THE POSSIBILITIES OF NEAR-INFRARED REFLECTION SPECTROSCOPY TO PREDICT TOTAL-PHOSPHORUS, PHYTATE-PHOSPHORUS AND PHYTASE ACTIVITY IN VEGETABLE FEEDSTUFFS

Two hundred thirty eight samples, representing 19 vegetable feedstuffs, were analyzed for total- and phytate phosphorus (P). Phytase activity was determined on a limited number of feedstuffs with an activity of more than 100 units kg(-1). Near infrared reflection spectra (NIRS) were taken between 1100 and 2500 nm in steps of 4 nm. By means of principal component analysis the feedstuffs were grouped in so called starchy (n = 150) and protein-rich feedstuffs (n = 88). NIRS-calibrations were developed using partial least square regression and tested by cross-validation. Total-P varied from 0.22 to 1.25% and phytate-P from 0.05 to 1.02% for starchy feedstuffs and respectively from 0.46 to 1.37% and from 0.22 to 0.56% for protein-rich feedstuffs. Within these broad ranges, NIRS-values were highly correlated to determined total- and phytate-P with prediction errors of 0.08% and 0.08%, respectively for starchy feedstuffs and 0.08% and 0.04%, respectively for protein-rich feedstuffs. However, considering the mostly small deviation of mean or calculated values for the separate feedstuffs, NIRS only makes practical sense to predict total-P for wheat by-products and phytate-P for maize gluten feed. On the other hand, NIRS could be used for unknown or not tabulated products. Spectral signals from total and phytate-P are partly based on direct responses from organic complexes but also on secondary relationships through protein and fat. NIRS seems not sensitive enough to detect phytase.