Lecture 7: lipids Flashcards
what is the role of lipids in food?
- physical characterstics: flavour, texture, taste, appearance
- have a role as well in bad tastes and making harmful products as they are prone to lipid oxidation
What is the importance of anyalzing total fat in foods?
- legally (complay with standards for labeling and identity)
- quality (some properties depend on lipid content)
- health (low fat food development)
- oxidation (unsaturted fats particullary)
- adulteration (compare with an expected profile of an unlatered sample)
- processing (conditions for proccessing depend on total lipid content)
what are the three categories of classification for lipid analysis
- solvent extraction
- solvent free extraction
- instrumental methods
what principle is solvent extraction based on?
lipids are not soluble in water but soluble in organic solvents
Samples must be prepared when using solvent what are the 4 consdierations and briefly summarize them
- drying of sample: to allow more easy penetration of solvent
- reduce particle size: increase SA exposed and create a more homogenous sample by grinding at a low temperature which also reduces oxidation tendancys of lipids
- acid/base hydrolysis: some lipids are in complexes with non-lipids so need to break bonds
- selection of solvents: polar lipids and polar solvents work better and non polar with non polar work better
for solvent extraction there are three categories, what are they and what is the main method associaed with them?
- discontinous extraction: mojannier method
- semi-continous method: soxhlet method
- continous extraction: goldfisch method
describe the discontious extraction: mojannier method
- refernce method for fat in dairy products
- no need for drying
- dairy product measure→put in bottle of mejonnier→dissolved in aquous phase (ammonium hydroxide and ethyl alchol)→fat extracted using organic solvent (ethyl ether + petroleum ether)→ solvents evaported→ weigh sample
what is the role of the folowing reagents and solvents in the mojannier method: ammonium hydroxide, ethyl alcohol, ethyl ether, petroleum ether
- destabilizes lipid miccile, neatrulizes acidty, reduces viscoity to prevent gel forming and helps action of solvent
- helps extraction since its miscible with ether and breaks bonds with protiens
- dissolves fat and keeps it in the solution
- mix of hydrocarbons that remove water that has any amount of non-greasy solids and ethyl ether
describe the semi-continous extraction soxhelt method
- used for determinng fat in dehyradted solid foods
- gravimetric method as sample is weighed at beginning and end
1. Weighing and Setup:- Weigh the food sample and put it in a special cartridge.
- Solvent Process:
- Use a solvent (like ether or hexane) to dissolve the fat in the sample.
- The solvent circulates into the sample for a short time and then returns.
- Extraction:
- The solvent, now boiling, falls as droplets into the sample, dissolving the fat.
- The fat-laden solvent is siphoned back into a flask.
- Evaporation:
- Evaporate the solvent, leaving the fat behind in the flask.
- Measurement:
- Measure the weight of the remaining fat to determine the lipid conten
- Weigh the food sample and put it in a special cartridge.
Describe the continous extraction goldfisch method
- gravimetric
- product weighed→ placed in cellulose catrride/porous capsule in goldfisch extractor → sample extracted with boiling ethyl ether/petroluem ether→ fat dissolved→ evaporation of solvent→ weigh
describe solvent free extraction and name the two main methods
- babocks method
- gerber method
- wet extraction procedures relying on other molecules
- no removal of water needed
- lipids quantified volumetrically
describe the babcocks method
- offical method for dairy products
- fast and inexpensive
- not very accurate higher than mojonnier
- dairy product weighed→ dissolved in sulphuric acid to digest protien, make heat and realease lipids→ water is added and centrifuged to have fat into graduated part to measure
describe gerber method
similar to babcocks but uses different bottle and adds isomyl alcohol to prevent carbonization of sugars by heat and acid
what are the three categories of intstrumental methods
- measurments of global physical properties
- measurment of radtion absorbtion
- measurment of radation scattering
What are the three proprties when measruing the physical properties of mass
- density: density of liquid oil is lower than most foods, so increase fat content decrease density
- electrical conducctivity: lipids conductivity us lower than aqueous substances so increase fat decrease conductivity
- ultrasonic speed: speed depends on [] of fat in food
