Grease Spot Test: One Of The Tests For Lipid Identification

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Grease spot test is one of the tests for lipid identification. The working principle is that most lipid or grease are non-volatile due to their high boiling point. In room temperature, the water spot will disappear because water can absorb enough heat from the surrounding air and evaporated. But, the lipid spot can never absorb enough heat to evaporate and hence the lipid will stuck inside the paper sheet. Thus, lipid diffracts the light ray so that light can pass from one side of the paper to another side. This gives the phenomenon of "translucent". In practical 8.1, water gives a negative test whereas both corn oil and olive oil give a positive test which is indicated by the formation of translucent patches on the paper. For food sample, full cream milk and ground nut show a positive result with the presence of lipid while rice gives a negative result with the absence of lipid. Lipids are predominantly composed of …show more content…

Acrolein is the simplest unsaturated aldehyde that produced widely but is most often immediately reacted with other products due to its instability and toxicity. When a fat is heated strongly in the presence of a dehydrating agent such as potassium bisulfate (KHSO), the glycerol portion of the molecule is dehydrated to form the unsaturated aldehyde, acrolein which has the odour peculiar to burnt cooking grease. Further heating results in polymerization of acrolein, which is indicated by the slight blackening of the reaction mixture. In practical 8.4, corn oil, olive oil, full cream milk and ground nut show positive test with both the rancid burnt grease smell and the black colour sample formed that indicate the presence of glycerol or fat. Only rice shows negative test with un-rancid caramel-like smell and the formation of little black solid. Student are strictly have to be extra careful when heating the sample such as using the test tube holder to hold the test tube and not by bare

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