lecture 6 Flashcards
why do we analyze food lipids
- to categorize them and differinate them which can help understand the relationship between structure and functionality
- establish proper processing conditions
- understand health implications
- compare with standards
- to establish regulatory steps in processing, storage, transport and nutrition labelling
- legal aspects
- quality
- adulteration
- food processing)
so in summary for legal, economic, health, qualuty and processing/technlogical aspects
define batch solvent extraction
its when sample is mixed with solvent in a container and then seperation is done by gravity, centrifugation or shaking. The lipid concentration in the solvent is then determined by solvent evaporation and then by measuring the remaining mass. But for batch its done in one batch and done
define the method of semi-continous extraction
Soxhlet is the most common method. Basically dry ground sample is placed into the thimble and the flask will be heated to evaporate the solvent, the sample and solvent interact and the solvent extracts the lipids and carrys them to the flask, and because lipids are low in volatility they will stay in the flask. After a few hours the flask is removed and the solvent is evaporated
define the most common method of continous extraction
The goldfish method, which is kinda like dripping coffee. Its similar to soxhelt but instead of building up solvent around the sample the way its designed allows the solvent to trickle through the sample
whats the disadvanatage with the goldfish method
it can result in channeling of solvent with can decrease effeciency
whats accelerated solvent extraction
Its basically solvent extraction but with a higher temperature and pressure (to keep solvent in liquid state), this increases the efficiency and also reduces cost and time as u dont need as much solvent
Describe the babcock method and the modified babcock
It digests protien and liberates fat by destabilzation using sulphiric acid which is a strong acid. The fat content is then measured volumetically. The modified one is similar but uses acetic perchloric acid mixture instead and its used for things like essential oil in flavor extracts
describe the mechanism of the gerber method
Similar to babcock, it also uses sulfuric acid but also uses pentanol in combination. This addition of pentanol prevents sugar from charring and therefore is used for dairy based food products
describe the detergent method and why its used
Its used to avoid using highly corrosive acids. Itg uses detergent to create a detergent protien complex which displaces the fat gobule and seperates it from protien
what is the physical method
its where compression force is applied to extract lipids. Its especially used for getting lipids from dry matter
Describe how and why enzymes are used and some common ones
they are used as an enviromentally friendly technique. They are used to engance oil recovry through breaking cell walls and oil bodies. Some comercial ones include Alcalse, Neutrase, and Flavourzyme
how do we remove contaminats from lipid extracts like pigments, amino acids, sugars etc
Using a washing technique of cholorform-methanol and then wash with water or dilute KCL
define instrumental methods
These methods measure different properties but overall are non destructive, require little or no sample preperation and are precise, simple and rapid
what are the bulk physical properties measured of lipids and describe them
- density: as fat content increases→ density decreases
- electrical conductivity: conductivity decreases as fat increases
- ultrasanoic velocity: the concentration of fat influences the speed of an ultrasonic wave so by using this measaure u can determine fat content
describe the methods of adsorption of radiation
UV-visible+ Infrared: both are measurements of the lipid absorbance just in different light ranges . Uv visible requires extraction and diluation prior so is more time consuming and labor intensive.
NMR: by measuring the area under a peak in an NMR u can determine lipid structure. No need for sample prep and very fast
XRay: used to measure fat content in meat. Lean meat absorbs more x rays compared to fat. Absorbance will decrease as lipid concentration increases
describe light scattering
It measures turbidity. The turbidity of an emulsion is directly proprotional to the concentration of oil droplets present so it can be used to determine the oil content in emulsions
describe ultrasonic scattering
this uses the fact that ultrasonic velocity and absorption of ultrasound by an emulsion are related to concentration of oil droplets to determine content of oil
describe chromatogrophy in general
it is a powerful tecnique especially when used in combo with another technique. It seperates based on strength of their interaction with the matrix and provides a complete profile of molecules in a lipid
what can u detect or calculate with chromotagraphy?
- the amounts of saturated, unsaturatedm poly fat and cholesterol
- degree of lipid oxidation
- extent of heat or radiation damage
- detect adulteration
- determine the presence of antioxidant
define differential scanning calorimetry
is a calorimetric method which measures the thermal behaviour of sample and can determine things like phase transitions, melting points and gives info about molecular organization of lipids on polymorphisim and packing behaviour
define and desribe what refractive index indicates
Its a measure of how much light bends when it passes through a substance. Its a ratio of the speed of light in a vaccum to the spead of light in a oil. RI increases with more double bonds. Lower RI therefore means more saturated fats.
how is solid in a fat determined, whats the instrument used
Its determined via Solid fat index which is measured with a dilatomerty which measures the change of volume with regards to temperature. There is a bulb connected to a capillary tube where colored water or mercury will idnicate the expansion of fat upon heating. As the fat melts the volume will increase
differeniate what is determiend between TLC and GC
TLC: determines lipid fraction, it seperates diffeernt lipid classes
GC: indentifies individual fatty acids and specifically FAMEs (fatty acid methyl esters)
Compare and contrast the following methods (sohlext, batch solvent/non solvent, instrumental)
- soxhelt is most common for dried foods
- it is time consuming and destructive
- batch and nonslevent are beter for high moisture foods
- intrumental technqiues are good because they are fast and nondestructive only issue is theyh are expensivve and need calibration curve they are used more quality assurance
