FOOD2150 Set 4 Flashcards
What is water used for in nutrition?
- hydrolysis of large molecules
- some produced by oxidation of small molecules and water found in foods
- need sufficient water to dilute waste components
- to get rid of excess electrolytes
What are the biological functions of water?
- cellular structure (muscle, membranes, skin): healthy, turgid cells
- nutrient transport: throughout body
- lubrication: saliva, tears, hip, etc joints
- metabolism: for reactions (digestion, breaks macronutrients down)
What happens if we do not drink water?
- die in 4 days
- can be toxic in excess (too low blood solute concentration)
What increases need for fluids?
alcohol, cold, fiber, diseases, heated environments, high altitude, medications, activity, etc
What is obligatory water loss?
amount needed to dilute solutes from diet (mainly salt and urea)
What is urine production like with water?
- max amount we can conc.
- kidneys filter blood, reabsorb -99% of passing water
- osmotic and hormonal control
What is amazing about water?
- dissolves more substances than any liquid
- freezing point lowers as amount of salt dissolved increases
- expands (by 9%) when frozen (why ice floats)
- if salt is poured in water: volume decreases
- boils at high temp (100C)
- extremely high surface tension (non-covalent interactions with other H2O)
Why does methane have a lower BP compared to water?
- tetrahedral (groups with 4 VE) (no dipole movement), symmetrical, weak van der waal’s forces
- water has a large dipole moment since it has a bent molecular geometry
What is cohesion?
- the action or property of like molecules sticking together, being mutually attractive.
What is adhesion?
tendency of dissimilar particles or surfaces to cling to one another
What is the uses of water in agriculture?
- application of a pesticide/herbicide
- transports nutrients
What is the uses of water in agriculture?
- hydration
- why we add surfactants to emulsions
- why gels/dough exists
What is the uses of water in nutrition?
- Water is the transport molecule of the blood
- Allows NaCl and sugars to be soluble
- Due of small size O2 is soluble
- Solubilization of proteins and carbohydrates
Describe water and its symmetry
- Bent configuration (asymmetry) of water
(bond angle 104.5) - Water has no net electric charge, one side is
positive and the other is negative - Strong dipole moment
- Hydrogen Bonds (12-30 kJ/mol)
What is water’s high latent heat of vaporization and fusion and heat capacity used for (agr,fs,nut) ?
AGR: Evaporative cooling to protect enzymes in plants
FS: steam as a heating medium in processing plants, an energy intensive process to heat and cool foods
NUT: removes lots of heat energy when it evaporates
How does changing the temperature of water modify the dipole moment, and what does this cause?
- changes the hydrogen bond length which is correlated with the hydrogen bond strength
increase in the hydrogen bonding: - increased cohesion, density (down to 4oC), viscosity
- decreased adhesion, density (from 4 to 0 oC), thermal conductivity
What is water’s nanostructure?
- Strong Cohesion
- Strong Adhesion
- High Boiling and melting points
- High latent heat of vaporization
What is water activity?
measure of the availability of water molecules to enter into microbial, enzymatic and chemical reactions
* Bound water is unavailable for reactions
* Capillary water is somewhat available for chemical reactions
* Free water is available for chemical reactions
* More predictive of shelf-life than measuring total water content of a food
What are the two types of water?
- water binding-bound water
- water holding-entrapped water
What is water binding-bound water?
- molecular interaction of water with solutes (sugars) and ions
(salts). - “hydration”
- Water bound to solutes behave differently than “bulk” water.
- molecularly immobile or unavailable
What is water holding-entrapped water?
- entrapment of water in a gel by high-MW molecules such as
proteins and polysaccharides in a way that prevents water from flowing and from being “exudated”. - Entrapped water, free or capillary water behaves, like pure
water and maintains its molecular availability and mobility.
How does water’s large dipole moment disrupt electrostatic interactions between ions dissolving them?
-Negative ends of the water dipole (oxygen-free electron pairs) will orient themselves towards cations and positive ends of the same dipole (hydrogen atoms) will orient themselves towards anions.
