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