Central Department Of Chemistry

Central Department Of Chemistry
Me at Central Department of Chemistry(CDC), Kirtipur, Kathmandu, Nepal

Tuesday, January 13, 2015

What affects the color of meat?

In our daily life, when we go to the grocery or meat shop, we see that some meat is red whereas some meat is pale. What causes the change in color of meat? Actually, the muscle that are frequently used are red where as those infrequently used are pale in color. We can notice that the leg meat of chicken is darker and the breast meat is white. The different colors of meat reflect the concentration of myoglobin in the muscle tissue.
What is myoglobin?
Myoglobin is the globular protein that functions as an oxygen storage in muscles. Myoglobin is a monomer whereas hemoglobin is a tetramer. That is, myoglobin consists of a single peptide chain and a heme unit, and hemoglobin has four-peptide chains and four heme units. Thus only one oxygen molecule can be carried by a myoglobin molecule. Myoglobin has a higher affinity for oxygen than does hemoglobin. Thus, transfer of oxygen from hemoglobin to myoglobin occurs readily. Oxygen stored in myoglobin molecules serves as a reserve oxygen source for working muscles when their demand for oxygen exceeds that which can be supplied by hemoglobin.
 The meat that humans eat is composed primarily of muscle tissue. The major proteins present in the muscle tissue are myosin and actin, which lie in alternating layers and which slide past each other during muscle contraction. Contraction is temporarily  maintained through interactions between these two types of proteins.
Structurally, myosin consists of a rod like coil of two alpha helices (fibrous protein) with two globular protein  heads. The head portions of myosin interact with the actin.
Structurally, actin has the appearance of two filaments spiraling about one another. Each circle in the structural diagram represents a monomeric unit of actin (called globular actin). The monomeric actin units associate to form a long polymer (called fibrous actin). Each identical monomeric  actin unit is a globular protein containing many amino acid residues.
The chemical process associated with muscle contration ( interaction between myosin and actin)  requires molecular oxygen. The oxygen storage protein myosin is the oxygen source. The amount of myoglobin present in a muscle is determined by how the muscle is used. Heavily used muscle require larger amount of myoglobin than infrequently used muscles require.
The amount of myoglobin present in muscle tissue is a major determiner of the color of the muscle tissue. Myoglobin molecules have a red color when oxygenated and a purple color when deoxygenated. Thus, heavily worked muscles have a darker color than infrequently used muscles.
The different colors of meat reflect the concentration of myoglobin in the muscle tissue. In turkeys and chickens, which walk around a lot but rarely fly , the leg meat is dark, the breast meat is white.  On the other hand, the flying birds have dark breast meat.
Fish have lighter flesh than the land animals and birds because they do not need to support their own weight (supported by water) while moving/swimming.  This reduces the need for myoglobin oxygen support.    The fish that spend most of their time lying on the bottom of a body of water have lightest meat.
Why meat turns brown in cooking?
Meat, when cooked, turns brown as a result of changes in myoblobin structure caused by the heat; the iron atom in the heme unit of myoglobin becomes oxidized. When meat is salted with preservatives (NaCl, NaNO2 etc.) the myoglobin picks up nitrite ions, and its color changes to pink.

Sunday, November 23, 2014

How to make Chemistry an interesting Science?

