Food Component Part 2
Proteins and Amino Acids in Food
Proteins and amino acids significantly influence color, texture, and flavor in food. Their interactions and reactions contribute to the overall sensory experience and chemical composition of food products.
Maillard Reaction
The Maillard reaction is a critical chemical process in food chemistry, responsible for the browning and development of complex flavors in many cooked foods.
It requires an amine group (from protein/amino acid) and a reducing sugar. The presence of both is essential for the reaction to occur.
The primary amine (NH_2) group from amino acids reacts with the aldehyde group from the reducing sugar, initiating a cascade of chemical reactions.
The reaction results in Maillard products (e.g., glycosylamine), which are responsible for the characteristic flavors and colors.
The details of the reaction are extremely complex, involving numerous intermediate compounds and pathways.
Occurs in various food processes:
Steak on the grill: Development of the browned, savory crust.
Roasting coffee: Formation of coffee's characteristic aroma and color.
Making french fries: Production of the golden-brown color and distinctive flavor.
In the broadest sense, protein and carbohydrate molecules are involved.
Specifically, it is an amine group with a reducing sugar that triggers the reaction.
The reaction proceeds through a Schiff base and Amadori compounds, which are key intermediates in the Maillard reaction pathway.
The reaction is influenced by pH, temperature, and holding time, all of which can alter the rate and products of the reaction.
Impacts color, flavor, and nutrition through the formation of melanoidins and other Maillard products.
Can kill bugs and microbes due to the production of antimicrobial compounds during the reaction.
Interactions Between Phases
Emulsions
Oil does not mix with water without stabilization.
Proteins can stabilize emulsions by acting at the oil-water interface, reducing surface tension and preventing separation.
Example: Mayonnaise, where egg proteins stabilize the oil and vinegar mixture.
Salad dressings are also emulsions that require stabilizers to maintain their structure.
Emulsions are metastable and eventually fall apart due to the natural tendency of oil and water to separate.
Foams
Involves mixing water with air, creating a dispersion of air bubbles in a liquid.
Proteins stabilize the interface between air and water, preventing the bubbles from collapsing.
Examples: Ice cream, beer, meringue.
Gelation
Proteins form a matrix holding a high water content, creating a semi-solid structure.
Examples: Dough, gelatin dessert, tofu, yogurt.
Milk
Milk exhibits emulsion, foaming, and gelation properties depending on processing and composition.
Emulsion - Milk as a drink demonstrates the stable dispersion of fat in water.
Foaming - Cappuccinos use milk proteins to create stable foam.
Gelation - Yogurt, custard, and quark are formed by protein gelation.
Carbohydrates in Food
Definition: "Carbo hydrate" - carbon and water atoms in one molecule CH2O
Carbohydrates play a crucial role in the chemical structure and sensory attributes of food.
Carbohydrates in Common Foods
Different foods have different amounts of carbohydrates, influencing their nutritional content and texture.
Examples: Apple, peanut, honey
Carbohydrates consist of C:H_2O in a 1:1 ratio, providing a basic structural formula.
Provide energy through breakdown to glucose, which is the primary metabolic fuel for the body.
Larger polymers form structure in many foods (e.g., cellulose in plant cell walls).
Glucose
Core sugar in life science, serving as the fundamental energy source for most organisms.
Exists in cyclic and open-chain forms, with the cyclic form being more stable and predominant.
Most glucose exists in the cyclic form due to its lower energy state.
Saccharides
Glucose is a monosaccharide, the simplest form of sugar.
Sucrose, maltose, and fructose are hexoses, containing six carbon atoms.
Fructose can polymerize into starch (a polysaccharide), serving as a storage form of energy in plants.
Monosaccharides
Glucose, fructose, and galactose are the primary monosaccharides found in food.
They are the same molecules with the majority existing in cyclic form, differing in their atomic arrangement.
Glucose is the main fuel for all living things (archaea, bacteria, animals, plants), underscoring its central role in metabolism.
