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FUNCTION AND COMPONENTS OF PROTEIN. Protein is essential to building and maintaining body tissuesAmino acids are building blocks of proteinPlant and animal proteins are made of up of 20 common amino acids. Mahan, L.K., Escott-Stump, S. Krause\'s Food, Nutrition,
PROTEIN QUALITY Methods for Evaluating Protein Quality of Fo...

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1. PROTEIN QUALITY Methods for Evaluating Protein Quality of Food Proteins An Educational Programme* by Dupont Protein Technologies in cooperation with the American Soybean Association This programme describes the evaluation of protein quality of food proteins. It focuses on new methodology that changes the way food protein quality is determined.This programme describes the evaluation of protein quality of food proteins. It focuses on new methodology that changes the way food protein quality is determined.

2. FUNCTION AND COMPONENTS OF PROTEIN Protein is essential to building and maintaining body tissues Amino acids are building blocks of protein Plant and animal proteins are made of up of 20 common amino acids Proteins are fundamental components of all living cells. Protein is essential to? 1. Building body tissues during periods of growth and development and 2. Repairing and maintaining body tissues. Proteins have numerous functions in the human body, including their vital role in muscle, hormones, enzymes, and various fluids and body secretions, and as antibodies in the immune system. Proteins also are essential to the transportation of lipids, fat-soluble vitamins, and minerals and contribute to homeostasis by maintaining a balance among body fluids. Amino acids are the building blocks of protein. At least twenty of these amino acids commonly make up both plant and animal proteins.Proteins are fundamental components of all living cells. Protein is essential to? 1. Building body tissues during periods of growth and development and 2. Repairing and maintaining body tissues. Proteins have numerous functions in the human body, including their vital role in muscle, hormones, enzymes, and various fluids and body secretions, and as antibodies in the immune system. Proteins also are essential to the transportation of lipids, fat-soluble vitamins, and minerals and contribute to homeostasis by maintaining a balance among body fluids. Amino acids are the building blocks of protein. At least twenty of these amino acids commonly make up both plant and animal proteins.

3. PROTEIN COMPOSITION The molecular weight of proteins varies between some thousand and several million Dalton. Proteins are biopolymers consisting of carbon, hydrogen, oxygen, nitrogen and partly sulphur. Some proteins contain metal ions, such as iron, copper, phosphorus or zinc. The total hydrolysis of the proteins yields a-amino acids in the L-configuration. These amino acids differ in their side chains. The molecular weight of proteins varies between some thousand and several million Dalton. Proteins are biopolymers consisting of carbon, hydrogen, oxygen, nitrogen and partly sulphur. Some proteins contain metal ions, such as iron, copper, phosphorus or zinc. The total hydrolysis of the proteins yields a-amino acids in the L-configuration. These amino acids differ in their side chains.

4. BASIC STRUCTURE OF AN AMINO ACID This is the basic structure of most amino acids. With the exception of proline and hydroxyproline, amino acids are alpha-amino carboxylic acids, consisting of a basic amino group and an acid carboxyl group attached to the same carbon atom. The structure of the remainder of the molecule?indicated in this diagram as ?R??is what differentiates amino acids.This is the basic structure of most amino acids. With the exception of proline and hydroxyproline, amino acids are alpha-amino carboxylic acids, consisting of a basic amino group and an acid carboxyl group attached to the same carbon atom. The structure of the remainder of the molecule?indicated in this diagram as ?R??is what differentiates amino acids.

5. PROPERTIES OF AMINO ACIDS Each amino acid has its own typical side chain (R) affecting its physiological and physico-chemical properties, and the properties of the proteins containing it. Amino acids may be divided into five groups according to the polarity of the side chains: Non-polar aliphatic side chains: these amino acids are less water-soluble than polar amino acids. The water solubility decreases with increasing length of the aliphatic side chain. Polar, not charged (hydrophilic) side chains: these amino acids possess neutral and polar functional groups which are able to form hydrogen bonds. The polarity is determined by the side chains. Amino acids with positively charged side chains at pH 7. Amino acids with negatively charged side chains at pH 7. Amino acids with aromatic side chains are relatively non-polar and are involved in hydrophobic interactions. Each amino acid has its own typical side chain (R) affecting its physiological and physico-chemical properties, and the properties of the proteins containing it. Amino acids may be divided into five groups according to the polarity of the side chains: Non-polar aliphatic side chains: these amino acids are less water-soluble than polar amino acids. The water solubility decreases with increasing length of the aliphatic side chain. Polar, not charged (hydrophilic) side chains: these amino acids possess neutral and polar functional groups which are able to form hydrogen bonds. The polarity is determined by the side chains. Amino acids with positively charged side chains at pH 7. Amino acids with negatively charged side chains at pH 7. Amino acids with aromatic side chains are relatively non-polar and are involved in hydrophobic interactions.

6. AMINO ACIDS IN PROTEINS Protein hydrolysates may contain these 20 amino acids: 1. Non polar aliphatic side chains: alanine (Ala), glycine (Gly), isoleucine (Ile), leucine (Leu), methionine (Met), valine (Val) 2. Polar, not charged (hydrophilic) side chains: asparagine (Asp-NH2), cysteine (Cys), glutamine (Glu-NH2), serine (Ser), proline (Pro) (proline is actually not an amino but an imino acid) 3. Positively charged side chains: arginine (Arg), histidine (His), lysine (Lys) 4. Negatively charged side chains: aspartic acid (Asp), glutamic acid (Glu) 5. Aromatic side chains: phenylalanine (Phe), tryptophan (Trp), tyrosine (Tyr) More than 150 amino acids can be identified in animal, vegetable and microbial cells, in free or bound form. Many of these amino acids represent important metabolic intermediate products or chemical messengers in free form. They are also involved in nerve pulse transmission.Protein hydrolysates may contain these 20 amino acids: 1. Non polar aliphatic side chains: alanine (Ala), glycine (Gly), isoleucine (Ile), leucine (Leu), methionine (Met), valine (Val) 2. Polar, not charged (hydrophilic) side chains: asparagine (Asp-NH2), cysteine (Cys), glutamine (Glu-NH2), serine (Ser), proline (Pro) (proline is actually not an amino but an imino acid) 3. Positively charged side chains: arginine (Arg), histidine (His), lysine (Lys) 4. Negatively charged side chains: aspartic acid (Asp), glutamic acid (Glu) 5. Aromatic side chains: phenylalanine (Phe), tryptophan (Trp), tyrosine (Tyr) More than 150 amino acids can be identified in animal, vegetable and microbial cells, in free or bound form. Many of these amino acids represent important metabolic intermediate products or chemical messengers in free form. They are also involved in nerve pulse transmission.

