Detection of guaiacol produced by Alicyclobacillus acidoterrestris in apple juice by sensory and chromatographic analyses, and comparison with spore and vegetative cell populations

Spoilage of fruit juice by Alicyclobacillus acidoterrestris is characterize d by a distinct medicinal or antiseptic off, odor attributed to guaiacol, a metabolic by product of the bacterium. Detection of low populations of A. acidoterrestris that would precede sensory detection of guaiacol would enab le juice processors to select appropriate processing and storage conditions that would minimize or eliminate spoilage. The objective of this study was to determine the recognition threshold of guaiacol in apple juice by senso ry analysis and the population of A. acidoterrestris and incubation time at 21 and 37 degreesC necessary for chemical detection of guaiacol. Commercia lly sterilized apple juice (pH 3.54 +/- 0.04, 11.3 +/- 0.3 degrees Brix) wa s inoculated with a five-strain mixture of A. acidoterrestris spores (2.98 log(10) CFU/ml) and stored at 21 or 37 degreesC for up to 61 days. Using an experienced sensory panel and the forced-choice ascending concentration me thod of limits, the best estimate threshold (BET) for recognition of guaiac ol added to uninoculated apple juice was 2.23 ppb. Numbers of A. acidoterre stris spores and cells in inoculated juice remained constant during the 61- day storage period; however, the panel detected (P less than or equal to 0. 01) guaiacol in juice stored at 37 degreesC within 8 days. At three of four sampling times ranging from 13 to 61 days at which the sensory panel detec ted (P less than or equal to 0.001) guaiacol, concentrations of 8.1 to 11.4 ppb were detected by chromatographic analysis. The panel detected (P less than or equal to 0.1 to P less than or equal to 0.01) guaiacol in five samp les stored at 21 to 37 degreesC for 8 to 61 days in which the compound was not detected by chromatographic analyses. It appears that guaiacol content in apple juice inoculated with A. acidoterrestris is not always correlated with numbers of cells, and the limit of sensitivity of chromatographic quan titation of the compound is higher than the BET.