Rancidity- week 5

the process of deterioration of fats and oils by hydrolysis or oxidation to produce unpleasant tastes & odours

its the deuteriation of fats & oils in food: - Endogenous enzymes - Enzymes produced by invading microbes - chemical transformation

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.

-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

• initiation • Propagation • Termination

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)

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

• 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.

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

– Antioxidants – Metal chelators(chelating agents): metal ions (copper & iron) promote lipid peroxide decomposition

a compound that retards or delays rancidity or other flavour deuteriation due to oxidation

By titration, ROOH are mild oxidising agents and oxidise KI to iodine which can then be measured

TBARS method *The TBARS assay detects the level of MDA (malondialdehyde), the major lipid oxidation product, and also some minor related compounds.

Antioxidants – ideally lipid soluble ones

Vitamin E, BHA, BHT, ascorbyl palmitate

Citrate or citric acid (or similar)

It scavenges oxygen

-ENERGY: beta oxidation, ketone production -STRUCTURAL: cell membrane -SIGNALING MOLECULES/HORMONES: steroids, eicansanoids

-SATURATES: animal products(meat,cheese,butter), coconut. -MONOSATURATES: spreading fats, vegetable oils, nuts, olives. -POLYUNSATURATES: plant oils, cereals, spreading fats, fish -TRANS UNSATURATED FATS: meat & dairy products, processed foods, spreading fats

no absolute requirement for fats(except for essential fatty acids) -Total fat intake: UK DRV <33% of total energy -Saturates: UK is exceeding the DRV of <10%, but UKs intake is 13-14% -Trans fats: UK is below the DRV of <2% of total food energy