Lecture 7 HN 300 - Overview of Proteins and and Milk and...

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Unformatted text preview: Overview of Proteins and and Milk and Milk Products HN 300 HN Proteins Proteins Greatly influence the quality of foods Greatly containing them. containing Affected by many aspects of food Affected preparation, including heat and pH. preparation, Found in wide variety of foods that we Found commonly consume: meats, baked goods, nuts, dairy products, legumes, vegetables, and much more and Perspective of the Food Scientist Perspective Functional properties of proteins are those Functional properties that influence food quality and appeal. appeal. These properties are determined by the These primary, secondary, tertiary, and quaternary structures of proteins and vary widely among proteins. Heating, changes in pH, whipping, drying, and other treatments may alter the functional properties of proteins. properties Functional Qualities of Proteins Functional Protein functionality is difficult Protein to study in complex food systems. Most studies have been done in model systems with purified proteins under carefully defined conditions. carefully Functional Qualities of Proteins Functional Gelation, thickening, foaming, Gelation, water holding, emulsification, coloring (eg.,myoglobin, Maillard browning products), cohesion, dough formation, and texturization. Thus proteins are highly versatile food ingredients and are used in a wide range of products. in A key property of proteins is solubility, key because many of the functions of proteins depend on solubility. For example proteins must be in solution to form gels. Protein solubility is affected by pH, ionic strength, divalent cations, temperature, and amino acid composition of the protein. amino Functional Qualities of Proteins Functional Proteins are large molecules that Proteins have a strong tendency to interact with other protein molecules, metal ions, water, lipids, and carbohydrates. Thus proteins can have marked and sometimes unpredictable effects on foods. unpredictable Basic Composition of Proteins Basic Composed of amino acids Composed Amino acids are linked together by peptide Amino linkages linkages Amino acids contain an amino group (-NH2) and a carboxyl group (--COOH), as and well as various organic components, designated the R-group designated The amino group, carboxyl group (acid), The and R-group are all attached to a single carbon, called the α carbon Structure of Amino Acids Structure R Group Group The R-group can range from a single The hydrogen atom (Ex: glycine) to a complex structure, such as the dual ring structure found in tryptophan found Tryptophan Peptide Linkage Peptide Peptide bonds are a linkage Peptide between the nitrogen of one amino acid and the carbon of the carboxyl group of another. carboxyl This is a covalent bond. This a dehydrating reaction in that This one molecule of water is lost. one Formation of a Peptide Bond Formation Amino Acids in Foods Amino Table 13.3 in your book displays the 22 Table amino acids found in foods amino Of those 22, 9 are essential amino acids This means they cannot be synthesized by This humans and must provided through diet humans The R-group or side chain determines the The specific characteristics of the particular amino acid amino Proteins Proteins Contain amino acid residues linked by Contain peptide bonds peptide Results in a backbone with a repeating Results pattern: --N—C—C—N—C—C—N, etc. pattern: The R-groups and the =O extend out from The this backbone this This is the primary structure of the protein There are several levels to the structure of proteins structure 1. Primary structure: 1. Primary The linear arrangement of amino acids in a protein and the location of covalent linkages such as disulfide bonds between amino acids. as 2. Secondary structure: Areas of folding 2. Secondary Areas or coiling within a protein; examples include alpha helices and pleated sheets, which are stabilized by hydrogen bonding ng which There are several levels to the structure of proteins structure 3. Tertiary structure: The final three3. Tertiary dimensional structure of a protein, which dimensional results from a large number of nonresults covalent interactions between amino covalent acids. 