The Chemistry of Food - Part 2

These are some more facts...enjoy !!!!!!!!!!
Here is part 1 of this series

1. Why don’t oil and water mix?

When oil is poured on water, the oil rises to the top and does not mix with the water. A phenomenon called polarity causes these molecules to repel one another. In atoms, the positive electrical charge of the nucleus is balanced by the negative charge of the electrons: as a result, atoms have no net electrical charge. But in molecules, formed when atoms link up, one end of the molecule may have a positive charge and the other a negative charge, resulting in an unequal charge. Molecules possessing this electrical imbalance are said to be polar; molecules with no such imbalance are called nonpolar. Water consists of polar molecules because the oxygen atom has a partial negative charge and the hydrogen atoms a partial positive charge. On the other hand, oil molecules, composed mainly of carbon and hydrogen are nonpolar, because they have the same positive charge everywhere. Polar molecules mix together because their positive and negative regions attract one another. Nonpolar molecules also attract one another but not as strongly. When a polar and a nonpolar substance are mixed together, the mutual attraction of the polar molecules squeezes out the nonpolar molecules, which are also drawn to one another. In this way, two substances remain separate.

2. How does soap remove dirt?

The simple act of washing one’s hands or clothing in soap and water involves chemical interactions at the molecular level. Typically, the dirt in clothes includes both dust from the air and greasy matter from the body. Because water is polar, that means it has a small electrical charge, and oil is non-polar or has no charge, the two substances do not mix, and water alone can’t remove oily dirt. But the soap molecule has both a polar end, known as hydrophilic or water-soluble and a non-polar hydrophobic or non-soluble end .

     Working together the two parts remove dirt. The non-polar hydrophobic ends in the soap molecules absorb, or cling to the non-polar oily dirt molecules. At the same time, the hydrophilic ends completely surround the oily dirt particles, forming sphere-like structures called micelles. The surrounded dirt molecules are held in suspension in the water and prevented from reattaching themselves to the fabric. Rinsing away the soapy water removes the dirt molecules suspended in it.

3. How is drinking water purified?

 The purification of drinking water proceeds in several stages. The first step is sedimentation, in which large particles suspended in the water settle to the bottom. The second is filtration, in which suspended solids and harmful bacteria are strained out. In the third stage, chlorine, a powerful disinfectant, is added to the water to kill the remaining microorganisms.

 Unfortunately, chlorine can give water a bad taste and in large doses can even cause serious health problems. A substitute used in some countries is ozone, a safe, tasteless gas consisting of three oxygen atoms bound together. But because ozone’s germ-killer power does not last long, a tiny amount of chlorine must still be added for long –term disinfection. How ozone  works--- An electrical discharge turns three molecules into two ozone molecules. In water, ozone splits into oxygen atoms and molecules that kill germs.

4. Why is flour cooked?

A major component of flour is starch, which consists of long chains of glucose molecules bound together. When  raw, these chains form a rigid pattern, known as beta-starch, that resists digestion by the body’s enzymes. But when the starch is boiled  with water, or baked as loaf of bread, its crystalline structures begin to break down. Water molecules seep in between the glucose molecules, giving the starch a pastelike consistency called alpha-starch. Since enzymes can break down the alpha-starch, the flour is much easier to digest.

  Unfortunately, alpha-starch returns to the beta-starch stage when the temperature falls and the moisture evaporates. This tendency, known as the aging phenomenon of starch, produces a hard form of beta-starch as in stale bread that is once again difficult to digest.

5. Are all sour food acidic?

Not all sour food can be classified as acidic, even though they may appear to be at first. The lemon, for example, tastes sour and tests highly acidic, but it is classified as a basic or alkaline food. The lemon’s high content of sodium, potassium, calcium and magnesium- substances that, when mixed with water, show up as alkaline in laboratory tests-is the cause for the rating. Conversely, foods that contain substances such as chlorine, phosphorus or sulfur, all of which show acidity when they are mixed with water, are categorized as acidic. Such foods include carrots and spinach.

 To determine if a food is acidic or alkaline, scientists heat it until all that remains are ashes- a process that mimics the digestive process that occurs in humans. Then they dissolve the ashes in water and measure the acidity of the solution, determining its pH value.

The pH value :

 The pH scale which ranges from 0 to 14, upto 7 is neutral. Foods with a low pH value are acidic, while those high values are alkaline. The pH of human blood is 7.4, which is nearly neutral. Milk measures an acid 6.5, oranges 3.5, Ammonia registers an alkaline value of 12.

6. Why foods have different freezing points:

The freezing rates of various foods differ depending on their moisture contents. At –15 degreeC, or 5 degreeF, 93 % of the milk and 88 % of the onion-two foods with a high water content will freeze. At the same temperature, only about 78% of the apple and 73% of the orange and 65% of the banana frozen.

The Chemistry of Food - Part 1

There is obviously great deal of Chemistry present in every steps of food formations. Do you want to know what happens when eggs are boiled and how it gets hard or why ice is hard but ice cream is soft or why oil and water can never be mixed?  Here are some facts chemically :

1. Why does a sliced Apple turn Brown?

An apple that has been cut open, turns brown because molecules called phenols that are in the skin and around the seeds protect apple. When an apple is sliced or peeled, special enzymes take oxygen from the air and combine it with the phenols in the exposed flesh to produce polyphenols. The polyphenols react further with the enzymes and oxygen to create a form of the molecule quinone, which links with other molecules to produce a brown pigment that covers the apple’s exposed flesh. This pigment forms a protective barrier that blocks the advance of harmful oxygen molecules through the apple’s interior.