- forms a “hydration sphere” about one layer deep around the ion, water in this sphere is called “bound water”.
- Bound water can form hydrogen bonds and this “structures” the
water several layers removed from the hydration sphere.
How can we calculate water activity?
measured instrumentally by determining Equilibrium Relative Humidity (ERH)
= ERH(%)/100
Describe hydration (bound, visceral) water
water molecules associated directly with food macromolecules (exchangeable, not covalently or H- bonded)
* gives macromolecules their structure
* not available for microbial growth nor chemical reactions
* it does not contribute to product deterioration
* present even in dry foods, e.g., powders
Why does water content vs water activity differ?
identity vs concentration
- 2 molecules dissociate have greater affect on Aw
- doesn’t deterioate: carb; binds water better than protein
Describe trapped (capillary) water
- ~ 5% of the total water in a food, may be much more in tissue products like leaves
- associated with cellular and tissue structures - not easily pressed out
- can be removed by drying
- does not support microbial growth but provides a“moist” texture, e.g., dried fruits or capillary water in vegetables, meats
3) Free Water - can be 90% + of the water in a food (e.g. orange juice)
- available for both microbial growth & chemical reactions
- easy to remove (just squeeze or press) out of product
Describe the phase diagram of water
Can exist in three physical states (very
unique)
* Gaseous, Liquid and Solid
* Both pressure and temperature may
be manipulated to change the physical
state of water
* Used in evaporative drying, freeze drying,
boiling,
*phys chem supercritical fluid graph
How are frozen foods stable during freezing?
some microbial survival
- physical: ice formation
- chemical: cryo-concentration
How are frozen foods stable during storage?
no microbial growth
- physical: recrystallization, sublimation
- chemical: slow reactions
How are frozen foods stable during thawing?
some possible microbial growth
- physical: drip loss
- chemical: decompartmentalization
When happens to the H bonds when water freezes?
- decrease in density
- liquid water, each molecule H-bonds to 3.4 other water molecules
- in each, each water binds to 4 others
What happens when water crystallizes?
- preserves the tetrahedral “structure” of liquid water
- crystallizes into an “open structure” that is less dense (91 %) than the liquid state
- ice formation can disrupt tissue structure
Give examples of colligative properties
- vapor pressure lowering (Raoults’ Law)
- boiling point elevation (Candy thermometers)
- freezing point depression (ice cream)
- osmotic pressure (Nutrition and processing)
What are colligative properties of solutions?
- properties that depend upon the concentration of solute molecules or ions, but not upon the identity of the solute
- BP elevation, freeze-concentration
What makes water a highly structured liquid?
When ice melts, only 15 % of hydrogen bonds are broken which
explains why the latent heat of fusion (333kJ/kg) is small
compared to the latent heat of vaporization (2230 kJ/kg).
Describe the colligative property of freeze-concentration
- solute concentration and molecular weight
- Freezing causes a concentration effect of solute molecules in a reduced amount of unfrozen water
- occurs when viscosity is so high, sugar molecules can no longer arrange in crystal lattice: become stuck: freeze
Describe glassy amorphous states
- rapid cooling increases viscosity rapidly, crystallization is impossible
- high viscosity makes it behave like a solid
- metastable, supercooled liquids (not true solids)
- difficulty of directly addressing glass behaviour (long time to attain because of high viscosities)
Give examples of glasses in foods
pasta, powders, instant coffee, hard candies, sugar in chocolate, boiled sweets
- pure sugars form a glass, pure sucrose will not form one; important in confections
- amorphous like water: disordered, no molecular order (you can see through)
- form due to high viscosity
What is molecular mobility
- kinetic approach to food stability
- excellent predictor of food stability
because deteriorative reactions occur very slow - exceptions: reactions that do not depend on diffusion (free-radical oxidation)
What are glass transitions characterized by?