7. AMINO ACID PROPERTIES Amino acids may form ions in aqueous solution. This property is of great biological importance. Some properties of amino acids such as melting point, water solubility, polarity, and dielectric constant are based on the uneven charge distribution in aqueous solutions. Amino acids appear in aqueous solution as a amphoteric molecules, i.e. with positive and negative charges in the same molecule (zwitterions). According to the pH-value, they can behave as an acid or a base. Amino acids may form ions in aqueous solution. This property is of great biological importance. Some properties of amino acids such as melting point, water solubility, polarity, and dielectric constant are based on the uneven charge distribution in aqueous solutions. Amino acids appear in aqueous solution as a amphoteric molecules, i.e. with positive and negative charges in the same molecule (zwitterions). According to the pH-value, they can behave as an acid or a base.

8. AMINO ACID STEREOCHEMISTRY All amino acids, except glycine, have optical activity. This is also called chirality and is based on the existence of at least one asymmetric C-atom. There are two stereoisomers or enantiomers of the D-and L-configuration corresponding to the four substituents in the tetrahedral symmetry. Animal and vegetable proteins consist exclusively of L-amino acids. D-isomers are to be found, e.g., in the cell walls of some micro-organisms as well as in polypeptides with antibiotic properties. All amino acids, except glycine, have optical activity. This is also called chirality and is based on the existence of at least one asymmetric C-atom. There are two stereoisomers or enantiomers of the D-and L-configuration corresponding to the four substituents in the tetrahedral symmetry. Animal and vegetable proteins consist exclusively of L-amino acids. D-isomers are to be found, e.g., in the cell walls of some micro-organisms as well as in polypeptides with antibiotic properties.

9. LINKING AMINO ACIDS INTO PEPTIDES and PROTEINS Amino acids are linked by amide bonds (in the case of proteins also called peptide bonds). In this way, up to several hundred amino acids can form long polypeptide chains with a wide range of molecular weights, each with a specific amino acid sequence. Molecules with up to 10 amino acids are called peptides; proteins consist of more than 10 amino acids.Amino acids are linked by amide bonds (in the case of proteins also called peptide bonds). In this way, up to several hundred amino acids can form long polypeptide chains with a wide range of molecular weights, each with a specific amino acid sequence. Molecules with up to 10 amino acids are called peptides; proteins consist of more than 10 amino acids.

10. PROTEIN TYPES The proteins can be divided into two groups: The homoproteins: they contain exclusively amino acids. The heteroproteins: they also contain a non- protein part, the so-called prosthetic group. Depending on the type of prosthetic group, these proteins can be further divided in nucleo-, lipo-, glyco-, phospho-, hemo-, flavo- and metalo-proteins. The most important metal ions in proteins are iron, zinc, calcium, molybdenum and copper. The proteins can be divided into two groups: The homoproteins: they contain exclusively amino acids. The heteroproteins: they also contain a non- protein part, the so-called prosthetic group. Depending on the type of prosthetic group, these proteins can be further divided in nucleo-, lipo-, glyco-, phospho-, hemo-, flavo- and metalo-proteins. The most important metal ions in proteins are iron, zinc, calcium, molybdenum and copper.

11. PROTEIN STRUCTURE Proteins are characterised by their amino acid sequence and conformation, i.e. three-dimensional structure. A primary, secondary and tertiary protein structure can be identified. The primary protein structure corresponds to the amino acid sequence, i.e. to the sequence in which the amino acid residues are added to one another. The majority of the proteins contain 100 to 500 amino acid units. The secondary protein structure corresponds to the spatial arrangement of the polypeptide chain, ignoring the effect of the side chains. It is stabilised by hydrogen bonds between the peptide chains. The chain is folded into sheet-like structures or wound into spiral-like structures. The type of folding depends considerably on the amino acid sequence (e.g., ?-sheet structure). Spiral-like structures are also called helices (mostly: alpha-helix). The interaction of the amino acid side chains determines the tertiary structure. The most important interactions are hydrogen bonds, hydrophobic interactions, ionic bonds, and disulfide bonds. The peptide chains - folded into a structured protein ? may assemble into higher aggregates stabilised by non-covalent bonds. Thee spatial arrangement of these interacting polypeptide units is called the quaternary structure. Proteins are characterised by their amino acid sequence and conformation, i.e. three-dimensional structure. A primary, secondary and tertiary protein structure can be identified. The primary protein structure corresponds to the amino acid sequence, i.e. to the sequence in which the amino acid residues are added to one another. The majority of the proteins contain 100 to 500 amino acid units. The secondary protein structure corresponds to the spatial arrangement of the polypeptide chain, ignoring the effect of the side chains. It is stabilised by hydrogen bonds between the peptide chains. The chain is folded into sheet-like structures or wound into spiral-like structures. The type of folding depends considerably on the amino acid sequence (e.g., ?-sheet structure). Spiral-like structures are also called helices (mostly: alpha-helix). The interaction of the amino acid side chains determines the tertiary structure. The most important interactions are hydrogen bonds, hydrophobic interactions, ionic bonds, and disulfide bonds. The peptide chains - folded into a structured protein ? may assemble into higher aggregates stabilised by non-covalent bonds. Thee spatial arrangement of these interacting polypeptide units is called the quaternary structure.

12. MAIN PROTEIN CLASSES Proteins exert different functions as building blocks of tissues and organisms. Two major classes related to major protein functionality can be identified: fibrous proteins and globular proteins. Fibrous proteins are found in tissues and structured material such as muscle, bone, skin, cell organelles and cell membranes. Fibrous proteins fulfil structural tasks and consist of single and repeated secondary structure units (?-helix and ?-sheet structure). Examples of fibrous proteins with ?-helix structure are collagen and keratin; silk fibrin has a ?-sheet structure. Globular proteins play an important role in metabolic systems. The enzymes, a group of proteins with highly-specific, catalytic activity are a major subgroup of the globular proteins. Other proteins in this group are: hormones (e.g., insulin), contractile proteins (e.g., myosin in muscle), transport proteins (e.g., haemoglobin), protecting proteins in the blood of vertebrate animals (e.g., immunoglobulin), and all major storage proteins (e.g., glycinin in soy, ovalbumin in egg). Proteins exert different functions as building blocks of tissues and organisms. Two major classes related to major protein functionality can be identified: fibrous proteins and globular proteins. Fibrous proteins are found in tissues and structured material such as muscle, bone, skin, cell organelles and cell membranes. Fibrous proteins fulfil structural tasks and consist of single and repeated secondary structure units (?-helix and ?-sheet structure). Examples of fibrous proteins with ?-helix structure are collagen and keratin; silk fibrin has a ?-sheet structure. Globular proteins play an important role in metabolic systems. The enzymes, a group of proteins with highly-specific, catalytic activity are a major subgroup of the globular proteins. Other proteins in this group are: hormones (e.g., insulin), contractile proteins (e.g., myosin in muscle), transport proteins (e.g., haemoglobin), protecting proteins in the blood of vertebrate animals (e.g., immunoglobulin), and all major storage proteins (e.g., glycinin in soy, ovalbumin in egg).

