No More Tears!

Since I came to Cheras to study, most of the weekend I cook my own meals, simply because its cheaper and more convenient (don't have to walk out from my house, hehe). Yea, I am lazy~ But somehow I realise everytime I want to cut up an onion, I end up torturing my eyes x_x

Unless you never cook before, most of you might have experienced this. Everytime I cut an onion, my eyes will feel like burning and tearing. Why will this happened? After I search through the Internet, finally I found the solution~ And I am going to share with you guys!

Firstly, let me explain what is actually happening when we're cutting an onion!

Onion cells contain enzymes called allinases. When we're cutting, peeling or slicing an onion, the cells are broken, and allinases are released to break down amino acid sulfoxides, which will eventually form sulfenic acids. Sulfenic acids are very unstable and rearrange to form a gas called thiopropanal S-oxide or syn-propanethial-S-oxide (C3H6OS).

Next, let's see how syn-propanethial-S-oxide make our eyes so painful and tearing?

When syn-propanethial-S-oxide in the air reach the cornea of our eyes, it will react with the water in our tears, to form sulfuric acid. Free nerve endings of our eyes detect the sulfuric acids and through the ciliary nerve, central nervous system of our brain interprets as a burning sensation. These nerves activities activates the autonomic fibers, which then send a signal to the lachrymal glands of the eyes to stimulate more tears, to wash the irritant (sulphuric acid) away.

After reading the long explanation, you guys must be wondering. 'Do we have any solution?' Of course!

1) You can chill the onion in the refrigerator before cutting it. This will slows down the reactions inside the onion, thus, reducing the amount of syn-propanethial-S-oxide released.

2) Cutting the onion under water. This will cause the gas released into the water instead of the air.

3) Wipe some vinegar at the chopping board. The acid of vinegar will denatures the enzyme of the onion.

4) Soak the onion in salt water. The ionic property of salt water can helps to denature the enzyme of the onion.

5) Light a candle beside the chopping board. The gas released by the onion will be drawn into the flame of the candle.

Thanks for reading! No more tears! Only smile =D

How does toothpaste works?

Since we're kids, we were taught how to brush teeth, and the importance of brushing teeth. Have you wonders, even if we were doing the same thing over and over again, how many of us actually know how toothpaste works? Hmm...

First of all, let me explain what is toothpaste and what is it made from. Toothpaste is basically a gel or paste dentifrice used with toothbrush to maintain oral hygiene and clean our teeth and gum. It can prevent tooth decay and the formation of dental plaque by delivering active ingredients such as fluoride and xylitol.

The most well known ingredient in toothpaste is fluoride. Surfactants (detergents) work well with fluoride to form foam that clean the tooth surface and wash away leftover food between our tooth. Another important ingredient is tetrasodium pyrophosphate (TSSP), which can helps to remove magnesium and calcium from our saliva, so they cannot form tartar or clacified plaque on our teeth. Sodium saccharin is often added as sweetener, to reduce the bitterness of TSSP.

Now, let's have a look at our teeth's structure!

As you can see, the part which we are brushing everyday is the outermost layer, the enamel. 95% of enamel is made from a hard and strong subtance, called hydroxyapatite, Ca10(PO4)6(OH)2. Although hydroxyapatite is strong and firm, it is easily decay if attacked by acid. The reaction occurs is:

Ca10(PO4)6(OH)2 ＋ 8H+ ↔ 10Ca²⁺＋ 6(HPO4)^2- ＋ 2H2O

This equation means that the reaction will proceed toward the right side by the addition of acid (H+ ion). Thus, the more acid added, the more hydroxyapatite that is dissolved into the saliva. This reaction is called 'decalcification'. Eventually, the enamel will start to decay and thus, plaque is formed.

You don't want your teeth to look like this right? Okay, continue reading then. =D

Now we shall see how toothpaste works to prevent decalcification or tooth decay! For your information, most of the food we consume are composed of different types of food acid. For instance, malic acid (apple), tannic acid (tea) and tartric acid (carrot).

Toothpaste act as a base which neutralise the acids in our mouth. From the above equation, we know that acids attack the teeth and the enamel diffuses into calcium ions and HPO4 2- ions. When we brush our teeth with toothpaste, fluoride ions are delivered to the enamel and replaces the OH ions in hydroxyapatite, to form fluoroapatite, Ca10(PO4)6F2. The reaction occurs is:

Ca10(PO4)6(OH)2 + 8H+ ---> 10 Ca²⁺+ 6HPO₄²+2H2O

Last but not least, remember to brush your teeth at least twice a day, and also after meal!

Save your smile! =D

Thanks for reading and have a good day!