- glass transition temperature
- higher molecular weight: higher glass transition temp
- glass achieved by increasing concentration or lowering water content, particularly of high molecular weight materials, and/or lowering temperature
What are the two types of emulsions
“dispersed phase” in “continuous phase”
- water-in-oil (butter, lard)
- oil-in-water (mayo, salad dressing)
- Hydrophobic phase is insoluble in the hydrophilic phase
- Requires an amphiphilic molecule to remain stable
How do we destabilize oil-in-water?
- hydrophobic phase is insoluble in the hydrophilic phase and without an emulsifier separation occurs spontaneously
What are types of oil-in-water emulsion destabilization?
creaming, phase separation, coalescence, sedimentation, time, flocculation, Ostwald ripening, phase inversion, partial coalescence
What is stokes’ law?
- particles rise; creaming
- particles fall; sedimentation
How does emulsion destabilization occur?
- differences in density between continuous and discontinuous phases
- differences in droplet sizes (Laplace pressure inside droplet)
Compare small and large droplets during destabilization
- smaller droplets have greater internal pressure causing an increase in solubility of the dispersed phase
- Large droplets grow at the cost of smaller droplets
How can we make emulsions more stable?
- adding proteins
- proteins sit at interface (hydrophobic and hydrophilic groups)
- when it arrives at interface, protein unfolds and exposes hydrophobic section to oil (philic to water)
How do emulsifiers use amphiphilic molecules?
- resides at interface between water and oil
- Reduces the interfacial tension or unbalanced H-bonds
- Stabilizes an emulsion preventing separation
What is the HLB (hydrophilic lipophilic balance) equation?
HLB= 20 x Mh/M
Mh: molar mass hydrophilic portion
M: molar mass
What are colligative carbs?
monosaccharides (pentose, hexose)
disaccharides (a-nomer, b-nomer)
What are noncolligative carbs?
- oligosaccharides (3-9 sugars)
- polysaccharides (10+ sugars) (homo (same subunit), hetero (dif. subunit)
What are the rules for the Fischer projection for linear sugars (monosaccharides)?
- Draw the carbon chain vertically
(carbonyl group at the top) - Vertical lines are below the plane
- Horizontal lines are above the plane
- Carbon numbering of the sugar always
starts at the most oxidized group (i.e.
the carbonyl group)
What are enantiomers
- isomers that are related by a reflection operation/mirror plane
What are stereoisomers?
- isomers that differ in the 3-dimensional arrangement of atoms (from a molecule) in space.
What is configuration?
- arrangement of stereogenic centers
- set at synthesis and is changed during chemical reactions
What is conformation?
- arrangement in space
- how the sugar orients itself due to the rotation of single bonds
- physical phenomenon
- temperature, pH dependent
- dictates the physical properties of sugars
and the reactions they partake in
What occurs during the formation of a ring structure?
- new chiral center
- previously achiral carbonyl carbon is now
chiral and can assume two configurations (α- and β-)
What is the process of interconversion between the α- and β- forms called?
- mutarotation
- a and b are anomers
- As long as this hemiketal or hemiacetal group remains, cyclization remains reversible (this is called a reducing sugar)
What are reducing sugars?
- preserves the hemiacetal group
- Glucose, galactose, fructose, lactose
- Undergoes Maillard reaction
- Undergoes caramelization
What are non-reducing sugars?
- No hemiacetal group
- sucrose
- Does not undergo Maillard reaction
- Undergoes caramelization
What is the maillard reaction?
- Reducing Sugar (glucose) + Protein (free amine) form Schiff base (shifting e- to become more stable)
- A series of molecular rearrangements
- Degradation productions (molecule shortens: aldehydes, carboxyls)
Important end products include:
- Melanoidins (pigment) (conjugated rings/double bonds)
- Flavours (breakdown products)
What is acrylamide?
- from Maillard reaction products
- class 4 carcinogen
- attempts to minimize asparagine or other proteins to prevent maillard
- released by thermal treatment of certain AA in combo with reducing sugars and of early Maillard reaction products (N-glycosides)
What is caramelization?
