Teaching Chemical Properties of Food
A Guide for Your Classroom
When students think about food science, they often imagine cooking, mixing ingredients, or checking textures. But beyond the physical changes, food also has chemical properties, and understanding these is just as important. The tricky part is that you can’t measure chemical properties without changing the food itself.
For example, to find out how much water is in a food, you have to dry it out—after that, the original food is no longer the same. That’s the difference between chemical and physical properties: chemical properties involve changes at the molecular level.
Let’s go over the main chemical properties of food so you can help your students understand this in a simple, relatable way.
Moisture Content
Water plays a big role in food quality, safety, texture, and even cost. If food has too much water, it tends to spoil faster because bacteria and molds grow more easily. On the other hand, too little water can cause food to become hard, crumbly, or gummy—unless that’s the texture you want, like in a crunchy cracker or chewy candy.
Water also affects how food feels in the mouth. Juicy fruits or tender baked goods have high moisture content, while dry snacks like chips have less.
There’s also a cost factor. Foods with a lot of water are heavier to ship, so they cost more to transport. That’s why companies sometimes remove water from foods to save money—think of dried fruits or concentrated juices.
To measure moisture, scientists usually use a convection oven or a moisture analyzer. The process is simple: they weigh the food, dry it out, and weigh it again. The difference tells them how much water was removed.
pH and Acidity
pH is one of the most important chemical properties in food. It tells us whether a food is acidic, neutral, or basic (alkaline). The pH scale goes from 1 to 14, with 7 being neutral (like pure water). Anything below 7 is acidic, and anything above 7 is alkaline.
One thing students may not realize is that the pH scale is logarithmic. That means a food with a pH of 5 is actually 100 times more acidic than a food with a pH of 7, not just a little more.
Controlling pH is essential for both safety and taste. For example, mayonnaise, ketchup, and pickles must be made with a pH of 3.4 or lower to stop dangerous bacteria from growing. Acidification doesn’t just protect food—it also changes how it tastes. Foods often taste better when they have the right level of acidity. Think about how adding a squeeze of lemon makes certain dishes pop with flavor.
pH is also important for food structure. In jam and jelly, for example, the correct pH helps the mixture form a gel. Without the right pH, the jelly would stay runny.
While pH tells you how acidic something is compared to other substances, acidity measures exactly how much acid is present. Both are important, but they aren’t the same thing. Acidity affects how sour a food tastes and also changes how it smells. Different foods contain different types of acids—like citric acid in oranges, lactic acid in yogurt, and acetic acid in vinegar.
Flavor Compounds
Flavor compounds are the chemicals that give food its taste and smell. These are usually volatile compounds, meaning they evaporate easily and reach your nose when you chew or cook food.
Fruits and vegetables develop many of their flavors as they ripen. That’s why an unripe banana tastes bland, but a ripe one is sweet and flavorful. However, flavors are rarely caused by just one chemical. The overall experience of eating is usually a mix of many compounds working together.
Some common examples of flavor compounds include menthol in peppermint, vanillin in vanilla, and limonene in citrus fruits. But not all flavors are pleasant. Some compounds create bad smells, like methanethiol, which smells like rotting cabbage, or putrescine, which smells like spoiled meat. Teaching students about these can be a fun way to link chemistry to real-life experiences—especially when discussing food spoilage.
Pigments
Pigments are the natural chemicals that give food its color. Green vegetables get their color from chlorophyll, carrots and mangoes get their orange color from carotenoids, and beets are red because of betanins.
Food colors can change during cooking or processing. For example, anthocyanins, which are found in red cabbage and berries, change color depending on pH. In acidic conditions, they look red. In basic (alkaline) conditions, they turn blue or purple.
Meat color also changes depending on how much oxygen it’s exposed to. Myoglobin, the pigment in meat, is bright pink when exposed to oxygen but turns brown when oxygen levels are low.
These color changes aren’t just cosmetic—they can tell you what’s happening chemically inside the food.
Enzymes
Enzymes are proteins that speed up chemical reactions. All living things use enzymes to survive, including humans, plants, and animals. In food, enzymes play a big role in processes like ripening, fermentation, spoilage, and digestion.
Sometimes we want to stop enzyme activity to slow down spoilage. That’s why we freeze food, cook it, or add acids—all of these slow down or stop enzymes from working.
Other times, we use enzymes on purpose to make new products. For example, cheese and beer making both rely on enzymes, even though we usually give the credit to yeast or bacteria. In reality, it’s the enzymes inside those organisms that do the work.
We also use purified enzymes directly in the food industry. For instance:
Amylase breaks down starch into sugar to make bread softer and moister.
Glucose isomerase turns glucose into fructose when making corn syrup.
Pectinase helps break down fruit pulp to extract more juice.
Papain (from papaya) and bromelain (from pineapple) are used to tenderize meat.
Enzymes are affected by a few key factors:
The amount of enzyme present (enzyme concentration)
The amount of food material (substrate) available for the enzyme to work on
Temperature—too cold and enzymes slow down; too hot and they get destroyed.
pH—extremes in pH can also denature enzymes, stopping them from working.
Wrapping It Up
Teaching chemical properties of food might sound complicated at first, but it doesn’t have to be. When you break it down into real-life examples—like why lemon juice stops apples from browning or why bread gets soft with amylase—students can connect the science to things they see and eat every day.