🍕Principles of Food Science Unit 5 – Proteins: Composition and Functionality

What Are Proteins?

• Proteins are essential macromolecules found in all living organisms
• Consist of long chains of amino acids linked together by peptide bonds
• Play crucial roles in various biological processes (cell signaling, immune response, and enzymatic reactions)
• Serve as building blocks for tissues (muscles, skin, and hair)
• Act as transporters for molecules (hemoglobin carries oxygen in the blood)
• Function as enzymes catalyzing biochemical reactions in the body
• Provide structure and support to cells and tissues
• Contribute to the overall health and proper functioning of organisms

Building Blocks: Amino Acids

• Amino acids are the monomeric units that make up proteins
• Consist of an amino group (NH2), a carboxyl group (COOH), and a unique side chain (R-group) attached to a central carbon atom
• There are 20 different standard amino acids found in proteins
  • Classified as essential (must be obtained from diet) or non-essential (can be synthesized by the body)
• The sequence of amino acids in a protein determines its unique structure and function
• Amino acids are joined together by peptide bonds formed through a condensation reaction
• The order of amino acids in a protein is determined by the genetic code
• The properties of amino acid side chains (hydrophobic, hydrophilic, charged, or neutral) influence protein folding and interactions

Protein Structure: From Simple to Complex

• Proteins have four levels of structural organization: primary, secondary, tertiary, and quaternary
• Primary structure refers to the linear sequence of amino acids in a polypeptide chain
• Secondary structure involves local folding of the polypeptide chain into alpha helices or beta sheets
  • Stabilized by hydrogen bonds between the amino acid backbone
• Tertiary structure is the three-dimensional shape of a single polypeptide chain
  • Determined by interactions between amino acid side chains (hydrophobic interactions, hydrogen bonds, ionic bonds, and disulfide bridges)
• Quaternary structure is the arrangement of multiple polypeptide chains into a multi-subunit complex
• The complex structure of proteins enables them to perform diverse functions in living organisms
• Protein folding is a spontaneous process driven by the minimization of free energy

Protein Sources in Food

• Proteins are essential nutrients that must be obtained through the diet
• Animal-based sources of protein include meat, poultry, fish, eggs, and dairy products
  • These proteins are considered "complete" as they contain all essential amino acids
• Plant-based sources of protein include legumes (beans, lentils, and peas), nuts, seeds, and whole grains
  • Most plant proteins are "incomplete" as they lack one or more essential amino acids
• Combining different plant-based protein sources (rice and beans) can provide a complete amino acid profile
• The quality of a protein source depends on its digestibility and amino acid composition
• Protein content varies among different food sources (high in meat, moderate in legumes, and low in fruits and vegetables)
• Adequate protein intake is crucial for growth, development, and maintenance of body tissues

Functional Properties of Proteins

• Proteins contribute to various functional properties in food systems
• Solubility: proteins can dissolve in water or salt solutions, affecting their extraction and purification
• Water holding capacity: proteins can bind and retain water, influencing food texture and stability
• Emulsification: proteins can act as emulsifiers, stabilizing oil-in-water or water-in-oil mixtures (mayonnaise and salad dressings)
• Foaming: proteins can form and stabilize foams by reducing surface tension (meringues and whipped cream)
• Gelation: proteins can form gels upon heating or cooling, providing structure to foods (gelatin and egg whites)
• Viscosity: proteins can increase the viscosity of food systems, affecting their flow properties
• Flavor binding: proteins can interact with flavor compounds, influencing the overall taste and aroma of foods

Protein Denaturation and Its Effects

• Protein denaturation is the loss of a protein's native three-dimensional structure
• Caused by various factors (heat, pH changes, mechanical agitation, and chemical agents)
• During denaturation, hydrogen bonds and other interactions maintaining the protein's structure are disrupted
• Denaturation can lead to changes in protein solubility, water holding capacity, and other functional properties
• In some cases, denaturation is reversible, allowing proteins to regain their native structure under favorable conditions
• Irreversible denaturation occurs when the protein cannot refold into its original structure
  • May result in protein aggregation or precipitation
• Denaturation can have both positive and negative effects on food quality
  • Positive: improved digestibility, enhanced emulsification, and gel formation
  • Negative: loss of solubility, reduced water holding capacity, and altered texture

Proteins in Food Processing

• Proteins play a significant role in various food processing applications
• In meat products, proteins contribute to texture, water holding capacity, and binding properties
  • Muscle proteins (myosin and actin) are responsible for the gelation and structure of processed meats (sausages and hamburgers)
• In dairy products, proteins (casein and whey) are essential for the formation and stability of cheese, yogurt, and other fermented products
• In baked goods, proteins (gluten) provide structure, elasticity, and gas retention in doughs and batters
• Protein ingredients (soy protein isolate, whey protein concentrate) are used to enhance the nutritional value and functional properties of various food products
• Protein modification techniques (enzymatic hydrolysis, cross-linking) can be employed to improve the functionality and stability of proteins in food systems
• Understanding the behavior of proteins during food processing is crucial for optimizing product quality and shelf life

Nutritional Importance of Proteins

• Proteins are essential macronutrients required for the growth, development, and maintenance of the human body
• Provide the building blocks (amino acids) for the synthesis of body proteins (muscles, enzymes, hormones, and antibodies)
• Amino acids obtained from dietary proteins are used for various physiological processes
  • Tissue repair, enzyme production, and neurotransmitter synthesis
• Proteins are a source of energy, providing 4 calories per gram
• The quality of dietary proteins depends on their essential amino acid content and digestibility
  • High-quality proteins (eggs, milk, and meat) contain all essential amino acids in adequate proportions
• Protein requirements vary depending on age, sex, body weight, and physiological state (growth, pregnancy, and lactation)
• Insufficient protein intake can lead to protein-energy malnutrition, impaired growth, and weakened immune function
• Excessive protein consumption may strain the kidneys and liver, and may contribute to the development of chronic diseases