- Browning reaction observed by the heating of both reducing (glucose) and non-reducing sugars (sucrose) in the absence of amine-containing compounds
- similar to the Maillard reaction, but requires higher temperatures and low pHs
- sucrose needs to be hydrolyzed
What are the steps of the Maillard reaction?
- amadory rearrangement and product
- Strecker degradation
- cyclization
- polymerization (really dark brown: cyclic compounds from large, unordered polymers)
Describe the steps of maltodextrin and high fructose corn syrups
most sugar from corn: high in amylose and amylopectin
1- liquify: viscosity reduced, (treat w alpha-amylase), breaking starch from oligosaccharides to disaccharides
2- saccharification: colligative properties develop, reduced viscosity, increased sweetness
Describe maltodextrin
- saccharification
- DE value
- high DE: sweet taste
What is the DE (dextrose equivalent) value?
- indicates the degree of hydrolysis of starch into glucose syrup
- percentage of the total solids that have been converted to reducing sugars
- higher DE: more sugars, less present dextrins
- glucose syrups above 55 DE termed to high starch conversion
- 35-55 DE: regular conversion (drinks)
- below 20: products of hydrolysis are maltodextrins
What are HFCS?
- Corn starch that has undergone saccharification, High DE glucose syrup is processed by glucose isomerase to convert some glucose to fructose
- Sweetener (cheaper than cane sugar), excellent water binding
- Corn sweeteners control freezing point in ice cream and frozen confections, and extend shelf life by limiting microbial growth.
Describe oligosaccharides
- specific type of sugar
- modifications to sugar
- anomeric carbon-hydroxyl bond angle important for digestion
- which carbons are bound together
- no viscosity, no colligative properties: not very useful
Describe polysaccharides
- linear, branched or cross-linked biopolymers consisting of monosaccharides (>10 monosaccharide units covalently bonded together)
- The structural diversity is limitless
Describe homopolysaccharides
- degree of polymerization from 100-100000
- digestible: glycogen (more branched), amylopectin (less branched), amylose
- indigestible: cellulose, b-glucan, inulin
Describe the amylose of starch
- Linked together by (1→4) bonds
- Starch content is typically 15 to 25 %
- Degree of polymerization can be anywhere from
100 to 10,000 - one reducing end, one non-reducing end
- The unbranched nature of amylose, the –OH
groups can form intermolecular hydrogen bonds
with other –OH groups - Amylose-amylose interaction reduce solubility
Describe the amylopectin of starch
- Highly branched polymer of (1→4) bonds and
branched by non-random, evenly spaced α-(1→6)
bonds - Branch points occur every 20 to 25 glucose residues
- Mol weight between 1 million to 1 billion g/mol
- Branched nature makes intermolecular hydrogen
bonding difficult.
Describe the makeup of starch
- exists as large particles called granules (2um-100um)
- granules composed of amylose and amylopectin
What is starch functionality attributable to?
- gelatinization (loss of molecular order)
- pasting (disruption of the starch granule)
- retrogradation (starch polymers (amylose) forms intermolecular hydrogen bonds and may recrystallize)
- graph
How is starch an important food polysaccharide?
- Digestible by humans (source of energy)
- contributes to the texture of foods
- Certain indigestible starches behave like fiber (resistant starches) and fermented by gut bacteria as a prebiotic
What is pectin?
- hemicelluloses found in the middle lamella of
plant cell walls - found in fruit peels and vegetables
- most complex hemicellulose polysaccharides ( consists of two main polymers covalently linked: smooth galacturonans t1 and hairy rhamnogalacturonans t2)
- pKa 3.5
What is low-methoxy pectin?
- less than 50 % of galacturonic acid –COOH groups methoxylated
- low pH- between 2.8 and 3.2
- 65-70% sugar to bind water so it will not interfere with hydrogen bonding
Describe extracted and graded pectin
- Most pectin when extracted has a degree of
esterification between 50-80% - Pectin are “graded” according to the degree of methoxylation/esterification
What is high-methoxy pectin?