4. Quaternary structure: Non4. Quaternary covalent interactions that bind multiple covalent polypeptides into a single, larger protein. Hemoglobin has quaternary structure due to association of two alpha globin and two Primary Structure of Proteins Primary Secondary Structure of Proteins Secondary o The two most common arrangements are the beta pleated sheet and the alpha helix. o There are also other, less common arrangements. o These configurations are held together by hydrogen bonds. Tertiary Structure Tertiary Caused by Caused convolution and folding as a result of secondary forces between the R groups groups Secondary forces Secondary include: H bonds, salt bridges, disulfide linkages, and hydrophobic interactions interactions Examples of Quaternary Structure Examples Types of Proteins Types Three general categories of Three proteins occur in foods: proteins Globular Fibrous Conjugated Globular Proteins Globular Native proteins with a tertiary structures Native that is rather spherical that Examples: Enzymes Some hormones Oxygen-transporting proteins Albumins Histones Protamines Fibrous Proteins Fibrous Insoluble, elongated protein molecules Ex: collagen and elastin (meats and Ex: poultry) poultry) Conjugated Proteins Conjugated Proteins combined with some other type of Proteins compound (carbohydrates, lipid, etc.) compound Examples: Mucoproteins (aka glycoproteins): contain Mucoproteins carbohydrate—ovomucoid in egg carbohydrate—ovomucoid Lipoproteins: contain lipid Metalloproteins: contain a metal—ferritin, Metalloproteins: hemoglobin hemoglobin Nucleoproteins: contain a nucleic acid Phosphoproteins: contain inorganic Phosphoproteins: phosphate—casein in milk phosphate—casein Proteins and Electrical Charge Proteins Some amino acid residues Some incorporated into a protein molecule can hold a charge, depending on the pH of the medium pH Amino acids are amphoteric: Capable of functioning as either an Capable acid or a base, depending on the pH of surrounding medium pH Isoelectric Point Isoelectric This is the pH at which a protein molecule This is electrically neutral is Differs for different proteins At pH below (acidic) isoelectric point, At molecule has a net positive charge molecule At pH above (basic) isoelectric point, At molecule has a net negative charge molecule The minimum solubility of a protein occurs The at the isoelectric point (So, when a fluid containing protein is brought to this point, curdling can occur.) curdling Hydrolysis Hydrolysis Protein molecules may Protein undergo hydrolysis to form shorter chains shorter Enzymatic action by Enzymatic peptidases is the usual cause peptidases Sometimes collagen cleaved Sometimes by acid hydrolysis by Denaturation and Coagulation Denaturation When proteins are subjected to stresses When (heat, agitation, and UV light), they may ), undergo changes such as decreased solubility and loss of ability to catalyze reactions (enzymes) reactions Changes are caused by physical alteration Changes of the shape of the protein molecule— of denaturation This causes different R groups to appear This on the surface of the molecule, which leads to a change in behavioral characteristics characteristics Denaturation Denaturation How does this occur? Protein molecules relax from Protein their tertiary state into their secondary structure Become more elongated Proteins align into clumps joined Proteins by H bonds (coagulation) by Causes an increase in viscosity Coagulation Coagulation This is the precipitation of protein as This molecules aggregate molecules Often a result of the input of energy: Heating (Egg cookeryclear egg Heating white turns opaque when cooked) white Beating (Egg white foam) Changes are typically irreversible Enzymes Enzymes Are proteins Capable of catalyzing specific chemical Capable reactions reactions Because they are proteins, they are Because subject to denaturation and coagulation subject If this occurs, the catalytic ability of the If enzyme can be destroyed enzyme Sometimes it is desirable to halt the Sometimes activity of the enzyme Enzymes in foods are important to Enzymes consider in food storage and preparation of foods of Milk and Milk Products Milk Composition of Milk Composition Milk is an array of chemical compounds in an Milk aqueous medium. aqueous The composition of whole cow’’s milk is s approximately: approximately: 88% water 5% carbohydrate 3.5% protein 3.3% fat Nutrient composition varies from breed to breed, Nutrient seasonally, as well as from beginning to end of milking session session Milk Usage/Production in the US Milk Primarily used as a beverage and in food Primarily preparation preparation In order to increase milk production of In cattle, many dairy farmers use recombinant bovine somatotropin (rbST) recombinant This hormone stimulates milk production It is genetically engineered by inserting the It gene for bovine somatotropin into bacteria and harvesting the protein and Lipids in Milk Lipids Fat: 3-4% in whole milk Most expensive component • Amount varies with breed 48% of calories Carries fat-soluble vitamins and cholesterol 1 cup whole milk = 33 mg cholesterol 1 cup skim milk = 4 mg cholesterol Milk fat is separated from whole milk at dairy to Milk form skim milk form Milk fat added back in to form 1% and 2% milk Milk Fat Milk Contains an array of fatty acid molecules in its Contains triglycerides (range from 4-24 carbons) triglycerides 64 fatty acids identified in milk Butyric acid gives it its unique flavor Fat exists in globules covered by a membrane Fat composed of lipid, protein, and lecithin composed Membrane = fat globule membrane Fat lighter than water, so globules rise to top (removal Fat of fat from top = creaming) of Fat-Globule Membrane Fat-Globule See figure 14.1 in your book for more