Chemistry is often described as the Central Science, highlighting its importance to numerous scientific disciplines, such as Biology, Biomedical and Chemical Engineering, Forensics, Geosciences, Materials Science, Toxicology and many more. It is the study of the structure and transformation of matter. It.is very difficult to say when the documentation of chemistry began from. When Aristotle wrote the first systematic treatises on chemistry in the 4th century BCE, his conceptual grasp of the nature of matter was tailor
ed to accommodate a relatively simple range of observable phenomena. In the 21stcentury, chemistry has become the largest scientific discipline, producing over half a million publications a year ranging from direct empirical investigations to substantial theoretical work.
Why study Chemistry? Many students take this question in mind when they feel difficult in the beginning phase. Well, understanding chemistry helps you to understand the world around you. Cooking is chemistry. Everything you can touch or taste or smell is a chemical. When you study chemistry, you come to understand a bit about how things work. Chemistry isn't secret knowledge, useless to anyone but a scientist. It's the explanation for everyday things, like why laundry detergent works better in hot water or how baking soda works or why not all pain relievers work equally well on a headache. If you know some chemistry, you can make educated choices about everyday products that you use.
This central science has certain difficulties among the beginners of chemistry. Let’s call them as pitfalls in Chemistry. The pitfalls in chemistry can be outlined in different headings. New words and new symbols are the first thing beginners usually trip of. If misunderstanding these new words and symbols is not addressed, it is very difficult to survive. Its effects are immediate and is the usual reason people give up on their exploration of chemistry. The remedy is to find those words or symbols and get a good explanation or definition for them. When looking up the meaning of words, it’s better to try to find the origin of the word and try to understand the words in a funny manner.
The second pitfall is learning without having enough reality on the subject. This means the student only have an abstract or vague familiarity with the subject. The initial reaction to a misunderstood word or symbol is that the mind goes blank. This is my own experience. Have you ever been reading a book and got to the bottom of the page and realized you don’t remember a word you just read? I have witnessed students reading a paragraph out loud, and when they came to a misunderstood word, they skipped right over it and didn't even realize that they had skipped it. Their mind just went blank when they saw it. If that happens to you when studying chemistry, back up and find the misunderstood word or symbol. Perhaps it will work.
The third pitfall is "jumping in over your head;" in other words, you move too fast by tackling difficult tasks without first mastering the simpler tasks. The symptoms may be feeling irritated, impatient and distracted. This is also the sequential cause of misunderstood words and/or misunderstood symbols. Once the mind disconnects from the subject matter due to misunderstood words, students find themselves growing more impatient, irritated, or distracted. Even little things annoy them. If this happens, go back and find the misunderstood words and learn their meanings. Furthermore, try to learn interesting facts about chemistry. They create interest in the subject matter. Do you know, lightning strikes produce O3, which is ozone, and strengthen the ozone layer of the atmosphere? Although oxygen gas is colorless, the liquid and solid forms of oxygen are blue. The human body contains enough carbon to provide 'lead' (which is really graphite) for about 9,000 pencils. One bucket full of water contains more atoms than there are bucket fulls of water in the Pacific Ocean. Is it amazing? Catch up chemistry you will feel amazed every day!

Saturday, November 1, 2014

Garlic: Chemistry behind Antibiotic Nature and Uses

Garlic is extensively used in the kitchen world-wide. It is an herb. Now-a-days the price of garlic is sky-rocketing not only in South Asia but as a whole in this world. When I was in my college life, I used to wonder why this bad smelling stuff has high price in comparison to other vegetables. Later, I found that it was a natural antibiotic! Amazingly, garlic can kill the antibiotic resistant Staphylococus aureus and Salmonella enteritidis too. Here, I have posted the chemistry behind its antibiotic property and its medicinal uses.
Research has identified four major chemical compounds in garlic viz. diallyl disulfide, allyl methyl sulfide, allyl mercaptan, and allyl methyl disulfide. Sulfur-containing compounds are involved in the antibacterial properties of garlic. Researchers tested these compounds on a type of bacteria found in animal faeces (E.coli), one of the most common bacterial causes of gastroenteritis, and found that the anti-microbial activity of the compounds increased with the number of sulfur atoms present; diallyl trisulfide being the most effective, followed by diallyl disulfide, then diallyl sulfide. These compounds are effective as they can penetrate the cell membranes of bacteria cells, and cause changes in structure in thiol (-SH) containing enzymes and proteins, injuring the cell.
Garlic is best known as a flavoring for food. Some scientists have suggested that it might have a role as a food additive to prevent food poisoning. But over the years, garlic has been used as a medicine to prevent or treat a wide range of diseases and conditions. Garlic is used for many conditions related to the heart and blood system. These conditions include high blood pressure, high cholesterol, coronary heart disease, heart attack, and “hardening of the arteries” (artherosclerosis). Some of these uses are supported by science. Garlic actually may be effective in slowing the development of atherosclerosis and seems to be able to modestly reduce blood pressure. Some people use garlic to prevent colon cancer, rectal cancer, stomach cancer, breast cancer, prostate cancer, and lung cancer. It is also used to treat prostate cancer and bladder cancer.

