Paz Etcheverry
Factors to take into account when choosing oils
Oils consist mostly of triglycerides, which are molecules composed of three fatty acids esterified to one glycerol molecule. Additionally, oils contain unsaponifiable compounds (i.e., unable to form soaps) and acyl lipids. The fatty acids that make up the triglycerides can be MUFAs (monounsaturated fatty acids), PUFAs (polyunsaturated fatty acids), or SFAs (saturated fatty acids).
There are basically two factors to take into account when choosing an oil: the proportion/fraction/percentage of PUFA in the oil and the smoke point (or temperature) of the oil:
- PUFAs are unsaturated fatty acids that contain more than one double bond in their structure; double bonds are susceptible to oxidative damage and conversion to hydroperoxides. On the other hand, MUFAs, which contain one double bond, are more stable. SFAs, which contain no double bonds (the carbons are said to be “saturated” with hydrogen molecules), are the most stable.
- Smoke point is the temperature at which the triglycerides start to decompose in the presence of air. Smoke is the visual sign of decomposition. The smoke point/temperature increases with the refining process of an oil.
What happens during cooking?
a. Fatty acids, bound to triglycerides, are released. Short chain fatty acids can lead to the development of off-flavor and odors (e.g., rancid flavors). This is the smoke point; inhaling the vapor/smoke can be harmful. Free PUFAs of any chain length are more susceptible to oxidation than when esterified to glycerol.
b. Free PUFAs, which are the most susceptible, undergo autoxidation (i.e., oxidation). When exposed to oxygen, free PUFAs can be converted into lipid hydroperoxides. This reaction is increased by the presence of some metals and light.
c. Soon after they are formed, the lipid hydroperoxides are decomposed into hydroxyl and alkoxy radicals and compounds known as aldehydes.
Non-refined versus refined oils There are non-refined (e.g., cold-pressed) and refined edible oils. Between the two, the former has a higher commercial value. The concentration of antioxidants in oils is influenced by the oil extraction procedures. In general, non-refined oils tend to have higher antioxidant properties compared to the refined oils. Refined oils go through physical and chemical procedures. Basically, they are neutralized with sodium hydroxide, and the fatty acid soaps formed are eliminated by cleansing with water and centrifugation. In addition, they are passed through charcoal filters and extracted with hexane at low temperatures and vacuum. The resulting oils are mostly colorless and aroma free.
Optimal oils based on cooking methods
Below is a summary of oils that are optimal for high-heat cooking and those that are optimal to low- heat cooking:
