U4AOS2: food chemistry Flashcards
aerobic respiration
requires oxygen and is the main source of energy for the human body
anaerobic respiration
does not require oxygen and yields less energy
calorimetry
the experimental methods of measuring the heat energy released or absorbed by a chemical reaction or physical process, such as by combustion of a fuel or a food
q=
mcAT
simple calorimetry
-measures the change in temperature of water in the calorimeter pot and this is used to determine the energy provided by the food being combusted
-limitation: heat loss
bomb calorimetry
-used to measure the heat of combustion of chemical reactions that involve gaseous reactants or products
-occurs in a reaction chamber made to withstand high pressures and high temp, maintaining constant volume
-contents can be electrically ignited to start comb, must have sufficient oxygen
solution calorimetry
-an insulated container holds a known volume of water in which a reaction in solution occurs like the dissolution of a solid
-limitation: cup may absorb some heat from water/cannot measure energy content of food as comb cannot occur in an aq sol
calibration factor
VIt/delta T = E/T
random errors with calorimeters
-poorly insulated calorimeters
-not all of the food/substance was combusted
-the temp recorded when the food was combusted was inaccurate
-impact of errors can be overcome by repeating multiple times
systematic errors
-problematic because will lead to results being consistently inaccurate
-calorimeter was calibrated incorrectly
-measurements used to calibrate the calorimeter were measured incorrectly
biomolecules
molecules present in living organisms including macronutrients such as carbs, proteins and triglycerides - created and synthesised by them
carbohydrates
-composed of carbon, hydrogen and oxygen with general formula Cx(H2O)y
-provide a source of energy, way of storing energy and structural material in plants
general structure of carbs
simplest = monosaccharides
can be joined by condensation polymerisation reaction between OH groups - with ether/glycosidic bond (only in carbs_
photosynthesis
go -> cow
endothermic reaction and absorbs energy
disaccharide formations
glucose + glucose -> maltose + water
glucose + fructose -> sucrose + water
glucose + galactose -> lactose + water
molar mass of carbs
mr (glucose) x how many molecules so 180n
subtract (n-1) water molecules, mr=18
starch - amylose and amylopectin
-made from alpha glucose molecules
-energy storage component of plants
-amylose = unbranched, linear polymer of starch that packs well together bc results in stronger hydrogen bonds and harder to break
-amylopectin = branched and occasional crosslinks, so less effective packing and weaker H bonds
glycogen
-made from alpha glucose molecules
-energy storage structure in humans and animals
-even more highly branched, less linear than amylopectin
-convert glucose into glycogen and store it in liver and muscle cells
cellulose
-made from beta glucose molecules
-structural material found in plants
-forms a tightly packed structure that leads to its strength as a plant fibre
-large, consistent linear structure and each glycosidic bond is inverted
artificial sweeteners
-artificial sweetener are similar sized molecules to many common sugars but are significantly sweeter than sugars
-allows people to require lower energy/calorie diets to obtain same amount of sweetness with much lower energy intake
aspartame
-made from condensation reaction between aspartic acid, phenylalanine, and methanol
-brings more 100-150 times more sweetness than sucrose
why can humans not digest cellulose?
-cellulose considered the dietary fibre as it helps food pass through the body in bulk amounts and reduces likelihood of constipation, cancers
-we lack the necessary enzyme cellulase, so cannot break it down for nutritional value
lactose intolerance
when people lack the sufficient amount of the enzyme lactase to hydrolyse the sugar.
various effects/symptoms = cramping/discomfort/bloating/diarrhoea
GI
-glycaemic index
-measure of how quickly glucose is released into the bloodstream after consuming food
-it is a comparison of how quickly glucose from carbs is released, compared to pure glucose via hydrolysis
low gi foods
-beans, fruits, lentils, milk, porridge
-slow hydrolysis, prolonged digestion
-slow rise in blood sugar
high gi foods
-potatoes, white bread, lollies
-fast hydrolysis, rapid digestion
-rapid rise in blood sugar
amylose vs amylopectin
linear vs branched
tight vs loose packing
low GI vs high GI
triglycerides
-they are esters
-contain CHO
-formed from a condensation reaction btw glycerol and three fatty acids
how to break up triglycerides
-reaction can be reversed by hydrolysis
-requires 3x water molecules and a catalystof lipase
general formulas for fatty acids
saturated: CnH2n+1COOH
monounsaturated: CnH2n-1COOH
diunsaturated: CnH2n-3COOH
define essential biomolecules
ones that cannot be synthesised by the human body, and must be consumed in diet
define non essential
molecules that can be synthesised by the human body, so don’t have to be consumed
omega-3 vs omega-6
the number after omega depends on the position of the first carbon-carbon double bond from the methyl end of the fatty acid (non carboxylic acid)
define rancidity
a notable deterioration/breakdown of fats and oils, resulting in deteriorated smell or taste
define oxidative rancidity
-the higher the degree of unsaturation of a triglyceride, the more susceptible it is to oxidation
-refers to fats and oils breaking down in presence of oxygen
-leads to formation of unpleasant smelling and potentially harmful short-chain aldehydes and ketones
auto oxidation
-formation of free radicals
-the fatty acid radical reacts with oxygen, forming another radical which also reacts with another fatty acid
-the reaction ends when two radicals combine
vitamins
are substances that are essential to our diet but in lower proportions - they are diverse molecules that are necessary to prevent various diseases like scurvy and rickets
water-soluble vitamins
water-soluble vitamins: contain higher proportion of hydroxyl groups, stored in aqueous environment of blood and not retained.
diet needs to regularly include intake of water soluble vitamins
fat-soluble vitamins
have long hydrocarbon chains but are low on hydroxyl groups, so cannot dissolve in water.
so, stored in fats (adipose cells) as fats contain many dispersion forces
how to prevent/slow rancidity
-vacuum packaging or using nitrogen
-filling containers up to the lid
-storing food in the dark and cold
-restricting access to copper, iron and nickel
-using dark containers or opaque containers for photooxidation