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PROTEIN FREQUENTLY ASKED QUESTIONS to Top

What are the basic structural components of protein?
Does the protein in the following foods primarily contribute to texture, color or flavor of the food product?
Egg custard
Mayonnaise
Cheese
Foam Cake
Spinach

Describe and draw a diagram of the basic structure of an amino acid.

What is the significance of the "R" group on amino acids?

Define the following:

___ term given to an organic compounds that have both basic and acidic characteristics.
___ point where the carboxyl and the amine groups are ionized and the charge is neutral.
___ two "R" groups of protein which are hydrophilic.
___

Define the following:

___ point at which an protein is least stable.
___ is the protein structure that is a combination of amino acids in a proper sequence by means of the peptide bonds.
___ is the protein structure which includes the folding of the coiled chain or chains and is thought to influence the degree of hydration association with the "R" groups.
___ Term for linkage between two amino acids that connects the amino group of one and the acid (carboxyl) group of the other.
___ Where is any protein least stable?
change from the native state.
___ two dominant ways that proteins are colloidally dispersed.
___ The name of the change (reaction phenomenon) that occurs when the protein is changed to free amino acids.

What is protein denaturation?

Define the following terms.

___ term referring to heat destruction of pathogenic microorganisms.
___ term for process involving heating raw milk at a sufficiently high temperature for a specified time to destroy pathogenic bacteria.

What is the primary denaturing agent for each of the following?

  • formation of clabber for large curd cottage cheese
  • preparation of curd for large curd cottage cheese
  • direct formation of clabber for small curd cottage cheese
  • preparation of cheddar cheese from clabber
  • formation of foam for angel food cake
  • preparation of unbaked foam for souffle.
  • preparation of unbaked meringue
  • formation of foam for angel food cake
  • baking of prepared souffle
  • formation of a baked meringue
  • preparation of whipped cream toppings
  • formation of baked custard
  • preparation of an unflavored yogurt
  • curdled milk in "southern" dry-cured ham
  • preparation of yogurt gel
  • frying of egg

    • Describe the differences and/or similarities between the following terms:
    syneresis vs. weeping
    coagulation vs. clabber
    coagulation vs. curdling
    gelation vs. clabber

    Discuss mechanical denaturation and foam formation.
    Discuss heat denaturation.
    Discuss chemical denaturation.
    Discuss pressure denaturation.
    Discuss major proteins in foods.
    Discuss isoelectric points of major proteins in foods.
    Discuss ultraviolet light and denaturation.
    What is the affect of protein hydrolysis?
    What is the average elemental composition of protein?
    What is the primary denaturing agent for the following? -curdled milk in "southern" dry-cured ham
    What is the primary denaturing agent for each of the following? - formation of clabber for large curd cottage cheese
    What is the significance of the "R" group on amino acids?
    DEFINE AND/OR EXPLAIN THE PHENOMENA OF THE FOLLOWING TERMS:
    amphoteric amino acid syneresis
    quaternary protein structure weeping
    tertiary protein structure coagulation
    milk "forewarming" curdling
    gluten clabber
    casein gelation
    secondary protein structure whey protein
    primary protein structure homogenization
    denaturation pasteurization
    peptide linkage rennin
    milk carmelization lactose
    gelation coagulation
    calcium caseinate casein
    albumin sweetended consensed milk
    albumen evaporated milk

    Describe and draw a diagram of the basic structure of an amino acid.

    How does the amino acid composition affect functional properties?

    What is the significance of the "R" roup on amino acids?

    List four "R" groups which make a protein hydrophilic.

    Which groups would you expect to be hydrophobic?

    List four roles or functions of proteins in foods.

    Indicate by diagram and definition why proteins are considered to be amphoteric substances. What is (are) the advantages(s) and/or disadvantage(s) of the amphoteric nature of a protein?

    Describe the isoelectric point of protein and indicate why it is important in food quality and/or food preparation.

    Describe and draw a diagram indicating the peptide linkage between amino acids.

    Define a protein.

    Which of the following most accurately represents an amino acid?

    Using "gluten proteins" explain specifically how the various charged, polar, hydrophobic and disulfide amino acids contribute to the "functional properties".

