Food is a place full of chemistry. Chemical reactions take place all the time. Sometimes it’s a good thing (think of browning of bread), but sometimes it isn’t so much. Fresh made pesto for instance tends to turn brown quite quickly.
This browning is caused by enzymes (very similar to the browning of a banana actually). Therefore, this post will dive into the details of these enzymes in food and how to prevent unwanted or accelerate wanted chemical reactions!
As I wrote before, food chemistry studies reactions taking place between molecules, in food. A very important group of molecules in these reactions are the so called enzymes. Enzymes in food influence a lot of different phenomena, to name just a few: browning of apples & bananas, making cheese from milk, ripening of sausages and last but not least the digestion of food by your body. This post will explain the basics of enzymes in food, helping you understand these phenomena.
What is an enzyme
Let us go back to the start, the very basics of enzyme chemistry. An enzyme is a specific type of protein. Enzymes are generally large complex proteins. They form a long chain of amino acids, the building blocks of proteins. This long chain will then curl up in a complex 3D structure.
Enzymes are very fascinating, they are large and complex but have a very specific spot in which another molecule will fit. This molecule is called a substrate. By sitting in this spot the enzyme can ‘help’ this molecule react into different molecules! The enzyme lowers the amount of energy required to start this reaction. That way the reaction takes place faster. In this process the enzyme is not used up, after it has transformed a substrate into its product, the enzyme hasn’t changed and can do the same thing again and again. That is why it is called a catalyst, it isn’t used up.
Influencing enzymatic reactions
Enzymes are these large structures which have to be folded up just fine to do their job, speed up reactions. They need the right conditions to be able to catalyze reactions. Several factors play a role which we will go through quickly.
Each enzyme has its optimal temperature to work out. Enzymes that have to work in our bodies for instance generally have an optimal temperature that is the same as our body temperature. But there are also enzymes that for instance prefer lower or higher temperatures. Enzymes will still be active within a range of their optimal temperature, however, if the temperature deviates too much, the reaction speed can go close to zero. The same goes up for the acidity level, pH. Each enzyme has its optimal pH at which it functions.
Another way to prevent enzymes from working is introducing an inhibitor. In the image below this is illustrated. The main thing that happens is that another molecule will interfer with the enzyme in such a way that it cannot anymore ‘receive’ a substrate and help it react.
Blanching & the effect of extreme heat on enzymes
Enzymatic reactions can be slowed down by various methods as discussed above. However, there is also a way to permanently stop enzymatic reactions from occuring. Proteins (remember, enzymes are proteins as well), get destroyed by intense heat. The exact temperature differs per protein, but most enzymes are broken down by placing them in boiling water.
This is were blanching comes into play! A lot of vegetables will turn brown after cutting them because of enzymes in the food. By placing them in hot boiling water for a short period of time these enzymes are broken down and further discolouration is stopped. A disadvantage of blanching of course is that is also changes the structure of the food…
A quicky thing about enzyme names. By knowing the name of an enzyme you can often deviate what the enzyme does. Enzyme names generally end with ‘ase’. The word placed in front is generally either the substrate that is transforms (the enzym amylase cuts up amylose in smaller pieces) or it specifies the reaction taking place.
Enzymes in food
Now that you know the basics of enzymes, let’s go back to the enzymes in food to close off. As mentioned at the starch, there are a lot of enzymes in food and involved with food. Enzymes play a crucial role in just about all living things. Complex regulation systems make sure the right reactions are catalyzed and the best complexes are formed.
A very well known enzyme is polyphenol oxidase (often abbreviated as PPO). This enzyme catalyzes the browning of a lot of fruits and vegetables (bananas, apples, celeriac, etc.). It does so by catalyzing a reaction in which polyphenols are formed, these polyphenols have red/brown to black colours.
Another group of enzymes in food are proteases from fruit. Proteases, as you might have expected, break down proteins. By adding the proteases from fruit in contact with meat and optimizing pH and temperature, the meat will tenderize (you might know of the combination of pineapple and pork?).
One last example is one that was also mentioned at the start is the use of enzymes to make cheese. Rennet contains various enzymes of which some proteases (yes, indeed, they interact with proteins). This group of enzymes cause milk to curdle. The casein (proteins!) molecules will curdle and form lumps. That way they can be removed from the rest of the liquid easily. Cheese can also be made by using an acid, read more about that in my food infographic on milk.
Pesto & Enzymes
To finish let’s get back to our pesto from the start. The main ingredients of this pesto are: crushed basil leaves, lemon juice and some other ingredients for flavour (e.g. cheese & pinenuts).
When making pesto basil leaves are broken down badly. By breaking down the plants structure enzymes and nutrients are all released. This frees them up to oxygen in their environment and reactions will occur. One of these is the browning of your pesto. By adding lemon juice the pH can be lowered which can slow down or completely prevent the enzymes from reacting!