Welcome to the second week of this mini course, making you familiar with the basics of food science and hopefully igniting a little food science spark in you. Last week was all about introductions. This week will be all about food chemistry basics.
You can follow this course in two ways: the first option is to read the series of 6 blog posts. The second option is to visit my course page and participate in the full course. It’s free, but you get some nice bonuses such as a quiz after each week to test your understanding!
Personally, food chemistry is one of my favorite topics to discuss (which is why we’ll be diving into the topic next week also!). It’s a great way to apply knowledge you’ve learned in chemistry classes to something you can actually see around you.
As you’ve learned in the previous week, food chemistry involves the study of molecules and molecular reactions. In this introduction to food chemistry we’ll try to cover some of the basics that will allow you to further develop your skills in this area. Here’s what:
- Atoms and ‘building’ a molecule.
- Drawing molecules.
- Carbohydrates, proteins and fats.
- Examples, exercises & application.
If you don’t have any chemistry knowledge you should be able to go through this course perfectly fine as well. Don’t worry if something’s not completely clear!
If you have quite some chemistry knowledge already the first few sections might be less interesting. You might want to skip to next week where we’ll be discussing chemical reactions and more complex molecules. Or scroll down to find links to more in-depth posts.
There’s a lot of ground to cover today, so let’s get started!
1. Atoms & Molecules
In order to understand chemistry, you have to understand molecules and in order to understand these, you should start with atoms.
Atoms are the building blocks of molecules. Each and everything in this world is built up of atoms. Chemists discovered that atoms are very important to understand chemical processes so they designed the periodic table in which all of these atoms are represented.
Not even all atoms are known yet, once in a while new atoms are ‘discovered’. However, this mainly involves very large, heavy atoms and aren’t very relevant to food. This great (super fast) song below names them all!
Atoms themselves are again built up of protons and neutrons in the center and electrons floating around (there’s a lot more theory, but there’s no reason to discuss that here). The number of protons in an atom determines which atom it is.
Protons have a positive charge. The electrons have a negative charge and swirl around the center of protons and neutrons. In a neutral atom the number of protons and electrons is equal, thus the atom will not have a charge. When the number of electrons and protons isn’t balanced, the atom is charged. This can be positive or negative and in this case the atom is called an ion.
Electrons are small compared to the protons and neutrons. Electrons are very important in chemical reactions, and also when making molecules. Electrons may be shared between atoms, transferred during reactions or cause a reaction to occur. If there are more electrons than protons the atom has a negative charge. If there are less electrons than protons the charge is positive.
1.2 The most important atoms for food
Atoms in general are abbreviated by one, two or three letters (as you could see in the periodic system movie). It is very helpful to know the most important letters so you can see them coming back in molecules. Within food there is a relatively small number of atoms that is very common. Other atoms might still play a role, but they will be less relevant.
- Carbon (C): this is the building block of most of the molecules we’ll come across in food. It’s important for fats, carbohydrates and proteins. Without carbon most molecules in food cannot be formed.
- Oxygen (O): oxygen is particularly good in participating in all sorts of chemical reactions. Oxygen has quite a lot of electrons available which are often used to attach two molecules to one another or split molecules in pieces.
- Nitrogen (N): this atom is essential for making proteins. Without nitrogen proteins couldn’t be formed. The nitrogen group is also a common place for reactions to take place.
- Hydrogen (H): is probably the most prevalent atom, however, not that interesting in most systems. Hydrogen often ‘fills up’ empty spaces in molecules. You will see that once we discuss acids and bases this is indeed a very important atom!
After the 4 ‘big’ atoms there are a few others worthy to discuss:
- Phosphorus (P) & Sulfur (S): often play an interesting role in protein chemistry.
- Sodium (Na) & Chloride (Cl): you’ve heard about salt which essentially is a combination of these two, thus sodium and chloride!
- Calcium (Ca): an important mineral for your bones.
Molecules are larger structures of atoms which have reacted with one another to form a stable component. Most atoms are not stable by themselves, you will not find a pure oxygen atom in the air, instead, two oxygen atoms will have reacted to form one oxygen molecule (O2). The same goes for hydrogen (H2).
