cooking oil reaches its smoke point, it will degrade and oxidize.
The smoke point is the temperature at which:
- triglycerides in the oil begin to separate into fatty acids
- free glycerol is converted into a toxic compound called acrolein
The more refined the oil, the higher the smoke point. Virgin
oils will have lower smoking points. For example:
- Olive Oil
- Unrefined: 320°F (160°C)
- Extra Virgin: 375°F (190°C)
- Virgin: 390°F (199°C)
- Pomace 460°F (242°C)
- Extra Light: 468°F (242°C)
- Avocado oil
- Virgin 375-400°F (190-205°C)
- Refined: 520°F (271°C)
See Comparison of Dietary and
Cooking Oils for list of smoking points.
Heating Polyunsaturated Fats
- Grootveld et al (2001) warns that heat degrades polyunsaturated
fatty acids to toxic compounds
- Possible risks of consumption or exposure of air-borne breakdown
products of heated oils (Grootveld 2001)
- atherosclerosis (heart diseases)
- inflammatory joint disease, including rheumatoid arthritis
- pathogenic conditions of the digestive tract
- mutagenicity and genotoxicity (carcinogenesis)
- teratogenicity (possible birth defects)
- Halvorsen & Blomhoff (2011) observed 2.911.2 fold
increases in alkenal concentrations (a measure of oxidation)
when various vegetable oils were heated to 225°C for 25 minutes.
- Despite the biological toxicity of several lipid oxidation
by-products (Halvorsen 2011)
- safe doses of these compounds have not been established
- little is known about what doses may constitute a health
hazard for humans.
- Guillén & Uriarte (2012) found that cooking oils
produce aldehydes when heated to frying temperature 190°C
for extended periods (20 hours).
- aldehydes were found in both oil and fried foods
- aldehydes may be associated with some neurodegenerative diseases
- Przybylski, et al (2012) did not detect partially hydrogenated
oils, or trans fats when the oil was heated to 275°C in a
stir fry pan and smoking heavily before the food was placed in
- It only decreased the amount of polyunsaturated fatty acids
because of oxidative degradation
- However, he noted that linolenic acid appears to be the most
prone to isomerization with the highest amount of trans isomers
formation irrespective of the cooking procedure.
See Comparison of Dietary and
Cooking Oils for amounts of polyunsaturated fat in various
- Unsaturated Fats, including polyunsaturated
and monounsaturated fats
are susceptible to rancidity
- There may be possible negative health effects from ingestion
of oxidized lipids from fish oils and cooking oils (Halvorsen
- Auto-oxidation and photo-oxidation during processing and
storage (Halvorsen 2011)
- Undesirable taste, decomposing nutritional quality, production
of toxic compounds
- Depends on fatty acid composition (degree of unsaturation),
processing, exposed heat, light, metals, and antioxidants.
- Plastic containers
- Placicides can contaminate food with Bisphenol A (BPA)
- BPA from plastics links to lipid molecules
- BPA is found in:
- certain plastic containers
- plastic coating in some metal cans
- and other plastics
- See Hormone Disrupters:
Bisphenal A (BPA)
- Shelf life for cooking oils vary from 2 to 12 months
- 3-6 weeks
- Flax and hemp oils
- May be kept up to a year in the freezer
- 2-4 Months
- 3 Months
- 3-6 Months
- 6 Months
- Safflower, Soybean, and Peanut oils
- 6-12 months
- Olive, Macadamia, and Almond Oils
- 9-12 months
- 12 months
- Coconut, Palm, Avocado, and Canola Oil
- Refined oils will keep refrigerated for 6 months to a year.
- Unrefined oils are less stable and will only keep for 4 or
- purchase them in small quantities
Grootveld M, Silwood CJL, Addis P, Claxson A, Serra BB,
Viana M (2001). "Health effects of oxidized heated oils".
Foodservice Research International 13: 4155.
Guillén M, Uriarte P (2012). Aldehydes contained
in edible oils of a very different nature after prolonged heating
at frying temperature: Presence of toxic oxygenated a,ß
unsaturated aldehydes. Food Chemistry 131 (3), 915926.
Halvorsen BL, Blomhoff R (2011). Determination of lipid
oxidation products in vegetable oils and marine omega-3 supplements.
Food Nutr Res. 2011;55. doi: 10.3402/fnr.v55i0.5792.
Przybylski O, Aladedunye FA (2012). Formation of trans
fats during food preparation. Can J Diet Pract Res. 2012 Summer.