Food Fundamentals

How We Categorize Food?

When categorizing food, what do you think of, or how might you categorize it?  Perhaps the ingredients, physical state of matter (i.e. Solid, liquid, gel, etc.), texture, the food pyramid, or where it might be found in a grocery store.  There are hundreds if not thousands of ways to categorize food.  Food is highly complex meaning that foods are typically not one pure substance, but instead mixtures of various substances.

There are 4 main categories of food: water, fats/oils, carbohydrates, and proteins.

1) Water

The one thing that almost all food has in common is that they all contain some % of water.  Just as water is vital to our survival, it is also a vital part of many foods.

2) Fats/Oils

Fats are a necessary part of our diet.  In addition, fats give our foods a nice comforting flavor along with a nice textures that are appealing to our sense of taste.

3) Carbohydrates

Carbohydrates give us energy!  In addition, carbohydrates give our food specific flavors, textures, and structures.

4) Proteins

Proteins are a complex network of small building blocks called amino acids.  There are 20 different amino acids which are responsible for the browning reactions of meats that generate the various and distinct flavors.

Wonderful Water Works

The one thing that almost all food has in common is that they all contain some percentage of water.  Just as water is vital to our survival, it is also a vital part of many foods.  Even sugar, a substance that appears to be a crystalline solid has a very small percentage of water in it.  Have you ever come across clumps in your white granulated sugar? Well that’s from individual sugar crystals absorbing moisture from the air and essentially fusing or sticking with one another to form hard clumps.

The formula for water is H2O with the following chemical structure where red represent oxygen and white represents hydrogen:

http://z.about.com/d/chemistry/1/G/U/a/water.jpg

http://z.about.com/d/chemistry/1/G/U/a/water.jpg

Since oxygen has more desire for electrons (higher electronegativity) than hydrogen, there will be more of a negative charge on the oxygen than the hydrogen.  In addition, the structure of water forms a V or bent shape which also contributes to a more negative charge on the oxygen.  This all results in what is called a polar molecule.  This polarity allows various contaminants (such as E. coli, cryptosporidium, and other bacterium) along with ions (atoms that have lost or gained electrons to result in charged particles) to become attracted to the water molecules and essentially form bonds with the water. Therefore,  before water leaves municipal water treatment facilities, it goes through various filtering processes including sedimentation and chlorination along with pH readjustment, which will remove the majority of contaminants and make the water, in most cases, safe to drink.  However, any contaminants and ions that are smaller than one micron in size might still be in the water once it reaches your home.

I use Brita disposable water filters.  Such filters contain activated charcoal and ion-exchange plastic beads.  Activated charcoal is carbon that has been processed into very small powder like particles that contain very large surface area.  This allows for the maximum absorption of contaminants that are smaller than one micron in size resulting in water that is clearer in color and lacks any odor.

The ion-exchange beads that are present in Brita water filters remove the ions in water that are responsible for hard water.  Calcium and magnesium are positively charged ions that bond to the negatively charged ends of water molecules.  These ions will combine with organic materials to precipitate out of the water to give the calcium deposits seen on shower heads and the soap scum that accumulates in showers.  The picture below shows the build up of calcium carbonate on a faucet:

http://i.ehow.com/images/GlobalPhoto/Articles/5224631/limescale-main_Full.jpg

http://i.ehow.com/images/GlobalPhoto/Articles/5224631/limescale-main_Full.jpg

These ion-exchange beads will supply the water with a surplus of sodium or potassium ions bonded to organic chains which will readily replace the calcium and magnesium ions with the positively charged sodium or potassium ions.  These sodium and potassium ions don’t have the hardening ability that calcium and magnesium have.

The Favorites: Fats and Oils

Lets first look at the chemical structure of fats, or better known as triglycerides.  First, fats are formed through a chemical reaction called esterification.  Essentially, a glycerol molecule with three active hydroxyl groups present on it will bond with three fatty acid chains which consist mainly of carbon-carbon and carbon-hydrogen bonds as represented by the letter R below along with a reactive carboxyl group.  The three fatty acid chains will form ester bonds in place of the 3 hydroxyl groups on the glycerol to form a triglyceride.

