Food Science - Exam #2 Flashcards
What are foods made of?
Matter;
-Which is composed of pure substances, as either elements or compounds
What are Elements?
The simplest form of matter - cannot be broken down further. (without physically changing them)
What are Compounds?
- Made of two or more elements chemically bonded in definite proportions by weight, to make a new material
- Basically makes up everything;
- Represented as formulas of elemental composition
What are the important compounds to food science?
- Organic compounds.
- All contain Carbon (C), Hydrogen (H), oxygen (O) and sometimes sulfur(S), nitrogen (N) or phosphorus (P)
What are Mixtures?
- Two or more substances are combined physically.
- Solutions, dispersions, emulsions**
What are Chemical Symbols?
one or two letter designations for elements depicted in the periodic table
What are Chemical Formulas?
depicts all of the elements in a compound, including proportions as subscribed numbers
What are Chemical Equations?
–A written description of a chemical reaction using chemical symbols and formulas.
-C6H12O6 + 6 O2 → 6 CO2 + 6 H20 (breakdown of glucose)
What happens in a chemical reaction?
- Atoms/molecules interact with each other through chemical bonding.
- Results in a new substance with different properties from the reactants
How do elements interact through CHEMICAL BONDS?
- Requires energy.
- Only ELECTRONS are involved in chemical bonds
How are protons and neutrons treated in compounds?
- Protons and neutrons are NOT involved.
- Protons only account for the mass of the chemical
How are electrons treated in compounds?
- Electrons are negatively charged and are attracted to positively charged nucleus.
- Atom can be seen as having a series of electron orbits.
How is the MAX number of electrons in each orbit determined?
-Use X=2n^2. •1st level – 2 •2nd level – 8 •3rd level – 18 •4th level –32
What is the Valence Electron Shell?
- OUTERMOST electron shell;
- Most atoms become chemically stable when they have 8 electrons in their outermost shell
What is the chemical formula for Propionic Acid?
C3H6O2
What do structural formulas show?
-Help visualize how the bonding takes place
What are Covalent Bonds?
- Occur when electrons are shared;
- One, two or three pairs of elections can be shared resulting in single, double, or triple bonds
What are the bonds in fats, proteins, carbs, and vitamins?
- Covalently bonded carbon atoms.
- Form the backbone of these molecules
- You can have 1 -3 bonds shared.
- The more bonds shared, the more energy stored.
What are Ionic Bonds?
- TRANSFER of elections between reactants.
- Resulting in a FULL valence shell of both elements;
- EX: Salt (NaCl) - most important bond in food science because we always use salt
What are Cations?
- Elements that donate electrons become positively charged in an ionic bond;
- EX: Sodium (Na+)
What Anions?
- Elements that receive electrons are negatively charged in an ionic bond;
- EX: Chlorine (Cl-)
What are Hydrogen Bonds?
- A type of covalent bond with unequal rather than equal sharing of electrons, resulting in a weak force;
- Type of intermolecular bond
What are Intermolecular Bonds?
-Bonds between two different MOLECULES.
When do hydrogen bonds occur?
- Occur when elements such as oxygen and nitrogen in one compound come into close proximity with hydrogen from another compound and share the electron of hydrogen;
- How was orients itself
What are the chemical reactions in foods?
- Composition reaction;
- Decomposition reaction
What are Composition Reactions?
- Two or more substances combine resulting in a single product (A+B = AB).
- EX: Synthesis of protein from amino acids
What are Decomposition Reactions?
- One substance becomes two products (AB à A+B).
- EX: Hydrolysis of maltose yields two glucose molecules
Enzymatic vs. Non-enzymatic
- Either reaction type may be either enzymatic or nonenzymatic.
- Nonenzymatic- don’t require enzymes, just happens
What are Enzymes?
- Specialized proteins and serve as biological catalysts (cause reactions to speed up) of chemical reactions;
- Positive effect = tenderization of meat;
- Negative effect = browning of cut fruits and veggies
What is an Active Sites in an enzymatic reaction?