13. PROTEIN DENATURATION The protein structure is very sensitive to physico-chemical effects. Various processes can induce protein denaturation, i.e. result in changes of the secondary, tertiary and quaternary structure. Physical effects are heating, cooling, mechanical effects, hydrostatic pressure or radiation. Chemical interaction also has a denaturing effect on proteins: acids and bases, metals and high salt concentrations, organic solvents. The protein structure is very sensitive to physico-chemical effects. Various processes can induce protein denaturation, i.e. result in changes of the secondary, tertiary and quaternary structure. Physical effects are heating, cooling, mechanical effects, hydrostatic pressure or radiation. Chemical interaction also has a denaturing effect on proteins: acids and bases, metals and high salt concentrations, organic solvents.

14. PROTEIN DENATURATION EFFECTS Protein denaturation is a complex process, which yields important conformational changes. During the denaturation process, partly unstable intermediates can appear. Every structural change of the native protein is called denaturation. Protein denaturation can be reversible or irreversible. The effects of the denaturation are various: change in the protein solubility due to a different exposure of hydrophilic and hydrophobic peptide units change of the water-binding capacity loss of the biological activity, for example in enzymes higher risk for chemical breakdown due to the exposure of less stable peptide bonds change of the viscosity of protein solutions changes in or loss of the crystallisation behaviour Protein denaturation is a complex process, which yields important conformational changes. During the denaturation process, partly unstable intermediates can appear. Every structural change of the native protein is called denaturation. Protein denaturation can be reversible or irreversible. The effects of the denaturation are various: change in the protein solubility due to a different exposure of hydrophilic and hydrophobic peptide units change of the water-binding capacity loss of the biological activity, for example in enzymes higher risk for chemical breakdown due to the exposure of less stable peptide bonds change of the viscosity of protein solutions changes in or loss of the crystallisation behaviour

15. FUNCTIONAL PROPERTIES OF FOOD PROTEINS The proteins have a major effect on the structure and sensory quality of numerous foods in fresh and processed conditions, for example on the consistency and texture of meat and meat products, milk and cheese, pasta and bread. Food quality most often depends on the structural and physico-chemical quality of the protein components. Some of these functional properties are: hydration, solubility, viscosity, gel formation, texture, dough formation, emulsification, foaming, aroma binding and interaction with other food components. The proteins have a major effect on the structure and sensory quality of numerous foods in fresh and processed conditions, for example on the consistency and texture of meat and meat products, milk and cheese, pasta and bread. Food quality most often depends on the structural and physico-chemical quality of the protein components. Some of these functional properties are: hydration, solubility, viscosity, gel formation, texture, dough formation, emulsification, foaming, aroma binding and interaction with other food components.

16. CLASSIFICATION OF AMINO ACIDS IN FOOD PROTEIN Amino acids in food protein can be classified as Essential (indispensable) - body synthesis inadequate to meet needs Non-essential (dispensable) - can be synthesised by the body Conditionally essential (indispensable) - become essential under certain conditions In the past, amino acids have typically been classified as essential or non-essential. However, it is becoming more common for the term ?dispensable? to be used in place of non-essential and ?indispensable? to be substituted for essential. Both sets of terminology are somewhat misleading since all of these amino acids are essential and indispensable to protein structure, although the terminology is meant to convey their nutritional or dietary significance. By definition, indispensable amino acids are those that must be supplied by the diet because the body cannot synthesise them in amounts sufficient to meet metabolic needs. Currently nine amino acids are classified as indispensable for all healthy human beings. Dispensable amino acids are those that the body can synthesise in order to meet its metabolic requirements. A third classification of amino acids is now recognised. Conditionally indispensable amino acids are those that become essential under certain clinical conditions. For example, glutamine and arginine are thought to be conditionally indispensable during times of metabolic stress.In the past, amino acids have typically been classified as essential or non-essential. However, it is becoming more common for the term ?dispensable? to be used in place of non-essential and ?indispensable? to be substituted for essential. Both sets of terminology are somewhat misleading since all of these amino acids are essential and indispensable to protein structure, although the terminology is meant to convey their nutritional or dietary significance. By definition, indispensable amino acids are those that must be supplied by the diet because the body cannot synthesise them in amounts sufficient to meet metabolic needs. Currently nine amino acids are classified as indispensable for all healthy human beings. Dispensable amino acids are those that the body can synthesise in order to meet its metabolic requirements. A third classification of amino acids is now recognised. Conditionally indispensable amino acids are those that become essential under certain clinical conditions. For example, glutamine and arginine are thought to be conditionally indispensable during times of metabolic stress.

17. ESSENTIAL AMINO ACIDS Histidine*** Methionine* (and Cysteine) Isoleucine Phenylalanine** (and Tyrosine) Leucine Threonine Lysine Tryptophan Valine * necessary for synthesis of cysteine ** necessary for synthesis of tyrosine *** necessary only for infants The nine amino acids considered indispensable in the human diet are: 1) histidine, 2) isoleucine, 3) leucine, 4) lysine, 5) methionine (and cysteine), 6) phenylalanine (and tyrosine), 7) threonine, 8) tryptophan, and 9) valine. Since methionine is a precursor of cysteine and phenylalanine is a precursor of tyrosine, these amino acids are often considered in pairs. Histidine is an essential amino acid only for infants.The nine amino acids considered indispensable in the human diet are: 1) histidine, 2) isoleucine, 3) leucine, 4) lysine, 5) methionine (and cysteine), 6) phenylalanine (and tyrosine), 7) threonine, 8) tryptophan, and 9) valine. Since methionine is a precursor of cysteine and phenylalanine is a precursor of tyrosine, these amino acids are often considered in pairs. Histidine is an essential amino acid only for infants.

18. COMPLETE AND INCOMPLETE PROTEINS Complete (balanced) protein ? single food protein containing all 9 essential amino acids in concentrations sufficient to meet effectively the requirements of humans Incomplete (unbalanced) protein ? single food protein deficient in 1 or more of 9 essential amino acids Food proteins are often classified as being either ?complete? or ?incomplete,? depending on their amino acid content. Complete proteins are those food proteins that contain all nine indispensable amino acids in concentrations sufficient to meet effectively the requirements of humans. Incomplete proteins are food proteins that are deficient in one or more of the nine indispensable amino acids that must be supplied by food.Food proteins are often classified as being either ?complete? or ?incomplete,? depending on their amino acid content. Complete proteins are those food proteins that contain all nine indispensable amino acids in concentrations sufficient to meet effectively the requirements of humans. Incomplete proteins are food proteins that are deficient in one or more of the nine indispensable amino acids that must be supplied by food.