In some cases, instead of 3 fatty acids bonding with the glycerol, only 2 or 1 fatty acid(s) will bond which forms what is called a diglyceride or a monoglyceride.

As mentioned above, the fatty acid chains contain long chains consisting carbon-carbon (C-C) bonds which may contain single or double bonds.  A saturated fatty acid chain contains only single C-C bonds while an unsaturated fatty acid chain contains at least one (monounsaturated) or more (polyunsaturated) double C=C bonds.  Saturated fatty acid chains nicely zipper with each other (or line up), while the double bonds in the unsaturated fatty acid chains results in a kinks and less of a zippering effect.

http://web.virginia.edu/Heidi/chapter8/Images/8883n08_01.jpg

In order to transport fats in our bodies, the liver wraps fats in water soluble proteins.  If these bundles contain little fat and are small and dense, they are called high-density lipoprotein (HDL) which is good for our health.  However, these bundles can also contain a lot of fat in a large and less dense bundle, and these are called low-density lipoproteins (LDL) which are not good for our health.   Now, monounsaturated fats have been found to lower our levels of LDLs without lowering the levels of HDLs which in turn is better for our health.  However, one has to be careful about what type of monounsaturated fats he/she is eating because some can act like saturated fats in our bodies and potentially raise LDL levels.  In addition, some saturated fats can act like monounsaturated fats in our bodies and again help us by lowering our levels of LDLs.  Therefore, we can no longer claim that all saturated fats are bad for us while all monounsaturated fats are good.

When cooking with fats, people want to consider the melting point, chemical composition (saturated, unsaturated), healthiness, and smoking point.  When stir or deep frying, one should use peanut oil over other oils/fats.  Peanut oil is composed of a large percentage of long unsaturated fatty acid chains which results in a high smoke point meaning that the fat wont decompose until it reaches very high temperatures above 450oF.  Olive oil in comparison has shorter fatty acid chains which results in it having a lower smoking point of 375oF.  In addition, the unsaturated fats in peanut oil may indeed be better for us since they might lower our LDLs without lowering our HDLs.  Lastly, peanut oil has 46% monounsaturated and 32% polyunsaturated fats which means that it will be less likely to oxidize with the oxygen in air (i.e. go rancid) as it would if the fat had a higher percentage of polyunsaturated fats.  During the process of oxidization, the oxygen in air will react with hydrogen along with the electron that are bonded with the carbon which is alpha to a double C=C bond.  This leaves an unstable extra electron (radical) on the alpha carbon in fatty acid chain which makes the chain unstable and results in the fat going rancid.  Therefore, since peanut oil has a larger ratio of mono- than poly-unsaturated fats, it is less likely to go rancid in comparison to for instance corn oil which has 59% polyunsaturated and only 25% monounsaturated fats.

What types of fats should be used to make an emulsification (i.e. salad dressing )?  In this case, the oil/fat you would like to use would be a diglyceride or a monoglyceride.  The hydroxyl positions of the glycerol become occupied with other polar groups of atoms.  In this case, the fatty acid chains are fairly non-polar (even distribution of charge within the molecule) since they consist of just C-C bonds while the other position(s) of the glycerol are polar.  Therefore, the polar heads of the diglyceride or monoglyceride are soluble in water (since both are polar) while the fatty acid chains are soluble in the fairly non-polar fats.  Therefore, the diglyceride or monoglycerides serve as emulsifiers which allow the fat and water to fix.

Curious Carbohydrates

Carbohydrates consist of carbon, hydrogen, and oxygen typically in a 1:2:1 ratio.  It is rare that you find a food that is purely made out of carbohydrates.  For instance, fruits, vegetables, potato starch, and for the most part candy is just carbohydrates.  There are two types of carbohydrates, those that are simple and those that are complex.  Simple carbohydrates, such as fructose and glucose are used in our bodies for instant energy and are responsible for diabetes.  On the other hand, those that are more complex, such as starch (amylose which is straight chained and amlyopectin which is branched) provide our bodies with longer lasting energy.

