Analysis of in vitro digestible phosphorus content in selected processed rye, wheat and barley products

The bioavailability of phosphorus (P) in foodstuffs is mostly unknown. The aim of this study was to test a method for in vitro digestible phosphorus (DP) analysis and analyse the DP content in variously processed cereal products by an in vitro method combined with inductively coupled plasma–mass spectrometry (ICP–MS). For DP analysis the samples were treated as chyme by adding alpha-amylase and proteases. The samples were dialysed, using equilibrium dialysis, and the DP was analysed by ICP–MS. The amount of total phosphorus (TP) was also analysed by ICP–MS. In soured wheat and rye breads, the proportion of DP/TP was higher (DP/TP: rye 83%, wheat 78%) than in flours (DP/TP: rye 45%; wheat 43%) or non-soured breads (DP/TP: wheat 46%). This indicates that, during processing, phytic acid degrades and releases soluble inorganic P, which increases the DP content. The DP content in the cereals was significantly lower than the TP content, which indicates that not all dietary P may be absorbed in the human body.