Garlic has been tried for treating an enlarged prostate (benign prostatic hyperplasia; BPH), diabetes, osteoarthritis, hay fever (allergic rhinitis), traveler's diarrhea, high blood pressure late in pregnancy (pre-eclampsia), cold and flu. It is also used for building the immune system, preventing tick bites, and preventing and treating bacterial and fungal infections.

Other uses include treatment of fever, coughs, headache, stomach ache, sinus congestion, gout, rheumatism, hemorrhoids, asthma, bronchitis, shortness of breath ,low blood pressure, low blood sugar, high blood sugar, and snakebites. It is also used for fighting stress and fatigue, and maintaining healthy liver function.

Some people apply garlic oil to their skin to treat fungal infections, warts, and corns. There is some evidence supporting the topical use of garlic for fungal infections like ring worm, jock itch, and athlete’s foot; but the effectiveness of garlic against warts and corns is still uncertain.

Sources: WHO, WebMed

Sunday, October 19, 2014

Microwave Ovens & Public Health

Microwave ovens are tremendously used in the kitchen. Though, its use in urban area of Nepal is relatively low due to the uneven schedule of load shedding. Many people have misconceptions that the food cooked with microwaves are as hazardous as the radio active elements. But actually it is not so. Food cooked with microwave ovens are safer to eat,condition is that proper handling of the oven and food is must.

                                                                                Fig: Microwave oven


Microwaves are high frequency radio waves (radiofrequency fields) and, like visible radiation (light), are part of the electromagnetic spectrum. Microwaves are used primarily for TV broadcasting, radar for air and sea navigational aids, and telecommunications including mobile phones. They are also used in industry for processing materials, in medicine for diathermy treatment and in kitchens for cooking food.
Microwaves are reflected, transmitted or absorbed by materials in their path, in a similar manner to light. Metallic materials totally reflect microwaves while non-metallic materials such as glass and some plastics are mostly transparent to microwaves.

Materials containing water, for example foods, fluids or tissues, readily absorb microwave energy, which is then converted into heat. This Information Sheet discusses the operation and safety aspects of microwave ovens used in the home. More details about the nature of electromagnetic fields and health effects of radiofrequency and microwave fields are available in WHO Fact Sheets 182 and 183.


When used according to manufacturers' instructions, microwave ovens are safe and convenient for heating and cooking a variety of foods. However, several precautions need to be taken, specifically with regards to potential exposure to microwaves, thermal burns and food handling.
Microwave safety: The design of microwave ovens ensures that the microwaves are contained within the oven and can only be present when the oven is switched on and the door is shut. Leakage around and through the glass door is limited by design to a level well below that recommended by international standards. However, microwave leakage could still occur around damaged, dirty or modified microwave ovens. It is therefore important that the oven is maintained in good condition. Users should check that the door closes properly and that the safety interlock devices, fitted to the door to prevent microwaves from being generated while it is open, work correctly. The door seals should be kept clean and there should be no visible signs of damage to the seals or the outer casing of the oven. If any faults are found or parts of the oven are damaged, it should not be used until it has been repaired by an appropriately qualified service engineer.

Microwave energy can be absorbed by the body and produce heat in exposed tissues. Organs with a poor blood supply and temperature control, such as the eye, or temperature-sensitive tissue like the testes, have a higher risk of heat damage. However, thermal damage would only occur from long exposures to very high power levels, well in excess of those measured around microwave ovens.

