Effect of freezing and grinding method on near-infrared reflectance (NIR) spectra variation and chemical composition of fresh silage

In order to evaluate possible effects of rapid freezing and grinding method s on near-infrared reflectance (NIR) spectra variability and chemical compo sition, samples from 18 pasture silages, previously pre-homogenized, were f rozen either with liquid nitrogen (LN) or dry ice (DI) and, subsequently, g round with a Tecator(R) homogenizer (Tec) or a Moulinex(R) food processor ( Mou). NIR spectra were taken (monochromator NIRSystems 6500) on four fresh subsamples per silage and root mean squares (RMS) computed on derivatized s pectra (software NIRS 3, ISI, 1992) as a means of estimating spectra dissim ilarities among subsamples. Principal components were computed and samples plotted according to the first three scores to visualize potential effects of treatments. Seven silages from the four treatments plus a control (pre-h omogenized only) were freeze-dried and analyzed for toluene dry matter (DMT ol), crude protein (CP) and acid detergent fiber (ADF). Average RMS value f or silages was 423.97 and no effect of freezing or grinding method, nor any interaction between them, was found (P > 0.05), although DI-Mou and DI-Tec treatments showed lower (402.8) and higher (459.4) mean RMS values, respec tively. Plotting of samples according to the main principal component score s of spectra did not show any effect of treatments, as samples tended to cl uster by silage instead as by treatment. Chemical composition of treated, a nd control samples, was not different (P > 0.05). On average, composition w as as follows: DMTol, 269.2 g kg(-1); CP and ADF (oven DM basis), 126.0 and 403.2 g kg(-1) DM, respectively. It is concluded that any sample handling method could be selected for calibration and subsequent routine analysis, b ut if a method is chosen, it is suggested to consistently adhere to that me thod. (C) 1999 Elsevier Science B.V. All rights reserved.