Chapter 11 -- Protein: Milk and Cheese
Proteolytic enzyme
enzyme capable of catalyzing a break in a protein at a peptide linkage
Mellorine
frozen dessert usually made with a vegetable fat
Parevine
frozen dessert usually made without any dairy or meat products
Iso-electric point of casein
pH 4.6 If milk reaches a 4.6 the casein will "denature" and clot
Iso-electric point
pH at which a molecule has a neutral charge
Grade A milk
pasteurized, lowest bacterial count (100,000/ml) Grade sold in retail stores, all fluid milk
Lactase
Enzyme needed for digesting lactose
Protein structure
Four structural levels -Primary -Secondary -Tertiary -Quaternary
Flavored milk with chocolated
adds sugars at about 5% or 7%
Grade B and C milk
manufacturing milk (3 million/ml) Safe and wholesome Milk used for processed milk products (butter and cheese)
Classifications of natural cheese
means of clotting (lactic acid or rennin) amount of ripening (cured or uncured) Firmness Source of milk
Curd treatment: salting
Further dehydrates the curd Controls bacterial growth
Non-fat dried milk foams
1.5 part solid to 1 part chilled water Lower in calories, limited stability due to lack of fat Addition of lemon juice to reach iso-electric point, casein proteins denature further and increase stability
Reduced fat milk
2% fat (reduced 25%)
Casein as amphoteric protein
Compound that behaves as acid or base Proteins have an amino group and a carboxylic group which can ionize
Nonfat or skim milk
.01% fat or less 50% of the kcal of whole milk Must be fortified with vitamin A and D Loss of richness of flavor
Low fat milk
1% fat
Cheese production
1. Milk selection (cow, sheep, goat, milk, whole milk, low, or nonfat) 2. Coagulation (add enzyme -- rennin, or add acids) 3. Curd treatment (curing and ripening)
Ultra high temperature pasteurization
280F for 2 seconds Sterilize milk in its package so it can be stored at room temperature until package is open
Process cheese spread
51% natural cheese by weight 16% more water than processed cheese Other ingredients: sugar, dextrose, maltose, corn syrup Softer and spreadable
Process cheese food
51% natural cheese by weight Other ingredients: milk, cream, oil, or whey Velveeta, cheez whiz
Evaporated milk
60% of water is evaporated 7.5% milk fat 25.5% milk solids Low fat/non fat, no more than 0.5% fat and 20% milk solids Fortified with A and D
Nutritional value of milk
87% water 4.9% carbohydrate 3.5% fat 3.5% protein pH of 6.6 (neutral)
Lactose used by the industry
A disaccharide (galactose and glucose) extracted from the whey found in milk Makes up around 2-8% of milk (by weight) Improves the water-holding capacity of processed meats (ham), texture of frozen desserts, browning ability
Denaturation: how it happens
A physical change in a protein due to: extreme heat exposure high acidity physical agitation Provide enough energy to break secondary bonding forces Physical shape of the protein begins to resemble the helical secondary structure (coiled spring)
Amphoteric
Able to act as an acid (carrying a + charge) or a base (carrying a - charge) Their carboxyl and amino groups permit proteins to do this
Cultured milks
Acidophilus milk Yogurt Lactose-reduced milk
Fortification of milk
Addition of vitamin D to reduce incidence of rickets among young children Vitamin D promotes absorption of calcium in milk
Curdling
Aggregates of precipitated casein proteins Acid or salt addition can lead to pH reaching the isoelectric point (pH 4.6) Effect of salt: ions of sodium and chloride from the salt interact with the electrical charges on the surface of the milk proteins Protein molecules form aggregates as hydrogen bonds link them
Fluid milk
All varieties Generally homogenized and pasteurized Fortified with 400 IU vitamin D/quart All reduced/low/non fat fortified with 2000 vitamin A
Ripened cheeses
Bacteria ripened (internal and external) Mold ripened (internal and external)
Addition of bacteria
Bacteria: streptococcus lactis Converts lactose into lactic acid, lowers pH Casein proteins are negatively charged, repel each other in fluid milk Once the isoelectric point is reached the proteins are neutralized At a pH of 4.6 the casein coagulates and precipitates into a curd Most of calcium is lost in the whey so curd is soft and spongy
Classifications of processed cheese
Based on basis of moisture and fat content
Whey protein concentrates (WPC) or whey protein isolates (WPI) in in the industry
Concentrated wheys are high in protein (35%, 50-80%, 80%) but low in lactose and minerals Dry beverage mixes Nutrition bars Protein fortified food Sports nutrition
Maillard Reaction
Browning caused by reaction between proteins and milk sugar (lactose)
Milk proteins
Casein alpha, Beta, and k-caseins Casein: main protein in milk, precipitated from manufacturing cheese from milk Large amphoteric proteins
Milk protein concentrates (MPC) or milk protein isolates (MPI) industry
Casein and whey proteins isolated from fresh nonfat milk (42-85% protein) that are high in bound calcium Infant formula Weight loss products Sports nutrition Cheese products liquid beverages
Scorching
Caused by overheating the serum proteins that precipitate during cooking Proteins undergo denaturation Denaturation carries calcium phosphate to the bottom of the pan, trapped in the protein precipitate Sugar in milk interacts with the protein precipirate to cause browning (Maillard reaction) Overheating of proteins result in creation of sulfur containing compounds -Result is sulfur containing compounds: hydrogen sulfide