    List three examples of the way an understanding of the amino acid composition of a food will give insight into its functional and quality characteristics.

    List 4 functional properties of proteins and an application where they are of importance.
    FUNCTIONAL PROPERTY APPLICATION

    Indicate the two predominant ways the proteins are colloidally dispersed. Give one example of a food protein which is primarily dispersed by each method.
    METHOD(S) OF COLLOIDAL DISPERSION
    FOOD PROTEIN EXAMPLE

    What would be the "likely" influence of substituting leucine for hydroxyproline in collagen?

    Figure 1. Structure of Proteins

    Protein A
    (alanine-glycine-phenylalanine-isoleucine)n

    Protein B
    (lysine-cysteine-phenylalanine-isoleucine)n

    Protein C
    (leucine-isoleucine-valine-alanine)

    Protein D
    (valine-phenylalanine-=isoleucine) n

    Basic "R" Group Amino Acid
    alanine -CH3
    asparagine -CH2-C=O
    NH2
    cysteine -CH2-SH
    glycine -H
    isoleucine -CH2CH(CH3(2
    leucine -CH2CH(CH3)2
    +
    lysine -(CH2)4NH3
    threonine -CHCH3 OH
    phenylalanine -CH2

    *Based on the partial proteins shown in the above figure 1, which would likely be most useful for supplementation in a frozen milk dessert mix?

    *In evaluating the amino acid composition of the protein sources shown in Figure 1, which do you think would be most appropriate for incorporation into our smooth homogeneous energy rich beverage concentrate (5% protein source, 95% plant oil).

    *In evaluating the amino acid composition of the protein sources shown in Figure 1, which of the following do you think best represents the advantages of this type of analysis.
    a. Amino acid analysis presents the total composition of the protein and presents an indication of the functional properties of the protein.
    b. Amino acid analysis presents the total composition of the protein and presents an indication of the hydrophobic/hydrophilic and change nature of the protein.
    c. Amino acid analysis presents the average composition of the protein and thus we can calculate the biological value and net protein utilization of the protein.
    d. Amino acid analysis presents the total composition of the protein. From it one can calculate the structure and thus hypothesize the functional properties of the protein itself.
    e. Amino acid analysis presents the total composition of the protein. From this one can accurately predict the isoelectric point. hydrophobic/hydrophilic nature, and the conformation of the protein.

    *Which of the peptide in figure 1 would be best to add to milk supplement to make a homogeneous, smooth beverage?

    *Using figure 1, which basic structure likely would function best to serve as a effective emulsifier, lowering both the surface tension of the water and of the oil phases?

    *Using figure 1, which basic structure represents a protein that is most likely to have great water-holding capacity-great water absorbing capacity?

    *The difference among amino acids is the "R" group. The difference will often affect water absorption. Using the indicated representative portion of a protein which would likely absorb the greatest amount of water (figure 1)

    *In analyzing the structure of the protein A show in figure , which of the following is the most true statement?
    a. This protein is a "relative" hydrophilic protein and so would be dispersible in beverages and baked products.
    b. This protein is a "relative" hydrophilic protein and so would not be readily dispersible in beverages and baked products.
    c. This protein is a "relative" hydrophobic protein and so would be readily dispersible in beverages and baked products.
    d. This protein is a "relative" hydrophobic protein and so would not be readily dispersible in beverages and baked products.

    Match the most important agents of denaturation to produce the indicated characteristics.

    MATCHING DENATURING AGENTS
    b. enzymes f. ultraviolet light
    c. freezing
    d. thermal denaturation

    ___formation of clabber for large curd cottage cheese
    ___preparation of unbaked meringue
    ___preparation of clabber for cheddar cheese
    ___baking of prepared souffle
    ___preparation of whipped cream toppings
    ___formation of baked custard
    ___preparation of cheddar cheese from clabber
    ___preparation of an unflavored yogurt
    ___formation of a baked meringue
    ___curdled milk in "southern" dry-cured ham
    ___formation of a milk clabber
    ___formation of foam for angel food cake
    ___preparation of unbaked foam for souffle.
    ___baking of cheese souffle
    ___preparation of dough for yeast bread
    ___direct formation of clabber for small curd cottage cheese
    ___preparation of whipped cream toppings
    ___preparation of yogurt gel
    ___formation of dough in flaky pastry
    ___frying of egg
    ___yeast bread dough preparation

    What is a physical change which usually occurs when any protein is denatured?

