with the same potential for increased functionality and digestibility noted for milk proteins, or in various soy foods such as miso, natto, tempeh, tofu, soynuts and soymilk products.  In October 1999, the FDA approved a new health claim for food products containing soy protein. If the product provides 6.25 grams of soy protein per serving in a food that is technically a low-fat, low-cholesterol food, the following claim may be made: "Diets low in saturated fat and cholesterol that include 25 grams of soy protein a day reduce the risk of heart disease. One serving of (name of food) provides __ grams of soy protein." This claim is based on recent clinical trials showing that consumption of soy protein can lower total and LDL cholesterol levels, which are risk factors for coronary heart disease. Also, because soy proteins contain no cholesterol, less cholesterol is introduced into the diet than with high-protein animal foods such as meats.  Work with soy protein is also going beyond lowering cholesterol. These proteins and associated isoflavones are being investigated for their role in inhibiting plaque formation (a cardioprotective effect); preventing bone loss from osteoporosis; decreasing risk of kidney disease; reducing menopausal symptoms; reducing risk of breast cancer; lowering risk of insulin resistance in diabetes; and combating hypertension and atherosclerosis. Isoflavones from soy are also being studied for their antioxidant (anti-cancer) effects.   Nine amino acids have been deemed essential for human nutrition. These essential amino acids are required in differing quantities depending on age. According to 1985 recommendations by the Food and Agriculture Organization of the United Nations/World Health Organization (FAO/WHO), the ideal milligrams of essential amino acids per gram of crude protein are as follows: Essential Amino AcidAge 2 to 510 to 12AdultHistidine191916Isoleucine282813Leucine664419Lysine584416Methionine + Cystine252217Phenylalanine +Tyrosine632219Threonine34289Tryptophan1195Valine352513   Besides soybeans, legumes in general are also good sources of protein. Lentils contain 29.6%; peas, 27.9%; and peanuts, 30.0%. Pea flour and pea-protein isolate are also commercially available. Peas and legumes complement cereal proteins well, an important factor in vegetarian diets. In general, the amino acids most deficient in legumes are methionine and cysteine, while seed proteins most often lack sufficient quantities of lysine, tryptophan and threonine.  Total protein in cereal grains averages about 10% to 15% on a dry basis, with about 80% found in the endosperm. The amino-acid balance of rice, oats, barley, wheat, corn and sorghum is generally acceptable, but lysine is low, and the percentage of available protein is also low. Tryptophan and methionine can also be limiting amino acids in these grains. Wheat gluten is valued mainly for its viscoelastic properties in baked products and meat products, but its nutritional quality is relatively low. Rice protein is bland and higher in lysine than other cereal proteins, and introduces less of an allergen issue than many other grains. Rice-protein concentrate, a byproduct of rice-syrup production from either white or brown rice, contains approximately 50% protein and 7% dietary fiber. Oat proteins are also hypoallergenic and have been used to replace wheat in some diets. Zein, a predominant corn protein, is an excellent film-former, and can be used in confections, although its characteristic flavor can potentially cause problems.Functional proteinsEnriching foods with protein is particularly important for products targeted toward those incapable of meeting requirements from a typical diet. When fortifying with protein, in addition to the nutritional value of the amino acids, flavor and functional characteristics of a particular ingredient also come into play.  Calcium caseinate is commonly used in nutritional foods for the elderly and infants, as are casein hydrolysates and whey-protein concentrates. "Whey-protein isolates," says Robert Beausire, technical sales manager for Avonmore Waterford Ingredients, Inc., Monroe, WI, "have come into high demand for nutritional bars, pastas and other nutraceutical foods. They are low in lactose and fat, and do not contribute negatively to the flavor profile of the food."  In milk-free formulations, soy-protein concentrates and isolates prevail. Soy and milk proteins are also used extensively in the meat industry as binders, fat replacers, bulking agents, emulsifiers, and for shrinkage control.  In baked goods, proteins may be used to improve flavor, texture, color and volume, or to decrease fat pick-up in fried products. Wheat gluten is a valued structure-builder in baked goods overall, but especially in bread products. Milk proteins are traditionally used for flavor and color, as well as volume. Soy proteins are making headway in this category, and nutritional claims and publicized health benefits will certainly increase their use.  Dairy products have traditionally used dairy proteins to support aeration, emulsification and water-binding. Caseinates are typically used in coffee whiteners for emulsion stability, but soy proteins also serve this function. Ice creams and yogurts often contain whey-protein concentrates, but soy and rice proteins are also appearing in dairy categories to help reduce allergenicity and improve nutrition.  Naturally, the percentage of protein in a food ingredient is of increased importance when nutrition is the primary use factor. Protein quality is also important when nutrition is the concern. As discussed previously, the PDCAAS of animal proteins is generally higher than that of plant proteins, unless the plant proteins are more concentrated. The score of isolated soy protein is equivalent to that of casein and egg white.Amino acids and athletes  In addition to high-protein diets, another protein-consumption quandary involves using specific amino acids for enhanced athletic performance. Regardless of scientific reports indicating a lack of benefits associated with increased levels of amino acids, L-carnitine or L-tryptophan, already by 1990 the dietary-supplement market had grown to $3.3 billion. One might assume, since athletes and the elderly require more protein, that amino-acid supplementation is a good idea. In general, though, reputable scientific studies to date don't provide a great deal of support to that hypothesis.  