19. COMPLEMENTARY PROTEINS1 People can meet their minimum daily requirements for protein and essential amino acids by ? Consuming sufficient quantities of complete protein(s) Consuming a sufficient amount of a variety of incomplete proteins Combining complete proteins with incomplete proteins2 Complementary proteins can be consumed over the course of a day3 The concept of complementary proteins is based on obtaining the nine indispensable amino acids by combining foods that alone are regarded as incomplete proteins. Two or more incomplete proteins can be combined in such a way that one or more of the indispensable amino acids deficient in one of the food proteins is provided by another protein and vice versa. When combined, these complementary proteins provide all of the indispensable amino acids needed by the human body in a balanced pattern of amino acids that is used efficiently. Another way to obtain the indispensable amino acids is to combine a small amount of a complete protein with larger amounts of incomplete protein foods. An example of a combination of complementary proteins is that of a mixture of food proteins from soy and corn or from wheat flour and casein. In these cases the protein quality of the best combination exceeds that of the individual protein sources and so the effect of combining them is synergistic. In the past, nutrition experts thought that incomplete proteins had to be consumed at the same time in order to be complementary. It is now accepted that complementary protein foods consumed during the course of a day, in combination with the body?s amino acid reserves, normally ensure an adequate amino acid balance.The concept of complementary proteins is based on obtaining the nine indispensable amino acids by combining foods that alone are regarded as incomplete proteins. Two or more incomplete proteins can be combined in such a way that one or more of the indispensable amino acids deficient in one of the food proteins is provided by another protein and vice versa. When combined, these complementary proteins provide all of the indispensable amino acids needed by the human body in a balanced pattern of amino acids that is used efficiently. Another way to obtain the indispensable amino acids is to combine a small amount of a complete protein with larger amounts of incomplete protein foods. An example of a combination of complementary proteins is that of a mixture of food proteins from soy and corn or from wheat flour and casein. In these cases the protein quality of the best combination exceeds that of the individual protein sources and so the effect of combining them is synergistic. In the past, nutrition experts thought that incomplete proteins had to be consumed at the same time in order to be complementary. It is now accepted that complementary protein foods consumed during the course of a day, in combination with the body?s amino acid reserves, normally ensure an adequate amino acid balance.

20. EVALUATING PROTEIN QUALITY Amino acid content of food protein Digestibility Amino acid requirements Based on standard amino acid requirement pattern for appropriate population age group Requirements for 2- to 5-year old child used as standard for all above 1 year How do you know which food proteins are complete and which are incomplete? In order to determine if a food protein is complete or incomplete, protein quality must be evaluated: 1. Determine the amino acid content of the food protein; 2. Calculate the food protein?s digestibility - what proportion of the protein consumed is digested, keeping in mind that only part of the protein that is digested is of benefit; and 3. Compare the food protein?s amino acid content, corrected for the digestibility of individual amino acids, with the reference amino acid requirement pattern for the population age group (pre-school age children, school-age children, young adults, adults, elderly people). The amino acid content used as the standard should reflect the amounts of the various indispensable amino acids needed to carry out the tasks of growth, repair, and maintenance of living tissues in humans. The FAO/WHO Expert Consultation, for example, uses the amino acid requirements of a 2- to 5-year old child as the standard. This age group has the most demanding amino acid requirements of any group except infants.How do you know which food proteins are complete and which are incomplete? In order to determine if a food protein is complete or incomplete, protein quality must be evaluated: 1. Determine the amino acid content of the food protein; 2. Calculate the food protein?s digestibility - what proportion of the protein consumed is digested, keeping in mind that only part of the protein that is digested is of benefit; and 3. Compare the food protein?s amino acid content, corrected for the digestibility of individual amino acids, with the reference amino acid requirement pattern for the population age group (pre-school age children, school-age children, young adults, adults, elderly people). The amino acid content used as the standard should reflect the amounts of the various indispensable amino acids needed to carry out the tasks of growth, repair, and maintenance of living tissues in humans. The FAO/WHO Expert Consultation, for example, uses the amino acid requirements of a 2- to 5-year old child as the standard. This age group has the most demanding amino acid requirements of any group except infants.

21. AMINO ACID AVAILABILITY Amino acids in a food are not necessarily entirely available. The protein degradation as well as the absorption can be incomplete. With animal proteins the digestion and absorption rate lies over 90 %, with vegetable proteins it only is around 60 to 70 %. There are several reasons for the limited digestibility of certain proteins : ? Protein conformation: proteases can attack insoluble fibrous protein less quickly than soluble, globular protein. However, the digestibility can easily be increased by protein denaturation, for example by moderate heat treatment. ? The proteins which are bound to metals, lipids, nucleic acids, cellulose or other polysaccharides, can be partially limited in digestibility. ? The digestibility of proteins can also be limited by antinutritional factors such as trypsin or chymotrypsin inhibitors. Other inhibitors affect the absorption of amino acids. ? Also the size and surface of the protein particle is important. The digestibility of grain proteins can be increased, for example, by fine grinding of the flour. ? The digestibility as well as the availability of amino acids can also be reduced by thermal treatment at high temperatures or alkaline pH value, or in the presence of reducing carbohydrates. ? Furthermore, biological differences between individuals may affect protein digestion as well as amino acid absorption. Amino acids in a food are not necessarily entirely available. The protein degradation as well as the absorption can be incomplete. With animal proteins the digestion and absorption rate lies over 90 %, with vegetable proteins it only is around 60 to 70 %. There are several reasons for the limited digestibility of certain proteins : ? Protein conformation: proteases can attack insoluble fibrous protein less quickly than soluble, globular protein. However, the digestibility can easily be increased by protein denaturation, for example by moderate heat treatment. ? The proteins which are bound to metals, lipids, nucleic acids, cellulose or other polysaccharides, can be partially limited in digestibility. ? The digestibility of proteins can also be limited by antinutritional factors such as trypsin or chymotrypsin inhibitors. Other inhibitors affect the absorption of amino acids. ? Also the size and surface of the protein particle is important. The digestibility of grain proteins can be increased, for example, by fine grinding of the flour. ? The digestibility as well as the availability of amino acids can also be reduced by thermal treatment at high temperatures or alkaline pH value, or in the presence of reducing carbohydrates. ? Furthermore, biological differences between individuals may affect protein digestion as well as amino acid absorption.