- Location where the substrate joins with the enzyme to form the enzyme substrate complex;
- Three dimensional region that contains amino acids that bind, non-covalently, to the substrate.
What scientists worked out the enzymatic reactions?
- The biochemists Michaelis and Menten worked out the kinetics of enzymatic reactions.
- E + S ←→ ES ←→E +P
What is Activation Energy?
- The amount of energy required for a reaction to take place.
- Enzymes reduce the activation energy thus speeding up the reaction.
What is Enzymatic Hydrolysis?
- Breakdown of large components into smaller ones
- Ex: carbohydrases, lipases, proteases (protein hydrolysis)
What is Enzymatic Oxidation-Reduction?
- Oxidation is the loss of electrons and reduction is the addition of electrons.
- Ex: the browning of fruits and vegetables via polyphenol oxidase.
- In nature, they are coupled.
- OIL-RIG
- Occurs everywhere.
What is Enzymatic Polymerization?
- Occur through CONDENSATION reaction;
- The joining of two compounds
- When many condensations occur within the same molecule, a POLYMER is formed.
- Water is released.
- Small molecules join to form long chain
- Happens a lot in protein and fats
What are Nonenzymatic Reactions?
-Reactions occur in nature in the absence of an enzyme catalyst; Types include = •Addition •Oxidation-reduction •Hydrolysis: adding water •Condensation: removing water
What are Addition Reactions?
-The addition of an element to a compound.
EX: Hydrogenation of unsaturated fatty acids where hydrogen is added to the double bonds.
EX: Margarine
What are Oxidation Reduction Reactions?
-Electrons are transferred between substances;
-Can affect color, quality, acceptability of foods.
•Oxidation – the ADDITION of oxygen
•Reduction – the GAIN of hydrogen
Can be caused by UV light, heat, high oxygen environment, metal catalyst, etc.
What are Condensation and Hydrolysis Reactions?
- Complimentary reactions;
- Generally catalyzed by heat or acid
What are Condensation Reactions?
-When two molecules are joined together with the formation of a new product and water.
What are Hydrolysis Reactions?
-When a molecule is broken apart in the presence of water, which is incorporated into the two new products
What are Functional Groups?
- Arrangements of atoms that create certain properties of molecules;
- Component molecules play an important role in functionality of the food itself.
Alcohol Group
- OH or hydroxyl;
- Important food alcohols include ethanol and glycerol.
Aldehyde Group
- Carbon at the end of the molecule which is double bonded to oxygen.
- Important in odors and flavor of foods
Amino Group
- Contains an amino (-NH2) functional group.
- Histamine, serotonin and dopamine are amines
Carboxylic Acid Group
- Carbon on the end of a molecule bonded to a hydroxyl and double bonded to an oxygen.
- Ex: citric acid, acetic acid (vinegar).
Ester Group
- Carbon double bonded to an oxygen and single bonded to a second oxygen which is bonded to another carbon.
- Associated with characteristic aroma of foods
Ketone Group
- Interior carbon atom is double bonded to an oxygen.
- Associated with flavor of food (cooking of meats, brewing of beer
Methyl Group
- Carbon bonded to three hydrogen. (CH3)
- One of the important building blocks of organic molecules;
- Found in pectins and gums
Phosphate Group
- Phosphorus bonded to two hydroxyls and double bonded to one oxygen and single bonded to one oxygen. (-PO4)
- Added to meat to improve texture, juiciness and water-holding capacity.
- High source of Energy (ATP)
Sulfyhydryl Group
-Sulfur bonded to a hydrogen (R-SH)
-Compounds containing sulfhydryl groups are called THIOLS;
-Important to structure of foods (e.g. in bread dough);
-Both bad and good
Ex: smell of rotten eggs
Ex: popcorn and baked bread
What are Functional Properties?
