From Sweetness to Structure

When we refer to food as containing “sugar,” we tend to picture white crystals we buy in bags or pour from sachets into our coffee, but to a food scientist sugar is not a single thing, but a type of thing. While, most commonly, when we say sugar we refer to sucrose, in reality there are many sugars that can be found in (or added to) food. They all have in common the chemical characteristic that they are carbohydrates, which means, as the name suggests, that they are based on carbon and water (giving hydrated carbon), and indeed the three core elements found in all sugars are carbon, hydrogen, and oxygen. One of the simplest sugars, molecularly speaking, is glucose, in which there are 6 carbon atoms, 6 oxygen atoms and 12 hydrogen atoms (so it is like 6 carbons plus 6 water molecules, as each water molecule has two hydrogens to one oxygen). These are arranged, not in a long chain, as in the proteins we discussed in the previous chapter, but rather in a ring structure (not technically round, but more like a hexagon might appear if you gave it a good twist). Glucose is the main sugar found in biology, being found in our bodies and also produced by plants by photosynthesis. Another simple sugar is fructose, found widely in fruit and honey, which has an even simpler structure, a pentagon structure, but again has 6 carbon atoms bound together with 6 oxygens and 12 hydrogens, while a rarer one (at least in its unbound state) is galactose, again with the same number of the core atoms but arranged in yet another slightly different state. Here is a wonderful example of the significance of chemistry for food, where the exact same number of atoms of the same three elements can naturally be found in (at least) three different arrangements, which reflect subtly different molecular shapes but yet give compounds that differ greatly in their sweetness, solubility, reaction with other components in food, and many other properties.