3 Flashcards
General protein components
Carbon, hydrogen, oxygen, sulfur, nitrogen. Sometimes iron, copper, phosphorus, zinc. Central C atom is Alpha carbon and is bonded to Amino(acts as base) group and carboxl(acts as acid) group, hydrogen atom and another functional group (side chain). 20-33,0000 AA can be linked together. = 50,000 dfferent types of proteins in human body.
Polarity of side chains
Polarity of side chains: nonpolar, uncharged polar, positively charged, negatively charged. Nonpolar will form hydrophobic groups with lipids, sterols, etc. Neutral will form Hbonds with water, polar side chains act as buffers.
List of essential and nonessential AA
Essential: Phenylalanine, Valine, Lysine, Leucine, Isoleucine, Threonine, Tryptophan, Methionine, Histidine.
Nonessential: Alanine, Asparagine, Aspartic acid, Glutamic acid, Serine
General importance of proteins in food (2)
Food allergies are often due to protein components in food.
Proteins give a lot of the characteristics to the food.
Protein structure
1: sequence of AA. Peptide bonds
2: Structure formed by Hbonds. Alpha helix, beta sheet or sometimes unordered structure (random coil).
3: Full 3-dimensional structure of a protein.
4: 3-dimensional arrangement of multi-subunit proteins. (2,4,8 subunits)
Protein denaturation
Loss of 2ndary or 3tiary structure. Caused by pH, T, or ionic strength.
Ex: solidification/opaqueness (egg whites when cooked). Production of foam (meringue due to air incorporated by surface denatured protein molecules.
Coagulation: changes physical properties permanently and alters ability to bind to water and interferes with biological interactions of enzymes.
Soundwave and irradiation may work. Mechanical actions like beating, kneading may disrupt structure.
Change in pH. Exposure to mineral salts/metals may work (Sodium, potassium)
3 types of proteins
Globular:Spherical. Water-soluble because of hydrophilic AA on surface of hydrophobic core. Denaturation results in exposing hydrophobic core to decrease solubility and cause aggregation.
Fibrous (ex:collagen): insoluble
Membrane: insoluble
4 characteristics that food scientists look at to determine a protein’s function in a food
Water absorption, viscosity, solubility, stability in acids/bases.
Functional properties of proteins in food
Thinkening agent: increasing viscosity because of water binding capacity and size.
Gelling agents: gelatin, b-lactoglobulin
Curd forming: milk proteins (casein), soy proteins (tofu)
Emulsifying: bring water and oil together
Meat analog formation: soy proteins (TVP)
Viscoelasticity: gluten in wheat (glutenin and gliadins)
Production of color/flavor: Myoglobin, (muscle protein) for oxygen (red fresh meat)
Maillard reaction
Amine group on alpha carbon on protein reacts with open-chain form of sugars. The proteins with an Amino group on the side chain (ex:lysine) also do Maillard reaction but it’s unfavorable because it is an essential amino acid and with Maillard reaction it’s transformed or not absorbable. With peptide formation, the amino group (on alpha carbon is converted to amide group which does not participate to Maillard reaction.
Enzyme activity useful in food industry
Production of HFCS or inverted sugar: amylase, glucose isomerase.
Meat tenderization: papain (in papaya)
Removal of headspace oxygen to prevent oxidation: glucose oxidase
Curd formation in cheese: rennet
Induced-fit model is important in
Enzyme activity as catalysts
Coenzymes
Coenzymes bind to enzymes to change their shape so the substrate can fit in active site. Or doing the same to the substrate. They do so by accepting an atom/molecule and transfer it to another compound. Ex: B vitamins, calcium, magnesium, zinc
Putrefaction is caused by
Proteolytic enzymes: degrade proteins to AA which undergo deamination and decarboxylation.
Lipases: liberate free FA = off-flavors are caused by short-chain FA. Lipoxygenases: are responsible for lipid oxidation = rancidity.
Factors that affect enzymes
Water availability: acts as a reactant and a solvent. Is essential for enzymatic activity.
Concentration of solution: more substrate = higher rate of reaction up to saturation point (vmax)
Temperature: Heat stops enzyme activity
pH: too high or too low denatures enzymes
Electrolytes: usually have charges that can bind to charged side chains of enzymes and inhibit them to bind to form products-enzymes complex
Enzyme inhibitor: prevents complex from forming by changing shape pf enzyme/substrate. Helps against bacteria/mold because block their enzymes.