22. METHODS FOR EVALUATING PROTEIN QUALITY Examples for older biological methodologies include1,2 ? Biologic value (BV) Net protein utilisation (NPU) Protein efficiency ratio (PER) New methodology is3 ? Protein digestibility-corrected amino acid score (PDCAAS) A number of methods for evaluating the quality of food proteins have been used over the years. Older methodologies include rat bioassays such as biological value (BV), net protein utilisation (NPU), and protein efficiency ratio (PER). Biological value is a method using nitrogen balance techniques to determine the amount of absorbed nitrogen that is retained in the body for repair and maintenance. retained N BV = ---------------------- x 100 absorbed N Net protein utilisation is based on a combination of biologic value and the food protein?s digestibility. retained N NPU = --------------------- x 100 N-application Protein efficiency ratio (PER) is based on the weight gain of a growing rat divided by its intake of a particular food protein during the test period. Protein digestibility-corrected amino acid score, or PDCAAS, is a new, and potentially more accurate method for evaluating the quality of food proteins. It is based on a food protein?s amino acid content, its true digestibility, and its ability to supply indispensable amino acids in amounts adequate to meet the amino acid requirements of a 2- to 5-year old child, the age group used as the standard. % amino acid in test protein AAS = -------------------------------------------------------- % corresponding amino acid requirement For the purposes of this discussion, PDCAAS will be compared with PER.A number of methods for evaluating the quality of food proteins have been used over the years. Older methodologies include rat bioassays such as biological value (BV), net protein utilisation (NPU), and protein efficiency ratio (PER). Biological value is a method using nitrogen balance techniques to determine the amount of absorbed nitrogen that is retained in the body for repair and maintenance. retained N BV = ---------------------- x 100 absorbed N Net protein utilisation is based on a combination of biologic value and the food protein?s digestibility. retained N NPU = --------------------- x 100 N-application Protein efficiency ratio (PER) is based on the weight gain of a growing rat divided by its intake of a particular food protein during the test period. Protein digestibility-corrected amino acid score, or PDCAAS, is a new, and potentially more accurate method for evaluating the quality of food proteins. It is based on a food protein?s amino acid content, its true digestibility, and its ability to supply indispensable amino acids in amounts adequate to meet the amino acid requirements of a 2- to 5-year old child, the age group used as the standard. % amino acid in test protein AAS = -------------------------------------------------------- % corresponding amino acid requirement For the purposes of this discussion, PDCAAS will be compared with PER.

23. PROTEIN EFFICIENCY RATIO ? PER Traditional method of evaluating protein quality. In United States PER was1 ? Standard in food industry for evaluating protein quality of food proteins From 1919 until just recently, the PER had been a widely used method for evaluating the quality of protein in food. In the United States, the food industry had long used the PER as the standard for evaluating the protein quality of food proteins. The U.S. Food and Drug Administration used the PER as the basis for the percent of the U.S. Recommended Daily Allowance (USRDA) for protein shown on food labels.From 1919 until just recently, the PER had been a widely used method for evaluating the quality of protein in food. In the United States, the food industry had long used the PER as the standard for evaluating the protein quality of food proteins. The U.S. Food and Drug Administration used the PER as the basis for the percent of the U.S. Recommended Daily Allowance (USRDA) for protein shown on food labels.

24. PROTEIN EFFICIENCY RATIO ? PER Measures the ability of a protein to support growth in young, growing rats, not humans Growing rats need more sulphur- containing amino acid, methionine Sulphur-containing amino acids considered ?limiting? amino acid in soy protein Using amino acid needs of rats led to ? Overestimation of protein quality in animal protein Underestimation of protein quality in plant protein What many people didn?t realise is that the PER method uses a rat assay, and therefore basically relates the amino acid content of a food protein to the amino acid requirement of the rat, rather than the human. However, there are important differences between the amino acid needs of rats and humans. For example, the rat appears to have a much higher requirement for the sulphur-containing amino acids to support growth than is the case for infants and children. Using the amino acid needs of the rat or using rats in feeding studies would lead to A relative overestimation of the quality of animal proteins, and A relative underestimation of the quality of at least some plant proteins.What many people didn?t realise is that the PER method uses a rat assay, and therefore basically relates the amino acid content of a food protein to the amino acid requirement of the rat, rather than the human. However, there are important differences between the amino acid needs of rats and humans. For example, the rat appears to have a much higher requirement for the sulphur-containing amino acids to support growth than is the case for infants and children. Using the amino acid needs of the rat or using rats in feeding studies would lead to A relative overestimation of the quality of animal proteins, and A relative underestimation of the quality of at least some plant proteins.

25. PROTEIN DIGESTIBILITY-CORRECTED AMINO ACID SCORE ? PDCAAS Factors used in calculating PDCAAS include ? Essential amino acid content of food protein Digestibility Ability to supply indispensable amino acids in amounts adequate to meet human needs Uses amino acid requirements of 2- to 5-year old child ? most demanding requirements in any group except infants Highest possible score is 1.0 The PDCAAS is based on a food protein?s? 1. Amino acid content, 2. Digestibility, and 3. Ability to supply indispensable amino acids in the amounts adequate to meet human needs. The amino acid content used as the standard for the PDCAAS is based on the requirements of a two- to five-year old child. This represents the most demanding amino acid requirements of any age group except infants. The highest PDCAAS value that any protein can achieve is 1.0. This score means that after digestion of the food protein, it provides per unit of protein, 100% or more of the indispensable amino acids required by the two- to five-year old child. A score above 1.0 is rounded down to 1.0. Any amino acids in excess of those required to build and repair tissue would not be used for protein synthesis, but would be catabolised and eliminated from the body or stored as fat.The PDCAAS is based on a food protein?s? 1. Amino acid content, 2. Digestibility, and 3. Ability to supply indispensable amino acids in the amounts adequate to meet human needs. The amino acid content used as the standard for the PDCAAS is based on the requirements of a two- to five-year old child. This represents the most demanding amino acid requirements of any age group except infants. The highest PDCAAS value that any protein can achieve is 1.0. This score means that after digestion of the food protein, it provides per unit of protein, 100% or more of the indispensable amino acids required by the two- to five-year old child. A score above 1.0 is rounded down to 1.0. Any amino acids in excess of those required to build and repair tissue would not be used for protein synthesis, but would be catabolised and eliminated from the body or stored as fat.

26. 1. Analyse for nitrogen content 2. Calculate protein (N x 6.25) 3. Analyse for essential amino acid (IAA) content 4. Calculate amino acid score (uncorrected) mg of IAA in 1 g test protein mg of IAA in 1 g amino acid requirement pattern* 5. Determine digestibility 6. Calculate PDCAAS: PDCAAS = lowest uncorrected IAA Ratio x true protein digestibility CALCULATING PDCAAS The following steps are necessary to calculate the PDCAAS of a food protein. The food protein must be analysed for its nitrogen content. Protein content is calculated by multiplying the nitrogen content by 6.25. The food protein is analysed to determine its indispensable amino acid content. The uncorrected amino acid score is calculated by dividing the milligrams of a particular indispensable amino acid in one gram of the test protein by the milligrams of the indispensable amino acids in one gram of the reference protein which is the amino acid requirement pattern for the 2- to 5-year old child The true digestibility of food protein needs to be determined. The traditional method for determining true digestibility is based on the nitrogen balance obtained from rat feeding trials. Nuptake ? (Nfaeces ? Nfaeces endogen) x 100 True digestibility = ----------------------------------------------------------------- Nuptake This method has been recommended by the FAO/WHO Expert Consultation Group for human digestibility model studies as well. The PDCAAS is calculated by multiplying the lowest uncorrected amino acid score by the food protein?s digestibility. AAS x true digestibility The following steps are necessary to calculate the PDCAAS of a food protein. The food protein must be analysed for its nitrogen content. Protein content is calculated by multiplying the nitrogen content by 6.25. The food protein is analysed to determine its indispensable amino acid content. The uncorrected amino acid score is calculated by dividing the milligrams of a particular indispensable amino acid in one gram of the test protein by the milligrams of the indispensable amino acids in one gram of the reference protein which is the amino acid requirement pattern for the 2- to 5-year old child The true digestibility of food protein needs to be determined. The traditional method for determining true digestibility is based on the nitrogen balance obtained from rat feeding trials. Nuptake ? (Nfaeces ? Nfaeces endogen) x 100 True digestibility = ----------------------------------------------------------------- Nuptake This method has been recommended by the FAO/WHO Expert Consultation Group for human digestibility model studies as well. The PDCAAS is calculated by multiplying the lowest uncorrected amino acid score by the food protein?s digestibility. AAS x true digestibility

