Fish Oil Freezer Test

fish oil

The Myths and The Facts

The DIY freezer test, claimed to accurately determine fish oil quality, has become a longstanding consumer belief. Simply put, the claim states: if, upon freezing, your fish oil becomes cloudy or opaque (a color similar to that of butter), you’ve purchased a poor quality fish oil supplement. It’s marketed as a simple solution to a complex issue- a clever, although inaccurate, tactic. The test does offer some merit: it gives you a rough estimate of the saturated/unsaturated fat balance in your supplement, which is yet a rougher estimate of omega-3 content. Omega-3 content, however, is only one of many indications of fish oil quality. The test cuts its analysis short of other important quality metrics, such as your supplements freshness/rancidity, EPA:DHA ratio, possible contamination, and presence of other important nutrients, like Vitamin D or CLA.

Fatty Acids: an Introduction

Fatty acid molecules can be seen as, simply stated, a structure with a head and a tail. The head element is composed of a chemical group called a carboxylic acid, which remains unchanged in all fatty acids. The tail end of the molecule is typically just a chain of hydrogen and carbon atoms glued together by chemical bonds. It is this component of the fatty acid molecule- the length of the hydrocarbon “tails” and the type of bonds that glue the carbon atoms together- that varies among different fatty acids and gives each their unique characteristics.

Saturated fats are built from fatty acid molecules whose “tails” are composed of carbon atoms connected to each other by single bonds (in chemistry, these carbon atoms are said to be saturated with hydrogen atoms). This composition gives the molecule a straight, almost stick-like build. On the other hand, unsaturated fats are built from fatty acid molecules whose “tails” contain one or more pair of carbon atoms glued to each other by double-bonds, which drastically changes the structure of the molecule, giving the tail a “kink”. Picture a drinking straw with its head bent to the side; the bend represents the double bond.

The Effects of Temperature on Structure: Fatty Acid edition

A materials state (i.e. solid, liquid, etc.) is governed solely by the strength of interaction between its component molecules. The strength of molecular interaction, in turn, depends (partially) on their proximity to one another. Temperature, due to its ability to control molecular proximity, is one of nature’s most prominent phase-change “switches.” Typically, molecules spread further apart at hot temperatures, pack together at colder temperatures and stay in between the two extremes at middle-tiered temperatures. The strength of their interaction usually follows a similar trend. Water serves as an example of the unseen physical chemsitry here: at hotter temperatures, when molecular interactions are weak, water vaporizes into a gas; at colder temperatures, when molecules are forced to pack together and strengthen their interaction, solidity is conferred and ice will form; at temperatures in between, interactions are neither strong enough to form solids nor weak enough to vaporize, so water simply becomes fluid.

So, as temperatures descend, molecules are forced to huddle up, form stronger bonds, and transition into a more solid state. So how does this apply to the saturated and unsaturated fats in question? Upon freezing, saturated fatty acids, which are defined by a straight, rigid structure, pack closely and tightly together, forming a solid. Coincidentally, because the molecules are packed so closely to one another, very little light is able to pass through their tight-knit architecture, giving the frozen material an opaque hue. Transfer of light through a “chemical” building, just as through a physical building, gives it transparency. When little or no light is able to pass through a structure (and is reflected off its surface instead), opacity results. Compare this to the “kinked” unsaturated fatty acids: upon freezing, they, too, are forced to pack together, but are unable to as closely as the saturated fatty acids due to their distinctive “kinked” (bent) design, which creates extra space between each molecule. Because the unsaturated structure is more loosely tied together, it not only becomes solid at a slower rate, but also lets greater amounts of light pass through, giving it a clear, transparent hue.

Compare, for example, saturated-fat heavy butter vs. unsaturated fat-rich olive oil at room temperature. Are there differences in form? Opacity? How about at freezing temperatures – which takes longer to freeze? Is olive oil still transparent? Identical logic is applied to the saturated and unsaturated fats in your fish oil supplement.

fish oil

The Fish Oil Breakdown: EPA, DHA and Palmitic Acid

The freezing point of DHA (Docosahexaenoic acid), the most important active ingredient in fish oil capsules, is -47.2°F (-44°C). Similarly, the freezing point of EPA (Eicosapentaenoic acid), the other key omega-3 compound in fish oil, is -65.2°F (-54°C). Palmitic acid (Hexadecanoic acid), the most common saturated fatty acid in salmon and other animal protein sources, however, has a freezing point of 145.2°F (62.9°C), much higher than that of EPA and DHA, meaning that it will solidify much faster. Even small amounts of palmitic acid, then, would cause some opacity in a home-based freezer test (0°F, -18°C).

Retail grade fish oil supplements are never exclusively unsaturated omega-3 fatty acids. They are often a combination of healthy omega-3’s, which typically command the majority, and other unsaturated and saturated fats. Here is where the Freezer Test truly triumphs: determining saturated fat vs. unsaturated fat balance. In general, supplements with higher amounts of saturated fats will turn opaque, while those higher in unsaturated fat content will typically be less opaque, if at all. While opacity/clarity gives some idea of unsaturated omega-3 fatty acid content, it is, by no means, an accurate measure. Moreover, it discloses very little about the products purity or quality. A supplement high in omega-3 content, for example, will pass the freezer test even if it is highly oxidized (rancid) and contaminated with high levels of mercury, PCB’s (polychlorinated biphenyls) and dioxins.

What You Can’t See in the Freezer Can Hurt You

  1. Rancidity: Is your fish oil fresh or rancid? The best way to find out is through a product’s TOTOX value. TOTOX is an analytical testing standard that measures the total oxidation of the fatty acids in a fish oil sample. It is made up of two metrics: Peroxide and p-Anisidine values. LabDoor performs both of these tests on every fish oil sample, and incorporates TOTOX values into our Product Purity score.
  2. Contaminants: Is your supplement contaminated with mercury? If so, how much is there? Are some supplements better than others? LabDoor performs inductively-coupled plasma mass spectrometry (ICP-MS), a test capable of detecting both metals and non-metals at part per trillion concentrations (significantly lower than usually found), on every product. Mercury levels are then incorporated into our Product Purity score.
  3. EPA:DHA Ratio: While unsaturated omega-3’s are healthy, different fatty acids undergo different biochemical processes and end up serving different functions. Understanding EPA:DHA ratios is an important step in maximizing your supplements benefits. Because both EPA and DHA are unsaturated fats, a freezer test will only give you a rough estimate of their total amount, and no information on their respective amounts. LabDoor performs gas chromatography (GC) tests on every fish oil supplement, accurately determining total omega-3 content as well as EPA and DHA levels.
  4. Label Accuracy: Are there other nutrients in your fish oil capsule, like conjugated linolenic acid (CLA) or vitamin D? The Freezer Test can’t predict nutritional value. LabDoor tests for the presence of these ingredients when listed on Nutrition Facts label and incorporates resulting values into our Label Accuracy score.
  • Header Image: Sam Catch (Flickr)
  • Co-author: Neil Thanedar
  • Lehninger’s Principles of Biochemistry, 4E. Albert L. Lehninger, David L. Nelson, Michael M. Cox, Macmillan, 2005. Chapter 10: Lipids.