lecture 4-lipids Flashcards
what are the 3 diffferent types of analytic techniques to determine total fat content and briefly describe
- solvent: relies on the fact that lipids are soluble in non-polar solvents
- non-solvent extraction: use other chemicals to seperate lipids from the rest of the food
- instrumental methods: determine lipid content using a instrument which measures different physiochemical principles like density, absorbtion or light scattering
why is acid hydrolysis sometimes needed in preparing food samples for solvent extraction?
Because some foods contain lipids that are complexed with protiens are polysaccharides so its important to break these bonds so the lipids are free for solvent extraction
what are the types of extraction by solvent?
- batch
- semi continous : soxhelt
- continous
- accelerated
what are the two ways to conduct batch extraction
- separatory funnel: shake hard and then you get two phases
- mojonnier method: uses a mokonnier tube
describe continous solvent extraction (goldfish)
The solvent will flow around the sample instead of pooling around it which will reduce extraction time as the solvent is continiously passing through the sample, carrying lipids more quickly. The only problem here is that the solvent might take preferential pathways which means some parts of the sample may not be exposed to the solvent properly.
why is soxhelt method more thorough
Because the sample is always surrounded by solvent due to the contious cycle of solvent evaporation and condensation.
describe accelerated solvent extraction and why it is beneficial
This type is done by increasing the temperature and pressure. This will reduce the amount of solvent needed to preform the analysis since the effeciancy of solvent increases when heated. This will therefore decrease the cost and is better for the enviroment.
define the acid value and what it means
It is the amount of mg of KOH needed to neutralized fatty acids present in 1 g of lipid. So it measures the breakdown of triglycerides into free fatty acids so therefore it is a relative measurement of rancidaty.
which method is used to determine the acid value
Direct titration with potassium hydroxide until a pink color remains. This is because Phenolphthalein is colorless in acidic solutions (before titration when free fatty acids are present). As NaOH or KOH neutralizes the acids, the solution gradually turns pink.
describe the steps to calculate FFA value
- calculate number of moles of FFA ( moles= V titrant (L) x N titrant (mol/L)
- calculate the mass of FFA in the sample ( mass= moles x molecular weight of oleic)
- calculate FFA per gram of sample and then multiply by 100% to get percent
- calculate mass of KOH needed to neutralize ( mass= moles x Mw of KOH)
whats the shortcut equation for FFA
% FFA= V x N x MW / W x 100
what are the molecular weights of oleic acid and KOH
oleic acid= 282 g/mol
KOH= 56.1
define saponifcation and what it indicates
it is the mg of KOH required to saponify one gram of lipid. Saponifcation is known as the process of breakdown a lipid into glycerol and fatty acids by treating with alkali. So here you are measuring the amount of ester linkages. And it is a measure of the average molecular weight of the triglycerides
High SV → The oil contains short-chain fatty acids, with a low molecular weight (easier to saponify).
Low SV → The oil contains long-chain fatty …
describe the method used for measuring saponifcation value
Uses Back titration with potassium hydroxide. An excess amount of KOH is added and heated under refluz to ensure hydrolization of triglycerides into glycerol and fatty acid salts. The remaining KOH that did not react is what is measured using HCl as it will react with KOH. The endpoint is reached when phenolphthalein changes color from pink to colorless meaning all the KOH is neutrilzed.
is higher or lower SV value better for soap making and give example
High SV is better, like cocunut or palm oil
what is the saponifcation equation
SaponificationValue= (B-S) x N x 56.1 / W
B= blank (ml)
S= sample titrantion volume (ml)
N= normality of KOH
56.1= MW of KOH
W= sample mass (g)
- Define iodine value and what it indicates
It is the mass of iodine in grams that is consumed by 100 grams of a lipid. It is used often to determine the degree of unsaturation of lipids. In fatty acids the double bonds are very reactive to iodine which is a halogen. So a higher iodine value means the greater the amount of unsaturation in the lipids.
describe the method of determining iodine value in the lab
1️⃣ A known excess of Wijs reagent (ICl) or Hanus reagent (IBr) reacts with the double bonds in unsaturated fats.
2️⃣Unreacted iodine reagent is treated with potassium iodide (KI) to release free iodine
3️⃣ The released iodine is titrated with sodium thiosulfate (Na₂S₂O₃) using starch as an indicator, with the endpoint marked by the disappearance of the blue color
4️⃣ The iodine value is calculated as the grams of iodine absorbed per 100g of fat/oil
what is the iodine value equation
iodine value =( (B-S) x N x 126.9/ W) x 100
B= blank (ml)
S= sample (ml)
N= normality of Na2S2O3 (mol/1000 ml)
126.9= Mw of iodine
W= sample mass
define the peroxide index
the amount of peroxide per kg of lipid or oil as determined in a titration procedure to measure the amount of peroxide or hydroperxoide groups
what is PV used for measuring and what is the highest amount
It is used to measure the oxidative detoration of oils since peroxides are a primary reaction products formed in the early stages of oxidation so they give an indication of the progress of lipid oxidation. In general they should not be higher than 10-20 meq/kg
how is peroxide index measured in the lab
1️⃣ The fat/oil sample is dissolved in a solvent mixture
2️⃣Potassium iodide (KI) is added, and peroxides oxidize KI, releasing iodine
3️⃣ The released iodine is titrated with sodium thiosulfate (Na₂S₂O₃) using starch as an indicator where the endpoint is the disappearance of the blue color
*this is a back titration
what is the peroxide value equation
Peroxide value= ((S-B) x N/ W )x 1000
- S = Volume of titrant (mL) used for the sample
- B = Volume of titrant (mL) used for the blank
- N= Normality of the titrant (mol/L)
- W = Sample weight (g)
- 1000 = Conversion factor to express the result in milliequivalents of peroxide per kilogram of fat (meq/kg fat)
whats the main titration equation
VxN = W/MW