Disaccharides
Table sugar is sucrose (glucose + fructose), commonly used as a sweetener.
Lactose (milk sugar) is glucose + galactose, found in dairy products.
Maltose (in malt) is two glucoses, produced during the germination of grains.
Glycosidic bond: Bond formed by taking out water (dehydration), linking two monosaccharides.
Hydrolyzing: Adding back water to split a disaccharide into its constituent monosaccharides.
Invert sugar: Mix of glucose and fructose (hydrolyzed sucrose), often used in confectionery for its moisture-retention properties.
Polysaccharides
Sugars can form one-dimensional chains but can also branch, creating complex structures.
Oligosaccharides: 3-20 monosaccharides, often found in plant-based foods.
Amylose: Starch, a linear polymer of glucose.
Amylopectin: Branched starch, also a polymer of glucose but with a branched structure.
Plant cells have amylopectins and branched polysaccharides as their primary energy storage form.
Water Solubility
Sugars are extremely water-soluble due to hydroxy groups, allowing them to dissolve readily in aqueous environments.
Hydroxy groups interact with water through hydrogen bonding.
Water builds hydration shells, dissolving the sugar and forming a stable solution.
Branched polysaccharides attract and bind water to a high degree, making them useful as thickening agents.
Example: Diapers utilize the water-binding properties of polysaccharides to absorb liquid.
Functional Properties of Sugars
Contain aldehyde and alcohol (hydroxy) groups, which contribute to their chemical reactivity and physical properties.
Hydroxy groups make them soluble in water, crucial for their role in food systems.
Aldehyde groups are important for reducing activity and Maillard reaction, contributing to flavor and color development.
Sugars are used for taste, water binding, texture, regulation of gelation, and prevention of spoilage in various food applications.
Honey is antibacterial because sugar pulls water out of living organisms, reducing water activity and inhibiting microbial growth.
Relative Sweetness
Different sugars have different levels of sweetness, influencing their use inSweetening foods.
Caramelization
Heating sugar until it caramelizes, resulting in brown stuff with characteristic flavors.
Involves furans, maltol, etc., which are not Maillard products but contribute to the overall flavor profile.
Crystallization
Desirable feature in confectionery (e.g., lollipops), providing texture and appearance.
Water Barriers
Sugars help in creating effective water barriers in food products.
Humectancy: The ability to attract and retain moisture.
Modulate humidity and water activity, preventing spoilage and maintaining texture.
Inversion
Creation of invert sugar (glucose and fructose) through hydrolysis of sucrose.
Changes sweetness and affects the texture of food products.
Gelatinization
Opening up starch molecules and altering accessibility to water, leading to swelling and thickening.
Occurs when starch is heated in the presence of water.
Swelling is based on water accessing individual sugar moieties, causing the starch granules to expand.
Freezing and Thawing (Pudding)
Freezing a pudding results in clumps in sugary liquid because ice pockets form, and the structure is not the same as the original gelatinized state, leading to a loss of smooth texture.
Lipids in Food
Lipids are fats and oils, essential components of food that provide energy and flavor.
Different foods have different fat/lipid content, influencing their nutritional value and sensory properties.
Examples: Apple (low fat), milk (some fat), soy (high fat).
Types: Triacylglycerol (triglycerides), steroids, phospholipids.
Chemical Definition
Broad group of naturally occurring molecules characterized by their hydrophobicity.
Key feature: Hydrophobic (not soluble in water) due to their nonpolar structure.
Lack hydroxy groups, which contributes to their insolubility in water.
Contain long chains with a carboxylic group at the end, forming fatty acids.
Free fatty acids are lipids that are not esterified to a glycerol backbone.
Triglycerides are esterified fatty acids with a glycerol backbone, serving as the main storage form of fat.
Fatty Acids
Represented with the carboxylic group (COOH) and a long zigzag chain of CH groups, forming the hydrophobic tail.
