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.
3)Lye: 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!

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!