- More than 50 % of galacturonic acid –COOH groups methoxylated
- Sugar CANNOT be be added so we don’t get the dehydration of pectin
- pH above 3.5 causing ionization (strong electrostatic repulsion
- Add a source of Calcium (Ca2+)
What are the challenges with pectin and the good and bad?
- issue when extracting juice so pectin enzymes used to increase juice yield and to clarify juices, orange juice settles
GOOD: - Pectin contributes to the viscosity of tomato products
- Pectin stabilizes juices that exist as colloidal dispersion
BAD: - Endogenous pectin enzymes break down pectin and decrease viscosity of tomato products
- Destabilizes juices that exist as clouds
Where are most predominant carbs?
- absorbed in digestive tract:
glucose, fructose, galactose - Derived from digestion of disaccharides by brush border enzymes
- derived from digestion of glycemic polysaccharides
What are glycemic carbs?
- Are available for metabolism (provide energy and
glucose) - Sugars (glucose, maltose, sucrose)
- Starches (Amylose, amylopectin, maltodextrins,
glycogen
What are non-glycemic carbs?
- Are not hydrolyzed/absorbed in the small intestine (Fiber)
- Insoluble: cellulose, hemicellulose
- Soluble: glucan, pectin, locust bean, alginates, carrageenan, guar
What are the methods of diffusion on the surface of the microvilli?
facilitated (luminal side), passive (luminal side), passive (capillary side)
Describe facilitated diffusion on the luminal side
- Na+ & energy dependent (ATP) secondary active transport (SGLT-1 symporter)
- Transports Glucose & Galactose
Describe passive diffusion on the luminal side
- Facilitated diffusion via GLUT-5
- Transports fructose
Describe passive diffusion on the capillary side
- Facilitated diffusion via GLUT-2
- Glucose, galactose, fructose transport
What is GLUT4?
- dominant regulator of whole-body glucose homeostasis
- Few physiological parameters are more tightly regulated in humans than blood glucose
- major cellular mechanism that diminishes blood glucose when carbohydrates are ingested is insulin-stimulated glucose transport (GLUT4) into skeletal muscle
What is type 1 diabetes?
- IDDM (insulin dependent diabetes mellitus)
- “juvenile onset”
- where absorption of glucose must be assisted with insulin
What is type 2 diabetes?
- NIDDM (Non-insulin dependent diabetes mellitus)
- “adult onset”
- insulin resistance, less effective
- associated with diets high in sugars and starches, obesity.
- fiber may have a protective role
- 90% of diabetes incidence in Canada is Type II
What happens on the surface of the microvilli?
- absorption (transport of glucose, galactose, fructose across epithelial cells)
- conversion (liver converts fructose and galactose to glucose)
- regulation (insulin regulation of glucose)
What are the steps of acid hydrolysis in carbohydrate metabolism?
- The food enters stomach where it is known as chyme.
- pH of the stomach inactivates salivary amylase
- There are enzymes but not involved in carbohydrate digestion
- Major morphological changes (changes the microstructure of the food)
What does pancreatic amylase do in carbohydrate metabolism?
- produces dextrin of various lengths, short oligosaccharides (maltotriose), maltose and limit dextrins, which are branch points in amylopectin
What should be our primary carb source?
- starch (amylose, amylopectin)
- how much maltose is produced effects how much glucose can be absorbed.
What is glycemic index?
area (food) / area (glucose)
- based on the blood glucose raising potential of a food
* Foods are compared to glucose at an equivalent glycemic carbohydrate concentration
- total carb composition of a food is not a good indicator of nutritional character
- GI designed to indicate the physiological function of the carbs coming from a particular food
- sucrose (92), glucose (138!!), fructose (32)
Give a study testing glycemic index values
- .Carbohydrate portions of three unprocessed foods (boiled rice, sweet corn, and potato) and six
processed foods (instant rice, Rice Bubbles, corn
chips, Cornflakes, instant potato, and potato crisps) - In six healthy volunteers who ingested 50 g
carbohydrate portions of the above foods the
processed foods produced a higher glycemic index (p< 0.05) in all but one instance. - The exception was potato crisps which gave a similar glycemic response to boiled potato.