Carbohydrates give our food structure, flavor and texture.   Simple carbohydrates provide a sweet taste while those that are more complex tend to provide a blander taste.  Various carbohydrates will also combine with water differently to provide samples of different structure and texture.   

Experiment to determine relationship between carbohydrates and structure/texture!!!

1)      Try this at home…in a bowl mix corn starch and some cold water (approximately in a 2:1 ratio).        Corn starch has a structure similar to amylose, or straight chain of glucose molecules.  Once you have mixed the corn starch and water, try to form a ball out of the mixture, or try to punch your fist into the bowl.  Play with it and take note of its physical properties!

Check out this video where two guys made a pool filled with a mixture of corn starch and water…

2)      Make a mixture of potato starch and hot/boiling water.  Potato starch, which has more of a branched amlyopectin structure, will combine with boiling water to yield a gel like substance.   This gel is formed from water getting trapped within the solid matrix.  The hydroxyl groups present on the carbohydrate allow for hydrogen bonding which results in the formation of a complex network of bonds between carbohydrates that lump together and trap water inside.

Proteins with a Purpose

Proteins are a complex network of small building blocks called amino acids.  There are 20 different amino acids which are responsible for the browning reactions of meats that generate the various and distinct flavors.  The actual structure of the proteins varies depending on water sequence of amino acids is present to form helices or sheets/folds.  The solubility of proteins in water rich environments varies based on the type of amino acids are present in the protein which dictate the type and strength of chemical bonds.

There are 3 different types of tissues in meats, poultry, and fish: muscle cells, connective tissue, and fat cells.  As the animal grows, the number of fibers and muscle cells stay the same but just mature and grow in size.  Therefore, the meat of older animals is tougher than that of younger animals.   In addition, where the meat is harvested from an animals body is directly related to the type of muscle fibers present and the texture of said fibers.  Animals that are raised in confined spaces and receive little exercise tend to produce more tender muscle fibers with less complex fiber networks.  As muscle fibers bulk up so does the connective tissue (which consists mainly of molecules and not living cells).  Connective tissues will soften with cooking unlike muscle fibers.  Fat tissue is mainly present to store energy and add some extra flavor and softening effect to the texture of the meat as it cooks.

Meats, poultry, and fish have their own various tastes and textures which are directly related to their living environments and how they are harvested according to the demands of the general populous.  Birds and chicken in particular served as an economically favorable alternative to larger meat producing animals.  Chickens can grow 4 lbs in 6 weeks off of only 8 lbs of feed.  Fish were a healthy alternative to meats and even birds because many fish have very low fat content.  However, fish tend to harbor industrial toxins that have been disposed of into water, biological toxins, and disease causing microbes and parasites.  The toxins need to be cleaned from the fish thoroughly before consumption.  The parasites can be killed by simply freezing or cooking the fish.

Meats, poultry, and fish can either be cooked or preserved.  When meats, poultry, or fish are cooked, the protein molecules denature or unfold from their natural state and coagulate to produce the opaque color that you see in for instance eggs.

http://cdavies.files.wordpress.com/2008/03/egg-protein-coagulation-5-in-width.jpg

In cooking older or tougher meat, poultry or fish, it is best to cook the muscle fibers for a long time at low heat.  This acts to tenderize the fibers.  Since proteins are so delicate, one can also cook with an acid and produce a ceviche.  Instead of cooking meat, poultry, or fish, people choose to freeze them or preserve them by drying them with salt.  When you freeze any meat, poultry, or fish, the water molecules present will expand and rupture the actual muscle cells which may have a negative effect on the texture of the final cooked product.  You can also create an environment high in dry air and salt to rid the meat, poultry or fish of all water molecules thus preventing bacterial growth without altering the actual chemical properties of the proteins.

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