    Denaturation is a phenomena which will determine the characteristics of many foods. Indicate the most specific denaturation phenomena which creates the following food items.
    a. coagulation
    b. clabber
    c. curdling
    d. gelation
    junket
    baked custard (optimum product)
    stirred custard (overheated)

    What is the cause of syneresis in a protein system?

    Define protein denaturation.

    If denaturation is to be a meaningful term it needs a sharper definition than it now seems to have. Give a sharp definition that would be recommended. Describe/discuss the basis and considerations in arriving at a "sharp" definition.

    Indicate several visual or physical ways "we" determine if proteins are denatured.

    Indicate if the following are true or false and explain the reason for your answer. Be sure to support your answer with examples as much as possible.
    TRUE OR FALSE Maillard browning rate between reducing sugars and amines will be increased by a more acid pH.
    TRUE OR FALSE Proteins will denature less readily if the water activity (Aw) is high.
    TRUE OR FALSE Peroxidases are enzymes which may cause an off- flavor in vegetables during freezing and dehydration.
    Fortunately, these peroxidases are denatured by blanching process so they are no problem to the industry.
    TRUE OR FALSE Only the polar side chains of proteins are important to properties of proteins in foods.
    TRUE OR FALSE Amino acid analysis presents the total composition of protein and gives an indication of the functional properties of the protein.

    TRUE OR FALSE The endpoint temperature of custards is 82C for optimum quality characteristics.

    Discuss the factors in food preparation which could cause disruption of
    primary structure of proteins
    secondary structure of proteins
    quaternary structure of proteins

    What sequence of changes occurs in proteins during denaturation and coagulation?

    List five methods of protein denaturation and one food which is primarily formed or preserved by the single denaturation stress.
    DENATURING STRESS FOOD FORMED BY THIS DENATURATION STRESS
    Describe the differences and/or similarities between the following terms:
    a. syneresis vs. weeping
    b. coagulation vs. clabber
    c. coagulation vs. curdling
    d. gelation vs. clabber

    Contrast the phenomena that occur in the custard, bread, and meat.

    Be specific in designated temperature range.

    CUSTARD MEATBREAD
    0-40C
    40-60C
    60-80C
    80-100C
    100C+

    What is the primary protein responsible for the quality of the following food items? How is the protein changed to make a quality product from the "native protein"? What is the mechanism of change?
    a. stirred custard
    b. cottage cheese large curd
    c. cottage cheese small curd
    d. sponge cake
    e. baked custard

    From your viewpoint of the information, what is the single most interesting or unique similarity or difference between eggs and milk?

    The composition of the constituents in eggs and milk are most critical in food preparation; however, a number of factors will change their "quality" or "amount"./ To indicate sources of lessened contribution to quality of a product, list five source of variation in composition or quality of milk and eggs. SOURCES OF COMPOSITION SOURCES OF COMPOSITION VARIATION IN EGGS VARIATION IN MILK

    Probably the changes which occur in the colloidal systems has the greatest overall impact on preparation of a variety of foods. In the following, different products indicate the way the colloidal systems are changed to form the characteristics of the food. Do this in detail on a micro- and a macro-molecular level.
    butter
    yogurt
    large curd cottage cheese.
    curdled scalloped potatoes
    scalded milk
    baked custard
    meringues

    The approximate percentage of protein in each of the following is:
    % in egg white.
    % in wheat endosperm of hard wheats.
    % in whole milk.

    How does the amino acid composition affect functional properties?

    Using "gluten proteins" explain specifically how the various charged, polar, hydrophobic and disulfide amino acids contribute to the "functional properties".

    The composition of the constituents in eggs and milk are most critical in food preparation; however, a number of factors will change their "quality" or "amount". To indicate sources of lessened contribution to quality of a product, list five storage changes which occur in eggs and 5 sources of variation in composition of milk.

    Tofu preparation follows the basic approach to extraction of plant protein isolates. Describe the approach and the basic reason for the extraction process as applicable to other protein resources.

