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How Professional Food Scientists Test Lipids, Fats and Oil

how to test for lipids in food

Often, the first evidence of a spoiled product is rancidity. It occurs when lipids are exposed to air, light, or moisture or certain bacterial actions. A lipid is a macromolecule that is soluble in nonpolar solvents. As lipids pertain to food products, they are most commonly identified as fats and oils. However, waxes, certain vitamins and other items can also be included.

The primary issue affected by rancidity is shelf life. Not only are there different types of rancidity (oxidative, hydrolytic, etc.), but there are also several different analytical rancidity markers (Hexanal, PV, Anisidine, enzyme assays, etc.).

Food items must be able to maintain their product integrity to meet customer expectations for safety and satisfaction. Therefore, when a lipid becomes rancid, it can create undesirable taste and odor characteristics, negatively impacting the customer experience with the food product. However, color and texture often remain unaffected. To ensure your food product’s quality and shelf life expectation/promise, it must be tested for rancidity.

A rancidity test identifies the level of lipid oxidation in a provided sample. If the lipids in a food product go rancid, it can diminish the product’s value and usability. This is why testing of lipids is part of establishing a product’s shelf life. Of course, the usefulness of the test findings can extend into other areas as well, but establishing shelf life is among the major drivers.

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Using the Correct Test for Lipids, Fats and Oil Stability

Testing for lipids, fats and oils in food is not as straightforward as we—or you—may wish. Ideally, there would be a single, general rancidity assay that Medallion Labs could use in all cases. That, however, is simply not feasible.

Differences in the characteristics of fats, product type, fat levels, ingredients/product composition and even packaging can impact testing results. Therefore, these must all be factored into selecting the right test and when evaluating the findings.

In order to deliver our customers with accurate results regarding rancidity, Medallion Labs offers a number of testing options. Of course, the final choice is up to the customer. Ultimately, as it is with all Medallion Lab testing, our goal is to deliver accurate, actionable and reportable results.

For testing fats, lipids and oils, Medallion Labs provides ten testing options. However, there are four assays that tend to be among the most relevant to our customers. They include:

Peroxide Value Test

The Peroxide Value Test is the most widely used option for measuring the state of oxidation in fats and oils. Any detection of peroxide suggests rancidity in unsaturated fats and oils. This test also measures to what extent an oil sample has undergone primary oxidation, but not it’s stability.

The test works by having a fat or oil sample dissolved. Then an excess amount of potassium iodide is added. Peroxides present oxidize a portion of the iodide forming iodine. The iodine is titrated with sodium thiosulfate and the peroxide value is calculated.

The hydrogen ion concentration of the sample is determined by measuring the electrical potential produced by an electrode that responds to hydronium ions. The electrical potential is converted to hydrogen ion concentration expressed as the negative logarithm of its concentration (pH). If dissolution or dispersion of the sample is necessary (a 10% solution), carbon dioxide-free water is used.

Medallion Labs reports findings as meq/kg of fat—milliequivalents of peroxide—oxygen per/kg.

The Peroxide Value Test requires 7–9 business days to complete and a 100g sample is required to ensure results are representative of the sample submitted. At least 0.50 grams of fat extracted from food products is needed to run this analysis. Rush testing is available if needed.


Our peroxide value testing can help you measure the state of oxidation in fats and oils.

Free Fatty Acids Test

When food items are deep-fried, the oil will degenerate as it is exposed to high temperature, oxygen and moisture. This combination leads to chemical changes including the formation of hydrolysis products such as free fatty acids. These free fatty acids are often associated with undesirable effects, including undesirable coloration, off-flavors and a lower smoke point.

 The Medallion Labs Free Fatty Acids Test extracts a sample of fat into an organic solvent and titrated with sodium hydroxide. Rancidity is calculated as percent oleic acid for most fats and oils. Coconut and palm kernel oils are calculated as percent lauric acid and palm oil is calculated as percent palmitic acid.

Medallion Labs reports findings as a percent of FFA as oleic acid. May also be reported as a percent of lauric acid and percent of palmitic acid upon request.

The Free Fatty Acids Test requires 7–9 business days to complete and a 100g sample. Of which, at least 0.50 grams of fat extracted from food products to run the analysis. Rush testing is available if needed.


Our free fatty acid testing can help you measure the degeneration of deep-fried foods.

Anisidine Value (in Oils) Test

The Anisidine Value (in Oils) Test is used to measure the aldehyde levels in vegetable and animal oils, especially those that are unsaturated. This test assesses the secondary oxidation of the oils and can therefore tell the oxidation history.

Oil samples are diluted in isooctane and reacted with an anisidine reagent (anisidine in glacial acetic acid). Colored complexes are formed and measured at 350nm on a spectrophotometer.

The Anisidine Value (in Oils) Test requires 7–9 business days to complete and a 5g sample (highly pigmented oils are not accepted).


Our anisidine value testing can help you understand the oxidation history of vegetable and animal oils that are unsaturated.

Hexanal Test

Hexanal is created when omega-6 fatty acids (the most common fatty acid in food) are oxidized. It is an aromatic compound, sometimes described as being similar to fresh-cut grass. Medallion Labs uses the Hexanal Test to measure the oxidation level of omega-6 fatty acid-rich food products. The existence of hexanal can impact both the aroma and flavor of food.

For the Hexanal Test, a homogeneous portion of the sample is mixed with water containing an internal standard. It is heated in a heating block for a specified amount of time, after which a sample of the headspace over the mixture is taken and injected into the gas chromatograph. The hexanal released into the headspace is quantitated via comparison of the hexanal gas’s chromatographic response to that of the internal standard.

Medallion Labs reports findings as ppm (parts per million). The lower detection level is 0.3 ppm (parts per million); with an upper limit of 50 ppm.

The Hexanal Test requires 7–9 business days to complete and a 20g sample. Rush testing is available if needed.


Our hexanal testing measures the oxidation of omega-6 fatty acid rich food products.

Accurate Rancidity Lab Testing for Food Items

Testing foods for lipids, fats and oils is an essential part of shelf-life testing. In fact, for some foods, it’s the biggest indicator of establishing an accurate and reliable expiration date.

Working with Medallion Labs, you can arrive at the proper results by using the proper testing methods for fats and oils. Our broad assortment of testing options, be it Peroxide Value, Free Fatty Acids, Anisidine Value, Hexanal or another option, means you can select the right test to determine your results. This helps you to avoid wasting time, money or samples. All of which are food companies have and continue to turn to Medallion Labs for trusted, accurate and standardized testing results.

Medallion Labs is ready to use our testing options, expertise and skills for your lipid, fats and oil testing. Connect with us or call 1-800-245-5615 to discuss the criteria and testing needs for your food products.

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