Drying of herbage samples for analyses

Authors

• Maija-Liisa Salo Department of Animal Husbandry, University of Helsinki
• Kaija Kotilainen Department of Animal Husbandry, University of Helsinki

DOI: https://doi.org/10.23986/afsci.71768

Abstract

The influence of erroneous drying methods on the analysis results was investigated. The test series included herbage and faeces samples, and pure mixtures. The samples were analysed for sugars, lignin, crude fibre and crude protein. The following results were noted: Samples dried in a vacuum at 40°C yielded the same results as those treated by freeze drying. No attention need be paid to the sample thickness. From the technical point of view, vacuum drying is preferable to freeze drying. Oven-drying gave good results when the following technique was used: The herbage sample is first heated as a thin layer at 100°C for 30—60 min., depending on the water content. Final drying is carried out at 50°C. The conventional drying temperature, 65 °C, is too high. The thin-layer drying technique causes errors in the sugar content, the thick-layer drying also in the figures for lignin and crude fibre. Between 50 and 100°C, the thickness of the sample layer induces in many wet samples a larger error than does the high temperature. Different materials react to heat-drying in different ways. The major factors are the water content and the composition of the dry matter. The drying method does not affect the data for the crude protein, as determined by the Kjeldahl method. The following facts were noted for the pure mixtures; A high temperature is sufficient to cause sugar losses; proteins are not necessary. A reaction between carbohydrates and amino acids brings about the drying error in the lignin and crude fibre results. High temperature and high water content magnifies the error. Application of a protein correction for the crude lignin eliminates only a part of the error introduced.