GC–MS quantification and sensory thresholds of guaiacol in orange juice and its correlation with Alicyclobacillus spp.

Guaiacol is a profoundly negative taint/off-flavour produced by the increasingly common microbial contamination of fruit juices with Alicyclobacillus spp. The objectives of this study included: determining sensory thresholds for guaiacol in orange juice (OJ), developing an analytical method whose detection limits were equivalent to sensory thresholds and determining levels of Alicyclobacillus spp. that would produce detectable levels of guaiacol. A 12 member trained panel was used to establish guaiacol detection and recognition thresholds. Guaiacol ortho and retro nasal detection thresholds in OJ were 0.70 and 0.53 μg/l respectively. Odour recognition threshold was 2.0 μg/l. A SPME GC–MS Selected Ion Monitoring (SIM) procedure was optimised to achieve analytical detection limits of 0.5 μg/l. Optimum guaiacol detection limit was achieved using only responses from m/z 109 and 124. Ion ratios (m/z 109/124) and linear retention index value matching were used to confirm the identification of guaiacol. Quantification was achieved using peak areas from standard guaiacol additions in orange juice between 0.5 and 100 μg/l. Alicyclobacillus growth of 2.2 log CFU/ml in OJ produced just detectable levels (0.7 μg/l) of guaiacol.