Lipids are a diverse group of organic molecules and are present as fats and oils in foods. Fatty acids, such as omega-3s and omega-6s, are made of long chain fatty acids containing an ester group. Whether the fat is saturated or unsaturated depends on the structure. For example, triglycerides, predominately solid or semisolid at room temperature, are most likely animal-based fats, whereas liquid triglycerides are plant-based, such as olive oil. Testing for lipids in foods is a rather simple process that requires a few simple items.
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Cut a piece of the solid food to expose the inside. If the food sample is liquid, apply a small amount to the cotton swab.
Rub the solid food piece or the liquid on the cotton swab on the paper bag.
Allow the sample to dry for at least three to four minutes.
Place the paper bag against a light source, such as a lamp. If the bag shows a grease spot causing a translucent appearance of the paper bag, lipids are present.
Pipette or suction out using a dropper 2 mL of water and 2 mL of a liquid food sample and put it in a beaker or test tube. If you’re testing a solid food source, you will need to either puree it in a food processor or grate the sample. If you are using a food processor, you can combine the water and the food together. Measure out 4 mL of the puree to the beaker or test tube.
Use a new dropper to obtain a small amount of Sudan red indicator.
Release three drops of the indicator into the test tube or beaker.
Swirl the contents around and allow it to settle. If lipids are present, they will be dyed red.