-The chemical and physical factors that impact the behavior of food during formulation, processing and storage
Why is the functionality of water so important?
- Because most food contains a large proportion of water, its functionality is a highly critical factor relative to the quality of food.
- Helps determine: shelf life, taste, texture.
What are functions attributed to water?
- Diluent and carrier of hydrophilic components = Things that can dissolve in water
- Medium for chemical reactions = Provides a place for things to float around in.
- Solvent
- Medium of heat transfer (And freeze)
- Participates in chemical reactions = Due to it’s negative and positive sides
What is the molecular structure of water?
- Two hydrogens bonded to one oxygen;
- Each H shares an electron pair with the O (pulls more);
- DIPOLE created with Oxygen more negative and Hydrogen more positive (Magnet)
What does the Hydrogen Bonding of water result in?
- High boiling point and freezing point
- High vapor pressure
- High interfacial tension (spider walking on water)
What is Solubility?
- Ability to be dispersed into solution;
- Hydrophilic compounds disperse readily in water
What is Hydration?
- Water molecules contact and surround polar molecules by acting as a solvent.
- Polar molecules
What are Amphiphilic Molecules?
-Contain BOTH polar and nonpolar regions.
-When water interacts with these compounds, micelles are formed.
Ex: proteins, phospholipids, sterols, and soap.
(Soap and dissolve water on one side and oil on the other)
What is Moisture?
- Amount of water in a food.
- Because of bacteria
- Determines your shelf life and risk for contamination.
- A lot of water can cause reactions to occur and change the product
What is Water Activity?
- Amount of water available for chemical reactions or to support microbial growth, enzymatic/chemical reaction;
- Free, Structural, or Bound water in foods
What is Free Water?
Participates in chemical reactions and support microbial growth
What is Structural Water?
Participates in chemical reactions and support microbial growth
What is Bound Water?
- Tightly associated with food components and does NOT act as typical water molecules do.
- Not available for reactions or microbial growth.
- When you have salt and sugars (which is attractions water), all of the sugar and salt will bind to the water (Making a jam)
What is an Emulsion?
- Colloidal dispersion in which two normally immiscible fluids are mixed.
- Has a continuous phase into which a dispersed phase is mixed
What are Emulsifiers?
- Amphiphilic compound;
- Generally needed to establish and stabilize EMULSIONS.
- Soaps and fats.
- One polar side and nonpolar side.
- Pic= oil droplet are SMOOTH in the pic, means suspended in water.
- Protein pic=the arm is water soluble, and the other isn’t; “theyre holding hands”
How is water involved in Heat Transfer?
-Acts as a conductor of thermal energy to foods (AKA heat transfer)
What must be done to water in foods, especially frozen?
Must be stabilized
What are the food acids?
-Food acids come in a variety of forms including amino acids, fatty acids, fruit acids such as acetic and citric acids, etc;
-The acid donates a proton to the water molecule and form charges.
oLost proton= negative charge
oGain proton= positive charge
What is the structure of food acids?
- Primarily carboxylic acid based (i.e. organic acids).
- Differences in size, number of carboxylic units and location of carboxylic acid within the molecular structure, all influence the characteristics of the acids
What are Acids?
- Donate (or lose) protons
- Acid strength is dependent on its ability to dissociate.
Strong vs. Weak Acids
-Weak acid– a small amount of H ions have separated.
(Foods are usually weak acids)
-Strong acid– have large amounts of dissociated ions
What are food acids considered?
- All food acids are considered weak acids because of a small dissociation, or IONIZATION CONSTANT;
- Determines how strong an acid is in a food product
What is Fumaric Acid?
-Can soften bread doughs by breaking disulfide bonds between cysteine molecules.;
-Flour proteins contain amino acid CYSTEINE.
•**know that it contains –SH.
What is a Salt?
-A hydrogen atom in the carboxyl group is replaced by a metal ion (charged) such as Na, Ca, or K;
-In water, the Na and Cl separate to form ions;
-When they bind with something else, it still makes a salt.