detailed figure. Carbohydrates in Milk Carbohydrates 1 cup of milk contains about 11- 12 grams of carbohydrates Most of which is lactose Milk also contains small amounts Milk of glucose and galactose of Minor quantities of Minor oligosaccharides oligosaccharides Lactose: Lactose: Disaccharide 1/5th as sweet as sucrose Fairly uncommon, except in milk and milk products Not easily digested by non-caucasian adults Difficult to dissolve and keep in solution Precipitates easily, especially at low temps α-lactose less soluble than β-lactose -lactose As α-lactose crystals precipitate, can lead to a gritty As -lactose texture texture α-lactose crystals form during processing of dried -lactose milk solids milk They are hygroscopic (hold water) causing lumping Protein in Milk Protein 3-4% of milk Two major constituents: Casein Soluble whey proteins Most of the casein in milk do not exist as Most isolated molecules but instead aggregate together to form a complex structure known as the casein micelle known Also a small amount of enzymes Casein Casein Comprise 80% of the protein in milk The caseins are a group of proteins that are designated The by Greek letters: alpha-,beta-, and kappa-caseins by Casein molecules aggregate with each other, as well as Casein calcium and phosphorus to form micelles (raspberry-like clusters) clusters) The surface of micelles are composed of κ-casein, which The -casein, block the aggregation of micelles block Micelles: hydrophobic core, hydrophilic on surface, Micelles: therefore natural emulsifier therefore Casein micelles form a colloid in milk Casein cont.. Casein κ-casein has a hydrophilic portion, -casein allowing the micelles to be easily dissolved dissolved Other caseins are all hydrophobic, but Other are in the center of the micelles and are hence shielded are Casein molecules block light Casein transmission, causing it to be opaque transmission, Casein Micelles Casein Formation of Curd Formation The casein coagulates to form the The structural backbone of cheese curd, casein molecules combine to form structures called micelles and are held together by calcium. together Can clot milk using two means: Acid Rennin Curd Formation with Acid Curd As casein is brought to it’s ’s isoelectric point, it begins to curdle curdle The combined isoelectric point of The the four casein molecules is 4.6 the This occurs when acid is added to This milk milk Clotting of Casein Micelles Clotting Formation of Curd with Rennin Formation Splits off the hydrophilic portion of Splits kappa casein, which is responsible for stabilizing the micelles micelles Micelles can now aggregate and Micelles form a gel, this is a cheese curd form Rennin is a proteolytic enzyme Rennin found in the stomach of ruminates found Whey Proteins Whey Contained in the liquid portion that Contained drains from the curd of clotted milk milk Make up about 20% of milk Make proteins proteins Lactalbumins and lactoglobulins Sensitive to heat (but doesn’t ’t coagulate at pH of 4.6) coagulate Enzymes in Milk Enzymes Milk contains many enzymes Many are resistance to denaturation and Many depends on the specific enzyme depends Common milk enzymes: Lipase (breaks down lipids) Protease (breaks down proteins) Alkaline phosphatase: activity indicates lack of Alkaline pasteurization, as it is denatured when milk is heat treated to destroy microorganisms treated Xanthine oxidase: Breaks down flavin-adenine Xanthine dinucleotide (FAD) to yield riboflavin dinucleotide Vitamins and Minerals in Milk Vitamins Good source of both water and fat soluble Good vitamins vitamins Excellent source: riboflavin (light Excellent sensitive), calcium, phosphorus sensitive), Good source: thiamin, niacin, vitamin A Not a good source: iron and vitamin C Vitamin D is added to almost all milk today Vitamin (fortification) (fortification) What creates the flavor of milk? What Aldehydes, ketones, acids Flavor is influenced by milks treatment after Flavor harvesting: harvesting: Heating (causes a cooked flavor) Fermentation (acid formed from lactose) Storage can change the flavor profile Lipase acts on lipids, releasing butyric acid and Lipase other FA’s which affect flavor other Sunlight can trigger formation of sulfur Sunlight containing compounds containing Feed of cattle can affect flavor as well Milk Production Milk Milk is produced by mammals. The major Milk production is from cows. Less amounts are collected from goats, and sheep, and this milk goes mainly into cheese production production Amount of milk fat and quantity of milk Amount produced varies with breed: produced Holstein produces most milk Guernsey and Jersey produce highest milk fat Holstein Cow Holstein Pasteurization Pasteurization Raw milk (directly from animal) is Raw medium in which micro-organisms can thrive: Tuberculosis, Diptheria, Salmonellosis, Typhoid fever, undulant fever, Q fever, Listeria Listeria Issue is as soon as milk Issue expressed from the udder it can become contaminated become Pasteurization Pasteurization Milk must be refrigerated Milk