    Although there are different constituents with different characteristics in eggs and milk, there are some similarities between these two protein products. On eggs and milk to compare the protein, carbohydrates, water and ash content of fresh chicken eggs with homogenized milk.

    Table 3. Exploration data of Planet KZKLMSERPTMFN, Star 81591307624, Sector 4.
    MILK PROTEIN
    T R E A T M E N T C O D E
    Parameters and Characteristics A B C D E
    PROTEIN COMPOSITION:
    alanine, % 7055 5 0
    aspartic acid, %.710300
    cysteine, % 10 5 3020
    cystine, % 3 230 30
    glycine, % 10 35 0
    hydroxproline, % 0 25040
    leucine 0 0 0 10
    EGG-LIKE PRODUCTS
    Total White10.910.910.910.910.9
    Ovalbuminl 63.0 16.0 63.0 63.062.0
    Globulins 8.06.0 18.010.0 8.0
    lysozyme
    globulins
    Ovomucinl2.015.030.02.012.0
    Ovomucoidl12.049.00.012.08.0
    Avidinl0.54.05.0 0.050.0
    Conalduminl 12.010.010.012.0 10.0
    pH - Set A 4.9 5.17.6 8.49.3
    pH - Set B 6.20 5.667.746.96.78
    CUSTARD
    Viscosity (cm) 2 5.67 12.14 9.36 2.3 3.20
    Gel Strength (%) 2 19.70 3.53 53.97 29.72 97.73
    Heating Time (min) 33.40 56.94 32.82 33.51 35.61
    Endpoint Temperature C 82.00 86.00 75.00 65.00 89.00
    FOAMING AGENTS
    volume 5 4 435 495 100
    stability (ml)3 10 5 4 30 50
    specific gravity .867 .812 .109 .173 .281
    SPONGE CAKE
    Specific Gravity
    Foam .167 .912 .131 .196 .173
    Batter .260 .212 .211 .272 .298
    Volume (cc) 680 689 696 664 597
    Casein - %5 80 80 80 80 80
    alpha 55 80 55 60 50
    beta 29 2 28 15 25
    gamma 5 1 6 10 15
    kappa 15 17 11 15 15
    Whey Protein 20% 20% 50% 20% 20%
    Milk pH 6.7 6.6 6.6 6.8 6.7
    Milk isoelectric point, pH 4.9 4.6 9.0 12.0 12.0
    Coagulation Conditions for Cheeses 3,4
    Coagulation Time (min) 14.4 15.6 17.2 40.0 13.6
    Gel Strength (%)5 60.0 63.1 71.9 92.0 58.0
    Viscosity (cm) 2.10 1.67 1.69 41.54 2.40
    pH 6.6 4.8 8.8 14.0 10.0
    pH 5.1 7.0 3.8 12.0 6.0
    Temperature optimum (c) 10 5 85 50 37.0

    _________________________________________________________________
    Percent of total protein of white plus yolk.
    Viscosity determined by linespread, gel strength determined by percent sag.
    Rennin enzyme: the number of enzyme activity units was identical when used.
    Assume cheese could be produced.
    Percent of casein.
    Gel strength of clabber, % sag.

    discuss the contribution and roles of protein to food quality.

    Proteins are fundamental food components, both functionally and nutritionally. A basic understanding of protein structure and characteristics is critical for the total understanding of how these function in foods. The actual characteristics of the proteins will influence if you can whip, beat, add ingredients, or heat to form the type of food desired. The characteristics of the proteins will influence how they will behave in colloidal systems, how they contribute to the major roles of color, texture and flavor of foods.
    Color

    The role of protein in color of foods is fairly ubiquitous but not clear cut. In most instances it may either play a role through its interaction or as part of a complex molecule. One of the biggest roles is through the MaillardReaction, a browning reaction between an amine group and a reducing group of a carbohydrate. The reactions between proteins and sugars is the most common of these browning reactions which occur in baked products and a number of other foods. Selected color pigments, such as chlorophyll, are bound in the chloroplasts in a protein-lipid matrix.