This has not halted the promotion of certain products for their purported activities, however. L-tryptophan specifically has been sold for its ergogenic effects. The assumption is that, by increasing seratonin levels in the brain, fatigue is delayed. A 1988 study reported a 49% increase in total exercise time with 1.2 grams of L-tryptophan supplementation per day. This report was not, however, supported by two later, more intense, studies. Some of the amino acids implicated, such as arginine, histidine, lysine, methionine, ornithine and phenylalanine do stimulate release of insulin, but have not been shown to increase athletic endurance.   Creatine monohydrate, synthesized in the liver, pancreas, and kidneys from arginine and glycine, has been used extensively by a large percentage of athletes. Creatine theoretically acts by increasing the bioavailability of phosphocreatine in skeletal muscle cells. This has the ultimate effect of increasing the force of muscular contraction and prolonging anaerobic exercise. A number of studies have supported this theory, and no negatives have been reported to date.  Most experts do not recommend L-carnitine, on the other hand, due to questionable studies and questionable purity. Carnitine is a quaternary amine synthesized in the liver and kidneys from lysine and methionine. It is thought that carnitine may prolong exercise by sparing muscle glycogen and buffering pyruvate, which reduces the lactic-acid accumulation leading to fatigue. Early reports on L-carnitine have not been substantiated however, and no study to date has shown a benefit. In addition, many supplements on the market contain D-carnitine, which is inactive in humans.   A verdict on protein supplementation for athletes is complicated by the many varying reports of its benefits. Richard B. Kreider, Ph.D., reviewed 97 research articles, 78 abstracts and 38 review articles for a review published in 1998 in the Journal of Exercise Physiology, in which he concludes that athletes "typically do not need to supplement their normal diets with protein, provided they ingest enough quality protein to maintain protein balance." (For more information on this topic, see Food Product Design's March 1998 Nutrition Notes, entitled "Maximizing Athletic Performance.")Allergen issues  While most prize proteins for their nutritional value, to some they present the risk for food allergenicity. Sensitive individuals' immune responses to allergenic substances can lead to anything from itching and hives to anaphylactic shock and possible death. The department of food science and technology at the University of Nebraska has identified about 160 foods that have produced an allergic reaction. Of these, eight foods - peanuts, milk, eggs, shellfish, tree nuts, soybeans, wheat and fish - cause 90% of allergic reactions in this country.  The number of protein-sensitive individuals is estimated at 1% to 2% of adults and between 5% and 8% of children, according to an article entitled "Food Allergens - Managing the Risk" in Medallion Laboratories' June 1997 Analytical Progress publication. Allergies generally develop during the first one or two years of life, but may be experienced at any point. It's generally accepted that allergic reactions develop in immature digestive tracts, but allergic reactions may also be genetic. If it appears that a child younger than 2 years may be sensitive, or if there is a family history of allergenicity, then soybeans, peanuts, wheat, eggs, fish and milk are not recommended. Allergies in young children may disappear over time, but some are problems for life. Children tend to be most allergic to milk and eggs, but often outgrow these reactions, while allergies to peanuts are generally permanent.Protein Content of Functional Ingredients
Product % Protein Hydrolyzed gelatin..........................................92
Pea-protein isolate........................................>90
Soy-protein isolate........................................>90
Wheat gluten................................................>90
Whey-protein isolate.....................................>90
Dried egg white..............................................81
Soy-protein concentrate.............................65-72
Rice-protein concentrate.................................50
Soy flour...................................................40-54
Non-fat dry milk.............................................38
Whey-protein concentrate..........................35-85  Public awareness of allergens in foods has dramatically increased, as have recalls due to mislabeling or lack of labeling. Fortunately, this has increased employee education at food-manufacturing plants, a process that stresses the importance of cleaning, separation of products during scheduling and re-work, and proper documentation. Many companies have eliminated peanuts and tree nuts from primary facilities, and are producing foods with these ingredients in dedicated plants.  In addition to the conditions induced by allergenicity or by too much or too little protein consumption, certain other protein-related health issues may also become a concern. For example, homocysteine may present another problem area, although whether it causes a problem or merely indicates one remains to be proven. Homocysteine is an amino acid usually metabolized in the body if adequate quantities of folate and vitamins B6 and B12 are present. A meta-analysis of 27 studies published in the September 7, 1999 Annals of Internal Medicine estimates that about 10% of coronary heart disease is attributable to elevated levels of homocysteine in blood plasma. The authors state that a recent survey found that 80% to 90% of the U.S. population averages slightly over half of the RDA of 400 micrograms of folate/day. While more studies are needed to confirm any direct connection, the authors do note that folate is known to reduce homocysteine levels.  What's the bottom line for protein? Eat fruits, vegetables and fiber, along with the right amount of good-quality protein, but don't overdo it. When selecting ingredients, consider nutrition, functionality and cost. Ask which claims are allowed on the label, and if allergens are a concern. Also consider the target market - is it athletes, infants, the elderly or the general population? The formulation options for protein continue to grow as nutrition issues becomes ever more prevalent.Ronald C. Deis, Ph.D., is a consulting food scientist based in West Chester, PA. He specializes in food ingredient technology and process/ingredient troubleshooting, and has a strong formulation background in baked goods and wet systems. He hosts a website at http://hometown.aol.com/rcdeis/deiswebpage.htm.
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