OIL AND FAT: MODIFIED FATS
Diagram
Two ways to make a liquid oil solid
Hydrogenated fat
Hydrogen gas is added across the double bonds of an oil, with a catalyst. The oil turns solid and keeps longer.
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Interesterified fat
Fatty acids are moved between triglyceride molecules, with no hydrogen added. The fat turns solid without changing the fatty acids.
Figure 1: Hydrogenation adds hydrogen to the fat, while interesterification rearranges the fatty acids already there. Drawn in our own style from the fat modification chapters in Akoh and Min, Food Lipids, and in O’Brien, Fats and Oils.
Introduction
Hydrogenated fat and interesterified fat are both modified fats made to turn a liquid oil solid, so that spreads and shortenings hold their shape, but the chemistry is different. Hydrogenation adds hydrogen gas across the double bonds of the unsaturated fatty acids, with a catalyst, so the fatty acids become more saturated and the fat firms up. Interesterification rearranges the fatty acids between triglyceride molecules, so the same fatty acids sit in new positions, and the melting behaviour changes without any hydrogen being added and without changing the fatty acids themselves.
Quick comparison
Table 1: Hydrogenated Fat compared with Interesterified Fat
| Aspect | Hydrogenated Fat | Interesterified Fat |
|---|---|---|
| What changes | Hydrogen is added across double bonds | Fatty acids are moved between triglycerides |
| Double bonds | Double bonds are removed, so unsaturation falls | Double bonds stay as they are |
| Fatty acids | Unsaturated fatty acids become saturated, and some trans fatty acids can form | The same fatty acids remain, in new positions |
| Catalyst | A metal catalyst, with hydrogen gas | A chemical catalyst or an enzyme, with no hydrogen gas |
| Saturation | Saturation rises | Saturation does not change |
| Trans fatty acids | Can form during partial hydrogenation | Do not form, because no hydrogenation happens |
| Melting behaviour | Melting point rises and the fat firms up | Melting behaviour changes because the triglycerides are rearranged |
| Purpose | Make a liquid oil solid and more stable to oxidation | Make a liquid oil solid while keeping its fatty acid profile |
| Use | Shortenings, margarines and frying fats made by the older route | Spreads and shortenings made as a replacement for partial hydrogenation |
| Effect on keeping quality | More stable to oxidation, because fewer double bonds remain | Keeping quality is like the starting oil, because unsaturation is unchanged |
Scientific explanation
Definition
A hydrogenated fat is a fat made by hydrogenation, the addition of hydrogen gas across the double bonds of unsaturated fatty acids in the presence of a catalyst, so that a liquid oil becomes solid. An interesterified fat is a fat made by interesterification, the rearrangement of fatty acids between triglyceride molecules, so that the melting and crystallisation behaviour changes without adding hydrogen and without changing the fatty acids.
Working principle
In hydrogenation, hydrogen gas is passed through hot oil with a metal catalyst, and hydrogen atoms add across the carbon to carbon double bonds. Each double bond that is hydrogenated removes one site where oxygen could attack, so the fat becomes firmer and more stable, but partial hydrogenation can also flip some double bonds into the trans form. In interesterification, fatty acids are detached from one triglyceride and reattached to another, either with a chemical catalyst or with an enzyme. No fatty acid is created or destroyed and no hydrogen is added: the mix of triglycerides changes, so the fat melts and crystallises differently and can be made solid at room temperature from a blend of liquid oil and solid fat.
Apparatus
The books used here name no laboratory apparatus for measuring or comparing either term, so no apparatus list is given.
Measurement procedure
The books used here give no standard laboratory procedure with volumes and steps for either term, so no procedure is invented here.
Factors affecting readings
For hydrogenation, the temperature, the hydrogen pressure, the catalyst and the time decide how far the reaction goes: longer and hotter gives a harder fat and more saturated fatty acids. For interesterification, the catalyst, the temperature, the time and the starting blend decide the result: the rearrangement is random with a chemical catalyst and selective with an enzyme. In both cases the starting oil decides the outcome, because only the fatty acids present can be hydrogenated or rearranged.
Formulas and calculations
The books used here give no formula for either term, so no formula is given here.
Industrial applications
- Hydrogenated fat: shortenings and margarines made by the older route, where a firm, stable fat is wanted.
- Hydrogenated fat: frying fats, where a solid fat that resists oxidation is wanted.
- Interesterified fat: spreads and shortenings made as a replacement for partially hydrogenated fat.
- Interesterified fat: bakery fats, where a solid fat with a chosen melting range is wanted.
- Interesterified fat: blending liquid oils with solid fats to set the melting behaviour without hydrogenation.
Advantages and limitations
- Hydrogenated fat, advantage: it makes a liquid oil solid and more stable to oxidation, so shortenings keep longer.
- Hydrogenated fat, limitation: partial hydrogenation can form trans fatty acids, and full hydrogenation raises saturation.
- Interesterified fat, advantage: it makes a fat solid without adding hydrogen and without forming trans fatty acids.
- Interesterified fat, limitation: it does not change the fatty acid profile, so an unsaturated oil stays as open to oxidation as before.
FAQ
What is the difference between hydrogenated and interesterified fat?
Hydrogenation adds hydrogen across double bonds, while interesterification moves fatty acids between triglycerides without adding hydrogen.
Does interesterification make trans fat?
No. Trans fatty acids form during partial hydrogenation, and interesterification uses no hydrogenation.
Why hydrogenate an oil at all?
To make a liquid oil solid and more stable, so it works as a shortening or frying fat.
Why use interesterification instead?
To make a fat solid while keeping the same fatty acids and avoiding trans fatty acids.
Does interesterification change saturation?
No. The fatty acids stay the same, only their positions on the glycerol change.
References and further reading
- FTN books on disk: Technology of Fats and Oils.
- Akoh, Casimir C. and David B. Min (eds). Food Lipids: Chemistry, Nutrition, and Biotechnology. 2nd ed., CRC Press, 2002 (Google Books page read)
- O’Brien, Richard D. Fats and Oils: Formulating and Processing for Applications. 3rd ed., CRC Press, 2008 (Google Books page read)
- Google Books pages read for this article:
- Akoh, Casimir C. and David B. Min (eds). Food Lipids: Chemistry, Nutrition, and Biotechnology. 2nd ed., CRC Press, 2002 (Google Books page read)
- O’Brien, Richard D. Fats and Oils: Formulating and Processing for Applications. 3rd ed., CRC Press, 2008 (Google Books page read)
