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| Spaghetti Bolognese |
In this part, we will encounter another food recipe, spaghetti bolognese, from the point of view of a chemist. Spaghetti bolognese is a simpler dish than rice curry as we saw in previous article, but in point of view of a chemist is still a complicated dish as it comprises a lot of ingredient. In this section, we will try to focus on the main ingredients; garlic, lycopene from tomatoes, olive oil, and cooking meat. We will not discuss about the pasta because it is simply carbohydrate in similar way as rice (have a look in
curry recipe).
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| Allium sativum |
Firstly is garlic for more specifically Allium sativum which the garlic plant that is common for cooking and it has been used for more than centuries. As the proves, garlic is mentioned in Bible and some say the builders of Khufu's Great Pyramid ate it. However, in traditional English cuisine garlic was rare, though it is said to have been grown in England before 1548.
"We remember the fish, which we did eat in Egypt freely; the cucumbers,
and the melons, and the leeks, and the onions, and the garlic."
Numbers 11:5 (King James Version)
Garlic is claimed to help prevent heart diseases, including artherosclerosis, high cholesterol, high blood pressure, and to improve immune system. In 1858, Louis Pasteur observed garlic's antibacterial activity, and it was used as an antiseptic to prevent gangrene during World War I and World War II. However, it is left with the big question, what are the important neutraceuticals?
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| Allicin |
The main component of garlic is allicin which is a powerful antibacterial and anti-fungal compound. However, allicin is only produced when a garlic is chopped. The formation of allicin is followed 3 main steps. Firstly is the formation of alliin from amino acid cysteine. Then, alliin is converted by an enzymatic process into a sulfenic acid and lastly, the sulfenic acid condenses with another sulfenic acid to form allicin.
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| The synthesis of Allicin |
Besides that, allicin decomposes quickly one made into volatile compounds because of the clash of electron cloud of sulphur atom. Moreover, onions also contain organosulphur compounds and
syn-propanethial-S-oxide is the compound that responsible for causing eyes water.
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| Decomposition of allicin (left) and syn-propanethial-S-oxide (right) |
Secondly is lycopene which is a carotenoid found in fruits such as tomatoes and it gives the bright red colour of tomato. The bioavailability of lycopene can be increased by processing it and lycopene is a powerful carotenoid quencher of singlet oxygen; hence it is anti-oxidant.
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| Lycopene quenching mechanism |
The third ingredient is olive oil which is a triacylglyceride, 3 fatty acids attached to a glycerol backbone by ester functional group. Besides that, triacylglycerols are the major energy reserve for plants and animals.
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| Olive oil and triacylglycerides |
Moreover, olive oil is not only comprised of triacylglycerol, but it is a complex mixture of fatty acids, vitamins, volatile components, water soluble components, and microscopic bits of olive. There are 3 primary fatty acids in olive oil, oleic acid (55-85%), linoleic acid (9%), and a small amount of linolenic acid (0.1%). Linolenic acids and linoleic acids are examples of omega 3 and omega 6 fatty acids, and it is commonly found in fish. Moreover, these fatty acids have implications in health, especially brain development.
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| 3 primary fatty acids in olive oil |
The unsaturated fatty acid can be used to synthesis hydrogenated oils. Hydrogenated oils are used to replace animal fats which are generally saturated. This process is carried by passing hydrogen gas through oil at 250
°C - 400 °C with a Ni or Pt (precious metal) catalyst. Moreover, partial hydrogenation is used to control the physical properties and this can lead to formation of trans-fatty acids which increases the risk of coronary heart disease. In general with the same number of carbon, hydrogenated fatty acid has higher melting point than unsaturated fatty acid.
Lastly is cooking the meat which forms a brown colour to provides the taste and this process is very complex series of chemical reactions. The complexity of the process because meat is not only comprises of protein, but also another components such as glucose.
However, the important step (or the first step) in these process is the Maillard reaction.
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| The Maillard reaction |
In this video below is a short clip about the Maillard reaction (taken from The Chemistry Calendar 2011 for November edition)
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