Thermal safety: Burn injuries can result from handling hot items heated in a microwave oven, in the same way as items heated using conventional ovens or cooking surfaces. However, heating food in a microwave oven presents some peculiarities. Boiling water on a conventional stove allows steam to escape through bubbling action as the water begins to boil. In a microwave oven there may be no bubbles on the walls of the container and the water will super-heat and may suddenly boil. This sudden boiling may be triggered by a single bubble in the liquid or by the introduction of a foreign element such as a spoon. People have been severely burned by super-heated water.

Another peculiarity of microwave cooking relates to the thermal response of specific foods. Certain items with non-porous surfaces (e.g. hotdogs) or composed of materials that heat at different rates (e.g. yolk and white of eggs) heat unevenly and may explode. This can happen if eggs or chestnuts are cooked in their shells.

Food safety: Food safety is an important health issue. In a microwave oven, the rate of heating depends on the power rating of the oven and on the water content, density and amount of food being heated. Microwave energy does not penetrate well in thicker pieces of food, and may produce uneven cooking. This can lead to a health risk if parts of the food are not heated sufficiently to kill potentially dangerous micro-organisms. Because of the potential for uneven distribution of cooking, food heated in a microwave oven should rest for several minutes after cooking is completed to allow the heat to distribute throughout the food.

Food cooked in a microwave oven is as safe, and has the same nutrient value, as food cooked in a conventional oven. The main difference between these two methods of cooking is that microwave energy penetrates deeper into the food and reduces the time for heat to be conducted throughout the food, thus reducing the overall cooking time.

Only certain microwave ovens are designed to sterilize items (for example baby’s milk bottles). The user should follow the manufacturer's instructions for this type of application.

Misconceptions: To dispel some misconceptions, it is important to realize that food cooked in a microwave oven does not become "radioactive". Nor does any microwave energy remain in the cavity or the food after the microwave oven is switched off. In this respect, microwaves act just like light; when the light bulb is turned off, no light remains.


Domestic microwave ovens operate at a frequency of 2450 MHz with a power usually ranging from 500 to 1100 watts. Microwaves are produced by an electronic tube called a magnetron. Once the oven is switched on, the microwaves are dispersed in the oven cavity and reflected by a stirrer fan so the microwaves are propagated in all directions. They are reflected by the metal sides of the oven cavity and absorbed by the food. Uniformity of heating in the food is usually assisted by having the food on a rotating turntable in the oven. Water molecules vibrate when they absorb microwave energy, and the friction between the molecules results in heating which cooks the food.

Unlike conventional ovens, microwaves are absorbed only in the food and not in the surrounding oven cavity. Only dishes and containers specifically designed for microwave cooking should be used. Certain materials, such as plastics not suitable for microwave oven, may melt or burst into flames if overheated. Microwaves do not directly heat food containers which are designed for microwave cooking. These materials usually get warm only from being in contact with the hot food.

Oven manufacturers do not recommend operating an empty oven. In the absence of food, the microwave energy can reflect back into the magnetron and may damage it.

Microwave oven users should carefully read and comply with the manufacturer’s instructions because new ovens vary widely in design and performance. While most modern ovens can tolerate some food packaging made of metal, oven manufacturers generally recommend not placing metal in the oven, particularly not close to the walls, as this could cause electrical arcing and damage the oven walls. Also, because metal reflects microwaves, food wrapped in metal foil will not be cooked, while food not in metal wrap may receive more energy than intended, causing uneven cooking.


Several countries, as well as the International Electrotechnical Commission (IEC), the International Committee on Electromagnetic Safety (ICES) of the Institute of Electrical and Electronics Engineers (IEEE) and the European Committee for Electrotechnical Standardization (CENELEC), have set a product emission limit of 50 watts per square metre (W/m2) at any point 5 cm away from the external surfaces of the oven. In practice, emissions from modern domestic microwave ovens are substantially below this international limit, and have interlocks that prevent people being exposed to microwaves while the oven is on. Moreover, exposure decreases rapidly with distance; e.g. a person 50 cm from the oven receives about one one-hundredth of the microwave exposure of a person 5 cm away.