immediately and handled under sanitary conditions— under udders cleaned, all equipment udders cleaned, milk parlor kept spotless and sanitized spotless Majority of milk on market today is pasteurized today Pasteurization Pasteurization Heat treatment of milk adequate to kill Heat microorganisms that can cause illness in humans humans The higher the temp, the shorter the time The required to kill the dangerous microorganisms microorganisms Increases shelf life Goal is to minimize breakdown of vitamins Goal and proteins, while killing microorganisms and Methods of Pasteurization Methods Hold (Batch): low temperature (145ºF), long time F), (30 minutes) HTST: high temperature (161ºF), short time (15 F), seconds) UHT pasteurization: 280ºF for 2 seconds for Longer shelf life Longer Allows for storage of milk in a closed, sterile container Allows at room temperature at May cause a cooked flavor Must be refrigerated once opened Diagram of Pasteurization Diagram Homogenization Homogenization Creaming: the separation of fat from the Creaming: aqueous portion of milk that takes place when fat globules cluster into larger aggregates and rise to the surface of the milk milk Homogenization: Mechanical process in Homogenization: which milk is forced through tiny apertures under a pressure of 2000-2500 psi, which breaks up the fat globules into smaller units that do not separate from the milk units Can occur before or after pasteurization Homogenization… Homogenization… Causes milk to lose its ability to cream Causes (due to protein layer around globules) (due Causes increased viscosity and whiter Causes appearance of milk appearance Causes milk to be less stable to heat, Causes more sensitive to light, and foams more readily readily Flavor less distinctive Evaporation Evaporation Milk is mostly water: expensive to Milk store and transport store Milk can be evaporated to lower costs Doubles concentration of protein and Doubles fat fat Can be accomplished under partial Can vacuum, so the temp need not be as high, which will minimize flavor/color changes changes Evaporated Milk Products: Evaporated Evaporated Milk: concentrated Evaporated to ½ its original volume to Reconstituted 1:1 with water Slightly tan in color due to Slightly Malliard reaction Malliard Sweetened Condensed Milk: Sweetened Canned milk to which sugar (40-45%) is added; evaporation of about ½ the water and heat treatment to kill microorganisms precede the canning process canning Dried Milk Dried Instantized dried milk is milk that has been Instantized dried, moistened until sticky, and then redried, dried into spongy aggregates of solids that dried re-hydrate readily without clumping—key is double drying is Can be stored for a long period of time Can without refrigeration without Milk powder contains: lactose, fat Milk (globules or free), protein (precipitated whey and casein micelles), and air interspersed interspersed Lumping is an issue—must have airtight Lumping packaging packaging Fermentation Fermentation Various microorganisms used to Various ferment milk products ferment Frequently used: Streptococcus Frequently lactis, various lactobacilli lactis, They produce lactic acid, which They eventually leads to the association of casein micelles association Buttermilk somewhat thickened Buttermilk due to action of lactic acid due Fermentation Fermentation Yogurt acidified until forms a gel —fermentation and controlled —fermentation heat heat Undesirable microorganisms can Undesirable also grow under these conditions also —ropy consistency, putrid odors, —ropy off flavors may result—therefore must control which microorganisms present (sanitation and quality control) (sanitation Milk Products Milk Fluid Milk Fluid FDA regulates: FDA percentage of fat percentage percentage of Non-Fat Milk Solids percentage (everything but the water and the fat) Lactose-Free Milk Lactose-Free Treated with enzyme lactase to Treated remove lactose Milk Products cont… Milk Cream Cream High Fat part of milk: High • Light Cream: 18% Fat Light • Heavy Cream: 36% Fat Heavy • Half and Half (cream diluted with nonfat milk): Half 10.5% Fat 10.5% Produced by centrifugation to separate cream from Produced aqueous portion aqueous Cultured sour cream created by adding lactic acidforming bacteria to cream Reduced fat version requires many more stabilizers, Reduced because there is not enough fat to give it body because Milk Products cont… Milk Butter Butter Techinically a dairy product, actually water in Techinically oil emulsion (15% water, 80% fat) oil Churning reverses colloidal dispersion—water Churning goes from continuous phase to dispersed Subsequent chilling results in formation of Subsequent β΄fat crystals β΄ Sweet Cream butter Sweet • Streptococcus diacetyllactis added Streptococcus Produces diacetyl, major flavor of sweet cream butter Milk Products Cont… Milk Sweet acidophilus milk Inoculated c/ Lactobacillus acidophilus, but Inoculated not allowed to ferment; therefore is sweet not Kefir Is a fermented milk that is inoculated with Is