Tuesday, July 28, 2009

What keeps your food fresh and delicious?

Yeah, it's my 5th post~! As a Food Science and Nutrition student, rather than just complete this assignment because Ms.Alice asked me to do so, I would also like to take the chance know more about the chemistry of food, which is related to my study field.

Before you continue reading, have a look at your kitchen and refrigerator! Have you noticed that there are so much canned food and food kept in plastic bags or bottles? Have you wondered why food such as fruit jam, sausages, spagheti, can kept for so long but still taste fresh and delicious? This is all because of FOOD PRESERVATION~

History of food preservation
Once upon a time... this is not a FAIRYTALE, when food preservation technology was not as advance as today, the evolving human race had eaten food raw and uncooked for hundreds of thousands of years! The first cooked food is roasted using fire, in Africa, 1,400,000 B.C.! After the discovery of fire to cook food, many variations to process food are invented too, one of them is FOOD PRESERVATION. There is evidence that as early as 12,000 B.C., Egyptian tribes people on the lower Nile dried fish and poultry using the hot desert sun. Areas with similar hot and dry climates found drying to be an effective method of preservation.This is the first method human used to preserve food, but there are actually many more ways of food preservation.

Methods of Food Preservation
1) Flash Freezing: Used in the food industry to quickly freeze perishable food items. In this case, food items are subjected to temperatures well below water's melting/freezing point (273.15K or 0°C), inhibit the growth of bacteria. For example, meat.
2)Salting/Curing: Table salt, which consists primarily of sodium chloride, kills and inhibits the growth of microorganisms by drawing water out of the cells of both microbe and food alike through osmosis. For example, kimchi.
Sodium hydroxide (lye) makes food too alkaline for bacterial growth. Lye will saponify fats in the food, which will change its flavor and texture. For example, century egg.
There are still many types of preservation method, but I am going to focus on the most common type of preservation method used in food processing industry, that is by adding chemical food preservatives into food product. The most popular and commonly used preservatives are BHA and BHT.

What are BHA and BHT?
Butylated Hydroxyanisole (BHA)
BHA, C11H16O2 is a mixture of the isomers 3-tert-butyl-4-hydroxyanisole and 2-tert-butyl-4-hydroxyanisole. It has a white yellowish waxy solid appearance. The structural formula of BHA:
Butylated Hydroxytoluene (BHT)
BHT, C15H24O is known as 3,5-di-tert-butyl-4-hydroxytoluene. It has a white powder appearance. BHT is prepared by the reaction of p-cresol (4-methylphenol) with isobutylene (2-methylpropene) catalysed by sulfuric acid. The structural formula of BHT:
How do BHA and BHT preserve food?
BHA and BHT are actually antioxidant. Without BHA and BHT, oxygen in air will react with fat or oil in food. This will cause the fats become rancid and spoilt the food. However, with the addition of BHA or BHT, oxygen will react with them instead of fats, hence prevent the spoilage of food. Besides the oxidative rancidity of fats, food odour, colour and flavour can also be preserved.

In terms of chemistry, BHA and BHT acting as a terminating agent that supresses oxidation (a process where unsaturated organic compound such as oil attacked by oxygen). The conjugated aromatic ring of BHA and BHT are able to stabilize free radicals by converting peroxy radicals to hydroperoxides by donating a hydrogen atom:

RO2. + ArOH → ROOH + ArO.
RO2. + ArO. → nonradical products

R is alkyl or aryl, and where ArOH is phenolic antioxidants (BHA and BHT). One can see that each BHT consumes two peroxy radicals. This can prevent further free radical reactions of the food.

Are these food preservatives safe to consume?
-Present researches shows that the concentration of BHA and BHT used in food are most probably harmless.
-HOWEVER, after high dosage and long-term consume, there is evidence that certain persons may have difficulty metabolizing BHA and BHT, resulting in health and behavior changes. For example, hyperactivity in children.
-Experiments show that BHA may induces in animals tumours of the forestomach, which are dose dependent, whereas BHT induces liver tumours in long-term experiments. Because there is no indication of genotoxicity of BHA and BHT, all published findings agree with the fact that BHA and BHT are tumour promoters.

Food is undeniably the most important factor to achieve good health. After reading so much about food preservatives and how it works, I bet you know what is the better way to consume food! Too much canned or processed food can lead harmful effects to our body, we should consume the food we need in the most natural and healthy way, for example, pluck from the trees!

Natural is healthy, from now on, eat smartly!

Saturday, July 18, 2009

No Batteries, No Life~!

I guess many of you will agree with me right? Nowadays, almost everyone rely on electrical appliances everyday. Imagine, what you'll be doing if battery was not invented? And do you know chemistry is the driving force behind the magics of batteries?

Firstly, let's see what's a battery.

