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Separating out foods into component molecules

Food is made up of many different chemical components or parts, including vitamins, minerals, sugars, fibres, water, lipids, proteins and starches.

In addition to these main nutrient components, many foods contain smaller amounts of biologically active chemicals. In plants, these are referred to as phytochemicals. Scientists can separate out all of these different components of foods.

Why separate food into its component parts?

There are many reasons why scientists might want to separate out the component parts of food. For example, Nutrigenomics New Zealand (NuNZ) is investigating why different people respond differently to different foods. It seems that sometimes these variations arise because of differences in our genes. This is because our genes can affect the way that our bodies deal with the chemical components that make up a particular food. As a result, some food components might be particularly good for some people, and cause problems for others!

The aim of the nutrigenomics project is to work out which specific food compounds are most helpful (or most harmful) to people with particular food-related diseases, like Crohn’s disease. Go to the focus story to find out more.

How can different food components be separated?

A range of different methods can be used to separate specific molecules out of foods using a range of different methods. These methods include: Differential solubility, ion exchange chromatography, size exclusion chromatography, and selective adsorption chromatography.

Differential solubility

Some molecules dissolve easily in water; other molecules will dissolve in hexane but not in water. This is because some molecules are more polar than others. Polar molecules dissolve in polar solvents, like water. Non-polar molecules dissolve in non-polar solvents, like hexane. Molecules like sugar are polar, whereas fat molecules are non-polar.

Ion exchange chromatography

Molecules have different charges (positive and negative). This property can be used as the basis of separation. The food sample (as a solution) is passed through a column containing beads that are charged. If the beads have a positive charge, negatively charged molecules in the food will attach but positively charged molecules will run easily through the column and can be collected.

Size exclusion chromatography

This has a sieving effect. Because molecules have different sizes, they move through a size exclusion chromatography column at different rates. Larger molecules are collected first, smaller molecules are collected last.

Selective adsorption chromatography

Because different molecules have different chemical properties, they are more or less able to adsorb (or stick) to materials such as silica gel. This means that they can be separated based on their polarity (degree of surface charge). For example, hydrocarbons (molecules with lots of carbon and hydrogen atoms) have no affinity for silica, whereas alcohols have strong affinity.

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