Changes of phosphorus and trace elements species in rye and oat flakes and oat porridge induced by simulated digestion

Fractionation of chemical species of phosphorus, manganese, iron, nickel, copper, zinc and molybdenum in rye and oat flakes and porridge made of oat flakes was studied by size exclusion chromatography coupled to inductively coupled plasma mass spectrometry. The effect of in vitro simulated digestion of the samples was elucidated by comparison of the digestates and the extracts of the samples (in the Tris–HCl buffer solution, pH = 7.5). The procedure of simulated digestion included two steps: the pepsin-catalysed hydrolysis in diluted hydrochloric acid (pH = 1.7) followed by the pancreatin-catalysed hydrolysis at pH = 7.5. The enzyme-catalysed digestion of the samples results in alteration of iron, copper and zinc species distribution. The species of phosphorus in original cereal samples are distributed between two fractions: a medium-molecular mass fraction (15 kDa) and a low-molecular mass fraction (2 kDa). This pattern is also kept basically in the sample digestates. In digested samples, the majority of soluble iron is bound in a medium-molecular mass fraction (20 kDa), while in the extracts only traces of iron were found in a high-molecular mass fraction. Approximately 90% of the soluble zinc in the digestates of cereal flakes is represented by non-bound zinc ions. The bound zinc is mostly concentrated in a low-molecular mass fraction (1–2 kDa) together with some copper and almost all nickel. The low-molecular mass fractions (1–2 kDa) of nickel, copper and zinc present in extracts of original samples correspond quite well to those in the respective digestates. Molybdenum species occurs in another low-molecular mass fraction.