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.