    Texture

    Texture contributions of protein foods are not uncommon. For example, custards are protein gels where the gel strength is influenced by the ovalbumin denaturation. Another clear example is in the production of yogurt. In this particular case the texture of yogurt is influence by the gelation of casein.

    Flavor

    The contribution of flavor is not as clear cut. Some proteins and the amino acids may add flavor. Amino acids may contribute bitterness, sweetness and other flavors.

    REVIEW QUESTIONS Does the protein in the following foods primarily contribute to texture, color or flavor of the food product?

    Egg custard
    Mayonnaise
    Cheese
    Foam Cake
    Spinach

    odiagram the basic structure of amino acids. Protein is made up of hydrogen, carbon, oxygen and nitrogen and sometimes phosphorus and sulfur. These compounds are organized into the basic unit, amino acids. Amino acids are made up of a central pivotal carbon with bonded amino groups, carboxyl groups, hydrogen and a "R" group. The "R" group of the amino acid is the primary portion that makes the amino acid nonpolar or polar, aromatic or nonaromatic, and hydrophobic or hydrophilic. The essentiality of the amino acid has to do with the physiology of the species. Following is the basic structure.

    Review Questions Describe and draw a diagram of the basic structure of an amino acid.

    oidentify the affect and importance of the structural differences between amino acids. Chemically proteins are high polymers of the basic residue-an amino acide. Amino acids usually contain an amino group and a carboxyl group. In he table below the general formula for an amino acid is shown. The "R" group designates that portion of the amino acid which varies to give the different types of amino acids of varying characteristics. There are approximately 20 common amino acids.

    Amino acids are amphoteric organic compounds, otherwise, they have both basic and acidic characteristics. on the basis of the characteristics of the general formula this is indicated by the following:

    H2NCHROOO- (pH about 10:basic)

    +H3NCHROOO- (pH around 4 to 9)

    +H3NCHFROOOH (pH around 2 to 3: acid)

    The ionized amino acid at pH 4 to 9, depending upon the type of amino acid, is sometimes called a ZWITTERION as both the carboxyl and the amine group are ionized. When this situation is present we sometimes indicate that this is the isoelectric point of the amino acid complex - a protein. The side chains of the amino acid have basic or acidic characteristics and thus would alter the extent of ionization at any given pH

    The characteristics of the amino acids is critical to defining how they are going to behave in foods. Generally, the longer the hydrocarbon chain (carbon and hydrogen structures) the more likely it is to be nonpolar and hydrophobic. The presence of hydroxyl groups, amino groups, carboxyl groups, sulfur will increase the liklihood of the amino acid having a polar and hydrophilic aspect.

    AMINO ACIDCLASSIFICATION OF CHARACTERISTIC
    ALANINENONPOLAR
    NEUTRAL
    HYDROPHOBIC
    NONESSENTIAL
    ARGININEPOLAR
    BASIC HYDROPHILIC
    NEUTRAL
    ESSENTIAL
    ASPARAGINEPOLAR
    NEUTRAL
    NONESSENTIAL
    ASPARATIC ACIDPOLAR
    ACIDIC HYDROPHILIC
    NONESSENTIAL
    CYSTEINEPOLAR
    NEUTRAL
    ESSENTIAL
    GLUTAMIC ACIDPOLAR
    ACIDIC HYDROPHILIC
    NONESSENTIAL
    GLUTAMINE POLAR
    NEUTRAL
    NONESSENTIAL
    GLYCINEPOLAR
    NEUTRAL
    HYDROPHOBIC
    NONESSENTIAL
    HISTIDINE POLAR
    NEUTRAL
    BASIC HYDROPHILIC
    ESSENTIAL
    ISOLEUCINE NONPOLAR
    HYDROPHOBIC
    ESSENTIAL
    LEUCINE NONPOLAR
    HYDROPHOBIC
    ESSENTIAL
    LYSINE BASIC HYDROPHILIC
    ESSENTIAL
    METHIONINENONPOLAR
    HYDROPHOBIC
    ESSENTIAL
    PHENYLALAINE NONPOLAR
    AROMATIC
    HYDROPHOBIC
    ESSENTIAL
    PROLINE NONPOLAR
    HYDROPHOBIC
    NONESSENTIAL
    SERINE POLAR
    NEUTRAL
    NONESSENTIAL
    THREONINE POLAR
    NEUTRAL
    ESSENTIAL
    TRYPTOPHANEPOLAR
    NEUTRAL
    HYDROPHOBIC
    ESSENTIAL
    TYROSINE POLAR
    AROMATIC
    ACIDIC HYDROPHILIC
    NEUTRAL
    NONESSENTIAL
    VALINE NONPOLAR
    HYDROPHOBIC
    ESSENTIAL

