Partially Hydrogenated Oil (PHO) | American Society of Baking
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Partially Hydrogenated Oil (PHO)

What is partially hydrogenated oil (PHO)?

Partially Hydrogenated Oil (PHO) is vegetable oil in a solid form at room temperatures.

PHO is typically made by this process:

  • Vegetable oil is placed in the presence of hydrogen and a catalyst.
  • During this process, the C=C bonds are dismantled, forming a solid fat which increases the melting point of the ingredient.
  • This results in incomplete hydrogenation which partially converts the oil to trans isomers, forming trans fat.
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In the 1890s, Nobel laureate Paul Sabatier discovered the chemical process for the hydrogenation of vapors. In 1901, Wilhelm Normann showed that liquid oils could be hydrogenated. In 1909, Procter & Gamble acquired the US rights to the Normann patent, selling the first hydrogenated shortening under the brand name Crisco®.


To convert soybean, cottonseed, or other liquid oils into a solid shortening, the oil is heated in the presence of hydrogen and a catalyst. The hydrogenation process eliminates part of the double bonds and converts some unsaturated fatty acids to saturated fatty acids.1 This process solidifies the oil,  increases its melting point, improves consistency for use as a margarine and increases the resistance to oxidation.2

Also, during the partially hydrogenation process, trans-fatty acids are formed due to the cis/trans conversion on positional shifted in the fatty acid chain.


PHOs is very versatile in all pastry, cookie and frosting applications.  Baker’s who are seeking to replace the PHOs in their formulas can now find alternatives. Palm kernel oil is the most prevalent alternative for PHOs today, as it provides similar structural integrity.

Other techniques are also used to produce shortenings or margarine from vegetable oil instead of using partially hydrogenation, such as blending fully hydrogenated oils with other oils, and interesterification.3

Nutritive properties and caution

The consumption of partially hydrogenated oils (PHOs) high in trans fat is associated with an increased risk of cardiovascular disease and other non-communicable diseases.3 Consumption of PHO raises levels of low-density lipoprotein cholesterol and triglycerides, lowers levels of high-density lipoprotein cholesterol, induces an inflammatory response, and even at low levels of intake (e.g., 2 to 4% of total calories) significantly increases the risk of coronary events.4

FDA regulation

Based on new scientific evidence and the findings of expert scientific panels, the Food and Drug Administration (FDA) has tentatively determined that partially hydrogenated oils (PHOs), which are the primary dietary source of industrially-produced trans fatty acids, or trans fat, are not generally recognized as safe (GRAS) for any use in food based on current scientific evidence establishing the health risks associated with the consumption of trans fat.

A compliance date of June 18, 2018 has been established by the FDA to remove all PHOs, either directly or as ingredients in another food product, for use as a food additive.5


  1. Center for Science in the Public Interest. “About Trans Fat and Partially Hydrogenated Oils.” 18 May, 2004. Accessed 21 June 2017.
  2. Karabulut I, Kayahan M, Yaprak S. “Determination of Changes in Some Physical and Chemical properties of Soybean Oil During Hydrogenation.” Journal of Food Chemistry. 2003. (81) 453-456.
  3. Lee, Jeung Hee, Casimir C. Akoh, and Ki-Teak Lee. “Physical Properties of Trans-Free Bakery Shortening Produced by Lipase-Catalyzed Interesterification.” Journal of the American Oil Chemists’ Society 85.1 (2007): 1-11.
  4. Mozaffarian D, Jacobson M, Greenstein J. “Food Reformulations to Reduce Trans Fatty Acids.” The New England Journal of Medicine. May 27, 2010. 362;21.
  5. “Final Determination Regarding Partially Hydrogenated Oils.” Federal Register. 17 June 2015. Accessed 23 June 2017.