Rancidity- week 5 Flashcards
define rancidity
the process of deterioration of fats and oils by hydrolysis or oxidation to produce unpleasant tastes & odours
what are the causes of rancidity
its the deuteriation of fats & oils in food:
- Endogenous enzymes
- Enzymes produced by invading microbes
- chemical transformation
Distinguish between different types of rancidity
1)hydrolytic rancidity- caused by exposure of heat & water presence
2) Ketonic rancidity-Hydrolysis of TAG followed by incomplete beta oxidation of FA- characteristics of xerophilic moulds(dry conditions)
3)Chemical mechanisms(chemical hydrolysis) -Occurs when oils are heated-Water MUST be present.
how rancidity can be controlled
-To reduce activity of endogenous enzymes: reduce temp or heat treat food
-To Minimise microbial growth: reduce temp or heat treat food
-To control oxidation: omit air &add antioxidants(e.g. vitamin E), & adding citrate
what are the different aspects of auto-oxidation
- initiation
- Propagation
- Termination
what is the role of photosensitizers and O2 in Auto-oxidation
They activate triplet ground state
oxygen to activated singlet oxygen
(photo-/sensitizers produce the first few radicals which increases activity of oxygen to a different state so that’s its more active & causes oxidation)
what are the differences in reactivity between different fatty acids
saturated fatty acids have no double bond and therefore there is no where to attack so rates basically zero, the increase in double bonds influence that initiation or susceptibility to initiation
how is rancidity measured
- Sensory methods-typical smells: *Acetaldehyde- green apple smell( caused by bacteria spoilage & oxidation)
*Phenolic-TCP, caused by bacteria spoilage - Chemical methods:
Hyperoxides(formed in by RH + 1/2O2–> ROOH(lipid peroxide))
*Determined by titration using potassium iodide.
how do we predict the susceptibility of a
food to rancidity, explain the 3 methods
Iodine value: measures the degree of saturation- iodine monochloride binds to the double bonds, able to measure how much of this compound will bind to 100grams- will have to measure by titration to see how many FA are free
RI: passing light through the oil & how much of that oil is refracted or changed or bent gives an indication oh how much UFA there are
abuse tests: heat oil (130), bubble through oxygen, measure peroxides overtime, the more UFA& PUFA the more oxidation
how can rancidity be prevented or
delayed
– Antioxidants
– Metal chelators(chelating agents): metal ions (copper & iron) promote lipid peroxide decomposition
what is an antioxidant
a compound that retards or delays rancidity or other flavour deuteriation due to oxidation
How can lipid peroxides be measured?
By titration, ROOH are mild oxidising agents and oxidise KI to iodine which can then be measured
Name a method used to determine secondary products of oxidation.
TBARS method
*The TBARS assay detects the level of MDA (malondialdehyde), the major lipid oxidation product, and also some minor related compounds.
What types of compounds inhibit lipid oxidation?
Antioxidants – ideally lipid soluble ones
Name a lipid soluble antioxidant used in foods.
Vitamin E, BHA, BHT, ascorbyl palmitate
