Hydrogenation
food-scienceAn industrial process adding hydrogen to unsaturated fats to make them more solid and stable.
Definition
An industrial process adding hydrogen to unsaturated fats to make them more solid and stable. Partial hydrogenation creates trans fats. Full hydrogenation creates saturated fat (no trans fats). Used in margarine and shortening.
The Chemistry of Hydrogenation
Hydrogenation is an industrial process in which hydrogen gas is added to liquid vegetable oils in the presence of a metal catalyst (typically nickel) under heat and pressure. This reaction converts some or all of the double bonds in unsaturated fatty acids to single bonds, increasing the degree of saturation and raising the melting point of the oil. The result is a fat that is solid or semi-solid at room temperature, offering improved texture, spreadability, and extended shelf life compared with liquid oils.
Partial vs. Full Hydrogenation
The process can be carried out partially or completely, yielding products with very different compositions:
- Partial hydrogenation: Only some double bonds are converted. This process produces a plastic-like fat useful in shortenings and margarines, but it generates trans fatty acids as a byproduct. Trans fats increase low-density lipoprotein (LDL) cholesterol while simultaneously reducing high-density lipoprotein (HDL) cholesterol, creating a particularly unfavorable cardiovascular risk profile.
- Full hydrogenation: All double bonds are converted, producing a fully saturated fat with no trans fatty acids. However, the resulting product is very hard and is typically blended with liquid oils through a separate process called interesterification to achieve a usable consistency.
Regulatory Changes and Health Impact
The evidence linking partially hydrogenated oils (PHOs) and industrial trans fats to cardiovascular disease led major regulatory agencies to restrict or ban their use. The U.S. Food and Drug Administration finalized a determination in 2015 that PHOs are no longer "generally recognized as safe," effectively requiring their removal from the food supply by 2018. The World Health Organization has called for the global elimination of industrially produced trans fats. As a result, food manufacturers have reformulated many products using fully hydrogenated oils, interesterified fats, tropical oils, or high-oleic varieties of sunflower and canola oil as alternatives.