Protein in Food Science - Meat

Protein in Food Science

Proteins

• Present in every living cell.
• Distinguished from fats and carbohydrates by the presence of Nitrogen and, in some cases, Sulfur.

Amino Acids

• Amino Acids meaning ‘nitrogen containing’
• Peptide bonds between amino acids
• Amino Acids contain an acid group COOH, a base group NH3, a H, and an “R” group or side chain
• Long amino acid chains repel and attract each other due to this structure.
• Form secondary and tertiary structure.
• Isoelectric point is the pH at which the protein is neutral.

Amino Acid Composition

• 22 amino acids
• 9 essential (must be supplied in the diet)
• 13 non-essential
• Most animal sources are “complete” except for gelatin
• Most plant sources are “incomplete” except for soy, quinoa, and amaranth

Limiting and Complementary Proteins

Protein Roles in Food Processing

• Binding water – hydration
• Producing gels.
• Producing foams
• Aids in browning -- Maillard Reaction and Enzymatic browning
• Buffering

Enzymes

• Enzymes are Proteins
• Enzymes are important biological catalysts
• Names end in –ase (for ex lactase)
• 'good' Enzymes Used in Food Processes
  • Alter texture (rennin or chymosin in cheese making)
  • Tenderize (in meat processing)
  • Retard staling
• 'bad' Enzymes controlled in Food Processes
  • Browning of fruit and vegetables
  • Rancidity in milk lipoxygenase
  • Inactivated by heat, pH

Browning Reactions

Maillard Browning

• Maillard Browning – creates color and flavors in food
• Named for Louis Maillard
• Conditions needed:
  • Heat $194°F$
  • Increased pH promotes
  • Reducing sugar - has a carbonyl group R- C=O
    • Glucose, fructose, lactose, maltose
  • Amino Acid with a free amine group

Enzymatic Browning

• Reaction between a phenol, oxygen, and the enzyme polyphenol oxidase
• Reaction forms melanin a black pigment
• Not harmful can be beneficial (tea and coffee)
• Reaction inhibited by low pH, lack of oxygen, and heat inactivation of the enzyme

Hydration

• Protein dissolves in and attracts water
• Gluten is formed when water is added to flour proteins glutenin and gliadin
• The proteins are kneaded to form the bread structure which holds the generated $CO_2$
• Proteins act as gels, thickeners, and stabilizers in food – collagen (gelatin), egg white, whey

Buffering Agents

• Buffering capacity – ability of a solution to maintain its pH when acid or base are added.
• Used in beverages

Denaturation

Protein structures altered Denaturation – occurs when the protein molecule unfolds yet retains some of its peptide linkages

• pH extremes – cheese, yogurt,
• Physical disruption – foams and meringues
• Heat - egg whites

Coagulation

Changes Protein Structures Coagulation – occurs when the unfolded parts of the molecule recombine to form a new molecular shape

• Can produce a gel or solid mass (egg white)

Protein States

Native State -> Denaturation -> Denatured State -> Coagulation -> Coagulated State

Actions that Lead to Change

These are all actions that can occur during food preparation or processing:

• Aging
• Cooking - denaturation
• Mechanical beating and Change in acidity - coagulation
• Freezing

Physical Structure of Protein Sources

• Fat
• Muscle
• Bones
• Connective tissue
• Water

Muscle & Bone Composition

• Protein – 18%
• Water – ~75%
• Water content fluctuates with fat content
• As fat increases, water decreases
• Bones – used to identify specific cuts of meat
• Rib eye, short ribs, tbone etc

Chemical Structure

• Protein – muscles – amino acids and water
• Carbohydrate – glycogen in muscle à coverts to lactic acid during aging after slaughter
• Lactic acid important to flavor development

Muscle Fibers

• Skeletal muscle
• Epimysium
• Muscle fascicle
• Muscle fiber
• Muscle fascicles
• Nucleus
• Muscle fiber
• Light I band
• Dark A band
• Sarcomere
• Perimysium
• Endomysium
• Muscle fibers
• Sarcoplasmic
• reticulum
• Thin (actin)
• filament
• Myofibril
• Z disc
• H zone
• Z disc
• Mitochondrion
• Sarcolemma
• Thick (myosin)
• filament
• I band
• A band
• I band
• M line
• Sarcolemma