EX: -COOH + ion = salt
What are Buffers?
- A system of a weak acid and a salt of the acid in which the pH is maintained;
- “regulators”;
- Can be used for different levels of pH.
How do buffers regulate pH in foods?
- Keep the pH stable in the reaction by accepting and donating proton;
- Most foods need to be buffered to below 4 to have a good shelf life
What is Leavening?
- Production of gas by either yeast fermentation, the reaction of an acid with baking soda, or by heating of salts.
- Natural = Anaerobic respiration of yeast
What is Chemical Leavening?
- Requires an acid (leavening acid) and a carbonate, usually sodium bicarbonate.
- The acid releases the CO2 from the carbonate in a multi-step process;
- React with acids to produce CO2, causing dough to rise without yeast.;
- Baking soda- reacts with acid immediately
- Baking powder-double acting
What is Baking Powder?
- Complete leavening system;
- Mixture of cream of tartar and baking soda.
- Has two reactions at different temp: one to raise the bread and another to stop it.
- “DOUBLE ACTING” = increases the quality in the bread
What is pH?
- The dissociated hydrogen ion concentration on a logarithmic scale according to the equation;
- pH=- log of hydrogen ion concentration [H+];
- Range from 1-14;
- LOW pH (acidic) can prevent microbial growth and spoilage
What is Titratable Acidity?
- Another indication (dyes) of a food’s acidity;
- Measure of dissociated and non-dissociated H;
- Critical quality control tool in many food products.
- Ex) fermented products (i.g. beer, peppers, sour kraut) you use the titrability of acidity to see if you’ve reach the acidity level in your product. Figures out quality
How is Titratable Acidity measured?
-By titration with a known concentration of base to a predetermined pH.
What are Acid Foods?
-Possessing a natural pH of less than 4.6
What are Low Acid Foods?
- Possessing a natural pH greater than 4.6.
- Our limit for few microbials to grow
What are Acidified Foods?
- A low acid food to which an acid is added such that the resulting pH is less than 4.6.
- Ex) Adding vinegar.
What are Fermented Foods?
-Low acid foods that undergo natural fermentation that results in the reduction of pH
What is the structure of Sugars?
- Carbon, hydrogen and oxygen.
- Simple sugars = Monosaccharides, Disaccharides;
- Structural features, which are dependent on the location of FUCNTIONAL GROUPS, have an influence on functional properties;
- Simple sugars can be syrups or crystals in food
What are Sugar Alcohols?
- Sugars with modification of one corner of their molecule = –OH group that binds to the reducing end of a monosaccharide unit making the sugar NONREDUCING;
- Cause slow rise in blood insulin levels.
- Do NOT participate in BROWNING reactions
- Lacking ALDEHYDE group
- NOT good for cooking, no browning!;
- “ol”= sugar alcohol ingredient
What are the Monosaccharides?
-Trioses - 3 carbons.
-Pentoses – 5 carbons.
-Hexoses – 6 carbons.
= Glucose, fructose, galactose – C6H12O6
What is the difference between Glucose and Fructose?
-Glucose has a SIX member ring (aldose)
-Fructose has a FIVE member ring (ketose)
= This difference is partially responsible for the fact that fructose is sweeter and more soluble than glucose.
-Fructose is the KETOSE version of Glucose (ALDOSE)
What are the Disaccharides?
- Two monosaccharides bonded together by a glycosidic bond;
- Sucrose – glucose + fructose) - common table sugar;
- Lactose – glucose + galactose) - milk sugar;
- Maltose – glucose + glucose) - common breakdown product from starch
What is the Alcohol (-OH) functional group important for?
Solubility and sweetness
What is the Carbonyl (C=O) functional group important for?
- Reducing activity and MAILLARD browning for color/flavor development;
- Functional group artificial sweeteners DON’T express
What are Reducing Sugars?