Alpha (α) end: Carboxylic group, the reactive end of the fatty acid.
Omega (ω) end: Methyl group, the terminal carbon of the fatty acid chain.
Omega-3 fatty acids: Double bond at the C3 position from the omega end, known for their health benefits.
Most often, an even number of carbons is present in fatty acids due to their biosynthesis.
Best energy storage due to being the most reduced, providing more energy per gram compared to carbohydrates or proteins.
9 kcal/gram of fat
4 kcal/gram of protein or carbohydrate
Short Chain Fatty Acids (SCFAs)
Examples: Acetate, propionate, butyrate, produced by gut bacteria.
Metabolites produced by gut microbiota through fermentation of dietary fiber.
Important for brain development in infants and preventing autism spectrum disorder, highlighting the gut-brain connection.
Medium Chain Fatty Acids
Play a role in the brain, particularly toward the end of life, influencing cognitive function.
Modulate cognitive decline and may provide an alternative energy source for brain cells.
Long Chain Fatty Acids
Key role in membrane action potential and simple biological functionalities, essential for cell signaling and function.
Saturated vs. Unsaturated Fatty Acids
Double bonds prevent rotation, altering the physical properties of fatty acids.
Cis double bond introduces a kink in the fatty acid structure, affecting membrane fluidity and packing.
Impacts membrane fluidity, permeability, and packing, influencing cellular processes.
Fatty acids may be saturated (all single bonds) or unsaturated (contain double bonds).
Unsaturated fatty acids can be in cis or trans form, affecting their shape and biological activity.
Cis double bond: Kinked, naturally occurring configuration.
Trans double bond: Straight, often produced during industrial processing.
Naturally occurring fatty acids are generally in cis confirmation, contributing to membrane fluidity.
Mono-unsaturated: One double bond.
Poly-unsaturated: Two or more double bonds.
Fatty Acid Nomenclature
Carbon atoms at different numbers are associated with different acids (e.g., butyric acid).
If there is a double bond, it needs to be known where, indicating the position of unsaturation.
If Omega 3, the double bond is at C3, specifying the location of the first double bond from the omega end.
Based on interaction and kink of the length of the molecules, they have different melting points, influencing their physical state at room temperature.
Triglycerides
Formed via esterification, linking fatty acids to a glycerol backbone.
Glycerol backbone: The central structure to which fatty acids are attached.
Esters formed when a carboxylic group binds with a hydroxy group (COOR).
Broken down by lipases, enzymes that hydrolyze triglycerides into fatty acids and glycerol.
Phospholipids
Key building blocks of biological membranes, forming the lipid bilayer.
Core structure: Glycerol, phosphoester configuration, fatty acid esterified molecules.
Double bond introduces a kink, affecting membrane fluidity.
Lipid hydrophobic parts meet in the middle, and water-soluble phosphoglyceride parts are exposed to water forming membranes.
The membranes surround each and every living cell, providing a barrier and regulating transport.
It has bilayer that includes phosphoglycerol head groups, creating a polar surface.
Role of Fats in Food
Source of essential fatty acids, which the body cannot synthesize.
Caloric density (energy), providing more energy per gram than carbohydrates or proteins.
Carry flavor, enhancing the taste of food.
Fat-soluble vitamins, facilitating their absorption and utilization.
Contribute to texture and mouthfeel, influencing the sensory experience of food.
Chemical Reactions of Lipids
Hydrogenation
Used to create margarine by saturating unsaturated fats.
Adds hydrogens to polyunsaturated fats to harden liquid oil into semi-solid fats.
Not widely used anymore due to health concerns related to the formation of trans fats.
Hydrolysis
Reversing esterification by adding water.
Putting in water to split what's outside.
Rancidity is involved with fatty acid hydrolysis, leading to off-flavors and odors.
Products of the Hydrolysis Reaction
When hydrolyzing a fat, you end up having three