10 - Proteins + Meat (1)

Proteins

  • Proteins are essential macromolecules that play critical roles in cells and biological systems.

  • Basic structure includes hydrogen (H), nitrogen (N), oxygen (O), and an R-group that varies among different amino acids.

Chemistry of Food Proteins

  • Building Blocks of Cells: Proteins provide structure, function, and regulation to tissues and organs.

  • Key Differences: Unlike carbohydrates and lipids, proteins contain nitrogen.

  • Proteins are long chains made of amino acids; humans cannot synthesize about half of the 20 essential amino acids (9 essential).

Protein Structure

Primary Structure

  • Defined by the amino acid sequence; e.g., Phe-Gly-Glu-Asn-Gln.

  • Amino acids include: Ala, Arg, Pro, Tyr, Trp, Ser, Asp, Ile, Met, Cys, Leu, Lys.

Secondary Structure

  • Formed by hydrogen bonds between amino acids, resulting in structures such as:

    • Alpha helix

    • Pleated sheet

Tertiary Structure

  • Results from interactions among R-groups forming a complex 3D shape, e.g., hemoglobin.

Quaternary Structure

  • Consists of multiple polypeptide chains, forming a larger functional protein complex.

Amino Acids

Essential Amino Acids (must be obtained through diet)

  • Leucine, Isoleucine, Valine, Histidine, Lysine, Methionine, Phenylalanine, Threonine, Tryptophan.

Non-Essential Amino Acids (can be synthesized by the body)

  • Alanine, Arginine, Asparagine, Aspartic Acid, Cysteine, Glutamic Acid, Glutamine, Glycine, Proline, Serine, Tyrosine.

Main Functions of Proteins in Foods

  • Hydration: Proteins can dissolve in and attract water, forming gels and aiding in dough formation.

  • Denaturation/Coagulation: Structures are disrupted causing loss of function; coagulation forms semi-solid protein from liquid.

  • Enzymatic Reactions: Proteins act as enzymes to catalyze reactions (most end in -ase).

  • Browning Reactions:

    • Enzymatic Browning: Involves enzymes acting on phenolic compounds in the presence of oxygen.

    • Non-Enzymatic Browning (Maillard Reaction): Reaction between sugars and proteins resulting in brown complexes.

Denaturation and Coagulation

  • Denaturation: Disruption of protein structure resulting in loss of function (irreversible).

  • Coagulation: Semi-solid formation of protein in liquid, essential in cooking.

Enzymatic Browning

  • Enzymatic browning occurs in fruits/vegetables on exposure to air, turning brown due to phenolic compounds.

    • Requires: Phenolic compounds, polyphenol oxidase enzymes, oxygen.

Non-Enzymatic Browning: Maillard Reaction

  • Occurs during cooking at 140-165°C, involves reaction between reducing sugars and amino acids, producing flavor and color.

  • Three Stages:

    1. Initial reaction with formation of glycosylamine.

    2. Isomerization to form Amadori compounds.

    3. Further breakdown producing various flavor compounds.

Reducing Sugar

  • Capable of forming aldehyde or ketone groups; glucose, fructose, galactose, maltose, and lactose are reducing sugars.

  • Caramelization: Process by which sugars change color through heat.

Differences between Maillard and Caramelization

  • Both processes brown food but occur differently, requiring low moisture environments for optimal reactions.

Structure of Meat

Composition

  • Composed of water, muscle, connective tissue, adipose (fatty) tissue, and bone.

Muscle Structure

  • Muscle fibers filled with cell fluid (sarcoplasm) and muscle fibrils surrounded by a membrane (sarcolemma).

  • Contains contractile proteins: actin (thin) and myosin (thick).

Muscle Types

Slow-Twitch Muscles

  • Require significant oxygen, support sustained activity in larger animals.

Fast-Twitch Muscles

  • Involved in quick bursts of activity; anaerobic with less oxygen dependency.

Color of Meat

  • Dominated by myoglobin; can change from purplish-red to bright red or brownish-red with exposure to oxygen.

Effects of Heat on Color

  • Cooking causes denaturation, resulting in grayish-brown meat.

Connective Tissue

  • Contains collagen (most abundant), elastin, and reticulin.

  • Toughness and cooking methods depend on the amount of connective tissue.

Nutritional Aspects of Meat

  • Protein Content: Excellent source (~7 grams/ounce).

  • Fat Content: Varies widely.

  • No carbohydrates.

Meat Inspection and Grading

  • Inspection: Mandatory for meat entering the market; guarantees wholesomeness but not quality.

  • Grading: Voluntary based on cut characteristics, includes factors like color and fat distribution.

I can't analyze pictures directly, but I can help interpret or explain content related to protein structures or meat if you describe what the pictures depict. Let me know how I can assist further!

I can't analyze pictures directly, but I can help interpret or explain content related to protein structures or meat if you describe what the pictures depict. Let me know how I can assist further!