  

To prevent a cut apple fron turning brown, it must be kept from oxygen in the air. Dipping slices in water is the simpliest solution. Coating the exposed surfaces with vitamin C , found in products such as lemon juice , or adding vitamin C in the water. Since the vitamin reacts faster with oxygen than the phenols do, the brown pigment does not form and the apple stays white. 

2. Why does instant coffee dissolve?

 

 There are two ways to make instant coffee: the freeze-dry method and the spray-dry method. Both start identically as coffee beans water to produce a concentrated liquid.

In the freezing method----(1) The liquid is frozen at a temperature of –40degreeC or –40degreeF. The temperatures turn brewed coffee into a hard mass resembling a chocolate bar. This solid is then broken down into fine granules. (2) The frozen coffee granules are riddled with ice, which is removed in the drying chamber.  (3) The reduced pressure in the drying chamber causes the ice in the coffee particles to sublime. What remains are porous granules of  instant coffee.

  In the hot air or spray dry process---(1) the concentrated coffee passes through a steam of hot air. The coffee’s water instantly evaporates.  (2) The evaporating water leaves behind particles of pure coffee, which combine into larger granules.

Instant coffee dissolves quickly because its crystals are shot through with small holes. When water comes in contact with the crystals, it quickly seeps into these holes, dissolving the crystals from the inside as well as the outside. 

3. Why is ice cream softer than ice?

Although ice cream contains a lot of water, it retains a fairly soft consistency at 0 degree C, or 32 degree F.- the temperature at which water freezes. The secret to ice cream’s smooth consistency lies in the nature of its ingredients and the way they are combined.

 To make ice cream, the ingredients - which include milk, cream, eggs and other substances- are stirred together with sugar in a special freezer. At first only the water in the ingredients freezes, leaving particles of fat in liquid form. But as the stirring continues and the temperature decreases, tiny air bubbles become trapped in the mixture. These air bubbles, as well as the globules of fat, help separate the ice crystals, preventing the ice from forming large chunks that would turn the ice cream solid.

  Some people like to make their own ice cream, using special home freezers. The ingredients are placed in a freezing chamber that is surrounded by salt and cracked ice to produce the necessary low temperatures. Then the mix is stirred by a special “dasher” that is driven by a hand crank or by an electric motor. Since a small machine can not stir the ingredients as thoroughly as industrial ice cream makers, the homemade product usually contains less air and is not as smooth as commercial brands.

4. How is Yoghurt made?

In the days before refrigeration and modern processing of milk, early nomadic herdsman searched for a way to preserve milk and transport it without spilling. Their solution was to ferment milk, a process that turns it into semisolid yoghurt. Today yoghurt is still valued because it is easy to digest and refreshing as a snack.

    The yoghurt making process begins when raw milk is pasteurized, or heated to 82 degree C.  or 180 degree F . to kill any bacteria that may live in it. A yoghurt culture is added to the pasteurized milk, and the mixture is incubated at temperatures between 37 and 45 degree C, or 100 and 113 degree F, which converts the milk’s natural sugars to acids, or ferments it. The newly formed acids connects the milk’s protein chains into large, complex networks, turning liquid milk into tart yoghurt.

 Other foods produced from fermented milk include sour cream, Cheese and buttermilk.

 

 The two stages of yoghurt formation:  Yoghurt forms in two stages. In first step, bacteria break sugars down into acids that raise the milk’s acidity. The second step begins as the milk’s increasing acidity induces protein molecules to form bulky bridge like structures, and the milk takes on the familiar semisolid form of yoghurt.

5. Why do boiled eggs become hard?

The liquid interior of a raw egg hardens when boiled in water because the water’s intense heat changes the structure of the egg’s proteins. At room temperature, the protein strands are tightly folded in a complex three-dimentional configuration. But at higher temperatures the strands loosen up, and as they unravel, their ends become exposed. These ends bond with other protein strands, fastening the individual proteins into a mesh that turns the egg solid.

  Because the protein structures of egg yolk and egg white vary slightly, they harden at different temperatures. Up to 60 degree C or 140 F, there is little change in either yolk or white. But above that temperature, the white part of the egg begins to resemble a semitransparent jelly. The yolk gets somewhat sticky at 65C or 149F and starts to harden at 70C or 158F. At this temperature, the egg becomes soft boiled. The white hardens fully at 80C or 176F and 85C or 185F, both yolk and white are hard boiled.

6. How are food preserved?

Food spoils for two main reasons. In fruits and vegetables, the neutral ripening process- caused by continued cellular respiration after the food is picked- can proceed too far, producing overripe, inedible food. Or, in a process that affects all foods, microorganisms that include bacteria, molds, and yeasts can attack the food and cause it to rot. Over the millennia scientists and cooks have developed a number of preserving methods that successfully delay or prevent these two processes.

    Because food-spoiling microorganisms thrive only under specific conditions that include oxygen , moisture and warm temperatures, it is possible  to destroy the organisms by altering these conditions. Storing food at low temperatures or sterilizing it with heat  delays spoilage. Other methods of preservation-either by vacuum-packing the food or storing it with some carbon dioxide – minimize exposure to oxygen, which causes overripening  and fosters bacterial growth.  Sealing food off from air – a process known as vacuum-packing- isolates the food both oxygen and microorganisms. Foods that are preserved by this method keep their taste and aroma for a long time. Still other techniques include drying food and preserving it with salt and sugar. These are used to draw moisture from foods. The lower a food’s water content, the harder  it is for bacteria to survive in it.

    Another way is to freeze the food. Freezing puts foods in a kind of suspended animation. Cellular respiration and overripening stop, and the cold arrests the growth of bacteria.