lactobacillus acidophilus and yeast, this results in a yogurt like drink with alcohol and tiny bubbles produced by the yeast tiny Cheese! Cheese! " A product made from curd obtained from product the whole, partly skimmed, or skimmed milk of cows, or from milk of other animals, with or without added cream, by coagulating with rennet, lactic acid, or other suitable enzyme or acid, and with or without further treatment of the separated curd by heat or pressure, or by means of ripening ferments, special molds, or seasoning" - FDA Cheese… Cheese… Curd (coagulated casein) is formed using Curd Rennet (Rennin, Chymosin) Rennet • Enzyme from lining of calves stomach that cleaves Enzyme casein to coagulate milk • Now 70% of Rennet (Chymosin) is from Now Genetically Engineered microorganisms Acid produced by Streptococcus lactus and Acid Lactobacillus bacteria • Lactose fermentation produces acid which Lactose coagulates casein • Cottage cheese made this way Cottage Natural Cheeses Natural See FDA definition Categorized according to firmness or Categorized moisture content moisture Soft cheeses Hard cheeses Natural Cheeses Natural Soft Cheeses contain 40-75% water, large fat Soft globules Hard Cheeses contain 30-40% water, very tiny Hard fat globules Ripening (aging period) also known as affinage may require 2-12 months depending of the may type of cheese type Result of bacteria, yeast, or mold action Result • ferment lactose ferment • break down some fat break • break down some protein to amino acids break • yield distinctive flavors/textures Ripened Cheeses Ripened Not Ripened Not Bacterial Ripened Bacterial Cottage cheese Cottage Cream cheese Cream Swiss cheese: holes due to carbon dioxide produced Swiss by bacteria Cheddar Cheddar Parmesan Parmesan Mold Ripened Mold Blue cheese Blue Camembert Camembert Brie Brie Pasteurized Process Cheese Pasteurized American Cheese American Contains one or more Ripened Cheeses Contains Melted and Pasteurized Melted Emulsifier added to allow cheese to withstand heat Emulsifier Result: smooth cheese in jar or solidified in square Result: mold Process cheese food has more moisture, softer Process (45% water) (45% Process cheese spread has even more Process moisture, easily spread (50% water) moisture, Fat and Cheese Fat Fat contributes to: Mouth feel Flavor Firmness Adhesiveness Not desirable if lowered below 25% in Not cheese cheese Sometimes the butterfat is removed and Sometimes some oil added back in to lower the fat content content Whey Whey protein is a by-product of the cheese Whey industry industry Because of large quantity available, researchers Because always looking for new uses always Current uses: Whey protein isolate and concentrate used to Whey promote water retention in foods promote Simplesse—fat subsitute composed of whey protein Simplesse—fat solution and egg white solution Various other textural roles Ice Creams and Frozen Desserts Ice Plain Ice Cream Frozen dessert containing at Frozen least 10 percent milk fat and 20 percent total milk solids and no more than 0.5 percent edible stabilizer; flavoring particles must not show must Composite Ice Cream Composite Frozen dessert containing at Frozen least 8 percent milk fat and 18 percent total milk solids and no more than 0.5 percent edible stabilizer; flavoring particles not to exceed 5 percent by volume to Other Frozen Desserts Other Frozen Custard Ice cream like product that is a frozen, Ice egg-yolk thickened custard egg-yolk Low Fat Ice Cream Contains 2-7 percent milk fat and 11 Contains percent milk solids—often add microcrystalline-cellulose-based stabilizer/emulsifier system, sugar alcohols, and polydextrose alcohols, Sherbet Frozen dessert containing acid, from 2-5 Frozen percent milk solids and no milk fat percent Other Frozen Desserts Other Mellorine Imitation ice cream in which milk fat Imitation has been removed and replaced by another fat (market for people trying to remove all butterfat) to Parevine Imitation ice cream in which both Imitation the milk fat and the milk solids have been replaced by non-dairy ingredients (Fits within guidelines of Jewish food laws) Jewish Ice Cream: A Foam Ice Frozen ice cream is a colloidal dispersion Frozen classified as a foam classified Continuous phase = solid ice crystals Dispersed phase = air incorporated durin Dispersed agitation agitation Making ice cream Making Physical and Chemical Effects on Milk Products Milk Heat Enzyme action Rennet, forms clots Acid Denatures proteins in milk, browning and flavor Denatures changes, scum formation changes, Change pH, bring proteins to isoelectric point, clotting Salts Affect pH, cause coagulation Foams—Milk and Cream Foams—Milk Milk foam—Proteins in milk extended Milk to thin films by agitation to form a foam, must use evaporated milk, because protein content to low in fluid milk milk Cream foam—whipping cream of high Cream fat content easily beaten into a foam, fat contributes rigidity, must be cold to remain a foam remain ...
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