Mineral deficiency is a serious worldwide problem, and while a balanced diet should contain all the essential elements, it can be difficult to know which foods are the best sources of different minerals. Not only do different foods contain elements in different forms, but other components of food can also make nutrients more or less available for absorption in the digestive system.

Juwadee Shiowatana and colleagues in Thailand have developed a method for estimating the bioavailability of several essential elements at once from a continuous in vitro digestion system.

Ideally, assessment of bioavailability of nutrients from different foodstuffs should be carried out via in vivo studies using human volunteers. However these studies are expensive, time consuming, difficult and unreliable. In vitro methods estimate bioavailability by using a simulated enzymatic digestion of food and measuring the ability of nutrients to pass through a semi-permeable membrane. These methods are simple, fast and cheap but need to be carefully optimised to make them as similar as possible to in vivo studies.

Shiowatana's team used inductively coupled plasma optical emission spectrometry (ICP-OES) coupled on-line to the simulated digestion system allowing rapid determination of a range of nutritionally important elements.

The in vitro apparatus developed by the group at Mahidol University in Bangkok mimics the absorption of food in the human digestive system more closely than previous methods. Coupling the system with ICP-OES allows much more rapid assessment of mineral bioavailability as several elements can be measured in the same analytical run. The researchers applied the technique to various foodstuffs including rice, meat, beans and milk powder. In the future they hope to apply the system to nutritionally evaluate a wide range of foods to improve management of mineral intake and reduce the health risk from mineral deficiency.

Christopher P Ingle