Meat Structure

• Muscle tissue - composed of myofibrils - of actin and myosin filaments
• Actin-thin fibers; myosin-thick fibers

Fat

• Subcutaneous – under skin – undesirable
• Internal – around organs – cushions from injury
• Intermuscular – between muscles – seen on large cuts; undesirable
• Intramuscular fat – inside muscles – marbling – desirable, but last to be deposited

Aging Beef

• Beef is aged – leads to breakdown of proteins by enzymes
• Breakdown of Glycogen to lactic acid
• 7-20 days
• Beef is the only meat commonly aged

Chemical Structure of Fat

• Fat – steric acid primary source of fat in beef – 18 Carbon chain saturated fat; also source of fat soluble vitamins A, D, E, K
• Important to palatability, but if stored too long à “stale or leftover” flavor
  • due to oxidation of unsaturated fat
• Color of fat indication of animal age
  • White – young; older à yellow

Chemical Structure - Vitamins & Minerals

• Vitamins – B vitamins, particularly B12, and Folic Acid
• Minerals – iron, zinc, phosphorous, potassium
• Animal’s diet affects composition of animal, particularly fat

Wholesale Cuts of Meat

• Chuck
• Rib
• Loin
• Sirloin
• Round
• Brisket
• Shortplate
• Flank
• Shank
• Short
• Rump

Retail Cuts of Meat

• Chuck eye roast
• Blade roast or steak
• Chuck shortribs
• Arm pot roast- or steak
• Crosscut shank
• Stew meat
• Ground beef
• Rib roast
• Rib steak
• Ribeye roast or steak
• Top loin steak
• T-bone steak
• Tenderloin steak or roast
• Porterhouse steak
• Sirloin steak
• Rolled rump
• Round steak
• Bottom round roast or steak
• Eye of round
• Tip steak
• Tip roast
• Stew meat
• Ground beef
• Flank steak
• Heel of round
• Short ribs
• Cross rib pot roast

Types of Muscle

• Muscles of Attachment – are the most tender – attached to the skeleton, but not used to move the animal
• Muscles of Locomotion - used to move the animal → to collagen formation

Meat Pigments

• Myoglobin (purplish-red) $Fe^{2+}$
• Oxymyoglobin (bright red) $Fe^{2+} + O_2$
• Metmyoglobin (brownish) $Fe^{3+}$
• Oxygenation/Deoxygenation $Fe^{2+}$
• Oxidation/Reduction $Fe^{3+}$

Meat Pigments & Heat

• Affect of heat – initially à bright red à browning
• Browning the result of Maillard reaction
• Storing cooked meat too long à further breakdown à green, yellow or faded color

Tenderness Factors

• Fat
• Muscle development
• Connective tissue
• Age

Cooking Temperature

• internal temps for meats
• Ground beef cooked for public consumption must be cooked to internal temp $155°F$ (FDA) $160°F$ (USDA)
• Cooking temperature – less tender cuts of meat will tenderize more if cooked at lower temperatures

Cooking Moisture

• Amount used in cooking
• Composition of meat – the greater the amount of connective tissue and the lower the amount of fat the greater the need for moist cooking methods
• Cut of meat – muscles of locomotion vs attachment

Storage

• High % of water & protein are ideal for growth of microorganisms
• Should be stored in refrigerator or freezer
• Refrigerated
  • $32ºF$ to $36º F$
  • Wrap meat
  • Refrigeration times
    • Fresh meat – No longer than 3-5 days
    • Ground & variety – Cook within 1 to 2 days
    • Cooked – 3 to 4 days

Frozen Storage

• Tightly wrapped to limit exposure to air
• Best below $0ºF$ ($-18ºc$)
• Freezer times
  • Cuts of meat– 6-12 mo
  • Ground meats no longer than about 3 months