27. CALCULATION OF PROTEIN DIGESTIBILITY-CORRECTED AMINO ACID SCORE OF ISOLATED SOY PROTEIN This table shows the calculation of PDCAAS for isolated soy protein, the most concentrated type of soy protein ingredient. Take a look at histidine, for example. Isolated soy protein has 26 milligrams of histidine per gram of protein. The digestibility factor of 97% means that out of 26 milligrams of histidine reaching the intestinal tract, 25.2 milligrams are absorbed. A two- to five-year old child requires 19 milligrams of histidine per gram of protein, giving isolated soy protein a PDCAAS of 1.3 for this amino acid. This means that isolated soy protein provides 130% of the histidine required by the reference pattern, which reflects the requirements of a two- to five-year old child. The PDCAAS for a food protein is equal to the lowest score for a single indispensable amino acid (or amino acid pair). In this case, methionine and cysteine have a PDCAAS of 1.0, which becomes the score for the entire protein. Had all of the individual amino acid scores exceeded 1.0, the PDCAAS would still have been rounded down to 1.0, the highest PDCAAS possible.This table shows the calculation of PDCAAS for isolated soy protein, the most concentrated type of soy protein ingredient. Take a look at histidine, for example. Isolated soy protein has 26 milligrams of histidine per gram of protein. The digestibility factor of 97% means that out of 26 milligrams of histidine reaching the intestinal tract, 25.2 milligrams are absorbed. A two- to five-year old child requires 19 milligrams of histidine per gram of protein, giving isolated soy protein a PDCAAS of 1.3 for this amino acid. This means that isolated soy protein provides 130% of the histidine required by the reference pattern, which reflects the requirements of a two- to five-year old child. The PDCAAS for a food protein is equal to the lowest score for a single indispensable amino acid (or amino acid pair). In this case, methionine and cysteine have a PDCAAS of 1.0, which becomes the score for the entire protein. Had all of the individual amino acid scores exceeded 1.0, the PDCAAS would still have been rounded down to 1.0, the highest PDCAAS possible.

28. INDISPENSABLE AMINO ACID REQUIREMENT PATTERNS (FAO/WHO/UNU) This graph compares the amino acid requirements of the 2- to 5-year old child, the 10- to 12-year old child, and adults to the amino acid content of isolated soy protein. The requirements of the 2- to 5-year old child are obviously the most demanding of these three groups. WHO: World Health Organization FAO: Food and Agriculture Organization of the United Nations UNU: United Nation University This graph compares the amino acid requirements of the 2- to 5-year old child, the 10- to 12-year old child, and adults to the amino acid content of isolated soy protein. The requirements of the 2- to 5-year old child are obviously the most demanding of these three groups. WHO: World Health Organization FAO: Food and Agriculture Organization of the United Nations UNU: United Nation University

29. PROTEIN DIGESTIBILITY-CORRECTED AMINO ACID SCORE ? PDCAAS In 1993 U.S. Food and Drug Administration (FDA) adopted PDCAAS as standard for calculating percent Daily Value (%DV) of protein of food labels because ? PDCAAS is based on human amino acid requirements, making it more appropriate for evaluating protein quality of foods consumed by humans PDCAAS is recommended by Food and Agricultural Organisation/World Health Organisation (FAO/WHO), international organisation experienced in establishing such standards In January 1993 the U.S. Food and Drug Administration (FDA) replaced the PER with PDCAAS in food labeling. The agency adopted this new, and potentially more accurate method of evaluating protein quality as the standard by which the percent Daily Value (%DV) of protein is calculated for food labels. The PDCAAS is currently used for labelling protein on food products for adults and for children over one year of age. The FDA gave two reasons for adopting the PDCAAS over PER. 1. PDCAAS is based on human amino acid requirements, which makes it more appropriate for humans than a method based on the amino acid needs of animals. 2. The Food and Agricultural Organisation/World Health Organisation (FAO/WHO) had previously recommended PDCAAS for regulatory purposes. FAO/WHO is a recognised international organisation, which is experienced in establishing these types of standards.In January 1993 the U.S. Food and Drug Administration (FDA) replaced the PER with PDCAAS in food labeling. The agency adopted this new, and potentially more accurate method of evaluating protein quality as the standard by which the percent Daily Value (%DV) of protein is calculated for food labels. The PDCAAS is currently used for labelling protein on food products for adults and for children over one year of age. The FDA gave two reasons for adopting the PDCAAS over PER. 1. PDCAAS is based on human amino acid requirements, which makes it more appropriate for humans than a method based on the amino acid needs of animals. 2. The Food and Agricultural Organisation/World Health Organisation (FAO/WHO) had previously recommended PDCAAS for regulatory purposes. FAO/WHO is a recognised international organisation, which is experienced in establishing these types of standards.

30. PLANT AND ANIMAL PROTEIN SOURCES Traditionally ? Animal proteins considered complete according to the composition of the amino acids All plant proteins considered incomplete according to the composition of the amino acids Actually ? Some soy protein products and some animal proteins have a complete composition of amino acids A look at many nutrition books shows that a basic misconception about protein quality is still being promoted. Traditionally, the thinking has been that proteins of animal origin, with the exception of gelatin and some fibrous proteins, are complete proteins, while proteins of plant origin were considered incomplete proteins. Adoption of the PDCAAS to evaluate protein quality has shown that some soy proteins are also complete proteins; that is, they provide all the indispensable amino acids in sufficient quantity to meet the needs of humans. The PDCAAS of some soy protein products is equal to milk protein and egg white.A look at many nutrition books shows that a basic misconception about protein quality is still being promoted. Traditionally, the thinking has been that proteins of animal origin, with the exception of gelatin and some fibrous proteins, are complete proteins, while proteins of plant origin were considered incomplete proteins. Adoption of the PDCAAS to evaluate protein quality has shown that some soy proteins are also complete proteins; that is, they provide all the indispensable amino acids in sufficient quantity to meet the needs of humans. The PDCAAS of some soy protein products is equal to milk protein and egg white.

