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)