Dimethyl sulfide (DMS) and its precursor S-methylmethionine sulfonium (MMS) were investigated for off-flavors on heating Satsuma mandarin juice. A method of headspace gas analysis in gas chromatography with a flame photometric detector (FPD) was developed for DMS determination. The DMS calibration curve was linear between 2.0 and 30 ppb on a log-log graph paper. A new method for MMS determination was established. In this method, 2μl of juice was introduced directly into an injection port. MMS in the juice was decomposed to DMS at 200°C in situ, and DMS was analyzed by FPD-GC. The calibration curve for MMS was linear between 4.0 and 100μM. on a log-log graph paper. This method required only 2min. The MMS concentrations in juices were determined. Of 23 citrus varieties, six varieties had less than 5.0 μM MMS, seven from 5.0 to 10 μM, seven from 10 to 15 μM, one from 15 to 20 μM and two more than 20 μM. The level in Satsuma mandarin juice was 21 pM. The contents of MMS and DMS in heated Satsuma mandarin juice were measured and they agreed stoichiometrically.
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