    Relating these to the protein is important. The backbone of protein is the linking of amino acids head to tail; the carboxyl group of one unit is joined with the amino group of the next. This linkage occurs by removing a molecule of water, leaving the structure -CO-NH- The carbon-nitrogen linkage created in this way is called a peptide bond. The protein chain is a polypeptide. Because of the configuration of the peptide bond and the basic molecular structure, it constrains the polymer so it does not easily fold. Review Questions What is the significance of the "R" group on amino acids?

    Define the following:

    ___ term given to an organic compounds that have both basic and acidic characteristics.
    ___ point where the carboxyl and the amine groups are ionized andthe charge is neutral.
    ___ two "R" groups of protein which are hydrophilic.
    ___

    ohypothesize the relationship between composition and protein characteristics. A protein's three-dimensional structure impacts its function. The structure is maintained by chemical bonds such as covalent, electrostatic charges and hydrogen bonds. These different types of bonds occur due to the "R" groups and their differences.

    The amino acids form the protein due to the reaction between the amine group of one amino acid and the carboxyl group of another. The conformation of a protein molecule in the native state is determined by: the primary structure, the secondary structure, a tertiary structure.

    The PRIMARY STRUCTURE is the combination of amino acids in a proper sequence by means of the peptide bonds. No other forces or bonds are implied by this structural level designation.

    SECONDARY STRUCTURE is that which forms a pleated or helix structure. The alpha-helix is stabilized by hydrogen bonding between carbonyl and the amide groups of the peptide bonds which generally appear in a regular sequence along the chain of amino acides.

    A TERTIARY structure is the folding of the coiled chain or chains and is thought to influence the degree of hydration associated with the "R" groups. The stabilization of this structure has been ascribed to the side chain characteristics and their interaction. Covalent, hydrogen and hydrophobic bonding, ionic bridges, disulfide linkages and van der Waals forces may be involved in the structural organization of protein molecules.

    The question is frequently asked How does the composition of proteins impact the functional properties?

    This page looks at the way the different amino acids will contribute to the functionality of proteins, that is, how the proteins will behave in a food. For example, in the diagram below, one sees that the ability to gel, bind water, and become more soluble as the charge decreases. A protein is more likely to contribute to foam and emulsify as the hydrophobic nature decreases.

    The following table gives another look at this. Again look how the structure of the protein and hydrophobicity contributes to foaming. These same factors improve emulsification. Note how solubility decreases as hydrophobicity of the number of amino acids increases. The increases in alpha helix, beta-sheets will also decrease solubility.

    Contribution of Charge Frequency, Hydrophobicity and Structural Factors to Functionality of Proteins.
    Functional PropertyCharge FrequencyHydrophobicityStructural Factors
    Emulsification(-)+ surface+
    Fat binding(-)+ surface-
    Foaming-+ total+
    Heat coagulation-+ total+
    Solubility+--
    Water holding+-.?

    ( )contributes to a lesser extent, surface refers to surface hydrophobicity, total refers to total hydrophobicity, + positive contribution, - negative contribution.
    Modified from Fennema, 1996.

    Review Questions Define the following:

    ___ point at which an protein is least stable.
    ___ is the protein structure that is a combination of amino acids in a proper sequence by means of the peptide bonds.
    ___ is the protein structure which includes the folding of the coiled chain or chains and is thought to influence the degree of hydration association with the "R" groups.
    ___ Term for linkage between two amino acids that connects the amino group of one and the acid (carboxyl) group of the other.
    ___ Where is any protein least stable?
    change from the native state.
    ___ two dominant ways that proteins are colloidally dispersed.
    ___ The name of the change (reaction phenomenon) that occurs when the protein is changed to free amino acids.

    odefine protein denaturation.