Determination of aliphatic aldehydes in maize and grass silages using on-fibre derivatisation with O-(2,3,4,5,6-pentafluoro)benzylhydroxylamine

Aldehydes and ketones are volatile compounds of silages which probably affect feed preference, palatability and intake. A sensitive and fast method was developed to determine aliphatic aldehydes in maize and grass silages. The method is based on the solid phase micro-extraction and on-fibre derivatisation of aldehydes with O-(2,3,4,5,6-pentafluoro)benzylhydroxylamine hydrochloride (PFBHA). The derivatisation agent was adsorbed onto divinylbenzene/poly(dimethylsiloxane) 65 μm fibre and then exposed to the aldehydes in the headspace of the silage samples. Aldehydes selectively react with PFBHA forming volatile oximes, which were desorbed in the injection port of a gas chromatograph and analysed by mass spectrometry. Using this method, eight aldehydes were detected in maize and grass silages being ethanal, propanal, butanal, 2-methylpropanal, pentanal, 3-methylbutanal, hexanal and heptanal, at levels ranging from tens to 200 mg/kg fresh matter. In two pilot laboratory experiments, contents of butanal and 3-methylbutanal decreased in silages prepared from grasses inoculated with Lactobacillus plantarum (1 × 105 CFU/g) or prepared from wilted forage.