31. PROTEIN DIGESTIBILITY-CORRECTED AMINO ACID SCORES OF SELECTED FOOD PROTEINS This graph, which provides the PDCAAS for a number of food proteins, shows that for example isolated soy protein has a PDCAAS equal to the protein in milk and in egg white. Other properly cooked or denatured soy protein products also have a PDCAAS close to 1. As an example, an adult who needs 50 grams of protein per day could satisfy all of his or her protein needs by consuming 50 grams of isolated soy protein. Whole wheat has a PDCAAS of 0.40. This means that it would take about 125 grams of protein from whole wheat to supply the amounts of all the indispensable amino acids provided by 50 grams of this isolated soy protein. It should be noted, that use of the 2- to 5-year old reference pattern or amino acid scoring pattern for all age groups means there will be some uncertainty as to how accurately protein quality is predicted for older children and adults and that there could be some underestimation of protein quality. However, the FAO/WHO Expert Consultation considered that this would lead to a smaller error than when the FAO/WHO/UNU adult amino acid requirement pattern is used.This graph, which provides the PDCAAS for a number of food proteins, shows that for example isolated soy protein has a PDCAAS equal to the protein in milk and in egg white. Other properly cooked or denatured soy protein products also have a PDCAAS close to 1. As an example, an adult who needs 50 grams of protein per day could satisfy all of his or her protein needs by consuming 50 grams of isolated soy protein. Whole wheat has a PDCAAS of 0.40. This means that it would take about 125 grams of protein from whole wheat to supply the amounts of all the indispensable amino acids provided by 50 grams of this isolated soy protein. It should be noted, that use of the 2- to 5-year old reference pattern or amino acid scoring pattern for all age groups means there will be some uncertainty as to how accurately protein quality is predicted for older children and adults and that there could be some underestimation of protein quality. However, the FAO/WHO Expert Consultation considered that this would lead to a smaller error than when the FAO/WHO/UNU adult amino acid requirement pattern is used.

32. PROTEIN QUALITY - A SUMMARY Amino acids are the building blocks of protein, which is essential to building and maintaining body tissues The body cannot synthesise essential (indispensable) amino acids in amounts adequate to meet its needs; therefore, they must be obtained from the diet The protein quality of food protein depends on its digestibility and its ability to provide all essential (indispensable) amino acids to meet human requirements In summary, amino acids are the building blocks of protein, which is essential to building and maintaining body tissues. Amino acids are classified as indispensable, dispensable, and conditionally indispensable. Indispensable amino acids are those nine amino acids that the body cannot synthesise in amounts adequate to meet its needs. Therefore, they must be obtained directly from food. The protein quality of food protein depends on its digestibility and its ability to provide all indispensable amino acids to meet human requirements.In summary, amino acids are the building blocks of protein, which is essential to building and maintaining body tissues. Amino acids are classified as indispensable, dispensable, and conditionally indispensable. Indispensable amino acids are those nine amino acids that the body cannot synthesise in amounts adequate to meet its needs. Therefore, they must be obtained directly from food. The protein quality of food protein depends on its digestibility and its ability to provide all indispensable amino acids to meet human requirements.

33. SUMMARY PDCAAS is superior to other methods of evaluating the protein quality of food proteins for humans Isolated soy protein, with a PDCAAS of 1.0, is a complete protein and has the same score as milk protein and egg white The PDCAAS is superior to other methods for evaluating the protein quality of food proteins for humans because it measures the quality of a protein based on the amino acid requirements of the human in its appropriate age group, adjusted for digestibility. It has replaced the PER method, which has been the preferred method for evaluating protein quality since 1919. Since PER measures the ability of protein to support growth in young, growing rats, it overestimated the need for sulphur-containing amino acids. This led to an erroneous conclusion that only animal sources of protein were complete proteins and all plant sources of protein were incomplete. Adoption of PDCAAS allows evaluation of food protein quality based on the needs of humans. Isolated soy protein, with a PDCAAS of 1.0, is a complete protein and has the same score as milk protein and egg white.The PDCAAS is superior to other methods for evaluating the protein quality of food proteins for humans because it measures the quality of a protein based on the amino acid requirements of the human in its appropriate age group, adjusted for digestibility. It has replaced the PER method, which has been the preferred method for evaluating protein quality since 1919. Since PER measures the ability of protein to support growth in young, growing rats, it overestimated the need for sulphur-containing amino acids. This led to an erroneous conclusion that only animal sources of protein were complete proteins and all plant sources of protein were incomplete. Adoption of PDCAAS allows evaluation of food protein quality based on the needs of humans. Isolated soy protein, with a PDCAAS of 1.0, is a complete protein and has the same score as milk protein and egg white.

34. Teaching Objectives Major objectives of the Protein Quality Module for students and dieticians: to understand the relationship between amino acids and proteins, to understand the concept of indispensable (essential) and dispensable (non-essential) amino acids, to understand the difference between complete (balanced) and incomplete (unbalanced) proteins, to learn about the concept of complementary proteins, to be able to calculate the Protein digestability-corrected amino acid score (PDCAAS) and the Protein Efficiency Ratio (PER) to be able to explain the difference between both, to know that properly heated soy protein products and ingredients are complete proteins having a PDCAAS equal 1.0, equal to the PDCAAS for milk and egg protein.Major objectives of the Protein Quality Module for students and dieticians: to understand the relationship between amino acids and proteins, to understand the concept of indispensable (essential) and dispensable (non-essential) amino acids, to understand the difference between complete (balanced) and incomplete (unbalanced) proteins, to learn about the concept of complementary proteins, to be able to calculate the Protein digestability-corrected amino acid score (PDCAAS) and the Protein Efficiency Ratio (PER) to be able to explain the difference between both, to know that properly heated soy protein products and ingredients are complete proteins having a PDCAAS equal 1.0, equal to the PDCAAS for milk and egg protein.