- Contain a CARBONYL group (aldehyde or ketone)
- ALL monosaccharides are reducing sugars.
- Gives the ability to form disaccharides and polysaccharides by allowing bonding between monosaccharides;
- Reative -OH group at C1 (aldehydes) or C2 (ketones) in cyclic structure
What are the browning reactions that occur in sugars?
- Maillard Reactions
- Caramelization Reactions
- Both are categorized as NONENZYMATIC
What is the Maillard Reaction?
- Complex series of reactions that requires a REDUCING SUGAR and AMINO ACID in foods and results in Browning of sugars;
- Intermediate products: pyrazines which tend to have pleasant aromas and flavor;
- End products: brown pigments called melanoids;
- IRREVERSIBLE and result in darkening of food
What are the conditions for the Maillard Reaction?
- Takes place at relatively low temperatures and can be accelerated by lower molecular weight sugars, low moisture content (<15%) and in the pH range of 5-8.;
- Condensations, Rearrangement, Polymerization
What is Caramelization?
- Takes place at high temperature (200C);
- Only occurs at high temps, but very easily burns;
- Due to the DEHYDRATION of the sugar molecule;
- BREAKS DOWN the sugar by the use of heat and forms crystals
What is the difference in Caramel Coloring and Caramel?
- Caramel coloring = refers to a brown coloring used in the food industry.
- Caramel = refers to sauces or candies made from carbohydrates that have been allowed to caramelize
What is Crystallization?
- Implies organized 3-D arrays of unit cells into solid form;
- As the sugars cool, the solids reforms in crystalline structures
- In candy manufacture, control of the crystallization process is highly critical to the ultimate quality of the candy
What is a Humectant?
- Substance that has an affinity for moisture, also referred to as HYGROSPOPIC substances;
- Hygroscopic – substance that ATTRACTS water;
- This is ultimately related to their ability to form bonds with WATER
What is Inversion?
- Process where sucrose is hydrolyzed to fructose and glucose, which are then called Invert Sugars;
- Can be done by heat, acids, specific enzymes;
- Inversion can be induced by heat, acid, or a special enzymes called INVERTASE
What are the effects of Oxidation Reduction reactions?
- Promote important functional characteristics of sugars;
- Oxidation of the ALDEHYDE group in sugars causes a LOSS of sweetness and converts it to an acid;
- Reduction of the carbonyl group of reducing sugars causes the formation of SUGAR ALCOHOLS, which are moderately sweet.
- Ex: mannitol and sorbitol
How are sugars ranked by sweetness?
- SUCROSE is usually used as the reference with other sugars;
- Fructose > sucrose > glucose > maltose > galactose > lactose
What effects do sugars have on the textures of foods?
- Effect on texture through their interaction with water.
- Sugar can provide bulk, tenderization (e.g. in baked goods) and can influence other texture promoting compounds such as starch;
- Sugar is HYGROSCOPIC – ultimately affects texture
- Hydrogen bonds are formed between water and sugar
What happens to Sugar when heated in the presence of an acid?
- Breaks down into glucose and fructose resulting in an invert sugar
- Invert sugars are viscous liquids and very hygroscopic
- Brown sugars are coated with molasses and therefore have more invert sugar
What are the Complex Carbs?
- Oligosaccharides (3-10 units);
- Polysaccharides (>10 units)
What are the Oligosaccharides?
EX: Raffinose and Stachyose;
- Present in dried beans. → “-ose” means sugar
- NOT digested in the small intestine but are fermented by microorganisms in the large intestine.
What Polysaccharides?
- Much more abundant in foods than oligosaccharides;
- Commonly used as additives to food for specific aspects of functionality
What are Beta-Glucans?
-Polymers of glucose;
-SOLUBLE dietary fibe;
-Been found to lower serum cholesterol;
-Primarily in OATS, along with BARLEY and YEAST,
-Fat replacer in many different manufactured food products.
= Oatrim – used in baked goods, fillings and frostings, frozen desserts, salad dressings, etc.
