The type of thermal feed treatment influences the inositol phosphate composition

The content and composition of inositol phosphate phosphorus (InsP-P) in maize, wheat, barley and heat treated soybean meal, rapeseed meal and sunflower meal was determined by high-performance ion chromatography (HPIC). Approximately 0.88–0.96 of the InsP-P in the feedstuffs was present in the inositol hexaphosphate (InsP6) form, whereas the rest was in the inositol pentaphosphate (InsP5) form and for oilseeds a very small amount was present as inositol tetraphosphate (InsP4). Rapeseed differed from this pattern by having as much as 300 and 60 g InsP4-P/kg of the total InsP-P pool. The effect of pelleting (90 °C) and extrusion cooking (130–140 °C, 6.5 MPa) on the composition of InsP-P was investigated. Neither treatment had any major effect on the total content of InsP-P in the feedstuffs. However, as indicated by the statistically significant effects on the proportion of the inositol phosphates, extrusion cooking shifted the inositol phosphates from InsP6-P towards InsP5-P both in cereals (P=0.002) and in oilseeds (P<0.001), which show a slight degradation of phytate during this treatment. The degradation of InsP6 to InsP5 appeared to be unspecific with regard to isomers in all feedstuffs, indicating that the degradation was non-enzymatic, i.e. a result of the high temperature and pressure during the extrusion cooking. The degradation of InsP6 in the feedstuffs during extrusion is too limited to have any nutritional effect on the availability of phosphorous and minerals.