Molecules are represented by showing the letters of the atoms they are built from and using a small subscript number to indicate how many of this atom are present in the molecule (as I did for the oxygen and hydrogen molecules). For chemists these molecular formula are essential to describe the processes they’re studying.
I’ve written a separate post about these formulas to help you understand them, using several examples. Read through this post if you’d like some more background information.
2. Drawing molecules
It’s very helpful to know which atoms are present in a molecule as we did with the molecular formulas. However, that doesn’t tell chemists the complete story. Instead, they also need to know how these atoms are attached to one another. The way the atoms are attached to each other greatly influences the way they will react.
There are molecules which may have the same chemical formula but have a totally different structure and thus structural formula! These can actually react and behave pretty differently, even though they might look similar at first.
2.1 Bonds and structural formulas
It would be far too much to discuss all the aspects of atoms bonding and reacting. Instead we’ll focus on the basics again, more specifically on the 4 most prevalent atoms.
Carbon is great at forming large complex structures. One of the reasons is that one carbon atom can attach itself to up to 4 other atoms. It has four so called bonds. These bonds can each be attached to a different atom, but they can also form double bonds.
Oxygen on the other hand only has two bonds available. Nitrogen has three and hydrogen has only one bond available. Those basic rules can lead to the following possible molecules:
What might be confusing is that chemists are a little lazy. Since there tend to be a lot of carbon and hydrogen atoms, they are often left out. So wherever you see a split of bonds, that’s where a carbon atom sits. For example: the left molecule contains a carbon atom in the center with one bond attached to another carbon, one to a single oxygen atom and two to another oxygen atom. What’s more, chemists tend to leave out all the obvious hydrogen atoms. These are generally those that sit on a carbon atom, but are not at the end of a chain.
2.2 More complex molecules
Drawing molecules is essential when they start becoming larger as there’s no way to see by the chemical formula how the atoms are attached to one another. For even larger molecules (for a lot of proteins this is the case), the molecules become so large and complex that even structural formulas aren’t useful anymore. Other ways of representation have to be used in those cases.
3. Main groups of molecules in food, macronutrients
The three main groups of molecules are the carbohydrates, proteins and fats. These molecules are also called ‘macronutrients’, they are essential for us from a nutritional point of view. The three groups of molecules have very distinct characteristics that will influence how your food will turn out. They play a major role in browning reactions for example as well as flavour development and taste.
Carbohydrates are built from carbon, oxygen and hydrogen atoms. Most carbohydrates can be described by the following chemical formula: CxH2yOy. In other words, the number of hydrogen atoms is twice that of oxygen. The number of carbon atoms does not have to be related to the number of oxygen and hydrogen atoms. (Note, there are a few exceptions to this rule!)
Carbohydrates are also called saccharides. It a different name, for the same group of molecules. When talking about saccharides they are often split up into four groups: monosaccharides, disaccharides, oligosaccharides and polysaccharides. The split is done based on the size of molecules.
Monosaccharides are the smallest carbohydrates, they cannot split to form even smaller saccharides. Glucose and fructose are probably the most well known monosaccharides. Both have the same chemical formula: C6H12O6. Nevertheless, they are built in a slightly different way which makes them react completely different in your body. Glucose will form a ring of 5 C-atoms and 1 O-atoms, the 6th C-atom will form a ‘tail’. Fructose on the other hand forms a ring of 4 C-atoms and 1 O-atom. The other two C-atoms each form a ‘tail’. This difference is caused by the fact that the reactive group of these molecules sits on a different C-atom.
Disaccharides are the next smallest saccharides. They are always built from 2 monosaccarchides. For instance, lactose is made from glucose and galactose. Sucrose (regular table sugar) is made from fructose and glucose.
The next step are the oligosaccharides, they are made from more than 2 monosaccharides, generally 3 to 10. These molecules can often be found in plants, giving them structure. Oligosaccharides often form the fibrous part of a plant.
