Rancidity And corrosion

Made By- Pranav Ahlawat, class X-A,

4540/RH

Chemistry Holiday Assignment

Contents

What is rancidity and how it occurs? Factors causing rancidity. Some food items that are likely to turn rancid. Preventive measures. Harmful effects of consuming rancid food. What is corrosion and how it occurs? Ill-effects of corrosion. Corrosion of different metals and alloys. Preventive measures.

What is Rancidity and how it occurs?

Rancidity is a very general term and in its most general meaning, it refers to the spoilage of a food in such a way that it becomes undesirable (and usually unsafe) for consumption.It is characterized by an unpleasant smell and taste. The term “rancid” particularly applies to oils and fats. When food scientists talk about rancidity, they are often talking about a specific type of rancidity Involving oxygen damage to foods, and this type of rancidity is called "oxidative rancidity.”Oxidation of fats (rancidity) is caused by a biochemical reaction between fats and oxygen. In this process the long-chain fatty acids are degraded and short-chain compounds are formed. One of the reaction products is butyric acid, which causes the typical rancid taste.

Factors causing Rancidity

1. Temperature – Rancidity rate increases with increase in temperature.2. Duration – For the more time you keep a thing unattended or without using it, it has more chances to turn rancid.3. Oxygen – Oxygen promotes the decomposition of food.4. Light - In the presence of oxygen, light promotes the decomposition of unsaturated fatty acids.5. Microorganisms and fungi (molds) – They are the most common reason for the food to become rancid . They use their enzymes on the food material and destroy its chemical composition. 6. Moisture - Moist air helps the microbes in their activity upon the food material. 7. Trace elements – Trace elements like Fe and Zn also increase the rate of rancidity.

Some food items that are likely to turn rancid

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- Various Vegetable oils.

- Clarified butter (Ghee).

- Butter

Some food items that are likely to turn rancid

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- Fishes and crustaceans.

- Bread.

- Pickle

Some food items that are likely to turn rancid

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- Baked Potato.

- Shell eggs.

- Meat

Preventive measures

1. Adding Inert gases – Inert gas can be added to the packet or the container like nitrogen, which does not react with oxygen. Example – Chips packets are flushed with nitrogen gas, so they don’t become rancid.

2. Adding antioxidants- Antioxidants are added to some foods to slow down or eliminate oxidative deterioration. Examples-

* BHA – Butylated Hydroxy Anisole.* BHT – Butylated Hydroxy Toluene.

3. Refrigeration – Refrigerators reduce the temperature and hence don’t allow the microbes to continue their processes.

4. Vacuum packaging – Vacuum packaging is done to keep oxygen out.

5. By using oxygen scavengers- Oxygen scavengers or oxygen absorbers are added to enclosed packaging to help remove or decrease the level of oxygen in the package. They are used to help maintain product safety and extend shelf life.

6. Keeping food in air tight containers – Less air too prevents rancidity.

7. By storing food in dark place.

Preventive measures

Ways to prevent rancidity

Using inert gases in packaging

Using oxygen scavengers

Refrigeration

Storing in a dark place

Using air-tight containers

Vacuum packaging

Using anti-oxidants

(BHA, BHT)

Harmful effects of consuming rancid food

Consuming rancid food products is unlikely to cause immediate illness or harm. Rancidification can reduce the nutritional value of food, and some vitamins are highly sensitive to degradation. In addition, rancidification can produce potentially toxic compounds associated with long-term harmful health effects concerning advanced aging and neurological disorders. Rancid fats have also been implicated in increased rates of heart disease, atherosclerosis and are carcinogenic (cancer causing).

Rancid food can cause cancer

Rancid food can cause heart diseases

What is Corrosion and how it occurs?Corrosion is the oxidization of metals in the presence of air(oxygen) and moisture to form compounds of the metals. Corrosion converts refined metal to their more stable oxide. It is the gradual destruction of materials (usually metals) by chemical reaction with their environment. Corrosion can occur in two general ways:Generalized Corrosion: Typically never Happens , aside from in acidic conditions. This uniform corrosion over the entire surface of the metal is rare and leads to overall thinning which has little effect outside of fatigue and stress conditions.Localized Corrosion: The most common, and most detrimental, form of localized corrosion is pitting. Pitting is when the attack happens in one single location on the surface and creates a pit, or small cavity, in the metal. This type of corrosion attack is hard to prevent, engineer against, and often times difficult to detect before structural failure is met due to cracking. Pipes are often compromised due to pitting.

Ill-effects of Corrosion

Losses are economic and safety:• Reduced Strength• Downtime of equipment• Decrease in weight• Lost surface properties• Reduced value of goods

The consequences of corrosion are many and varied and the effects of these on the safe, reliable and efficient operation of equipment or structures are often more serious than the simple loss of a mass of metal. Failures of various kinds and the need for expensive replacements may occur even though the amount of metal destroyed is quite small. 

Corrosion of different metals and alloys

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- Iron (Fe) (Rusting)

- Copper (Cu)

- Silver (Ag)

Corrosion of different metals and alloys

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- Lead (Pb)

- Gold (Au)

- Platinum (Pt)

Corrosion of different metals and alloys

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- Steel

- Brass

- Zinc (Zn)

Preventive measures

1. Painting - Paints can protect metals from the degrading effect of environmental gases.

2. Galvanization – It is the process of applying a protective zinc coating to steel or iron, to prevent rusting. The most common method is hot-dip galvanization, in which parts are submerged in a bath of molten zinc.

3. Electroplating – This helps in avoiding the metal to have a direct contact with the environment.

4. Alloying - Corrosion can also be prevented by making alloys.

5. Anodization – It is a surface treatment which prevents corrosion.

6. Cathodic protection (CP) - It is a technique to control the corrosion of a metal surface by making that surface the cathode of an electrochemical cell.

7. Enameling – It too helps in preventing corrosion.

Preventive measures

Ways to prevent

corrosion

Painting

Galvanization

Alloying

ElectroplatingAnodization

Cathodic Protection

(CP)

Enameling