These product emission limits are defined for the purpose of compliance testing, not specifically exposure protection. The International Commission on Non-Ionizing Radiation Protection (ICNIRP) has published guidelines on exposure limits for the whole EMF part of the spectrum. Exposure guidelines in the microwave range are set at a level that prevents any known adverse health effect. Exposure limits for workers and for the general public are set well below levels where any hazardous heating occurs from microwave exposure. The emission limit for microwave ovens mentioned above is consistent with the exposure limits recommended by ICNIRP.

Source: WHO

Tuesday, May 27, 2014

Nepal Chemical Society (NCS) aims to organize Conference on Advanced Materals and Nanotechnology

Nepal Chemical Society (NCS), an association of all Chemistry Professionals of Nepal is going to organize an "International Conference on Materials and Nano-Technology" on 4-6 November 2014 in Kathmandu, Nepal. NCS organizes different programs in certain intervals of time.  The society is dedicated to contribute for the overall progress and prosperity of nation by promoting the research activities and capabilities as well as the quality chemical education of the country. According to NSC executive member Ram Chandra Kandel, the conference is the continuation of International Conference on Advanced Materials and Nano- Technology (ICAMN) for Sustainable Development, 2011.

Current president of NCS is Dr. Deba Bahadur Khadka. He had been elected as president along with 11 executive members by more than thousands of members recently.

Any query about the conference can be directed to the President of NCS. He can be contacted directly at: khadkadeba@yahoo.com.

Sunday, May 11, 2014

How Sugar is produced from Sugarcane?

Most of we in our childhood might have wondered about the production of sugar from sugarcane. Moreover than production we wonder how fine crystals might have formed. Sugar (chemically sucrose) is produced mainly from sugarcane. Beside sugarcane, sugar beats and other chemical synthesis can be utilized for the manufacture.

Fig: Sugarcane
Sugarcane is traditionally refined into sugar in two stages. In the first stage, raw sugar is produced by the milling of freshly harvested sugarcane. In a sugar mill, sugarcane is washed, chopped, and shredded (tear into narrow pieces) by revolving knives. The shredded cane is mixed with water and crushed. The juices (containing 10-15 percent sucrose) are collected and mixed with lime to adjust pH to 7, prevent decay into glucose and fructose, and precipitate impurities. The lime and other suspended solids are settled out, and the clarified juice is concentrated in a multiple-effect evaporator to make a syrup with about 60 weight percent sucrose. 

What is multiple-effect evaporator?

A multiple-effect evaporator, invented by American Engineer Norbert Rillieux, is an apparatus for efficiently using the heat from steam to evaporate water. In a multiple-effect evaporator, water is boiled in a sequence of vessels, each held at a lower pressure than the last. Because the boiling temperature of water decreases as pressure decreases, the vapor boiled off in one vessel can be used to heat the next, and only the first vessel (at the highest pressure) requires an external source of heat.

The syrup is further concentrated under vacuum until it becomes supersaturated, and then seeded with crystalline sugar. Upon cooling, sugar crystallizes out of the syrup. Centrifuging then separates the sugar from the remaining liquid (molasses). Raw sugar has a yellow to brown color. Sometimes sugar is consumed locally at this stage, but usually undergoes further purification. Sulfur dioxide is bubbled through the cane juice subsequent to crystallization in a process, known as "sulfitation". This process inhibits color forming reactions and stabilizes the sugar juices to produce “mill white” or “plantation white” sugar.

The fibrous solids, called bagasse, remaining after the crushing of the shredded sugarcane, are burned for fuel, which helps a sugar mill to become self-sufficient in energy. Any excess bagasse can be used for animal feed, to produce paper, or burned to generate electricity for the local power grid.

Fig: Flow chart of refining of Sugar from Sugarcane (source: www.wikipedia.org)