Last but not least come the polysaccharides. These are huge molecules made up of more than 10 monosaccharides. They can form complex structures, the monosaccharide don’t necessarily form one long chain, instead they can form complex networks. Even though polysaccharides are all made of monosaccharides, they can behave pretty different. A common example of a polysaccharide in food is starch (again consisting of two different polysaccharides: amylose & amylopectin).
Proteins are another main nutrient for us humans with a distinct molecula structure. Unlike carbohydrates, there isn’t a distinction based on the size of the proteins. There are loads of different proteins and they all tend to be huge and highly complex. You won’t often find drawings of proteins using structural formulas. Generally they are greatly simplified, using simple lines and generated using a computer.
When discussing proteins the most important thing is to understand the basic build. This can help explain all sorts of things happening with them. So we will start with the smallest molecule, slowly zooming out.
All proteins are made from amino acids (see below for the basic structure). There are currently 23 known different amino acids (each with a different R-group in the drawing) which, when combined, can create all proteins. Amino acids form proteins by forming one long strand. The OH-group will react with the NH2 group, releasing a water molecule and forming a bond between the two amino acids.
Unlike carbohydrates amino acids will not form complex networks. Each protein is one long chain of amino acids. However, the amino acids along the chain can interact with one another! The side groups of the amino acids (indicated with an R in the formula above) can repel or attract one another. There are a lot of different interactions that can occur. These interactions can cause the strands to fold up, or twirl around into all sorts of three dimensional structures and these again will organize themselves in a specific way.
The overall shape of protein molecules is very important for its biological activity. That shape is determined by how this long strand of amino acids folds and turns itself. This is for instance the case with enzymes, a specific group of proteins. They can catalyze reactions, requiring a very specific 3D structure.
Last but not least: fats. Even though low-fat products can be seen all around, you cannot go without consuming any fats. Fats are just as important for us humans as proteins and carbohydrates are.
Fats belong to a larger group of molecules which are called lipids, fats are a specific subgroup of lipids. All lipids are hydrophobic molecules (they don’t like water). An example of a lipid that is not a fat is cholesterol.
The chemically correct description for fats is: triglycerides. When fats are liquid at room temperature they are commonly called oils. The name triglyceride describes the basic structure of fats: one glycerol molecule, with three fatty acids attached to it (see below).
As was the case with proteins and carbohydrates, there are a lot of different fats. There are a lot of different fatty acids and those again can be combined in a lot of different ways to form different triglycerides!
In the structural drawing of a fatty acid above you can see an A. This A stands for the fact that there can be a lot of different chains starting at this point. The A will always consist of a long chain of carbon atoms. The number of carbon atoms in this chain can vary from only 4 to over 20 carbon atoms.
Another very important characteristic is whether there are so called double-bonds between carbon atoms. As you can see in the image below these double bonds can cause molecules to change direction instead of forming a straight line. Fatty acids without a double bond are called saturated, those with a double bond are unsaturated.
The types of fatty acids present in a triglyceride will determine the properties of the actual fat or oil. One of them is the melting point.
The longer the chain of the fatty acids, the higher the melting point of the fat will be. Smaller molecules can move around more easily so they need a lower temperature to become liquid. The same goes for molecules which have double bonds, if the double bond is of the type that causes the fatty acid to have a kink in is structure it will lower the melting point. Reason being that these kinks make it harder for the fats to structure themselves next to one another.
4. Applying our knowledge
This has all been quite theoretical, unfortunately, if you’re new to the topic, that’s what you’ll need to understand the phenomena you see in your food. But now it’s time to see some knowledge come to life!
After you’ve completed this section head over to this weeks test in which we’ll come back to several topics. Again, tests are fun and I like to ask some questions for which you might have to browse through my website or the internet in general… Want to participate? Sign up for the full course on my course page!
Learn more about a common chemical reaction that can occur in oil: oxidation.
Learn what proteins can do when it comes to browning of fruit.
Gluten are probably one of the most well-known types of proteins, learn more about their role here.