Which oil is the best for cooking?
In
foods, fatty acids are mainly found in lipid complexes called triglycerides. Fatty
acids are long aliphatic chains consisting of carbon and hydrogen atoms. The
carbon chains vary in length, degree of unsaturation (number of double bonds
between carbon atoms) and structure. So some fatty acids are saturated, while
other have different degrees of unsaturation. When you are frying or cooking at a high temperature (at
or close to 180 0C) the molecular structures of the fats and
oils you are using change. They undergo oxidation, when we talk about lipid oxidation it is only
the polyunsaturated fatty acids, which are of interest. Polyunsaturated fatty
acids contain two or more double bonds, and it is these double bonds, which are
prone to oxidation. Consequently, the risk of oxidation increases with the
number of double bonds present in the fatty acid. The degradation of unsaturated fatty acids
by oxidation is directly related to nutritional, flavour, safety and storage
problems. There are two major oxidation reactions, which can occur in foods containing
lipids; auto-oxidation and photo-oxidation. The auto-oxidation is the most
common. Auto-oxidation occurs in the presence of oxygen. It is initiated when a
hydrogen atom is abstracted in the presence of initiators such as light, heat,
metals or oxygen, forming a lipid radical (a very reactive molecular part), which
reacts with oxygen making a lipid peroxide radical (another reactive substance).
These peroxide radicals react with a second lipid, yielding a lipid radical and
a hydroxyperoxide. The hydroxyperoxides will be decomposed into secondary
oxidation products. The products of secondary oxidation: reactive aldehydes,
alcohols and ketones have negative health inferences due to their cytotoxic,
mutagenic and neurotoxic action. Lipid oxidation may also
severely change the nutritional quality of foods by damaging vitamins and
polyunsaturated fatty acids.
This
chain of reactions may be staggered by antioxidants producing a combination of
radical species to give non-radical and non-propagating species.
Photo-oxidation occurs when norma triplet oxygen are converted to singlet
oxygen by the exposure of UV radiation. The singlet oxygen interacts with
polyunsaturated fatty acids to form hydroxyperoxide, which initiate the
auto-oxidation reaction.
Prof Grootveld’s (De
Montfort University in Leicester) team measured levels of “aldehydic lipid
oxidation products” (LOPs), produced when oils were heated to varying
temperatures. The tests suggested coconut oil produces the lowest levels of
aldehydes, and three times more aldehydes were produced when heating corn oil
and sunflower oil than butter.
Some advices
Try to do less frying, particularly at high temperature. If you
are frying, minimise the amount of oil you use, and also take steps to remove
the oil from the outside of the fried food, perhaps with a paper towel. To
reduce aldehyde production go for an oil or fat high in monounsaturated or
saturated lipids (greater than 70%), and low in polyunsaturated (less than
20%). Probably the olive oil is the compromised cooking oil but the antioxidant
levels present in the extra virgin products are insufficient to protect us
against heat-induced oxidation. Important: always keep your oils in a cupboard,
out of the light, and try not to reuse them as this also leads to the
accumulation of nasty side-products.
When you eat food such nuts, seeds, fish and leafy greens, they
have clear health benefits, which
contain polyunsaturated fats. Monounsaturated fats are in avocados,
olives, olive oil, almonds and hazelnuts, and also in lard and goose fat. Olive
oil, which is approximately 76% monounsaturated, is a key component in the
Mediterranean diet, which has been shown to reduce the risk of heart disease. The
extra-virgin olive oil has its smoke point about 160-190 0C so it is
best for drizzling on salad and finishing soup and pasta. The refined olive oil
smokes at 240 0C so it is still not recommended for deep fry. Eating
saturated fats, particularly dairy and other fats derived from animals, the
benefits of doing so confronted.
Coconut
oil is on the top of the table. It is high in saturated fat; contains lauric
acid, a medium chain saturated fatty acid with 6 carbon atoms in the molecule.
It does raise cholesterol levels, mainly increases HDL, the healthy type of
cholesterol. Coconut oil contains medium-chain triglycerides, which are used
directly for energy by your body. All forms of coconut are high in
calories and should be consumed in moderation. Avoid partially hydrogenated
coconut oils, which are not natural and are associated with increased risk of numerous
diseases.
Rapeseed
oil has
delicate, nutty flavour, is high
in monounsaturated fats and it has high
level of vitamin E. When extra-virgin and cold-pressed, it is delicious in dressings
and dips, as well as in baking, frying and general cooking.
Butter
is the second best in the table for cooking. It is rich in the most easily absorbable form of Vitamin A and vitamin
E, K and D. It also contains lauric acid, lecithin, essential for cholesterol
metabolism, calcium, anti-oxidants that protect against free radical damage,
conjugated linoleic acid, which is a potent anti-cancer agent and immunity
booster.
In cooking, baking and
frying you should vary three oils mentioned above; coconut oil, butter and rapeseed oil.
No comments:
Post a Comment