Determination of off-flavour compounds in apple juice caused by microorganisms using headspace solid phase microextraction–gas chromatography–mass spectrometry Original Research Article

In apple juice the presence of off-flavour is one of the most frequent causes for consumers rejections and, consequently, represents an important problem to apple juice producers. In this study, special emphasis was put on microbial caused off-flavours. Special attention is drawn to two bacteria species and their metabolites, Alicyclobacillus acidoterrestris and Actinomycetes. Both species produce aroma-active compounds (e.g. guaiacol, dibromophenol, geosmin, 2-methylisoborneol), which may lead to characteristic off-flavour in apple juice. They are described as musty/earthy or medicinal-like, even when they are present in very low concentrations. In this study, appropriate analytical methods were established to identify and quantify the compounds of interest. Gas chromatography–mass spectrometry was used after headspace solid phase microextraction (SPME) as sample preparation/extraction technique. The influence of the different parameters for headspace SPME (i.e. type of added salt, SPME fibre materials, time and temperature during thermostating of the sample and exposure of the fibre) on the sensitivity of the method are discussed. The final methods were fully validated. Limits of determination (LOD) and limits of quantification (LOQ) for the mentioned off-flavour compounds are located in the range of 0.08–7.7 μg L−1 for LOD and 0.27–25 μg L−1 for LOQ, depending on the compound. The presented analytical method provides a selective and sensitive technique to further investigate the off-flavour problem in apple juice.