Modelling phytate degradation kinetics in soaked wheat and barley

The objective of this study was to identify an appropriate mathematical function describing the in vitro phytate degradation profile of soaked wheat or barley (20 °C; 1 cereal: 2.75 water (w/w)) as affected by heat-treatment (stem pelleting at 90 °C) and phytase addition (Phytase 1: 0, 250, 500, 750, 1000, 1500, 2000 or 2500 FTU/kg; Phytase 2: 0, 375, 750, 1125, 1500, 2250, 3000 or 3750 FYT/kg). Samples were collected at 0, 2, 4, 8 and 24 h of soaking. The full dataset was split in two sub-sets as Phytase 1 and Phytase 2 are defined by different phytase activities. A segmented linear (SL) function, a first-order (FO) function and a Generalised Michaelis Menten (GMM) function were considered. The GMM fitted the data best. The GMM function was used to derive the relative instantaneously degradable fraction of phytate (F0) and the half-life (t1/2) of phytate in hours (K). Addition of Phytase 1 or Phytase 2 had no effect on the degradation of phytate. The F0 was greater in the heat-treated barley compared with the heat-treated wheat (0.19 vs. 0.14; P=0.02; Phytase 1). Heat-treatment of the cereals increased the F0 from 0.05 to 0.15 (P=0.0007; Phytase 2). The K was lower in the non-heat-treated wheat compared with the non-heat-treated barley (averaging 23.3 vs. 43.5 h), whereas K was higher in the wheat compared with the barley (averaging 12.3 vs. 11.1 h; P=0.02 and P=0.006; Phytase 1 and Phytase 2) when the cereals were heat-treated. In conclusion, the GMM function is a suitable model for describing the phytate degradation profiles of the soaked wheat and barley. The in vitro results showed that heat-treatment of the cereals increased the F0 and reduced the K although the plant phytase activity was reduced. This was possible due to induced structural changes of the grain that increased the contact between phytate and plant phytases. The lack of effect of additions of Phytase 1 or Phytase 2 on the phytate degradation in the cereals was possible due to a poor access of the microbial phytases to phytate. Therefore, more knowledge is needed about processing technologies that increase the access of plant and microbial phytases to phytate in the grains.