In electronics, a battery or voltaic cell is a combination of many electrochemical Galvanic cells of identical type to store chemical energy and to deliver higher voltage or higher current than with single cells. There are many types of batteries, such as carbon-zinc batteries, lead acid-batteries, alkaline cells and others.
In this post, I'll talk more about carbon-zinc battery, since it's the most common and least expensive type of battery. Carbon-zinc cell is also known as Lechlanche's cell. It is a type of dry cell and is described as primary cell, because it cannot be recharged after used up.

Let's have a look at the cross-section diagram of a carbon-zinc cell.
Now, do you know how a battery produces electricity when connected in a circuit?

If you look at a battery, it will have two ends, a positive terminal and a negative terminal. If you connect the two terminals with wire, a circuit is formed. Electrons will flow through the wire and a current of electricity is produced. Inside the battery, a reaction between the chemicals takes place. But reaction takes place only if there is a flow of electrons.

How the reaction works?
The reaction inside battery is closely related to the oxidation and reduction in chemistry studies. The container of the carbon-zinc battery is a zinc case. Inside the case contains a layer of NH4Cl with ZnCl2 aqueous paste separated by a paper layer from a mixture of powdered carbon and manganese(IV) oxide(MnO2), packed around a carbon rod.

The outer zinc container of a dry cell is the negative terminal. So, the zinc is oxidised, the half equation is as below.
Zn(s) → Zn2+(aq) + 2 e-

Refer to the cross-section diagram, the carbon rod surrounded by a powder containing manganese(IV) oxide is the positive terminal. In the following reaction, The manganese dioxide is mixed with carbon powder to increase the conductivity.
2MnO2(s) + H2(g)→ Mn2O3(s) + H2O(l)
Note: The H2 comes from NH4+(aq) => 2NH4+(aq) + 2 e- → H2(g) + 2NH3(aq)

The NH3 combines with the Zn2+ and manganese is reduced from an oxidation state of (+4) to (+3). Hence the overall reaction happens in a carbon-zinc battery is:

Zn(s) + 2MnO2(s) + 2NH4+(aq) → Mn2O3(s) + Zn(NH3)22+(aq) + H2O(l)
I bet you've learn something about battery after sacrificing so much patience to read this post. Congratulation! No choice, chemistry battery is boring. =P
Lastly, even though batteries can bring us so much benefits and convenience, it is still recommended to avoid the excessive usage of electricity, to save the Earth!

Saturday, June 6, 2009

What makes your heart melts?

What makes your heart melts? For me, the answer is ICE CREAM~!

Isn't it so tempting and seducing? XD

Well, I believe that every kid loves ice cream, me too! Even until now, I still love ice cream. If you ask me, what's so great about ice cream? I would say the creamy texture and the chilling sensation of it, that melts my heart everytime I eat an ice cream! =P
Don't eat me~ Sob sob~

If I ask you, 'What's an ice cream?'. What will you answer? Think about it. Haha. Before I wrote this post, I most probably will say that ice cream is a type of sweet food keep in refrigerator or the big blue ice box =P If you only know how to eat like me, then you should really continue reading and click the advertisement at the right side =X

What's in ice cream?
Ice cream is basically composed from milk, cream, sweeteners (syrup or sugar), flavorings, emulsifiers, stabilizers, milk solids, and milk fat.

Milk fat is the ingredient that gives ice cream it's unique richness, creamy and smooth texture. For your information, the higher the content of milk fat, the smoother the texture of ice cream. Despite the high calorie content of milk fat, many premium brands ice cream have as much as 16% of this component.

So, don't complain next time when you eat a bad texture ice cream, perhaps it contains less milk fat =D

Why ice cream freezes into chilling cream instead of hard solid ice?
Before the freezing process, 20-50% of ice cream is air whipped into the mix, forming tiny air bubbles between the ice cream mix. Ice cream is a colloid (a type of emulsion). In ice cream, molecules of fat are suspended in a water-sugar-ice structure along with air bubbles. The presence of air means that ice cream is also technically a foam. A colloid is stable, so one substance does not settle out of the other.

The picture below shows the formation of colloidal structure of ice cream.
This colloidal structure also gives ice cream the ability to be scooped and chewed with ease =D
Another picture of ice cream to give you strength to continue reading =P

Ice crystal in ice cream and it's freezing point?
Ice crystal is another major component of ice cream that begin to form when the mixture is cooled after whipping. It plays an important role to keep the cooling and chilling sensation of ice cream. Ice cream mix won't freeze at 0°C due to the sugar concentration in it. It has to be cooled to even lower temperatures before any crystals form.

This is known as 'freezing point depression' or 'colligative theory'. As water form ice crystal, the sugar concentration in the solution increases, depressing the freezing point further (refer to the picture below). In fact, although ice cream is typically served at temperature of -16°C, only 72% of the water component is frozen. The rest remains as a very concentrated sugar solution.
After reading so much about ice cream...
Are you hungry?
Can you resist the mouth-watering ice cream?
Well, seriously I can't!
It's time for a cup of ice cream =D

Saturday, May 16, 2009

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

Wednesday, May 13, 2009

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!