Acidophilus milk
Contains lactobacillus acidophilus Bacteria metabolizes lactose into lactic acid Maybe slightly easier to digest Unique flavor
Whipping cream
Cream with a fat content high enough to be whipped (almost 30%)
Whey powder in the food industry
Crystallizing whey creates a sweet or acidic powder high in lactose and minerals Demineralized and delactosed whey powders are available Used for infant formulas Baked items Dry mixes Processed cheeses Sausages Weight loss product formation
Curd treatment: knitting
Curd is melted into a solid mass with heat
Protein synthesis
Dehydration reaction: A chemical reaction in which molecules combine by removing water
Acid coagulation
Direct: acid added Indirect: acidic environment created by adding bacterial structures
Dairy foam as colloidal dispersion
Dispersed phase: air bubbles Continuous phase: liquid
Canned milk products
Evaporated milk Condensed milk
Dry milk
Evaporating of water from pasteurized non-fat milk under vacuum and then sprayed dried to concentrate product Reconstituted fully as beverage or partially for whipped topping Typically non-fat Whole or low fat milk dried products have limited shelf life The greater the fat content the more prone to rancidity
Yogurt
Fermented with bacteria (streptococcus thermophilus and bacterium bulgaricus) Milk is clotted by lactic acid-producing bacteria Acid production alters the pH, proteins precipitate, becomes soft curd Greek yogurt high protein because its strained to remove the whey Warm milk is inoculated by a bacterial culture Bacteria digest lactose to lactic acid Lactic acid accumulates, pH decreases, approaching isoelectric point
Pasteurization
Heat treatment to inactivate disease producing microorganisms that could cause disease, spoilage, or undesired fermentation
Scum formation
Heated milk forms a "skin" on the surface particularly when the pan is uncovered Evaporation concentrated milk solids Proteins (casein) and calcium salts are at the surface Skin traps steam and causes milk to boil over
Homogenization of milk
Heated milk is forced through tiny holes at high pressure Large fat globules break into tiny droplets Surrounded lipoprotein membrane, prevents separation Sensory changes resulting in a smooth creamier texture Denatures some of the milk proteins (casein) Makes homogenized milk more digestible
Whipped cream
Highest fat content of dairy foams Stability due to fat particles forming a structural wall, stabilizing air bubbles Higher temps cause fat to soften and foam loses its strength Over-agitation will reverse the oil in water emulsion (cream) to a water in oil emulsion (butter) Sugar helps keep fat from clumping within the films surrounding the air bubbles, thus requiring additional beating if it is added before the desired end point
Fresh cheese
Highly perishable Moisture content is 80% Soft, white in color, mild-tasting Not cured or aged Cottage cheese, cream cheese, ricotta cheese
How proteins are arranges
Hydrophobic proteins (casein) at center/interior Hydrophilic protein (k-casein) located in exterior
Overcoagulation/curdling
If extreme chemical and physical conditions continue only the strong bonds will remain Proteins pack together more tightly and irreversibly, water is squeezed out
Clotting
Intentional curdling Products that rely on clotting include yogurt, pudding, and cheese
Whey proteins
Lactalbumin and lactoglobulin Small and compact proteins Water soluble - liquid portion of milk Remain in solution after acid or enzyme treatment for cheese production
Lactose-reduced milk
Lactose free milk due to addition of lactase Lactose digested to glucose and galactose Essential for lactose intolerant individuals
Carbohydrate in milk
Lactose, sugar that can be metabolized and serves as a source of energy
Dairy foams
Liquid milk products can be made into a foam by whipping air into a liquid Foams are colloidal dispersions Milk foams gain stability from protein and fat
Whey
Liquid removed from clotted milk in cheese production
How caseinates are used by the industry
Made from casein by adding sodium, calcium, potassium, or combinations of these salts (to make it water soluble) Food bars, medical foods, soups, sauces, whipped toppings, bakery products
How casein is used by the industry
Major protein found in milk extracted from skim milk via acidification or enzyme precipitation Improves nutritive value of bakery items Medical foods: binder in processed meats
Hydrolysates used by the industry
Manufactured by the enzymatic hydrolysis of milk proteins Improves the proteins' stability, solubility, viscosity, emulsification, whipping ability
Milk grades
Milk grades apply only to degree of sanitation, not related to quality or richness
High temperature short time (HTST)
Milk heated to 161F for 15 seconds, cooled to 50F and below
Processed cheeses definition
Mixture of natural cheeses, water, and emulsifiers blended with controlled heating Emulsifier allows for effective blending of the high fat content with added water for desired consistency Moisture content should not exceed 40% Fat content must be similar as the natural cheeses used
Hard cheese
Moisture content from 40-40% Longer aged time Cheddar and Swiss
Semi-hard cheese
Moisture content of 40-50% Aged for longer periods of time Roquefort, blue, Muenster, brick, Gouda, Edam, Gorgonzola, Stilton
