Fats and Oils Flashcards
Why determine fat: omegas and nutrition
Nutrition = 37 kJ/g = most energy dense food source
Presence of Linoleic (n-6) and alpha-linolenic (n-3) (current ratio in Uk diet is 15:1 n6:n3 need to be 4:1 so need to analyse and ascertain good sources of n-3 (Wall et al, 2010) (n-3 reduce risk of cardiovascular disease - SACN, 2004)
Why legal need to understand fat composition
for example butter must contain no less than 80% milk fat - skimmed milk must not have more than 0.3% fat - to comply with regulations e.g. butter regulations 1966
Proximate analysis = total fat content - procedure to prep the sample
Procedure - first need to dry the sample - 105 degrees for 16 hours to determine the water content - then the residue is transferred to an extraction thimble and extracted with hexane (grinding the sample increases efficiency) - could protect loss of volatiles by drying under vacuum
Extraction apparatus
Either Soxhlet or Bolton - both use solvent extraction - soxhlet is intermittent and bolton is continuous - these methods are poor for bound lipid, sugary samples and polar lipids - Tecator is a semi-automated version uses chloroform as a preference as polar and more effective than hexane with is non-polar - negative is they all use flammable solvents which are unpleasant to work with - Folsh is an alternative for wet samples
Rose-Gottlieb
Method which is good for dairy, sweetened condensed milk and desserts - food is treated with conc NH3 and ethanol - the ethanol precipitates the protein which then dissolves in the ammonia - fat then extracted into ether - hexane sometimes added to prevent non-fatty substances dissolving into ether (lactose) - extraction performed by Monjonnier extraction flask (gravimetric method where phenolpthalein used as an indicator to view interface - ether poured off, sample re-extracted, pool ether - evaporate ether and weigh residue - Gravimetric method must be followed exactly to give accurate results
Gerber
Non-gravimetric - food shaken with sulphuric acid and extracted with pentanol - test preformed in a butyrometer - for milk use 10.94 ml and shake thoroughly with 10 ml sulphuric acid and 1ml pentanol - centifuge immediately and tranfer to a water bath at 65 degress - read the fat content from the scale - good for cheese and condensed milk - problem = corrosive acid - accurate to 0.05%
Infrared
Multi-spek used as a non-destructive method to determine fat - absorpbance at 1745 cm -1 relating to the C=O - useful for rapid measurement of milk and ice cream - production line?
Gas chroamtography
Used to determine FA comp - partitions compounds between a gas and a liquid phase - fatty acids seperated due to their molecular weight - double bond number - compared to FAME - fatty acid methyl ester mixture to identify peaks and calculate percentage composition - identified using retention times - measure cholesterol in animals and phytosterols in plants - could also used thin layer chromatography
HPLC
Seperation of lipids is effective but lacks of suitable detectors - UV detection requires derivatisation with p-bromophenacyl
Olive oil
Oleic acid
Hydrogentation
Saturation of double bonds using hydrogena and a nickel catalyst - can form trans-fatty acids - margarine - iodine value shows the level of unsaturation e.g. sunflower = 128 palm oil = 50
Commercial parameters of oils and fats
- melting point
- specific gravity = viscosity
- refractive index
- iodine value
- trans unsaturated fatty acid content which can be determined by infrared
Example of oil adulteration
Spanish toxic oil syndrome - fatal - 1981 - denatured rape seed oil
Fatty acid composition
can help to determine which oil - however palm oil can be adulterated with inferior palm oil - by plotting the iV against the m.pt can differentiate 3 groups of palm oil - peanut and sunflower seed oil lack C18:3 - so if there is presence of C18:3 shows adulturation - use CODEX fatty acid composition charts - only palm oil contains tocotrienols - so if present in other oils shows adulturation - you can tell if sunflower oil have been adulterated due to the ratio of alpha to delta tocopherol which is usually 200 - but if added maize oil for example this greatly decreases
Rancidity
either enzymatic - lipases or chemical - catalysed by hydrogen ions or hydroxides - measured by taste panals (soapy tastes/off odours) or determiantion of free fatty acids by titration = total acids or chromatography for indiviudal fatty acids - different taste propeties - oxidation occurs by the autoxidation chain reaction involving free radicals catalysed by pro-oxidants eg. iron and copper (initiation, propagation and termination) - measure rancidity by the peroxide value - the amount of iodine produced
