The influence of phytate-bound-phosphorus on the near infrared spectra of wheat grains

Near infrared (NIR) spectroscopy has been used to determine total phosphorus (total-P), phytate, and phytate-bound phosphorus concentrations in grains and animal feeds. However, since more than 50% of the total-P in grains of most cultivated cereals occurs as phytate (myo-inositolhexakisphosphate), there is a strong linear correlation between total-P and phytate-bound-P. If near infrared spectroscopy is used to analyse cereal products simultaneously for both total-P and for phytate-bound-P there is a risk that the intercorrelation effects will be dominant in models for each. This paper presents NIR spectra of whole wheat grains from progeny of a normal and a low phytate parent genotype. For these progeny there was a weak correlation between the phytate-bound-P and total-P concentrations (r = 0.5) and no correlation with grain protein (r = 0.1). The spectra of grains with lower phytate-bound-P differed at wavelengths that aligned mainly with O-H, C-H and P-OH bonds and included 7124 cm−1 (1404 nm), 5882 cm−1 (1701 nm) and 5245 cm−1 (1907 nm). Loading weights for partial least squares regression models indicated that models for both total-P and phytate-bound-P utilized essentially the same wavelengths. This supports the hypothesis that NIR calibrations for total-P and phytate-bound-P in wheat and wheat-based feeds are inter-dependent. This may not be critical for the determination of P in grain of most current genotypes due to the strong linear correlation between total-P and phytate-bound-P. However, to ensure more accurate analysis of P in grains of cereal varieties that carry genes for low phytate NIR calibration models for total-P, phytate-bound-P and phytate should be updated.