Condensed milk
More than 50% of water removed Addition of 44% sucrose and/or glucose Increases viscosity Helped retard bacterial growth Stored at room temperature for over a year
Classifications of cheese
Natural and process
Non-homogenized milk
Natural separation of the cream (fat) occurs in unprocessed milk Fat is less dense than water, floats to the top Natural emulsion is broken
Proteins
Organic polymers comprised of sub units called amino acids Anywhere from 12 to several hundred amino acids bonded together Bonded together by peptide bonds
Protein bonds
Peptide bonds Covalent, very strong bond between the acid (carboxyl) group of one amino acid and the amino group of another amino acid Linkage formed with the loss of the molecule of water Form dipeptide
Curd treatment: pressing
Physical pressure applied to compress curd into a solid mass
Butter
Primarily a fat (80%) Not useful source of calcium Buttermilk is drained to concentrate the butter to its high fat content
Protein structure: secondary structures
Primary structure is twisted into a helix or folded into a pleated sheet -Held by hydrogen bonds -Amino (H) and Carboxylic acid (O)
Processed cheese
Process cheeses are all made from blended cheeses but they differ on the basis of their ingredients and manufacturing methods
Rennin
Protein-digesting enzyme from the calf's stomach Clotted milk production
Amino Acids - R groups
R group represents different structures R group for each amino acid differs, giving unique quality to each specific amino acid
Enzyme coagulation
Rennin activation: milk is heated to provide optimal environments for enzyme Hydrolysis: enzymes cleave dipeptide bonds in the k-casein proteins, producing para k-casein (hydrophobic) All fat soluble protein allowed to aggregate producing the curd used to make the cheese Calcium remains in curd, curd is tough and rubbery
Curd treatment: cutting
Slicing increases surface area More whey is removed
Evaporated milk foams
Substitute: lower calorie but less stable Lower fat and higher protein content Stabilized by the viscosity of concentrated milk protein dispersion
Coagulation
The clumping together of partially denatured molecules to make a relatively insoluble protein mass The second step of denaturation Reactive side chains are free to form new bonds in a continuous network Water molecules become trapped between the newly formed protein networks
Milk
The fluid secreted by lactating mammals Complex fluid containing macronutrients Allergy: an immunce reaction to the protein in milk (casein or whey) Intolerance: inability to digest the carbohydrate (lactose) in milk due to decreased amount of lactase
Protein structures: quaternary structure
The fourth level of protein structure; the shape resulting from the association of two or more polypeptide subunits. Large proteins having multiple peptide chains working together Structure determined by R groups, via H- bonds, S-S bonds, +/- bonds, hydrophobic bonds
Protein structure: primary
The linear sequence of amino acids -Held together by peptide bonds (covalent bonds) -C-C-N-C-C-N Basic backbone of the protein Proteolytic enzymes attack this backbone -enzymatic hydrolysis causes uptake of water at the peptide linkage, two shorter peptides/chains of amino acids will result -Same in all proteins, the difference comes from the R groups
Protein structure functions
The structure of a protein dictates its function Enzyme, receptor, transporter, muscle protein, etc
Protein structure: tertiary structure
The third level of protein structure; the overall, three-dimensional shape of a polypeptide due to interactions of the R groups of the amino acids making up the chain -Helix or sheets are further folded into themselves, forming a globular like shape -Attractions between R groups -Hydrophobic interactions, ionic bonds (+/-), S-S bonds, H-bonds Hydrogen bonds, low energy state, stabilized by hydrogen bonding occuring every fourth amino acid residue
Denaturation
Unfolding of tertiary structure and clumping of protein molecules due to heating or beating Change in shape leads to loss of function -Proteins dissociate from quaternary/tertiary structures to their secondary/primary structures -R groups become exposed and exhibit different electrical charges The protein becomes less soluble and tends to precipitate or resist movement
Sour cream
Viscous, acidic cream containing at least 18% fat Acidified by action of lactic acid bacteria on lactose
Very hard cheese
Water content of 30% Aged the longest Hard in texture Will not slice easily, grated or crumbled Parmesan and Romano
Soft cheese
Water content ranges from 50 to 75% Aged for a short period of time Ex: Camembert, brie, hispanic cheeses
Curd treatment: heating
Whey is evaporated Lactic acid increases producing a firmer texture Heat destroys harmful microorganisms
Casein proteins vary in solubility
a and B casein are hydrophobic proteins k-casein is a hydrophilic protein
Whole milk
at least 3.25% fat
Natural cheese
concentrated milk curd; ripening is optional Goal is to remove water from milk under a solid mass or curd remains Moisture content of cheese decreases, during aging
Peptide Bond Breaking
hydrolysis reaction: A chemical reaction that breaks apart a larger molecule by adding a molecule of water Peptide bonds are resistant to various forms of food preparation -Proteolytic enzymes: cleave peptide backbone Results in uptake of water (hydrolysis)