What is Cellulose?
- Plant polysaccharide of glucose;
- Structural component of all plant cell walls;
- Main source of INSOLUBLE dietary fiber;
- We don’t possess the enzymes to digest
- Microparticulate form of cellulose is used as a bulking agent and to increase dietary fiber in foods
Where do Dextrin and Maltodextrin come from?
Breakdown of starch;
- Dextrin = any start undergone heat degradation, usually with heat;
- Maltodextrin = specifically related to commercially generated products, usually cornstarch (Used in sauces, baking, processed meat as fat replacer) and bulking agent
What are Fructooligosaccharides?
- Polymers of FRUCTOSE usually with sucrose;
- Variety of plants like garlic, onions, bananas;
- PREBIOTICS because they are not broken down in the small intestine and make it to the large intestine where they nourish good bacteria (probiotics)
- Prebiotics → feed the probiotics
- Probiotics → Good bacteria the utilize prebiotics
What is Inulin?
- Type of fructooligosaccharide found in onions, asparagus and especially chicory root.
- Serves as a prebiotic to stimulate the growth of good bacteria.
- Can be used to adjust textural attributes
What are Pectic Substances?
- High molecular weight polysaccharides found in plant cell walls, primarily for support. ;
- Composed of galacturonic acid units some of which are METHYLATED, which determines functionality;
- Protopectin;
- Pectinic Acid;
- Pectic Acid
What is Protopectin?
-Nonmethylated and found in immature fruit → NO GEL
What is Pectinic Acid?
-Methylated and produced during ripening → GELS
What is Pectic Acid?
Demethylated derivative of pectinic acid and associated with overripe fruit → NO GEL
What is Degree of Esterification?
- Methoxylation = deterimines functionality of pectins;
- High methoxyl (HM) pectin have > 50% methylation, whereas low methoxyl (LM) pectin generally has < 30% methylation.
What is Pectin Gelation?
Pectins are able to form colloidal dispersions (sols and gels) =
- To convert a HM pectin sol to a gel it is necessary to reduce the association of pectin with water by incorporating sugar and reduce the repulsive forces between pectin molecules.
- LM pectin can be converted into a gel without sugar by adding divalent CATIONS such as calcium (makes sugar free jelly)
What is Starch?
- Predominate source of dietary energy in the world’s food supply;
- Packaged in plants as starch granules;
- Can be modified to change functionality (pre gelatinized)
- Polymer of glucose molecules, found in two forms =
- Amylose – a straight chain;
- Amylopectin - numerous branches; lots of reducing ends so can form a lot of bonds
What is starch gelatinization?
- NOT soluble in cold water, but if agitated and heated it undergoes a conversion that is referred to as gelatinization;
- The heated starch granules absorb water and swell.
- Irreversible reaction.
- Increased viscosity
What is Starch Paste?
- A starch/water system the has both thick liquid and solid-like properties.
- In a paste, majority of starch granules have gelatinized, producing swollen and disrupted granules;
- Pasting = continuation of gelatinization where thickening of a slurry occurs
What is Gelation?
- The formation of a gel from a cooled paste.;
- Starch gel – a thick starch/water mixture that has properties of a solid.
What is Starch Retrogradation?
- Contraction of starch gels due to interactions between amylose molecules;
- As the gel tightens it can loose water, which is referred to as SYNERSIS
What is the starch content of potatoes?
16-22% starch
What are Vegetable Gums?
- Broad category of complex polysaccharides that contain a variety of sugars including pentoses and hexoses;
- Can be used to add texture to foods without altering caloric content;
- Gums are derived from a variety of sources including plant seeds (guar) seaweed (carageenans) and microorganisms (xanthan)
What is the chemical structure of fats lipids?
- Triglyceride;
- Glycerol backbone (3-C alcohol) with 3 fatty acids chains attached;
- Fatty acids contain a carboxyl end and a methyl end