35. Key Learnings Protein promotes the development of body tissue during growth and development. Only twenty different amino acids are found in animal and plant protein. Amino acids are classified as indispensable (essential), dispensable (non-essential) and conditionally indispensable (conditionally essential) amino acids. Nine amino acids are classified as indispensable, because body synthesis is inadequate to meet needs. Indispensable amino acids: histidine, isoleucine, leucine, lysine, methionine (and cysteine), phenylalanine (and tyrosine), threonine, tryptophan and valine. Complete (balanced) proteins are single food proteins containing all nine essential amino acids in concentrations sufficient to meet effectively the requirements of humans. Incomplete (unbalanced) protein is single food protein deficient in 1 or more of 9 essential amino acids. Complementary proteins are a combination of two or more incomplete proteins or smaller quantities of complete proteins with incomplete proteins that provide effectively the requirements of indispensable amino acids over the course of a day. The Protein Efficiency Ratio (PER) was the traditional protein quality measure in food. It is based on weight gain obtained when feeding protein to rats which is not necessarily appropriate for determining protein quality for humans.Protein promotes the development of body tissue during growth and development. Only twenty different amino acids are found in animal and plant protein. Amino acids are classified as indispensable (essential), dispensable (non-essential) and conditionally indispensable (conditionally essential) amino acids. Nine amino acids are classified as indispensable, because body synthesis is inadequate to meet needs. Indispensable amino acids: histidine, isoleucine, leucine, lysine, methionine (and cysteine), phenylalanine (and tyrosine), threonine, tryptophan and valine. Complete (balanced) proteins are single food proteins containing all nine essential amino acids in concentrations sufficient to meet effectively the requirements of humans. Incomplete (unbalanced) protein is single food protein deficient in 1 or more of 9 essential amino acids. Complementary proteins are a combination of two or more incomplete proteins or smaller quantities of complete proteins with incomplete proteins that provide effectively the requirements of indispensable amino acids over the course of a day. The Protein Efficiency Ratio (PER) was the traditional protein quality measure in food. It is based on weight gain obtained when feeding protein to rats which is not necessarily appropriate for determining protein quality for humans.

36. Key Learnings The Protein digestibility-corrected amino acid score (PDCAAS) is the new method for analysing protein quality. It is based on the amino acid availability and efficiency to cover the human needs for indispensable amino acids in a balanced way. The World Health Organisation, Food and Agriculture Organisation of the United Nations and (FAO / WHO / UNU) defined the amino acid requirement for 2- to 5-year old children as the Standard for analysing food protein quality for all age groups ? except babies. The US Food and Drug Administration (FDA) and the FAO / WHO adopted the PDCAAS Method PDCAAS for labelling protein on food products for adults and for children over one year of age. Isolated and heat treated soy protein products have a PDCAAS score equal 1.0, the highest score possible, equal to the value obtained with milk and egg protein. Isolated and /or properly heat treated soy protein products with a PDCAAS equal 1.0 are complete (balanced) proteins.The Protein digestibility-corrected amino acid score (PDCAAS) is the new method for analysing protein quality. It is based on the amino acid availability and efficiency to cover the human needs for indispensable amino acids in a balanced way. The World Health Organisation, Food and Agriculture Organisation of the United Nations and (FAO / WHO / UNU) defined the amino acid requirement for 2- to 5-year old children as the Standard for analysing food protein quality for all age groups ? except babies. The US Food and Drug Administration (FDA) and the FAO / WHO adopted the PDCAAS Method PDCAAS for labelling protein on food products for adults and for children over one year of age. Isolated and heat treated soy protein products have a PDCAAS score equal 1.0, the highest score possible, equal to the value obtained with milk and egg protein. Isolated and /or properly heat treated soy protein products with a PDCAAS equal 1.0 are complete (balanced) proteins.

37. References Biesalski, H.K., Grimm, P., Taschenatlas der Ern?hrung, Georg Thieme Verlag Stuttgart, 1999 Cheftel, J.C., Cuq, J.L., Lorient, D.: Lebensmittelproteine: Biochemie, funktionelle Eigenschaften, Ern?hrungsphysiologie, chemische Modifizierung. 1. Auflage, Behrs Verlag Hamburg, 1992 Elmadfa, I., Leitzmann, C., Ern?hrung des Menschen, 3. Auflage, Verlag Eugen Ulmer Stuttgart, 1998 Energy and Protein Requirements, Report of the Joint FAO/WHO/UNU Expert Consultation. Technical Report Series No. 724, 1985 FDA. Food Labeling. Fed Reg 1993; 58(3):2101-2106 FDA. Food labeling; general provisions; nutrition labeling; label format; nutrient content claims; health claims; ingredient labeling; state and local requirements; and exemptions; final rules. Food and Drug Administration, Fed Reg 1993; 58 (3):2101-2106 Mahan, L.K., Escott-Stump, S. Krause?s Food, Nutrition, & Diet Therapy, 9th edition. Philadelphia: W.B. Saunders Company, 1996 Nelson, D., Cox, M., Lehninger, A.: Biochemie, 3. Auflage, Springer Verlag Berlin, 2001 Protein Quality Evaluation, Report of the Joint FAO/WHO Expert Consultation Rome: FAO Food and Nutrition Paper No. 51, 1991 Rehner, G., Daniel, H.: Biochemie der Ern?hrung, Spektrum Akademischer Verlag Heidelberg, 1999 Rome: FAO Food and Nutrition Paper No. 51, 1991 Williams, S.R. Basic Nutrition and Diet Therapy, 10th edition. St. Louis (MO): Mosby, 1995 Young, V.R., Pellett, P.L. Am J Clin Nutr 1994; 59 (Suppl): 1203S-1212S Young, V.R., Pellett, P.L. J Nutr 1991; 121: 145-150Biesalski, H.K., Grimm, P., Taschenatlas der Ern?hrung, Georg Thieme Verlag Stuttgart, 1999 Cheftel, J.C., Cuq, J.L., Lorient, D.: Lebensmittelproteine: Biochemie, funktionelle Eigenschaften, Ern?hrungsphysiologie, chemische Modifizierung. 1. Auflage, Behrs Verlag Hamburg, 1992 Elmadfa, I., Leitzmann, C., Ern?hrung des Menschen, 3. Auflage, Verlag Eugen Ulmer Stuttgart, 1998 Energy and Protein Requirements, Report of the Joint FAO/WHO/UNU Expert Consultation. Technical Report Series No. 724, 1985 FDA. Food Labeling. Fed Reg 1993; 58(3):2101-2106 FDA. Food labeling; general provisions; nutrition labeling; label format; nutrient content claims; health claims; ingredient labeling; state and local requirements; and exemptions; final rules. Food and Drug Administration, Fed Reg 1993; 58 (3):2101-2106 Mahan, L.K., Escott-Stump, S. Krause?s Food, Nutrition, & Diet Therapy, 9th edition. Philadelphia: W.B. Saunders Company, 1996 Nelson, D., Cox, M., Lehninger, A.: Biochemie, 3. Auflage, Springer Verlag Berlin, 2001 Protein Quality Evaluation, Report of the Joint FAO/WHO Expert Consultation Rome: FAO Food and Nutrition Paper No. 51, 1991 Rehner, G., Daniel, H.: Biochemie der Ern?hrung, Spektrum Akademischer Verlag Heidelberg, 1999 Rome: FAO Food and Nutrition Paper No. 51, 1991 Williams, S.R. Basic Nutrition and Diet Therapy, 10th edition. St. Louis (MO): Mosby, 1995 Young, V.R., Pellett, P.L. Am J Clin Nutr 1994; 59 (Suppl): 1203S-1212S Young, V.R., Pellett, P.L. J Nutr 1991; 121: 145-150


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