8. Flavor/Quality evaluation of fats/oils
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How to do flavor quality evaluation? (4 ways)
• sensory evaluation • peroxide value • thiobarbituric acid test • gas chromatographic analysis of volatile compounds
2 things needed for sensory eval?
• trained people • controlled temp and environment
Peroxide value: - addition of ____A______ and _______B______ in an organic solvent to oil 1) A + B –> salt + _C__ 2) ROOH + 2 C –> ____ + _____ + __D___ 3) D (what color) + ____________ –> ____ + 2 _____ (color?)
A: potassium iodine B: acetic acid C: hydroiodic acid ROOH + 2 HI –> ROH + I2 + H2O I2 (purple) + sodium thiosulfate –> Na2S4O6 + 2 NaI (no color)
what color is the we react TBA and malondialdehyde?
red!
what is gas chromatographic analysis of volatile compounds?
gas syringe sucks gas from oil –> gas is put through gas chromatography –> generates figure with peaks!
increase hours of light exposure = increase/decrease size of 2,4 decadienals in GC?
increase!
Does soybean or corn oil have faster degradation?
soybean bc more omega 3!
Flavor stability measurement: what is active oxygen method? - more O2 sample takes = more _________ it makes –> measure weight!
O2 passing at controlled rate at 98°C into sample at 2.33 mL/sec until it becomes rancid - more hydroperoxide it makes
what is deep fat frying?
process of immersing food in hot oil
Deep fat frying: - combination of cooking and dehydrating of food produces unique fried foods by simultaneous ______ and _______ transfer - flavor compounds are formed and retained in a ____________ on the food
• heat and mass • crips crust
4 physical changes of oil during deep-fat frying
• thickening of oil (increase in viscosity) • decrease of interfacial tension • increase in density • increase of specific heat
4 chemical changes during deep fat frying
• formation of flavor • flavor stability and quality changes • changes in color and texture of fried foods • nutritional changes
4 chemical reactions in frying oil
• hydrolysis of TG • oxidation • polymerization (FR from oxidation) • pyrolysis
2 noteworthy compounds formed in deep fat frying conditions
• hexyl benzene • 2,4 decadienal
high temp in deep fat frying can also cause _____________
isomerization!
sticky stuff on your pan after frying = _____________ - btw what?
• dimerization • 2 acyl groups of same TG or of 2 dif TG